Rediscovered Specimen Draws Dinosaur Origins Down Into the Middle Triassic

I've been peripherally involved in the recent renaissance regarding dinosaur origins since my discovery of the skeleton of Revueltosaurus callenderi in 2004 and the subsequent recognition that it was not a dinosaur. With my good friends and colleagues Sterling Nesbitt and Randall Irmis, I proceeded to reexamine much of the Late Triassic dinosaur record using an apomorphy-based approach emphasized by UT Austin professor Chris Bell and his colleagues for Neogene vertebrates. Our findings were that Triassic dinosaurs were actually rarer than previously believed, especially in North America. In addition, extensive fieldwork by Sterling and Randy led to the discoveries of Dromomeron romeri, Tawa hallae, and Asilisaurus kongwe, filling in some key gaps in our understanding of the early diversification of the Ornithodira.  Nonetheless it has become readily apparent that many important specimens crucial to this issue were not weathering out of outcrops in the field, but rather were sitting un- or misidentified in museum collections around the globe. Our new understanding of character states and polarities for early diverging dinosauriforms provided us with specific search criteria leading to the discoveries and/or reinterpretations of taxa such as Eucoelophysis baldwini, Dromomeron gregorii, Technosaurus smalli, Daemonosaurus chauliodus, and of course Effigia okeeffae, all from previously collected material including fossils collected for Edward Cope in the 1800s. Furthermore, Randy's work found that the rise of dinosaurs was diachronous, although the timing is still poorly understood.

The discovery of the silesaurid Asilisaurus kongwe (published in 2010) pulled the split between Silesauridae and Dinosauria into the Middle Triassic creating a significant ghost lineage for Dinosauria as the earliest known bona fide dinosaurs do not appear until the end of the Carnian stage of the Late Triassic. Amazingly it appears that we did not need to wait very long for this ghost lineage to be filled.

Today's issue of Biology Letters has a paper by Sterling Nesbitt, Paul Barrett, Sarah Werning, Christian Sidor, and the late Alan Charig on a probable new dinosaur from the Middle Triassic of Tanzania. Even more amazing is that this is not a new specimen, but was actually collected in the 1930s, and never described, except in Charig's 1950s dissertation, until today. Charig named the new specimen Nyasasaurus parringtoni and until now this name has been a nomen nudum.

Known from a partial humerus and several vertebrate (three cervical, five presacral and three sacral), reanalysis places Nyasasaurus as either a dinosaur or as the sister taxon to Dinosauria. The humerus bears a ventrally elongated deltopectoral crest with a deflected apex, both synapomorphies of Dinosauria. The cervical vertebrae are elongate and possess deep lateral fossae, consistent with character states found in dinosaurs. The presence of three sacral vertebrae, although not restricted to Dinosauria, also supports this placement. This interpretation is supported not only by a phylogenetic analysis but also by bone histology, which shows high, continuous growth rates similar to that of early diverging dinosaurs. 

This material suggests that dinosaurs probably appeared in the fossil record 10 to 15 million years earlier than we expected. Furthermore, Nesbitt et al. argue that this strongly supports the hypothesis that dinosaurs were not a dominant group during their early history. Finally, Nyasasaurus also provides more support for a Gondwanan origin of dinosaurs.

One thing that is now definitely clear is that workers interested in dinosaur origins will need to spend more time in Middle Triassic terrestrial units. Back in 2004 I don't think any of us fathomed what discoveries and interpretations the next decade would bring. As I often state, it is not necessarily what we already know that dirves our work, but what is still out there for us to learn.

Nesbitt, S. J., Barrett, P. M., Werning, S., Sidor, C. A., and A. J. Charig. 2012. The oldest dinosaur? A Middle Triassic dinosauriform from Tanzania. Biology Letters.
 

Abstract - The rise of dinosaurs was a major event in vertebrate history, but the timing of the origin and early diversification of the group remain poorly constrained. Here, we describe Nyasasaurus parringtoni gen. et sp. nov., which is identified as either the earliest known member of, or the sister-taxon to, Dinosauria. Nyasasaurus possesses a unique combination of dinosaur character states and an elevated growth rate similar to that of definitive early dinosaurs. It demonstrates that the initial dinosaur radiation occurred over a longer timescale than previously thought (possibly 15 My earlier), and that dinosaurs and their immediate relatives are better understood as part of a larger Middle Triassic archosauriform radiation. The African provenance of Nyasasaurus supports a southern Pangaean origin for Dinosauria.

Dr. Farish Jenkins 1940-2012

Many of you are already aware, but Professor Farish Jenkins of Harvard University passed away earlier this month at the age of 72. A vertebrate paleontologist, Dr. Jenkins was well known for his Triassic work in Greenland and even more so for his work in the Triassic and Jurassic of the Colorado Plateau, especially regarding early mammals.

http://www.nytimes.com/2012/12/01/us/farish-jenkins-fossils-expert-dies-at-72.html

Biomechanical Comments about Triassic Dinosaurs from Brazil

Delcourt, R., de Azevedo, S. A. K., Grillo, O. N., and F. O. Deantoni. 2012. Biomechanical comments about Triassic dinosaurs from Brazil. Papáis Avulsos de Zoologia 52:341-347.
 Abstract - Triassic dinosaurs of Brazil are found in Santa Maria and Caturrita formations, Rio Grande do Sul state, Brazil. There are three species known from the Santa Maria Formation (Staurikosaurus pricei, Saturnalia tupiniquim and Pampadromaeus barberenai), and two from Caturrita Formation (Guaibasaurus candelariensis and Unaysaurus tolentinoi). These dinosaur materials are, for the most part, well preserved and allow for descriptions of musculature and biomechanical studies. The lateral rotation of the Saturnalia femur is corroborated through calculations of muscle moment arms. The enhanced supracetabular crest of Saturnalia, Guaibasaurus, Staurikosaurus, Herrerasaurus ischigualastensis, Efraasia minor and Chormogisaurus [sic] novasi suggests that basal dinosaurs may have maintained an inclination of the trunk at least 20° on the horizontal axis. The pectoral girdle articulation of basal sauropodomorphs (Saturnalia and Unaysaurus) was established using a new method, the Clavicular Ring, and the scapular blade remains near 60° on the horizontal axis. This is a plesiomorphic condition among sauropodomorphs and is also seen in the articulated plateosauridae Seitaad ruessi. The Brazilian basal dinosaurs were lightweight with a body mass estimated around 18.5 kg for Staurikosaurus, 6.5 kg for Saturnalia, and 17 kg for Guaibasaurus. Pampadromaeus probably weighed 2.5 kg, but measures of its femur are necessary to confirm this hypothesis. The Triassic dinosaurs from Brazil were diversified but shared some functional aspects that were important in an evolutionary context.

Postcranial Anatomy of a Late Triassic Sauropodomorph from Argentina

Apaldetti, C., Diego Pol, D.,  and A. Yates. 2012. The postcranial anatomy of Coloradisaurus brevis (Dinosauria: Sauropodomorpha) from the Late Triassic of Argentina and its phylogenetic implications. Palaeontology (Early View) DOI: 10.1111/j.1475-4983.2012.01198.x

Abstract - Basal sauropodomorphs from the Upper Triassic Los Colorados Formation
 of north-western Argentina have been known for several decades but
 most of them are only briefly described. New postrcanial remains of
Coloradisaurus brevis, the most gracile sauropodomorph from this unit,
are described here and evaluated within a phylogenetic context. These
materials belong to a single individual and include elements of the
vertebral column, pectoral girdle, incomplete forelimb, pelvis and
hindlimb. These elements share an autapomorphic feature with the type
specimen of Coloradisaurus brevis and provide novel and unique
features that diagnose this taxon, such as pubic apron with
semicircular cross-section and with a depression on its anterior
surface, distal surface of the tibia deflected and facing
posterodistally and well-developed pyramidal dorsal process of the
posteromedial corner of the astragalus. Several postcranial characters
of Coloradisaurus are exclusively shared with Lufengosaurus, from the
Lower Jurassic of China. The inclusion of this information in two
recent phylogenetic data sets depicts Coloradisaurus as closely
related to Lufengosaurus and well nested within Plateosauria. Both
data sets used indicate strong character support for the inclusion of
Coloradisaurus and Lufengosaurus within Massospondylidae.

New Data on Small Theropod Footprints from Massachusetts

Dalman. S. G. 2012. New Data on Small Theropod Footprints from the Early Jurassic (Hettangian) Hartford Basin of Massachusetts, United States. Bulletin of the Peabody Museum of Natural History 53:333-353. doi:http://www.bioone.org/doi/abs/10.3374/014.053.0201

Abstract - A Portland Formation Lower Jurassic (Hettangian) dinosaur tracksite in Granby, Massachusetts, USA, has yielded a diverse dinosaur footprint assemblage. The tracksite preserves 140 theropod dinosaur footprints, ranging in length from 15 to 35 cm; the ichnofauna includes Anchisauripus, Eubrontes, Grallator and other extremely small theropod dinosaur footprints. The small tracks are compared with similar ichnites from the Lower Jurassic of western North America and central Poland. The small theropod footprints, which are described in detail, show some resemblance to the poorly known ichnogenus Stenonyx (Lull, 1904), which is considered an invalid ichnotaxon by many other workers. The footprints exhibit a distinct morphology of the metatarsophalangeal area, suggesting that these small ichnites are closely related to Kayentapus and Grallator. These small tracks are the first reported from the Hartford Basin of Granby, Massachusetts.

More on the Taxonomic Affinities of Isolated Leaf-Shaped Teeth from the Triassic

In the conclusions section of the recent paper by Kammerer et al., there is a worthwhile discussion regarding the taxonomic assignment of isolated Triassic teeth.  In the past some isolated leaf-shaped, denticulated teeth were considered apomorphic and used to erect discrete ornithischian dinosaur taxa (e.g., Hunt and Lucas, 1994; Heckert, 2004). Parker et al. (2005) argued that at least in Revueltosaurus callenderi, the teeth were apomorphic allowing assignment of non-dental material to the taxon. Irmis et al. (2007) discussed this in more detail, arguing the teeth of other purported ornithischians were not assignable to dinosaurs based solely on morphology and in fact could not be assigned to a more inclusive taxonomic level than Archosauromorpha.

However, in this recent paper Kammerer et al. note that many of these Triassic tooth taxa are very similar to the teeth of the traversodontid cynodonts Dadadon isaloi and Arctotraversodon plemmyridon. They especially note that the lower incisors of D. isaloi are very similar to the holotype teeth of Tecovasaurus murryi and the fourth upper incisor of D. isaloi has a similar morphology to Lucianosaurus wildi. Thus the characters that have been used to diagnose at least several of these 'tooth taxa' converge on other forms and are not autapomorphic. Although it would be tempting to use the teeth of Tecovasaurus and Lucianosaurus to suggest the further presence of cynodonts in the Triassic of the American southwest, we cannot discount the similarities of these teeth to archosaurian forms as well and therefore as noted by Kammerer et al., these isolated teeth can presently only be assigned to the level of Amniota  rather than Archosauriformes.

REFERENCES

Heckert, A.B. 2004. Late Triassic microvertebrates from the lower Chinle Group (Otischalkian-Adamanian: Carnian), southwestern U. S. A. New Mexico Museum of Natural History and Science Bulletin 27:1-170.

Hunt, A. P., and S.G. Lucas. 1994. Ornithischian dinosaurs from the Upper Triassic of the United States. pp. 227–241 in In the Shadows of the Dinosaurs: Early Mesozoic Tetrapods (ed. N. C. Fraser & H.-D. Sues). Cambridge University Press.
Irmis, R. B., Parker, W. G., Nesbitt, S. J., and J. Liu. 2007. Early ornithischian dinosaurs: the Triassic record. Historical Biology 19:3-22.

Kammerer, C. F., Flynn, J. J., Ranivoharimanana, L., and A. R. Wyss. 2012. Ontogeny in the Malagasy traversodontid Dadadon isaloi and a reconsideration of its phylogenetic relationships. Fieldiana Life and Earth Sciences 5:112-125.

Parker, W.G., Irmis, R.B., Nesbitt, S.J., Martz, J.W., and L.S. Browne. 2005. The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs. Proceedings of the Royal Society B 272:963-969.
 

 

Ontogeny of the Malagasy Traversodontid Dadadon isaloi

Kammerer, C. F., Flynn, J. J., Ranivoharimanana, L., and A. R. Wyss. 2012. Ontogeny in the Malagasy Traversodontid Dadadon isaloi and a Reconsideration of its Phylogenetic Relationships. Fieldiana Life and Earth Sciences 5:112-125. doi: http://www.bioone.org/doi/abs/10.3158/2158-5520-5.1.112

Abstract - New craniodental material of the traversodontid Dadadon isaloi from Middle/Upper Triassic basal “Isalo II” beds of southwestern Madagascar is described. These specimens reveal several new autapomorphies of Dadadon, including paired foramina on the frontal near the anterior border of the postorbital and lower incisors with denticulated distal margins. The new material covers a broad size range, providing the first information on ontogeny in Dadadon. Larger (presumably older) specimens of Dadadon isaloi have more postcanine teeth, relatively longer, narrower snouts, and a higher degree of cranial ornamentation than smaller specimens. Postcanine replacement in Dadadon was similar to that of other traversodontids: new teeth erupted at the posterior end of the postcanine tooth row and moved forward. Using information from the new specimens, the position of Dadadon was tested in a new phylogenetic analysis of traversodontids. In the new analysis, Dadadon is strongly supported as a member of a clade also including the South American taxa Massetognathus and Santacruzodon, here named Massetognathinae subfam. nov. This clade is diagnosed by the presence of denticulated lower incisors, relatively small canines, three cusps in the labial margin of the upper postcanines, and low, flat skulls. Massetognathinae is the sister-group of Gomphodontosuchinae, which includes Gomphodontosuchus, Menadon, Protuberum, Exaeretodon, and Scalenodontoides. The Laurasian traversodontids (Arctotraversodon, Boreogomphodon, and Nanogomphodon) form a clade that is the sister-taxon of Massetognathinae + Gomphodontosuchinae. Denticulated incisors evolved multiple times in traversodontid evolution (in massetognathines and Arctotraversodon), and thus this group represents another possibility (besides various archosauromorphs) to be considered when attempting to identify isolated Triassic teeth with denticulated carinae lacking cingula.

Biomechanical Analysis of Triassic Cynodonts from Madagascar

Ranivoharimanana, L. 2012. Analyse biomécanique masticatrice chez des traversodontidés eucynodontes du Trias de Madagascar. [Biomechanical analysis of the jaw apparatus in eucynodont traversodontids from the Triassic of Madagascar]. Geodiversitas 34: 505–515.

Abstract - Mandible biomechanics analysis cannot take place without the understanding of the development degree and the arrangement pattern of the adductor muscles. In the non mammalian cynodonts, the temporal and the superficial masseter muscles play a primordial role in the lower jaw motion during the food processing. They constitute the key elements of this analysis. Previous studies on non mammalian cynodonts including Dadadon isaloi Flynn, Parrish, Rakotosamimanana, Simpson & Wyss, 1999 and Menadon besairiei Flynn, Parrish, Rakotosamimanana, Simpson & Wyss, 1999 demonstrated the realization, by these animals, of a complex dynamic occlusion of the lower and superior postcanine teeth. The consideration of the bite point as second occlusal fulcrum equal in status to the cranio-mandibular joint is the basis of the bifulcral model. This methodology allows: 1) to quantify the resistance opposed by food at the level of the occlusal site; and 2) to highlight a positive net vertical load, of compressive nature, acting to the level of the cranio-mandibular joint during the interactivity of the elevator muscles, i.e. during mastication.

 

RÉSUMÉ - L'analyse de la biomécanique de la mandibule ne peut s'effectuer sans la compréhension du degré de développement et du type d'arrangement des muscles adducteurs. Chez les cynodontes non mammaliens, le muscle temporal et le masséter superficiel jouent un rôle primordial dans les mouvements de la mâchoire inférieure lors de la transformation alimentaire. Ils constituent ainsi les éléments clés de cette analyse. Des études antérieures sur des cynodontes non mammaliens dont Dadadon isaloi Flynn, Parrish, Rakotosamimanana, Simpson & Wyss, 1999 et Menadon besairiei Flynn, Parrish, Rakotosamimanana, Simpson & Wyss, 1999, ont démontré la réalisation, par ces animaux, d'une occlusion dynamique complexe des dents postcanines, inférieures et supérieures. La considération du point de morsure comme second point d'appui au même titre que l'articulation crânio-mandibulaire est le fondement même du système à double leviers. Cette méthodologie a permis de: 1) quantifier la résistance opposée par la nourriture au niveau du site occlusal; et 2) mettre en évidence l'existence d'une charge verticale nette positive, de nature compressive agissant au niveau de l'articulation crânio-mandibulaire chez Dadadon isaloi et Menadon besairiei durant l'interactivité des muscles élévateurs au cours de la mastication.

Early Triassic Ichnoassemblages of Wyoming

This new paper suggests the presence of dinosauromorph (cf. Rotodactylus) and turtle-like (cf. Chelonipus) trackmakers from the Lower Triassic of Wyoming.

Lovelace, D. M., and S. D. Lovelace. 2012. Paleoenvironments and paleoecology of a Lower Triassic invertebrate and vertebrate ichnoassemblage from the Red Peak Formation (Chugwater Group), central Wyoming. Palaios 27:636-657. doi: 10.2110/​palo.2012.p12-011r

Abstract - The Lower Triassic Red Peak Formation of the Chugwater Group has long been considered to have an extremely poor paleontological record, although the cause for the apparent dearth of fossils has yet to be been determined. During the course of fieldwork in central Wyoming numerous vertebrate and invertebrate ichnogenera (n ≥ 11) were observed. Vertebrate tracks and trackways representative of dinosauromorph, archosaur, lepidosaur, and testudinate trackmakers were found (cf. Rotodactylus, Chirotherium barthii, Rhynchosauroides, and cf. Chelonipus respectively). An invertebrate ichnoassemblage composed of at least 6 ichnogenera consistent with the Scoyenia ichnofacies were also found (e.g., Diplichnites, Lockeia, Fuersichnus communis, Palaeophycus striatus, cf. Scoyenia, and cf. Scolicia). The majority of these tracks and traces were found in the upper platy facies (upper 10–20 m of the Red Peak Formation), which is thought to be no younger than upper Spathian in age. Sedimentary structures, architectural elements, and lateral stratigraphic relationships support the interpretation of floodplain, fluvial, and lacustrine deposition for the upper platy facies in central Wyoming. The Red Peak Formation vertebrate and invertebrate ichnoassemblages, along with their associated depositional environments, are consistent with a fluviolacustrine (continental) setting comparable to those described from Lower to Middle Triassic strata with a Pangean distribution, including the Moenkopi Formation in the southwestern United States. This ichnoassemblage provides the first opportunity to observe paleoecological diversity and associated paleoenvironments within the Lower Triassic of the Chugwater Group.

New Triassic Animal Video Clips (Museum in a Minute) from the New Mexico Museum of Natural History and Science

The New Mexico Museum of Natural History and Science has released a bunch of short, one minute video clips on a variety of fossil animals. I've linked a few of the Triassic-themed ones below. I think this is a great idea.

Revueltosaurus

Coelophysis

What is a Metoposaur?

Numerous Triassic Presentation Abstracts from the Fourth Latinamerican Congress of Vertebrate Paleontology

A new issue of the South American journal Ameghiniana includes (starting on page 32) the set of published abstracts from the IV Congreso Latinamericano  de Paleontologia Vertebrados, which was held in San Juan Argentina in September of 2011.  There are numerous Triassic themed abstracts in here as there were sessions of basal archosaurs, early theropods, therapsids, as well as geological sessions. I gave two talks at the meeting, one on newly discovered cranial material of Poposaurus gracilis; the other on the stratigraphic position of the Placerias Quarry of Arizona, which contains the earliest known neotheropod dinosaur. A volume is currently in press containing many of the papers from the basl archosaurs session.

You can download the published abstract volume here:

http://www.ameghiniana.org.ar/index.php/ameghiniana

Once the page loads, click on the small text "PDF" in the lower right corner.

Footprints of Large Theropod Dinosaurs from the Late Triassic of Brazil

The Caturrita Formation may be younger than previously thought and there is a currently undiscovered large theropod in the latest Triassic of Brazil.

da Silva, R. C., Barboni, R., Dutra, T., Godoy, M. M., and R. B. Binotto. 2012. Footprints of large theropod dinosaurs and implications on the age of Triassic biotas from southern Brazil. Journal of South American Earth Sciences 39:16-23. http://dx.doi.org/10.1016/j.jsames.2012.06.017

Abstract - Dinosaur footprints found in an outcrop of the Caturrita Formation (Rio Grande do Sul State, Southern Brazil), associated with a diverse and well preserved record of fauna and flora, reopen the debate about its exclusive Triassic age. The studied footprints were identified as Eubrontes isp. and are interpreted as having been produced by large theropod dinosaurs. The morphological characteristics and dimensions of the footprints are more derived than those commonly found in the Carnian–Norian, and are more consistent with those found during the Rhaetian–Jurassic. The trackmaker does not correspond to any type of dinosaur yet known from Triassic rocks of Brazil. Recent studies with the paleofloristic content of this unit also support a more advanced Rhaetian or even Jurassic age for this unit.

A New Ctenosauriscid from Eastern Europe, Bystrowisuchus flerovi May Represent the Oldest Known Crown-Group Archosaur

This paper describes a new ctenosauriscid archosaur from the Early Triassic of Europe. Bystrowisuchus flerovi is based upon a series of fragmentary cervical vertebrae and a partial right ilium. It differs from other ctenosauriscids in the presence of expanded spine tables on the apices of the neural spines, and by possessing generally shorter neural spines. Based on these characters Sennikov considers Bystrowisuchus to be transitional between rauisuchids and ctenosauriscids. Note that Sennikov prefers to use traditional Linnaean systematics rather than cladistics (and still recognizes Thecodontia as a taxonomic entity). A new family Lotosauridae is erected and considered distinct from other ctenosauriscids [Ctenosauriscidae]. The type locality is dated latest Olenekian, which means that Bystrowisuchus  is probably older than Xilousuchus which is ambiguously from the latest Olenekian-early Anisian of China and therefore could represent the oldest record of a ctenosauriscid and crown-group archosaur.

Sennikov, A. G. 2012. The first ctenosauriscid (Reptilia: Archosauromorpha) from the Lower Triassic of Eastern Europe. Paleontological Journal [Paleontologicheskii Zhurnal] 46:499-511.

Abstract - A new Early Triassic thecodont from the Donskaya Luka locality is described. A new species and genus of Rauisuchidae, Bystrowisuchus flerovi gen. et sp. nov., the first East European and earliest known member of the family Ctenosauriscidae is established. The taxonomy and phylogeny of Rauisuchidae and their stratigraphical and geographical distribution in connection with new finds are discussed.

A New Turtle Dominated Fossil Biota from the Late Triassic (Norian) of Poland

This paper documents a newly discovered fauna from the Norian of Poland that is important because it is dominated by fossils of what is most likely a new taxon of turtle. Of course Late Triassic terrestrial turtles are very rare so we will watch further research from this site with interest. The locality also includes other vertebrate taxa including a coelophysoid dinosaur and an aetosaur.  The aetosaur is of interest because the dorsal vertebra possesses a distinct hyposphene, a character previously only found in Desmatosuchus from North America and Aetobarbakinoides from Brazil.  This new site is also significant because it preserves micro and macrofloral fossils, which are generally uncommonly associated with vertebrate remains. Large temnospondyls are also rare in the Norian, but this site has one as well.

Sulej, T., Niedźwiedzki, G., and R. Bronowicz. 2012. A new Late Triassic vertebrate fauna from Poland with turtles, aetosaurs, and coelophysoid dinosaurs. Journal of Vertebrate Paleontology 23: 1033-1041. DOI:10.1080/02724634.2012.694384

Abstract - We report a new site with an occurrence of isolated bones of a Palaeochersis-like turtle in Norian-Rhaetian fluvial sediments from southern Poland. The turtle remains are associated with bones of a medium-sized aetosaur, a coelophysoid dinosaur, and a larger carnivorous archosaur, as well as a hybodontid shark, ganoid and dipnoan fishes, and a large temnospondyl.