Friday, February 28, 2014

Remember Teyuwasu?

Way back in the days of yore, I had DML post style called "Details on..." where I would report information about obscure dinosaur taxa.  This was before the modern methods of organized file exchange, so to learn more about a newly reported taxon, you'd generally have to request a paper copy from Tracy Ford.  We were all pretty clueless, so I hoped to spread some knowledge around.  One of my posts from 2000 was "Details on Teyuwasu"*, an enigmatic dinosaur described briefly in an abstract and based on  bones first described in an old German paper that was even harder to acquire.  It seems online information on Teyuwasu is still hard to find, so here's an update 14 years later.

* Btw, while I interpreted Kischlat's statement "the distal process is so developed as to encompass the ascending process of astragalus" as being similar to coelophysoids' anterior overlap, it's actually the posterolateral process extending laterally a bit behind the ascending process as in most dinosauriforms.  Hooray for imprecise translations.

Teyuwasu Kischlat, 1999 vide Kischlat, 2000
= "Teyuwasu" Kischlat, 1999
T. barberenai Kischlat, 1999 vide Kischlat, 2000
= "Teyuwasu barberenai" Kischlat, 1999
Late Carnian-Early Norian, Late Triassic
Alemoa Member of Santa Maria Formation, Brazil
Holotype
- (BSPG AS XXV 53) femur (276 mm)
....(BSPG AS XXV 54) tibia (264 mm)
?...(BSPG AS XXV 56-59) dorsal centrum (40 mm), partial ilium, (?) distal ischium, femur
Diagnosis- (proposed) extremely robust femur and tibia (minimum transverse femoral width 19% of length); mound-like fourth trochanter.



A-F: Holotype femur BSPG AS XXV 53 of Teyuwasu barberenai in anterior, medial, posterior, lateral, proximal and distal views respectively. G-L: Holotype tibia BSPG AS XXV 54 in proximal, distal, anterior, medial, posterior and lateral views respectively.  Scale = 100 mm. (after Ezcurra, 2012)

Comments- The material was originally described by Huene (1938) as possibly belonging to his new taxon Hoplitosaurus raui, from slightly higher in the formation. Huene later (1942) renamed it Hoplitosuchus, as Hoplitosaurus was preoccupied by an ankylosaur. The taxon was based on two supposed osteoderms described as aetosaurian, but more recently these have been found to be unidentifiable bones by Kischlat (2000) and Desojo and Rauhut (2008). Kischlat (1999) reinterpreted the femur and tibia as being dinosaurian, though only listed features identifying it to the level of Dinosauriformes. He provided a very brief description and named the taxon Teyuwasu barberenai, but as the publication is a symposium abstract, it is invalid under the ICZN (Article 9.10). Kischlat's (2000) later article has similar information, credits the name to the 1999 paper, but is a valid publication. Ezcurra (2012) described the material in depth, finding it certainly belongs to the silesaurid+dinosaur clade, but that the only dinosaurian character is the inturned femoral head. As the bones have been heavily altered taphonomically, Ezcurra was uncertain if the femoral head orientation was artificial. He notes Kischlat's "two paralell ridges running proximodistally" are fractures formed when the medial femoral head was sheared distally. While Ezcurra declared Teyuwasu to be indeterminate, the robusticty itself is vastly different from other basal dinosauriforms, so should be enough to validate the taxon. If added to the Nesbitt archosaur matrix along with all later published additions (including Nyasasaurus and Saltopus), Teyuwasu emerges as a saurischian based on femur longer or about the same length as the tibia, and medial articular facet of the proximal femur rounded.  It's outside Eusaurischia based on the femoral head being unexpanded, symmetrical fourth trochanter (considered tentative by Ezcurra), cnemial crest not laterally curved, and posterior face of distal tibia without longitudinal ridge.  Some of these characters vary within basal saurischians, which are incompletely sampled by Nesbitt, so I wouldn't bet on a non-eusaurischian identity being most parsinomious once all data are in.  Additionally, the coding indicates the moundlike fourth trochanter is unique among sampled ornithodirans, making this another diagnostic character.

Besides the femur and tibia, Huene referred additional material to this individual. A centrum identified by Kischlat (2000) as dorsal was stated by Huene to be possibly but not certainly referrable to this specimen. It is 40 mm long, 45 mm tall and wide, rounded in section and barely amphicoelous to amphiplatyan. A ventral ilium was considered very likely to belong to this individual. It has a supracetabular crest and 'strongly recessed' acetabulum, and narrows to 70 mm between the peduncles and blade. An element tentatively identified by Huene as a distal ischium is much too large to belong to this individual, with the distal end 90 mm deep and 60 mm wide. At the proximal break, these dimensions are 53 and 30 mm respectively. The distal end is triangular in section, which is a saurischian character. Finally, Kischlat (2000) mentioned an additional femur which was not noted by Huene. These were all noted by Kischlat as supplementary material for Teyuwasu, though Desojo and Rauhut stated referred Hoplitosuchus material belongs to Rauisuchia and Dinosauria. The centrum, ilium and/or ischium may comprise the 'rauisuchian' material, or this may refer to the two non-avemetatarsalian calcanea also referred to Hoplitosuchus by Huene.

References- Huene, 1938. Ein grosser Stagonolepid aus der jungeren Trias Ostafrikas. Neues Jahrbuch fur Mineralogie, Geologie und Palaontologie. 80(2), 264-278.

Huene, 1942. Die fossilen Reptilien des sudamerikanischen Gondwanalandes. Ergebnisse der Sauriergrabungen in Sudbrasilien 1928/29. Munich: Becksche Verlegbuchhandlung. 332 pp.

Kischlat, 1999. A new dinosaurian "rescued" from the Brazilian Triassic: Teyuwasu barbarenai, new taxon. Paleontologia em Destaque, Boletim Informativo da Sociedade Brasileira de Paleontologia. 14(26), 58.

Kischlat, 2000. Tecodoncios: A aurora dos Arcosaurios no Triassico. in Holz and De Rose (eds.). Paleontologia do Rio Grande do Sol. 273-316.

Desojo and Rauhut, 2008. New insights on "rauisuchian" taxa (Archosauria: Crurotarsi) from Brazil. SVPCA 2008 Programme and Abstracts. 18-19.

Ezcurra, 2012. Comments on the taxonomic diversity and paleobiogeography of the earliest known dinosaur assemblages (Late Carnian-Earliest Norian). Historia Natural. 2(1), 49-71.

4 comments:

  1. Very interesting observations Mickey, apparently it could be that we had a robust silesaur, at least there are large Silesaurs in Zambia (Peecook, Huttenlocker & Sidor, 2013) and Tanzania (Barrett, Peecook & Nesbitt, 2013)

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    1. Teywasu's femur is 96 mm across distally compared to 58 mm for the Tanzanian femur. What's the full reference for the large Zambian silesaur, since Lutungutali seems normal in size? Forcing Teyuwasu to be a silesaurid is 3 more steps, which is normally pretty plausible but bad when only the femur and tibia are known.

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  2. My idea was that Teyuwasu Silesaur is possible for different reasons. Carnivores are usually not as robust as herbivores, hence I am inclined to think that this animal could be slow and heavy, even though most of the Dinosauriformes and basal Dinosauria were quite graceful.

    Should not be Silesauridae barely fits in the typical plan of the basal dinosaurs if we consider its robustness but that does not mean it is not possible that it belongs to another taxon.

    Leveraging basal dinosaurs may be the remains of Spondylosoma was a chimera between a basal Dinosauria and Rauisuchia?

    Lutungutali have a femur of 175 mm if I support the bar (should be an obligation to put measures before they put all publications, with many now add a bar and met believe, is so hard to take them and put them in a scientific paper? )

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    1. For your statement: "Leveraging basal dinosaurs may be the remains of Spondylosoma was a chimera between a basal Dinosauria and Rauisuchia"

      In his 2009 thesis concerning basal archosaur relationships, Nesbitt (2009) could not find any characters that link Spondylosoma with any clade of pseudosuchians or ornithodirans and places Spondylosoma at Archosauria incertae sedis. In fact, the characters that Galton used to re-assign Spondylosoma to Rauisuchidae are also found in aetosaurs and it's possible that Spondylosoma could be part of an unknown clade of archosaurs.

      NESBITT, S.J.2009. The early evolution of archosaurs: rela-tionships and the origin of major clades [dissertation].New York: Columbia University. Available from: Pro-Quest Dissertations & Theses [online database]; http://www.proquest.com (publication number AAT 3374209).

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