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.