Stocker, M. R.. 2013. A new taxonomic arrangement for Paleorhinus scurriensis. Earth and Environmental Science Transactions of the Royal Society of Edinburgh (advance online publication)DOI: http://dx.doi.org/10.1017/S1755691013000340
Abstract - The paraphyletic genus ‘Paleorhinus’ is understood currently as a cosmopolitan phytosaur taxon from the Late Triassic. There is no consensus regarding the number of species of ‘Paleorhinus,’ with multiple species and genera synonymised into a single genus or even a single species at various points in its published history. The taxonomy is confounded by historical descriptions without the benefit of comparisons to more recently collected specimens, emphasis on plesiomorphic cranial morphology as diagnostic features of the genus,
and lack of cladistic analyses. When included in a recent explicitly cladistic phylogenetic analysis, the holotype of ‘Paleorhinus’ scurriensis (TTU P-00539) was found to be the earliest-branching phytosaur with respect to other North American specimens previously referred to ‘Paleorhinus,’ and is generically distinct from Paleorhinus. ‘Paleorhinus’ scurriensis differs from all known phytosaurs in five unambiguous characters: basitubera widely separated mediolaterally; ridge present on lateral surface of jugal; thickened shelf present along posteroventral edge of expanded pterygoid-quadrate wing; ‘septomaxillae’ separated and excluded from internarial septum; and nasal swelling present posterior to posterior borders of nares. This detailed morphological description of an early-branching phytosaur taxon is a first step towards resolving long-standing issues surrounding specific anatomical features and relationships among early members of the clade.
Hungerbühler, A., Mueller, B., Chatterjee, S., and D. P. Cunningham. 2013. Cranial anatomy of the Late Triassic phytosaur Machaeroprosopus, with the description of a new species from West Texas. Earth and Environmental Science Transactions of the Royal Society of Edinburgh (advance online publication) DOI: http://dx.doi.org/10.1017/S1755691013000364
Abstract - The skull anatomy of a new species of the phytosaur Machaeroprosopus is described for the first time on the basis of two specimens from the Upper Triassic Cooper Canyon Formation of Texas. Additional information is provided by a third specimen referred to Machaeroprosopus sp. A paranasal bone, an additional paired element of the narial region, is identified. Important new data are presented for the braincase, including the morphology of the epipterygoid and presphenoid, an anterior process of the prootic, an anteroventral process of the laterosphenoid, and a parasphenoid process. Machaeroprosopus lottorum n. sp. is characterised by four apomorphies: a supratemporal fenestra closed on the skull roof with beveled anterior rim, a comparatively short squamosal, a flat and rugose narial rim, and medially extended palatines that come close to form an ossified secondary palate. With respect to the supratemporal fenestra, the supraoccipital–parietal complex and several features of the squamosal, Machaeroprosopus lottorum n. sp. bridges the morphological gap between species previously referred to the genera Pseudopalatus and Redondasaurus. A parsimony analysis of known species of Machaeroprosopus supports the hypothesis that the development of the rostral crest in Machaeroprosopus is a sexually dimorphic feature, and questions the validity of the genus Redondasaurus. Consequently, Redondasaurus is here considered a junior synonym of Machaeroprosopus.
Showing posts with label phytosaur. Show all posts
Showing posts with label phytosaur. Show all posts
Reintroducing the Phytosaur Genus Machaeoroprosopus
I had posted about the taxonomic problem caused by the loss of the holotype specimen Machaeroprosopus validus before with a plea for people to help look for the specimen. Come to find out a careful reading of the literature and the ICZN demonstrates that the specimen is not as important as previously believed regarding the taxonomic status of the name Machaeroprosopus. It will take awhile for Triassic and phytosaur workers to get used to using the name again and I am sure that some will just flat out refuse, but according to the ICZN the name Machaeoroprosopus is the proper one if the holotype specimen of "Belodon" buceros is truly diagnosable and if the other nominal species of "Pseudopalatus" are referable to the same genus represented by "B." buceros.
Parker, W. G., Hungerbühler, A., and J. W. Martz. 2013. The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States. Earth and Environmental Science Transactions of the Royal Society of Edinburgh First View Article. DOI: http://dx.doi.org/10.1017/S1755691013000339
Abstract - The genus Machaeroprosopus has long been considered invalid because the type specimen of the Late Triassic phytosaur species, M. validus, has been lost. Re-examination of the primary literature regarding the establishment of the Late Triassic phytosaur genus Machaeroprosopus demonstrates that M. buceros is the correct type species, not M. validus. Thus, the genus level name Machaeroprosopus has priority over the genera Pseudopalatus and Arribasuchus and all nominal species should be reassigned. Reassignment of these species to Machaeroprosopus satisfies the requirements of the International Code of Zoological Nomenclature (ICZN) and preserves historical context. The name Pseudopalatinae is retained as the valid clade name for these phytosaurs because its usage falls outside of the ICZN.
Parker, W. G., Hungerbühler, A., and J. W. Martz. 2013. The taxonomic status of the phytosaurs (Archosauriformes) Machaeroprosopus and Pseudopalatus from the Late Triassic of the western United States. Earth and Environmental Science Transactions of the Royal Society of Edinburgh First View Article. DOI: http://dx.doi.org/10.1017/S1755691013000339
Abstract - The genus Machaeroprosopus has long been considered invalid because the type specimen of the Late Triassic phytosaur species, M. validus, has been lost. Re-examination of the primary literature regarding the establishment of the Late Triassic phytosaur genus Machaeroprosopus demonstrates that M. buceros is the correct type species, not M. validus. Thus, the genus level name Machaeroprosopus has priority over the genera Pseudopalatus and Arribasuchus and all nominal species should be reassigned. Reassignment of these species to Machaeroprosopus satisfies the requirements of the International Code of Zoological Nomenclature (ICZN) and preserves historical context. The name Pseudopalatinae is retained as the valid clade name for these phytosaurs because its usage falls outside of the ICZN.
"Francosuchus" trauthi is Not a Phytosaur - Implications for Late Triassic Global Vertebrate Biostratigraphy
This eliminates the marine tie for the Otischalkian Land Vertebrate Faunachron, although the identification of this specimen as 'Paleorhinus' was already pretty weak as argued by Irmis et al. (2010).
Butler, R. J., 2013. ‘Francosuchus’ trauthi is not Paleorhinus: implications for Late Triassic
vertebrate biostratigraphy, Journal of Vertebrate Paleontology, 33:858-864.
Abstract - A rostrum fragment from the marginal marine upper Lunz Formation of Austria (early Late Triassic: late Carnian) was previously identified as a new species of phytosaurian archosauriform, ‘Francosuchus’ trauthi. ‘Francosuchus’ trauthi was subsequently synonymized with the non-phytosaurid phytosaur Paleorhinus, and this synonymy was used as evidence to correlate the ‘Paleorhinus biochron’ and the Otischalkian land-vertebrate faunachron to the marine timescale. Here, I provide a redescription of ‘Francosuchus’ trauthi and document anatomical features that differ substantially from all known species of non-phytosaurid phytosaur. There is no evidence to support synonymy of ‘Francosuchus’ trauthi with Paleorhinus, and no unambiguous features to support a phytosaurian identification. However, ‘Francosuchus’ trauthi possesses a unique combination of characters that distinguish it from all other Triassic tetrapods, and necessitates referral of the species to a new genus, Dolerosaurus, gen. nov. Rejection of the proposed synonymy between ‘Francosuchus’ trauthi and Paleorhinus means that the ‘Paleorhinus biochron’ cannot be tied to the marine late Carnian as previously suggested, and provides further evidence of the problems inherent in attempting to correlate the terrestrial Triassic to the marine timescale.
Butler, R. J., 2013. ‘Francosuchus’ trauthi is not Paleorhinus: implications for Late Triassic
vertebrate biostratigraphy, Journal of Vertebrate Paleontology, 33:858-864.
Abstract - A rostrum fragment from the marginal marine upper Lunz Formation of Austria (early Late Triassic: late Carnian) was previously identified as a new species of phytosaurian archosauriform, ‘Francosuchus’ trauthi. ‘Francosuchus’ trauthi was subsequently synonymized with the non-phytosaurid phytosaur Paleorhinus, and this synonymy was used as evidence to correlate the ‘Paleorhinus biochron’ and the Otischalkian land-vertebrate faunachron to the marine timescale. Here, I provide a redescription of ‘Francosuchus’ trauthi and document anatomical features that differ substantially from all known species of non-phytosaurid phytosaur. There is no evidence to support synonymy of ‘Francosuchus’ trauthi with Paleorhinus, and no unambiguous features to support a phytosaurian identification. However, ‘Francosuchus’ trauthi possesses a unique combination of characters that distinguish it from all other Triassic tetrapods, and necessitates referral of the species to a new genus, Dolerosaurus, gen. nov. Rejection of the proposed synonymy between ‘Francosuchus’ trauthi and Paleorhinus means that the ‘Paleorhinus biochron’ cannot be tied to the marine late Carnian as previously suggested, and provides further evidence of the problems inherent in attempting to correlate the terrestrial Triassic to the marine timescale.
More Photos from the Petrified Forest
I'm currently creating a database of all of our photos from the last decade of paleontological work at Petrified Forest National Park and am working through 2002. These photos were taken by Daniel Woody who was investigating the Sonsela Member of the Chinle Formmation and assisting with the paleontology work. I'm amazed how far the quality of digital photos have over the decade!
 |
| Phytosaur lower jaw in the Crystal Forest |
 |
| Phytosaur quadrate bone in the Blue Mesa Member |
First Record of Late Triassic Vertebrate Fossils from Lithuania and the Paleobiogeography of Phytosaurs
Brusatte, S. L., Butler, R. J., Niedźwiedzki, G., Sulej, T., Bronowicz, R., and J. Satkūnas. 2012. First record of Mesozoic terrestrial vertebrates from Lithuania: phytosaurs (Diapsida: Archosauriformes) of probable Late Triassic age, with a review of phytosaur biogeography. Geological Magazine (early online) 13 pp. doi:10.1017/S0016756812000428
Abstract – Fossils of Mesozoic terrestrial vertebrates from Lithuania and the wider East Baltic region
of Europe have previously been unknown.We here report the first Mesozoic terrestrial vertebrate fossils
from Lithuania: two premaxillary specimens and three teeth that belong to Phytosauria, a common
clade of semiaquatic Triassic archosauriforms. These specimens represent an uncrested phytosaur,
similar to several species within the genera Paleorhinus, Parasuchus, Rutiodon and Nicrosaurus.
Because phytosaurs are currently only known from the Upper Triassic, their discovery in northwestern
Lithuania (the Šaltiškiai clay-pit) suggests that at least part of the Triassic succession in this region
is Late Triassic in age, and is not solely Early Triassic as has been previously considered. The new
specimens are among the most northerly occurrences of phytosaurs in the Late Triassic, as Lithuania
was approximately 7–10◦ further north than classic phytosaur-bearing localities in nearby Germany and
Poland, and as much as 40◦ further north than the best-sampled phytosaur localities in North America.
The far northerly occurrence of the Lithuanian fossils prompts a review of phytosaur biogeography
and distribution, which suggests that these predators were widely distributed in the Triassic monsoonal
belt but rarer in more arid regions.
Introducing Protome batalaria, a New Phytosaur from the Chinle Formation of Petrified Forest National Park, Arizona
In the Fall of 2004 Michelle Stocker and I were out at the Battleship NW fossil locality in Petrified Forest National Park with several researchers from Northern Arizona University. They were working on completing the geological map of the area and had noted that they could not get the current stratigraphic scheme we were using (introduced in 2002) to work out on the map. The stratigraphic position of this quarry was an important issue behind this work as I had just collected a good skeleton of the aetosaur Calyptosuchus wellesi here just above a prominent sandstone that previous workers had correlated to the "Sonsela Sandstone Bed". If this bed correlation was correct then the specimen would be from the Revueltian biozone. This was problematic because Calyptosuchus is considered an index taxon of the Adamanian. As we hemmed and hawed back and forth and discussed various possible correlations to work out these problems, Michelle noted some scraps of bone in unconsolidated sand at top of this bed and very near to where we were standing. She was very surprised, as was I, when she reached down and pulled up part of the skull roof of a phytosaur.
After the NAU researchers moved on to complete their work, we examined Michelle's new "quarry" much closer. By literally sifting our fingers through the loose sand we easily collected numerous parts of the skull including large portions of the rostrum and skull roof. We also uncovered a ramus of the mandible, but this was actually in-situ in the bedrock just underneath the loose sand. We were able to jacket this element, but it was wintertime and I distinctly remember how frozen our hands were after each application of a plaster bandage. Luckily the truck was very nearby, so after each application we would run to the running truck to stick our hands under the heater.
Back in the lab we were able to piece back together much of the skull and it later became part of the focus of Michelle's Masters Thesis. Prior to this Randall Irmis and I mentioned (and figured) this specimen in a 2005 paper where we referred it to "Leptosuchus" adamanensis based on the overall morphology of the squamosals following work by Long and Murry. However, Michelle's detailed phylogenetic analysis in her thesis suggested something different, specifically the specimen did not form a clade with Smilosuchus adamanensis and instead was something else.
In her new paper in the Journal of Vertebrate Paleontology Michelle has described this specimen as a new taxon, which she names Protome batalaria. The name reflects the condition of the specimen, "face of an animal" and where it was found "warship" (for the Battleship Quarry). It can be diagnosed by a unique combination of characters as well as three autapomorphies of the braincase and lower jaw. Her phylogenetic analysis recovers it as a non-pseudopalatine leptosuchomorph.
Important discussion in her paper revolves around the importance of the use of apomorphies to describe and classify specimens. In this particular case past workers (myself) had focused on the generally morphology of the squamosal and robustness of the specimen to make a taxonomic assignment and ignored other discrete apomorphies of the material, which a phylogenetic analysis later determined to be of significance. Thus the longtime practice of assigning isolated phytosaur squamosals to taxa based on general similarity and utilizing these for Late Triassic biochronology is called into question. This general squamosal morphology used to assign (fragmentary and complete) specimens to Rutiodon or Leptosuchus instead just appears to be a shared character of non-pseudopalatine leptosuchomorphs, a paraphyletic assemblage.
As recommended by Michelle it is now necessary to go back to collections such as those from the Petrified Forest and look carefully at all of the specimens assigned to "Leptosuchus" and sort them out using apomorphies. Hopefully this will provide a clear distribution pattern and biochronological signal for these specimens, testing their importance in phytosaur biochronology and biogeography. Overall this new paper provides a great description and discussion that Michelle should be proud of and will be landmark (along with her 2010 paper) for sorting out the labyrinth that is phytosaur taxonomy.
By the way, the stratigraphic problem mentioned at the beginning of this post was finally figured out by Jeff Martz and I in 2009 when we discovered that the bed in question was definitely not the "Sonsela Sandstone Bed", but rather an isolated sandstone lens in the older Lot's Wife Beds and Adamanian in age.
Stocker, M. R. 2012. A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 32(3): 573-586 DOI:10.1080/02724634.2012.649815
Abstract - A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.
After the NAU researchers moved on to complete their work, we examined Michelle's new "quarry" much closer. By literally sifting our fingers through the loose sand we easily collected numerous parts of the skull including large portions of the rostrum and skull roof. We also uncovered a ramus of the mandible, but this was actually in-situ in the bedrock just underneath the loose sand. We were able to jacket this element, but it was wintertime and I distinctly remember how frozen our hands were after each application of a plaster bandage. Luckily the truck was very nearby, so after each application we would run to the running truck to stick our hands under the heater.
Back in the lab we were able to piece back together much of the skull and it later became part of the focus of Michelle's Masters Thesis. Prior to this Randall Irmis and I mentioned (and figured) this specimen in a 2005 paper where we referred it to "Leptosuchus" adamanensis based on the overall morphology of the squamosals following work by Long and Murry. However, Michelle's detailed phylogenetic analysis in her thesis suggested something different, specifically the specimen did not form a clade with Smilosuchus adamanensis and instead was something else.
In her new paper in the Journal of Vertebrate Paleontology Michelle has described this specimen as a new taxon, which she names Protome batalaria. The name reflects the condition of the specimen, "face of an animal" and where it was found "warship" (for the Battleship Quarry). It can be diagnosed by a unique combination of characters as well as three autapomorphies of the braincase and lower jaw. Her phylogenetic analysis recovers it as a non-pseudopalatine leptosuchomorph.
Important discussion in her paper revolves around the importance of the use of apomorphies to describe and classify specimens. In this particular case past workers (myself) had focused on the generally morphology of the squamosal and robustness of the specimen to make a taxonomic assignment and ignored other discrete apomorphies of the material, which a phylogenetic analysis later determined to be of significance. Thus the longtime practice of assigning isolated phytosaur squamosals to taxa based on general similarity and utilizing these for Late Triassic biochronology is called into question. This general squamosal morphology used to assign (fragmentary and complete) specimens to Rutiodon or Leptosuchus instead just appears to be a shared character of non-pseudopalatine leptosuchomorphs, a paraphyletic assemblage.
As recommended by Michelle it is now necessary to go back to collections such as those from the Petrified Forest and look carefully at all of the specimens assigned to "Leptosuchus" and sort them out using apomorphies. Hopefully this will provide a clear distribution pattern and biochronological signal for these specimens, testing their importance in phytosaur biochronology and biogeography. Overall this new paper provides a great description and discussion that Michelle should be proud of and will be landmark (along with her 2010 paper) for sorting out the labyrinth that is phytosaur taxonomy.
By the way, the stratigraphic problem mentioned at the beginning of this post was finally figured out by Jeff Martz and I in 2009 when we discovered that the bed in question was definitely not the "Sonsela Sandstone Bed", but rather an isolated sandstone lens in the older Lot's Wife Beds and Adamanian in age.
Stocker, M. R. 2012. A new phytosaur (Archosauriformes, Phytosauria) from the Lot’s Wife beds (Sonsela Member) within the Chinle Formation (Upper Triassic) of Petrified Forest National Park, Arizona. Journal of Vertebrate Paleontology 32(3): 573-586 DOI:10.1080/02724634.2012.649815
Abstract - A new phytosaur taxon from Petrified Forest National Park, Arizona, is here described based on cranial material from a single individual. This specimen previously was included in an extensive phylogenetic analysis, and it was found to possess a combination of character states that differs from all known phytosaur taxa in addition to two autapomorphies within the braincase and an autapomorphy of the mandible. The new taxon adds to the taxonomic diversity recognized from the Sonsela Member of the Chinle Formation. The continued increase in phytosaur diversity emphasizes the need to more accurately characterize and identify taxa within a phylogenetic systematic context in order to produce a more refined signal for biostratigraphic correlations, biochronologic inferences, and faunal dynamics during the Late Triassic.
Logo of the 2012 Annual Meeting of the Society of Vertebrate Paleontology
This was just flashed all over Facebook.... the logo for the 2012 meeting in Raleigh, North Carolina by Kristin Lamm. It features the phytosaur Rutiodon carolinensis . I have to get a few of the t-shirts.
![]()
1921 Excavation of the Holotype of the Phytosaur "Machaeroprosopus" adamanensis
Today (June 17th) is the 90th Anniversary of Charles Camp initiating collection of the holotype of the phytosaur "Machaeroprosopus" adamanensis (now Smilosuchus adamanensis) from the Blue Forest at Petrified Forest National Park (Arizona, USA). Susan Drymala, Rachel Guest (summer interns), and I took the opportunity to revisit the site. We started at the 1921 campsite (where Rachel found an old sardine can) and headed east, climbing the 50 foot ridge above the arroyo where the specimen was collected. We sat in the quarry for a bit, reminensed for a bit with old photos, thunked our rock hammers in a few times in honor of camp and departed on to other sites. It's always pretty cool to be able to literally follow in the footsteps of these older paleontologists, especailly one who was such a huge influence on Late Triassic vertebrate paleontology as Charles Lewis Camp. Below are Susan (left) and Rachel (right) at the site. Rachel is in the actual old diggings.
![]()
Below, Rachel holds up an old slat of wood from the 1921 excavation.
![]()
![]()
Charles L. Camp photo of the skeleton of "Machaeroprosopus" adamanensis as partially excavated in June 1921 (courtesy of the UCMP and PEFO).
![]()
Below is the camp of Annie Alexander and Charles L. Camp in the Blue Forest in June of 1921 (courtesy of the UCMP and PEFO)
"Belodon" from Creatures of Other Days by Hutchinson and Flower (1894)
The small animals in the reconstruction are the aetosaur Aetosaurus. The one of the left seems to be wondering why the phytosaur is wearing aetosaur armor.
Smilosuchus in Color
What makes Jeff Martz's Smilisuchus (Phytosauridae) reconstruction even better? A bit of color.
"Old Paleontologists Never Die. Their Knees Just Give Out"
This is an excellent account of the joys and importance of field paleontology (and some of the luck involved) in an interview with one of the 'greats' in the field of vertebrate paleontology, Dr. Mary Dawson of the Carnegie Museum.
http://www.post-gazette.com/pg/11072/1131175-51.stm
This article also mentions why it is important to revisit your previous digs and look for the pieces you are missing, many times they are often turned up by further erosion. In 2006 Randall Irmis and I described a new species of phytosaur, Pseudopalatus jablonskiae. One of the crucial preserved portions of the specimen was its braincase, which is one of the best preserved Pseudopalatus braincases ever found and in this particular species gives clues of the phylogenetic relationships between Pseudopalatus and the earlier Smilosuchus. Unfortunately, the specimen had been trampled and slowly kicked apart (it was located on a trail). Many of the fragments had been washed downslope and reburied. We were able to piece together the braincase but lacked the lower portion, the basicranium.
In 2008 I revisited the site and found more fragments that had eroded out from the downslope area and one of these was the nearly complete basicranium! At some point I will have to prepare a redescription of the entire braincase of this very cool (and important) specimen,
http://www.post-gazette.com/pg/11072/1131175-51.stm
This article also mentions why it is important to revisit your previous digs and look for the pieces you are missing, many times they are often turned up by further erosion. In 2006 Randall Irmis and I described a new species of phytosaur, Pseudopalatus jablonskiae. One of the crucial preserved portions of the specimen was its braincase, which is one of the best preserved Pseudopalatus braincases ever found and in this particular species gives clues of the phylogenetic relationships between Pseudopalatus and the earlier Smilosuchus. Unfortunately, the specimen had been trampled and slowly kicked apart (it was located on a trail). Many of the fragments had been washed downslope and reburied. We were able to piece together the braincase but lacked the lower portion, the basicranium.
In 2008 I revisited the site and found more fragments that had eroded out from the downslope area and one of these was the nearly complete basicranium! At some point I will have to prepare a redescription of the entire braincase of this very cool (and important) specimen,
"Fossil Time Capsules": Opening 70 Year Old Jackets of Triassic Fossils at the University of Texas at Austin
"The new quarry is looking damn good," wrote [paleontologist Grayson] Meade to his colleague Glen Evans in May 1940. "[W]e have found quite a portion of a partially articulated phytosaur skeleton. About four or five feet of the vertebrae are mostly in articulation. There are leg bones, some ribs, and the mandible. ? There is every indication that the skull should be there, and more of the skeleton. I didn't reach the end of it knowingly at any rate."
You can read the rest of this story here. There are dozens of unopened jackets of fossils collected in the late 1930s and early 40s in the basement of the Vertebrate Paleontology Lab at UT Austin. I've previously published on some of the prepared material and it is all just spectacular. These specimens are especially important because the Otis Chalk quarries are possibly older than any Chinle Formation exposures and might be giving us a unique view into latest Carnian or earliest Norian faunal assemblages in the western U.S. I cannot wait to see what the rest of those jackets hold!
Kudos to my friends and colleagues Michelle Stocker and Sterling Nesbitt for their opportunity to work on these fossils and at the original quarries.
You can read the rest of this story here. There are dozens of unopened jackets of fossils collected in the late 1930s and early 40s in the basement of the Vertebrate Paleontology Lab at UT Austin. I've previously published on some of the prepared material and it is all just spectacular. These specimens are especially important because the Otis Chalk quarries are possibly older than any Chinle Formation exposures and might be giving us a unique view into latest Carnian or earliest Norian faunal assemblages in the western U.S. I cannot wait to see what the rest of those jackets hold!
Kudos to my friends and colleagues Michelle Stocker and Sterling Nesbitt for their opportunity to work on these fossils and at the original quarries.
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.
Pravusuchus hortus the Wicked Phytosaur from the Petrified Forest
Stocker, M. R. 2010. A new taxon of phytosaur (Archosauria: Pseudosuchia) from the Late Triassic (Norian) Sonsela Member (Chinle Formation) in Arizona, and a critical re-evaluation of Leptosuchus Case 1922. Palaeontology 53:997-1022. doi: 10.1111/j.1475-4983.2010.00983.x
Abstract - Leptosuchus Case, 1922 (Reptilia: Phytosauria) from the Late Triassic of the American West is represented by many specimens. Here, I present complete morphological descriptions of the skull material of a new taxon from the Sonsela Member (Chinle Formation) of Petrified Forest National Park, Arizona, with the first rigorous phylogenetic analysis focused on the interrelationships of Leptosuchus. The new taxon is recovered as the sister taxon to Pseudopalatinae. It possesses one unambiguous synapomorphy (the ‘septomaxillae’ form part of the lateral borders of the nares) and shares the presence of a subsidiary opisthotic process with Pseudopalatinae. The new taxon does not fall within the restricted clade Leptosuchus. In my analysis, the previously proposed, but undemonstrated, sister taxon relationship between Angistorhinus and Rutiodon is not supported, Paleorhinus is recovered as paraphyletic, and a subset of taxa traditionally included within Leptosuchus are found to be more closely related to Pseudopalatinae, rendering Leptosuchus paraphyletic. ‘Leptosuchus’ adamanensis emerges as sister taxon to Smilosuchus gregorii and is here referred to as Smilosuchus adamanensis nov. comb., and ‘Machaeroprosopus’ lithodendrorum is also transferred to Smilosuchus lithodendrorum nov. comb. Documentation of the variation present within Phytosauria, and specifically within Leptosuchus sensu lato, demonstrates higher diversity within Phytosauria than previously appreciated and places the character states previously proposed for Pseudopalatinae into a broader context of shared characters.
One specific subject that even the heartiest of Triassic workers will often go out of their way to avoid is the issue of phytosaur taxonomy, and for good reason, it is a mess. I previously supplied a flowchart I created in 2001 that demonstrates how much of a mess I’m talking about. Recent revisions (e.g., Hungerbühler 2002) have dealt almost exclusively with the pseudopalatine phytosaurs and the rest of the group has been relatively neglected since Long and Murry’s (1995) treatment. The genus Leptosuchus (still assigned to Rutiodon by some) has been poorly understood, and most new specimens assigned to this genus have been lumped into existing species without clear discussion of the characters used to support these assignments (I’m am guilty of this myself).
In the Spring of 2003 Daniel Woody and I discovered a large phytosaur skull in the Devil’s Playground portion of Petrified Forest National Park during a geological reconnaissance. That summer a crew consisting of Randall Irmis, Michelle Stocker, Jeff Shuman, and I collected the skull (now PEFO 31218) and our group initiated preparation. A couple of months later Jeff, Randy, and I discovered a second skull very close by; however, this skull appeared to only consist of a set of badly eroded lower jaws and was not collected. Interestingly we made the discovery while we were relocating and rephotographing a photo taken by Edwin Colbert of a phytosaur skull excavation conducted by the AMNH in 1946. Amazingly both skull sites are in this historic photo.
In 2006 Michelle and I reinvestigated the lower jaws and discovered that much of the skull was indeed present. This skull (PEFO 34239) was collected and Michelle began the preparation. About this time Michelle was looking for a good project for her Master’s thesis at the University of Iowa and despite knowing the potential pitfalls in the morass of phytosaur taxonomy, I suggested that maybe she should describe the two PEFO skulls (she had helped excavate and prep both of them) and determine their taxonomic affinities. Fast forwarding to the present it would seem that this was indeed a very good project and Michelle produced a very fine thesis (Stocker 2008), a portion of which is presented in this paper. She has since become quite the expert in the phytosaurs of the American Southwest and I look forward to more of her work on this subject (it is badly needed).
Some important points from this paper and details on the specimens:
1) Erects a new phytosaur taxon, Pravusuchus hortus, from the Sonsela Member of the Chinle Formation of Petrified Forest National Park. Existing specimens of Pravusuchus were originally assigned to the genus Leptosuchus, but detailed analysis shows that the taxon is distinct, possessing skull characters found in both ‘leptosuchines’ and pseudopalatines.
2) The holotype (AMNH FR 30646) was originally collected from the Petrified Forest in 1946 by Edwin Colbert of the American Museum of Natural History. The referred specimens are from the same geographical area and stratigraphic horizon and were collected by park staff (including Michelle Stocker) in 2003 and 2006.
3) Stratigraphically the specimens were found between the highest specimens of “Leptosuchus” and the lowest specimens of Pseudopalatus (Parker and Martz in press).
4) The genus Leptosuchus (sensu Long and Murry 1995) is paraphyletic and specimens referred to the genus are now only found in the Dockum Group. Arizona specimens of “Leptosuchus” are reassigned to Pravusuchus and Smilosuchus.
5) Stocker considers there to be three valid species of Smilosuchus; S. gregorii (the type species), S. adamanensis, and S. lithodendrorum. These last two are new combinations and this study resurrects the species S. lithodendrorum, which was considered a junior sysnonym of Leptosuchus crosbiensis by Long and Murry (1995).
This paper contains the most inclusive phylogenetic analysis of the Phytosauria since Ballew (1989). Some results:
1) The genus Paleorhinus is paraphyletic. Although this idea has been floating around for awhile (e.g., Fara and Hungerbuehler 2000) this is the first time it has been supported with a phylogenetic analysis.
2) The genera Anghistorhinus and Rutiodon are distinct. This synonymy was first put forth in an abstract by Hungerbuehler and Sues in 2001, but is not recovered in this study.
3) The name Rutiodon is restricted to specimens from the eastern United States. The name Rutiodon is often used for phytosaur specimens from the western United States stemming back to work by Gregory (1962) and Ballew (1989); however, this paper clearly shows that these referrals are erroneous and Rutiodon should be restricted to material from the eastern U.S.
This analysis should form the basis of future studies on the lower part of the phytosaur tree for a long time to come.
REFERENCES
Ballew, K. L. 1989. A phylogenetic analysis of Phytosauria from the Late Triassic of the western United States. 309–339. In LUCAS, S. G. and HUNT, A. P. (eds). Dawn of the age of dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, 414 pp.
Fara, E., and Hungerbühler, A. 2000. Paleorhinus magnoculus from the Upper Triassic of Morocco: a juvenile primitive phytosaur (Archosauria). Comptes Rendus de l’Académie des Sciences, Paris, Sciences de la Terre et des planétes, 331, 831–836.
Gregory, J. T. 1962. The genera of the phytosaurs. American Journal of Science, 260, 652–690.
Hungerbühler, A. 2002. The Late Triassic phytosaur Mystriosuchus westphali, with a revision of the genus. Palaeontology, 45, 377–418.
Hungerbühler, A., and Sues, H.-D. 2001. Status and phylogenetic relationships of the Late Triassic phytosaur Rutiodon carolinensis. Journal of Vertebrate Paleontology, 21(3-Suppl.), 64A.
Long, R. A. and Murry, P. A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. Bulletin of the New Mexico Museum of Natural History and Science, 4, 1–254.
Stocker, M. R. 2008. Relationships of the phytosaur Leptosuchus Case 1922 with descriptions of new material from Petrified Forest National Park, Arizona. Unpublished MS thesis, University of Iowa, Iowa City, 220 pp.
Abstract - Leptosuchus Case, 1922 (Reptilia: Phytosauria) from the Late Triassic of the American West is represented by many specimens. Here, I present complete morphological descriptions of the skull material of a new taxon from the Sonsela Member (Chinle Formation) of Petrified Forest National Park, Arizona, with the first rigorous phylogenetic analysis focused on the interrelationships of Leptosuchus. The new taxon is recovered as the sister taxon to Pseudopalatinae. It possesses one unambiguous synapomorphy (the ‘septomaxillae’ form part of the lateral borders of the nares) and shares the presence of a subsidiary opisthotic process with Pseudopalatinae. The new taxon does not fall within the restricted clade Leptosuchus. In my analysis, the previously proposed, but undemonstrated, sister taxon relationship between Angistorhinus and Rutiodon is not supported, Paleorhinus is recovered as paraphyletic, and a subset of taxa traditionally included within Leptosuchus are found to be more closely related to Pseudopalatinae, rendering Leptosuchus paraphyletic. ‘Leptosuchus’ adamanensis emerges as sister taxon to Smilosuchus gregorii and is here referred to as Smilosuchus adamanensis nov. comb., and ‘Machaeroprosopus’ lithodendrorum is also transferred to Smilosuchus lithodendrorum nov. comb. Documentation of the variation present within Phytosauria, and specifically within Leptosuchus sensu lato, demonstrates higher diversity within Phytosauria than previously appreciated and places the character states previously proposed for Pseudopalatinae into a broader context of shared characters.
One specific subject that even the heartiest of Triassic workers will often go out of their way to avoid is the issue of phytosaur taxonomy, and for good reason, it is a mess. I previously supplied a flowchart I created in 2001 that demonstrates how much of a mess I’m talking about. Recent revisions (e.g., Hungerbühler 2002) have dealt almost exclusively with the pseudopalatine phytosaurs and the rest of the group has been relatively neglected since Long and Murry’s (1995) treatment. The genus Leptosuchus (still assigned to Rutiodon by some) has been poorly understood, and most new specimens assigned to this genus have been lumped into existing species without clear discussion of the characters used to support these assignments (I’m am guilty of this myself).
In the Spring of 2003 Daniel Woody and I discovered a large phytosaur skull in the Devil’s Playground portion of Petrified Forest National Park during a geological reconnaissance. That summer a crew consisting of Randall Irmis, Michelle Stocker, Jeff Shuman, and I collected the skull (now PEFO 31218) and our group initiated preparation. A couple of months later Jeff, Randy, and I discovered a second skull very close by; however, this skull appeared to only consist of a set of badly eroded lower jaws and was not collected. Interestingly we made the discovery while we were relocating and rephotographing a photo taken by Edwin Colbert of a phytosaur skull excavation conducted by the AMNH in 1946. Amazingly both skull sites are in this historic photo.
In 2006 Michelle and I reinvestigated the lower jaws and discovered that much of the skull was indeed present. This skull (PEFO 34239) was collected and Michelle began the preparation. About this time Michelle was looking for a good project for her Master’s thesis at the University of Iowa and despite knowing the potential pitfalls in the morass of phytosaur taxonomy, I suggested that maybe she should describe the two PEFO skulls (she had helped excavate and prep both of them) and determine their taxonomic affinities. Fast forwarding to the present it would seem that this was indeed a very good project and Michelle produced a very fine thesis (Stocker 2008), a portion of which is presented in this paper. She has since become quite the expert in the phytosaurs of the American Southwest and I look forward to more of her work on this subject (it is badly needed).
Some important points from this paper and details on the specimens:
1) Erects a new phytosaur taxon, Pravusuchus hortus, from the Sonsela Member of the Chinle Formation of Petrified Forest National Park. Existing specimens of Pravusuchus were originally assigned to the genus Leptosuchus, but detailed analysis shows that the taxon is distinct, possessing skull characters found in both ‘leptosuchines’ and pseudopalatines.
2) The holotype (AMNH FR 30646) was originally collected from the Petrified Forest in 1946 by Edwin Colbert of the American Museum of Natural History. The referred specimens are from the same geographical area and stratigraphic horizon and were collected by park staff (including Michelle Stocker) in 2003 and 2006.
3) Stratigraphically the specimens were found between the highest specimens of “Leptosuchus” and the lowest specimens of Pseudopalatus (Parker and Martz in press).
4) The genus Leptosuchus (sensu Long and Murry 1995) is paraphyletic and specimens referred to the genus are now only found in the Dockum Group. Arizona specimens of “Leptosuchus” are reassigned to Pravusuchus and Smilosuchus.
5) Stocker considers there to be three valid species of Smilosuchus; S. gregorii (the type species), S. adamanensis, and S. lithodendrorum. These last two are new combinations and this study resurrects the species S. lithodendrorum, which was considered a junior sysnonym of Leptosuchus crosbiensis by Long and Murry (1995).
This paper contains the most inclusive phylogenetic analysis of the Phytosauria since Ballew (1989). Some results:
1) The genus Paleorhinus is paraphyletic. Although this idea has been floating around for awhile (e.g., Fara and Hungerbuehler 2000) this is the first time it has been supported with a phylogenetic analysis.
2) The genera Anghistorhinus and Rutiodon are distinct. This synonymy was first put forth in an abstract by Hungerbuehler and Sues in 2001, but is not recovered in this study.
3) The name Rutiodon is restricted to specimens from the eastern United States. The name Rutiodon is often used for phytosaur specimens from the western United States stemming back to work by Gregory (1962) and Ballew (1989); however, this paper clearly shows that these referrals are erroneous and Rutiodon should be restricted to material from the eastern U.S.
This analysis should form the basis of future studies on the lower part of the phytosaur tree for a long time to come.
REFERENCES
Ballew, K. L. 1989. A phylogenetic analysis of Phytosauria from the Late Triassic of the western United States. 309–339. In LUCAS, S. G. and HUNT, A. P. (eds). Dawn of the age of dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, 414 pp.
Fara, E., and Hungerbühler, A. 2000. Paleorhinus magnoculus from the Upper Triassic of Morocco: a juvenile primitive phytosaur (Archosauria). Comptes Rendus de l’Académie des Sciences, Paris, Sciences de la Terre et des planétes, 331, 831–836.
Gregory, J. T. 1962. The genera of the phytosaurs. American Journal of Science, 260, 652–690.
Hungerbühler, A. 2002. The Late Triassic phytosaur Mystriosuchus westphali, with a revision of the genus. Palaeontology, 45, 377–418.
Hungerbühler, A., and Sues, H.-D. 2001. Status and phylogenetic relationships of the Late Triassic phytosaur Rutiodon carolinensis. Journal of Vertebrate Paleontology, 21(3-Suppl.), 64A.
Long, R. A. and Murry, P. A. 1995. Late Triassic (Carnian and Norian) tetrapods from the southwestern United States. Bulletin of the New Mexico Museum of Natural History and Science, 4, 1–254.
Stocker, M. R. 2008. Relationships of the phytosaur Leptosuchus Case 1922 with descriptions of new material from Petrified Forest National Park, Arizona. Unpublished MS thesis, University of Iowa, Iowa City, 220 pp.
Jurassic Phytosaur??
A new paper by Maisch and Kapitzke (2010) describes a mandibular fragment from a phytosaur from marine shales in England. This is supposedly the first record of a phytosaur from the Jurassic (Hettangian) as the specimen was found in-situ beneath beds that provide the lowest occurrence of the ammonoid Psiloceras. Thus some phytosaurs, in this case a marine one from Europe, purportedly survived the end-Triassic extinction.
However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.
I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata. Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians.
The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.
Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.
Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.
However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.
I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata. Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians.
The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.
Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.
Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.
Phytosaur Skull Preparation IV
Phytosaurs as the Likely Trackmaker for Apatopus from the Late Triassic of North America
Padian, K., Li, C., and J. Pchelnikova. 2009. The trackmaker of Apatopus (Late Triassic: North America): implications for the evolution of archosaur stance and gait. Palaeontology (early view). doi: 10.1111/j.1475-4983.2009.00924.x
Abstract - For some decades, a major focus of research has been on how locomotor modes changed in some archosaurian reptiles from a more or less ‘sprawling’ to an ‘erect’ posture, whether there were discrete intermediate stages, and how many times ‘erect’ posture evolved. The classic paradigm for the evolution of stance and gait in archosaurs, a three-stage transition from sprawling to ‘semi-erect’ to erect posture, has been replaced by a subtler understanding of a continuum of changing limb joint angles. We suggest a further separation of terminology related to stance vs. gait so as not to entail different processes: ‘sprawling’ and ‘erect’ should refer to continua of stance; ‘rotatory’ and ‘parasagittal’ are more appropriate ends of a continuum that describes the motions of gait. We show that the Triassic trackway Apatopus best fits the anatomy and proportions of phytosaurs, based on a new reconstruction of their foot skeleton; it is less likely to have been made by another pseudosuchian or nonarchosaurian archosauromorph. Moreover, the trackmaker was performing the high walk. A phytosaurian trackmaker would imply that the common ancestor of pseudosuchians, and therefore archosaurs could approximate the high walk (depending on phylogeny), and if so, erect stance and parasagittal gait did not evolve independently in pseudosuchians and ornithosuchians, although the kinematic mechanisms differed in the two groups. It remains to be seen how far outside Archosauria, if at all, more or less erect posture and parasagittal gait may have evolved.
Abstract - For some decades, a major focus of research has been on how locomotor modes changed in some archosaurian reptiles from a more or less ‘sprawling’ to an ‘erect’ posture, whether there were discrete intermediate stages, and how many times ‘erect’ posture evolved. The classic paradigm for the evolution of stance and gait in archosaurs, a three-stage transition from sprawling to ‘semi-erect’ to erect posture, has been replaced by a subtler understanding of a continuum of changing limb joint angles. We suggest a further separation of terminology related to stance vs. gait so as not to entail different processes: ‘sprawling’ and ‘erect’ should refer to continua of stance; ‘rotatory’ and ‘parasagittal’ are more appropriate ends of a continuum that describes the motions of gait. We show that the Triassic trackway Apatopus best fits the anatomy and proportions of phytosaurs, based on a new reconstruction of their foot skeleton; it is less likely to have been made by another pseudosuchian or nonarchosaurian archosauromorph. Moreover, the trackmaker was performing the high walk. A phytosaurian trackmaker would imply that the common ancestor of pseudosuchians, and therefore archosaurs could approximate the high walk (depending on phylogeny), and if so, erect stance and parasagittal gait did not evolve independently in pseudosuchians and ornithosuchians, although the kinematic mechanisms differed in the two groups. It remains to be seen how far outside Archosauria, if at all, more or less erect posture and parasagittal gait may have evolved.
Phytosaur Taxonomy Flowchart
I remember sitting down one evening back in 2001 and putting this together. It proceeds through time from left to right. This is why nobody wants to research phytosaur taxonomy!
John Muir in the Petrified Forest: Part 2
Continuing the post on John Muir and his paleontological work in the Petrified Forest. Below are photos of a couple of the actual fossil vertebrate specimens that Muir collected in the Petrified Forest along with the tags included with the specimens. Muir gave the specimens to his friend John C. Merriam of the University of California Museum of Paleontology (UCMP). The upper tag is in Muir's own handwriting. The middle tag is Merriam's writing, whereas the locality and specimen numbers written on the middle tag are in Charles Camp's handwriting. The photos were taken by Randy Irmis and are courtesy of the UCMP.
Merriam's tag states that the specimens were all collected from the Second Forest (now the Crystal Forest); however, the osteoderm fragment below is from the aetosaur Typothorax, which does not occur at the stratigraphic level of the Crystal Forest but instead is found a bit higher in the section. Muir also visited the Northern (Black) Forest, which is higher stratigraphically and it is possible that the specimen is from there instead.
Merriam's tag states that the specimens were all collected from the Second Forest (now the Crystal Forest); however, the osteoderm fragment below is from the aetosaur Typothorax, which does not occur at the stratigraphic level of the Crystal Forest but instead is found a bit higher in the section. Muir also visited the Northern (Black) Forest, which is higher stratigraphically and it is possible that the specimen is from there instead.Below is a well preserved portion of a phytosaur jaw. This specimen probably is from the Crystal Forest.
Phytosaur Skull Preparation III
It's been awhile since any work was done on the phytosaur skull we've been following the preparation on. This is mainly because we have been without a preparator for the last few months. Now we have two new preparators and my interns are getting in on the action as well.
This photo is of my intern Chuck working on the left side of the skull with an air-scribe. These are essentially "mini-jackhammers" that use compressed air to vibrate a sharp stylus on the tip of the tool. This vibration slowly removes the hard rock matrix from the bone. The bone is purple, sandstone matrix is gray, and the white is the field jacket of air conditioning foam soaked in plaster and hardened around the skull and matrix in the field to provide safe transport back to the preparation lab. This field jacket will be slowly cut away and removed as preparation continues and will eventually be replaced by a similarly made cradle for permanent and safe storage.
Here is what has been exposed so far. The entire rear left portion of the skull is very well preserved and the elements are freeing nicely from the sandstone matrix. Anterior (forward) is to the left. Abbreviations are as follows: f, frontal; ltf, lateral temporal fenestra; na, nasal; orb, orbit; po, postorbital; q, quadrate; qj, quadratojugal; and sq, squamosal.
We'll keep following as preparation continues. We are pretty excited about this skull as it appears to be relatively pristine.
Subscribe to:
Posts (Atom)