Many of you may have already seen these, while others may have missed out. These are all definitely worth a read.
Phytodinosauria returns!
http://theropoda.blogspot.com/2010/08/coming-soon-triassic-phythodinosaurs-or.html
South American Basal Saurichians
http://theropoddatabase.blogspot.com/2010/08/brief-thoughts-on-chromogisaurus-and.html
http://theropoda.blogspot.com/2010/08/chromogisaurus-novasi-ezcurra-2010-ed.html
http://chasmosaurs.blogspot.com/2010/08/cheerio-chromogisaurus.html
Dicynodonts
http://chasmosaurs.blogspot.com/2010/08/dicynodonts-other-white-meat.html
[Sorry for any other recent Triassic posts I have missed]
The Importance in Understanding Historical Context in Solving Taxonomic Problems - A Case Study With Aetosaurs
Parker, W. G. and Martz, J. W. 2010. Using positional homology in aetosaur (Archosauria: Pseudosuchia) osteoderms to evaluate the taxonomic status of Lucasuchus hunti, Journal of Vertebrate Paleontology 30:1100-1108.
Abstract - The Otis Chalk quarries in the Upper Triassic Dockum Group of West Texas have produced aetosaur material that most workers have suggested represents two distinct morphotypes. We use characters from aetosaur specimens with articulated or semi-articulated carapaces in which the anteroposterior placement of osteoderms can be established with certainty to compare homologous osteoderms in the Otis Chalk material. This study confirms that the genera Longosuchus and Lucasuchus are distinct morphotypes, which differ in that the former taxon has paramedian osteoderms with random pitted ornamentation and low pyramidal bosses that contact the posterior margin, and spines on the lateral osteoderms that are posteriorly emarginated, whereas the latter taxon has paramedians with a strongly radial ornamentation and large conical eminences, and spines on the lateral osteoderms that are not posteriorly emarginated. Both taxa also have paramedians that are overlapped anteriorly by the laterals, a character that may be a synapomorphy of desmatosuchine aetosaurs. The arguments that these morphotypes represent ontogenetic stages or sexual dimorphs of a single biological species cannot be corroborated using either comparisons with modern pseudosuchians, other aetosaur taxa, or stratigraphic ranges. Longosuchus is known only from the type area and has no utility as an index taxon of the Otischalkian land-vertebrate faunachron, although Lucasuchus suggests a tentative correlation between part of the Dockum Group of Texas and the Pekin Formation of North Carolina.
Discussion
Study and management of any resource, including vertebrate fossils, requires in-depth understanding of the context under which previous work on these materials was conducted. For example, where, how, and by whom were the specimens collected? What was their original association? How were they prepared? Who identified them and why did they apply the identification that they did? Often in vertebrate paleontology we are faced with taxonomic questions, which to answer properly we need this detailed contextural information. A good example of this in aetosaurs (the group I mainly work with) is the ongoing debate regarding the proposed synonymy of Longosuchus meadei and Lucasuchus hunti. Much confusion exists regarding the specimens assigned to these taxa, much which stems from the original collection, as well as the subsequent curation and description of these materials. Recently I, along with my co-author Jeffrey Martz, tried to tackle this taxonomic problem and our resulting paper was just published in the most recent issue of the Journal of Vertebrate Paleontology. This article necessitated discussion of the history of the collection, study, and curation of these specimens and unfortunately some of the information I now have did not make it into the final article. At the time this article was in press I came across more important information on the collection and study of these specimens and unfortunately it was too late to add to the introductory section. Some of this new information (from quarry reports and correspondence), included here, clarifies or corrects introductory statements made in our paper.
In the late 1930s and early 1940s a paleontology inventory of portions of Texas was conducted under the Works Progress Administration (WPA), a relief program established by the U.S. Government to put millions of unemployed American men to work. Extensive quarrying was conducted at several sites in Texas including a series of Late Triassic age quarries near Otis Chalk in Howard County. These quarries contained thousands of bones of metoposaurs, phytosaurs, aetosaurs, etc., and are especially known for the well preserved skeletons of the archosauromorph Trilophosaurus buettneri (Gregory, 1945; Elder, 1978; Spielmann et al, 2008). Quarries 3 and 3A contained the majority of the aetosaur material including several partial to fairly complete aetosaur skeletons, only some of which has been prepared. The “best” two skeletons; however, were prepared and subject to a full description by Sawin (1947). Specimen lists compiled at the time of collection as well as work reports reveal that all of the aetosaur material was assigned to the genus Desmatosuchus at the time of collection. Many of the specimens still contain field numbers, which include the county name, quarry number, the year collected, and a fourth number that represents the order in which the specimen was removed from the ground and documented. Furthermore, collection records sometimes provide the name of the collector. Unfortunately, this number just reflects the collection order and often can be ambiguous about the association of specimens in the ground. In our paper we state that no excavation records could be found, but specimen lists and reports have since come to light although no detailed quarry maps are still known to exist.
Workers prepared the two associated skeletons, as well as the articulated tail of a third individual, and a variety of isolated elements. In the final publication (Sawin, 1947) the majority of these specimens are assigned to a new species, Typothorax meadei, based mainly on the sigmoidal shape of the femur (Sawin, 1947). Sawin also recognized a second species, T. coccinarum, as present in the quarry, but restricted this assignment to several osteoderms with large conical dorsal eminences, which he thought resembled the conical eminences in T. coccinarum osteoderms figured and described by von Huene (1915) and originally studied by Cope in 1887. Sawin (1947) designated the two main skeletons (Typothorax meadei) as syntypes and one of the specimens (TMM 31185-84a) was partially incorporated into a museum mount (some of the armor as well as the limbs) along with the articulated tail of the third individual. Much of the remaining material was left identified and catalogued in the collections as Desmatosuchus (contra Parker and Martz, 2010), including many lateral plates which were superficially similar to those of T. meadei. What is important is that none of this material is actually referable to Desmatosuchus (Parker and Martz, 2010).
In an unpublished M.S. thesis Elder (1978) noted this similarity and argued that Desmatosuchus and Typothorax were therefore synonymous. This was later refuted by Small (1989), but what is important to note is that like Sawin, Elder recognized two distinct morphologies in the Otis Chalk material.
Later recognition of the utility of osteoderms ornamentation in aetosaur taxonomy by Long and Ballew (1985) led those workers as well as others (e.g., Small, 1989) to recognize that T. meadei represented a distinct genus from T. coccinarum. Hunt and Lucas (1990) accordingly supplied the name Longosuchus meadei. Curiously, in their renaming of the material and designation of a lectotype Hunt and Lucas (1990) also included the material that Sawin (1947) had assigned to T. coccinarum. Unfortunately, no explanation is given for this and from the article it is not clear if Hunt and Lucas (1990) recognized that some of the material had originally been assigned to a different taxon. They also provide no discussion of the material referred to Desmatosuchus, but infer in their biochronology section that all of the Otis Chalk material belongs to a single taxon.
Subsequent re-examination of the material by Long and Murry (1995) led to the separation of Sawin’s (1947) “T. coccinarum” material as well as the “Desmatosuchus” material from the original T. meadei material of Sawin. Long and Murry (1995) assigned these specimens to a new taxon, Lucasuchus hunti (presumably in return for the name Longosuchus, named for Long). This reassigned was criticized, particularly by Heckert and Lucas (1999, 2000; and in numerous subsequent papers) and Lucas and Heckert (1996) who all stated that the diagnosis of Lucasuchus is “based on minor differences in scute morphology, some so subjective they cannot be replicated”. They also stated that Long and Murry (1995) “split” Longosuchus; however, this is incorrect as they only recognized the originally division of the material set forth by Sawin (1947).
In my own initial examination of the material (Parker, 2003) I felt that there actually were pretty clear differences between the holotype osteoderms of Lucasuchus and Longosuchus, especially in the paramedian osteoderm ornamentation and in the position of the dorsal eminence (see Parker and Martz, 2010). Moreover, although superficially similar there were also key differences between the lateral osteoderms of L. meadei and those catalogued as “Desmatosuchus” and assigned to Lucasuchus by Long and Murry (1995). What was ambiguous; however, was the association of these lateral osteoderms with the Lucasuchus paramedian osteoderms. Although Sawin (1947) felt that there were two morphotypes represented by the paramedian osteoderms in the collections, he clearly stated that no lateral osteoderms were associated with his “T. coccinarum” (Lucasuchus) material.
This last puzzle was solved unintentionally by Ron Tykoski, who while working for the Texas Memorial Museum (TMM) made a small collection of osteoderms to place around the base of the mount. One of the osteoderms he selected was a paramedian of Lucasuchus (TMM 31100-66) and nearby was a lateral osteoderm with the same number. Amazingly these two osteoderms fit together perfectly and unambiguously to form a conjoined pair, and thus must have come from the same individual. Even better, this lateral was of the Lucasuchus morphology and not from Longosuchus. Finally we were able to compare homologous series from both morphotypes to strongly (we feel) demonstrate support for Long and Murry’s (1995) reseparation of the material into two distinct taxa. This was the basis for the entire paper by Parker and Martz (2010).
One final puzzle (at least for me) was why Sawin had assigned the material to Typothorax in the first place? This is where knowledge of the historical context is crucial. At the time the material was collected (1939-1940) there were only three aetosaur taxa known from western North America, Typothorax, Episcoposaurus, and Desmatosuchus. By the time Sawin conducted his study it had been hypothesized by many workers that Episcoposaurus and Desmatosuchus were congeneric, something that was finalized later by Gregory (1953). This was based mainly on the material of Episcoposaurus haplocerus; however, another referred species E. horridus, had been collected in the same general area as the holotype and referred material of Typothorax coccinarum. Personal correspondence between Dr. John Wilson of the TMM and Dr. E. C. Case of the University of Michigan written in the 1940s clarify that Sawin travelled to the American Museum of Natural History to examine Cope’s material of E. horridus and T. coccinarum. This material, figured by Lucas et al (2007) contains two distinct femur morphologies. A gigantic straight femur was referred (by Cope) to E. horridus, whereas a much more gracile and strongly sigmoidal femur was assigned to T. coccinarum. The femora of Longosuchus meadei are nearly identical to that of the referred T. coccinarum specimens contra the statement by Heckert et al. (2010:637) that they are “dramatically different”. It was also on this visit that Sawin noted the conical eminences in the caudal osteoderms of T. coccinarum that formed the basis of his assignment of the Lucasuchus material to that taxon. Thus, finding the Wilson-Case correspondence solves the last part of the puzzle.
I hope that this case provides a good example of how essential understanding the context of the specimens on hand are when we try to determine aspects such as original association, curation, and taxonomy. With this information we can now understand why certain taxonomic assignments were made by past researchers. Allowing ourselves the opportunity to “walk in their boots” of our predecessors for awhile is an important tool in solving important scientific problems.
REFERENCES
Elder, R. L. 1978. Paleontology and paleoecology of the Dockum Group, Upper Triassic, Howard County, Texas. M.S. thesis, University of Texas, Austin, Texas, 205 pp.
Gregory, J. T. 1945. Osteology and relationships of Trilophosaurus. University of Texas Publication 4401: 273-359.
Gregory, J. T. 1953. Typothorax and Desmatosuchus. Postilla 16:1–27.
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late
Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt für Geologie und Paläontologie, Teil I, Heft 11–12:1539–1587.
Heckert, A. B. , Lucas, S. G. , Rinehart, L. F. , Celeskey, M. D. , Spielmann, J. A. and Hunt, A. P. 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: early-mid Norian), eastern New Mexico, USA. Journal of Vertebrate Paleontology 30:619 — 642
Huene, F. v. 1915. On reptiles of the New Mexican Trias in the Cope collection. Bulletin of the American Museum of Natural History 34:485–507.
Hunt, A. P., and S. G. Lucas. 1990. Re-evaluation of “Typothorax” meadei, a Late Triassic aetosaur from the United States. Paläontologische Zeitschrift 64:317–328.
Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45–68.
Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1–254.
Lucas, S. G., and A. B. Heckert. 1996. Late Triassic aetosaur biochronology. Albertiana 17:57–64.
Lucas, S. G., J. A. Spielmann, A. B. Heckert, and A. P. Hunt. 2007. Topotypes of Typothorax coccinarum, a Late Triassic aetosaur from the American Southwest. New Mexico Museum of Natural History and Science Bulletin 41:241–247.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. M.S. thesis, Northern Arizona University, Flagstaff, 315 pp.
Sawin, H. J. 1947. The pseudosuchian reptile Typothorax meadei. Journal of Paleontology 21:201–238.
Small, B. J. 1989. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry,West Texas; pp. 301–308 in S. G. Lucas and A. P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.
Spielmann, J. A., Lucas, S. G., Rinehart, L. F. and A. B. Heckert. 2008. The Late Triassic archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43: 1–177.
Abstract - The Otis Chalk quarries in the Upper Triassic Dockum Group of West Texas have produced aetosaur material that most workers have suggested represents two distinct morphotypes. We use characters from aetosaur specimens with articulated or semi-articulated carapaces in which the anteroposterior placement of osteoderms can be established with certainty to compare homologous osteoderms in the Otis Chalk material. This study confirms that the genera Longosuchus and Lucasuchus are distinct morphotypes, which differ in that the former taxon has paramedian osteoderms with random pitted ornamentation and low pyramidal bosses that contact the posterior margin, and spines on the lateral osteoderms that are posteriorly emarginated, whereas the latter taxon has paramedians with a strongly radial ornamentation and large conical eminences, and spines on the lateral osteoderms that are not posteriorly emarginated. Both taxa also have paramedians that are overlapped anteriorly by the laterals, a character that may be a synapomorphy of desmatosuchine aetosaurs. The arguments that these morphotypes represent ontogenetic stages or sexual dimorphs of a single biological species cannot be corroborated using either comparisons with modern pseudosuchians, other aetosaur taxa, or stratigraphic ranges. Longosuchus is known only from the type area and has no utility as an index taxon of the Otischalkian land-vertebrate faunachron, although Lucasuchus suggests a tentative correlation between part of the Dockum Group of Texas and the Pekin Formation of North Carolina.
Discussion
Study and management of any resource, including vertebrate fossils, requires in-depth understanding of the context under which previous work on these materials was conducted. For example, where, how, and by whom were the specimens collected? What was their original association? How were they prepared? Who identified them and why did they apply the identification that they did? Often in vertebrate paleontology we are faced with taxonomic questions, which to answer properly we need this detailed contextural information. A good example of this in aetosaurs (the group I mainly work with) is the ongoing debate regarding the proposed synonymy of Longosuchus meadei and Lucasuchus hunti. Much confusion exists regarding the specimens assigned to these taxa, much which stems from the original collection, as well as the subsequent curation and description of these materials. Recently I, along with my co-author Jeffrey Martz, tried to tackle this taxonomic problem and our resulting paper was just published in the most recent issue of the Journal of Vertebrate Paleontology. This article necessitated discussion of the history of the collection, study, and curation of these specimens and unfortunately some of the information I now have did not make it into the final article. At the time this article was in press I came across more important information on the collection and study of these specimens and unfortunately it was too late to add to the introductory section. Some of this new information (from quarry reports and correspondence), included here, clarifies or corrects introductory statements made in our paper.
In the late 1930s and early 1940s a paleontology inventory of portions of Texas was conducted under the Works Progress Administration (WPA), a relief program established by the U.S. Government to put millions of unemployed American men to work. Extensive quarrying was conducted at several sites in Texas including a series of Late Triassic age quarries near Otis Chalk in Howard County. These quarries contained thousands of bones of metoposaurs, phytosaurs, aetosaurs, etc., and are especially known for the well preserved skeletons of the archosauromorph Trilophosaurus buettneri (Gregory, 1945; Elder, 1978; Spielmann et al, 2008). Quarries 3 and 3A contained the majority of the aetosaur material including several partial to fairly complete aetosaur skeletons, only some of which has been prepared. The “best” two skeletons; however, were prepared and subject to a full description by Sawin (1947). Specimen lists compiled at the time of collection as well as work reports reveal that all of the aetosaur material was assigned to the genus Desmatosuchus at the time of collection. Many of the specimens still contain field numbers, which include the county name, quarry number, the year collected, and a fourth number that represents the order in which the specimen was removed from the ground and documented. Furthermore, collection records sometimes provide the name of the collector. Unfortunately, this number just reflects the collection order and often can be ambiguous about the association of specimens in the ground. In our paper we state that no excavation records could be found, but specimen lists and reports have since come to light although no detailed quarry maps are still known to exist.
Workers prepared the two associated skeletons, as well as the articulated tail of a third individual, and a variety of isolated elements. In the final publication (Sawin, 1947) the majority of these specimens are assigned to a new species, Typothorax meadei, based mainly on the sigmoidal shape of the femur (Sawin, 1947). Sawin also recognized a second species, T. coccinarum, as present in the quarry, but restricted this assignment to several osteoderms with large conical dorsal eminences, which he thought resembled the conical eminences in T. coccinarum osteoderms figured and described by von Huene (1915) and originally studied by Cope in 1887. Sawin (1947) designated the two main skeletons (Typothorax meadei) as syntypes and one of the specimens (TMM 31185-84a) was partially incorporated into a museum mount (some of the armor as well as the limbs) along with the articulated tail of the third individual. Much of the remaining material was left identified and catalogued in the collections as Desmatosuchus (contra Parker and Martz, 2010), including many lateral plates which were superficially similar to those of T. meadei. What is important is that none of this material is actually referable to Desmatosuchus (Parker and Martz, 2010).
In an unpublished M.S. thesis Elder (1978) noted this similarity and argued that Desmatosuchus and Typothorax were therefore synonymous. This was later refuted by Small (1989), but what is important to note is that like Sawin, Elder recognized two distinct morphologies in the Otis Chalk material.
Later recognition of the utility of osteoderms ornamentation in aetosaur taxonomy by Long and Ballew (1985) led those workers as well as others (e.g., Small, 1989) to recognize that T. meadei represented a distinct genus from T. coccinarum. Hunt and Lucas (1990) accordingly supplied the name Longosuchus meadei. Curiously, in their renaming of the material and designation of a lectotype Hunt and Lucas (1990) also included the material that Sawin (1947) had assigned to T. coccinarum. Unfortunately, no explanation is given for this and from the article it is not clear if Hunt and Lucas (1990) recognized that some of the material had originally been assigned to a different taxon. They also provide no discussion of the material referred to Desmatosuchus, but infer in their biochronology section that all of the Otis Chalk material belongs to a single taxon.
Subsequent re-examination of the material by Long and Murry (1995) led to the separation of Sawin’s (1947) “T. coccinarum” material as well as the “Desmatosuchus” material from the original T. meadei material of Sawin. Long and Murry (1995) assigned these specimens to a new taxon, Lucasuchus hunti (presumably in return for the name Longosuchus, named for Long). This reassigned was criticized, particularly by Heckert and Lucas (1999, 2000; and in numerous subsequent papers) and Lucas and Heckert (1996) who all stated that the diagnosis of Lucasuchus is “based on minor differences in scute morphology, some so subjective they cannot be replicated”. They also stated that Long and Murry (1995) “split” Longosuchus; however, this is incorrect as they only recognized the originally division of the material set forth by Sawin (1947).
In my own initial examination of the material (Parker, 2003) I felt that there actually were pretty clear differences between the holotype osteoderms of Lucasuchus and Longosuchus, especially in the paramedian osteoderm ornamentation and in the position of the dorsal eminence (see Parker and Martz, 2010). Moreover, although superficially similar there were also key differences between the lateral osteoderms of L. meadei and those catalogued as “Desmatosuchus” and assigned to Lucasuchus by Long and Murry (1995). What was ambiguous; however, was the association of these lateral osteoderms with the Lucasuchus paramedian osteoderms. Although Sawin (1947) felt that there were two morphotypes represented by the paramedian osteoderms in the collections, he clearly stated that no lateral osteoderms were associated with his “T. coccinarum” (Lucasuchus) material.
This last puzzle was solved unintentionally by Ron Tykoski, who while working for the Texas Memorial Museum (TMM) made a small collection of osteoderms to place around the base of the mount. One of the osteoderms he selected was a paramedian of Lucasuchus (TMM 31100-66) and nearby was a lateral osteoderm with the same number. Amazingly these two osteoderms fit together perfectly and unambiguously to form a conjoined pair, and thus must have come from the same individual. Even better, this lateral was of the Lucasuchus morphology and not from Longosuchus. Finally we were able to compare homologous series from both morphotypes to strongly (we feel) demonstrate support for Long and Murry’s (1995) reseparation of the material into two distinct taxa. This was the basis for the entire paper by Parker and Martz (2010).
One final puzzle (at least for me) was why Sawin had assigned the material to Typothorax in the first place? This is where knowledge of the historical context is crucial. At the time the material was collected (1939-1940) there were only three aetosaur taxa known from western North America, Typothorax, Episcoposaurus, and Desmatosuchus. By the time Sawin conducted his study it had been hypothesized by many workers that Episcoposaurus and Desmatosuchus were congeneric, something that was finalized later by Gregory (1953). This was based mainly on the material of Episcoposaurus haplocerus; however, another referred species E. horridus, had been collected in the same general area as the holotype and referred material of Typothorax coccinarum. Personal correspondence between Dr. John Wilson of the TMM and Dr. E. C. Case of the University of Michigan written in the 1940s clarify that Sawin travelled to the American Museum of Natural History to examine Cope’s material of E. horridus and T. coccinarum. This material, figured by Lucas et al (2007) contains two distinct femur morphologies. A gigantic straight femur was referred (by Cope) to E. horridus, whereas a much more gracile and strongly sigmoidal femur was assigned to T. coccinarum. The femora of Longosuchus meadei are nearly identical to that of the referred T. coccinarum specimens contra the statement by Heckert et al. (2010:637) that they are “dramatically different”. It was also on this visit that Sawin noted the conical eminences in the caudal osteoderms of T. coccinarum that formed the basis of his assignment of the Lucasuchus material to that taxon. Thus, finding the Wilson-Case correspondence solves the last part of the puzzle.
I hope that this case provides a good example of how essential understanding the context of the specimens on hand are when we try to determine aspects such as original association, curation, and taxonomy. With this information we can now understand why certain taxonomic assignments were made by past researchers. Allowing ourselves the opportunity to “walk in their boots” of our predecessors for awhile is an important tool in solving important scientific problems.
 |
| Paramedian osteoderms of Longosuchus meadei |
 |
| Paramedian osteoderm of Lucasuchus hunti. Note strong radial patterning and prominent, centralized raised eminence. |
REFERENCES
Elder, R. L. 1978. Paleontology and paleoecology of the Dockum Group, Upper Triassic, Howard County, Texas. M.S. thesis, University of Texas, Austin, Texas, 205 pp.
Gregory, J. T. 1945. Osteology and relationships of Trilophosaurus. University of Texas Publication 4401: 273-359.
Gregory, J. T. 1953. Typothorax and Desmatosuchus. Postilla 16:1–27.
Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.
Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late
Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt für Geologie und Paläontologie, Teil I, Heft 11–12:1539–1587.
Heckert, A. B. , Lucas, S. G. , Rinehart, L. F. , Celeskey, M. D. , Spielmann, J. A. and Hunt, A. P. 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: early-mid Norian), eastern New Mexico, USA. Journal of Vertebrate Paleontology 30:619 — 642
Huene, F. v. 1915. On reptiles of the New Mexican Trias in the Cope collection. Bulletin of the American Museum of Natural History 34:485–507.
Hunt, A. P., and S. G. Lucas. 1990. Re-evaluation of “Typothorax” meadei, a Late Triassic aetosaur from the United States. Paläontologische Zeitschrift 64:317–328.
Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45–68.
Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1–254.
Lucas, S. G., and A. B. Heckert. 1996. Late Triassic aetosaur biochronology. Albertiana 17:57–64.
Lucas, S. G., J. A. Spielmann, A. B. Heckert, and A. P. Hunt. 2007. Topotypes of Typothorax coccinarum, a Late Triassic aetosaur from the American Southwest. New Mexico Museum of Natural History and Science Bulletin 41:241–247.
Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. M.S. thesis, Northern Arizona University, Flagstaff, 315 pp.
Sawin, H. J. 1947. The pseudosuchian reptile Typothorax meadei. Journal of Paleontology 21:201–238.
Small, B. J. 1989. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry,West Texas; pp. 301–308 in S. G. Lucas and A. P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.
Spielmann, J. A., Lucas, S. G., Rinehart, L. F. and A. B. Heckert. 2008. The Late Triassic archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43: 1–177.
Bite Traces on Dicynodont Bones and the Early Evolution of Large Terrestrial Predators
Niedźwiedzki, G., Gorzelak, P. & Sulej, T. 2010: Bite traces on dicynodont bones and the early evolution of large terrestrial predators. Lethaia, DOI: 10.1111/j.1502-3931.2010.00227.x.
Abstract - Dicynodont (Synapsida: Anomodontia) bones from the Late Triassic (late Norian ⁄ early Rhaetian) of Poland yield characteristic tooth marks that can be attributed to three ichnotaxa (Linichnus serratus, Knethichnus parallelum and Nihilichnus nihilicus). The general shape and dimension of these traces perfectly match the dental morphology of a co-occurring carnivorous dinosaur. It is therefore concluded that early carnivorous dinosaurs were feeding on dicynodonts. This discovery constitutes one of the oldest evidence of dinosaur predator–prey interaction. It is suggested that an evolutionary increase in the size of dicynodonts across the Late Triassic may have been driven by selection pressure to reach a size refuge from early dinosaur predators.
Abstract - Dicynodont (Synapsida: Anomodontia) bones from the Late Triassic (late Norian ⁄ early Rhaetian) of Poland yield characteristic tooth marks that can be attributed to three ichnotaxa (Linichnus serratus, Knethichnus parallelum and Nihilichnus nihilicus). The general shape and dimension of these traces perfectly match the dental morphology of a co-occurring carnivorous dinosaur. It is therefore concluded that early carnivorous dinosaurs were feeding on dicynodonts. This discovery constitutes one of the oldest evidence of dinosaur predator–prey interaction. It is suggested that an evolutionary increase in the size of dicynodonts across the Late Triassic may have been driven by selection pressure to reach a size refuge from early dinosaur predators.
More Triassic Articles From the "New Aspects of Mesozoic Diversity" Book
Kemp, T. 2010. New Perspectives on the Evolution of Late Palaeozoic and Mesozoic Terrestrial Tetrapods; pp. 1-26 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7
Abstract - Palaeobiology, like all sciences, progresses by a combination of the discovery of new information, in this case fossils, the application of new techniques, and the development of new concepts with which to generate novel kinds of hypotheses. Research in the field of Late Palaeozoic and Mesozoic terrestrial tetrapods has involved major advances in all three of these over the last decade or so. Several new discoveries fill in gaps in the evolution of higher tetrapod taxa such as Tetrapoda, Dicynodontia, and birds, while others add significantly to the understanding of patterns of faunal turnover and palaeo-community structure.
The molecular revolution in biology is having a profound effect on several aspects of palaeobiology, in particular the use of large amounts of sequence data for phylogenetic studies and estimating branching dates. In some cases, notably placental mammals, this has produced results that highlight the limitations of purely morphological evidence in this, and probably other cases, and points to the desirability of seeking other kinds of evidence of relationships. Molecular developmental biology is starting to suggest new evolutionary hypotheses about the molecular genetic basis of the evolutionary transitions that can be inferred from the fossil record, such as how the tetrapod limb arose. In the field of functional analysis of fossils, CT scanning has opened the way to the application of such methods as finite element analysis for studying the mechanical design of fossil tetrapod skulls and skeletons. Geochemistry has also introduced new methods, notably stable isotope analysis, that have a direct bearing on the interpretation of the palaeoenvironmental background of major evolutionary events such as mass extinctions.
The principal new concept in palaeobiology arises from a shift towards the systems view that it is the interactions of the parts of a complex system, rather than the nature of the parts themselves that provide the main key to understanding how the system works. Correlated progression is a model based on this concept which offers a more realistic view of major evolutionary transitions such as the origins of tetrapods, mammals, and potentially all the higher taxa of tetrapods. Earth sciences are also moving more towards a systems way of thinking, such as when seeking explanations for mass extinctions.
Ray, S., Bandyopadhyay, S., and R. Appana. 2010. Bone Histology of a Kannemeyeriid Dicynodont Wadiasaurus: Palaeobiological Implications; pp. 73-89 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7
Abstract - Examination of the bone microstructure of several skeletal elements shows that the cortex comprises fibrolamellar bone tissue suggesting rapid osteogenesis and overall fast growth for Wadiasaurus, a kannemeyeriid dicynodont from India. Three distinct stages have been identified in the ontogeny of Wadiasaurus. In the juvenile stage, when up to 30% of adult size is attained, growth was fast and sustained, whereas in the sub-adult stage when up to 60% of adult size is attained, growth was fast but periodically interrupted as evident from the presence of growth marks. During the adult stage the bone microstructure is characterized by the presence of peripheral parallel-fibred bone that suggested considerable slowing down of growth, possibly with the onset of sexual maturity. A flexible and indeterminate growth strategy is proposed for Wadiasaurus. The cortical thickness (RBT) and the correspondingly low optimal k values of the various limb bones of Wadiasaurus were comparable with that of the land vertebrates such as Ceratotherium, suggesting that the limbs were selected for impact loading.
Abstract - Palaeobiology, like all sciences, progresses by a combination of the discovery of new information, in this case fossils, the application of new techniques, and the development of new concepts with which to generate novel kinds of hypotheses. Research in the field of Late Palaeozoic and Mesozoic terrestrial tetrapods has involved major advances in all three of these over the last decade or so. Several new discoveries fill in gaps in the evolution of higher tetrapod taxa such as Tetrapoda, Dicynodontia, and birds, while others add significantly to the understanding of patterns of faunal turnover and palaeo-community structure.
The molecular revolution in biology is having a profound effect on several aspects of palaeobiology, in particular the use of large amounts of sequence data for phylogenetic studies and estimating branching dates. In some cases, notably placental mammals, this has produced results that highlight the limitations of purely morphological evidence in this, and probably other cases, and points to the desirability of seeking other kinds of evidence of relationships. Molecular developmental biology is starting to suggest new evolutionary hypotheses about the molecular genetic basis of the evolutionary transitions that can be inferred from the fossil record, such as how the tetrapod limb arose. In the field of functional analysis of fossils, CT scanning has opened the way to the application of such methods as finite element analysis for studying the mechanical design of fossil tetrapod skulls and skeletons. Geochemistry has also introduced new methods, notably stable isotope analysis, that have a direct bearing on the interpretation of the palaeoenvironmental background of major evolutionary events such as mass extinctions.
The principal new concept in palaeobiology arises from a shift towards the systems view that it is the interactions of the parts of a complex system, rather than the nature of the parts themselves that provide the main key to understanding how the system works. Correlated progression is a model based on this concept which offers a more realistic view of major evolutionary transitions such as the origins of tetrapods, mammals, and potentially all the higher taxa of tetrapods. Earth sciences are also moving more towards a systems way of thinking, such as when seeking explanations for mass extinctions.
Ray, S., Bandyopadhyay, S., and R. Appana. 2010. Bone Histology of a Kannemeyeriid Dicynodont Wadiasaurus: Palaeobiological Implications; pp. 73-89 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7
Abstract - Examination of the bone microstructure of several skeletal elements shows that the cortex comprises fibrolamellar bone tissue suggesting rapid osteogenesis and overall fast growth for Wadiasaurus, a kannemeyeriid dicynodont from India. Three distinct stages have been identified in the ontogeny of Wadiasaurus. In the juvenile stage, when up to 30% of adult size is attained, growth was fast and sustained, whereas in the sub-adult stage when up to 60% of adult size is attained, growth was fast but periodically interrupted as evident from the presence of growth marks. During the adult stage the bone microstructure is characterized by the presence of peripheral parallel-fibred bone that suggested considerable slowing down of growth, possibly with the onset of sexual maturity. A flexible and indeterminate growth strategy is proposed for Wadiasaurus. The cortical thickness (RBT) and the correspondingly low optimal k values of the various limb bones of Wadiasaurus were comparable with that of the land vertebrates such as Ceratotherium, suggesting that the limbs were selected for impact loading.
New Late Triassic Sauropodomorph, Chromogisaurus novasi from Argentina
Ezcurra, M. D. 2010. A new early dinosaur (Saurischia: Sauropodomorpha) from the Late Triassic of Argentina: a reassessment of dinosaur origin and phylogeny. Journal of Systematic Palaeontology 8: 371-425.
Abstract - It was traditionally thought that the oldest known dinosaur assemblages were not diverse, and that their early diversification and numerical dominance over other tetrapods occurred during the latest Triassic. However, new evidence gathered from the lower levels of the Ischigualasto Fm. of Argentina challenges this view. New dinosaur remains are described from this stratigraphical unit, including the new species Chromogisaurus novasi. This taxon is distinguished from other basal dinosauriforms by the presence of proximal caudals without median notch separating the postzygapophyses, femoral lateral surface with deep and large fossa immediately below the trochanteric shelf, and metatarsal II with strongly dorsoventrally asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first time suggested for Guaibasaurus, whereas Panphagia is not recovered as the most basal sauropodomorph. Furthermore, Chromogisaurus is consistently located as more closely related to Saturnalia than to any other dinosaur. Thus, the Saturnalia + Chromogisaurus clade is named here as the new subfamily Saturnaliinae. In addition, Eoraptor is found to be the sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian saurischians. The new evidence presented here demonstrates that dinosaurs first appeared in the fossil record as a diverse group, although they were a numerically minor component of faunas in which they occur. Accordingly, the early increase of dinosaur diversity and their numerical dominance over other terrestrial tetrapods were diachronous processes, with the latter preceded by a period of low abundance but high diversity.
Besides the information provided in the abstract here are a couple of other tidbits:
1) Diagnosis: the holotype material is very fragmentary, but Chromogisaurus novasi is diagnosed by "the following combination of characteristics (autapomorphies∗): proximal caudals without median notch separating the postzygapophyses; ilium with strongly posteriorly developed postacetabular process; incipiently perforated acetabulum; a femoral lateral surface with deep and large fossa immediately below the trochanteric shelf;∗ and a metatarsal II with strongly dorsoventrally asymmetric distal condyles" (Ezcurra, 2010:374).
2) Etymology: The generic name is a combination of the Greek "chroma" (color) and "gi" (ground or land) for the Painted Valley where the specimen was collected.
3) Clades: This paper provides definitions for the newly recovered clades Guaibasauridae and Saturnaliinae.
4) Chindesaurus: The paper contains discussion on the phylogenetic position of Chindesaurus bryansmalli from the Chinle Formation. This study (378 characters) finds Chindesaurus as eithr a basal theropod or as a non-eusaurischian saurischian.
5) Photos: There is a nice comparative figure (photos) of the skulls of Herrerasaurus, Eoraptor, and Zupaysaurus.
I'm looking forward to reading the rest of this....
Abstract - It was traditionally thought that the oldest known dinosaur assemblages were not diverse, and that their early diversification and numerical dominance over other tetrapods occurred during the latest Triassic. However, new evidence gathered from the lower levels of the Ischigualasto Fm. of Argentina challenges this view. New dinosaur remains are described from this stratigraphical unit, including the new species Chromogisaurus novasi. This taxon is distinguished from other basal dinosauriforms by the presence of proximal caudals without median notch separating the postzygapophyses, femoral lateral surface with deep and large fossa immediately below the trochanteric shelf, and metatarsal II with strongly dorsoventrally asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first time suggested for Guaibasaurus, whereas Panphagia is not recovered as the most basal sauropodomorph. Furthermore, Chromogisaurus is consistently located as more closely related to Saturnalia than to any other dinosaur. Thus, the Saturnalia + Chromogisaurus clade is named here as the new subfamily Saturnaliinae. In addition, Eoraptor is found to be the sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian saurischians. The new evidence presented here demonstrates that dinosaurs first appeared in the fossil record as a diverse group, although they were a numerically minor component of faunas in which they occur. Accordingly, the early increase of dinosaur diversity and their numerical dominance over other terrestrial tetrapods were diachronous processes, with the latter preceded by a period of low abundance but high diversity.
Besides the information provided in the abstract here are a couple of other tidbits:
1) Diagnosis: the holotype material is very fragmentary, but Chromogisaurus novasi is diagnosed by "the following combination of characteristics (autapomorphies∗): proximal caudals without median notch separating the postzygapophyses; ilium with strongly posteriorly developed postacetabular process; incipiently perforated acetabulum; a femoral lateral surface with deep and large fossa immediately below the trochanteric shelf;∗ and a metatarsal II with strongly dorsoventrally asymmetric distal condyles" (Ezcurra, 2010:374).
2) Etymology: The generic name is a combination of the Greek "chroma" (color) and "gi" (ground or land) for the Painted Valley where the specimen was collected.
3) Clades: This paper provides definitions for the newly recovered clades Guaibasauridae and Saturnaliinae.
4) Chindesaurus: The paper contains discussion on the phylogenetic position of Chindesaurus bryansmalli from the Chinle Formation. This study (378 characters) finds Chindesaurus as eithr a basal theropod or as a non-eusaurischian saurischian.
5) Photos: There is a nice comparative figure (photos) of the skulls of Herrerasaurus, Eoraptor, and Zupaysaurus.
I'm looking forward to reading the rest of this....
Pterosauria from the Late Triassic of Southern Brazil
This is an article in a recent book titled New Aspects of Mesozoic Biodiversity, part of SpringerLinks Lecture Notes in Earth Sciences book series.
Bonaparte, J. F., Schultz, C. L., and M. B. Soares. 2010. Pterosauria from the Late Triassic of Southern Brazil, pp. 63-71 in Bandyopadhyay, S. (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, Springer-Verlag Berlin/ Heidelberg, DOI: 10.1007/978-3-642-10311-7
Abstract - A few postcranial remains of a Late Triassic pterosaur from the early Coloradian Caturrita Formation of Rio Grande do Sul are communicated. The general morphology of the coracoid, proximal portion of the humerus, femur, tibia and fibula suggests that it is more primitive than the pterosaurs from the Norian of northern Italy. The morphology and proportions of the different bones support their assignment to a primitive pterosaur. An almost complete maxilla with three teeth is tentatively referred to the same taxon because it was collected at some distance from the postcrania cited above. This pterosaur is possibly older than other Triassic pterosaurs and was recorded from a typical terrestrial environment. It suggests that the earliest pterosaurs evolved in continental and littoral marine environments.
Bonaparte, J. F., Schultz, C. L., and M. B. Soares. 2010. Pterosauria from the Late Triassic of Southern Brazil, pp. 63-71 in Bandyopadhyay, S. (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, Springer-Verlag Berlin/ Heidelberg, DOI: 10.1007/978-3-642-10311-7
Abstract - A few postcranial remains of a Late Triassic pterosaur from the early Coloradian Caturrita Formation of Rio Grande do Sul are communicated. The general morphology of the coracoid, proximal portion of the humerus, femur, tibia and fibula suggests that it is more primitive than the pterosaurs from the Norian of northern Italy. The morphology and proportions of the different bones support their assignment to a primitive pterosaur. An almost complete maxilla with three teeth is tentatively referred to the same taxon because it was collected at some distance from the postcrania cited above. This pterosaur is possibly older than other Triassic pterosaurs and was recorded from a typical terrestrial environment. It suggests that the earliest pterosaurs evolved in continental and littoral marine environments.
New in Palaeotologia Electronica: The Digital Plateosaurus.
The new issue of Palaeontologia Electronica is now available online including this article:
Mallison, H. 2010. The digital Plateosaurus I: body mass, mass distribution and posture assessed using CAD and CAE on a digitally mounted complete skeleton. Palaeontologia Electronica Vol. 13, Issue 2; 8A: 26p; http://palaeo-electronica.org/2010_2/198/index.html
Abstract - Plateosaurus from the late Triassic of Central Europe is one of the best known dinosaurs. Despite the large number of finds, including complete and articulated skeletons, its posture and locomotion capabilities are still being debated. While recent assessments of the range of motion of the forelimb indicate that Plateosaurus was incapable of manus pronation, and thus an obligate biped, practically all other possible alternatives have been suggested in the literature. Here, I present evidence, derived from a detailed mounting of a 3D digital skeleton and a computer-aided engineering assessment of a digital 3D model of the living animal, that Plateosaurus was indeed an obligate biped. The position of the center of mass is assessed in several variations of the basic model to account for differing interpretations of soft tissue amounts. All models allow a stable bipedal pose with a subhorizontal back that is consistent with the requirements of both slow and rapid locomotion. Quadrupedal models, in contrast, suffer from locomotion restrictions due to highly uneven limb lengths and a limited motion range in the forelimb, and result in a smaller feeding envelope.
Mallison, H. 2010. The digital Plateosaurus I: body mass, mass distribution and posture assessed using CAD and CAE on a digitally mounted complete skeleton. Palaeontologia Electronica Vol. 13, Issue 2; 8A: 26p; http://palaeo-electronica.org/2010_2/198/index.html
Abstract - Plateosaurus from the late Triassic of Central Europe is one of the best known dinosaurs. Despite the large number of finds, including complete and articulated skeletons, its posture and locomotion capabilities are still being debated. While recent assessments of the range of motion of the forelimb indicate that Plateosaurus was incapable of manus pronation, and thus an obligate biped, practically all other possible alternatives have been suggested in the literature. Here, I present evidence, derived from a detailed mounting of a 3D digital skeleton and a computer-aided engineering assessment of a digital 3D model of the living animal, that Plateosaurus was indeed an obligate biped. The position of the center of mass is assessed in several variations of the basic model to account for differing interpretations of soft tissue amounts. All models allow a stable bipedal pose with a subhorizontal back that is consistent with the requirements of both slow and rapid locomotion. Quadrupedal models, in contrast, suffer from locomotion restrictions due to highly uneven limb lengths and a limited motion range in the forelimb, and result in a smaller feeding envelope.
Feeding-Related Characters in Basal Pterosaurs
Osi, A. 2010: Feeding-related characters in basal pterosaurs: implications for jaw mechanism, dental function and diet. Lethaia, DOI: 10.1111/j.1502-3931.2010.00230.x.
Abstract - A comparative study of various feeding-related features in basal pterosaurs reveals a significant change in feeding strategies during the early evolutionary history of the group. These features are related to the skull architecture (e.g. quadrate morphology and orientation, jaw joint), dentition (e.g. crown morphology, wear patterns), reconstructed adductor musculature and post-cranium. The most basal pterosaurs (Preondactylus, dimorphodontids and anurognathids) were small-bodied animals with a wingspan no greater than 1.5 m, a relatively short, lightly constructed skull, straight mandibles with a large gape, sharply pointed teeth and well-developed external adductors. The absence of extended tooth wear excludes complex oral food processing and indicates that jaw closure was simply orthal. Features of these basal-most forms indicate a predominantly insectivorous diet. Among stratigraphically older but more derived forms (Eudimorphodon, Carniadactylus, Caviramus) complex, multicuspid teeth allowed the consumption of a wider variety of prey via a more effective form of food processing. This is supported by heavy dental wear in all forms with multicuspid teeth. Typical piscivorous forms occurred no earlier than the Early Jurassic, and are characterized by widely spaced, enlarged procumbent teeth forming a fish grab and an anteriorly inclined quadrate that permitted only a relatively small gape. In addition, the skull became more elongate and body size increased. Besides the dominance of piscivory, dental morphology and the scarcity of tooth wear reflect accidental dental occlusion that could have been caused by the capturing or seasonal consumption of harder food items.
Abstract - A comparative study of various feeding-related features in basal pterosaurs reveals a significant change in feeding strategies during the early evolutionary history of the group. These features are related to the skull architecture (e.g. quadrate morphology and orientation, jaw joint), dentition (e.g. crown morphology, wear patterns), reconstructed adductor musculature and post-cranium. The most basal pterosaurs (Preondactylus, dimorphodontids and anurognathids) were small-bodied animals with a wingspan no greater than 1.5 m, a relatively short, lightly constructed skull, straight mandibles with a large gape, sharply pointed teeth and well-developed external adductors. The absence of extended tooth wear excludes complex oral food processing and indicates that jaw closure was simply orthal. Features of these basal-most forms indicate a predominantly insectivorous diet. Among stratigraphically older but more derived forms (Eudimorphodon, Carniadactylus, Caviramus) complex, multicuspid teeth allowed the consumption of a wider variety of prey via a more effective form of food processing. This is supported by heavy dental wear in all forms with multicuspid teeth. Typical piscivorous forms occurred no earlier than the Early Jurassic, and are characterized by widely spaced, enlarged procumbent teeth forming a fish grab and an anteriorly inclined quadrate that permitted only a relatively small gape. In addition, the skull became more elongate and body size increased. Besides the dominance of piscivory, dental morphology and the scarcity of tooth wear reflect accidental dental occlusion that could have been caused by the capturing or seasonal consumption of harder food items.
Why Were Dicynodonts so Successful Before and After the End-Permian Extinction?
Botha-Brink, J., and K. Angielczyk. 2010. Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction? Zoological Journal of the Linnean Society, early online, doi: 10.1111/j.1096-3642.2009.00601.x
Abstract - Dicynodonts were the most diverse and abundant herbivorous therapsids of the Permo-Triassic. They include Lystrosaurus, one of the few taxa known to survive the end-Permian extinction and the most abundant tetrapod during the Early Triassic postextinction recovery. Explanations for the success of Lystrosaurus and other dicynodonts remain controversial. This study presents an assessment of dicynodont growth patterns using bone histology, with special focus on taxa associated with the end-Permian extinction event. Bone histological analysis reveals a high cortical thickness throughout the clade, perhaps reflecting a phylogenetic constraint. Growth rings are absent early in ontogeny, and combined with high vascular density, indicate rapid, sustained growth up to the subadult stage. Extraordinarily enlarged vascular channels are present in the midcortex of many dicynodonts, including adults, and may have facilitated a more efficient assimilation of nutrients and rapid bone growth compared to other therapsids. Both increased channel density and enlarged vascular channels evolved at or near the base of major radiations of dicynodonts, implying that the changes in growth and life history they represent may have been key to the success of dicynodonts. Furthermore, this exceptionally rapid growth to adulthood may have contributed to the survival of Lystrosaurus during the end-Permian extinction and its dominance during the postextinction recovery period.
Abstract - Dicynodonts were the most diverse and abundant herbivorous therapsids of the Permo-Triassic. They include Lystrosaurus, one of the few taxa known to survive the end-Permian extinction and the most abundant tetrapod during the Early Triassic postextinction recovery. Explanations for the success of Lystrosaurus and other dicynodonts remain controversial. This study presents an assessment of dicynodont growth patterns using bone histology, with special focus on taxa associated with the end-Permian extinction event. Bone histological analysis reveals a high cortical thickness throughout the clade, perhaps reflecting a phylogenetic constraint. Growth rings are absent early in ontogeny, and combined with high vascular density, indicate rapid, sustained growth up to the subadult stage. Extraordinarily enlarged vascular channels are present in the midcortex of many dicynodonts, including adults, and may have facilitated a more efficient assimilation of nutrients and rapid bone growth compared to other therapsids. Both increased channel density and enlarged vascular channels evolved at or near the base of major radiations of dicynodonts, implying that the changes in growth and life history they represent may have been key to the success of dicynodonts. Furthermore, this exceptionally rapid growth to adulthood may have contributed to the survival of Lystrosaurus during the end-Permian extinction and its dominance during the postextinction recovery period.
Functional Implications of Dermal Bone Ornamentation in Basal Tetrapods
Metoposaurs are a very common component of the Chinle Formation fauna, especially the lower portions. I often get questions on the function of the ornament of metoposaur dermal bones (skull, clavicles, interclavicle) and finally some of those questions can be answered.
Witzmann, F., Scholz, H., Mueller, J., and N. Kardjilov. 2010. Sculpture and vascularization of dermal bones, and the implications for the physiology of basal tetrapods. Zoological Journal of the Linnean Society, early online. doi: 10.1111/j.1096-3642.2009.00599.x
Abstract - Sculpture of dermal bones and their vascularization in basal tetrapods are closely connected. Ontogenetic data suggest that the large vessels that coursed to the superficial bone surface induced the formation of sculptural ridges and tubercles around their openings. Imprints show that the vessels continued on the bone surface and coursed within furrows or pits, where they were protected by the sculpture from mechanical damage. Dermal bone histology indicates a consolidation of the integument in basal tetrapods by strong, mineralized Sharpey’s fibres in the sculptural ridges and tubercles, and by the presence of metaplastic tissue in several taxa. Because of the tight integration of bone and dermis, the large vessels were not able to spread over the sculptural elements, but instead had to pass interosseously. The diverse sculptural morphologies depend on the variation in height and width of the ‘nodal points’ and their connecting ridges, and in the size and shape of the enclosed cells and furrows. A principal component analysis (PCA) and discriminant function analysis (DFA) of 47 basal tetrapod taxa with 12 discrete characters shows that dermal sculpture is suited for distinguishing some main basal tetrapod lineages. Taxa that are interpreted as being largely aquatic have generally a more regular sculpture than presumably terrestrial ones.
Witzmann, F., Scholz, H., Mueller, J., and N. Kardjilov. 2010. Sculpture and vascularization of dermal bones, and the implications for the physiology of basal tetrapods. Zoological Journal of the Linnean Society, early online. doi: 10.1111/j.1096-3642.2009.00599.x
Abstract - Sculpture of dermal bones and their vascularization in basal tetrapods are closely connected. Ontogenetic data suggest that the large vessels that coursed to the superficial bone surface induced the formation of sculptural ridges and tubercles around their openings. Imprints show that the vessels continued on the bone surface and coursed within furrows or pits, where they were protected by the sculpture from mechanical damage. Dermal bone histology indicates a consolidation of the integument in basal tetrapods by strong, mineralized Sharpey’s fibres in the sculptural ridges and tubercles, and by the presence of metaplastic tissue in several taxa. Because of the tight integration of bone and dermis, the large vessels were not able to spread over the sculptural elements, but instead had to pass interosseously. The diverse sculptural morphologies depend on the variation in height and width of the ‘nodal points’ and their connecting ridges, and in the size and shape of the enclosed cells and furrows. A principal component analysis (PCA) and discriminant function analysis (DFA) of 47 basal tetrapod taxa with 12 discrete characters shows that dermal sculpture is suited for distinguishing some main basal tetrapod lineages. Taxa that are interpreted as being largely aquatic have generally a more regular sculpture than presumably terrestrial ones.
Two New Triassic Papers in Palaeo 3
Algeo, T. J., Kuwahara, K., Sano, H., Bates, S., Lyons, T., Elswick, E., Hinnov, L., Ellwood, B., Moser, J., and J. B. Maynard. 2010. Spatial variation in sediment fluxes, redox conditions, and productivity in the Permian-Triassic Panthalassic Ocean, Palaeogeography, Palaeoclimatology, Palaeoecology (2010), doi: 10.1016/j.palaeo.2010.07.007
Abstract - Two Permian/Triassic boundary sections in central Japan provide a rare window into environmental conditions within the Panthalassic Ocean, which encompassed more than half the Earth’s surface at 252 Ma. Integration of petrographic, geochemical, and time-series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site. The Ubara section was located in a high-productivity peri-equatorial location, whereas the Gujo-Hachiman section was located in a moderate-productivity location at some distance from the paleoequator. An upward transition from gray organic-poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity, intensified euxinia within the oxygen-minimum zone (OMZ), and decimation of the radiolarian zooplankton community. Euxinia in the OMZ of the equatorial Panthalassic Ocean developed episodically for a ~200-250 kyr interval during the Late Permian, followed by an abrupt intensification and lateral expansion of the OMZ around the Permian-Triassic boundary. Throughout the study interval, bottom waters at both sites remained mostly suboxic, a finding that counters hypotheses of development of a “superanoxic” Permo-Triassic deep ocean as a consequence of stagnation of oceanic overturning circulation.
Shukla, U. K., Bachmann, G. H., and I. B. Singh. 2010. Facies architecture of the Stuttgart Formation (Schilfsandstein, Upper Triassic), central Germany, and its comparison with modern Ganga system, India, Palaeogeography Palaeoclimatology, Palaeoecology (2010), doi: 10.1016/j.palaeo.2010.07.019
Abstract - The Stuttgart Formation (Schilfsandstein) is approximately 50 m thick in Thuringia, representing deposition during the “Mid-Carnian Wet Intermezzo”. Stratigraphically it occurs between the Grabfeld and Weser formations, which formed under arid conditions. It comprises NNE-SSW-trending elongate, anastomosing channelised sand-rich bodies with erosional bases (channel belts) that are several kilometres wide and pass laterally into predominantly mudstones deposited in interfluve areas. The source area of these clastics was the uplifted Norwegian Caledonides. Muddy interfluve facies is dominant in exposures in Thuringia, Central Germany. The Lower Stuttgart Formation has an unconformable base that is locally overlain by meter-thick “Basal Beds”. These consist of grey mudstones and thin sandstones deposited under humid conditions in predominantly shallow brackish water environments after a marine ingression via the Eastern Carpathian/Upper Silesian Gate. The following 30–40 m- grey, finegrained sandstones, siltstones and mudstones were deposited in fluvial environments in channel belts and interfluve areas under humid conditions. These are followed by predominantly reddish mudstones and sandstones of mainly fluvial origin, deposited under somewhat drier conditions with seasonal droughts. The Upper Stuttgart Formation may be more than 16 mthick; it comprises reddish and grey sandstones and mudstones that were mostly deposited in lake-delta settings by recurring flash floods. During the deposition of this unit climate was weakly humid with less prominent seasonal draughts. The modern Ganga Plain of India is an analogue for the depositional setting of the Stuttgart Formation. Climatic conditions in Ganga Plain are humid monsoonal with seasonal droughts and roughly comparable with those interpreted for Mid-Carnian times in Germany. The sandy deposits of incised channel belts and channels and muddy deposits of interfluve areas in the Ganga Plain are comparable with the sandstone-dominated channelized facies and mudstone-dominated interfluve facies of the Stuttgart Formation, respectively.
Abstract - Two Permian/Triassic boundary sections in central Japan provide a rare window into environmental conditions within the Panthalassic Ocean, which encompassed more than half the Earth’s surface at 252 Ma. Integration of petrographic, geochemical, and time-series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site. The Ubara section was located in a high-productivity peri-equatorial location, whereas the Gujo-Hachiman section was located in a moderate-productivity location at some distance from the paleoequator. An upward transition from gray organic-poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity, intensified euxinia within the oxygen-minimum zone (OMZ), and decimation of the radiolarian zooplankton community. Euxinia in the OMZ of the equatorial Panthalassic Ocean developed episodically for a ~200-250 kyr interval during the Late Permian, followed by an abrupt intensification and lateral expansion of the OMZ around the Permian-Triassic boundary. Throughout the study interval, bottom waters at both sites remained mostly suboxic, a finding that counters hypotheses of development of a “superanoxic” Permo-Triassic deep ocean as a consequence of stagnation of oceanic overturning circulation.
Shukla, U. K., Bachmann, G. H., and I. B. Singh. 2010. Facies architecture of the Stuttgart Formation (Schilfsandstein, Upper Triassic), central Germany, and its comparison with modern Ganga system, India, Palaeogeography Palaeoclimatology, Palaeoecology (2010), doi: 10.1016/j.palaeo.2010.07.019
Abstract - The Stuttgart Formation (Schilfsandstein) is approximately 50 m thick in Thuringia, representing deposition during the “Mid-Carnian Wet Intermezzo”. Stratigraphically it occurs between the Grabfeld and Weser formations, which formed under arid conditions. It comprises NNE-SSW-trending elongate, anastomosing channelised sand-rich bodies with erosional bases (channel belts) that are several kilometres wide and pass laterally into predominantly mudstones deposited in interfluve areas. The source area of these clastics was the uplifted Norwegian Caledonides. Muddy interfluve facies is dominant in exposures in Thuringia, Central Germany. The Lower Stuttgart Formation has an unconformable base that is locally overlain by meter-thick “Basal Beds”. These consist of grey mudstones and thin sandstones deposited under humid conditions in predominantly shallow brackish water environments after a marine ingression via the Eastern Carpathian/Upper Silesian Gate. The following 30–40 m- grey, finegrained sandstones, siltstones and mudstones were deposited in fluvial environments in channel belts and interfluve areas under humid conditions. These are followed by predominantly reddish mudstones and sandstones of mainly fluvial origin, deposited under somewhat drier conditions with seasonal droughts. The Upper Stuttgart Formation may be more than 16 mthick; it comprises reddish and grey sandstones and mudstones that were mostly deposited in lake-delta settings by recurring flash floods. During the deposition of this unit climate was weakly humid with less prominent seasonal draughts. The modern Ganga Plain of India is an analogue for the depositional setting of the Stuttgart Formation. Climatic conditions in Ganga Plain are humid monsoonal with seasonal droughts and roughly comparable with those interpreted for Mid-Carnian times in Germany. The sandy deposits of incised channel belts and channels and muddy deposits of interfluve areas in the Ganga Plain are comparable with the sandstone-dominated channelized facies and mudstone-dominated interfluve facies of the Stuttgart Formation, respectively.
Deposition and Preservation in the Upper Triassic Solite Quarry Lagerstätte in Virginia
Liutkus, C.M., Beard, J.S., Fraser, N.C., and P. C. Ragland. 2010. Use of fine-scale stratigraphy and chemostratigraphy to evaluate conditions of deposition and preservation of a Triassic Lagerstätte, south-central Virginia. Journal of Paleolimnology 44(2):645-666. doi: 10.1007/s10933-010-9445-1.
Abstract - The rich, fossiliferous Triassic sediments exposed in the Virginia Solite Quarry include a 34-mm-thick “insect layer” that is notable for detailed preservation of soft-bodied invertebrate and vertebrate remains. We describe this unique Konservat-Lagerstätte and use sedimentologic and geochemical analyses to interpret the environmental conditions necessary to preserve such delicate fossils. This work is among the first attempts to apply detailed geochemical/stratigraphic analysis to the study of Lagerstätten and we report on a 332-mm-thick section that includes the insect layer and the rocks immediately below and above it. Our analysis successfully constrains various aspects of the depositional and diagenetic history of the Lagerstätte and permits a detailed analysis of changing conditions prior to, during, and after deposition. Geochemical and sedimentologic analyses of the insect layer and surrounding lithologies reveal a change from siliciclastic-dominated layers (Unit 1) to dolomite-siliciclastic laminites above (Unit 2 and the insect layer), separated by a boundary dolostone layer that is traceable for over 200 m. We interpret this sedimentary shift as the initial stages in the transgression of a shallow, saline, alkaline rift-basin lake over lake margin deposits. The absence of bioturbation by plants and benthic organisms, as well as a lack of predation on the insects, is not explained by significant water depth, but is instead more reasonably considered a result of the chemistry of the water at the lake margin, affected by groundwater seeps, which provided F-, Mg-, and Ca-rich fluids. Although the initial conditions of preservation are remarkable, it is equally impressive that the fossils survived extensive diagenesis, e.g. dissolution of quartz and coarsening of dolomite.
Abstract - The rich, fossiliferous Triassic sediments exposed in the Virginia Solite Quarry include a 34-mm-thick “insect layer” that is notable for detailed preservation of soft-bodied invertebrate and vertebrate remains. We describe this unique Konservat-Lagerstätte and use sedimentologic and geochemical analyses to interpret the environmental conditions necessary to preserve such delicate fossils. This work is among the first attempts to apply detailed geochemical/stratigraphic analysis to the study of Lagerstätten and we report on a 332-mm-thick section that includes the insect layer and the rocks immediately below and above it. Our analysis successfully constrains various aspects of the depositional and diagenetic history of the Lagerstätte and permits a detailed analysis of changing conditions prior to, during, and after deposition. Geochemical and sedimentologic analyses of the insect layer and surrounding lithologies reveal a change from siliciclastic-dominated layers (Unit 1) to dolomite-siliciclastic laminites above (Unit 2 and the insect layer), separated by a boundary dolostone layer that is traceable for over 200 m. We interpret this sedimentary shift as the initial stages in the transgression of a shallow, saline, alkaline rift-basin lake over lake margin deposits. The absence of bioturbation by plants and benthic organisms, as well as a lack of predation on the insects, is not explained by significant water depth, but is instead more reasonably considered a result of the chemistry of the water at the lake margin, affected by groundwater seeps, which provided F-, Mg-, and Ca-rich fluids. Although the initial conditions of preservation are remarkable, it is equally impressive that the fossils survived extensive diagenesis, e.g. dissolution of quartz and coarsening of dolomite.
Two New Biology/Paleontology Blogs
By some strange cosmic cooincidence both the Witmer Lab and the Holliday Lab launched new blogs at nearly the same microsecond. Check them out.
http://witmerlab.wordpress.com/
http://hollidaylab.wordpress.com/
I see that Paleo Errata, but not Chinleana, made the Blogroll at Pick & Scapel, Guess I need to make my posts a little more ....um...how do you say it? Martzified? ;)
http://witmerlab.wordpress.com/
http://hollidaylab.wordpress.com/
I see that Paleo Errata, but not Chinleana, made the Blogroll at Pick & Scapel, Guess I need to make my posts a little more ....um...how do you say it? Martzified? ;)
New Triassic Paper in PloS ONE
Klein, N. 2010. Long Bone Histology of Sauropterygia from the Lower Muschelkalk of the Germanic Basin Provides Unexpected Implications for Phylogeny. PLoS ONE 5(7): e11613. doi:10.1371/journal.pone.0011613
Abstract
Background
Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic material from the Germanic Basin and uniformity of postcranial morphology of eosauropterygians. In the current paper, morphotypes of humeri along with their corresponding bone histologies for Lower to Middle Muschelkalk sauropterygians are described and interpreted for the first time in a phylogenetic context.
Methodology/Principal Findings
Nothosaurus shows a typical plesiomorphic lamellar-zonal bone type, but varying growth patterns and the occurrence of a new humerus morphotype point to a higher taxonomic diversity than was known. In contrast to the enormous morphological variability of eosauropterygian humeri not assigned to Nothosaurus, their long bone histology is relatively uniform and can be divided into two histotypes. Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. Histotype B is related to the pachypleurosaur Anarosaurus. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus.
Conclusions/Significance
Histological results hypothetically discussed in a phylogenetical context have a large impact on the current phylogenetic hypothesis of Sauropterygia, leaving the pachypleurosaurs polyphyletic. On the basis of histological data, Neusticosaurus would be related to Nothosaurus, whereas Anarosaurus would follow the pistosaur clade. Furthermore, the presence of fibrolamellar bone, which is accompanied with increased growth rates and presumably even with increased metabolic rates, already in Anarosaurus and Cymatosaurus can explain the success of the Pistosauroidea, the only sauropterygian group to survive into the Jurassic and give rise to the pelagic plesiosaur radiation.
Abstract
Background
Sauropterygia is an abundant and successful group of Triassic marine reptiles. Phylogenetic relationships of Triassic Sauropterygia have always been unstable and recently questioned. Although specimens occur in high numbers, the main problems are rareness of diagnostic material from the Germanic Basin and uniformity of postcranial morphology of eosauropterygians. In the current paper, morphotypes of humeri along with their corresponding bone histologies for Lower to Middle Muschelkalk sauropterygians are described and interpreted for the first time in a phylogenetic context.
Methodology/Principal Findings
Nothosaurus shows a typical plesiomorphic lamellar-zonal bone type, but varying growth patterns and the occurrence of a new humerus morphotype point to a higher taxonomic diversity than was known. In contrast to the enormous morphological variability of eosauropterygian humeri not assigned to Nothosaurus, their long bone histology is relatively uniform and can be divided into two histotypes. Unexpectedly, both of these histotypes reveal abundant fibrolamellar bone throughout the cortex. This pushes the origin of fibrolamellar bone in Sauropterygia back from the Cretaceous to the early Middle Triassic (early Anisian). Histotype A is assigned to Cymatosaurus, a basal member of the Pistosauroidea, which includes the plesiosaurs as derived members. Histotype B is related to the pachypleurosaur Anarosaurus. Contrary to these new finds, the stratigraphically younger pachypleurosaur Neusticosaurus shows the plesiomorphic lamellar-zonal bone type and an incomplete endochondral ossification, like Nothosaurus.
Conclusions/Significance
Histological results hypothetically discussed in a phylogenetical context have a large impact on the current phylogenetic hypothesis of Sauropterygia, leaving the pachypleurosaurs polyphyletic. On the basis of histological data, Neusticosaurus would be related to Nothosaurus, whereas Anarosaurus would follow the pistosaur clade. Furthermore, the presence of fibrolamellar bone, which is accompanied with increased growth rates and presumably even with increased metabolic rates, already in Anarosaurus and Cymatosaurus can explain the success of the Pistosauroidea, the only sauropterygian group to survive into the Jurassic and give rise to the pelagic plesiosaur radiation.
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