Field of Science

Diverse New Microvertebrate Assemblage from the Late Triassic of North Carolina


Heckert, A. B., Mitchell, J. S., Schneider, V. P., and P. E. Olsen. 2012. Diverse New Microvertebrate Assemblage from the Upper Triassic Cumnock Formation, Sanford Subbasin, North Carolina, USA. Journal of Paleontology 86(2): 368-390 doi: http://dx.doi.org/10.1666/11-098.1


Abstract - The Moncure microvertebrate locality in the Cumnock Formation, Sanford sub-basin, North Carolina, dramatically increases the known Late Triassic age vertebrate assemblage from the Deep River Basin. The 50,000 recovered microvertebrate fossils include osteichthyans, amphibians, and numerous lepidosauromorph, archosauriform, and synapsid amniotes. Actinopterygian fossils consist of thousands of scales, teeth, skull, and lower jaw fragments, principally of redfieldiids and semionotids. Non-tetrapod sarcopterygians include the dipnoan Arganodus sp., the first record of lungfish in the Newark Supergroup. Temnospondyls are comparatively rare but the preserved centra, teeth, and skull fragments probably represent small (juvenile) metoposaurids. Two fragmentary teeth are assigned to the unusual reptile Colognathus obscurus (Case). Poorly preserved but intriguing records include acrodont and pleurodont jaw fragments tentatively assigned to lepidosaurs. Among the archosauriform teeth is a taxon distinct from R. callenderi that we assign to Revueltosaurus olseni new combination, a morphotype best assigned to cf. Galtonia, the first Newark Supergroup record of Crosbysaurus sp., and several other archosauriform tooth morphotypes, as well as grooved teeth assigned to the recently named species Uatchitodon schneideri. Synapsids represented by molariform teeth include both “traversodontids” assigned to aff. Boreogomphodon and the “dromatheriid” Microconodon. These records are biogeographically important, with many new records for the Cumnock Formation and/or the Newark Supergroup. In particular, Colognathus, Crosbysaurus, and Uatchitodon are known from basins of Adamanian age in the southwestern U.S.A. These new records include microvertebrate taxa more typical of non-Newark basins (abundant archosauriforms, temnospondyls, lungfish) as well as more typical Newark osteichthyans and synapsid-rich faunal elements.

Photos of Preserved Permian Forest

http://gizmodo.com/5887454/first-photos-of-chinas-298+million+year+old-buried-forest

Amazing Preservation of a Permian Forest Redux


Here is the abstract and link (open access) to the previously mentioned article.  It is too bad that with instantaneous preservation of a Permian ecosystem that no animals are mentioned as found. I also mistakenly stated in my previous post that the site was in China. It is actually from Mongolia.

Wang, J., Pfefferkorn, H. W., Zhang, Y., and Z. Feng. 2012.  Permian vegetational Pompeii from Inner Mongolia and its implications for landscape paleoecology and paleobiogeography of Cathaysia. PNAS, published online before print. doi: 10.1073/pnas.1115076109 


Abstract - Plant communities of the geologic past can be reconstructed with high fidelity only if they were preserved in place in an instant in time. Here we report such a flora from an early Permian (ca. 298 Ma) ash-fall tuff in Inner Mongolia, a time interval and area where such information is filling a large gap of knowledge. About 1,000 m2 of forest growing on peat could be reconstructed based on the actual location of individual plants. Tree ferns formed a lower canopy and either Cordaites, a coniferophyte, or Sigillaria, a lycopsid, were present as taller trees. Noeggerathiales, an enigmatic and extinct spore-bearing plant group of small trees, is represented by three species that have been found as nearly complete specimens and are presented in reconstructions in their plant community. Landscape heterogenity is apparent, including one site where Noeggerathiales are dominant. This peat-forming flora is also taxonomically distinct from those growing on clastic soils in the same area and during the same time interval. This Permian flora demonstrates both similarities and differences to floras of the same age in Europe and North America and confirms the distinct character of the Cathaysian floral realm. Therefore, this flora will serve as a baseline for the study of other fossil floras in East Asia and the early Permian globally that will be needed for a better understanding of paleoclimate evolution through time.


Amazing Preservation of a Permian Forest

The upcoming issue of PNAS has an article documenting amazing preservation of a Permian paleobotanical locality in China, the result of rapid burial by volcanic ash.  The actual article is not up yet but you can read about the study here.

Reassessment of the Triassic "Bee Nest" from Petrified Forest National Park

Tapanila, L., and E. M. Roberts. 2012. The earliest evidence of holometabolan insect pupation in conifer wood. PLoS ONE 7(2): e31668. doi:10.1371/journal.pone.0031668.

Background

The pre-Jurassic record of terrestrial wood borings is poorly resolved, despite body fossil evidence of insect diversification among xylophilic clades starting in the late Paleozoic. Detailed analysis of borings in petrified wood provides direct evidence of wood utilization by invertebrate animals, which typically comprises feeding behaviors.

Methodology/Principal Findings

We describe a U-shaped boring in petrified wood from the Late Triassic Chinle Formation of southern Utah that demonstrates a strong linkage between insect ontogeny and conifer wood resources. Xylokrypta durossi new ichnogenus and ichnospecies is a large excavation in wood that is backfilled with partially digested xylem, creating a secluded chamber. The tracemaker exited the chamber by way of a small vertical shaft. This sequence of behaviors is most consistent with the entrance of a larva followed by pupal quiescence and adult emergence — hallmarks of holometabolous insect ontogeny. Among the known body fossil record of Triassic insects, cupedid beetles (Coleoptera: Archostemata) are deemed the most plausible tracemakers of Xylokrypta, based on their body size and modern xylobiotic lifestyle.

Conclusions/Significance

This oldest record of pupation in fossil wood provides an alternative interpretation to borings once regarded as evidence for Triassic bees. Instead Xylokrypta suggests that early archostematan beetles were leaders in exploiting wood substrates well before modern clades of xylophages arose in the late Mesozoic.

Best Practices for Justifying Fossil Calibrations

This is a pretty substantial article from a large number of authors working in a variety of taxonomic groups regarding the proper presentation of data when looking at historical patterns in paleontology and geology. This is a must read for anyone using fossils to calibrate anything.

Parham, J. F., et al. 2012. Best practices for justifying fossil calibrations. Systematic Biology. doi: 10.1093/sysbio/syr107 [open access].

First Evidence of Late Triassic Dicynodonts from Germany

Schoch, R. R. 2012. A dicynodont mandible from the Triassic of Germany forms the first evidence of large herbivores in the Central European Carnian. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 26:119-123. DOI: http://dx.doi.org/10.1127/0077-7749/2012/0216


Abstract - A new partial mandible from the Schilfsandstein (Stuttgart Formation, Middle Carnian) of southern Germany forms the first unambiguous evidence of dicynodonts in the German Triassic. The preserved anterior part of the mandible is most consistent with kannemeyeriiform dicynodonts known from the Middle and Late Triassic of South America, southern Africa, North America, and the Eastern European Platform. Extrapolation of body size from the mandible indicates that the Schilfsandstein dicynodont was moderately large (∼2m estimated body length). This find is significant as it forms the first evidence of large herbivores in the Carnian pre-dinosaur faunas of Central Europe.         

Timing of the Earliest Known Feathered Dinosaurs



Edging a bit closer......


Liu, Y.-Q., Kuang, H.-W., Jiang, X.-J., Peng, N., Xu, H.,  and H.-Y. Sun. 2012. Timing of the earliest known feathered dinosaurs and transitional pterosaurs older than the Jehol Biota. Palaeogeography, Palaeoclimatology, Palaeoecology (advance online publication) http://dx.doi.org/10.1016/j.palaeo.2012.01.017


Abstract - The Early Cretaceous Jehol Biota in China has produced numerous well preserved fossils of feathered theropods and early birds. Recent discoveries of feathered dinosaurs, as well as transitional pterosaurs and a sexually mature individual of Darwinopterus preserved together with an egg from the Daohugou Biota of an earlier age than the Jehol Biota, in northeastern China, have greatly enriched our knowledge of the transition from dinosaurs to birds and primitive to derived pterosaurs. The age estimate of fossils or host strata, however, has proven to be contentious and varies widely from the Middle Jurassic to the Early Cretaceous. Here, we report a SHRIMP U-Pb zircon date unambiguously associated with the fossil horizons, and thus, for the first time, provide an age calibration for the earliest appearance of feathered dinosaurs and transitional pterosaurs. Date results indicate that the feathered dinosaurs of China were present more than 161 Ma ago, unquestionably older than Archaeopteryx in Germany, and are the earliest known feathered dinosaurs in the world. Furthermore, feathers appeared in ornithischians before 159 Ma rather than late in the Early Cretaceous. The known transitional pterosaurs first emerged before 161 Ma. The Daohugou Biota, containing mammals, primitive pterosaurs, insects and plants, in addition to the feathered dinosaurs, was living in Inner Mongolia, western Liaoning and northern Hebei in northeastern China during the Middle Jurassic.

Guest Post - Roland Sookias Discusses His New Study Examining How Dinosaurs Came to Fill Most Ecological Niches During the Mesozoic

Why were dinosaurs, and other archosauromorphs (the group of animals including crocodiles, dinosaurs, pterosaurs and several other extinct groups), so big? Was natural selection for increasing size responsible for archosauromorphs’ dramatic rise to larger sizes and did selection for decreasing size drive therapsids’ (‘mammal-like reptiles’, which were the dominant land vertebrates before archosauromorphs) reduction in size during the Triassic (see picture)? These are the questions which my, Richard Butler’s and Roger Benson’s recent publication in Proceedings of the Royal Society B – “Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution” – attempts to answer.
   
Most of the work in the paper was done as part of my MSc thesis project, which Richard, Roger and Andrew Smith supervised. To carry out the project I spent a good deal of last summer collecting femur and skull length measurements (which we used as proxies for body mass) in the Natural History Museum Library, London. Though barely seeing daylight for a month or two, I managed to collect measurements for ~200 species, which, in combination with data from Benson et al. 2011 got us to >400 species in total. To answer the questions above we focused on getting data for archosauromorphs and therapsids from the Late Permian to Middle Jurassic. This allowed comparison between the two groups, and the interval brackets the rise of archosauromorphs to become the dominant terrestrial vertebrates, replacing therapsids. Thus it allowed us to look at body size evolutionary dynamics during a major faunal transition.


Archosauromorphs (dinosaurs, crocodiles, pterosaurs and their relatives) increased greatly in maximum size (black line, black triangles) from the Permian to Jurassic, and therapsids (‘mammal-like reptiles’) decreased. However in both this was due to expansion in the size variance (i.e. both size increase and decrease), but with subsequent extinction of larger therapsid species. Figure from Sookias et al. 2012, Proc Roy Soc B.

Once we’d got the data together we analysed them using maximum likelihood model fitting approaches. We tried both phylogenetic – i.e. incorporating evolutionary relationships – and time series (ignoring within-group evolutionary relationships and simply averaging size within time ‘bins’) models. Time series models confirmed that on average archosauromorphs tended to increase across the time interval, and that therapsids got smaller. However when we included phylogeny (evolutionary relationships) we found that there was no directional trend in either group along individual lineages. Thus the apparent trends through time were in fact due to ‘passive expansion’ in size, but as the original size was nearer the bottom than the top of the eventual size range the average size tended to increase (see picture). We thus can say that the long-repeated idea of “Cope’s rule” – that taxa in a clade tend to get larger over time due to within-lineage natural selection for larger body sizes – is not found in either archosauromorphs or therapsids during this time interval.

Our work excludes larger size in archosauromorphs as an explanation for their success, as if larger size was especially beneficial one would expect a directional evolutionary trend towards larger sizes. Instead, archosauromorphs probably replaced therapsids opportunistically, as many have hypothesized before. However, the exceptionally high growth, and thus reproductive, rates of archosauromorphs may have allowed them to re-fill empty ecological niches especially easily and rapidly after they went empty due to extinction of therapsids. Thus, while size and growth rate probably did not allow archosauromorphs to outcompete therapsids, it did allow them to fill up free niches quickly.

We also found that archosauromorph predators exceeded the size of the largest herbivores – anomodont therapsids – during the Middle-early Late Triassic. This finding – that the largest carnivores are larger than herbivores - is extremely rare in ecosystems throughout time. It demonstrates that extinct archosauromorphs really were exceptionally large, and that they were able to grow to larger sizes than therapsids given the same resources.

Well, there’s not much more to say about that paper except hope you enjoy it! However, we should be publishing some more work based on my MSc thesis in the near future, so stay tuned, and I’ve just started a PhD with Richard Butler on the early archosauromorph radiation, so hopefully I’ll be involved in answering a few more interesting questions in the coming years. Finally, a very big thank you to Bill Parker for giving us a guest slot here on the esteemed Chinleana.

The paper’s full citation is:


Sookias, R. B., Butler, R. J., Benson, R. B. J. (2012). Rise of dinosaurs reveals major body size transitions are driven by passive processes of trait evolution. Proceedings of the Royal Society B.
doi: 10.1098/rspb.2011.2441 



Abstract- A major macroevolutionary question concerns how long-term patterns of body-size evolution are underpinned by smaller scale processes along lineages. One outstanding long-term transition is the replacement of basal therapsids (stem-group mammals) by archosauromorphs, including dinosaurs, as the dominant large-bodied terrestrial fauna during the Triassic (approx. 252–201 million years ago). This landmark event preceded more than 150 million years of archosauromorph dominance. We analyse a new body-size dataset of more than 400 therapsid and archosauromorph species spanning the Late Permian–Middle Jurassic. Maximum-likelihood analyses indicate that Cope’s rule (an active within-lineage trend of body-size increase) is extremely rare, despite conspicuous patterns of body-size turnover, and contrary to proposals that Cope’s rule is central to vertebrate evolution. Instead, passive processes predominate in taxonomically and ecomorphologically more inclusive clades, with stasis common in less inclusive clades. Body-size limits are clade-dependent, suggesting intrinsic, biological factors are more important than the external environment. This clade-dependence is exemplified by maximum size of Middle–early Late Triassic archosauromorph predators exceeding that of contemporary herbivores, breaking a widely accepted ‘rule’ that herbivore maximum size greatly exceeds carnivore maximum size. Archosauromorph and dinosaur dominance occurred via opportunistic replacement of therapsids following extinction, but were facilitated by higher archosauromorph growth rates.



Popular press coverage:

http://news.discovery.com/animals/how-dinosaurs-got-so-big-120131.html

http://news.sciencemag.org/sciencenow/2012/01/the-secret-of-dinos-success.html?ref=hp