The Year In Crocs

Each year, thanks to the hard work of a lot of great paleontologists, we get to add some new members to our favorite clade. In 2011, a total of  9 11 crurotarsans were named (and by this I mean they were named in a peer-reviewed paper with a publication date in 2011). Check out the list below:

• Theriosuchus grandinaris - a Late Jurassic/Early Cretaceous neosuchian from Thailand - in Lauprasert, K., C. Laojumpon, W. Saenphala, G. Cuny, K. Thirakhupt, and V. Suteethorn. 2011. "Atoposaurid crocodyliforms from the Khorat Group of Thailand: first record of Theirosuchus from Southeast Asia." Paläontologische Zeitschrift 85(1): 37-47. DOI: 10.1007/s12542-010-0071-z

• Decuriasuchus quartacolonia - a Triassic rauisuchian from Brazil - in Franca, M. A. G. and J. Ferigolo. 2011. 'Associated skeletons of a new middle Triassic "Rauisuchian" from Brazil' Naturwissenschaften 98 (5): 389-395 DOI: 10.1007/s00114-011-0782-3 

• Neptunidraco ammoniticus - a Jurassic metriorhynchid from Italy - in Cau, A. & F. Fanti. (2011) "The oldest known metriorhynchid crocodylian from the Middle Jurassic of North-eastern Italy, Neptunidraco ammoniticus gen. et sp. nov." Gondwana Research 19(2): 550-565. doi:10.1016/j.gr.2010.07.007

Andrea Cau, study co-author, posing with the counter top and a reconstruction of Neptunidraco (from Nat Geo)

• Campinasuchus dinizi - a Cretaceous baurusuchid from Brazil - in Carvalho, I. D. S., V. D. P. A. Teixeira, M. L. D. F. Ferraz, L. C. B. Ribeiro, A. G. Martinelli, F. M. Neto, J. J. W. Seritch, G. C. Cunha, I. C. Cunha, and P. F. Ferraz. 2011. "Campinasuchus dinizi gen. et sp. nov., a new Late Cretaceous baurusuchid (Crocodyliformes) from the Bauru Basin, Brazil" Zootaxa 2871: 19-42 Open access online.

Life reconstruction (by Rodolfo Nogueira) of Campinasuchus dinizi from Carvalho et al 2011

• Arenysuchus gascabadiolorum - a Cretaceous crocodyloid from Spain - in Puertolas, E., J. I. Canudo, P. Cruzado-Caballero. 2011. "A New Crocodylian from the Late Maastrichtian of Spain: Implications for the Initial Radiation of Crocodyloids." PLoS ONE 6(6) doi:10.1371/journal.pone.0020011

• Pissarrachampsa sera -a Cretaceous baurusuchid fro Brazil - in Montefeltro, F. C., H. C. E. Larsson, and M. C. Langer. 2011. "A New Baurusuchid (Crocodyliformes, Mesoeucrocodylia) from the Late Cretaceous of Brazil and the Phylogeny of Baurusuchidae." PLoS ONE 6(7). doi:10.1371/journal.pone.0021916

From Figure 3 of Montefeltro et al 2011

• Archerontisuchus guajiraensis -a Paleocene dyrosaurid from Colombia - in Hastings, A. K., J. I. Bloch, and C. A. Jaramillo. 2011. "A new longirostrine dyrosaurid (Crocodylomorpha, Mesoeucrocodylia) from the Paleocene of north-eastern Colombia: biogeographic and behavioural implications for New-World Dyrosauridae." Palaeontology, 54: 1095–1116. doi: 10.1111/j.1475-4983.2011.01092.x

• Caipirasuchus paulistanus - a Cretaceous sphagesaurid from Brazil - in 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 DOI:10.1080/02724634.2011.602777  

Reconstruction of Caipirasuchus by D. Silva in Fabiano et al.

[Edit] I have been informed that there are three additional new crocs for this year. I overlooked them because they are named in a massive volume published by the Palaeontological Association, number 14 in their Field Guide to Fossils series. The contents of English Wealden Fossils are not available in any digital format, so reading about the new crocs requires purchasing the book. Fortunately, some brief comments are available over at Tetrapod Zoology.

• Goniopholis willetti - an Early Cretaceous goniopholidid from England
• Anteophthalmosuchus hooleyi - an Early Cretaceous goniopholidid from England
• Leiokarinosuchus brookensis - an Early Cretaceous neosuchian from England

in Salisbury, S. W. & Naish, D. 2011. "Crocodilians." In Batten, D. J. (ed.) English Wealden Fossils. The Palaeontological Association (London), pp. 305-369

SVP 2011 Roundup - American Alligator Special Edition

Oops! Looks like I forgot to post my summaries of  the remaining 8 crurotarsan-themed abstracts from this year's SVP. In my defense though, several of them were focused on making inferences about dinosaurs, so my subconscious mind may have let things slip. Better late than never.

The American alligator (Alligator mississippiensis) seemed to be particularly popular this year, with a total of 8 abstracts dedicated to discussing aspects of the species' anatomy. Considering the alligator's availability for research and usefulness in studying extinct archosaurs, it's no surprise that these animals are such popular subjects for study.

Talks

"An intra-skeletal bone microanalysis of Alligator mississippiensis and its application to non-avian dinosaur osteohistology." Woodward, H.

• Osteohistologic analysis of Alligator mississippiensis. Results:
• each bone in an individual forms the same growth marks
• femur, humerus, and tibiae have the highest growth rates
• captive individuals show higher periodic growth than wild individuals = eco-phenotypic plasticity
• Used results to infer aspects of ornithiscian dinosaur growth. Results:
• basal ornithopods: rapid mineral deposition (tibia and femur) for only 2-3 growth cycles followed by slow deposition
• Maiasaurus shows high growth rates throughout ontogeny

"Development of the lung in Alligator mississippiensis (Archosauria: Crocodylomorpha) and the evolution of the Archosaurian respiratory system." Schachner, E., Metzger, R., and Farmer, C. G.

• description of the development of Alligator mississippiensis bronchi (and comparison with those of chickens)
• investigation of the effects on oxygen tension morphogenesis during development
• formation of bronchial chambers by branching morphogenesis with striking similarities in formation between alligators and birds
• data suggest that lung development in extant archosaurs is determined by similar molecular and genetic programs 

"Microstructure of the femoral growth plate in the American alligator: effects of growth rate, locomotor activity and circulatory pattern." Owerkowicz, T., Yang, J., Blank, J., Eme, J., and Hicks, J.

• Are growth plates with a highly irregular border at the chondro-osseous junction a synapomorphy of dinosaur? Can growth plate thickness be used to determine skeletal growth rate?
• Alligator growth plates show highly irregular chondro-osseous borders
• Alligator growth plate height shows significant correlation with longitudinal growth rate
• data suggest that growth plates are sensitive to systemic arterial oxygen tension and that an irregular chondro-osseous junction is an ancestral character of archosaurs
• "propose a thicker growth plates appeared concurrently with the origin of in-series circulation, and may thus have set the stage for later acquisition of fast growth and endothermic metabolism in birds."

"Pelvic anatomy of Alligator mississippiensis and its significance for interpreting limb function in fossil archosaurs." Tsai, H., Holliday, C., and Ward, C.

• test the hypothesis that accurately predicting in-vivo range of motion in the hip of the American alligator cannot be done using hard tissue manipulation alone
• first description of American alligator acetabular anatomy
• data show that the bone-only model enabled for more movement than the soft-tissue model
• "this study provides new insight into soft tissue structures and their osteological correlations in the archosaur hip joint."

Posters

"Skeletochronology of the American alligator (Alligator mississippiensis): the utility of various elements for determining growth patterns and longevity." Garcia, B.

• histological analysis of every bone type in American alligators
• shows that, aside from long bones, elements like ribs and phalanges exhibit LAG deposition
• developed a "map" of the alligator skeleton showing the best areas for finding unobstructed LAG deposition, helping determine which bones are best for analysis and where information is best preserved along those bones
• information will allow researchers to make more informed sampling decisions given the destructive nature

"Variation in hindlimb muscle attachment sites in the American alligator (Alligator mississippiensis) and implications for paleobiological reconstructions." Taylor, E., Schachner, E., and Farmer, C.G.

• examined hindlimb musculature in 19 specimens of Alligator mississippiensis
• found high degrees of individual variation in most muscle attachments
• suggests a need for caution when using osteological correlates in myological reconstruction

"Trigeminal nerve morphology in Alligator mississippiensis: implications for inferring sensory potential in extinct crocodyliforms." George, C.

• cross-sectional study (histology, morphometrics, and 3D imaging) to identify patterns in neural and bony structures in Alligator mississippiensis and comparison with similarly-sized fossil crocodyliforms
• "data suggest that trigeminal nerve morphology can be accurately inferred among living crocodilians."
• extinct taxa:
• Leidysuchus (eusuchian) and Phabdognathus (dyrosaur) have trigeminal ganglia similar to alligators
• Hamadasuchus (peirosaur) had a much smaller ganglion (dome-pressure system not as well developed)
• "these findings suggest that neural osteological correlates of the trigeminal system are informative features useful for investigation of crocodyliform as well as archosaur somatosensory evolution."

"Structure and function of a protosuchian mandibular symphysis using anatomical insights from Alligator mississippiensis." Skiljan, R., Gant, C., and Holliday, C.

• comparison of the structure and function of the jaws (especially the mandibular symphysis) of protosuchians with Alligator mississippiensis
• data suggest a transitional form of the symphysis is present in protosuchians, compared to the derived condition in crocodyliforms

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

Abstract
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

Abstract
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

Abstract
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.

SVP 2011 Roundup - Crocodylomorph Edition Part 3

Crocodylomorph Morphology and Systematics

(in order of presentation)

Talks

"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

Posters
"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

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 DOI: 10.1098/rsbl.2011.0357

Abstract

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.

SVP 2011 Roundup - Crocodylomorph Edition Part 2

New Crocodylomorph Species and Specimens

(in order of presentation)

Talks

" 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

Posters

"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

SVP 2011 Roundup - Crocodylomorph Edition Part 1

General Crocodylomorph Ecology and Evolution

(in order of presentation)

Talks

"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!!!!)

Posters

"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.

SVP 2011 Roundup - Triassic Crurotarsan/Pseudosuchian Edition

Talks

"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"

Posters

"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)

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

Abstract
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

Abstract
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)

Talks

"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

Posters

"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!).

Happy Halloween!

Happy Halloween Everyone! This year, I decided to carve my pumpkin as Smilosuchus. I got a lot of compliments from trick-or-treeters, although a lot thought it was a dinosaur. A few managed to guess it was a crocodile, which I figured was close enough for 8-year-olds. Did anyone else carve paleo-inspired pumpkins?

Alright, I'm off to Vegas. See you all at SVP!

SVP 71st Annual Meeting

The annual meeting of the Society of Vertebrate Paleontology is just one week away. Incorporated into the logo for this year's meeting is the Nevada state fossil, Shonisaurus popularis, a Late Triassic ichthyosaur, as well as the dinosaur track Eubrontes (the suit on the cards).

There will be no shortage of talks and posters on "forgotten archosaurs" at this years meeting. On Wednesday, there will be a handful of general archosaur talks in the morning and afternoon. Thursday talks will be sparse, but there will be dozens of good posters. All day Friday and Saturday morning are almost completely devoid of non-dinosaurian archosaur talks, but Saturday afternoon will bring us the croc talks. Not a bad way to end the meeting.

A message from the Student & Post-Doctoral Liaison Committee

As a member of the committee, I have a small request to ask of my lovely readers: PLEASE BRING LOTS OF REPRINTS! Each year, the S&PLC hosts the Student Roundtable Forum and Reprint Exchange. We rely entirely on generous donations from SVP members for reprints so, if you have a bunch of reprints sitting around your office and wouldn't mind contributing, please bring them to the meeting. You can bring them to the S&PLC table, where we will be selling raffle tickets and offering guidance to first time attendees. 

Each year, the student committee sells raffle tickets for a chance to win a free student membership or fabulous door prizes. Not a student? You can still buy a raffle ticket (or 20) and donate it to a student. Proceeds benefit the SVP Education and Research Fund. More info can be found at the annual meeting website.

The Sail-Backed Poposauroid - Ctenosauriscus

Butler RJ, Brusatte SL, Reich M, Nesbitt SJ, Schoch RR, et al. 2011. "The Sail-Backed Reptile Ctenosauriscus from the Latest Early Triassic of Germany and the Timing and Biogeography of the Early Archosaur Radiation." PLoS ONE 6(10): e25693. doi:10.1371/journal.pone.0025693


Abstract

Background
Archosaurs (birds, crocodilians and their extinct relatives including dinosaurs) dominated Mesozoic continental ecosystems from the Late Triassic onwards, and still form a major component of modern ecosystems (>10,000 species). The earliest diverse archosaur faunal assemblages are known from the Middle Triassic (c. 244 Ma), implying that the archosaur radiation began in the Early Triassic (252.3–247.2 Ma). Understanding of this radiation is currently limited by the poor early fossil record of the group in terms of skeletal remains.

Methodology/Principal Findings
We redescribe the anatomy and stratigraphic position of the type specimen of Ctenosauriscus koeneni (Huene), a sail-backed reptile from the Early Triassic (late Olenekian) Solling Formation of northern Germany that potentially represents the oldest known archosaur. We critically discuss previous biomechanical work on the ‘sail’ of Ctenosauriscus, which is formed by a series of elongated neural spines. In addition, we describe Ctenosauriscus-like postcranial material from the earliest Middle Triassic (early Anisian) Röt Formation of Waldhaus, southwestern Germany. Finally, we review the spatial and temporal distribution of the earliest archosaur fossils and their implications for understanding the dynamics of the archosaur radiation.

Conclusions/Significance
Comprehensive numerical phylogenetic analyses demonstrate that both Ctenosauriscus and the Waldhaus taxon are members of a monophyletic grouping of poposauroid archosaurs, Ctenosauriscidae, characterised by greatly elongated neural spines in the posterior cervical to anterior caudal vertebrae. The earliest archosaurs, including Ctenosauriscus, appear in the body fossil record just prior to the Olenekian/Anisian boundary (c. 248 Ma), less than 5 million years after the Permian–Triassic mass extinction. These earliest archosaur assemblages are dominated by ctenosauriscids, which were broadly distributed across northern Pangea and which appear to have been the first global radiation of archosaurs.

Rauisuchian Osteoderms

Scheyer, T. M. and J. B. Desojo. 2011. "Palaeohistology and external microanatomy of rauisuchian osteoderms (Archosauria: Pseudosuchia)." Palaeontology. DOI: 10.1111/j.1475-4983.2011.01098.x

Abstract

The presence of postcranial dermal armour is plesiomorphic for Archosauria. Here, we survey the external microanatomy and histology of postcranial osteoderms (i.e. dorsal paramedian and caudal osteoderms) of rauisuchians, a widely distributed assemblage of extinct predatory pseudosuchians from the Triassic. The osteoderms of eight rauisuchian taxa were found to be rather compact bones, which usually lack significant bone remodelling or large areas of cancellous bone. The presence of highly vascularized woven or fibrolamellar bone tissue deposited in the core areas indicates higher growth rates during earlier life stages, whereas a more compact parallel-fibred bone matrix indicates reduced growth rates in later development. This pattern of change corroborates earlier studies on long bone histology. With the exception of a bone tissue found in the sample of Batrachotomus kupferzellensis, which might be the result of metaplastic ossification, the general mode of skeletogenesis is comparable with intramembraneous ossification. The lack of cancellous bone tissue and remodelling processes associated with bone ornamentation, as well as the predominantly intramembraneous mode of ossification, indicates that rauisuchian osteoderm formation differs profoundly from that of the osteoderms of the only extant pseudosuchian lineage, the crocodylians.

Taxonomy of Diplocynodon and Tooth Wear in Caiman latirostris

Martin, Jeremy E. and Martin Gross. 2011. "Taxonomic clarification of Diplocynodon Pomel, 1847 (Crocodilia) from the Miocene of Styria, Austria" Neues Jahrbuch für Geologie und Paläontologie - Abhandlunge, 261:2 DOI: 10.1127/0077-7749/2011/0159

Abstract
A re-examination of the original type series of Prangner (1845) and Hofmann (1887a) of the primitive alligatoroids from the middle Miocene of Styria, led to a reappraisal of the taxonomy of the following species of Diplocynodon: D. steineri and D. styriacus. Of unsettled affinities, Enneodon ungeri was also re-examined. It is here demonstrated that it belongs to the same taxon of the specimens described by Hofmann (1887a). These taxa are in fact junior synonyms of the previously erected Enneodon ungeri. Moreover, comparison with other European alligatoroids reveals that the Austrian specimens described by Prangner (1845) and Hofmann (1887a) belong to the same genus: Diplocynodon Pomel, 1847. According to the rules of the International Commission on Zoological Nomenclature (ICZN), Diplocynodon has priority over Enneodon. Under the principle of priority, it is therefore proposed to rename all the Miocene remains of alligatoroids from Styria as Diplocynodon ungeri Prangner, 1845. Comparison of almost complete skulls from various Miocene contemporaneous localities reveals that there is no reason to erect another taxon for the French specimens of D. "styriacus" described in Ginsburg & Bulot (1997). However, these specimens need to be redefined as D. ungeri as well. D. ungeri was coded and included in a character matrix to cladistically test its affinities with other alligatoroids. A total of six species of Diplocynodon were analysed including: D. ratelii, D. hantoniensis, D. tormis, D. muelleri, D. darwini and D. ungeri. The results are consistent with previous studies and favour a monophyletic diplocynodontid clade. D. ungeri is the first species of the genus to be recognized from distant coeval European deposits, namely the Paris and the Pannonian Basins.

_____

Ősi, Attila and Paul M. Barrett. 2011. "Dental wear and oral food processing in Caiman latirostris: analogue for fossil crocodylians with crushing teeth" Neues Jahrbuch für Geologie und Paläontologie - Abhandlunge, 261:2 DOI: 10.1127/0077-7749/2011/0161

Abstract
Almost all of the 23 extant species of crocodylians are opportunistic predators that consume their food without extensive intraoral food processing. Posterior bulbous crushing teeth with heavy dental wear in two specimens of Caiman latirostris, however, indicate that oral food processing can be an important factor during feeding. Wear pattern analysis in two specimens of C. latirostris clearly indicates crushing of hard food items that produced large wear surfaces on tooth crowns in the posterior part of the tooth row. This type of wear suggests that the diet was predominantly composed of durable, hard-shelled prey (e.g.molluscs, crustaceans, turtles), a supposition confirmed by recent studies on the stomach contents of several C. latirostris specimens. The absence of similar wear patterns in other ontogenetically mature specimens of C. latirostris, however, indicates that specific, possibly regional differences in food resources might affect the degree and type of dental wear. The dental features we report in C. latirostris can provide an important extant analogue for fossil forms with similar dentitions (e.g. Bernissartia, Unasuchus and globidontan eusuchians).

Summer Field Work 2011 - Part 4 - Ghost Ranch

My 10th and final week at PEFO was actually spent mostly outside of PEFO, at Ghost Ranch in New Mexico. At the last minute (with a little pushing from Bill), we interns decided to go join the fun (Bill had wilderness training, so he couldn't join us). We left late on Sunday, arriving Monday morning. We arrived just in time to meet up with Alan Turner, Michelle Stocker, and crew as they surveyed the lab and quarry. We would be working in the Hayden Quarry (know for its wealth of data associated with dinosaur origins as well as from the paintings of Georgia O'Keefe) and would soon be joined by a rather large field crew comprised of paleontologists from University of Utah (Randy Irmis et al), UC Berkely (Kevin Padian et al), and several other institutions. Due to the large number of people, Rachel, Chuck, and I would have to camp at the quarry instead of the Ghost Ranch campsite.

Hayden Quarry 2 and 4 as viewed from 3.

Last year, they had started working on a large block of Typothorax material, so our fist goal was to get that ready to be pulled out. Step 1 was cleaning off all the material that had fallen from the quarry wall over the year (lots and lots of shoveling involved). Then we had to add several more layers of plaster and continue excavating around the base of the jacket. This took quite a while because of the amount of bone that was in the rock around and underneath the jacket. We just collected the bone on top of the jacket whilst removing the "underburden" (read Bill's post on when a large quarry block becomes furniture).

Unfortunately, we couldn't stay for longer than a few days. And although we were still working in the Chinle Formation, it was a vastly different experience compared to working the Chinle of PEFO. We returned to the park in time for me to get to spend one last day in the field. Reflecting on those 10 weeks, I can certainly say that the Chinle can be a frustrating formation to work in but its wealth of data us well worth it. I just hope that I get to spend many more field seasons working in the Chinle, especially the PEFO Chinle.

Summer Field Work 2011 - Part 3

Week 7

Surface bone. What could it be? (Photo by Andrea Thomer)

Phytosaur skull.

This was a somewhat slow week between office days and unproductive prospecting. Friday was spent back at Billings Gap where we had noticed several surface exposures of bone previously. Most of the bone we were finding was fragmentary and did not go far under the surface, a common frustration in the Chinle, but rule #7 is that if something catches your eye, you must examine it. So that afternoon, after prospecting for a while I started walking back to where Rachel was working on an aetosaur osteoderm, and something caught my eye. In the Chinle of PEFO, highly weathered bone is typically a dark purple or maroon, but what caught my eye was much lighter in color - a good sign. I started digging, and digging, and digging, and before long I had uncovered a complete phytosaur cranium. What had caught my eye turned out to be the parietals. Since it was getting late and the skull was so big, we would have to come back another day to finish excavating it and collect it. We dug a drainage ditch and covered it with a plastic bag. We'd be back.

Summer Field Work 2011 - Part 2

Week 4

Excavating aetosaur plates at Billing's Gap.

Always buckle up for safety.

Petrified Forest is currently in a phase of expansion. The federal government has authorized the addition of 125,000 acres to the park which is composed of private, state, and federal (primarily Bureau of Land Management) lands. We spent a good portion of the week in the eastern part of that boundary expansion, including an area known as Billing's Gap (the place you go if you want a phytosaur skull). Besides doing field work, we also got to teach the park law enforcement what petrified wood theft looks like.

Summer Field Work 2011 - Part 1

I have recently returned from 10 weeks of field work at Petrified Forest National Park (plus 2 weeks on the road with family) working with Bill Parker. Internet access was generally problematic at PEFO. Therefore, blog posts became an issue. And hey, it's hard, tiring work being in the field and most things that aren't food, sleep, or beer can get set aside. But I did take lots of notes and pictures, so I'll tell you a bit about my summer field work now:

Week 1:

Bill at the Bowman site, taking field notes.

My first day started a bit slow due to requisite air quality monitoring, but we did find a phytosaur quadrate before lunch. The rest of the week was spent learning the ropes along with two guys from Chaco Culture NHP. Chaco is known for it's archeological resources, but with recent findings in their Cretaceous bedrock, they hired a geocorps participant to do a paleontological inventory. So we had Jim (Chaco Natural Resources) and Phil (GeoCorps) out with us for a few days to learn how to do paleo field work and inventories from the best (Bill got his start doing paleo inventory work for the US Forest Service). We also had the new park superintendent join us one day. It was a pretty full truck. We spent most of our time at a location known as the Bowman Site, stratigraphically situated in the Jim Camp Wash beds of the Sonsela Member of the Chinle Formation, just above the Adamanian-Revueltian transition. We collected several vertebrae, armor plates, and other unarticulated bones. Our lovely fossil preparator, Kenny Bader, was even able to find some tiny freshwater shark teeth in the rock he cleaned from the other bones.

The Early Evolution of Archosaurs

I hope you all have seen Sterling Nesbitt's new monograph on the evolution and phylogenetic relationships of archosaurs. Below is the abstract as well as a link to the nearly 300 page paper.

It is one of the most comprehensive studies to date and has some major implications for archosaur origins and much of the crocodile-line. As Sterling himself says 'the most interesting outcome of the
phylogenetic position of phytosaurs as the sister taxon of Archosauria is that the classic ‘‘crocodile normal ankle’’ is rendered plesiomorphic for Phytosauria + Archosauria (= Crurotarsi)'. Obviously, this is a major, novel result and it certainly will have a great impact on the future direction of this blog.

For now, I will continue to post on phytosaurs and will asses their place in my posts as more data becomes available. I certainly have to reconsider the focus of this blog, whether I'll discuss all "forgtten archosaurs" or simply "crurotarsans" and/or croc-line archosaurs (depending on definitions).

A simplified phylogeny from the cover.

Nesbitt, S. J. 2011. "The early evolution of archosaurs : relationships and the origin of major clades." Bulletin of the American Museum of Natural History, no. 352 Online

Abstract

Archosaurs have a nearly 250 million year record that originated shortly after the Permian-Triassic extinction event and is continued today by two extant clades, the crocodylians and the avians. The two extant lineages exemplify two bauplan extremes among a diverse and complex evolutionary history, but little is known about the common ancestor of these lineages. Renewed interest in early archosaurs has led to nearly a doubling of the known taxa in the last 20 years.
This study presents a thorough phylogenetic analysis of 80 species-level taxa ranging from the latest Permian to the early part of the Jurassic using a dataset of 412 characters. Each terminal taxon is explicitly described and all specimens used in the analysis are clearly stated. Additionally, each character is discussed in detail and nearly all of the character states are illustrated in either a drawing or highlighted on a specimen photograph. A combination of novel characters and comprehensive character sampling has bridged previously published analyses that focus on particular archosauriform subclades.
A well-resolved, robustly supported consensus tree (MPTs 5 360) found a monophyletic Archosauria consisting of two major branches, the crocodylian-line and avian-line lineages. The monophyly of clades such as Ornithosuchidae, Phytosauria, Aetosauria, Crocodylomorpha, and Dinosauria is supported in this analysis. However, phytosaurs are recovered as the closest sister taxon to Archosauria, rather than basal crocodylian-line archosaurs, for the first time. Among taxa classically termed as ‘‘rauisuchians,’’ a monophyletic poposauroid clade was found as the sister taxon to a group of paraphyletic ‘‘rauisuchians’’ and monophyletic crocodylomorphs. Hence, crocodylomorphs are well nested within a clade of ‘‘rauisuchians,’’
and are not more closely related to aetosaurs than to taxa such as Postosuchus. Basal crocodylomorphs such as Hesperosuchus and similar forms (‘‘Sphenosuchia’’) were found as a paraphyletic grade leading to the clade Crocodyliformes. Among avian-line archosaurs, Dinosauria is well supported. A monophyletic clade containing Silesaurus and similar forms is well supported as the sister taxon to Dinosauria. Pterosaurs are robustly supported at the base of the avian line.
A time-calibrated phylogeny of Archosauriformes indicates that the origin and initial diversification of Archosauria occurred during the Early Triassic following the Permian-Triassic extinction. Furthermore, all major basal archosaur lineages except Crocodylomorpha were established by the end of the Anisian. Early archosaur evolution is characterized by high rates of homoplasy, long ghost lineages, and high rates of character evolution. These data imply that much of the early history of Archosauria has not been recovered from the fossil record. Not only were archosaurs diverse by the Middle Triassic, but they had nearly a cosmopolitan biogeographic distribution by the end of the Anisian.

Postosuchus heads to PEFO

Toast-asuchus!

So, you've likely seen me post about my little Safari Ltd. Postosuchus toy. As I traveled out to Petrified Forest this summer, I took a series of photos of the little guy, searching for his home. Below are some of my favorites, complete with geologic context.

By the way, I would like to apologize for the lack of posts. Internet has been problematic.

On Rt 24, headed to Colorado Springs, CO. The road was built on the Paleogene Dawson Formation.

Metriorhynchid Functional Morphology and A New Baurusuchid

Life reconstruction (by Rodolfo Nogueira) of Campinasuchus dinizi from Carvalho et al 2011.

Carvalho, I. D. S., V. D. P. A. Teixeira, M. L. D. F. Ferraz, L. C. B. Ribeiro, A. G. Martinelli, F. M. Neto, J. J. W. Seritch, G. C. Cunha, I. C. Cunha, and P. F. Ferraz. 2011. "Campinasuchus dinizi gen. et sp. nov., a new Late Cretaceous baurusuchid (Crocodyliformes) from the Bauru Basin, Brazil" Zootaxa 2871: 19-42 Open access online.

Abstract
A remarkably diverse terrestrial mesoeucrocodylian fauna has been recovered from the continental Cretaceous of the Bauru Basin in fluvial and lacustrine deposits. Members of at least six distinct groups are now recognized, including notosuchids, sphagesaurids, candidodontids, peirosaurids, trematochampsids, and baurusuchids. These mostly terrestrial crocodyliforms potentially developed ecological strategies that allowed them to live in a hot and arid climate during the Cretaceous. A new genus and species of Baurusuchidae, Campinasuchus dinizi gen. et sp. nov., is established on the basis of several partial skulls and skeletons from the Turonian-Santonian Adamantina Formation. This taxon is notable for its relatively short, anteriorly tapering snout, marked maxillary heterodonty with third maxillary and fourth dentary teeth extremely enlarged relative to other teeth, and the presence of a large anteroposterior depression on each palatine between the palatal fenestrae. The presence of yet another crocodyliform from the Adamantina Formation reinforces the idea that aridity, or maybe a seasonally warm and dry climate alternating with periods of higher rainfall, drove the diversification of terrestrial crocodyliforms throughout the Late Cretaceous.

Young, M. T., M. A. Bell, and S. L. Brusatte. 2011. "Craniofacial form and function in Metriorhynchidae (Crocodylomorpha: Thalattosuchia): modelling phenotypic evolution with maximum-likelihood methods." Biology Letters. Published online. doi:10.1098/rsbl.2011.0357

Abstract
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.

Poposaurus and the future of 'Crurotarsi'

Like many rauisuchians, Poposaurus has been plagued with a lack of fossil material. However, a recent find in the Upper Triassic Chinle Formation of Utah has helped shed some light into this early archosaur. Although a skull still remains to be found, paleontologists have managed to uncover  an almost complete post-cranial skeleton. What is also interesting is the phylogenetic analysis associated with the new Poposaurus material. The most startling result is that Phytosauria falls out of the crocodile side of the archosaur tree and becomes the sister taxon of Archosauria. Depending on your definition of Crurotarsi, this could mean that dinosaurs are crurotarsans. However, under the Sereno 2005 definition, Crurotarsi is safe. For now ;-). Rauisuchia may also be in trouble based on the new phylogeny, which preserves Poposauroidea, but not Rauisuchidae. A more detailed phylogeny by Sterling Nesbitt will be coming out soon in the Bulletin of the American Museum of Natural History.

Gauthier, J. A., Nesbitt, S. J., Schachner, E. R., Bever, G. S., and W. G. Joyce. 2011. "The bipedal stem-crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion." Bulletin of the Peabody Museum of Natural History 52: 107-126.  

We introduce a spectacular new specimen of a Late Triassic stem crocodilian identified as Poposaurus gracilis. It is part of a poorly known group, Poposauroidea, that, because of its striking similarities with contemporaneous stem avians (“dinosaurs”), has long puzzled archosaur paleontologists. Observed vertebrate locomotor behaviors, together with exceptional preservation of distinctive anatomical clues in this fossil, enable us to examine locomotor evolution in light of new advances in phylogenetic relationships among Triassic archosaurs. Because this stem crocodilian is unambiguously an archosaur, a diapsid, a tetrapod and a choanate sarcopterygian, we can safely infer major components of its locomotor behavior. These inferences, together with form-function constraints, suggest that P. gracilis was a fleet-footed, obligately erect-postured,
striding biped. That behavior seems to have been superimposed on the ancestral archosaur’s innovative locomotor repertoire, which includes the capacity to “high walk.” These novelties persist in a recognizable form in archosaurs for at least 245 million years and are widely distributed across Earth’s surface in diverse ecological settings. They thus qualify as evolutionary innovations even regardless of significant differences in diversification rates among extant diapsid reptiles.