Field of Science

Redescription of the Holotype Skull of the Late Triassic Rauisuchian Postosuchus kirkpatricki

I'm glad to see this out, the long awaited skull description of the rauisuchian Postosuchus kirkpatricki, which was previously only available in M.S. and PhD theses by Johnathan Weinbaum. The holotype skull was originally described by Chatterjee in 1985; however, repreparation of the material, including the removal of much matrix and plaster, has resulted in the determination of many new features.  It is an absolutely fantastic skull.

One thing I have always wondered is if P. kirkpatricki was named for the Kirkpatrick family, how come no one ever  amended the species name to P. kirkpatrickorum? Although such changes are no longer required by the ICZN, does this still apply to taxa named before the rule change occurred? 

Weinbaum, J.C.2011. The skull of Postosuchus kirkpatricki (Archosauria: Paracrocodyliformes) from the Upper Triassic of the United States. PaleoBios 30: (February 18, 2011)


Abstract - The skull of Postosuchus kirkpatricki Chatterjee 1985 is known from the holotype and paratype specimens along with disassociated skull elements from several Triassic localities in the southwestern and eastern United States. Recent preparation of the holotype skull allows for more careful examination of the cranial elements and comparison with related taxa. This description indicates that Postosuchus shares several previously unrecognized synapomorphies with crocodylomorphs, including fossae and foramina in the dermatocranium that are not present in other basal pseudosuchians. The sutural arrangements of the skull of Postosuchus presented in this paper differ considerably from previous descriptions, due in part to the reassignment of what was previously considered the prefrontal to the palpebral bone. Also, further preparation of skull elements revealed morphologies that differ from previous descriptions. This new description also indicates a close relationship with Polonosuchus silesiacus Sulej 2005. The only autapomorphic characters of the skull are a distinct, rounded lateral ridge on the maxilla and a foramen present in a large fossa on the anteromedial surface of the maxilla.

What Did Triassic Pseudosuchians Eat? Little Ornithodirans of Course!

Here is another scene from the new mural by Victor Leshyk at the Rainbow Forest Museum at Petrified Forest National Park.  In this scene two silesaurs are chased (and one is caught) by a hungry Postosuchus. I just find it so fitting that the tables are turned and it is the dinosaurians getting their due rather than those cool aetosaurs which are always depicted as prey or dead in most Late Triassic themed murals.

Don't Get Too Close to the Water!

The Rainbow Forest Museum at Petrified Forest National Park has a new mural depicting a scene from the lower part (Blue Mesa Member) of the Chinle Formation.  The mural was completed by Sedona artist Victor Leshyk (who also did the Museum of Northern Arizona's therizinosaur exhibit). The centerpiece of this new mural (at least in my eyes) is this moment when an unwary ornithodiran gets a little to close to the rivers edge and becomes a meal for the true rulers of the North American Triassic. I apologize for the poor lighting in the exhibit room (which isn't completely finished yet), but welcome everyone to check out this new scene when you visit the Park.


Cycadalean and Bennettitalean Foliage from the Triassic Madygen Lagerstätte

Moisan, P., Voigt, S., Pott, C., Buchwitz, M., Schneider, J. W., and H. Kerp. 2011. Cycadalean and bennettitalean foliage from the Triassic Madygen Lagerstätte (SW Kyrgyzstan, Central Asia). Review of Palaeobotany and Palynology 164:93-108. doi:10.1016/j.revpalbo.2010.11.008

Abstract - Plant fossils recently collected from the Middle–Late Triassic Madygen Formation in SW Kyrgyzstan, Central Asia are described in detail. Based on the combination of gross morphology and epidermal/cuticular anatomy, four different taxa are identified, assigned to the Cycadales, i.e. Pseudoctenis lanei and Bennettitales, Pterophyllum pinnatifidum, P. firmifolium and Otozamites sp. All taxa are new for the Madygen Formation. Remarkable is the first occurrence of Pseudoctenis and two Pterophyllum species in the Triassic of Central Asia. The fossils are generally well preserved, but without cuticles. Nevertheless, epidermal and cuticular features can be recognized because the cuticles left behind imprints in the very fine-grained matrix. Silicon casts, examined under a stereomicroscope and with SEM, revealed xeromorphic features that are traditionally considered as indicators of arid conditions. However, comparisons of the functionality of the xeromorphic features in living plants show that these features occur in xerophytic, as well as in hygrophytic and halophytic plants. Sedimentological data from Madygen show that the fossil flora grew in alluvial plains, delta plains, and shallow lacustrine environments. The xeromorphic features are consequently interpreted as functional adaptations to environmental influences involved in the self-cleaning of the leaf surface, regulation of excessive radiation and leaf temperature and as an effective mechanical defense against phytophagous insects.

Carbon-isotope Variability of Triassic Amber, as Compared with Wood and Leaves

Dal Corso, J., Preto, N., Kustatscher, E., Mietto, P., Roghi, G., and H. C. Jenkyns. In Press Carbon-isotope variability of Triassic amber, as compared with wood and leaves (Southern Alps, Italy). Palaeogeography, Palaeoclimatology, Palaeoecology(2011).  doi:10.1016/j.palaeo.2011.01.007

Abstract - The carbon-isotope signatures of Carnian (Late Triassic) amber drops from Rifugio Dibona (Southern Alps, Italy) were studied and compared with that of other Middle-early Late Triassic fossil plant remains, namely wood and leaves. Amber, wood and leaf carbon-isotope data are highly variable within the same beds. δ13Camber values vary by up to 5.4‰ and are enriched by ~ 2.5‰ with respect to associated wood. δ13Cwood and δ13Cleaf ranges are narrower than that of amber (~ 2–3‰) and the isotopic offset within each bed is similar over time. The high Triassic amber carbon-isotope variability is similar to that of recent resin. Despite the high variability, δ13Cwood and δ13Cleaf illustrate a Middle-early Late Triassic secular positive trend that is similar to that of marine δ13Cinorg data and must record the carbon-isotope evolution of the ocean–atmosphere system.

Two New Papers on the Timing of the Placement of the Central Atlantic Magmatic Province

Marzoli, A., Jourdan, F., Puffer, J. H., Cupponea, T., Tanner, L. H., Weems, R. E., Bertrand, H., Cirilli, S., Bellienia, G., and A. De Minh. 2011. Timing and duration of the Central Atlantic magmatic province in the Newark and Culpeper basins, eastern U.S.A. Lithos 122:175-188. doi:10.1016/j.lithos.2010.12.013

Abstract - New major and trace element data and 40Ar/39Ar plateau ages constrain the timing, duration and time-related geochemical evolution of the Central Atlantic magmatic province in the U.S.A. (Newark and Culpeper basins) and refine correlations with basaltic lava flows from other Late Triassic–Early Jurassic circum-Atlantic basins. The precise, statistically robust 40Ar/39Ar plateau ages were obtained on biotite and on fresh plagioclase and calculated using the latest 40K decay constants. These ages are supported by a general consistency of the Ca/K calculated from 37Ar/39Ar of the plateau steps and the Ca/K obtained by detailed electron microprobe analyses on plagioclase phenocrysts. The ages of five analyzed basalt lava flows, from all three lava flow units in the Newark basins, and the ages of two sill samples are indistinguishable, indicating a brief magmatic peak phase at 201.8 ± 0.7 Ma. Recalibrated 40Ar/39Ar plateau ages from the entire province indicate a near-synchronous onset and peak volcanic activity at the Triassic–Jurassic boundary within the circum-Atlantic basins from the U.S.A., Canada and Morocco. The early erupted magmas (Moroccan Lower to Upper basalts, the Fundy basin North Mountain Basalt, and Orange Mountain and equivalent U.S.A. flows) yield an enriched geochemical signature (e.g., with relatively high La/Yb), whereas late magmas in the U.S.A. (Hook Mountain and Hampden basalts) and Morocco (Recurrent basalt) yield relatively depleted geochemical compositions (low La/Yb). A slight, but significant age difference for eruption of Hook Mountain and Hampden basalts (200.3 ± 0.9 Ma) and Recurrent basalts (198.2 ± 1.1 Ma) is interpreted as evidence of a diachronous northward rift–drift transition during break-up of Pangea. Our data indicate also a prolonged intrusive sequence that continued until about 195 Ma at the Palisades sill and is consistent with sporadic late CAMP magmatism for dykes from the south-eastern U.S.A. and for intrusions from Guinea.

Merle, R., Marzoli, A., Bertrand, H., Reisberg, L., Verati, C., Zimmermann, C., Chiaradia, M., Bellieni, G., and M. Ernesto. 2011. 40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from Western Maranhão basin (NE Brazil). Lithos 122:137-151. doi:10.1016/j.lithos.2010.12.010

Abstract - The Central Atlantic Magmatic Province (CAMP), emplaced at the Triassic–Jurassic (T–J) boundary (~ 200 Ma), is among the largest igneous provinces on Earth. The Maranhão basin in NE Brazil is located around 700 km inland and 2000 km from the site of the earliest Pangea disruption. The CAMP tholeiites occur only in the western part of the basin and have been described as low and high-Ti. Here we document the occurrence of two sub-groups among the high-Ti tholeiites in the Western Maranhão basin. The major and trace elements and the Sr–Nd–Pb isotopic ratios define three chemical groups corresponding to the low-Ti (TiO2 < 1.3 wt.%), high-Ti (TiO2 ~ 2.0 wt.%) and evolved high-Ti (TiO2 > 3 wt.%) western Maranhão basin tholeiites (WMBT). The new 40Ar/39Ar plateau ages obtained on plagioclase separates for high-Ti (199.7 ± 2.4 Ma) and evolved high-Ti WMBT (197.2 ± 0.5 Ma and 198.2 ± 0.6 Ma) are indistinguishable and identical to those of previously analyzed low-Ti WMBT (198.5 ± 0.8 Ma) and to the mean 40Ar/39Ar age of the CAMP (199 ± 2.4 Ma). We also present the first Re–Os isotopic data for CAMP basalts. The low and high-Ti samples display mantle-like initial (187Os/188Os)i ranging from 0.1267 to 0.1299, while the evolved high-Ti samples are more radiogenic ((187Os/188Os)i up to 0.184) We propose that the high-Ti WMBT were derived from the sub-lithospheric asthenosphere, and contaminated during ascent by interaction with the subcontinental lithospheric mantle (SCLM). The evolved high-Ti WMBT were derived from the same asthenospheric source but experienced crustal contamination. The chemical characteristics of the low-Ti group can be explained by partial melting of the most fertile portions of the SCLM metasomatized during paleo-subduction. Alternatively, the low-Ti WMBT could be derived from the sub-lithospheric asthenosphere but the resulting melts may have undergone contamination by the SCLM. The occurrences of high-Ti basalts are apparently not restricted to the area of initial continental disruption which may bring into question previous interpretations such as those relating high-Ti CAMP magmatism to the initiation of Atlantic ridge spreading or as the expression of a deep mantle plume. We propose that the CAMP magmatism in the Maranhão basin may be attributed to local hotter mantle conditions due to the combined effects of edge-driven convection and large-scale mantle warming under the Pangea supercontinent. The involvement of a mantle-plume with asthenosphere-like isotopic characteristics cannot be ruled out either as one of the main source components of the WMBT or as a heat supplier.

End-Permian Biotic Disturbances: Floral Changes From the Permian Through Middle Triassic of Pakistan

Hermann, E., Hochuli, P. A., Bucher, H., Brühwiler, Hautmann, M., Ware, D., and G. Roohi. In Press. Terrestrial ecosystems on North Gondwana following the end-Permian mass extinction. Gondwana Research (2011). doi:10.1016/j.gr.2011.01.008
 Abstract - The impact of the end-Permian mass extinction on terrestrial ecosystems is still highly controversial. Here, new high-resolution palynological data from biostratigraphically well-dated Upper Permian to Middle Triassic successions of the Salt Range and Surghar Range (Pakistan) are presented. Our results reveal seven successive floral phases between the Late Permian and the Middle Triassic. At the onset of the Mesozoic, the flora is characterised by high abundances of lycopods associated with pteridosperms and conifers. This association prevails up to the middle Smithian and is followed by a prominent spore spike similar to the global spore spike reported from the Permian-Triassic boundary. Like that of the end-Permian, the middle Smithian spore spike is associated with a negative isotope excursion and is succeeded by a major marine faunal extinction event in the late Smithian. The recurrent patterns observed at the Permian-Triassic boundary and in the middle–upper Smithian suggest a common cause such as massive ejections of volcanic gases. The increasing abundance of conifers still associated with common lycopods in the Spathian suggests fading volcanically induced environmental perturbations and stabilisation of terrestrial ecosystems ca. 2.1 My after the end-Permian event.




Revised Biostratigraphy-based Correlations for Determining the Position of the TR/J Boundary on the Colorado Plateau

This is an online published corrected proof utilizing paleomagnetic and biostratigraphic data to attempt to precisely locate the Triassic/Jurassic boundary in terrestrial strata of the Colorado Plateau in the Western U.S.  It provides corrections based on conchostracan biostratigraphy for previous proposed correlations to other global magnetostrat sections presented in a paper just published by many of the same authors this last October. Unfortunately, because of a lack of isotopic dates to calibrate the magnetostrat sections and the limitations of biostratigraphy for such correlations (e.g., Irmis et al., 2010; Olsen et al., in press), it is not yet clear how reliable these corrections are.

One interesting conclusion of this paper is that pseudosuchian extinctions and the first appearance of large theropod dinosaurs (represented by the ichnotaxon Eubrontes) may have occurred within the Late Triassic and not at or even near the Triassic-Jurassic boundary. Of course this observation is simply a result of moving the TR/J boundary upwards in terrestrial strata.

Lucas, S.G., Tanner, L.H., Donohoo-Hurley, L.L., Geissman, J.W., Kozur, H.W., Heckert, A.B., Weems, R.E.in press. Position of the Triassic-Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA, Palaeogeography, Palaeoclimatology, Palaeoecology (2011). doi: 10.1016/j.palaeo.2011.01.009

Abstract - Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah–Arizona, U.S.A., represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic–Jurassic boundary. We present a synthesis of new biostratigraphic and magnetostratigraphic data collected from across the Moenave Formation outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These data include palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four overlapping magnetostratigraphic sections. Placement of the Triassic–Jurassic boundary in strata of the Moenave Formation has long been imprecise and debatable, but these new data (especially the conchostracans) allow us to place the Triassic–Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation, stratigraphically well above the highest occurrence of crurotarsan body fossils or footprints. Correlation to marine sections based on this placement indicates that major terrestrial vertebrate extinctions preceded marine extinctions across the Triassic–Jurassic boundary and therefore were likely unrelated to the Central Atlantic Magmatic Province (CAMP) volcanism.

REFERENCES

Donohoo-Hurley, L. L., Geissman, J. W., and S. G. Lucas. 2010. Magnetostratigraphy of the uppermost Triassic and lowermost Jurassic Moenave Formation, western United States: Correlation with strata in the United Kingdom, Morocco, Turkey, Italy, and eastern United States. Geological Society of America Bulletin 122: 2005-2019; doi: 10.1130/B30136.1

Irmis, R. B., Martz, J. W., Parker, W. G., and S. J. Nesbitt. 2010. Re-evaluating the correlation between Late Triassic terrestrial vertebrate biostratigraphy and the GSSP-defined marine stages. Albertiana 38:40-52.

Olsen, P. E., Kent, D. V., and J. H. Whiteside. In Press. Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria. Environmental and Earth Science Transactions of the Royal Society of Edinburgh.

Cynodont Burrows from the Upper Triassic of Poland

Tałanda, M., Dzieçioł, S., Sulej, T., and G. Niedźwiedzki. 2011. Vertebrate burrow system from the Upper Triassic of Poland. Palaios 26:99-105. DOI: 10.2110/palo.2010.p10-024r
 Abstract - In this paper we report on a rare fossil vertebrate burrow system in Upper Triassic (Norian) fluvial deposits of the Holy Cross Mountains in central Poland. The burrows are preserved mainly by prominent green infillings in red mudstone and claystone exposed in the wall of a clay pit. The mode of occurrence, morphology, and size of the burrows suggests that cynodont therapsids most likely constructed them.


Procolophonid-like Tetrapod from the Middle Triassic of Germany

Schoch, R. R. 2011. A procolophonid-like tetrapod from the German Middle Triassic. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 259: 251–255. DOI: 10.1127/0077-7749/2011/0124
Abstract - A new find of a tetrapod mandible with unique teeth is reported from the Middle Triassic Lower Keuper. The outline of the dentary, morphology of the teeth and their emplacement suggest that the remain represents a new procolophonid parareptile. The abbreviated dentary, the high coronoid process, and the shape of the teeth resemble those of leptopleuronines. Unique features are the crown morphology, marked parallel striations, the possession of two similar, very large durophagous teeth, the edentulous anterior portion, and the lack of a coronoid suture. Thus, although the jaw resembles procolophonids in some features, it is argued that referral to this group needs recognition of more clearly established character-states, prompting the search for more complete material in the same deposits.

Albinykus baatar, a New Small Alverezsaurid From the Late Cretaceous of Mongolia

I know it's not Triassic, but I have to give props to my friends, colleague, and two of my grad school advisors!

Nesbitt, S. J., Clarke, J. A., Turner, A. H., and M. A. Norell. 2011. A small alvarezsaurid from the eastern Gobi Desert offers insight into evolutionary patterns in the Alvarezsauroidea. Journal of Vertebrate Paleontology 31:144-153. DOI: 10.1080/02724634.2011.540053

Abstract - A partial postcranial skeleton of a small alvarezsaurid from the Late Cretaceous of the Mongolian eastern Gobi Desert locality of Khugenetslavkant represents the first reported articulated theropod material from that locality. The specimen is recognized as the holotype of a new taxon herein named Albinykus baatar, gen. et sp. nov. Phylogenetic analysis places Albinykus within Alvarezsauridae as the sister taxon of Shuvuuia, another Late Cretaceous Mongolian taxon from the slightly younger Djadokhta Formation. The complete coossification of the proximal tarsals with the tibia, and of the distal tarsals and proximal metatarsals, present in Albinykus are previously unknown in Alvarezsauridae. Extensive fusion is consistent with histological data from the tibia indicating that the individual was a subadult. These results are striking given that Albinykus is among the smallest known non-avian dinosaurs with a body mass no greater than 1 kg and ranks among the smallest known alvarezsaurids. Alvarezsauridae shows a decreasing size trend throughout its evolutionary history, a rarity among dinosaurian clades. Within maniraptoran dinosaurs, such a trend has thus far only been recognized within Avialae and at the origin of Paraves with respect to other coelurosaurs. The holotype was recovered articulated in a 'seated' position, with hind limbs aligned and the feet tucked under the body. This body posture, which is present in Aves, has been previously noted in other maniraptoran clades (i.e., Oviraptoridae Troodontidae) and is now recognized in Alvarezsauridae.

Recovering Missing Morphological Data in Vertebrate Animals

An interesting new paper that proposes a method using regression equations to determine the position of preserved vertebrae in the caudal region (tail) of the herrerasaurid Staurikosaurus pricei and also provides estimates for the number and dimensions of missing vertebral elements.

Grillo, O. N., and S. A.K. Azevedo. in press.Recovering missing data: estimating position and size of caudal vertebrae in Staurikosaurus pricei Colbert, 1970. Anais da Academia Brasileira de Ciências ahead of print Epub Feb 04, 2011. doi: 10.1590/S0001-37652011005000003  



Abstract - Missing data is a common problem in paleontology. It makes it difficult to reconstruct extinct taxa accurately and restrains the inclusion of some taxa on comparative and biomechanical studies. Particularly, estimating the position of vertebrae on incomplete series is often non-empirical and does not allow precise estimation of missing parts. In this work we present a method for calculating the position of preserved middle sequences of caudal vertebrae in the saurischian dinosaur Staurikosaurus pricei, based on the length and height of preserved anterior and posterior caudal vertebral centra. Regression equations were used to estimate these dimensions for middle vertebrae and, consequently, to assess the position of the preserved middle sequences. It also allowed estimating these dimensions for non-preserved vertebrae. Results indicate that the preserved caudal vertebrae of Staurikosaurus may correspond to positions 1-3, 5, 7, 14-19/15-20, 24-25/25-26, and 29-47, and that at least 25 vertebrae had transverse processes. Total length of the tail was estimated in 134 cm and total body length was 220-225 cm.

"Fossil Time Capsules": Opening 70 Year Old Jackets of Triassic Fossils at the University of Texas at Austin

"The new quarry is looking damn good," wrote [paleontologist Grayson] Meade to his colleague Glen Evans in May 1940. "[W]e have found quite a portion of a partially articulated phytosaur skeleton. About four or five feet of the vertebrae are mostly in articulation. There are leg bones, some ribs, and the mandible. ? There is every indication that the skull should be there, and more of the skeleton. I didn't reach the end of it knowingly at any rate."

You can read the rest of this story here. There are dozens of unopened jackets of fossils collected in the late 1930s and early 40s in the basement of the Vertebrate Paleontology Lab at UT Austin.  I've previously published on some of the prepared material and it is all just spectacular.  These specimens are especially important because the Otis Chalk quarries are possibly older than any Chinle Formation exposures and might be giving us a unique view into latest Carnian or earliest Norian faunal assemblages in the western U.S. I cannot wait to see what the rest of those jackets hold!

Kudos to my friends and colleagues Michelle Stocker and Sterling Nesbitt for their opportunity to work on these fossils and at the original quarries.

What End-Permian Terrestrial Mass Extinction? Negative Evidence from South China

Xiong, C., and Q. Wang. 2011. Permian–Triassic land-plant diversity in South China: Was there a mass extinction at the Permian/Triassic boundary? Paleobiology 37:157-167; DOI: 10.1666/09029.1


Abstract - Diversity dynamics of the Permian–Triassic land plants in South China are studied by analyzing paleobotanical data. Our results indicate that the total diversity of land-plant megafossil genera and species across the Permian/Triassic boundary (PTB) of South China underwent a progressive decline from the early Late Permian (Wuchiapingian) to the Early-Middle Triassic. In contrast, the diversity of land-plant microfossil genera exhibited only a small fluctuation across the PTB of South China, showing an increase at the PTB. Overall, land plants across the PTB of South China show a greater stability in diversity dynamics than marine faunas. The highest extinction rate (90.91%) and the lowest origination rate (18.18%) of land-plant megafossil genera occurred at the early Early Triassic (Induan), but the temporal duration of the higher genus extinction rates (>60%) in land plants was about 23.4 Myr, from the Wuchiapingian to the early Middle Triassic (Anisian), which is longer than that of the coeval marine faunas (3–11 Myr). Moreover, the change of genus turnover rates in land-plant megafossils steadily fluctuated from the late Early Permian to the Late Triassic. More stable diversity and turnover rate as well as longer extinction duration suggest that land plants near the PTB of South China may have been involved in a gradual floral reorganization and evolutionary replacement rather than a mass extinction like those in the coeval marine faunas.