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[dinosaur] Rhynchocephalian tooth implantation + Mesozoic lizards from Brazil + Cretaceous reptiles of Saxony





Ben Creisler
bcreisler@gmail.com


Some recent and not so recent reptile items:

Kelsey M. Jenkins, Marc E. H. Jones, Tomas Zikmund, Alan Boyde, and Juan D. Daza (2017)
A Review of Tooth Implantation Among Rhynchocephalians (Lepidosauria).
Journal of Herpetology 51(3):300-306 
https://doi.org/10.1670/16-146
http://www.bioone.org/doi/abs/10.1670/16-146



Acrodont dental implantation is widely considered an important character for referring fossil material to Rhynchocephalia. Under its purest definition, acrodonty involves teeth being attached to the crest of the marginal bones without roots. A similar mode of tooth attachment is known in a variety of other reptile groups including some squamates and procolophonids. There is a lack of consensus on the definition of acrodont, how best to characterize tooth implantation, and the relationship between implantation and tooth replacement. Rhynchocephalians already are known to demonstrate variation in their mode of tooth attachment. Unambiguous acrodonty associated with little or no tooth replacement has been associated with Sphenodon, but it appears to have been the most widespread condition for much of the Mesozoic. A form of pleurodonty, where teeth are attached to the inside of the jaw bone with shallow roots, appears to be the plesiomorphic condition for both Lepidosauria and Rhynchocephalia. Jaws with anterior pleurodont teeth and posterior acrodont teeth appear to have been common for early rhynchocephalians in the Triassic, and Ankylosphenodon from the early Cretaceous of Mexico demonstrates that at least some later rhynchocephalians possessed continually replacing dentition, but identification of this trait requires inspection of internal anatomy. When cross-sections of teeth are unavailable or the lingual view of jaws is obscured, one cannot be 100% confident of acrodont implantation, and “acrodonty” should not be used as a single character to refer incomplete jaw material to Rhynchocephalia. Tooth implantation is a component that was highly variable in a once-diverse reptile group.



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Tiago R. Simões, Michael W. Caldwell, Luiz C. Weinschütz, Everton Wilner, and Alexander W. A. Kellner (2017)
Mesozoic Lizards from Brazil and Their Role in Early Squamate Evolution in South America.
Journal of Herpetology 51(3): 307-315 
https://doi.org/10.1670/16-007
http://www.bioone.org/doi/abs/10.1670/16-007



The diversity of extant squamates in South America is in deep contrast to the extremely scarce knowledge of squamates from that continent during the Mesozoic, particularly regarding terrestrial lizards. Here, we provide a review of the most recent advances in the knowledge of Cretaceous lizards from South America, focusing on named species (all from Brazil). These forms included scansorial, as well as cursorial taxa, likely displaying facultative bipedalism. In the case of Crato Formation specimens, only juveniles were reported so far, which raises questions about the role of taphonomic biases and community structure. Iguanians (acrodontans and non-acrodontans), as well as scincomorphs, are known since the Aptian/Albian. All iguanians had a broad Late Cretaceous distribution that, along with findings in the Early–Middle Jurassic of India, suggests an early radiation of the group before the final break up of Laurasia and Gondwana. Gondwanan regions may have played a fundamental role in the initial history of acrodontan iguanians despite the fact that, at least in South America, only non-acrodontans and scincomorphs are known to have passed through the Cretaceous–Paleogene boundary.



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Sven Sachs, Jahn J. Hornung, Joschua Knüppe, Markus Wilmsen and Benjamin P. Kear (2016)
15. Reptilien [15. Reptiles] (in German)
Cretaceous fossils of Saxony, part 2
Geologica Saxonica 62: 169-179

Free pdf:

http://www.senckenberg.de/files/content/forschung/publikationen/geologicasaxonica/62/15__geologica-saxonica_62_2016_sachs-et-al.pdf



Reptilian fossils are rare in the Saxonian Cretaceous (Elbtal Group). The few known specimens are historical finds, first described by Hanns Bruno Geinitz in the 19th century. They derive from two stratigraphical units, the Dölzschen Formation (upper Upper Cenomanium) and the Stehlen and Weinböhla Limestone of the lower Strehlen Formation (mid-Upper Turonian) and were collected almost exclusively within the current city limits of Dresden. Remains from the Dölzschen Formation are very fragmentary and cannot be referred to any taxonomic group with certainty. On the other hand, better preserved material from the Strehlen and Weinböhla Limestone reveals the presence of at least two different plesiosaurian families (Elasmosauridae and ?Polycotylidae) as well as different marine turtles of the family Protostegidae. However, evidence of mosasaurid and dolichosaurid marine squamates, as suggested by Geinitz (1875a), is missing.