Sorry to dredge this up again, but I'd really like some input here from my readers. In the past there has been much discussion of how new taxonomic names (i.e. genera and species) published solely in electronic format do not meet the requirements of the ICZN, nor will they meet the requirements of the most recent draft of PhyloCode when it is finally enacted. Journals such as PLoSONE and Palaeontologica Electronica have averted this by providing hard copy as well. However, past discussion has only discussed articles that are officially published.
A new dinosaurian taxon currently hitting the blogosphere is a ceratopsian dinosaur on exhibit at the Sam Noble Museum of Natural History in Norman, OK. Norman hosted the annual SVP meeting less than a decade ago and many of us got to see this monster up close, it is quite amazing. A recent blog post on this manuscript over at Love in the Time of Chasmosaurs (one of the best dino news blogs out there IMO, and thus this is not a critique of that post or the site) states that this new specimen has been published this week in the journal Cretaceous Research. However, a visit to the journal website shows that this paper is not in the most recent paper copy of the journal, nor is it even a finished paper published online in advance of print. Instead it is currently only an accepted manuscript and still has to go through the steps of being assigned to a journal issue, not to mention the final proof stage. Thus this new taxonomic name is still pretty far out from the final publication stage. How far? Depends on the journal. Back around this time in 2006 I had a proposed taxonomic name in a paper that had been in the "accepted" stage for almost a year! Most of you probably know how that situation ended. "Accepted" technically is "in press", but until it has been assigned to an issue and the proof stage has been passed there really is no guarantee that the paper will be published anytime soon. Furthermore, various aspects of the paper, including the name, could still change at this stage.
What is to stop someone from providing a really quick publication through a faster outlet (including unfortunately something purportedly called "lulu press")? Nothing except personal ethics of individual researchers and maybe the fear that if someone ever did something so unscrupulous (after having seen the accepted paper) they would get called out by their peers. It seems like a risk to me, especially as this is a specimen that has been on public display for years and there are numerous photos out there.
Also, what if the authors themselves think of a name (genus and/or species) they like better than the current one? At this stage they could still change it. Although they still get the credit for the new name, the old name technically would still be available for another specimen in the future and could cause confusion if someone decided to use it. This does happen. For example, Adamanasuchus was a name originally proposed for the animal now known as Vancleavea. It was published first as a nomen nudum in a 1983 issue of Arizona Highways magazine. Lucas et al 2006 have since used this name (currently valid) for an aetosaur from the same stratigraphic horizon and geographical location.
Furthermore, a purview through the list of "in press" papers at Cretaceous Research shows that this is not the only newly proposed taxonomic name hanging out there. I understand that the journal provides these papers early as a "service" to the readers, but given the taxonomic rules we all abide by that provides the accepted name to the first published in PRINT, I feel that the journals are taking a chance on our hard work going into this research. Sorry but a DOI reference still does not count.
I like readers opinions on this type of extreme early "publishing". Am a sounding overly cautious? Maybe, but I personally don't feel like getting burned twice nor seeing any other researcher burned as well. I you believe testimony given in my past case you might argue that having the name out early might have averted the whole situation; however, knowing the whole history of what really happened I'm not buying it and neither should you.
[P.S. I've mentioned Aetogate as an example of what could happen and really don't want this to degenerate into a discussion of that particular case. What I really want to know is if people really think it is a good idea to put new taxonomic names out there in the accepted manuscript stage where they have no protection against the priority rules in taxonomic nomenclature].
Calmasuchus acri, a new Capitosaur from the Middle Triassic of Spain
Just when I had been thinking that things had been rather slow this year regarding Triassic temnospondyl studies:
Fortuny, J., Galobart, À, and C. De Santisteban. In press. A new capitosaur from the Middle Triassic of Spain and the relationships within the Capitosauria. Acta Palaeontologica Polonica, available online 29 Dec 2010 doi:10.4202/app.2010.0025
Abstract - Capitosaurs were the largest and homogeneous group of Triassic temnospondyl amphibians with cosmopolitan distribution. However, their interrelationships are debated. The first capitosaur cranial remains found in the Iberian Peninsula were assigned to Parotosuchus; herein, a re-description of this material, together with information on other remains recovered from the same site, enables us to classify them as a new genus: Calmasuchus acri gen. et sp. nov. (Amphibia: Temnospondyli) from the early-to-middle Anisian (early Middle Triassic). This capitosaur had a combination of plesiomorphic and non-plesiomorphic characters, such as posterolaterally directed tabular horns, paired anterior palatal vacuities, and unique morphology of the lower jaw. By cladistic analysis, we propose a new phylogeny for the monophyletic capitosaurs. In the analysis, Capitosauria is supported by seven synapomorphies. Wetlugasaurus is the most basal member of the clade. The score of the Russian taxon Vladlenosaurus alexeyevi resulted in a clade including Odenwaldia and the latter taxa. The Madagascarian Edingerella is the sister taxon of Watsonisuchus. Finally, Calmasuchus acri, the new taxon described here, appears as a more derived form than Parotosuchus. The new genus is the sister taxon of the Cyclotosaurus-Tatrasuchus and Eryosuchus-Mastodonsaurus clades.
Fortuny, J., Galobart, À, and C. De Santisteban. In press. A new capitosaur from the Middle Triassic of Spain and the relationships within the Capitosauria. Acta Palaeontologica Polonica, available online 29 Dec 2010 doi:10.4202/app.2010.0025
Abstract - Capitosaurs were the largest and homogeneous group of Triassic temnospondyl amphibians with cosmopolitan distribution. However, their interrelationships are debated. The first capitosaur cranial remains found in the Iberian Peninsula were assigned to Parotosuchus; herein, a re-description of this material, together with information on other remains recovered from the same site, enables us to classify them as a new genus: Calmasuchus acri gen. et sp. nov. (Amphibia: Temnospondyli) from the early-to-middle Anisian (early Middle Triassic). This capitosaur had a combination of plesiomorphic and non-plesiomorphic characters, such as posterolaterally directed tabular horns, paired anterior palatal vacuities, and unique morphology of the lower jaw. By cladistic analysis, we propose a new phylogeny for the monophyletic capitosaurs. In the analysis, Capitosauria is supported by seven synapomorphies. Wetlugasaurus is the most basal member of the clade. The score of the Russian taxon Vladlenosaurus alexeyevi resulted in a clade including Odenwaldia and the latter taxa. The Madagascarian Edingerella is the sister taxon of Watsonisuchus. Finally, Calmasuchus acri, the new taxon described here, appears as a more derived form than Parotosuchus. The new genus is the sister taxon of the Cyclotosaurus-Tatrasuchus and Eryosuchus-Mastodonsaurus clades.
Triassic Mystery Fossil
Things are a bit slow news wise over the holidays and I have not done this for awhile, so here goes. Any guesses on what this is? Should be relatively easy I think.
All I Want for Christmas is a Lagerstätte like this one: Exceptional Preservation of the Middle Triassic Luoping Biota of China
This new paper has been getting a lot of attention already (here and here). It basically provides some preliminary discussion of a well preserved marine fossil assemblage from the Middle Triassic of China which is rich in invertebrates, plants, and vertebrates. A detailed community structure and food web is proposed and the presence of top predators (e.g., ichthyosaurs) suggests a full recovery of the ecosystem following the end Permian extinction. Based on the photographs in the article (one reproduced below), the specimens from this site are absolutely suberb, and this biota should be actively researched for years to come. I just need to find a Chinle lakebed that was full of microbial mats.
Hu, S.-x,. Zhang, Q.-y., Chen, Z.-Q., Zhou, C.-y., Lü, T., Xie, T., Wen, W., Huang, J. -y., and M. J. Benton, 2010. The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction. Proceedings of the Royal Society: B (advance online publication) doi: 10.1098/rspb.2010.2235
Abstract - The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.
There is more information here.
Hu, S.-x,. Zhang, Q.-y., Chen, Z.-Q., Zhou, C.-y., Lü, T., Xie, T., Wen, W., Huang, J. -y., and M. J. Benton, 2010. The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction. Proceedings of the Royal Society: B (advance online publication) doi: 10.1098/rspb.2010.2235
Abstract - The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.
There is more information here.
New Triassic Insect from Kyrgystan and a New Species of Palaeoxyris from Germany
Béthoux, O., Voigt, S., and J. W. Schneider. 2010. A Triassic palaeodictyopteran from Kyrgyzstan. Palaeodiversity 3: 9–13.
Abstract - A specimen belonging to the species reliquia n. sp. is described from the Dzaylyaucho locality (Madygen, Kyrgyzstan; late Middle to early Late Triassic). It is interpreted as a palaeodictyopteran. It is therefore the latest occurrence of this group, previously considered as extinct during Middle to earliest Late Permian.
Böttcher, R. 2010. Description of the shark egg capsule Palaeoxyris friessi n. sp. From the Ladinian (Middle Triassic) of SW Germany and discussion of all known egg capsules from the Triassic of the Germanic Basin. Palaeodiversity 3: 123–139.
Abstract - The new shark egg capsule Palaeoxyris friessi n. sp. is described from the Hauptsandstein of the Lower Keuper (Erfurt Formation, Ladinian, Middle Triassic). The type and only specimen is complete and remarkably well preserved. With a length of 27 cm it is the longest complete Palaeoxyris egg capsule known so far. It is interpreted as an egg capsule of the hybodontid sharks Polyacrodus polycyphus or cf. Polyacrodus keuperianus. The capsule is associated with a rich flora, the brackish water bivalve Unionites and conchostracans, but other vertebrate remains were absent. All known records of Triassic and Lower Jurassic egg capsules from the Germanic Basin and their potential producers are discussed. All of the capsules have been found in deltaic or prodeltaic deposits.
Abstract - A specimen belonging to the species reliquia n. sp. is described from the Dzaylyaucho locality (Madygen, Kyrgyzstan; late Middle to early Late Triassic). It is interpreted as a palaeodictyopteran. It is therefore the latest occurrence of this group, previously considered as extinct during Middle to earliest Late Permian.
Böttcher, R. 2010. Description of the shark egg capsule Palaeoxyris friessi n. sp. From the Ladinian (Middle Triassic) of SW Germany and discussion of all known egg capsules from the Triassic of the Germanic Basin. Palaeodiversity 3: 123–139.
Abstract - The new shark egg capsule Palaeoxyris friessi n. sp. is described from the Hauptsandstein of the Lower Keuper (Erfurt Formation, Ladinian, Middle Triassic). The type and only specimen is complete and remarkably well preserved. With a length of 27 cm it is the longest complete Palaeoxyris egg capsule known so far. It is interpreted as an egg capsule of the hybodontid sharks Polyacrodus polycyphus or cf. Polyacrodus keuperianus. The capsule is associated with a rich flora, the brackish water bivalve Unionites and conchostracans, but other vertebrate remains were absent. All known records of Triassic and Lower Jurassic egg capsules from the Germanic Basin and their potential producers are discussed. All of the capsules have been found in deltaic or prodeltaic deposits.
Chuxiongosaurus lufengensis, a New Basal Sauropod from the Early Jurassic of China
Lü J., Y. Kobayashi, Li T. & Zhong S., 2010. A new basal sauropod dinosaur from the Lufeng Basin, Yunnan Province, southwestern China. Acta Geologica Sinica 84: 1336-1342.
Abstract - A new dinosaur Chuxiongosaurus lufengensis gen. et sp. nov. is erected based on a nearly complete skull. The taxon is characterized by the lacrimal perpendicular to the ventral margin of the upper jaw, which is similar to that of Thecodontosaurus; a depression present on the dorsal profile of the snout behind the naris; the rostral profile of the maxilla slopes continuously towards the rostral tip; and the presence of 25 dentary teeth. It also displays prosauropod characters such as a relatively long skull, the slope of the maxillary rostral profile, and teeth that do not have basically constricted crowns. The new specimen is more basal than Anchisaurus and represents the first basal sauropod dinosaur from the Early Jurassic of China.
Abstract - A new dinosaur Chuxiongosaurus lufengensis gen. et sp. nov. is erected based on a nearly complete skull. The taxon is characterized by the lacrimal perpendicular to the ventral margin of the upper jaw, which is similar to that of Thecodontosaurus; a depression present on the dorsal profile of the snout behind the naris; the rostral profile of the maxilla slopes continuously towards the rostral tip; and the presence of 25 dentary teeth. It also displays prosauropod characters such as a relatively long skull, the slope of the maxillary rostral profile, and teeth that do not have basically constricted crowns. The new specimen is more basal than Anchisaurus and represents the first basal sauropod dinosaur from the Early Jurassic of China.
New Hypothesis on European Phytosaur Ecology
Before you read this new paper you should read this older one:
Nesbitt, S.J. and M.R. Stocker. 2008. The vertebrate assemblage of the Late Triassic Canjilon Quarry (Northern New Mexico, USA), and the importance of apomorphy-based assemblage comparisons. Journal of Vertebrate Paleontology 28:1063-1072.
I'm afraid that I don't find the identifications in this paper to be rigorously determined (see the Nesbitt and Stocker paper for further discussion) nor the ecological implications to be strongly supported, thus I have doubts about the overall findings in this paper. I'm also not convinced that all phytosaur genera with robust and gracile morphs represent sexual dimorphs (as proposed in passing for Nicrosaurus and Mystriosuchus). The data to support this (i.e. monotaxic bonebeds showing both morphs) simply do not exist with the possible exception of Pseudopalatus pristinus and P. buceros from the Canjilon Quarry (Chinle Formation) of New Mexico. This quarry contains over a dozen skulls of robust and gracile morphs of these two species and has been interpreted first by Colbert (1947) and later by Ziegler et al (2002) as representing sexual dimorphs. Nonetheless the ecological criteria proposed in this new paper suggests different feeding strategies for the dimorphs (which have different dentitions), thus males and females would have different food sources (e.g., piscivorous vs. generalist).
Kimmig, J., and G. Arp. 2010. Phytosaur remains from the Norian Arnstadt Formation (Leine Valley, Germany), with reference to European phytosaur habitats. Palaeodiversity 3: 215–224.
Abstract - Most inferences on phytosaur ecology are based on comparisons with extant crocodilians, in particular with reference to similarities in their skull morphology. In addition, the sedimentary environment of their place of embedding provides information on their life habitat and the potential lifestyle of these animals. Here we report on newly discovered phytosaur remains from the Norian Arnstadt Formation, which support the interpretation that the European phytosaur genera Mystriosuchus and Nicrosaurus had different ecological preferences. While Mystriosuchus, similar to Paleorhinus, was semi-aquatic and piscivorous, Nicrosaurus had a terrestrial lifestyle and probably preyed on tetrapods. Comparing the habitats of the different European phytosaur genera reported in literature, it is also concluded, that Mystriosuchus and Paleorhinus tolerated, contrary to Nicrosaurus, a wide range of salinity.
Nesbitt, S.J. and M.R. Stocker. 2008. The vertebrate assemblage of the Late Triassic Canjilon Quarry (Northern New Mexico, USA), and the importance of apomorphy-based assemblage comparisons. Journal of Vertebrate Paleontology 28:1063-1072.
I'm afraid that I don't find the identifications in this paper to be rigorously determined (see the Nesbitt and Stocker paper for further discussion) nor the ecological implications to be strongly supported, thus I have doubts about the overall findings in this paper. I'm also not convinced that all phytosaur genera with robust and gracile morphs represent sexual dimorphs (as proposed in passing for Nicrosaurus and Mystriosuchus). The data to support this (i.e. monotaxic bonebeds showing both morphs) simply do not exist with the possible exception of Pseudopalatus pristinus and P. buceros from the Canjilon Quarry (Chinle Formation) of New Mexico. This quarry contains over a dozen skulls of robust and gracile morphs of these two species and has been interpreted first by Colbert (1947) and later by Ziegler et al (2002) as representing sexual dimorphs. Nonetheless the ecological criteria proposed in this new paper suggests different feeding strategies for the dimorphs (which have different dentitions), thus males and females would have different food sources (e.g., piscivorous vs. generalist).
Kimmig, J., and G. Arp. 2010. Phytosaur remains from the Norian Arnstadt Formation (Leine Valley, Germany), with reference to European phytosaur habitats. Palaeodiversity 3: 215–224.
Abstract - Most inferences on phytosaur ecology are based on comparisons with extant crocodilians, in particular with reference to similarities in their skull morphology. In addition, the sedimentary environment of their place of embedding provides information on their life habitat and the potential lifestyle of these animals. Here we report on newly discovered phytosaur remains from the Norian Arnstadt Formation, which support the interpretation that the European phytosaur genera Mystriosuchus and Nicrosaurus had different ecological preferences. While Mystriosuchus, similar to Paleorhinus, was semi-aquatic and piscivorous, Nicrosaurus had a terrestrial lifestyle and probably preyed on tetrapods. Comparing the habitats of the different European phytosaur genera reported in literature, it is also concluded, that Mystriosuchus and Paleorhinus tolerated, contrary to Nicrosaurus, a wide range of salinity.
New Data on the Early Triassic Land Flora Recovery
Yu, J., Broutin, J., Huang, Q., and L. Grauvogel-Stamm. 2010. Annalepis, a pioneering lycopsid genus in the recovery of the Triassic land flora in South China. Comptes Rendus Palevol 9:479-486. doi:10.1016/j.crpv.2010.09.004 Abstract - Fossil plants are scarce in the Earliest Triassic marine deposits of western Guizhou and eastern Yunnan. Only Annularia shirakii, Lobatannularia sp., Paracalamites stenocostatus, Gigantopteris sp., Pecopteris sp. were reported from the base of the Kayitou Formation dated as Early Induan by marine fauna. Recently, we discovered numerous representatives of the genus Annalepis in the same Lowermost Triassic beds: A. latiloba, A. brevicystis, A. angusta, Annalepis spp. occur associated with a basal Triassic marine fauna. This discovery fills the biostratigraphic gap between the Late Permian “Gigantonoclea guizhouensis-Ullmannia cf. bronnii-Annularia pingloensis” and the late Lower Triassic “Neuropteridium–Albertia–Voltzia” assemblages reported from South China. It represents an important datum dealing with the very beginning of a new terrestrial flora installation after the Permian flora disappearance following the Permian–Triassic boundary mass extinction. This “starting point” of a new vegetal cover in South China is to be taken into account in reconstructing through space and time the settlement process of the Mesozoic floristic provinces.
Pterosaurs are Archosauriforms
Nesbitt, S. J., and D. W. E. Hone. 2010. An external mandibular fenestra and other archosauriform character states in basal pterosaurs. Palaeodiversity 3: 225–233.
Abstract - Pterosauria, a successful clade of extinct flying vertebrates, possesses a radical body plan that offers few clues about their origin and closest relatives. Whereas most researchers hypothesize an origin within Archosauria as the sister-group to Dinosauromorpha, others favor a position among non archosauriform archosauromorphs. Here we present evidence that supports a placement within Archosauriformes: the presence of an external mandibular fenestra in two basal pterosaur taxa, Dimorphodon macronyx and a specimen referred to Eudimorphodon cf. ranzii (= ‘Seefeld Eudimorphodon’; BSP 1994 I 51). Furthermore, the arrangement of the mandibular bones surrounding the mandibular fenestra and the presence of a posterior process of the dentary that laterally overlaps the angular in the mandible of Dimorphodon and BSP 1994 I 51 are identical to those of Erythrosuchus, Euparkeria, and Archosauria. When mapped on a cladogram, presence or absence of an external mandibular fenestra in basal pterosaurs possibly indicates that the feature is primitive for Pterosauria but later lost. The presence of an external mandibular fenestra, along with morphological evidence elsewhere in the body of pterosaurs(serrated teeth, antorbital fossa present, fourth trochanter on the femur present), supports a placement of Pterosauria within Archosauriformes and is consistent with a position within Archosauria.
Abstract - Pterosauria, a successful clade of extinct flying vertebrates, possesses a radical body plan that offers few clues about their origin and closest relatives. Whereas most researchers hypothesize an origin within Archosauria as the sister-group to Dinosauromorpha, others favor a position among non archosauriform archosauromorphs. Here we present evidence that supports a placement within Archosauriformes: the presence of an external mandibular fenestra in two basal pterosaur taxa, Dimorphodon macronyx and a specimen referred to Eudimorphodon cf. ranzii (= ‘Seefeld Eudimorphodon’; BSP 1994 I 51). Furthermore, the arrangement of the mandibular bones surrounding the mandibular fenestra and the presence of a posterior process of the dentary that laterally overlaps the angular in the mandible of Dimorphodon and BSP 1994 I 51 are identical to those of Erythrosuchus, Euparkeria, and Archosauria. When mapped on a cladogram, presence or absence of an external mandibular fenestra in basal pterosaurs possibly indicates that the feature is primitive for Pterosauria but later lost. The presence of an external mandibular fenestra, along with morphological evidence elsewhere in the body of pterosaurs(serrated teeth, antorbital fossa present, fourth trochanter on the femur present), supports a placement of Pterosauria within Archosauriformes and is consistent with a position within Archosauria.
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| from Nesbitt & Hone 2010 - Palaeodiversitas 3 |
An Upclose Look at the Microanatomy of Aetosaur Osteoderms
Aetosaurs are characterized by their elaborate bony carapaces composed of numerous osteoderms. In fact aetosaur taxonomy is almost based solely on the morphology (especially the surface ornamentation) of osteoderms. Despite this detailed studies of the microstructure of aetosaur oseoderms are lacking. In 2008 I published a paper with Michelle Stocker and Randall Irmis that provided the first histological data for aetosaur osteoderms, but we were mostly looking at providing an estimated age at time of death for the holotype of Sierritasuchus macalpini to determine the ontogenetic stage of the specimen.
This new study focuses on aetosaurine osteoderms from Argentina and Brazil, including specimens assigned to Aetosauroides scagliai. One of the very cool things these authors did was not only to look a parasaggital sections of the rectangular osteoderms, they also looked at transverse sections. Some of the key findings are as follows:
- Aetosaur osteoderms lend themselves well to this type of study as secondary remodeling is minimal.
-Unlike all other sampled archosaurs, aetosaur osteoderm ossification was not metaplastic in nature (i.e. pre-existing, fully developed tissue is ossified), instead the osteoderms seemingly underwent intermembraneous ossification where new tissue displaces preformed tissue rather than incorporating it. This is currently unique among archosaurs.
- Cyclic growth lines (Lines of arrested growth of LAG's) are well developed. Based on this the specimens sampled belonged to a range of subadult animals between two and nine years of age at time of death (minimum ages).
- The center of ossification in aetosaur osteoderms is at the level of the raised dorsal eminence.
- Aetosaur plates probably grew by adding peripheral layers. Interestingly most faster growth occurred along the medial and lateral margins. This accounts for the assymetrical placement of the dorsal eminence that is characteristic of aetosaurines.
- Well-developed Sharpey's fibers along the medial and lateral margins of the osteoderms suggest strong lateral and medial attachments along a row of osteoderms. In contrast the attachments with anterior of posterior plates were poor, presumably allowing for flexion and movement in the carapace.
-Finally, the ornamentation of the osteoderms is formed by local resorption and partitial redeposition of the cortical bone. Acceleration of growth in particular areas enhances the degree of sculpture through time and the pattern is established early and then maintained through future growth. This is seemingly why the ornamentation in juvenile specimens does not differ significantly from that of adults. This is extremely significant if you are using this patterning to diagnose taxa.
Overall an important study and excellent paper.
Cerda, I. A., and J. B. Desojo. 2010: Dermal armour histology of aetosaurs (Archosauria: Pseudosuchia), from the Upper Triassic of Argentina and Brazil. Lethaia, DOI: 10.1111/j.1502-3931.2010.00252.x.
Abstract - One of the most striking features documented in aetosaurs is the presence of an extensive bony armour composed of several osteoderms. Here, we analyse the bone microstructure of these elements in some South American Aetosaurinae aetosaurs, including Aetosauroides scagliai. In general terms, Aetosaurinae osteoderms are compact structures characterized by the presence of three tissue types: a basal cortex of poorly vascularized parallel-fibred bone tissue, a core of highly vascularized fibro-lamellar bone, and an external cortex of rather avascular lamellar bone tissue. Sharpey’s fibres are more visible at the internal core, toward the lateral margins and aligned parallel to the major axis of the dermal plate. No evidence of metaplastic origin is reported in the osteoderms, and we hypothesize an intramembranous ossification for these elements. The bone tissue distribution reveals that the development of the osteoderm in Aetosaurinae starts in a position located medial to the plate midpoint, and the main sites of active osteogenesis occur towards the lateral and medial edges of the plate. The osteoderm ornamentation is originated and maintained by a process of resorption and redeposition of the external cortex, which also includes preferential bone deposition in some particular sites. Given that no secondary reconstruction occurs in the osteoderms, growth marks are well preserved and they provide very important information regarding the relative age and growth pattern of Aetosaurinae aetosaurs.
This new study focuses on aetosaurine osteoderms from Argentina and Brazil, including specimens assigned to Aetosauroides scagliai. One of the very cool things these authors did was not only to look a parasaggital sections of the rectangular osteoderms, they also looked at transverse sections. Some of the key findings are as follows:
- Aetosaur osteoderms lend themselves well to this type of study as secondary remodeling is minimal.
-Unlike all other sampled archosaurs, aetosaur osteoderm ossification was not metaplastic in nature (i.e. pre-existing, fully developed tissue is ossified), instead the osteoderms seemingly underwent intermembraneous ossification where new tissue displaces preformed tissue rather than incorporating it. This is currently unique among archosaurs.
- Cyclic growth lines (Lines of arrested growth of LAG's) are well developed. Based on this the specimens sampled belonged to a range of subadult animals between two and nine years of age at time of death (minimum ages).
- The center of ossification in aetosaur osteoderms is at the level of the raised dorsal eminence.
- Aetosaur plates probably grew by adding peripheral layers. Interestingly most faster growth occurred along the medial and lateral margins. This accounts for the assymetrical placement of the dorsal eminence that is characteristic of aetosaurines.
- Well-developed Sharpey's fibers along the medial and lateral margins of the osteoderms suggest strong lateral and medial attachments along a row of osteoderms. In contrast the attachments with anterior of posterior plates were poor, presumably allowing for flexion and movement in the carapace.
-Finally, the ornamentation of the osteoderms is formed by local resorption and partitial redeposition of the cortical bone. Acceleration of growth in particular areas enhances the degree of sculpture through time and the pattern is established early and then maintained through future growth. This is seemingly why the ornamentation in juvenile specimens does not differ significantly from that of adults. This is extremely significant if you are using this patterning to diagnose taxa.
Overall an important study and excellent paper.
Cerda, I. A., and J. B. Desojo. 2010: Dermal armour histology of aetosaurs (Archosauria: Pseudosuchia), from the Upper Triassic of Argentina and Brazil. Lethaia, DOI: 10.1111/j.1502-3931.2010.00252.x.
Abstract - One of the most striking features documented in aetosaurs is the presence of an extensive bony armour composed of several osteoderms. Here, we analyse the bone microstructure of these elements in some South American Aetosaurinae aetosaurs, including Aetosauroides scagliai. In general terms, Aetosaurinae osteoderms are compact structures characterized by the presence of three tissue types: a basal cortex of poorly vascularized parallel-fibred bone tissue, a core of highly vascularized fibro-lamellar bone, and an external cortex of rather avascular lamellar bone tissue. Sharpey’s fibres are more visible at the internal core, toward the lateral margins and aligned parallel to the major axis of the dermal plate. No evidence of metaplastic origin is reported in the osteoderms, and we hypothesize an intramembranous ossification for these elements. The bone tissue distribution reveals that the development of the osteoderm in Aetosaurinae starts in a position located medial to the plate midpoint, and the main sites of active osteogenesis occur towards the lateral and medial edges of the plate. The osteoderm ornamentation is originated and maintained by a process of resorption and redeposition of the external cortex, which also includes preferential bone deposition in some particular sites. Given that no secondary reconstruction occurs in the osteoderms, growth marks are well preserved and they provide very important information regarding the relative age and growth pattern of Aetosaurinae aetosaurs.
Pangean Great Lake Paleoecology on the Cusp of the End-Triassic Extinction
Very cool study of the fish community in a large scale lake responding to changing environmental conditions during the earliest Jurassic.
Whiteside, J. H., Olsen, P. E., Eglinton, T. I., Cornet, B., McDonald, N. G., and P. Huber. In press. Pangean great lake paleoecology on the cusp of the end-Triassic extinction. Palaeogeography (2010), doi:10.1016/j.palaeo.2010.11.025.
Abstract - Triassic and Early Jurassic age lacustrine deposits of eastern North American rift basins preserve a spectacular record of precession-related Milankovitch forcing in the Pangean tropics in the wake of the end-Triassic extinction event (ETE). The abundant and well preserved fossil fish assemblages from these great lakes show cyclical changes that track the permeating hierarchy of climatic cycles. To detail ecosystem processes correlating with succession of fish communities, bulk δ13C was measured through a 100 ky series of precession-forced lake level cycles in the lower Shuttle Meadow Formation of the Hartford rift basin, Connecticut that were deposited within 50 ky after the ETE. The deep-water phase of one of these cycles, the Bluff Head Bed, has produced thousands of articulated fish. There are fluctuations in the bulk δ13Corg in the cyclical strata that reflect differing degrees of lake water stratification, nutrient levels, and relative proportion of algal vs. plant derived organic matter that trace fish community changes. Extrinsic changes in the global exchangeable reservoirs can be excluded as an origin of this variability because molecule-level δ13C of n-alkanes from plant leaf waxes in the same strata show no such variability. Although higher taxonomic levels of the fish communities responded largely by sorting of taxa by environmental forcing, at the species level the holostean genus Semionotus responded by in situ evolution, and ultimately extinction, of a species flock. Fluctuations at the higher frequency, climatic precessional scale are mirrored at lower frequency, eccentricity modulated, scales, all following the lake-level hierarchical pattern. Thus, changes in lacustrine isotopic ratios amplify the Milankovitch climate signal that was already intensified by sequelae of the end-Triassic extinctions. The degree to which the ecological structure of modern lakes responds to similar environmental cyclicity is largely unknown, but similar patterns and processes are present within the Neogene history of the East African great lakes.
Whiteside, J. H., Olsen, P. E., Eglinton, T. I., Cornet, B., McDonald, N. G., and P. Huber. In press. Pangean great lake paleoecology on the cusp of the end-Triassic extinction. Palaeogeography (2010), doi:10.1016/j.palaeo.2010.11.025.
Abstract - Triassic and Early Jurassic age lacustrine deposits of eastern North American rift basins preserve a spectacular record of precession-related Milankovitch forcing in the Pangean tropics in the wake of the end-Triassic extinction event (ETE). The abundant and well preserved fossil fish assemblages from these great lakes show cyclical changes that track the permeating hierarchy of climatic cycles. To detail ecosystem processes correlating with succession of fish communities, bulk δ13C was measured through a 100 ky series of precession-forced lake level cycles in the lower Shuttle Meadow Formation of the Hartford rift basin, Connecticut that were deposited within 50 ky after the ETE. The deep-water phase of one of these cycles, the Bluff Head Bed, has produced thousands of articulated fish. There are fluctuations in the bulk δ13Corg in the cyclical strata that reflect differing degrees of lake water stratification, nutrient levels, and relative proportion of algal vs. plant derived organic matter that trace fish community changes. Extrinsic changes in the global exchangeable reservoirs can be excluded as an origin of this variability because molecule-level δ13C of n-alkanes from plant leaf waxes in the same strata show no such variability. Although higher taxonomic levels of the fish communities responded largely by sorting of taxa by environmental forcing, at the species level the holostean genus Semionotus responded by in situ evolution, and ultimately extinction, of a species flock. Fluctuations at the higher frequency, climatic precessional scale are mirrored at lower frequency, eccentricity modulated, scales, all following the lake-level hierarchical pattern. Thus, changes in lacustrine isotopic ratios amplify the Milankovitch climate signal that was already intensified by sequelae of the end-Triassic extinctions. The degree to which the ecological structure of modern lakes responds to similar environmental cyclicity is largely unknown, but similar patterns and processes are present within the Neogene history of the East African great lakes.
Surprise! Scientists now say that Crocodiles are not "Living Fossils".
Here are some excerpts from a BBC article that was posted online today:
"Crocodiles can no longer be referred to as "living fossils", according to scientists".
"Members of the crocodilian [sic] family have previously been thought to have changed little since prehistoric times. However, new fossil analyses suggests that modern crocodilians actually evolved from a very diverse group".
"Recently discovered ancient ancestors include small cat-like specimens, giant "supercrocs" and a pug-nosed vegetarian species".
"Modern crocodilians are adapted to aquatic environments with long snouts, strong tails and powerful jaws. Yet contrary to popular belief, scientists now suggest that the basic body structure of crocodiles, alligators and ghariels [sic] evolved from a diverse group of prehistoric reptiles with different body shapes".
You can read the rest of this story here. I am always flabbergasted how these "popular beliefs" still persist and how this "revelation" can be considered new.
Can't wait to get my copy of the new JVP memoir though. It sounds incredible.
"Crocodiles can no longer be referred to as "living fossils", according to scientists".
"Members of the crocodilian [sic] family have previously been thought to have changed little since prehistoric times. However, new fossil analyses suggests that modern crocodilians actually evolved from a very diverse group".
"Recently discovered ancient ancestors include small cat-like specimens, giant "supercrocs" and a pug-nosed vegetarian species".
"Modern crocodilians are adapted to aquatic environments with long snouts, strong tails and powerful jaws. Yet contrary to popular belief, scientists now suggest that the basic body structure of crocodiles, alligators and ghariels [sic] evolved from a diverse group of prehistoric reptiles with different body shapes".
You can read the rest of this story here. I am always flabbergasted how these "popular beliefs" still persist and how this "revelation" can be considered new.
Can't wait to get my copy of the new JVP memoir though. It sounds incredible.
Two New Cynodont Papers from the Middle Triassic of Gondwana
The first paper is a short note so there is no abstract.
Kammerer, C. F., Flynn, J. J., Ranivoharimanana, L. and A. R. Wyss. 2010. The first record of a probainognathian (Cynodontia: Chiniquodontidae) from the Triassic of Madagascar. Journal of Vertebrate Paleontology 30:1889-1894. DOI: 10.1080/02724634.2010.520784
Note: The authors state that this specimen is probably Middle Triassic in age, but could possibly be as young as Carnian.
Martinelli, A. G. 2010. On the postcanine dentition of Pascualgnathus polanskii Bonaparte (Cynodontia, Traversodontidae) from the Middle Triassic of Argentina. Geobios 43:629–638
Abstract - The dental morphology of Pascualgnathus polanskii Bonaparte (Therapsida, Eucynodontia, Traversodontidae), from the Middle Triassic RÃo Seco de la Quebrada Formation (Puesto Viejo Group, Argentina), is described and compared with that of other basal traversodontid cynodonts. Albeit Pascualgnathus is frequently used in phylogenetic analyses, neither a detailed description nor drawings of its postcanines have been published so far. The upper postcanines of Pascualgnathus are transversely wide, rectangular in occlusal view, with a lingual cusp connected to the transverse ridge which is located in the center of the crown, and one main labial cusp followed by one posterior labial, both forming the labial margin. The lower postcanines, mostly worn out in the known specimens, are quadrangular until pc6 and then they are rectangular with the major axis anteroposteriorly oriented. They have a tall mesial border, possibly constituted by one labial and one lingual cusp, and a transverse ridge. After comparisons, the number of cusps in the sectorial, labial border of the upper gomphodont teeth, frequently used in phylogenetic analyses, would not necessary implies real homologies. For example, postcanine morphologies with one or more cusps anterior to the main labial cusp would not be homologous to morphologies with one or more cusps posterior to the main labial cusp, while resulting in a similar count of labial cusps.
Kammerer, C. F., Flynn, J. J., Ranivoharimanana, L. and A. R. Wyss. 2010. The first record of a probainognathian (Cynodontia: Chiniquodontidae) from the Triassic of Madagascar. Journal of Vertebrate Paleontology 30:1889-1894. DOI: 10.1080/02724634.2010.520784
Note: The authors state that this specimen is probably Middle Triassic in age, but could possibly be as young as Carnian.
Martinelli, A. G. 2010. On the postcanine dentition of Pascualgnathus polanskii Bonaparte (Cynodontia, Traversodontidae) from the Middle Triassic of Argentina. Geobios 43:629–638
Abstract - The dental morphology of Pascualgnathus polanskii Bonaparte (Therapsida, Eucynodontia, Traversodontidae), from the Middle Triassic RÃo Seco de la Quebrada Formation (Puesto Viejo Group, Argentina), is described and compared with that of other basal traversodontid cynodonts. Albeit Pascualgnathus is frequently used in phylogenetic analyses, neither a detailed description nor drawings of its postcanines have been published so far. The upper postcanines of Pascualgnathus are transversely wide, rectangular in occlusal view, with a lingual cusp connected to the transverse ridge which is located in the center of the crown, and one main labial cusp followed by one posterior labial, both forming the labial margin. The lower postcanines, mostly worn out in the known specimens, are quadrangular until pc6 and then they are rectangular with the major axis anteroposteriorly oriented. They have a tall mesial border, possibly constituted by one labial and one lingual cusp, and a transverse ridge. After comparisons, the number of cusps in the sectorial, labial border of the upper gomphodont teeth, frequently used in phylogenetic analyses, would not necessary implies real homologies. For example, postcanine morphologies with one or more cusps anterior to the main labial cusp would not be homologous to morphologies with one or more cusps posterior to the main labial cusp, while resulting in a similar count of labial cusps.
Lamy Amphibian Quarry Taphonomy Redux and "Forensic Taphonomy"
The Lamy amphibian quarry is a famous quarry in the Garita Creek (=Tecovas) Formation of the Dockum Group in New Mexico. The quarry is well known for its large assemblage of metoposaurs, all presumably belonging to the taxon Koskinonodon perfectum (previously known as Buettneria perfecta). Anyone who has visited the Triassic portion of the Smithsonian Museum of Natural History in Washington, D.C. has probably seen the block of metoposaur skulls from this quarry on exhibit. It was originally interpreted to represent a group of metoposaurs dying in a small body of water dessicated by drought, but this new study proposes little evidence of this. Furthermore, the quarry was reopened and new blocks collected providing new information.
This paper also coins a new term "forensic taphonomy", which is the study of the taphonomy of a site solely utilizing field notes and previous publications without actually visiting the study area first hand. This type of work had been done previously for this site and while these authors defend this type of study in general, I'm left with the overall feeling that it is bad practice to discuss something as dependent on the proper interpretation of sedimentary structures and specimen orientations as taphomony without first hand observation of the site. Therefore, I'm glad they have revised their previous work by actually getting access to and reopening the quarry.
Finally, the authors briefly discuss an important caveat when studying specimens collected from bone-beds decades ago. To highlight what was thought to be key elements of the quarry, in this case the metoposaur skulls, the exhibitors had staff cover over many of the smaller bones around the skulls such as limb bones. Thus "forensic taphonomy" interpretations based on this display block were skewed by the preparation and exhibit technique used. This type of technique was also used to highlight two Coelophysis skeletons from the Late Triassic Coelophysis quarry, which are on exhibit at the American Museum of Natural History. "Undesirable" bones were removed or covered over, and tails were added to these specimens to make them complete. Recent preparation techniques discourage the use of materials to mimic bone to make specimens appear complete, and also the past practice of amalgamating different specimens in bone panel mounts such as these. Indeed, it can be extremely difficult to study older specimens prepared in this manner, as features of the specimens may not be real. In fact some older, well known specimen descriptions actually describe the reconstruction, not the real bones. Be careful out there.
Lucas, S. G., Rinehart, L. F., Krainer, K., Spielmann, J. A., and A. B. Heckert. 2010. Taphonomy of the Lamy amphibian quarry: A Late Triassic bonebed in New Mexico, U.S.A. Palaeogeography, Palaeoclimatology, Palaeoecology 298:388–398. doi:10.1016/j.palaeo.2010.10.025
Abstract - Located in Santa Fe County, New Mexico, USA, the Lamy amphibian quarry is a Late Triassic (Adamanian) bonebed stratigraphically low in the Garita Creek Formation of the Chinle Group. Well known for its mass accumulation of metoposaurid amphibians, it was initially interpreted as a drought-induced death assemblage. Based on microstratigraphic and sedimentological studies, additional and extensive collecting at the quarry and a revised understanding of the bonebed, we provide a detailed taphonomic analysis of the Lamy amphibian quarry that identifies it as a low diversity multitaxic and monodominant bonebed in pedogenically modified floodplain mudstone. The Lamy bonebed shows no evidence of drought and is characterized by a high density of completely dissociated bones that show clear alignment by current and sorting (enrichment of Voorhies Group II and III elements). The bones show no significant abrasion or weathering (stage 0), preserve virtually no evidence of scavenging and show no evidence of trampling. Based on skull lengths, the metoposaurid assemblage has a type I survivorship curve and lacks juveniles. We thus posit that the following sequence of events formed the Lamy amphibian bonebed: (1) aggregation (cause unknown) of a large number of metoposaurid amphibians at a site different from the location of the bonebed, though not distant; (2) catastrophic mass mortality; (3) complete disarticulation and disassociation of the skeletons; and (4) rapid transport of the disarticulated bones onto a floodplain surface that was undergoing pedogenesis. The Lamy amphibian bonebed is representative of the Late Triassic metoposaurid bonebeds from Morocco and the western USA, which are monodominant and nearly monotaxic. They indicate that aggregation (probably of breeding populations) and mass death of metoposaurids were relatively common across the riverine floodplains of Late Triassic Pangea.
This paper also coins a new term "forensic taphonomy", which is the study of the taphonomy of a site solely utilizing field notes and previous publications without actually visiting the study area first hand. This type of work had been done previously for this site and while these authors defend this type of study in general, I'm left with the overall feeling that it is bad practice to discuss something as dependent on the proper interpretation of sedimentary structures and specimen orientations as taphomony without first hand observation of the site. Therefore, I'm glad they have revised their previous work by actually getting access to and reopening the quarry.
Finally, the authors briefly discuss an important caveat when studying specimens collected from bone-beds decades ago. To highlight what was thought to be key elements of the quarry, in this case the metoposaur skulls, the exhibitors had staff cover over many of the smaller bones around the skulls such as limb bones. Thus "forensic taphonomy" interpretations based on this display block were skewed by the preparation and exhibit technique used. This type of technique was also used to highlight two Coelophysis skeletons from the Late Triassic Coelophysis quarry, which are on exhibit at the American Museum of Natural History. "Undesirable" bones were removed or covered over, and tails were added to these specimens to make them complete. Recent preparation techniques discourage the use of materials to mimic bone to make specimens appear complete, and also the past practice of amalgamating different specimens in bone panel mounts such as these. Indeed, it can be extremely difficult to study older specimens prepared in this manner, as features of the specimens may not be real. In fact some older, well known specimen descriptions actually describe the reconstruction, not the real bones. Be careful out there.
Lucas, S. G., Rinehart, L. F., Krainer, K., Spielmann, J. A., and A. B. Heckert. 2010. Taphonomy of the Lamy amphibian quarry: A Late Triassic bonebed in New Mexico, U.S.A. Palaeogeography, Palaeoclimatology, Palaeoecology 298:388–398. doi:10.1016/j.palaeo.2010.10.025
Abstract - Located in Santa Fe County, New Mexico, USA, the Lamy amphibian quarry is a Late Triassic (Adamanian) bonebed stratigraphically low in the Garita Creek Formation of the Chinle Group. Well known for its mass accumulation of metoposaurid amphibians, it was initially interpreted as a drought-induced death assemblage. Based on microstratigraphic and sedimentological studies, additional and extensive collecting at the quarry and a revised understanding of the bonebed, we provide a detailed taphonomic analysis of the Lamy amphibian quarry that identifies it as a low diversity multitaxic and monodominant bonebed in pedogenically modified floodplain mudstone. The Lamy bonebed shows no evidence of drought and is characterized by a high density of completely dissociated bones that show clear alignment by current and sorting (enrichment of Voorhies Group II and III elements). The bones show no significant abrasion or weathering (stage 0), preserve virtually no evidence of scavenging and show no evidence of trampling. Based on skull lengths, the metoposaurid assemblage has a type I survivorship curve and lacks juveniles. We thus posit that the following sequence of events formed the Lamy amphibian bonebed: (1) aggregation (cause unknown) of a large number of metoposaurid amphibians at a site different from the location of the bonebed, though not distant; (2) catastrophic mass mortality; (3) complete disarticulation and disassociation of the skeletons; and (4) rapid transport of the disarticulated bones onto a floodplain surface that was undergoing pedogenesis. The Lamy amphibian bonebed is representative of the Late Triassic metoposaurid bonebeds from Morocco and the western USA, which are monodominant and nearly monotaxic. They indicate that aggregation (probably of breeding populations) and mass death of metoposaurids were relatively common across the riverine floodplains of Late Triassic Pangea.
Preserved Bark on Middle Triassic Gymnosperm Wood from Antarctica
Bark is rarely preserved in fossil trees so this is pretty significant.
Decombeix, A.-L., Taylor, E. L., and T. N. Taylor. 2010. Anatomy and affinities of permineralized gymnospermous trunks with preserved bark from the Middle Triassic of Antarctica. Review of Palaeobotany and Palynology 163:26–34. doi:10.1016/j.revpalbo.2010.09.002
Abstract - Permineralized gymnosperm axes with pycnoxylic wood from the Middle Triassic Fremouw Formation of the Central Transantarctic Mountains, Antarctica, are assigned to the corystosperms (seed ferns) and conifers. Both groups have been previously described from this formation based on juvenile stems with attached leaf bases and decorticated trunks. Here we describe large axes with preserved bark from the Fremouw Peak permineralized peat locality. The specimens are characterized by a small parenchymatous pith with clusters of sclereids, a thick cylinder (> 10 cm) of pycnoxylic wood, and 1–2 cm of bark containing distinctive clusters of sclereids and a complex system of cortical vascular bundles. Comparison with axes previously described from the Middle Triassic of Antarctica shows that the new specimens are most similar to Kykloxylon, a corystosperm genus based on young stems bearing Dicroidium leaves, and with a portion of axis previously described as Rhexoxylon like. We suggest that both the new specimens and the Rhexoxylon-like axis represent proximal parts of a Dicroidium/Kykloxylon plant that possibly had a fluted trunk base, and we discuss the problem of delimiting features in corystosperm axes.
Decombeix, A.-L., Taylor, E. L., and T. N. Taylor. 2010. Anatomy and affinities of permineralized gymnospermous trunks with preserved bark from the Middle Triassic of Antarctica. Review of Palaeobotany and Palynology 163:26–34. doi:10.1016/j.revpalbo.2010.09.002
Abstract - Permineralized gymnosperm axes with pycnoxylic wood from the Middle Triassic Fremouw Formation of the Central Transantarctic Mountains, Antarctica, are assigned to the corystosperms (seed ferns) and conifers. Both groups have been previously described from this formation based on juvenile stems with attached leaf bases and decorticated trunks. Here we describe large axes with preserved bark from the Fremouw Peak permineralized peat locality. The specimens are characterized by a small parenchymatous pith with clusters of sclereids, a thick cylinder (> 10 cm) of pycnoxylic wood, and 1–2 cm of bark containing distinctive clusters of sclereids and a complex system of cortical vascular bundles. Comparison with axes previously described from the Middle Triassic of Antarctica shows that the new specimens are most similar to Kykloxylon, a corystosperm genus based on young stems bearing Dicroidium leaves, and with a portion of axis previously described as Rhexoxylon like. We suggest that both the new specimens and the Rhexoxylon-like axis represent proximal parts of a Dicroidium/Kykloxylon plant that possibly had a fluted trunk base, and we discuss the problem of delimiting features in corystosperm axes.
Embryonic Skeletal Morphology of the Jurassic Sauropodomorph Massospondylus
A few weeks ago I mentioned an upcoming article on sauropodomorph embryos from the Lower Jurassic of South Africa. That article is now published in the Journal of Vertebrate Paleontology. This find represents the oldest occurrence of dinosaur embryonic material, but it also represents one of the oldest records of eggshell in the fossil record. As far as I am aware (and someone please correct me if I am wrong) the only occurence of fossil eggs in the Triassic were associated with hatchlings of the sauropodomorph Mussaurus from the Upper Triassic El Tranquilo Formation of Argentina (Bonaparte and Vince, 1979). No calcified eggs are known from the Permian or earlier (Hirsch, 1979). Having worked in Cretaceous units where fossil eggshell is ubiquitous I'm always been curious about the lack of fossil eggshell in the Triassic. Years back I suggested that maybe fully calcified eggs hadn't developed yet, but was told by someone purportedly knowledgeable in fossil eggs that they were present, I just didn't know what look for. I'm not really advocating my initial suggestion, but I'm not buying the latter explanation either. Anyone else have any thoughts?
Reisz, R. R. , Evans, D. C. , Sues, H.-D. and D. Scott. 2010. Embryonic skeletal anatomy of the sauropodomorph dinosaur Massospondylus from the Lower Jurassic of South Africa. Journal of Vertebrate Paleontology 30:1653-1665. DOI:10.1080/02724634.2010.521604
Abstract - Two embryonic skeletons preserved inside thin-shelled eggs of a partially preserved clutch from the Upper Elliot Formation (Lower Jurassic) of South Africa have been attributed to the sauropodomorph dinosaur Massospondylus carinatus. A virtually complete skeleton is exposed in right lateral view, with the slightly telescoped skull and several cervical vertebrae extending beyond the eggshell. A second, partial skeleton has a skull preserved in dorsal view. The embryos have proportionately very large skulls, with the broad skull table formed by wide parietals and frontals. The wide posterolateral wing of the frontal separates the postorbital from contact with the parietal. The embryos have short rather than elongated cervical vertebrae, with tall rather than low neural arches. The large forelimbs are only slightly shorter than the hind limbs, which suggests an obligatory quadrupedal posture for the hatchlings. This pattern may represent an ontogenetic constraint related to the large size of the head and horizontally oriented neck. Similarities between the embryonic and post-hatchling specimens include the slenderness of the lower jaw and slight ventral curvature of the symphyseal portion of the dentary, the large supraorbital process of the prefrontal, and the tall antorbital and infratemporal fenestrae. There are 10 cervical, 14 dorsal, and three sacral vertebrae. The large distal claw-bearing phalanx of manual digit 1 is longer than any other phalangeal element of either manus or pes. The embryos of Massospondylus carinatus represent the oldest dinosaurian embryos known to date.
Reisz, R. R. , Evans, D. C. , Sues, H.-D. and D. Scott. 2010. Embryonic skeletal anatomy of the sauropodomorph dinosaur Massospondylus from the Lower Jurassic of South Africa. Journal of Vertebrate Paleontology 30:1653-1665. DOI:10.1080/02724634.2010.521604
Abstract - Two embryonic skeletons preserved inside thin-shelled eggs of a partially preserved clutch from the Upper Elliot Formation (Lower Jurassic) of South Africa have been attributed to the sauropodomorph dinosaur Massospondylus carinatus. A virtually complete skeleton is exposed in right lateral view, with the slightly telescoped skull and several cervical vertebrae extending beyond the eggshell. A second, partial skeleton has a skull preserved in dorsal view. The embryos have proportionately very large skulls, with the broad skull table formed by wide parietals and frontals. The wide posterolateral wing of the frontal separates the postorbital from contact with the parietal. The embryos have short rather than elongated cervical vertebrae, with tall rather than low neural arches. The large forelimbs are only slightly shorter than the hind limbs, which suggests an obligatory quadrupedal posture for the hatchlings. This pattern may represent an ontogenetic constraint related to the large size of the head and horizontally oriented neck. Similarities between the embryonic and post-hatchling specimens include the slenderness of the lower jaw and slight ventral curvature of the symphyseal portion of the dentary, the large supraorbital process of the prefrontal, and the tall antorbital and infratemporal fenestrae. There are 10 cervical, 14 dorsal, and three sacral vertebrae. The large distal claw-bearing phalanx of manual digit 1 is longer than any other phalangeal element of either manus or pes. The embryos of Massospondylus carinatus represent the oldest dinosaurian embryos known to date.
Unique Carapace Structure in a Triassic Tetrapod
Wow, and I thought that aetosaur carapaces were complex. Osteoderms provide more than defense and display. They also provide support and stabilization for the axial skeleton. Choniosuchians seem to take this to a unique level.
Buchwitz, M. and S. Voigt. 2010. Peculiar carapace structure of a Triassic chroniosuchian implies evolutionary shift in trunk flexibility. Journal of Vertebrate Paleontology 30:1697-1708. DOI: 10.1080/02724634.2010.521685
Abstract - Dermal ossifications are widespread in Permian and Triassic tetrapods, but only members of the Chroniosuchia possess a series of dorsal osteoderms with a complex plate-to-plate articulation mechanism in addition to a contact between each osteoderm and its associated vertebral spine. The stratigraphically youngest chroniosuchid, Madygenerpeton pustulatus, from the Triassic of Kyrgyzstan provides new insight on the function of the chroniosuchian osteoderm system. Osteoderms of M. pustulatus are broad, peaked-roof-shaped to arched, with enlarged posterodorsal and anteroventral articulation facets bearing unique sets of concentric rail-like ridges and furrows. Supplementing the multiple-overlap chroniosuchian type articulation, the interlocking ridges and furrows confined the relative motion of two neighboring osteoderms to a rotation in slightly oblique and curved contact planes. Given the significant lateral narrowing of the dorsal ornamented non-overlap area, the horizontal component of the plate-to-plate rotation angles could reach up to 7.5◦, enabling more extensive lateral flexion of the trunk than in other chroniosuchids. Considering functional analogs, the chroniosuchian osteoderm system probably stabilized the vertebral column against shearing, torsion, tension, and compression loads and thus facilitated terrestrial locomotion at the expense of trunk flexibility. With its particular morphology, the carapace of M. pustulatus, however, was more suitable for locomotion styles featuring lateral body undulation than the carapaces of Permian chroniosuchids. We interpret this speciality as a secondary adaptation to an aquatic habitat.
Buchwitz, M. and S. Voigt. 2010. Peculiar carapace structure of a Triassic chroniosuchian implies evolutionary shift in trunk flexibility. Journal of Vertebrate Paleontology 30:1697-1708. DOI: 10.1080/02724634.2010.521685
Abstract - Dermal ossifications are widespread in Permian and Triassic tetrapods, but only members of the Chroniosuchia possess a series of dorsal osteoderms with a complex plate-to-plate articulation mechanism in addition to a contact between each osteoderm and its associated vertebral spine. The stratigraphically youngest chroniosuchid, Madygenerpeton pustulatus, from the Triassic of Kyrgyzstan provides new insight on the function of the chroniosuchian osteoderm system. Osteoderms of M. pustulatus are broad, peaked-roof-shaped to arched, with enlarged posterodorsal and anteroventral articulation facets bearing unique sets of concentric rail-like ridges and furrows. Supplementing the multiple-overlap chroniosuchian type articulation, the interlocking ridges and furrows confined the relative motion of two neighboring osteoderms to a rotation in slightly oblique and curved contact planes. Given the significant lateral narrowing of the dorsal ornamented non-overlap area, the horizontal component of the plate-to-plate rotation angles could reach up to 7.5◦, enabling more extensive lateral flexion of the trunk than in other chroniosuchids. Considering functional analogs, the chroniosuchian osteoderm system probably stabilized the vertebral column against shearing, torsion, tension, and compression loads and thus facilitated terrestrial locomotion at the expense of trunk flexibility. With its particular morphology, the carapace of M. pustulatus, however, was more suitable for locomotion styles featuring lateral body undulation than the carapaces of Permian chroniosuchids. We interpret this speciality as a secondary adaptation to an aquatic habitat.
Bentonyx sidensis, a new Rhynchosaur from the Middle Triassic of England
A note in the newest issue of the Journal of Vertebrate Paleontology reviews the type and referred material of the rhynchosaur Fodonyx spenceri and concludes that a referred skull actually belongs to a new taxon. This new taxon is named Bentonyx sidensis in honor of Professor Mike Benton of the University of Bristol, and authority on rhynchosaurs and a mentor to many students of the Triassic. You can read more about this is a recent post by David Hone, the third author on this paper.
I would like to congratulate Mike regarding this honor, especially in having the member of a taxon so dear to him named accordingly.
Langer, M. C. , Montefeltro, F. C. , Hone, D. E. , Whatley, R. and C. L. Schultz. 2010. On Fodonyx spenceri and a new rhynchosaur from the Middle Triassic of Devon. Journal of Vertebrate Paleontology 30:1884 — 1888. DOI: 10.1080/02724634.2010.521901
I would like to congratulate Mike regarding this honor, especially in having the member of a taxon so dear to him named accordingly.
Langer, M. C. , Montefeltro, F. C. , Hone, D. E. , Whatley, R. and C. L. Schultz. 2010. On Fodonyx spenceri and a new rhynchosaur from the Middle Triassic of Devon. Journal of Vertebrate Paleontology 30:1884 — 1888. DOI: 10.1080/02724634.2010.521901
Rainforest Collapse Triggered Carboniferous Tetrapod Diversification in Euramerica
A new paper that argues that ecosystem devestation in the Carboniferous provided conditions that led to increased diversity in amniotes and basically set the stage for the rise of archosaurs in the Mesozoic.
From Science Daily article: "Global warming devastated tropical rainforests 300 million years ago. Now scientists report the unexpected discovery that this event triggered an evolutionary burst among reptiles -- and inadvertently paved the way for the rise of dinosaurs, 100 million years later". Read more here.
Sahney, S., Benton, M. J., and H. J. Falcon-Lang. 2010. Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology 38: 1079-1082. DOI: 10.1130/G31182.1
Abstract - Abrupt collapse of the tropical rainforest biome (Coal Forests) drove rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica. This finding is based on analysis of global and alpha diversity databases in a precise geologic context. From Visean to Moscovian time, both diversity measures steadily increased, but following rainforest collapse in earliest Kasimovian time (ca. 305 Ma), tetrapod extinction rate peaked, alpha diversity imploded, and endemism developed for the first time. Analysis of ecological diversity shows that rainforest collapse was also accompanied by acquisition of new feeding strategies (predators, herbivores), consistent with tetrapod adaptation to the effects of habitat fragmentation and resource restriction. Effects on amphibians were particularly devastating, while amniotes (‘reptiles’) fared better, being ecologically adapted to the drier conditions that followed. Our results demonstrate, for the first time, that Coal Forest fragmentation influenced profoundly the ecology and evolution of terrestrial fauna in tropical Euramerica, and illustrate the tight coupling that existed between vegetation, climate, and trophic webs.
From Science Daily article: "Global warming devastated tropical rainforests 300 million years ago. Now scientists report the unexpected discovery that this event triggered an evolutionary burst among reptiles -- and inadvertently paved the way for the rise of dinosaurs, 100 million years later". Read more here.
Sahney, S., Benton, M. J., and H. J. Falcon-Lang. 2010. Rainforest collapse triggered Carboniferous tetrapod diversification in Euramerica. Geology 38: 1079-1082. DOI: 10.1130/G31182.1
Abstract - Abrupt collapse of the tropical rainforest biome (Coal Forests) drove rapid diversification of Carboniferous tetrapods (amphibians and reptiles) in Euramerica. This finding is based on analysis of global and alpha diversity databases in a precise geologic context. From Visean to Moscovian time, both diversity measures steadily increased, but following rainforest collapse in earliest Kasimovian time (ca. 305 Ma), tetrapod extinction rate peaked, alpha diversity imploded, and endemism developed for the first time. Analysis of ecological diversity shows that rainforest collapse was also accompanied by acquisition of new feeding strategies (predators, herbivores), consistent with tetrapod adaptation to the effects of habitat fragmentation and resource restriction. Effects on amphibians were particularly devastating, while amniotes (‘reptiles’) fared better, being ecologically adapted to the drier conditions that followed. Our results demonstrate, for the first time, that Coal Forest fragmentation influenced profoundly the ecology and evolution of terrestrial fauna in tropical Euramerica, and illustrate the tight coupling that existed between vegetation, climate, and trophic webs.
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