Cranial Morphology of the Plagiosaurid Gerrothorax pulcherrimus as an Extreme Example of Evolutionary Stasis

Schoch, R. R. and F. Witzmann. 2011. Cranial morphology of the plagiosaurid Gerrothorax pulcherrimus as an extreme example of evolutionary stasis. Lethaia, DOI: 10.1111/j.1502-3931.2011.00290.x

Abstract - The plagiosaurid Gerrothorax pulcherrimus from the Triassic of Greenland and Germany is represented by skulls ranging from 4 to 12 cm in length and sheds light on ontogeny, individual variation, and variation in time and space. Ontogeny was remarkably stable in G. pulcherrimus, with the smallest known specimens resembling the adults closely in most features. A true ontogenetic change is evident in the ornament of dermal bones, in that the smallest specimens have ridges whereas in the successively larger ones, pustules spread over increasingly larger areas. The skull becomes proportionally longer, and the adductor chambers relatively narrower. The positive allometry of both the orbits and the interpterygoid vacuities suggests that the eye supporting musculature – rather than the jaw adductors – increased proportionally during growth. Individual, not age-related variation in the dermal skull roof affects partial fusion of parietals, presence and extent of the interfrontoparietal, and the morphological pattern of the posterior skull table. The ventral surface of the basal plate of the parasphenoid ranges from smooth over poorly to heavily ornamented or dentigerous. Considering the impressive longevity of more than 35 Myr, the morphological changes of G. pulcherrimus are minor. Our ecological interpretation for G. pulcherrimus is that it relied on the permanent presence of water, but was flexible with respect to the size and nature of the water body as well as to changes in salinity. The unparalleled extent of evolutionary stasis may therefore be based on the ecological flexibility of this morphologically so tightly constrained temnospondyl.

Vertebrate Fossils from the Marine Triassic of Austria

Krainer, K. Lucas, S. G., and M. Strasser. 2011. Vertebrate fossils from the Northalpine Raibl beds, Western Northern Calcareous Alps, Tyrol (Austria). Austrian Journal of Earth Sciences 104:97-106. [free pdf]

Abstract -

Aus den Nordalpinen Raibler Schichten des Karwendels und der Mieminger Kette in den westlichen Nördlichen Kalkalpen (Tirol,

Österreich) werden Vertebratenreste wie Fischzähne von Actinopetrygiern (

Fischzähne) und laterale Zähne von

beschrieben. Die Vertebratenreste wurden in Onkolithen und Schillagen gefunden, die in dunkle Tonschiefer eingeschaltet

sind. Wir interpretieren diese Lagen als hochenergetische Sedimente (Tempestite), entstanden durch Sturmereignisse in einem

inneren Schelfbereich. Die in dieser Arbeit dokumentierten Vertebratenreste der Raibler Schichten sind ein weiterer Nachweis typischer

Fisch- und Tetrapodentaxa, die in den Meeren der Mittel- und Obertrias in Westeuropa lebten.

Vertebrate fossils such as fish teeth derived from Actinopterygii (Saurichthys morphotype, Colobodus?, indeterminate) and lateral teeth of Paleobates (small sharks) as well as reptile fragments ascribed to Eusauropterygia? and Prolacertiformes are reported from the Northalpine Raibl Beds of the Karwendel and Mieming mountain ranges of the western Northern Calcareous Alps (Tyrol, Austria). The vertebrate fossils occur in oncolite and coquina beds that are intercalated in dark shales. We interpret these intercalated beds as high-energy sediments deposited during storm events (tempestites) in an inner shelf environment. The Raibl vertebrate fossils documented here add another well-established record of characteristic fish and tetrapod taxa that lived in the Middle-LateTriassic seaways that covered Western Europe.Saurichthys Morphotyp, Colobodus?, unbestimmbarePaleobates (kleine Haie) sowie Reptilienfragmente von Eusauropterygiern? und Prolacertiformes

New Findings on the Early Triassic Recovery of the Terrestrial Vertebrate Fauna - Redux

Here is the abstract and link to the new article and it is currently open access.

Irmis, R. B. and J. H. Whiteside. 2011.Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle. Proceedings of the Royal Society B (advance online publication) doi: 10.1098/rspb.2011.1895

Abstract - During the end-Permian mass extinction, marine ecosystems suffered a major drop in diversity, which was maintained throughout the Early Triassic until delayed recovery during the Middle Triassic. This depressed diversity in the Early Triassic correlates with multiple major perturbations to the global carbon cycle, interpreted as either intrinsic ecosystem or external palaeoenvironmental effects. In contrast, the terrestrial record of extinction and recovery is less clear; the effects and magnitude of the end-Permian extinction on non-marine vertebrates are particularly controversial. We use specimen-level data from southern Africa and Russia to investigate the palaeodiversity dynamics of non-marine tetrapods across
the Permo-Triassic boundary by analysing sample-standardized generic richness, evenness and relative abundance. In addition, we investigate the potential effects of sampling, geological and taxonomic biases on these data. Our analyses demonstrate that non-marine tetrapods were severely affected by the end-Permian mass extinction, and that these assemblages did not begin to recover until the Middle Triassic. These data are congruent with those from land plants and marine invertebrates. Furthermore, they are consistent with the idea that unstable low-diversity post-extinction ecosystems were subject to boom-bust cycles, reflected in multiple Early Triassic perturbations of the carbon cycle.

New Findings on the Early Triassic Recovery of the Terrestrial Fauna

Congratulations to Randall Irmis and Jessica Whiteside on this new study. This article is up on the Science Magazine website although the article is not up yet on the Royal Society Publishing website. I'll post the abstract and link when it appears.

http://news.sciencemag.org/sciencenow/2011/10/the-sunll-come-out-tomorrow-mayb.html

Long Bone Microstructure of Middle Triassic Pachypleurosaurids

Missed this article from May 2011 in the special issue of Compte Rendus Paleovol in honor of Dr. Armand de Ricqlès.

Hugi, J., Scheyer, T. M., Sander, P. M., Klein, N., and M. R. Sánchez-Villagra. 2011. Long bone microstructure gives new insights into the life of pachypleurosaurids from the Middle Triassic of Monte San Giorgio, Switzerland/Italy. Compte Rendus Palevol 10:413-426. doi:10.1016/j.crpv.2011.03.009

Abstract - The long bone microstructure of four pachypleurosaurid taxa from Monte San Giorgio (Switzerland/Italy) was studied. Pachypleurosaurids are secondarily aquatic reptiles that lived during the Middle Triassic in varying marine environments of the Tethys. All four pachypleurosaurids show high compactness values in their long bones based on a thick cortex and a calcified cartilaginous core, which remains in the medullary region throughout the ontogeny. Parts or even the entire embryonic bone layer composed of a mixture of woven fibered bone tissue and parallel-fibered bone tissue is preserved in both pachypleurosaurid genera. The rest of the cortex consists of lamellar-zonal bone tissue type. Differences in the microstructure of the bones between the pachypleurosaurids are reflected in the occurrence of remodelling processes, which, if present, affect the innermost growth marks of the cortex or the calcified cartilaginous core. Further variation is present in the spacing pattern of the growth cycles, as well as in the degree of vascularisation of the lamellar-zonal bone tissue type. Our data on the microstructure of the long bones support previous studies on morphology and facies distribution, which indicated different habitats and adaptation to a secondary aquatic lifestyle for each pachypleurosaurid taxon. Life history data furthermore reflect different longevities and ages at sexual maturity. The bone histological data of the stratigraphically youngest and oldest pachypleurosaurid species might indicate possible climate-dependant reproductive seasons similar to Recent lacertilian squamates.

Redescription of the Sail-backed Poposauroid Ctenosauriscus from the Early Triassic of Germany

Available now at PLoSONE is a redescription of this important historic Triassic taxon which is the namesake of a clade of sail-backed poposauroid archosaurs that have come into recent prominence given the discovery of a well-preserved specimen of Arizonasaurus babbitti in 2002. 

  

Butler, R. J., Brusatte, S. L., Reich, M., Nesbitt, S. J., Schoch, R. R., and J. J. Hornung. 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

 

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.

National Fossil Day

Today is the 2nd annual observance of National Fossil Day. Be sure to check out the official website for lists of events and activities taking place near you, with the biggest event on the National Mall in Washington D. C.

Please join in the activities and have fun!

Visiting Triassic Park - Ischigualasto Parque Triasico in Argentina

Last month I was fortunate to be able to travel to Argentina for some research time and to attend and present at the Fourth Latin American Vertebrate Paleontology Conference in San Juan. Part of the meeting involved a field trip to the nearby Ischigualasto National Park which is famous for its exposures of Triassic rocks and for fossils of some of the earliest dinosaurs including Eoraptor and Herrerasaurus.  As I work at the other Triassic Park, Petrified Forest National Park in Arizona, I was really looking forward to this visit and it did not dissappoint. Below I've posted some photos highlighting my visit. 

 The visitors center includes mounts (below) and life reconstructions (above) of many of the animals found in Triassic strata in the park. There are also exhibits of actual bones.

 Outcrops of the Upper Triassic Ischigualasto Formation. The expanse of the exposures is incredible.

 Bones, the Ischigualasto is full of bones.

 Christian Sidor and Zhe-Xi Luo getting excited about a cynodont skull that Chris found.

 Another in-situ cynodont skull. They are extremely (and amazingly) common here.

 Rhynchosaur bones weathering out. Again, the amount of fossil material in the exposures is staggering. Amazingly rhynchosaurs and cynodonts are so common, they are usually not collected. Working in a formation (the Chinle) where these types of animals are relatively unknown, it was very difficult to leave this material behind.

The younger Los Colorados Formation above the Ischigualsto.

Ischigualsto Park and the Ischigualsto Formation are absolutely incredible and I hope to be able to return someday to make new discoveries.