Early Evolution of Postcranial Skeletal Pneumaticity in Sauropodomorph Dinosaurs

I don't think I've posted this paper previously, but it has been in press for a year...

Yates, A. M., Wedel, M. J., and M. F. Bonnan. 2012. The early evolution of postcranial skeletal pneumaticity in sauropodomorph dinosaurs. Acta Palaeontologica Polonica 57:85-100.  

doi: http://dx.doi.org/10.4202/app.2010.0075

Abstract - Postcranial skeletal pneumaticity (PSP) is present in a range of basal sauropodomorphs spanning the basal sauropodomorph—sauropod transition. We describe the PSP of five taxa, Plateosaurus engelhardti, Eucnemesaurus fortis, Aardonyx celestae, Antetonitrus ingenipes, and an unnamed basal sauropod from Spion Kop, South Africa (hereafter referred to as the Spion Kop sauropod). The PSP of Plateosaurus is apparently sporadic in its occurrence and has only been observed in very few specimens, in which it is of very limited extent, affecting only the posterior cervical vertebrae and possibly the mid dorsals in one specimen. The PSP of Eucnemesaurus, Aardonyx, Antetonitrus, and the Spion Kop sauropod consists of subfossae (fossa within-fossa structures) that excavate the vertices of the posterior infradiapophyseal fossae of the posterior dorsal vertebrae. These subfossae range from simple shallow depressions (Eucnemesaurus) to deep, steepsided, internally subdivided and asymmetrically developed chambers (Antetonitrus). The middle and anterior dorsal vertebrae of these taxa lack PSP, demonstrating that abdominal air sacs were the source of the invasive diverticula. The presence of pneumatic features within the infradiapophyseal fossae suggest that the homologous fossae of more basal saurischians and dinosauriforms were receptacles that housed pneumatic diverticula. We suggest that it is probable that rigid non-compliant lungs ventilated by compliant posterior air sacs evolved prior to the origination of Dinosauria.

Panchetocynodon damodarensis, a New Cynodont from the Lower Triassic of India

Das, D. P., and A. Gupta. 2012. New cynodont record from the lower Triassic Panchet Formation, Damodar valley. Earth and Environmental Science Journal of the Geological Society of India Volume 79, Number 2, 175-180 DOI: 10.1007/s12594-012-0022-2


Abstract - This paper reports the find of a new non-mammalian cynodont from the Lower Triassic Panchet Formation of the Damodar valley, West Bengal, India. The fossil, recovered from a clay pellet rich calcareous sandstone bed, is a part of left lower jaw having five post canines that are damaged to various extents. A combination of mammal-like advanced characters such as much enlarged dentary, reduced post dentary bones, high coronoid process, large masseteric fossa, each post canine with a large central cusp flanked by a distal and a mesial accessory cusps with two additional lingually positioned cingular cusps, incipient root division and clearly demarcated crown-root juncture prompted to erect a new taxon Panchetocynodon damodarensis gen. et sp. nov.

Hind limb osteology of Gracilisuchus stipanicicorum

Lecuona, A., and J. B. Desojo 2011. Hind limb osteology of Gracilisuchus
stipanicicorum (Archosauria: Pseudosuchia). Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 102, 105–128.


Abstract - Gracilisuchus stipanicicorum Romer, 1972, from the Middle-Late Triassic of the Ischigualasto–Villa Unio´n Basin of Argentina, is an extinct pseudosuchian archosaur on the stem to Crocodylomorpha. The pelvic girdle and hind limb anatomy of a referred specimen of Gracilisuchus stipanicicorum is described and compared with that from a broad range of archosauriform taxa, including basal members such as crurotarsans and basal ornithodirans. The description of this specimen reveals new information on the anatomy of the pelvic girdle and hind limb of Gracilisuchus, through a detailed examination of some anatomical regions barely or not previously described, as well as reinterpretations of previous features. The phylogenetic affinities of Gracilisuchus within the Archosauria remain to be tested, but Gracilisuchus shares two putative synapomorphies with some non-crocodyliform crocodylomorphs, providing tentative support for the monophyly of Sphenosuchia (e.g., Sereno & Wild 1992; Wu & Chatterjee 1993) and the close relationship of Gracilisuchus to that clade. These characteristics are: (i) the morphology and poor development of the femoral fourth trochanter, closely resembling the condition of Pseudhesperosuchus and Trialestes; and (ii) a poor anterior development of the femoral head, shared with Pseudhesperosuchus. On the other hand there are characters that reject the inclusion of Gracilisuchus within Crocodylomorpha (Nesbitt 2011), such as the absence of an imperforated acetabulum, and that rather suggests a sister-taxon position to Crocodylomorpha.

Reevaluation of Therapsid Fossils from Antarctica

Huttenlocker, A. K., and C. A. Sidor. 2012. Taxonomic Revision of Therocephalians (Therapsida: Theriodontia) from the Lower Triassic of Antarctica. American Museum Novitates Number 3738 :1-19.

Abstract - We reevaluate the taxonomic status of therocephalian fossils recovered from the lower Fremouw Formation (Lower Triassic) of the central Transantarctic Mountains, Antarctica. The material, which includes mostly fragmentary juvenile specimens, is reidentified using an apomorphy-based approach. We recognize the presence of three higher-level taxa: Eutherocephalia, Akidnognathidae, and Baurioidea. The only genus-level identification is for a partial lower jaw and pterygoid tentatively attributed to the baurioid, Ericiolacerta parva. An indeterminate theriodont partial skull is reassigned to the therocephalian family Akidnognathidae. The holotypes of Pedaeosaurus parvus and Rhigosaurus glacialis are represented by indeterminate juvenile baurioids and, in the absence of clear autapomorphies, are considered nomina dubia. The results of the taxonomic revision indicate that the therocephalian fauna of Antarctica lacks endemic genera and thus corresponds to that of the Triassic Lystrosaurus Assemblage Zone fauna of South Africa's Karoo Basin. More generally, we consider the southern Gondwanan basins of South Africa and Antarctica to sample a broadly distributed Lower Triassic tetrapod fauna, although the latter basin documents the first occurrence of several taxa (e.g., Kombuisia, Palacrodon). More precise (i.e., species-level) identifications are needed to better constrain the biogeographic signal for therocephalians, but the presence of juveniles strongly suggests that this group of therapsids, like dicynodonts, were year-round high-latitude inhabitants during Early Triassic times.

Possible New Plateosaurid Sauropodomorph From Brazil

Bittencourt, J.S., Leal, L.A., Langer, M.C. & Azevedo, S.A.K., iFirst article. An additional basal sauropodomorph specimen from the Upper Triassic Caturrita Formation, southern Brazil, with comments on the biogeography of plateosaurids. Alcheringa, 1–10.

Abstract - We describe an additional saurischian specimen from the Caturrita Formation (Norian) of the Parana Basin, southern Brazil. This material was collected in the 1950s and remained unstudied due to its fragmentary condition. Detailed comparisons with other saurischians worldwide reveal that some characters of the ilium, including the low ventral projection of the medial wall of the acetabulum and its concave ventral margin, together with the short triangular shape of the pre-acetabular process and its mound-like dorsocaudal edge, resemble those of sauropodomorphs such as Plateosaurus and Riojasaurus. This set of traits suggests that MN 1326-V has affinities with basal Sauropodomorpha, probably closer to plateosaurians than to Saturnalia-like taxa. Previous records of this clade in the Caturrita Formation include Unaysaurus, which has been related to Plateosaurus within Plateosauridae. Alternative schemes suggest that plateosaurids include Plateosaurus plus the Argentinean ‘prosauropods’ Coloradisaurus and Riojasaurus. Both hypotheses raise biogeographic questions, as a close relationship between faunas from South America and Europe excluding Africa and North America is not supported by geological and biostratigraphical evidence. Additionally, the absence of plateosaurids in other continents suggests that the geographical distribution of this taxon is inconsistent with the geological history of western Pangaea, and this demands further investigations of the phylogeny of sauropodomorphs or improved sampling.

Arachana nigra, a New Temnospondyl from the Permo-Triassic of Uruguay

Piñeiro, G., Ramos, A., and C. Marsicano. 2012. A rhinesuchid-like temnospondyl from the Permo-Triassic of Uruguay. Compte Rendus Palevol 11:65-78. http://dx.doi.org/10.1016/j.crpv.2011.07.007

 

Abstract - A new temnospondyl species, Arachana nigra, from the Permo-Triassic Buena Vista Formation of Uruguay is described. The holotypic and only known specimen consists of an almost complete skull lacking most of the snout, the tabular horns and the posterolateral corners of the skull table. As with other specimens from the same unit, Arachana shows a transitional morphology. It shares several characters with rhinesuchids, such as the large size and the general shape of the skull, orbits positioned slightly posterior to the skull roof mid-length, a coarsely pitted dermal ornamentation lacking pustules, and a smoothly convex cheek contour. The palatal ramus of the pterygoid suturing with the vomer, and excluding the palatine and ectopterygoid from the margin of the interpterygoid vacuity, and the presence of a small basioccipital, visible in both occipital and ventral view, also resemble the conditions found in rhinesuchids and other basal temnospondyls. Other characters present in Arachana, however, are commonly found in lydekkerinids, but are absent in almost all rhinesuchids: supratemporal excluded from otic notch; supraorbital and infraorbital sensory sulci encroaching the lacrimal, although lacking a step-like lacrimal flexure; otic notch not deeply incised; post-temporal fenestra large and rounded; occipital condyles well-separated from each other; palatine tooth row behind the palatine tusk reduced; pterygoid corpus slightly ornamented; and presence of an interorbital depression. This combination of primitive and derived characters is consistently present in most components of the Buena Vista fauna, which could thus be transitional between typical Permian and Triassic tetrapod communities found elsewhere. The location of the PTB in the Uruguayan sequence is controversial, mainly due to the lack of clear faunal correlations with other well-known sequences, such as those of southern Africa and Russia. Moreover, the mosaic-like character combinations in most of the recorded tetrapods ally them to both Triassic and Paleozoic groups, and this has complicated even more the possibility of age assignment. Transitional faunas associated with the PTB, such as the Russian Uppermost Permian faunas, could be equivalent to the unique Colonia Orozco fauna. If true, this scenario will substantially change estimates about survivorship rates, suggesting a speciation rate increase in temnospondyls after the Permian-Triassic event. Based on taxonomic, phylogenetic, and geochronologic data, the Buena Vista fauna allows us to quantify faunal turnover across the PTB and in the aftermath of the end Permian extinction event.

---

"Romer's Gap" Is Filled

Taking a quick break from all of the current Triassic papers because this is pretty significant for the field of vertebrate paleontology.

Smithson, T. R.,Wood, S. P., Marshall, J. E. A., and J. A. Clack. 2012. Earliest Carboniferous tetrapod and arthropod faunas from Scotland populate Romer's Gap. PNAS [advance online] doi: 10.1073/pnas.1117332109

Abstract - Devonian tetrapods (limbed vertebrates), known from an increasingly large number of localities, have been shown to be mainly aquatic with many primitive features. In contrast, the post-Devonian record is marked by an Early Mississippian temporal gap ranging from the earliest Carboniferous (Tournaisian and early Viséan) to the mid-Viséan. By the mid-Viséan, tetrapods had become effectively terrestrial as attested by the presence of stem amniotes, developed an essentially modern aspect, and given rise to the crown group. Up to now, only two localities have yielded tetrapod specimens from the Tournaisian stage: one in Scotland with a single articulated skeleton
and one in Nova Scotia with isolated bones, many of uncertain identity. We announce a series of discoveries of Tournaisian-age localities in Scotland that have yielded a wealth of new tetrapod and arthropod fossils. These include both terrestrial and aquatic forms and new taxa. We conclude that the gap in the fossil record has been an artifact of collection failure.

Evidence of Avian-like Behavior in a Basal Saurischian Dinosaur

There has been a rash of Triassic vertebrate papers in the last two weeks.  Here is one that looks at the taphonomy of a specimen of the basal saurischian Guaibasaurus and suggests that it had a avian style of resting.

Agnolin, F., and Martinelli, A.G. 2012. Guaibasaurus candelariensis (Dinosauria, Saurischia) and the early origin of avian-like resting posture. Alcheringa (1–5) [advance online] DOI:10.1080/03115518.2012.634203

Abstract - A specimen of the basal saurischian Guaibasaurus candelariensis Bonaparte, Ferigolo and Ribeiro (UFRGS-PV-0725-T) from the Faxinal do Soturno locality, Rio Grande do Sul State, Brazil (Caturrita Formation; Late Triassic) lacks any sign of post-mortem transport and burial deformation, and exhibits features (flexed forelimbs, folded hindlimbs under the body and curved neck) that indicate a typical avian-like resting position. The presence in Guaibasaurus of an avian-like resting posture and related physiological implications would extend this unique trait, previously considered restricted to derived maniraptoran theropods, to the base of the Theropoda (or even
Saurischia) clade.

Another Example of the Phylogenetic Utility of Osteoderms in Triassic Vertebrates

Buchwitz, M., C. Foth, I. Kogan, and S. Voigt. 2012. On the use of osteoderm features in a phylogenetic approach on the internal relationships of the Chroniosuchia (Tetrapoda: Reptiliomorpha). Palaeontology [Early View]. DOI: 10.1111/j.1475-4983.2012.01137.x

Abstract:  Chroniosuchians are an enigmatic Permian to Triassic group of crocodile-like basal tetrapods. Their conspicuous dorsal osteoderm systems include most of the group’s yet documented postcranial morphological variability but have hardly been considered in cladistic approaches. Aiming at the clarification of the internal relationships of the Chroniosuchia, we have carried out a parsimony analysis including, among others, 23 morphological and osteohistological osteoderm characters and 12 chroniosuchian taxa. According to the most parsimonious trees, taxa usually referred to Chroniosuchidae form a paraphyletic succession with Madygenerpeton pustulatus and Chroniosaurus dongusensis as the basalmost chroniosuchians and Uralerpeton tverdochlebovae as the sister group of Bystrowianidae (hypothesis A). However, the concurrent hypothesis of a basal split into monophyletic subtaxa Chroniosuchidae and Bystrowianidae (hypothesis B) is only slightly less parsimonious and supported by an alternative analysis which includes embolomeres as the only reptiliomorph outgroup. Searching for the better hypothesis, we compare the respective order of branching to the order of first occurrences in the fossil record, demonstrating that hypothesis A provides a better stratigraphic fit than hypothesis B. Accordingly, the last common ancestor of the yet known chroniosuchians had a series of broad complexly interlocking ‘chroniosuchid’ osteoderms that served as a protection carapace apart from supporting the trunk during terrestrial locomotion. The later evolution of chroniosuchian carapaces was marked by a stepwise increase in flexibility and size reduction, which resulted in a loss of protective function and in a reduction in trunk support function. The flexibility increase is paralleled by the evolution of the Crocodylomorpha whose extant members do not possess as extensively interlocking osteoderm systems as some of their Mesozoic relatives.

In addition you can read about more new articles on Kyrgyzsaurus and Longisquama here.

Chanaresuchus ischigualastensis, a New Proterochampsid from the Late Triassic of Argentina and a Temporal Range Extension for the Genus Chanaresuchus

This is a short communication in the new issue of the Journal of Vertebrate Paleontology. As such there is no abstract available.

Trotteyn, M. J., Martinez, R. N., and O. A. Alcober. 2012. A new proterochampsid Chanaresuchus ischigualastensis (Diapsida, Archosauriformes) in the early Late Triassic Ischigualasto Formation, Argentina. Journal of Vertebrate Paleontology 32:485-489. DOI:10.1080/02724634.2012.645975

The specimen includes much of an articulated skeleton including a well preserved skull. This is the first occurrence of Chanaresuchus outside of the Chanares Formation and marks an extension of the taxon into the Late Triassic. As the authors state, this is interesting because it demonstrates only a species level turnover for the clade between the late Middle and early Late Triassic faunas in the Ischiguasto Basin. Several therapsids also show the same pattern. This also marks the presence of two different proterochampsids in the Ischigualasto Formation.

From the discussion: "PVSJ 567 is assignable to Chanaresuchus on the basis of diagnostic characters shared with Chanaresuchus bonapartei (e.g., skull ornamented by longitudinal crests and depressions on the dorsal surfaces of the premaxillae, maxillae, and nasals; lateral fossa in the centra of presacral vertebrae; low deltopectoral crest on the humerus; absence of phalanges on pedal digit V). PVSJ 567 exhibits several differences from Chanaresuchus bonapartei and can be assigned to a new species, C. ischigualastensis (e.g., basal tubera wide with rostrolateral contour transversely oriented; paroccipital processes distally expanded; articular surface of caudal prezygapophyses elliptical and notably anteriorly developed; astragalus lacking perforations in the posterior sulcus; osteoderms with longitudinal dorsal sulcus).

          

Diverse New Microvertebrate Assemblage from the Late Triassic of North Carolina

Heckert, A. B., Mitchell, J. S., Schneider, V. P., and P. E. Olsen. 2012. Diverse New Microvertebrate Assemblage from the Upper Triassic Cumnock Formation, Sanford Subbasin, North Carolina, USA. Journal of Paleontology 86(2): 368-390 doi: http://dx.doi.org/10.1666/11-098.1


Abstract - The Moncure microvertebrate locality in the Cumnock Formation, Sanford sub-basin, North Carolina, dramatically increases the known Late Triassic age vertebrate assemblage from the Deep River Basin. The 50,000 recovered microvertebrate fossils include osteichthyans, amphibians, and numerous lepidosauromorph, archosauriform, and synapsid amniotes. Actinopterygian fossils consist of thousands of scales, teeth, skull, and lower jaw fragments, principally of redfieldiids and semionotids. Non-tetrapod sarcopterygians include the dipnoan Arganodus sp., the first record of lungfish in the Newark Supergroup. Temnospondyls are comparatively rare but the preserved centra, teeth, and skull fragments probably represent small (juvenile) metoposaurids. Two fragmentary teeth are assigned to the unusual reptile Colognathus obscurus (Case). Poorly preserved but intriguing records include acrodont and pleurodont jaw fragments tentatively assigned to lepidosaurs. Among the archosauriform teeth is a taxon distinct from R. callenderi that we assign to Revueltosaurus olseni new combination, a morphotype best assigned to cf. Galtonia, the first Newark Supergroup record of Crosbysaurus sp., and several other archosauriform tooth morphotypes, as well as grooved teeth assigned to the recently named species Uatchitodon schneideri. Synapsids represented by molariform teeth include both “traversodontids” assigned to aff. Boreogomphodon and the “dromatheriid” Microconodon. These records are biogeographically important, with many new records for the Cumnock Formation and/or the Newark Supergroup. In particular, Colognathus, Crosbysaurus, and Uatchitodon are known from basins of Adamanian age in the southwestern U.S.A. These new records include microvertebrate taxa more typical of non-Newark basins (abundant archosauriforms, temnospondyls, lungfish) as well as more typical Newark osteichthyans and synapsid-rich faunal elements.

Photos of Preserved Permian Forest

http://gizmodo.com/5887454/first-photos-of-chinas-298+million+year+old-buried-forest

Amazing Preservation of a Permian Forest Redux

Here is the abstract and link (open access) to the previously mentioned article.  It is too bad that with instantaneous preservation of a Permian ecosystem that no animals are mentioned as found. I also mistakenly stated in my previous post that the site was in China. It is actually from Mongolia.

Wang, J., Pfefferkorn, H. W., Zhang, Y., and Z. Feng. 2012.  Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia. PNAS, published online before print. doi: 10.1073/pnas.1115076109 


Abstract - Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m2 of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time.

Amazing Preservation of a Permian Forest

The upcoming issue of PNAS has an article documenting amazing preservation of a Permian paleobotanical locality in China, the result of rapid burial by volcanic ash.  The actual article is not up yet but you can read about the study here.