Field of Science

New Postcranial Material of the Rauisuchian Saurosuchus galilei from the Late Triassic of Argentina

Trotteyn, M. J., Desojo, J. B., y O. A. Alcober. 2011. Nuevo material postcraneo de Saurosuchus galilei Reig (Archosauria: Crurotarsi) del Triasico Superior del centrooeste de Argentina. Ameghiniana 48:605 - 620.

ResumenSaurosuchus galilei Reig es un “rauisúquido” proveniente de la Formación Ischigualasto (Triásico Superior, Carniano), del centrooeste Argentino. En esta contribución se presenta la primera descripción detallada del complejo proatlas-atlas-axis; columna vertebral completa y articulada; y ambas escápulas de este taxón. La morfología general del complejo proatlas-atlas-axis es similar a la de otros “rauisúquidos”. Las vértebras cervicales son comprimidas axialmente y elongadas dorsoventralmente. El complejo atlas-axis y las cervicales, presentan los rasgos típicos de un animal con cuello corto y robusto. En las cervicales y en las dorsales puede observarse una serie de láminas, depresiones interlaminares y depresiones en el cuerpo vertebral que también se han descrito en otros “rauisúquidos”. En las vértebras presacras se observa una quilla ventral y una marcada expansión del extremo dorsal de la espina neural. La serie caudal presenta centros comprimidos axialmente, con un surco ventral orientado anteroposteriormente. La escápula es robusta, la hoja escapular es moderadamente expandida y levemente curvada. La notable diversidad que presentan los “rauisúquidos” en general, hace que sea necesario un análisis profundo para abordar problemáticas morfofuncionales y filogenéticas, con las cuales se espera que contribuya este nuevo material.

Abstract - New postcranial material of Saurosuchus galilei Reig (Archosauria : Crurotarsi) from the Late Triassic of Central-Western Argentina . Saurosuchus galilei Reig is a “rauisuchid” from the Ischigualasto Formation (late Carnian, Late Triassic) located in central-western Argentina. This paper is the first detailed description of the proatlas-atlas-axis complex of this taxon, of a complete and articulated vertebral column, and of both scapulae. Overall morphology of the proatlas-atlas-axis complex is similar to that of other “rauisuchids”. This complex and the post-axial cervical vertebrae show the typical traits of an animal with a short and strong neck. The cervical vertebrae are anteroposteriorly compressed and dorsoventrally elongated. Vertebral laminae, interlaminar depressions, and lateral depressions on the centra are present in the cervical and dorsal vertebrae, as in other “rauisuchids”. The presacral series bears ventrally keeled centra and large transversal expansions of the distal ends of the neural spines. The caudal series shows axially compressed centra with a longitudinal ventral groove. The scapulae are very robust and have a brief expansion and a slightly curved scapular blade. The remarkable diversity of “rauisuchids” in general, makes a detailed analysis necessary in order to approach morphofunctional and phylogenetic problems; this new material is expected to contribute towards the solution of these problems.

Rioarribasuchus chamaensis Reconstruction

Here is Jeff Martz's recent reconstruction of the aetosaur Rioarribasuchus chamaensis.

His reconstruction is a little different than the one in my 2007 paper. He felt that in the original reconstruction I had the paramedian plates with the pronounced spines too far forward and after much discussion I concur. 

I think that this new reconstruction is probably fairly accurate given what we know about Rioarribasuchus and other paratypothoracisin aetosaurs, and it contrasts strongly from other reconstructions that still portray it as a Desmatosuchus-like aetosaur. This relationship was refuted by phylogenetic analysis, and although I really like Matt Celeskey's artwork, the reconstruction as a desmatosuchine is not based upon any actually recovered fossil material. All of the osteoderms with spines in the Rioarribasuchus type material are paramedian plates from the caudal region and nothing homologous with the cervical lateral spines in Desmatosuchus are known.

REFERENCE

Parker, W. G. 2007. Reassessment of the Aetosaur 'Desmatosuchus' chamaensis with a

reanalysis of the phylogeny of the Aetosauria (Archosauria: Pseudosuchia). Journal of Systematic Palaeontology 5:41-68. DOI: 10.1017/S1477201906001994

Dinosaurs Are Crurotarsans

There is much confusion surrounding the taxonomic name given to the crocodylian branch of Archosauria. Two names are often given for this clade, Pseudosuchia and Crurotarsi, and despite detailed discussion by Brochu (1997) and others, most recently Senter (2005), these names are often used interchangeably. However, this general usage is not correct because both taxonomic names have been explicitly defined cladistically and their definitions vary. As I have stated in an earlier post, Pseudosuchia is a stem-based (branch-based) definition that includes all archosaurs closer to crocodylians than to avians; whereas Crurotarsi has a node-based definition delimited by the inclusion of specific taxa, including parasuchians or phytosaurs. It has long been recognized that the definition of Crurotarsi is unstable (e.g., Brochu, 1997), because if one of the specifier taxa used to define this clade is found to lie outside of Archosauria then the taxonomic composition of Crurotarsi would change, possibly to something not actually meant when one uses the name or Crurotarsi could actually end up being a synonym of another node-based clade such as Archosauria. On the other hand the content of Pseudosuchia would not change, and thus that definition is more stable. Nonetheless to date this has not really been a problem because as defined Crurotarsi and Pseudosuchia currently comprise the same taxa. The former name is used much more frequently by workers presumably because of a preference for the name itself rather than a dislike for its definition (Brochu, 1997).

Sterling Nesbitt’s upcoming detailed phylogenetic analysis of the Archosauria (Nesbitt, in press), which is previewed in the recent paper on Poposaurus by Gauthier et al. (2011), recovers phytosaurs as the sister taxon to Archosauria. This placement is extremely well-supported in his analysis and actually makes a lot of sense if you spend a lot of time working with this group and with pseudosuchians. As I noted earlier the recovery of Phytosauria outside of Archosauria changes the definition of Crurotarsi quite significantly, with Crurotarsi now the name of the clade Phytosauridae + Archosauria. This means that all ornithodirans including dinosaurs are now crurotarsans. Clearly this is not exactly what is meant when workers utilize this name.

This is also fairly significant in the evolutionary sense because it means that phytosaurs are ancestral to dinosaurs and other ornithodirans. Gauthier et al. (2011) discuss this ancestry in the sense of the functional ankle. They note that phytosaurs possess a primitive form of a crurotarsal joint that is quite different from that in suchians, and also that the ankle joint in the earliest ornithodiran, Lagosuchus, also utilizes crurotarsal motion that is lost in later ornithodirans with the development of the hinge-like ankle joint characteristic of that clade.

Overall the placement of phytosaurs outside of Archosauria is very well supported and may not be overturned. Thus, following Brochu (1997) I advocate the use of Pseudosuchia for the crocodylian branch of Archosauria to promote taxonomic stability. Furthermore, IMHO it is much easier and proper to use than non-ornithodiran crurotarsan, although I expect that more people will start to use Pan-Crocodylia for the clade because of the general dislike of the name Pseudosuchia.

“Careful attention to their [Crurotarsi and Pseudosuchia] ultimate distinctness can be a source of stability for future phylogenetic work. The definitions will remain stable, and we have a nomenclatural framework within which new fossils can be placed. Taxa more closely related to crocodiles than to birds, but not descended from the last common ancestor of parasuchians, ornithosuchids, prestosuchids, and suchians, will still be pseudosuchians. We fully expect diagnoses, group memberships, and minimum divergence times to change as new fossils or data sets are analyzed, and the parameters of Pseudosuchia and Crurotarsi will diverge as more basal pseudosuchians are found” (Brochu, 1997:448).


REFERENCES

Brochu, C. A. 1997. Synonymy, Redundancy, and the Name of the Crocodile Stem-Group. Journal of Vertebrate Paleontology 17:448-449.

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.

Nesbitt, S. J. in press. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352:1-292.

Senter, P. 2005. Phylogenetic taxonomy and the names of the major archosaurian (Reptilia) clades. PaleoBios 25:1–7.

A New Nearly Complete Articulated Skeleton of the Bipedal Pseudosuchian Poposaurus gracilis from the Upper Triassic of Utah

Back in 2003 I was fortunate to be part of a research team that discovered a mostly complete articulated skeleton of Poposaurus gracilis from the Chinle Formation of Utah. Uncovering such an amazing specimen is definitely one of the highlights of my career, especially the moment when we realized how amazingly complete and articulated the specimen was. Below is a photo of the articulated hind limb and pelvis at that moment during the excavation.


I've seen the specimen a couple of times at Yale in the process of preparation and the specimen is definitely a beauty. Furthermore is is extremely important because prior to this find P. gracilis was only known from the pelvis, hind limbs, and some vertebrae.  Unfortunately, the skull of this new specimen was unrecoverable, but the rest provides much information including an articulated forelimb and the pes (foot). I should also add that we met a lot of good friends on this trip.

The first paper out on this specimen is not a detailed osteological study but rather introduces the specimen and provides a detailed determination of the proposed locomotor abilities of this taxon, concluding from numerous lines of evidence (phylogenetic, extant phylogenetic bracketing, morphological) that Poposaurus was an obligatory biped. Morphological support for bipedality in P. gracilis includes a fully erect posture, relatively short forelimbs, elongate pes, five sacral vertebrae, partially open acetabulum, and an elongate tail. Gauthier et al. also provide an in-depth argument that the development of bipedality in Archosauria represents a major evolutionary innovation in vertebrate history.

Finally this paper gives a preview of Sterling Nesbitt's upcoming (in press, out very very shortly) extremely detailed phylogenetic analysis of the Archosauria (from his PhD dissertation).  Sterling's analysis provides some pretty surprising (and well-supported) placements of various taxa that will turn some heads and cause a good bit of discussion, especially regarding the revised definitions of some beloved (by some) clade names.

Although I am told that the Poposaurus paper is officially out, it is not up yet on either the Yale Peabody Museum website or the BioOne site, but should be soon. I'll post the link as soon as it does. In the meantime you can read more about the initial find here. I'm also looking forward to the complete osteological description of this amazng specimen.

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.

Abstract - 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 regardless of significant differences in diversification rates among extant diapsid reptiles.

Redescription of a Lower Triassic Synapsid and a Reappraissal of Lower Triassic Therocephalian Biostratigraphy

Botha-Brink, J., and S. P. Modesto. 2011. A new skeleton of the Therocephalian synapsid Olivierosuchus parringtoni from the Lower Triassic South African Karoo Basin. Palaeontology Early View. DOI: 10.1111/j.1475-4983.2011.01048.x

Abstract - We provide a redescription of the therocephalian therapsid Olivierosuchus parringtoni based on a new specimen recovered from the Lower Triassic Lystrosaurus Assemblage Zone of South Africa and discuss the biostratigraphic implications of Lower Triassic South African therocephalians. The new specimen comprises a skull and articulated anterior portion of the postcranial skeleton. Olivierosuchus parringtoni can be distinguished from its akidnognathid relatives, Promoschorhynchus and Moschorhinus, by the presence of a relatively slender snout. Features that further distinguish Olivierosuchus from Promoschorhynchus include fewer upper postcanines, an obtuse angle of the transverse process of the pterygoid and an oblique alignment of the suborbital fenestra margin of the palatine. Features that further distinguish Olivierosuchus from Moschorhinus include the presence of a sharp rather than blunt crista choanalis, a spatulate posterior portion of the ectopterygoid instead of a narrow shaft, the presence of prominent pterygoid tuberosities and a narrow, elongated tabular. A reappraisal of Lower Triassic therocephalian biostratigraphy reveals that most of these taxa are restricted to the lowermost part of the Lystrosaurus Assemblage Zone revealing a high diversity, whereafter the diversity decreases dramatically in the middle of the zone. However, despite their scarcity in the middle and upper Lystrosaurus Assemblage Zone, therocephalians in the Karoo Basin remain the most diverse therapsid clade in the lowermost Triassic, which suggests that they were able to recover relatively quickly from the end-Permian extinction event and form an important part of the postextinction earliest Triassic recovery.

Largest Spider Ever Recovered is from the Middle Jurassic of China


http://news.sciencemag.org/sciencenow/2011/04/scienceshot-jurassic-spider-not.html?etoc

Sheldon, P. A., Shih, C. k., and D. Ren. 2011. A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China. Biology Letters online early. doi: 10.1098/rsbl.2011.0228.

Abstract - Nephila are large, conspicuous weavers of orb webs composed of golden silk, in tropical and subtropical regions. Nephilids have a sparse fossil record, the oldest described hitherto being Cretaraneus vilaltae from the Cretaceous of Spain. Five species from Neogene Dominican amber and one from the Eocene of Florissant, CO, USA, have been referred to the extant genus Nephila. Here, we report the largest known fossil spider, Nephila jurassica sp. nov., from Middle Jurassic (approx. 165 Ma) strata of Daohugou, Inner Mongolia, China. The new species extends the fossil record of the family by approximately 35 Ma and of the genus Nephila by approximately 130 Ma, making it the longest ranging spider genus known. Nephilidae originated somewhere on Pangaea, possibly the North China block, followed by dispersal almost worldwide before the break-up of the supercontinent later in the Mesozoic. The find suggests that the palaeoclimate was warm and humid at this time. This giant fossil orb-weaver provides evidence of predation on medium to large insects, well known from the Daohugou beds, and would have played an important role in the evolution of these insects.

Reassessment of the Middle Triassic Rauisuchian Archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus

Note: One error I did find in this paper after a quick glance is that hyposphene-hypantrum vertebral articulations are not restricted to only rauisuchians within pseudosuchians, they are also found in the aetosaur Desmatosuchus spurensis (Parker 2003, 2008). In fact they are very well-developed in that taxon.

Lautenschlager, S.  and J. B. Desojo. 2011. Reassessment of the Middle Triassic rauisuchian archosaurs Ticinosuchus ferox and Stagonosuchus nyassicus. Paläontologische Zeitschrift Online First 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.

What I am Reading: Charming the Bones - A portrait of Margaret Matthew Colbert

I'm usually reading (or attempting to read) several books at any one time but the book that really has my attention right now is Charming the Bones - A portrait of Margaret Matthew Colbert by Ann Brimacombe Elliot.



Margaret Colbert was the granddaughter of botanist and geologist George Frederic Matthew, the daughter of vertebrate paleontologist William Diller Matthew, and the wife of vertebrate paleontologist Edwin Harris Colbert, as well as an artist in her own right. She illustrated Ned Colbert's doctoral dissertation and many of his books.  She also completed Triassic themed murals for the New Mexico Museum of Natural History and the Petrified Forest National Park, as well as a Cretaceous mural for Big Bend National Park in Texas.  She also designed the logo for the Society of Vertebrate Paleontology.

Margaret Colbert's mural on exhibit at the Rainbow Forest Museum at Petrified Forest National Park (photo by Karen Sweeny-Justice)
Interestingly her biography is written by Ann Brimacombe Elliot, who is the wife of geologist David H. Elliot who conducted important fieldwork with Ned Colbert in the 1960s.

Ned Colbert wrote two autobiographies which are essential reading for any vertebrate paleontologist, but I also urge you to read Margaret Colbert's biography as well and witness what an amazing woman she was.

Transitional Mammalian Middle Ear from a new Cretaceous Eutriconodont

Non Triassic per se but still relevent and extremely cool and important...

Meng, J., Wang, Y., and C. Li. 2011. Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont. Nature 472:181-185. doi:10.1038/nature09921

Abstract - The transference of post-dentary jaw elements to the cranium of mammals as auditory ossicles is one of the central topics in evolutionary biology of vertebrates. Homologies of these bones among jawed vertebrates have long been demonstrated by developmental studies; but fossils illuminating this critical transference are sparse and often ambiguous. Here we report the first unambiguous ectotympanic (angular), malleus (articular and prearticular) and incus (quadrate) of an Early Cretaceous eutriconodont mammal from the Jehol Biota, Liaoning, China. The ectotympanic and malleus have lost their direct contact with the dentary bone but still connect the ossified Meckel’s cartilage (OMC); we hypothesize that the OMC serves as a stabilizing mechanism bridging the dentary and the detached ossicles during mammalian evolution. This transitional mammalian middle ear narrows the morphological gap between the mandibular middle ear in basal mammaliaforms and the definitive mammalian middle ear (DMME) of extant mammals; it reveals complex changes contributing to the detachment of ear ossicles during mammalian evolution.

Earliest Use for the Name Chindesaurus for the Petrified Forest Dinosaur and it's Initial Classification as a 'Plateosaur'

Recently I posted where a 1986 newspaper article from Holbrook, Arizona revealed a quote from the then Petrified Forest National Park superintendent that the remains of a basal dinosaur recovered from the park in 1985 would be called "Holbrookosauras smallii".  This brought up some discussion of this name as a nomen dubium and that I had been wrong that the name Chindesaurus had been the first unoffical name mentioned for this specimen.

Well it turns out that I was originally correct. There is an article in Science News from May 25, 1985 where the lead paleontologist on the discovery (and future describer) Robert A. Long states that because the specimen was recovered off of Chinde Point and because it is the Navajo name for 'ghost' he may call the newly discovered specimen "Chindesaurus".

This is now clearly the earliest known reference to this name as applied to this specimen and because the interview that is the basis for the article was conducted before the excavation was even completed, it may stand as the earliest.  I am still puzzled where the name "Holbrookosauras" would have originated. Maybe Long was going back and forth between the two before finally settling on Chindesaurus in 1989.

This is actually the best article I have read discussing the initial discovery. Notice that the opening line mentions a quadrupedal animal.  This is because initially Chindesaurus was thought to be a sauropodomorph and based on the morphology of the astragalus (the first bone recovered), which actually made sense as there are sauropodomorph characters present in this elements as discussed by Nesbitt et al. (2007); however the 'confusing' aspects mentioned by Long are theropod dinosaur characteristics as well. Thus wehen Long and Greenwald are discussing that this may be a link between two lineages of dinosaurs they are talking about sauropodomorphs and theropods. Below is the initial 1985 reconstruction of Chindesaurus as a 'plateosaur' by artist Rick McCrea.



If you missed the above link you can access the article here:
http://findarticles.com/p/articles/mi_m1200/is_v127/ai_3784767/

The Buck-toothed Demon Reptile, Daemonosaurus chauliodus from the Upper Triassic of New Mexico

Historically it was long thought that the Upper Triassic Coelophysis Quarry at Ghost Ranch New Mexico contained, with the exception of an odd phytosaur, almost exclusively skeletons of the neotheropod dinosaur Coelophysis bauri. However, the recent discoveries of Effigia and Vancleavea demonstrate a much greater diversity of vertebrates present in the quarry. Now we can add to the list a second theropod dinosaur. Daemonosaurus chauliodus ('prominent toothed demon reptile') is known from only a single skull and several associated vertebrae found in the Carnegie Museum block (C-4-81) collected from the quarry in the early 1980s.

Daemonosaurus differs from Coelophysis bauri in the presence of the extreme protruding teeth, a significantly larger prefrontal, and in the dorsoventrally deep premaxilla. A phylogenetic analysis of basal dinosaurs recovers Daemonosaurus outside of Neotheropoda as the sister taxon to Tawa hallae + Neotheropoda.

One possibility I find interesting is that we now have four theropods known from the Upper Triassic in the Ghost Ranch area, Tawa, a coelophysoid, and Chindesaurus from the Hayden Quarry (Petrified Forest Member) and Coelophysis and Daemonosaurus from the Coelophysis Quarry (siltstone member). Currently Chindesaurus lacks a preserved cranium, whereas Daemonosaurus is known almost exclusively from the skull. Thus, it is possible that they could represent the same or a similar taxon. Only the discovery of more complete material of either taxon can test this idea.


Holotype specimen of Daemonosaurus chauliodus in left lateral view

Life reconstruction of Daemonosaurus chauliodus by Jeff Martz
Sues, H.-D., Nesbitt, S. J., Berman, D. S., and A. C., Henrici. 2011. A late-surviving basal theropod dinosaur from the latest Triassic of North America. Proceedings of the Royal Society B. doi:10.1098/rspb.2011.0410 [Free download]

Abstract - The oldest theropod dinosaurs are known from the Late Carnian of Argentina. However, the evolutionary diversification of this group after its initial radiation but prior to the Triassic–Jurassic boundary is still poorly understood because of a sparse fossil record near that boundary. Here, we report on a new basal theropod, Daemonosaurus chauliodus gen. et sp. nov., from the latest Triassic ‘siltstone member’ of the Chinle Formation of the Coelophysis Quarry at Ghost Ranch, New Mexico. Based on a comprehensive phylogenetic analysis, Daemonosaurus is more closely related to coeval neotheropods (e.g. Coelophysis bauri) than to Herrerasauridae and Eoraptor. The skeletal structure of Daemonosaurus and the recently discovered Tawa bridge a morphological gap between Eoraptor and Herrerasauridae on one hand and neotheropods on the other, providing additional support for the theropod affinities of both Eoraptor and Herrerasauridae and demonstrating that lineages from the initial radiation of Dinosauria persisted until the end of the Triassic. Various features of the skull of Daemonosaurus, including the procumbent dentary and premaxillary teeth and greatly enlarged premaxillary and anterior maxillary teeth, clearly set this taxon apart from coeval neotheropods and demonstrate unexpected disparity in cranial shape among theropod dinosaurs just prior to the end of the Triassic.


skeletal outline of Daemonosaurus chauliodus with a human for scale
News coverage of the find here, here, and this "gem". Alas there appears to be a preponderance of "mis**ng l**k" quotes in the many articles posted today.

Dino D-Day Trailer



Umm.... yes that is a Desmatosuchus with a machine gun mounted on its back. Aetosaurs = Tanks of the Triassic.

The Laws of Fieldwork

A group of us came up with these 'laws' a few years back after spending several seasons in the field at Petrified Forest National Park. They are a work in progress, but hopefully you will find them enjoyable and applicable.

THE LAWS OF FIELDWORK
Compiled by Sterling Nesbitt, Randy Irmis, Michelle Stocker, and Bill Parker

1. If you can’t find your tools, look under your butt.

2. What is said in the field stays in the field (unless you are out with the same people).

3. Always make it look like an accident.

4. If grass can grow on it, you can go on it (i.e. it is safe to climb up or down on).

5. No one really ever falls or slips, they are either doing pushups or looking closely at rocks or fossils.

6. Last one up at night must be the first one up in the morning.

7. If something catches your eye, you must examine it.

8. To work in the Chinle, you must love the Chinle (or else it will drive you crazy).

9. No matter how far from civilization you think you have hiked, you will always find some discarded bottle or can.

10. If you are not finding any bones, you can always eat a granola bar.

11. You always find the best stuff at the end of the last day of the season.

12. There is no “line” in the field*.

*Unfortunately this one was actually broken in 2005 by a student intern and much to our dismay.

New From Jeff Martz - Poposaurus in Color; and the Question of Bipedality in Animals with a Crocodile-normal Ankle Type

Jeff Martz has recently colo(u)rized his Poposaurus gracilis reconstruction and here it is in its new glory.


When I see reconstructions of pseudosuchians in a bipedal stance I always reflect upon the question of whether or not it is functionally possible for an animal with a crocodile-normal ankle type to actually be bipedal, especially an obligate biped.  I've perused the literature but have found very little to address this problem. I'm certain that Emma Schachner dealt with this in her recently completed PhD on the new equisitely preserved Poposaurus specimen from the Chinle Formation in Utah, but unfortunately I've not had a chance to borrow and read a copy.  Her 2009 SVP abstract suggests that myological developments differ between bipedal pseudosuchians and bipedal dinosaurs, suggesting that these myological changes compensate for the alternate ankle structures.

Paleoerrata = House of Bones + Flying Blind

As mentioned elsewhere my good friend and colleague (in Chinle stratigraphy and all things aetosaur) and paleoartist Dr. Jeffrey Martz has retired his blog Paleoerrata. However, in a sense this is not really a retirement as much as an evolution because his is now posting on two other blogs, House of Bones, which will deal with the science information themed posts and Flying Blind, which will deal with his interest in the evolution vs. creationism debate.  I urge everyone to update their blogrolls and check these two sites out.

Regarding his Triassic artwork, Jeff has always graciously let me post his new works here and has even chewed me out when they do not appear in  a timely manner. I will have a post up on his newest piece in a bit. In the meantime check out his two new sites.

New Archosauriform Remains from the Lower Keuper of Germany

Schoch, R. R. New archosauriform remains from the German Lower Keuper.: Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 260:87-100. DOI: 10.1127/0077-7749/2011/0133

Abstract - Isolated bones of archosauriforms form regular finds in deposits of the Lower Keuper (Erfurt Formation: upper Middle Triassic) of southwestern Germany. In addition to the fairly well known 3-5 m long rauisuchian Batrachotomus kupferzellensis and the very fragmentary Zanclodon laevis, remains of further, 1-2 m long archosauriforms have been identified. Although the number of taxa represented by this incomplete material is unknown, the distinctness of these finds from Batrachotomus and Zanclodon is indicated by the following features: (1) a "rauisuchian" type maxilla with well-developed interdental plates, which forms a long suture with a posterodorsal process of the premaxilla, (2) relatively long cervical and anterior dorsal vertebrae, (3) a gracile humerus with a narrow proximal head and a weak deltopectoral crest, (4) a slender and markedly curved tibia, and (5) tear-drop shaped, keeled armour plates. These findings highlight the diversity of large predators in Middle Triassic land vertebrate faunas of Central Europe.

First Well-Preserved Heterodontosaurid Material from South America: Manidens condorensis from the Middle Jurassic of Argentina

Pol, D., Rauhut, O. W. M., and M. Becerra. 2011. A Middle Jurassic heterodontosaurid dinosaur from Patagonia and the evolution of heterodontosaurids. Naturwissenschaften (online first) DOI 10.1007/s00114-011-0780-5

Abstract - Heterodontosauridae is a morphologically divergent group of dinosaurs that has recently been interpreted as one of the most basal clades of Ornithischia. Heterodontosaurid remains were previously known from the Early Jurassic of southern Africa, but recent discoveries and studies have significantly increased the geographical and temporal range for this clade. Here, we report a new ornithischian dinosaur from the Middle Jurassic Cañadón Asfalto Formation in central Patagonia, Argentina. This new taxon, Manidens condorensis gen. et sp. nov., includes well-preserved craniomandibular and postcranial remains and represents the only diagnostic ornithischian specimen yet discovered in the Jurassic of South America so far. Derived features of its anatomy indicate that Manidens belongs to Heterodontosauridae, as the sister taxon of Heterodontosaurus and other South African heterodontosaurids. The presence of posterior dentary teeth with high crowns but lacking extensive wear facets in Manidens suggests that this form represents an intermediate stage in the development of the remarkable adaptations to herbivory described for Heterodontosaurus. The dentition of Manidens condorensis also has autapomorphies, such as asymmetrically arranged denticles in posterior teeth and a mesially projected denticle in the posteriormost teeth. At an estimated total length of 60–75 cm, Manidens furthermore confirms the small size of basal heterodontosaurids.

New Triassic Terror: Rauisuchian Packs, New Evidence from the Middle Triassic of Brazil

I'm glad everyone enjoyed my April Fools joke; however, the Triassic is here to stay and especially Triassic vertebrate paleontology because the month of April is going to see the publication of numerous new papers on the subject. In fact, April 2011 has the possibility of being the best month ever for Triassic VP, especially archosaurs. We'll revisit this at the end of the month and see if this is true.

The first paper of April 2011 describes the recovery of nine articulated and associated rauisuchian skeletons from the Middle Triassic of Brazil. They have been assigned to a new Prestosuchus-like taxon named Decuriasuchus quartacolonia ("legion of ten crocodile from Quarta Colonia"). The material looks amazing and finds like this are extremely rare in the Triassic so I hope that a full description of the material will be forthcoming.

The phylogenetic analysis utilizes the dataset of Brusatte et al. (2010) and recovers a paraphyletic "rauisuchidae" with Decuriasuchus nesting with Prestosuchus and Batrachotomus; however, the paper and supplemental materials do discuss problems with the existing dataset and therefore these results should be considered very tentative.

One interesting point of the paper is the potential social implications of finding nine rauisuchians clustered together in a single spot. Franca et al., argue that the taphomomy of the site precludes that this is not a time averaged assemblage and instead it appears that these animals (all adults) congregated for some reason before dying. Whether the group was assembled and killed by a sudden catastrophy (e.g, flash flood) or accumulated and died because of another type of event (e.g., drought) is undeterminable with the current evidence, but in either case this would call for a certain degree of interaction between these predators. Modern crocodilians congregate in large number for various reasons, but mainly for feeding and in some cases have been reported to work together to herd fish. Thus, the circumstantial evidence from this new find may suggest that rauisuchians may also have worked together in some cases for hunting strategies. As stated by Franca et al in their concluding sentence, this would represent "the earliest evidence of possible group behavior among archosaurs". I personally would think that a hunting pack of large rauisuchians would be quite formidable, but then again this Brazilian group appears to have lacked invulnerability. Furthermore this would be extremely difficult to support with the evidence.

Note: The Revueltosaurus bonebed in Petrified Forest National Park is a monotypic assemblage of at least a dozen individuals (all of the same size and situated on a levee adjacent to the river channel).

Franca, M. A. G., Ferigolo, J., and M. C. Langer. 2011. Associated skeletons of a new middle Triassic “Rauisuchia” from Brazil. Naturwissenschaften (online first) DOI: 10.1007/s00114-011-0782-3

Abstract - For more than 30 million years, in early Mesozoic Pangea, “rauisuchian” archosaurs were the apex predators in most terrestrial ecosystems, but their biology and evolutionary history remain poorly understood. We describe a new “rauisuchian” based on ten individuals found in a single locality from the Middle Triassic (Ladinian) Santa Maria Formation of southern Brazil. Nine articulated and associated skeletons were discovered, three of which have nearly complete skulls. Along with sedimentological and taphonomic data, this suggests that those highly successful predators exhibited some kind of intraspecific interaction. Other monotaxic assemblages of Triassic archosaurs are Late Triassic (Norian-Rhaetian) in age, approximately 10 million years younger than the material described here. Indeed, the studied assemblage may represent the earliest evidence of gregariousness among archosaurs, adding to our knowledge on the origin of a behavior pattern typical of extant taxa.

Triassic Officially Loses Status as the First Period of the Age of Dinosaurs Because it Just Doesn't Have Many

The International Stratigraphic Council (ISC) announced today that it was stripping the Triassic Period of the privilege of representing the first period of the Mesozoic Era, otherwise known as the Age of Dinosaurs.

ISC Chairman Dr. Waldo Weatherbee stated that this decision was made based on the general paucity of Triassic dinosaurs. "Let's face it," he said, "Current research is demonstrating that many of the things in the Triassic we thought were dinosaurs are turning out to be all kinds of other types of critters, and the things that are still dinosaurs simply aren't that impressive."

Council member Dr. Geraldine Grundy agreed. "I'm sick and tired of paleontologists turning up little crumbly bits of bone from the Triassic and claiming these are the earliest dinosaurs. Give me a break. Show me some real bones!"

Asked about Coelophysis and Plateosaurus, Grundy plugged her ears and yelled "blah, blah, blah, I can't hear you!"

University of Riverdale paleontology graduate student Reggie Mantle argues, "the Triassic is lame man, there are no cool dinos such as raptors, longnecks, and T-rex.  At least the Jurassic has some cool movies made about it, what does the Triassic have? Triassic Attack? How completely lame!"

Fellow student Betty Cooper also agrees, "I can't even pronounce Chromigo-what ever you call it. Dinosaurs should only have easy names like Stegosaurus and Triceratops. Plus, now they tell us that the only cool Triassic dinosaur Eoraptor isn't even a raptor?! Why would anyone study this crap?"

The council voted 312 to 2 to officially dissolve the Triassic and reassign what was  the later part of the Late Triassic to the Jurassic (and thus to the beginning of the Mesozoic), and the Early, Middle and beginning of the Late Triassic epochs to the Permian.

Professor Flutesnoot, a noted dinosaur researcher from the Society for Dinosaur Dominance supports these reassignments. "Removal of the Triassic as a valid period of the Mesozoic solves the missing Triassic dinosaur problem that is currently recognized, especially regarding the lack of bonafide ornithischian dinosaurs from that period. Dinosaurs now first appear neatly in the Jurassic and clearly define the lower boundary of that period. Many of us will sleep better tonight knowing that this problem has been solved."

Weatherbee added "You simply can't be part of the Age of Dinosaurs without any bleedin' dinosaurs!"

"This is exactly how things should be," chimed in Grundy, "keep your non-dinosaur bearing units out of the Mesozoic!".

The council also voted 312 to 2 to combine and rename all of the eras prior to the Mesozoic as the Predinozoic and in a subsequent vote of 312 to 0 kicked out their two dissenting members.

"We don't need these bleedin' heart liberal Triassophiles messing up our wonderful timescale and relegating dinosaurs to 2nd class organisms against the desires of our founding fathers", explained Weatherbee.

As of press time the International Subcommision on the Triassic simply stated that they could not possibly think of any intelligent response whatsoever.

Revised timescale by the ISC (modified from here)