Field of Science

Jurassic Phytosaur??

A new paper by Maisch and Kapitzke (2010) describes a mandibular fragment from a phytosaur from marine shales in England. This is supposedly the first record of a phytosaur from the Jurassic (Hettangian) as the specimen was found in-situ beneath beds that provide the lowest occurrence of the ammonoid Psiloceras. Thus some phytosaurs, in this case a marine one from Europe, purportedly survived the end-Triassic extinction.

However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.

I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata.  Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians. 

The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.

Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.

Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.

...and one more from the End-Triassic Event.

Mander, L., Kuerschner, W. M., and J. C. McElwain. 2010. An explanation for conflicting records of Triassic–Jurassic plant diversity. PNAS Early Edition, www.pnas.org/cgi/doi/10.1073/pnas.1004207107. Suppl.files at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1004207107/-/DCSupplemental.

Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.

The End-Triassic Extinction Event is Really Popular Right Now....

here is another new paper...

Paris, G., V. Beaumont, A. Bartolini, M.-E. Clémence, S. Gardin, and K. Page. 2010. Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end-Triassic crisis, Doniford section, SW England, Geochemistry, Geophysics, Geosystems 11, Q08021, doi:10.1029/2010GC003161.

Abstract - The Triassic-Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic-walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end-Triassic crisis.

No Single Unambiguous Global End-Triassic Spore Spike

Bonis, N. R., Ruhl, M., and W. M. Kuerschner. 2010. Milankovitch-scale palynological turnover across the Triassic–Jurassic transition at St. Audrie’s Bay, SW UK. Journal of the Geological Society, London 167:877–888. doi: 10.1144/0016-76492009-141.

Abstract - A high-resolution palynological study of the Triassic–Jurassic boundary in the St. Audrie’s Bay section revealed a palynofloral transition interval with four pronounced spore peaks in the Lilstock Formation. Regular cyclic increases in palynomorph concentrations can be linked with periods of increased runoff, and correspond to the orbital eccentricity cycle. Spore peaks can be related to precession-induced variations in monsoon strength. An implication is that the initial carbon isotope excursion lasted for at least 20 ka. Emergence during deposition of the Cotham Member had an influence on one of the peaks, which is dominated by spore-producing pioneer plants (e.g. horsetails and liverworts). There is no compelling evidence of a global end-Triassic spore spike that, by analogy with the K–T boundary fern spike, could be related to a catastrophic mass extinction event. Climate change is a more plausible mechanism to explain the increased amount of spores.

Insights into North American Mesozoic Paleogeography and Paleotectonics

Dickinson, W. R., and G. E. Gehrels. 2010. Insights into North American Paleogeography and Paleotectonics from U–Pb ages of detrital zircons in Mesozoic strata of the Colorado Plateau, USA. International Journal of Earth Sciences 99:1247–1265.

Abstract - Individual U–Pb ages for 5,655 detrital zircons (DZ) in 61 sandstone samples from Mesozoic strata of the Colorado Plateau and nearby areas provide insights into paleogeographic relations across the interior of North America and the paleotectonic evolution of North American continental margins. Pre-Mesozoic DZ grains derived either directly, or ultimately through sediment recycling, from distant sources in eastern North America are more abundant than DZ grains derived from the nearby Cordilleran magmatic arc of western North America. Sediment dispersal patterns included Triassic fluvial transport of detritus westward from the Ouachita orogen uplifted along the northern flank of rift highlands precursor to the oceanic Gulf of Mexico, Jurassic eolian transport southward into widespread ergs from deflation of floodplains of transcontinental paleorivers with headwaters in pre-Atlantic Appalachian highlands, and Jurassic-Cretaceous recycling of eolianite DZ from retroarc Sevier thrust sheets and from sedimentary cover of the Mogollon paleohighlands flanking the Border rift system.

Increased fire activity at the Triassic/Jurassic Boundary Due to Climate Driven Floral Change

Belcher, C. M, Mander, L., Rein, G., Jervis, F. X., Haworth, M., Hesselbo, S. P., Glasspool, I. J., and J. C. McElwain. 2010. Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change. Nature Geoscience 3:426-429.

Abstract - One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers have been linked to a marked increase in atmospheric carbon dioxide levels, probably resulting from massive volcanism in the Central Atlantic Magmatic Province. Future climate change predictions suggest that fire activity may increase, in part because higher global temperatures are thought to increase storminess. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest
flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies.We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.

What I am Currently Reading

I appear to be on an late 19th - early 20th century paleontology fieldwork kick right now regarding the books I am reading.  I just finished Paul Brinkman's "The Second Jurassic Dinosaur Rush" book, which I found to be an enjoyable history of collecting Jurassic dinosaurs from the western U.S. by several institutions.  At times I found it was difficult to follow the chronological order of the work being done, but overall the book is a solid offering of this important time in American vertebrate paleontology.  For more see Brian Switek's recent review.

I am now starting "Bone Hunters in Patagonia" following John Bell Hatcher's work collecting fossil vertebrates in South America during the Princeton University expeditions of 1896-1899.  This is supposedly an absolutely amazing narrative of an amazing collecting trip and I hope I enjoy it thoroughly because...

the next book in the stack is "Barnum Brown: the man who discovered Tyrannosaurus rex" by Lowell Dingus and Mark Norell.  Several colleagues have told me that this is an excellent book.  I had actually started reading this book earlier in the summer and was enjoying it immensely, but stopped to read Paul Brinkman's book when it came out.  Reading Paul's book got me very interested in John Bell Hatcher and thus I've found myself reading "Bone Hunters in Patagonia" before going back to the Barnum Brown book.  I hope I'm not making a mistake here.

Overall, from what I have seen so far these are three great books covering the work of many great American early paleontologists.

Early Triassic Archosaur-dominated Footprint Assemblage from Morocco

Klein, H., Voigt, S., Hminna, A., Saber, H., Schneider, J., and D. Hmich. 2010. Early Triassic Archosaur-Dominated Footprint Assemblage from the Argana Basin (Western High Atlas, Morocco). Ichnos 17:1–13. DOI: 10.1080/10420940.2010.510030 


Abstract - An assemblage of abundant and well-preserved tetrapod footprints has been discovered in the Tanamert Member (T3) of the Triassic Timezgadiouine Formation (Argana basin, western High Atlas, Morocco). It is the first fossil record from T3. Surfaces from different localities show a uniform tetrapod ichnofauna that consists of chirotherian and small lacertoid forms. The chirotherians are assigned to the plexus ProtochirotheriumSynaptichnium, their trackmakers interpreted as basal archosaurs. The lacertoid imprints show close affinities with Rhynchosauroides and may reflect archosauromorphs or lepidosauromorphs. Protochirotherium—Synaptichnium assemblages are characteristic of the Early Triassic and were known previously only from units of this age in central Europe. Biostratigraphically, the European record implies a wide-spread pre-Anisian Protochirotherium—Synaptichnium dominated assemblage preceding the first appearance of Chirotherium barthii near the Olenekian-
Anisian boundary. The stratigraphic position of T3 between Late Permian (uppermost T2) and Middle Triassic (T4) and the European correlatives suggest an Early Triassic age of this unit. It is the first record of Early Triassic continental deposits in Morocco. The surfaces from T3 open up perspectives for further contributions to ecology, biogeography and locomotion of early archosaurs. Furthermore, excellent outcrops and quality of footprint preservation in the Argana basin offer a potential for clarification of ichnotaxonomic and biostratigraphic issues.

The Importance in Understanding Historical Context in Solving Taxonomic Problems - A Case Study With Aetosaurs

Parker, W. G. and Martz, J. W. 2010. Using positional homology in aetosaur (Archosauria: Pseudosuchia) osteoderms to evaluate the taxonomic status of Lucasuchus hunti, Journal of Vertebrate Paleontology 30:1100-1108.

Abstract - The Otis Chalk quarries in the Upper Triassic Dockum Group of West Texas have produced aetosaur material that most workers have suggested represents two distinct morphotypes. We use characters from aetosaur specimens with articulated or semi-articulated carapaces in which the anteroposterior placement of osteoderms can be established with certainty to compare homologous osteoderms in the Otis Chalk material. This study confirms that the genera Longosuchus and Lucasuchus are distinct morphotypes, which differ in that the former taxon has paramedian osteoderms with random pitted ornamentation and low pyramidal bosses that contact the posterior margin, and spines on the lateral osteoderms that are posteriorly emarginated, whereas the latter taxon has paramedians with a strongly radial ornamentation and large conical eminences, and spines on the lateral osteoderms that are not posteriorly emarginated. Both taxa also have paramedians that are overlapped anteriorly by the laterals, a character that may be a synapomorphy of desmatosuchine aetosaurs. The arguments that these morphotypes represent ontogenetic stages or sexual dimorphs of a single biological species cannot be corroborated using either comparisons with modern pseudosuchians, other aetosaur taxa, or stratigraphic ranges. Longosuchus is known only from the type area and has no utility as an index taxon of the Otischalkian land-vertebrate faunachron, although Lucasuchus suggests a tentative correlation between part of the Dockum Group of Texas and the Pekin Formation of North Carolina.

Discussion

Study and management of any resource, including vertebrate fossils, requires in-depth understanding of the context under which previous work on these materials was conducted. For example, where, how, and by whom were the specimens collected? What was their original association? How were they prepared? Who identified them and why did they apply the identification that they did? Often in vertebrate paleontology we are faced with taxonomic questions, which to answer properly we need this detailed contextural information. A good example of this in aetosaurs (the group I mainly work with) is the ongoing debate regarding the proposed synonymy of Longosuchus meadei and Lucasuchus hunti. Much confusion exists regarding the specimens assigned to these taxa, much which stems from the original collection, as well as the subsequent curation and description of these materials. Recently I, along with my co-author Jeffrey Martz, tried to tackle this taxonomic problem and our resulting paper was just published in the most recent issue of the Journal of Vertebrate Paleontology. This article necessitated discussion of the history of the collection, study, and curation of these specimens and unfortunately some of the information I now have did not make it into the final article. At the time this article was in press I came across more important information on the collection and study of these specimens and unfortunately it was too late to add to the introductory section. Some of this new information (from quarry reports and correspondence), included here, clarifies or corrects introductory statements made in our paper.

In the late 1930s and early 1940s a paleontology inventory of portions of Texas was conducted under the Works Progress Administration (WPA), a relief program established by the U.S. Government to put millions of unemployed American men to work. Extensive quarrying was conducted at several sites in Texas including a series of Late Triassic age quarries near Otis Chalk in Howard County. These quarries contained thousands of bones of metoposaurs, phytosaurs, aetosaurs, etc., and are especially known for the well preserved skeletons of the archosauromorph Trilophosaurus buettneri (Gregory, 1945; Elder, 1978; Spielmann et al, 2008). Quarries 3 and 3A contained the majority of the aetosaur material including several partial to fairly complete aetosaur skeletons, only some of which has been prepared. The “best” two skeletons; however, were prepared and subject to a full description by Sawin (1947). Specimen lists compiled at the time of collection as well as work reports reveal that all of the aetosaur material was assigned to the genus Desmatosuchus at the time of collection. Many of the specimens still contain field numbers, which include the county name, quarry number, the year collected, and a fourth number that represents the order in which the specimen was removed from the ground and documented. Furthermore, collection records sometimes provide the name of the collector. Unfortunately, this number just reflects the collection order and often can be ambiguous about the association of specimens in the ground. In our paper we state that no excavation records could be found, but specimen lists and reports have since come to light although no detailed quarry maps are still known to exist.

Workers prepared the two associated skeletons, as well as the articulated tail of a third individual, and a variety of isolated elements. In the final publication (Sawin, 1947) the majority of these specimens are assigned to a new species, Typothorax meadei, based mainly on the sigmoidal shape of the femur (Sawin, 1947). Sawin also recognized a second species, T. coccinarum, as present in the quarry, but restricted this assignment to several osteoderms with large conical dorsal eminences, which he thought resembled the conical eminences in T. coccinarum osteoderms figured and described by von Huene (1915) and originally studied by Cope in 1887. Sawin (1947) designated the two main skeletons (Typothorax meadei) as syntypes and one of the specimens (TMM 31185-84a) was partially incorporated into a museum mount (some of the armor as well as the limbs) along with the articulated tail of the third individual. Much of the remaining material was left identified and catalogued in the collections as Desmatosuchus (contra Parker and Martz, 2010), including many lateral plates which were superficially similar to those of T. meadei. What is important is that none of this material is actually referable to Desmatosuchus (Parker and Martz, 2010).

In an unpublished M.S. thesis Elder (1978) noted this similarity and argued that Desmatosuchus and Typothorax were therefore synonymous. This was later refuted by Small (1989), but what is important to note is that like Sawin, Elder recognized two distinct morphologies in the Otis Chalk material.

Later recognition of the utility of osteoderms ornamentation in aetosaur taxonomy by Long and Ballew (1985) led those workers as well as others (e.g., Small, 1989) to recognize that T. meadei represented a distinct genus from T. coccinarum. Hunt and Lucas (1990) accordingly supplied the name Longosuchus meadei. Curiously, in their renaming of the material and designation of a lectotype Hunt and Lucas (1990) also included the material that Sawin (1947) had assigned to T. coccinarum. Unfortunately, no explanation is given for this and from the article it is not clear if Hunt and Lucas (1990) recognized that some of the material had originally been assigned to a different taxon. They also provide no discussion of the material referred to Desmatosuchus, but infer in their biochronology section that all of the Otis Chalk material belongs to a single taxon.

Subsequent re-examination of the material by Long and Murry (1995) led to the separation of Sawin’s (1947) “T. coccinarum” material as well as the “Desmatosuchus” material from the original T. meadei material of Sawin. Long and Murry (1995) assigned these specimens to a new taxon, Lucasuchus hunti (presumably in return for the name Longosuchus, named for Long). This reassigned was criticized, particularly by Heckert and Lucas (1999, 2000; and in numerous subsequent papers) and Lucas and Heckert (1996) who all stated that the diagnosis of Lucasuchus is “based on minor differences in scute morphology, some so subjective they cannot be replicated”. They also stated that Long and Murry (1995) “split” Longosuchus; however, this is incorrect as they only recognized the originally division of the material set forth by Sawin (1947).

In my own initial examination of the material (Parker, 2003) I felt that there actually were pretty clear differences between the holotype osteoderms of Lucasuchus and Longosuchus, especially in the paramedian osteoderm ornamentation and in the position of the dorsal eminence (see Parker and Martz, 2010). Moreover, although superficially similar there were also key differences between the lateral osteoderms of L. meadei and those catalogued as “Desmatosuchus” and assigned to Lucasuchus by Long and Murry (1995). What was ambiguous; however, was the association of these lateral osteoderms with the Lucasuchus paramedian osteoderms. Although Sawin (1947) felt that there were two morphotypes represented by the paramedian osteoderms in the collections, he clearly stated that no lateral osteoderms were associated with his “T. coccinarum” (Lucasuchus) material.

This last puzzle was solved unintentionally by Ron Tykoski, who while working for the Texas Memorial Museum (TMM) made a small collection of osteoderms to place around the base of the mount. One of the osteoderms he selected was a paramedian of Lucasuchus (TMM 31100-66) and nearby was a lateral osteoderm with the same number. Amazingly these two osteoderms fit together perfectly and unambiguously to form a conjoined pair, and thus must have come from the same individual. Even better, this lateral was of the Lucasuchus morphology and not from Longosuchus. Finally we were able to compare homologous series from both morphotypes to strongly (we feel) demonstrate support for Long and Murry’s (1995) reseparation of the material into two distinct taxa. This was the basis for the entire paper by Parker and Martz (2010).

One final puzzle (at least for me) was why Sawin had assigned the material to Typothorax in the first place? This is where knowledge of the historical context is crucial. At the time the material was collected (1939-1940) there were only three aetosaur taxa known from western North America, Typothorax, Episcoposaurus, and Desmatosuchus. By the time Sawin conducted his study it had been hypothesized by many workers that Episcoposaurus and Desmatosuchus were congeneric, something that was finalized later by Gregory (1953). This was based mainly on the material of Episcoposaurus haplocerus; however, another referred species E. horridus, had been collected in the same general area as the holotype and referred material of Typothorax coccinarum. Personal correspondence between Dr. John Wilson of the TMM and Dr. E. C. Case of the University of Michigan written in the 1940s clarify that Sawin travelled to the American Museum of Natural History to examine Cope’s material of E. horridus and T. coccinarum. This material, figured by Lucas et al (2007) contains two distinct femur morphologies. A gigantic straight femur was referred (by Cope) to E. horridus, whereas a much more gracile and strongly sigmoidal femur was assigned to T. coccinarum. The femora of Longosuchus meadei are nearly identical to that of the referred T. coccinarum specimens contra the statement by Heckert et al. (2010:637) that they are “dramatically different”. It was also on this visit that Sawin noted the conical eminences in the caudal osteoderms of T. coccinarum that formed the basis of his assignment of the Lucasuchus material to that taxon. Thus, finding the Wilson-Case correspondence solves the last part of the puzzle.

I hope that this case provides a good example of how essential understanding the context of the specimens on hand are when we try to determine aspects such as original association, curation, and taxonomy. With this information we can now understand why certain taxonomic assignments were made by past researchers. Allowing ourselves the opportunity to “walk in their boots” of our predecessors for awhile is an important tool in solving important scientific problems.


Paramedian osteoderms of Longosuchus meadei

Paramedian osteoderm of Lucasuchus hunti. Note strong radial patterning and prominent, centralized raised eminence.

REFERENCES

Elder, R. L. 1978. Paleontology and paleoecology of the Dockum Group, Upper Triassic, Howard County, Texas. M.S. thesis, University of Texas, Austin, Texas, 205 pp.

Gregory, J. T. 1945. Osteology and relationships of Trilophosaurus. University of Texas Publication 4401: 273-359.
Gregory, J. T. 1953. Typothorax and Desmatosuchus. Postilla 16:1–27.

Heckert, A. B., and S. G. Lucas. 1999. A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs. Journal of Vertebrate Paleontology 19:50–68.

Heckert, A. B., and S. G. Lucas. 2000. Taxonomy, phylogeny, biostratigraphy, biochronology, paleobiogeography, and evolution of the Late

Triassic Aetosauria (Archosauria: Crurotarsi). Zentralblatt für Geologie und Paläontologie, Teil I, Heft 11–12:1539–1587.

Heckert, A. B. , Lucas, S. G. , Rinehart, L. F. , Celeskey, M. D. , Spielmann, J. A. and Hunt, A. P. 2010. Articulated skeletons of the aetosaur Typothorax coccinarum Cope (Archosauria: Stagonolepididae) from the Upper Triassic Bull Canyon Formation (Revueltian: early-mid Norian), eastern New Mexico, USA. Journal of Vertebrate Paleontology 30:619 — 642

Huene, F. v. 1915. On reptiles of the New Mexican Trias in the Cope collection. Bulletin of the American Museum of Natural History 34:485–507.

Hunt, A. P., and S. G. Lucas. 1990. Re-evaluation of “Typothoraxmeadei, a Late Triassic aetosaur from the United States. Paläontologische Zeitschrift 64:317–328.

Long, R. A., and K. L. Ballew. 1985. Aetosaur dermal armor from the Late Triassic of southwestern North America, with special reference to material from the Chinle Formation of Petrified Forest National Park. Museum of Northern Arizona Bulletin 54:45–68.

Long, R. A., and P. A. Murry. 1995. Late Triassic (Carnian and Norian) tetrapods from the Southwestern United States. New Mexico Museum of Natural History and Science Bulletin 4:1–254.

Lucas, S. G., and A. B. Heckert. 1996. Late Triassic aetosaur biochronology. Albertiana 17:57–64.

Lucas, S. G., J. A. Spielmann, A. B. Heckert, and A. P. Hunt. 2007. Topotypes of Typothorax coccinarum, a Late Triassic aetosaur from the American Southwest. New Mexico Museum of Natural History and Science Bulletin 41:241–247.

Parker, W. G. 2003. Description of a new specimen of Desmatosuchus haplocerus from the Late Triassic of Northern Arizona. M.S. thesis, Northern Arizona University, Flagstaff, 315 pp.

Sawin, H. J. 1947. The pseudosuchian reptile Typothorax meadei. Journal of Paleontology 21:201–238.

Small, B. J. 1989. Aetosaurs from the Upper Triassic Dockum Formation, Post Quarry,West Texas; pp. 301–308 in S. G. Lucas and A. P. Hunt (eds.), Dawn of the Age of Dinosaurs in the American Southwest. New Mexico Museum of Natural History, Albuquerque, New Mexico.

Spielmann, J. A., Lucas, S. G., Rinehart, L. F. and A. B. Heckert. 2008. The Late Triassic archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43: 1–177.

Bite Traces on Dicynodont Bones and the Early Evolution of Large Terrestrial Predators

Niedźwiedzki, G., Gorzelak, P. & Sulej, T. 2010: Bite traces on dicynodont bones and the early evolution of large terrestrial predators. Lethaia, DOI: 10.1111/j.1502-3931.2010.00227.x.


Abstract - Dicynodont (Synapsida: Anomodontia) bones from the Late Triassic (late Norian ⁄ early Rhaetian) of Poland yield characteristic tooth marks that can be attributed to three ichnotaxa (Linichnus serratus, Knethichnus parallelum and Nihilichnus nihilicus). The general shape and dimension of these traces perfectly match the dental morphology of a co-occurring carnivorous dinosaur. It is therefore concluded that early carnivorous dinosaurs were feeding on dicynodonts. This discovery constitutes one of the oldest evidence of dinosaur predator–prey interaction. It is suggested that an evolutionary increase in the size of dicynodonts across the Late Triassic may have been driven by selection pressure to reach a size refuge from early dinosaur predators.

More Triassic Articles From the "New Aspects of Mesozoic Diversity" Book

Kemp, T. 2010. New Perspectives on the Evolution of Late Palaeozoic and Mesozoic Terrestrial Tetrapods; pp. 1-26 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7

Abstract - Palaeobiology, like all sciences, progresses by a combination of the discovery of new information, in this case fossils, the application of new techniques, and the development of new concepts with which to generate novel kinds of hypotheses. Research in the field of Late Palaeozoic and Mesozoic terrestrial tetrapods has involved major advances in all three of these over the last decade or so. Several new discoveries fill in gaps in the evolution of higher tetrapod taxa such as Tetrapoda, Dicynodontia, and birds, while others add significantly to the understanding of patterns of faunal turnover and palaeo-community structure.

The molecular revolution in biology is having a profound effect on several aspects of palaeobiology, in particular the use of large amounts of sequence data for phylogenetic studies and estimating branching dates. In some cases, notably placental mammals, this has produced results that highlight the limitations of purely morphological evidence in this, and probably other cases, and points to the desirability of seeking other kinds of evidence of relationships. Molecular developmental biology is starting to suggest new evolutionary hypotheses about the molecular genetic basis of the evolutionary transitions that can be inferred from the fossil record, such as how the tetrapod limb arose. In the field of functional analysis of fossils, CT scanning has opened the way to the application of such methods as finite element analysis for studying the mechanical design of fossil tetrapod skulls and skeletons. Geochemistry has also introduced new methods, notably stable isotope analysis, that have a direct bearing on the interpretation of the palaeoenvironmental background of major evolutionary events such as mass extinctions.

The principal new concept in palaeobiology arises from a shift towards the systems view that it is the interactions of the parts of a complex system, rather than the nature of the parts themselves that provide the main key to understanding how the system works. Correlated progression is a model based on this concept which offers a more realistic view of major evolutionary transitions such as the origins of tetrapods, mammals, and potentially all the higher taxa of tetrapods. Earth sciences are also moving more towards a systems way of thinking, such as when seeking explanations for mass extinctions.



Ray, S., Bandyopadhyay, S., and R. Appana. 2010. Bone Histology of a Kannemeyeriid Dicynodont Wadiasaurus: Palaeobiological Implications; pp. 73-89 in S. Bandyopadhyay (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7

Abstract - Examination of the bone microstructure of several skeletal elements shows that the cortex comprises fibrolamellar bone tissue suggesting rapid osteogenesis and overall fast growth for Wadiasaurus, a kannemeyeriid dicynodont from India. Three distinct stages have been identified in the ontogeny of Wadiasaurus. In the juvenile stage, when up to 30% of adult size is attained, growth was fast and sustained, whereas in the sub-adult stage when up to 60% of adult size is attained, growth was fast but periodically interrupted as evident from the presence of growth marks. During the adult stage the bone microstructure is characterized by the presence of peripheral parallel-fibred bone that suggested considerable slowing down of growth, possibly with the onset of sexual maturity. A flexible and indeterminate growth strategy is proposed for Wadiasaurus. The cortical thickness (RBT) and the correspondingly low optimal k values of the various limb bones of Wadiasaurus were comparable with that of the land vertebrates such as Ceratotherium, suggesting that the limbs were selected for impact loading.