Field of Science

Postosuchus was Even Bigger Than we Thought

Holliday, C. M., Ridgely, R. C., Sedlmayr, J. C., and L. M. Witmer. 2010. Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs. PLoS ONE 5(9): e13120. doi:10.1371/journal.pone.0013120

Abstract - Extinct archosaurs, including many non-avian dinosaurs, exhibit relatively simply shaped condylar regions in their appendicular bones, suggesting potentially large amounts of unpreserved epiphyseal (articular) cartilage. This “lost anatomy” is often underappreciated such that the ends of bones are typically considered to be the joint surfaces, potentially having a major impact on functional interpretation. Extant alligators and birds were used to establish an objective basis for inferences about cartilaginous articular structures in such extinct archosaur clades as non-avian dinosaurs. Limb elements of alligators, ostriches, and other birds were dissected, disarticulated, and defleshed. Lengths and condylar shapes of elements with intact epiphyses were measured. Limbs were subsequently completely skeletonized and the measurements repeated. Removal of cartilaginous condylar regions resulted in statistically significant changes in element length and condylar breadth. Moreover, there was marked loss of those cartilaginous structures responsible for joint architecture and congruence. Compared to alligators, birds showed less dramatic, but still significant changes. Condylar morphologies of dinosaur limb bones suggest that most non-coelurosaurian clades possessed large cartilaginous epiphyses that relied on the maintenance of vascular channels that are otherwise eliminated early in ontogeny in smaller-bodied tetrapods. A sensitivity analysis using cartilage correction factors (CCFs) obtained from extant taxa indicates that whereas the presence of cartilaginous epiphyses only moderately increases estimates of dinosaur height and speed, it has important implications for our ability to infer joint morphology, posture, and the complicated functional movements in the limbs of many extinct archosaurs. Evidence suggests that the sizes of sauropod epiphyseal cartilages surpassed those of alligators, which account for at least 10% of hindlimb length. These data suggest that large cartilaginous epiphyses were widely distributed among non-avian archosaurs and must be considered when making inferences about locomotor functional morphology in fossil taxa.

Dentition and Tooth Replacement in an Upper Triassic Traversodont Cynodont from the Eastern United States

Liu, J., and H.-D. Sues. 2010. Dentition and tooth replacement of Boreogomphodon (Cynodontia: Traversodontidae) from the Upper Triassic of North Carolina, USA. Vertebrata PalAsiatica 48:169-184.


Abstract - The teeth of new specimens of the traversodontid cynodont Boreogomphodon from the Upper Triassic of North Carolina are described. Based on dental features, especially the postcanine morphology, the North Carolina specimens are tentatively referred to Boreogomphodon jeffersoni, although their lower gomphodont postcanines typically have two rather than three cusps on the anterior transverse ridge. Based on the tooth size, direct replacement on all available specimens, the gomphodont teeth were shed anteriorly and added posteriorly. Only one generation of gomphodont teeth, at least one and possibly two generations of sectorial postcanines were present.

Tonganosaurus hei A New Sauropod from the Lower Jurassic of China

Li, K.Yang C.-Y., Liu, J., and Wang, Z.-X. 2010.  A new sauropod from the Lower Jurassic of , Sichuan, China. Vertebrata PalAsiatica 48:185-202.
Huili

Abstract - A new sauropod, Tonganosaurus hei gen. et sp. nov. from the Yimen Formation (Lower Jurassic) of Sichuan, China, is described on the basis of a collection of bones. These fossils include about 20 vertebrae, a complete right pectoral girdle and right forelimb, the distal end of a left scapula, a pair of complete ischia, a somplete right hindlimb, the proximal and distal ends of a left femur, right metatarsals (mt. I, II, III, and V), a right pedal ungual, and ten neural spine and rib fragments. The third cervical and anterial caudals are most similar in shape to those of the mamenchisaurid Omeisaurus (from the Middle Jurassic, Sichuan Basin), and quite different from those of other sauropods. The material was therefore assigned to the Family Mamenchisauridae Young & Chao, 1972 and a new genus and species were established. This represents the first discovery of a sauropod in the Lower Jurassic of China since Gongxianosaurus was found in Sichuan Basin. The Tonganosaurus material is of great importance for understanding the phylogenetics of the early Sauropoda.

The Cranial Morphology of Trematosaurus galae From the Early Triassic of Russia

Novikov, I. V. 2010. New Data on Trematosauroid Labyrinthodonts of Eastern Europe: 2. Trematosaurus galae sp. nov.: Cranial Morphology. Paleontological Journal 44:94-104. DOI: 10.1134/S003103011004012X
Abstract - The cranial morphology of a new species of the genus of Trematosaurus, T. galae sp. nov., represented by fragmentary specimens from the Lower Triassic Donskaya Luka locality (Volgograd Region), is described in detail. The diagnosis of the genus Trematosaurus is amended.

New Isotopic Age Constraints for Middle Triassic Rocks in Argentina

Mancuso, A. C., Chemale, F., Barredo, S., Ávila, J. N., Ottone, E. G., and Marsicano, C. In Press. Age constraints for the northernmost outcrops of the Triassic Cuyana Basin, Argentina, Journal of South American Earth Sciences (2010), doi: 10.1016/j.jsames.2010.03.001

Abstract - Age constraints on the Cerro Puntudo Formation at the northernmost exposures of the continental Triassic Cuyana Basin are presented based on palynological data and U-Pb zircon dating. The lacustrine facies of the upper part of the Cerro Puntudo Formation contain a low diverse palynological assemblage that is dominated by spores of ferns and lycopsids with subordinated inaperturated forms of uncertain affinity. The U-Pb SHRIMP zircon age of 243.8 ± 1.9 Ma (Anisian), obtained from juvenile magmatic zircons in a tuff interbedded in the same beds, provides the first chronostratigraphic date of the Cuyana Basin infilling at its northernmost exposures. According to additional dates already known from the southern part of the basin, a new stratigraphic correlation is proposed thus restricting the first tectono-sedimentary sequence (Synrift I depositional event of Kokogian et al.) to the Anisian. This depositional event has already been recorded in the Cacheuta and Rincón Blanco sub-basins but it is for the first time timely constrained across the whole basin.

The Digital Plateosaurus II

Mallison, H. 2010. The digital Plateosaurus II: An assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. Acta Palaeontologica Polonica 55:433–458.

Abstract - Scientific literature and museum exhibits are full of explicit and implicit claims about the possible postures and motion ranges of dinosaurs. For the example of the prosauropod Plateosaurus engelhardti I assessed the motion range of limbs and vertebral column in a CAD program using a 3D virtual skeletal mount. The range of motion of the forelimb is very limited, allowing the grasping of objects placed directly ventrally and ventrolaterally of the anterior torso. The manus is adapted for grasping. The powerful fore limb can barely reach in front of the shoulder, making a quadrupedal walking cycle impractical. Only a digitigrade pose of the pes with a steeply held metatarsus is feasible, and the morphology of the stylopodium and zeugopodium indicates a slightly flexed limb posture. Hind limb protraction and retraction are limited
by the pelvic architecture. The neck has significant mobility both dorsoventrally and laterally, but blocks torsion. The dorsal vertebral column is flexible to a degree similar to the neck, mainly in the anterior half, but blocks torsion totally in the anterior and posterior thirds. The anterior dorsals are similar in shape to the posterior cervicals and significantly increase the motion range of the neck. The tail is highly flexible due to its large number of elements, showing more lateral than dorsoventral mobility. These results are compared to reconstruction drawings and museum skeletal mounts, highlighting a pattern of errors specific to certain widely used reconstruction methods.

Enigmatic Archosaur Remains from the Middle Triassic of the UK

Benton, M. J. 2010. Archosaur remains from the Otter Sandstone Formation(MiddleTriassic, late Anisian) of Devon, southern UK. Proceedings of the Geologists' Association (early online), doi:10.1016/j.pgeola.2010.08.004

Abstract - A new jaw from the Middle Triassic (Anisian) Otter Sandstone Formation of Devon confirms the existence of a derived archosaur(avesuchian). Numerous isolated teeth and vertebrae had already suggested the presence of archosaurs in the Otter Sandstone Formation, presumed predators on the fauna of temnospondyls, procolophonids, and rhynchosaurs, but the new fossil is the first to show some diagnostic characters. Other elements in the same block as the jaw, but not necessarily from the same animal, include a possible skull or pelvic bone, a slender long bone, a small tooth (perhaps prolacertiform), and two presumed archosaur dermal scutes. An additional scute is present, as well as the probable distal end of a pubis, perhaps from a large poposauroid archosaur like the Anisian-age Bromsgroveia or Arizonasaurus. The jaw and pubis represent animals of very different sizes, some 0.8m and 3m long in estimated body length respectively.

A Recent Mention of Two Possibly New Archosauriforms from the Middle Triassic of Germany

This very interesting article was recently brought to my attention.  It mentions several possibly new archosauriforms from the Middle Triassic of Germany, including a proterochampsid and a small bipedal form that could be a basal ornithodiran.

http://www.swp.de/crailsheim/lokales/land/art5509,632515

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. ‘Leptosuchusadamanensis emerges as sister taxon to Smilosuchus gregorii and is here referred to as Smilosuchus adamanensis nov. comb., and ‘Machaeroprosopuslithodendrorum 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.

Koilamasuchus gonzalezdiazi, a New Basal Archosauriform from the Lower Triassic of Argentina

Ezcurra, M. D. , Lecuona, A., and A. Martinelii. 2010. A new basal archosauriform diapsid from the Lower Triassic of Argentina, Journal of Vertebrate Paleontology 30:1433-1450, doi: 10.1080/02724634.2010.501446

Abstract - The best-known South American Early Triassic archosauriform belongs to a putative proterosuchid briefly reported by Jose Bonaparte in 1981, collected from the Quebrada de los Fosiles Formation (Puesto Viejo Group, Argentina). This specimen consists of well-preserved natural external molds of a partial postcranium that preserve dorsal vertebrae, osteoderms, a dorsal rib, a possible gastralium, a chevron, a humerus, an ilium, two metapodials, and an ungual. We re-describe this specimen and identify autapomorphies that allow us to recognize Koilamasuchus gonzalezdiazi, gen. et sp. nov. The presence of an iliac blade with a slightly convex dorsal margin and with a maximum length more than 3 times its maximum height places Koilamasuchus within Archosauriformes. A cladistic analysis of basal Archosauriformes positions Koilamasuchus more crownwards than Proterosuchus, Sarmatosuchus, Fugusuchus, and Osmolskina, as the sister taxon of the clade that includes Erythrosuchidae and Archosauria. Proterosuchidae is found to be paraphyletic. The presence of an iliac preacetabular process, a pubic peduncle that forms an angle lower than 45◦ to the longitudinal axis of the ilium, and dorsal body osteoderms positions Koilamasuchus in Archosauriformes more crownwards than proterosuchids. Koilamasuchus is more basal than erythrosuchids within Archosauriformes because of the presence of dorsal ribs with a poorly developed proximal end. Koilamasuchus importantly increases the diversity of Archosauriformes during the biotic recovery following the Permo-Triassic mass extinction.

This is an interesting paper from the new issue of the Journal of Vertebrate Paleontology describing a new archosauriform from the Early Triassic of South America.  Along with recent descriptions of the enigmatic form Vancleavea (Parker and Barton 2008; Nesbitt et al. 2009) as well as a modern description of Doswellia (Dilkes and Sues 2009), this new taxon helps flesh out relationships in this part of the tree.  I've only briefly skimmed the paper so far, but noticed some interesting conclusions from the study:

1) Proterosuchidae is paraphyletic - the monophyly of the group is rarely tested as most recent studies just use Proterosuchus as a terminal taxon in phylogenetic analyses.

2) Vancleavea and Doswellia form a clade which is closer to Archosauria than Euparkeria and Chanaresuchus are - as stated in the paper this is closer to the results that I obtained in my 2008 paper on Vancleavea (Parker and Barton 2008); however, the results of our phylogenetic analysis weren't very robust.

3) Turfanosuchus is a pseudosuchian - I've always hypothesized this as the calcaneum of Turfanosuchus is extremely similar to that of aetosaurs and the femur is almost identical to that of Revueltosaurus in overall morphology and in possessing a massive fourth trochanter (Parker et al. 2005).

One unfortunate preservational aspect of this material is the lack of the femur, which I feel is a key element in determining whether the taxon would be closer to Proterosuchus and Erythrosuchus with their primitive morphology, or to the more derived forms Vancleavea and Euparkeria (see the discussion in Parker and Barton 2008). Another key aspect that could affect the phylogenetic analysis (and possibly did in this paper) is the coding of osteoderms as present in Erythrosuchus, which could potentially place erythrosuchids in a more crownward position.  Despite the recovery of a couple of possible osteoderms with material of Erythrosuchus (Gower 2003) their actual presence in this taxon is ambiguous and should not be coded as present (Parker and Barton 2008; Nesbitt et al. 2009). This coding may explain why Koilamasuchus is recovered as more basal to erythrosuchids in this analysis.

REFERENCES

Dilkes, D.W., and H.-D. Sues. 2009. Redescription and phylogenetic relationships of Doswellia kaltenbachi (Diapsida: Archosauriformes) from the Upper Triassic of Virginia. Journal of Vertebrate Paleontology 29:58–79.

Gower, D. J. 2003. Osteology of the early archosaurian reptile Erythrosuchus africanus Broom. Annals of the South African Museum 110:1–84.

Nesbitt, S. J., Stocker, M. R., Small, B. J., and Downs, A. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157:814–864.

Parker, W. G., and B. J. Barton. 2008. New information on the Upper Triassic archosauriform Vancleavea campi based on new material from the Chinle Formation of Arizona. Paleontologia Electronica 11.3.14A:1–20.

Parker, W. G., R. B. Irmis, S. J. Nesbitt, J. W. Martz, and L. S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society of London, Series B: Biological Sciences 272:963–969.

Temnospondyl Paleoenvironmental Adaptations: Evidence from Bone Histology

Sanchez, S., Germain, D., De Ricqles, A., Abourachid, A., Goussard, F. and Tafforeau, P. 2010. Limb-bone histology of temnospondyls: implications for understanding the diversification of palaeoecologies and patterns of locomotion of Permo-Triassic tetrapods. Journal of Evolutionary Biology, early online. doi:10.1111/j.1420-9101.2010.02081.x

Abstract - The locomotion of early tetrapods has long been a subject of great interest in the evolutionary history of vertebrates. However, we still do not have a precise understanding of the evolutionary radiation of their locomotory strategies. We present here the first palaeohistological study based on theoretical biomechanical considerations among a highly diversified group of early tetrapods, the temnospondyls. Based on the quantification of microanatomical and histological parameters in the humerus and femur of nine genera, this multivariate analysis provides new insights concerning the adaptations of temnospondyls to their palaeoenvironments during the Early Permian, and clearly after the Permo-Triassic crisis. This study therefore presents a methodology that, if based on a bigger sample, could contribute towards a characterization of the behaviour of species during great evolutionary events.

Tracking Charles L. Camp in the Blue Hills of Arizona

 As my longtime readers know one of my favorite aspects of paleontological research is redocumenting historic localities.  It is important to exactly relocate these sites in order to place them in our modern stratigraphic framework, thus the fossils collected from these sites add more data to our local biostratigraphy.  But I also just get the thrill of following in our predecessors footsteps, seeing the terrain as they saw it.  It simply makes their data more relevant and in a way much more easier to understand when you take a walk in their shoes (or boots).  

Last week it was off to the Blue Hills northeast of St. Johns, Arizona.  In 1923 and 1924 Charles Camp of the UCMP made significant vertebrate fossil collections from these localities, including the type specimen of the phytosaur Machaeroprosopus zunii.  The stratigraphic position of this specimen was in doubt because Camp had misinterpreted underlying Chinle Formation strata as belonging to the Moenkopi Formation. Jeff Martz and I had been interested in the stratigraphic position of this specimen for awhile so with old field notes and photos in hand, and with one of the main local landowners showing us the best way to access the badlands, we were on our way. 

We were successful in relocating the M. zunii quarry almost immediately. The two photos directly below are one taken by Camp in 1923 of the M. zunii excavation (courtesy of the UCMP) and me at the same spot in 2010.



More difficult to find was Camp's "meal pots" locality, a greenish mudstone and fine sandstone horizon that produced numerous microvertebrates including plates of the diminuative aetosaur Acaenasuchus geoffreyi and some of the oldest recovered elements of the pseudosuchian Revueltosaurus.  Camp's field notes were a little ambiguous regarding this site, but we were able to finally relocate it (see photo below).


Of course to round out our day, no trip to the Blue Hills would be complete without exploring "Calamites Hill", a site famous since the 1940s for producing upright specimens of Neocalamites (giant horsetails).  The photo below is of a partially excavated specimen, and the ridge we were on contained numerous in-situ specimens.