Saturday, November 26, 2011

Metriorhynchid Body Size

Young, M. T., Bell, M. A., De Andrade, M. B. and Brusatte, S. L.. 2011. "Body size estimation and evolution in metriorhynchid crocodylomorphs: implications for species diversification and niche partitioning." Zoological Journal of the Linnean Society, 163: 1199–1216. doi: 10.1111/j.1096-3642.2011.00734.x

Metriorhynchids were a peculiar group of fully marine Mesozoic crocodylomorphs, some of which reached large body size and were probably apex predators. The estimation of their total body length in the past has proven problematic. Rigorous size estimation was provided using five complete metriorhynchid specimens, by means of regression equations derived from basicranial and femoral length against total body length. The use of the Alligator femoral regression equation as a proxy to estimate metriorhynchid total body length led to a slight underestimation, whereas cranial regression equations of extant genera resulted in an overestimation of body length. Therefore, the scaling of crania and femora to total body length of metriorhynchids is noticeably different from that of extant crocodylians, indicating that extant crocodylians are not ideal proxies for size reconstruction of extinct taxa that deviate from their semi-aquatic morphotype. The lack of a correlation between maximum, minimum, or the range of generic body lengths with species richness demonstrates that species diversification is driven by factors other than just variation in body size. Maximum likelihood modelling also found no evidence for directionality in body size evolution. However, niche partitioning in Metriorhynchidae is mediated not only by craniodental differentiation, as shown by previous studies, but also by body size variation.

Reassessment of Some Middle Triassic Rauisuchians

Stephan Lautenschlager and Julia Brenda Desojo. 2011. "Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus." Paläontologische Zeitschrift 85 (4): 357-381, DOI: 10.1007/s12542-011-0105-1

The Middle Triassic (Anisian) rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus are two of the earliest representatives of this group and therefore of special importance for our understanding of the evolution and early diversification of Rauisuchia. Both taxa are well preserved and, in the case of the holotype of Ticinosuchus ferox, nearly complete and articulated. However, the original descriptions and recent revisions of the material do not sufficiently cover all aspects of their osteology. We identify new skull elements previously unknown for Ticinosuchus ferox and present new reconstructions of the pectoral and pelvic girdle elements. Vertebral laminae and fossae are described for the first time in both Ticinosuchus ferox and Stagonosuchus nyassicus. Newly recognised character states of Stagonosuchus nyassicus include the presence of additional infraprezygapophyseal and infrapostzygapophyseal laminae in the cervical vertebrae, a hyposphene-hypantrum articulation in the dorsal vertebrae and a fibula with a posteromedial depression. Furthermore, we provide a revised and emended diagnosis for both taxa, including several autapomorphies for Stagonosuchus nyassicus (e.g. a boss-like protuberance on the postacetabular process of the iliac blade and a marked short dorsolateral crest on the proximal ischium). We review the taxonomic status of a further specimen of Ticinosuchus ferox, as well as material related to Stagonosuchus nyassicus from the Manda Beds of Tanzania. Additionally, we discuss the distribution and possible function of rauisuchian characters, such as accessory neural spines in the caudal vertebrae, in these and other rauisuchian taxa.

Pelvic and Hindlimb Myology in Poposaurus

Emma R. Schachner, Phillip L. Manning, and Peter Dodson. 2011. "Pelvic and hindlimb myology of the basal archosaur Poposaurus gracilis (archosauria: Poposauroidea)" Journal of Morphology 272 (12): 1464–1491 DOI: 10.1002/jmor.10997

The discovery of a largely complete and well preserved specimen of Poposaurus gracilis has provided the opportunity to generate the first phylogenetically based reconstruction of pelvic and hindlimb musculature of an extinct nondinosaurian archosaur. As in dinosaurs, multiple lineages of basal archosaurs convergently evolved parasagittally erect limbs. However, in contrast to the laterally projecting acetabulum, or “buttress erect” hip morphology of ornithodirans, basal archosaurs evolved a very different, ventrally projecting acetabulum, or “pillar erect” hip. Reconstruction of the pelvic and hindlimb musculotendinous system in a bipedal suchian archosaur clarifies how the anatomical transformations associated with the evolution of bipedalism in basal archosaurs differed from that of bipedal dinosaurs and birds. This reconstruction is based on the direct examination of the osteology and myology of phylogenetically relevant extant taxa in conjunction with osteological correlates from the skeleton of P. gracilis. This data set includes a series of inferences (presence/absence of a structure, number of components, and origin/insertion sites) regarding 26 individual muscles or muscle groups, three pelvic ligaments, and two connective tissue structures in the pelvis, hindlimb, and pes of P. gracilis. These data provide a foundation for subsequent examination of variation in myological orientation and function based on pelvic and hindlimb morphology, across the basal archosaur lineage leading to extant crocodilians.

Sunday, November 20, 2011

SVP 2011 Roundup - Crocodylomorph Edition Part 3

Crocodylomorph Morphology and Systematics
(in order of presentation)
"Comparative morphometrics and phylogenetic perspectives on the morphospace of the crocodyliform skull." Wilberg, E.
  • presents a quantitative approach for assessing skull shape in Crocodyliformes (helping to avoid subjective intermediate assignments)
  • compared multiple methodologies for comparing skull shape
    • 2D geometric morphometrics (homologous landmarks and sliding semi-landmarks) - results suggest 3 or 8 shape categories
    • Eliptical Fourier Analysis (EFA) of skull outlines - results suggest 3 shape categories
  • overall skull shape should not be used as a discrete character in phylogenetic analyses, but can help in evaluating ecological and functional trends within claes
"Evolution of the otic region of fossil Crocodyliformes." Montefeltro, F. and Larsson, H.
  • terrestrial taxa - large, more vertical otic apertures and recess, relatively large tympanic membranes
    • notosuchians show the most extreme expansion of the otic region and well developed scar for the attachment of the tympanic membrane = very good hearing
  • semi aquatic and aquatic taxa - reduced otic apertures and tympanic membranes
    • extreme reductions in Metriorhynchidae = hearing may have been insignificant
  • quadrate fenestra may have played a role in hearing

"Crocodyliform aquatic locomotion and axial flexibility: comparative vertebral anatomy of mesoeucrocodylians." Felice, R. and O'Connor, P.
  • quantified vertebral metrics to evaluate whether crocodylians possess specialized skeletal morphology associated with a semi-aquatic lifestyle
  • terrestrial taxa - dorsal centra are about as wide as they are tall
  • semi-aquatic taxa - dorsal centra are wider than tall
"Jaw mechanics of crocodiles reveal their fast mastication." Suzuki, D., Hayashi, S., Chiba, K., and Tanaka, K.
  • observed movement of the cartilago transiliens (CT) in the musculus pterygoideus anterior (MPA) in extant crocs using CAT scans
  • the CT retains a rough surface on the lateral wing of the pterygoid, making it useful for studying fossil taxa
  • MPA moves the CT anteriorly = rapid jaw closure
"Phylogenetic patterns, homoplasy, and the evolution of the antorbital fenestra in Crocodyliformes." Leardi, J., Pol, D., and Fernandez, M.
  • phylogenetic analysis to evaluate the pattern of character evolution of the antorbital fenestra
  • closure of the antorbital fenestra occurred independently up to 8 times within Crocodyliformes (mostly in Mesoeucrocodylia)
  • antorbital fenestra independently reappears in some notosuchians (possibly in basal thalattosuchians)
  • suggests that the antorbital fenestra in Crocodyliformes is extremely homoplastic
"Fleshing out the neosuchian tree: a reevaluation of the crocodyliform Shamosuchus from the Cretaceous of Asia." Turner, A. and Brochu, C.
  • Shamosuchus is important in understanding the character changes occurring at the origin of Eusuchia
  • reevaluation of Shamosuchus species reveals only three valid species: S. djadochtaensis, S. gradilifrons, and S. ancestralis
  • results suggest a diverse Shamosuchus clade in the Cretaceous of eastern Asia
"Cranial anatomy and osteology of Gavialis gangeticus using computerized axial tomography: implications for gavialoid phylogeny." Gold, M.
  • ontogenetic changes in gharials are likely obscuring data
  • description of the cranial anatomy of a hatchling G. gangeticus based on CT data
  • reveals numerous ontogenetic of the skull and braincase
  • morphological data seem to support the molecular data, that certain plesiomorphiuc states in   are secondarily reversed
"A geometric morphometric analysis of Crocodylus niloticus: osteological evidence for a cryptic species complex." Nestler, J.
  • geometric morphometric analysis of the variation in the skull of C. niloticus
  • variation in population in broadly based on river basins
  • at least 3 distinct populations within the species with at least 2 being more distinct from each other than from other members of the species (and at least one may be endangered) = cryptic species complex, supporting molecular data from previous studies
  • paleontology can inform on conservation and issues of diversity
"The evolution of exoskeletal ossifications in notosuchian crocodyliformes." Hill, R. and O'Connor, P.
  • most notosuchians show a general trend toward the reduction of dorsal osteoderms along with the expansion of the caudal osteoderm shield
  • general trend towards the reduction of surface ornamentation in favor of increased internalization
  • Pakasuchua - most extreme reduction of osteoderms; robust articulating shield of osteoderms surrounding the tail; reduced osteoderms around the dorsosacral transition; presence of ossified tendons (first reported in Crocodyliformes)
  • osteoderm reduction trend in notosuchians may be associated with decreased body size and terrestrial habitat

Thursday, November 17, 2011

Form and Function in the Metriorhychid Skull

Mark T. Young, Mark A. Bell and Stephen L. Brusatte. 2011. "Craniofacial form and function in Metriorhynchidae (Crocodylomorpha: Thalattosuchia): modelling phenotypic evolution with maximum-likelihood method." Biology Letters 7(6): 913-916
Metriorhynchid crocodylomorphs were the only group of archosaurs to fully adapt to a pelagic lifestyle. During the Jurassic and Early Cretaceous, this group diversified into a variety of ecological and morphological types, from large super-predators with a broad short snout and serrated teeth to specialized piscivores/teuthophages with an elongate tubular snout and uncarinated teeth. Here, we use an integrated repertoire of geometric morphometric (form), biomechanical finite-element analysis (FEA; function) and phylogenetic data to examine the nature of craniofacial evolution in this clade. FEA stress values significantly correlate with morphometric values representing skull length and breadth, indicating that form and function are associated. Maximum-likelihood methods, which assess which of several models of evolution best explain the distribution of form and function data on a phylogenetic tree, show that the two major metriorhynchid subclades underwent different evolutionary modes. In geosaurines, both form and function are best explained as evolving under ‘random’ Brownian motion, whereas in metriorhynchines, the form metrics are best explained as evolving under stasis and the function metric as undergoing a directional change (towards most efficient low-stress piscivory). This suggests that the two subclades were under different selection pressures, and that metriorhynchines with similar skull shape were driven to become functionally divergent.

Wednesday, November 16, 2011

SVP 2011 Roundup - Crocodylomorph Edition Part 2

New Crocodylomorph Species and Specimens
(in order of presentation)
" A new basal crocodylomorph from the Late Jurassic of Patagonia and its implications for the evolution of the crocodyloform braincase." Pol, D., Rauhut, O., Lecuona, A., and Leardi, J.
  • Late Jurassic Canadon Caleareo Formation, Patagonia
  • posterior region of the skull, fragmentary remains of the rostrum, palate, mandible, and postcranium
  • unique combination of autapomorphies, crocodylomorph plesiomorphies, and crocodyliform apomorphies
  • taxa found to be the closest to (just outside of) Crocodyliformes, closer than Junggarsuchus
  • suggests that the braincase articulation with the palate and quadrate occured before Crocodyliformes
"A new eusuchian crocodyliform with novel cranial integument and the origin of Crocodylia." Holiday, C. and Gardner, N.
  • found in the coastal deposits of the Early Late Cretaceous Kem Kem Beds, Morocco
  • cranial remains - long, flat skull, possibly over 2 meters
  • novel integumentary display structure (possible thermoregulatory function as well)
  • new taxon found to be a derived eusuchian and the sister taxon to crown Crocodylia
  • earliest eusuchian from Africa - biogeographic implications for the origin of modern crocodylians (circum-Tethys vs. North America)
"New remains of Miadanasuchus oblita from the Late Cretaceous of Madagascar and a reevaluation of Trematochampsidae." Sertich, J.
  • Upper Cretaceous Maevarano Formation, Madagascar
  • well preserved partial skull, numerous isolated cranial and postcranial elements, allowing for a comprehensive assessment of morphology
  • Miadanasuchus compares closely with other trematochampsids
  • a reevaluation of Trematochampsidae and Peirosauridae shows that there are 12 valid genera within a monophyletic Trematochamsidae and that Peirosauridae is synonymous with Trematochampsia. Trematochamsidae was found to be closely related to Mahajangasuchidae and Araripesuchus.
"New primitive caimanine (Crocodylia, Alligatoridae) from the Miocene of Panama." Hastings, A., Bloch, J., Rincon, A., MacFadden, B., and Jaramillo, C.
  • Culebra Formation, early Miocene, Panama
  • complete skull of a new taxon
  • found to be just outside of Caimaninae
  • important biogeographic implications, suggesting that caimans originated in the New World Tropics, entered North and South America in the Paleogene and persisted in the tropics into the Miocene after disappearing from higher latitudes

"A new specimen of Araripesuchus (Mesoeucrocodylia) with soft tissue preservation from the Lower Cretaceous Romualdo Formation (Araripe Basin), Brazil." Figueiredo, R. and Kellner, A.
  • nearly complete skeleton (skull, limbs, vertebral column, 2 rows of osteoderms)
  • the orbit size and proportions are consistent with A. gomesii while the long, slender limbs are consistent with A. gomesii, A. wegeneri, and A. tsangatsangana
  • significant soft tissue preservation (white substance, likely phosphatized) consisting mostly of muscle fibers but also epidermis
"A new crocodyliform from the middle Cretaceous Woodbine Formation of Texas." Allen, E., Main, D., and Noto, C.
  • Arlington Archosaur Site of the Woodbine Formation (delta plain deposits)
  • disarticulated partial skull and significant postcranial material of one individual along with disarticulated material of several other individuals
  • about 5 meters long, short dentary symphysis, paired dentary pseudocanines, and a robust triangular snout
  • new taxon is a mesoeucrocodylian, possibly a basal goniopholidid or thalattosuchian
"A new, small-bodied alligatoroid from the Hell Creek Formation (Late Maastrichtian) of Montana." Householder, M., Williams, S., and Tremaine, K.
  • small-bodied (about 1 meter), mature or nearly mature individual (based on fused neurocentral sutures)
  • bears some similarities to Brachychampsa montana and other small-bodied alligatoroids, but is a distinct taxon
  • represents the southern-most occurrence of a small-bodied alligatoroid within the Western Interior Basin during the Late Cretaceous
"The palate and braincase in goniopholidid crocodyliforms: insights from a new skull of Eutretauranosuchus delfsi." Pritchard, A. and Turner, A.
  • well-preserved, complete skull with CT scans revealing the palate and braincase
  • dorsoventral crushing distorted some braincase elements, although the anatomical positions are preserved
  • incorperation of the new skull data into a phylogenetic analysis unites Amphicotylus, Calsoyasuchus, Eutrerauranosuchus, and Sunosuchus into a clade of derived goniopholidids, all sharing a unique palatal morphology

Monday, November 14, 2011

SVP 2011 Roundup - Crocodylomorph Edition Part 1

General Crocodylomorph Ecology and Evolution
(in order of presentation)
"Campanian crocodyliforms of Laramidia: new insights from the Kaiparowits Basin of southern Utah." Irmis, R., Sertich, J., Hutchison, J. H., And Titus, A.
  • comprehensive survey of Kaiparowits crocodyliforms
    • large, goniopholidid-like mesoeucroc.
    • basal alligatorids: Deinosuchus hatcheri and Brachychampsa
    • small alligatoroid lacking globidont teeth
  • clear biogeographic relationship with the San Juan Basin (New Mexico) - some regionality but also endemic taxa
  • supports the hypothesis of a distinct southern biogeographic province
"Direct evidence of crocodyliform predation on small dinosaurians from the Kaiparowits Formation of Utah." Drumheller, S. and Boyd, C.
  • predation by a small crocodyliform on a juvenile basal ornithopod (new Hypsolophodont)
    • several bite marks characteristic of crocs
    • partial tooth embeded in femur (distal tip had been broken off previously)
"The myth of the living fossil: basal crown group relationships, reversing polarities, and restoration of the ancestral crocodylian." Brochu, C., Turner, A., Allen, E., and Wilberg, E.
  • outgroups of Crocodylia predominantly small bodied (less than 2 meters)
  • the crocodylian ancestral condition was likely equivalent to the small durophagous alligatorines of the Paleogene
  • living crocodylians are not generalized but independently highly specialized (NOT LIVING FOSSILS!!!!)

"Freshwater niche competition between choristoderes and crocodiles in the Mesozoic and Paleogene." Matsumoto, R.
  • Early Cretaceous of Asia - high diversity of choristoderes, no aquatic crocs
  • Middle Jurassic thru Eocene of Europe - only small lizard-like choristoderes, co-occuring with larger crocs
  • Cretaceous thru Paleogene of Euramerica - neochoristoderes co-occur with similar sized crocs, but neochoristoderes are the only strongly longirostrine reptiles
  • long-snouted crocs diversify in freshwater after the extinction of neochoristoderes (Oligo-Miocene)
"Late Neogene Alligator evolution and a description of specimens from the Gray Fossil Site, southern appalachians, USA." Schubert, B., Mead, J., and Stout, J.
  • abundant Alligator material
    • osteroderms and other fragmentary material
    • mostly complete juvenile
    • pathological adult skull
    • two adult partial post-cranial skeletons
  • Alligator of Gray Fossil Site posses a mixture of characters found in A. olseni, A. mefferdi, and A. mississippiensis
"Crocs not theropods were likely top predators on the Cretaceous dinosaur freeway: implications of a large track census." Lockley, M. and Lucas, S.
  • at least 1380 individual trackmakers
  • mostly ornithopods (71%)
  • only small theropods present (not large enough to prey on ornithopods)
  • abundant crocodylian tracks (walking and swimming), including large individual (around 4 meters)
"A taphonomic and paleoecological comparison of isolated crocodyliform teeth from the Woodbine Formation of Texas and the Hell Creek Formation of Montana." Bennett, G., Main, D., Peterson, R., and Anderson, B.
  • 4 different crocodyliforms in the Woodbine Formations, including Woodbinesuchus and a new genus
  • 2 different crocodyliforms in the Hell Creek (Brachychampsa montana and Borealosuchus sternbergi), showing similar population structure to A. mississippiensis.

Wednesday, November 9, 2011

SVP 2011 Roundup - Triassic Crurotarsan/Pseudosuchian Edition

"A new archosaur (Diapsida: Archosauriformes) from the marine Triassic of China." Wu, X., Li, C., Zhao, L., Sato, T., and Wang, L.
  • a new, nearly complete (except for some of the tail) crurotarsan archosaur from the Falanf Formation (Middle Triassic - Ladinian) of China 
    • likely a basal poposauroid (sensu Nesbitt 2011), about 1.5 meters in length
  • snout more than twice the length of the rest of the skull (about 24 cm total)
  • although found in marine sediments, it has few anatomical modifications toward an aquatic lifestyle but still not likely fully terrestrial (fish gut contents, posteriorly positioned external naris)
  • sister-group relationship with Qianosuchus (only other Middle Triassic archosaur found in marine sediments of China), but with a poor bootstrap value
"An enigmatic archosauriform from the Manda Beds (Middle Triassic) of Southwestern Tanzania: character conflict at the base of Pseudosuchia." Nesbitt, S., Sidor, C., Angielczyk, K., Smith, R., and Tsuji, L.
  • a new archosaur with an unusual mix of character states
  • basal pseudosuchian, closely related to/ just outside of Paracrocodylomorpha
  • new data produces little change in relationships but a drastic change in character optimization (overall data is still obscured by high rates of homoplasy and incomplete specimens)
  • shows that the plesiomorphic bauplan of archosaurs was likely "rauisuchian"

"Comparative paleohistology of Triassic rauisuchian and aetosaurian osteoderms (Archosauria:Pseudosuchia)." Scheyer, T., Desojo, J., and Cerda, I.
  • sampled 8 rauisuchian, 10 aetosaurs, and Revueltosaurus
  • rauisuchians had compact bone, showed high growth rates early, and reduced growth rates later in development
  • in aetosaurs, a few taxa showed rapid growth, but most showed slow growth (parallel-fibered/ lamellar-zonal bone)
  • Revueltosaurus showed mostly densely remodeled parallel-fibered bone
"A newly recognized specimen of the phytosaur Redondasaurus from the Upper Triassic Owl Rock Member (Chinle Formation) and its biostratigraphic implications." Parker, W., Martz, J., and Dubiel, R.
  • a phytosaur specimen from the Owl Rock Member (Chinle Fm) has been identified as Redondasaurus, not Pseudopalatus
  • this puts mush of the Owl Rock in the Apachean Biozone, drastically changing biostratigraphic correlations of the upper Chinle and Dockum
  • shows that there is no basis for the Tr-5 unconformity (no faunal turnover or depositional hiatus)
"The relationships and type locality of Heptasuchus clarki, Chugwater Group (Middle to Upper Triassic), Southeastern Big Horn Mountains, Wyoming, USA." Zawiskie, J., Dawley, R., and Nesbitt, S.
  • type locality is poorly constrained, but likely equivalent to the Popo Agie Formation
  • Heptasuchus is the sister taxon to Batrachotomus
  • minimum of four Heptasuchus individuals at the type locality, further suggesting that loricatans may have lived in groups (like Decuriasuchus)
"The trackmaker of the Late Triassic tetrapod footprint ichnotaxon Brachyirotherium was an aetosaur." Lucas, S., Heckert, A., and Lockley, M.
  •  aetosaurs have the appropriate manus/pes morphology, were capable of a nearly over-stepped stride, and have the appropriate geographic/stratigraphic distribution to be consistent with Brachyirotherium
  • rauisuchians and spenosuchians excluded by manus/pes morphology
"Diversity of aetosaurs (Archosauria: Stagonolepidae) in the Upper Triassic Pekin Formation (Deep River Basin), North Carolina." Schneider, V., Heckert, A., and Fraser, N.
  •  new specimen of a partial aetosaur carapace, composed of the first ten rows of osteoderms (including a full, articulated row of cervicals)
  • shows character states of both Longasuchus and Lucasuchus
  • at least three genera of aetosaur in the Pekin Formation (Lucasuchus, Coahomasuchus, and whichever genus is represented by the new specimen), correlating it with the lower Dockum Group
"A virtual phytosaur (Archosauria: Crurotarsi) endocast and its implications for sensory system evolution in archosaurs." Holloway, W. and O'Keefe, R.
  • cranial endocast (CT scan) of a complete Smilosuchus adamanensis skull
  • endocranial morphology very similar to Crocodylus johnstoni except for enlarged pineal body in Smilosuchus
  • "This highly conserved cranial endocast morphology is consistent throughout Crurotarsi, regardless of overall body morphology or ecology, with a trend of pineal body size reduction from the enlarged basal condition to a reduced crown condition." (quoted from the abstract)

Tuesday, November 8, 2011

A New Upper Cretaceous Sphagesaurid

Fabiano V. Ioria and Ismar S. Carvalhoa. 2011. "Caipirasuchus paulistanus, a new sphagesaurid (Crocodylomorpha, Mesoeucrocodylia) from the Adamantina Formation (Upper Cretaceous, Turonian–Santonian), Bauru Basin, Brazil" Journal of Vertebrate Paleontology 31(6): 1255-1264 - (Online November 8th) DOI:10.1080/02724634.2011.602777

A skull and mandible of a new species of notosuchian, Caipirasuchus paulistanus, belonging to the Sphagesauridae, were discovered in the rocks of the Adamantina Formation (Bauru Basin: Late Cretaceous). The main autapomorphies are external naris bordered only by premaxillae; very high pterygoids and ectopterygoids; palatines contacting maxillae by a cuneiform process; well-developed oval antorbital fenestra; premaxilla with four teeth; dentary with ten teeth and two diastemata; and one diastema in the premaxilla and another between the fourth alveolus of the premaxilla and the first of the maxilla. Morphological analysis and experimental data suggest an animal with a powerful bite and a dentition with specific regions of action, one adapted to apprehension and the other to food processing.

Osteohistology of Triassic Archosauromorphs

Jennifer Botha-Brink and Roger M. H. Smith. 2011. "Osteohistology of the Triassic archosauromorphs Prolacerta, Proterosuchus, Euparkeria, and Erythrosuchus from the Karoo Basin of South Africa." Journal of Vertebrate Paleontology 31(6): 1238-1254 - (Online November 8th) DOI:10.1080/02724634.2011.621797

The South African non-archosauriform archosauromorph Prolacerta and the archosauriforms Proterosuchus, Erythrosuchus, and Euparkeria were important constituents of the Early to early Middle Triassic Karoo ecosystem following the end-Permian mass extinction. We present new data on the osteohistology of these stem archosaurs and provide insight into their paleobiology. Bone tissues of the Early Triassic Prolacerta contain a poorly defined fibro-lamellar complex, with parallel-fibered bone in some regions, whereas the contemporaneous Proterosuchus exhibits rapidly forming uninterrupted fibro-lamellar bone early in its ontogeny, which becomes slow forming lamellar-zonal bone with increasing age. The early Middle Triassic Erythrosuchus deposited highly vascularized, uninterrupted fibro-lamellar bone throughout ontogeny, whereas the growth of the contemporaneous Euparkeria was relatively slow and cyclical. When our data are combined with those of previous studies, preliminary results reveal that Early and Middle Triassic non-crown group archosauromorphs generally exhibit faster growth rates than many of those of the Late Triassic. Early rapid growth and rapid attainment of sexual maturity are consistent with life history expectations for taxa living in the unpredictable conditions following the end-Permian mass extinction. Further research with larger sample sizes will be required to determine the nature of the environmental pressures on these basal archosaurs.

SVP 2011 Roundup - Archosauromorph Edition

Archosauromorphs and General Archosaur Evolution 
(in order of presentation)
"Archosauromorph bone histology reveals early evolution of elevated growth and metabolic rates." Werning, S., Irmis, R., Smith, N., Turner, A., and Padian, K.
  •  extant and extinct ornithodirans show high metabolic rates, but not extant crocodylians
  • study of evolution of growth rate in archosauromorphs through an expanded histological database and using much more rigorous methods for collecting data
  • characters associated with high metabolic rates appear in a short, stepwise accumulation along the archosauriform tree
  • a reversal likely occured along the pseudosuchian line
    • Aetosaurs and relatives show early rapid growth, but slow growth later on
    • Shuvosaurs show fast growth throughout life
"Postcranial skeletal pneumaticity and the evolution of archosaur respiratory systems." Barrett, P., Butler, R., Gower, D., and Abel, R.
  • unidirectional airflow present in extant archosaurs
  • soft tissue associated with unidirectional airflow/ postcranial skeletal pneumaticity (PSP) not preserved by fossil record but fossae, foramina, and laminae are preserved
  • pseudosuchians (phytosaurs, aetosaurs, poposaurs) posses many vertebral laminae and fossae, but no internal features
  • no conclusive evidence in extinct archosaurs other than saurischians and pterosaurs but still likely that they had less well-developed avian-like respiratory systems with non-invasive air sacs and unidirectional air flow
"Phylogenetic congruence between cranial and postcranial characters in archosaur systematics." Mounce, R. and Wills, M.
  •  showed a significant incongruence of cranial and postcranial signals (cranial characters appear to be significantly less homoplastic)
  • results may indicate different evolutionary rates between cranial and postcranial characters
"Osteohistology of Triassic archosauromorphs from the Karoo Basin of South Africa." Botha-Brink, J. and Smith, R.
  • looked at Prolacerta, Proterosuchus, Erythrosuchus, and Euparkeria
  • Early/Middle Triassic archosauromorphs (non-crown group) show fast growth early in their life
  • early rapid growth and early onset of sexual maturity are consistent with the life history expected from harsh, unpredictable conditions after the Permian/Triassic extinction 
"New information on the Triassic vertebrate faunas of Antarctica." Sidor, C., Smith, R., Huttenlocker, A., Peecook, B., and Hammer, W.
  •  small Prolacerta-like archosauromorph found under a Lystrosaurus and a Proterosuchus-like archosauriform
  • vertebrates of the lower Fremouw Formation likely correspond to the post-extinction recovery fauna of South Africa (Karoo Basin)
  • faunas of the two continents differentiate in the Middle Triassic
  • using network science for faunal analysis
"Uniting microevolution and macroevolution in deep time: the zone of variability in Archosauromorpha." Bhullar, B., Bever, G., Merck, J., Lyson, T. and Gauthier, J.
  •  a phylogenetic "zone of variability" (ZOV) occurs before apomorphies become fixed
  • detected indirectly - stem members of a clade show lots of variability in character states before they become fixed in crown group members
    • derived archosauriforms show an absence of a parietal foramen, an absence of supratemporals, and a complete lower temporal bar
    • stem archosauriforms show a ZOV of these characters 
  • detected directly - in a single taxon, variation in such character states occur between individuals
    • in Prolacerta broomi, the three characters listed above in derived archosaurs are variably present and absent (in almost all permutations) in fossil individuals
"Anatomy and affinities of large archosauromorphs from the lower Fremouw Formation (Early Triassic) of Antarctica." Crandall, J., Hellert, S., Smith, N., Hammer, W., and Makovicky, P.
  • first evidence of Archosauriformes in the Early Triassic of Antarctica
  • found a partial presacral vert and distal end of the left humerus of a large archosauriform from just after the P/Tr
    • large size is contra the "lilliput effect" of mass extinctions
"New data on the archosaur fauna of the Middle Triassic (Anisian) Ntawere Formation of Zambia." Peecook, B., Sidor, C., Nesbitt, S., Angielczyk, K., and Steyer, S.
  • first diagnostic remains of archosaurs from the Ntawere Formation - teeth, large pseudosuchian vertebra, pelvic and vertebral material of a silesaurid
  • Ntawere Formation (and Manda beds) shows a higher diversity of archosaurs than the ealier Karoo Basin

SVP 2011 - A Quick Summary

For those of you who missed this year's meeting of the Society of Vertebrate Paleontology, don't feel too bad. There were plenty of good talks this year, but also a fair share of disappointments.

I'll start with what was good about this meeting. At the business meeting, it was announced that of all the abstracts submitted on archosaurs, the dinosaurs were far outweighed by the non-dinosaurs - good news for those of us who are fans of the "forgotten archosaurs". I will be following this post with several summarizing the information presented on archosauromorphs, Triassic pseudosuchians/crurotarsans, and crocodylomorphs. The exhibitors this year had some good items for croc fans, including a life-size Sarchosuchus skull (Bone Clones, Inc) and prints of the mural from the Petrified Forest Rainbow Forest Museum (Paleovista), featuring the Adamanian (Triassic) fauna of the Chinle Formation (including Smilosuchus, Postosuchus, Desmatosuchus, and many others).

This year's meeting was somewhat disappointing due to a complete lack of food and the choice of venue. Las Vegas (especially a casino) is one of the last places I think of when I hear "academic/professional conference". Most of the people I spoke to felt sick all week, but no one could tell if they had a cold or if it was just the dry, cigarette smoke-filled air that was making them feel crummy.

I think we can all agree that we're looking forward to next year's meeting in Raleigh (there's a phytosaur on the logo!).