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.
Showing posts with label teeth. Show all posts
Showing posts with label teeth. Show all posts
New Species of the Late Triassic Venomous Archosauriform Uatchitodon
Mitchell, J. S., Heckert, A. B., and H.-D. Sues. 2010. Grooves to tubes: evolution of the venom delivery system in a Late Triassic “reptile”. Naturwissenschaften, online first. DOI 10.1007/s00114-010-0729-0
Abstract - Venom delivery systems occur in a wide range of extant and fossil vertebrates and are primarily based on oral adaptations. Teeth range from unmodified (Komodo dragons) to highly specialized fangs similar to hypodermic needles (protero- and solenoglyphous snakes). Developmental biologists have documented evidence for an infolding pathway of fang evolution, where the groove folds over to create the more derived condition. However, the oldest known members of venomous clades retain the same condition as their extant relatives, resulting in no fossil evidence for the transition. Based on a comparison of previously known specimens with newly discovered teeth from North Carolina, we describe a new species of the Late Triassic archosauriform Uatchitodon and provide detailed analyses that provide evidence for both venom conduction and document a complete structural series from shallow grooves to fully enclosed tubular canals. While known only from teeth, Uatchitodon is highly diagnostic in possessing compound serrations and for having two venom canals on each tooth in the dentition. Further, although not a snake, Uatchitodon sheds light on the evolutionary trajectory of venom delivery systems in amniotes and provide solid evidence for venom conduction in archosaur-line diapsids.
Supplemental data available here.
Abstract - Venom delivery systems occur in a wide range of extant and fossil vertebrates and are primarily based on oral adaptations. Teeth range from unmodified (Komodo dragons) to highly specialized fangs similar to hypodermic needles (protero- and solenoglyphous snakes). Developmental biologists have documented evidence for an infolding pathway of fang evolution, where the groove folds over to create the more derived condition. However, the oldest known members of venomous clades retain the same condition as their extant relatives, resulting in no fossil evidence for the transition. Based on a comparison of previously known specimens with newly discovered teeth from North Carolina, we describe a new species of the Late Triassic archosauriform Uatchitodon and provide detailed analyses that provide evidence for both venom conduction and document a complete structural series from shallow grooves to fully enclosed tubular canals. While known only from teeth, Uatchitodon is highly diagnostic in possessing compound serrations and for having two venom canals on each tooth in the dentition. Further, although not a snake, Uatchitodon sheds light on the evolutionary trajectory of venom delivery systems in amniotes and provide solid evidence for venom conduction in archosaur-line diapsids.
Supplemental data available here.
Dentition and Tooth Replacement in an Upper Triassic Traversodont Cynodont from the Eastern United States
Liu, J., and H.-D. Sues. 2010. Dentition and tooth replacement of Boreogomphodon (Cynodontia: Traversodontidae) from the Upper Triassic of North Carolina, USA. Vertebrata PalAsiatica 48:169-184.
Abstract - The teeth of new specimens of the traversodontid cynodont Boreogomphodon from the Upper Triassic of North Carolina are described. Based on dental features, especially the postcanine morphology, the North Carolina specimens are tentatively referred to Boreogomphodon jeffersoni, although their lower gomphodont postcanines typically have two rather than three cusps on the anterior transverse ridge. Based on the tooth size, direct replacement on all available specimens, the gomphodont teeth were shed anteriorly and added posteriorly. Only one generation of gomphodont teeth, at least one and possibly two generations of sectorial postcanines were present.
Abstract - The teeth of new specimens of the traversodontid cynodont Boreogomphodon from the Upper Triassic of North Carolina are described. Based on dental features, especially the postcanine morphology, the North Carolina specimens are tentatively referred to Boreogomphodon jeffersoni, although their lower gomphodont postcanines typically have two rather than three cusps on the anterior transverse ridge. Based on the tooth size, direct replacement on all available specimens, the gomphodont teeth were shed anteriorly and added posteriorly. Only one generation of gomphodont teeth, at least one and possibly two generations of sectorial postcanines were present.
Latest Literature - Distribution of Supernumerary Carinae in Archosauriforms
Beatty, B.L., and A.B. Heckert. 2009. A large archosauriform tooth with multiple supernumerary carinae from the Upper Triassic of New Mexico (USA), with comments on carina development and anomalies in the Archosauria. Historical Biology 21:57-65. DOI: 10.1080/08912960903154511.
Abstract-Here we report a tooth of a large archosauriform from the Upper Triassic of New Mexico, USA that displays developmental anomalies of carina formation. This tooth has two supernumerary carinae, both on the lingual side of the tooth. Previously, carina anomalies of this sort were primarily known from theropod dinosaurs, but always from the labial surface. Integrating this specimen into a reassessment of the published accounts of carina anomalies in other fossil diapsids reveals that supernumerary carinae are more widespread throughout Archosauriformes than previously reported. Our interpretation of this developmental anomaly highlights the present lack of understanding of tooth development in archosaurs, particularly carina formation, and suggests that crown morphology development in archosauriforms may be constrained differently than it is in mammals. This developmental constraint may explain the differences observed between the complexity found in mammal and archosauriform cusp morphology.
Abstract-Here we report a tooth of a large archosauriform from the Upper Triassic of New Mexico, USA that displays developmental anomalies of carina formation. This tooth has two supernumerary carinae, both on the lingual side of the tooth. Previously, carina anomalies of this sort were primarily known from theropod dinosaurs, but always from the labial surface. Integrating this specimen into a reassessment of the published accounts of carina anomalies in other fossil diapsids reveals that supernumerary carinae are more widespread throughout Archosauriformes than previously reported. Our interpretation of this developmental anomaly highlights the present lack of understanding of tooth development in archosaurs, particularly carina formation, and suggests that crown morphology development in archosauriforms may be constrained differently than it is in mammals. This developmental constraint may explain the differences observed between the complexity found in mammal and archosauriform cusp morphology.
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