Abstract
Borioteiioids comprise an extinct family of squamates that inhabited the Northern Hemisphere during the Cretaceous and were characterized by varying patterns of tooth replacement and dental morphology. Understanding the evolution of these tooth replacement patterns has, however, been largely hampered by an extremely fragmentary fossil record. Here we present new information on Dicothodon bajaensisfrom the Campanian of Baja California (Mexico), so far known only from isolated teeth and jaw fragments. Among abundant new materials there are ten maxillae and five dentaries belonging to distinct ontogenetic stages. Whereas juveniles display active tooth replacement, older specimens show no evidence of replacement. Dicothodon bajaensis is therefore inferred to have had arrested tooth replacement later in ontogeny. This provides the first evidence of cessation of tooth replacement during late ontogeny in lizards (living or extinct). This replacement type is also an evolutionary intermediate between the typical lizard replacement pattern, observed in some borioteiioids (e.g., Bicuspidon) and the complete absence of tooth replacement since early ontogeny as observed in other borioteiioids (e.g., Polyglyphanodon).
Highlights
Tooth replacement in most reptiles occurs throughout their whole life (Edmund 1960, 1969, Osborn 1974, Berkovitz 2000)
The anteriormost maxillary and dentary teeth in acrodontans are still replaced during post-embryonic ontogeny, but even among those, tooth replacement ceases during early ontogeny (Cooper et al 1970, Cooper and Poole 1973)
Observations and measurements on dental morphology, tooth replacement patterns, and overall morphology of tooth bearing bones in D. bajaensis were performed using a wide range of techniques
Summary
Tooth replacement in most reptiles occurs throughout their whole life (Edmund 1960, 1969, Osborn 1974, Berkovitz 2000). An unusual replacement pattern occurs within acrodontan lizards (agamids and chameleons), in which tooth replacement occurs during embryonic developmental stages, but ceases in post-embryonic ontogeny in the posterior tooth series ( new teeth continue to be added posteriorly on the tooth row until later in ontogeny). The anteriormost maxillary and dentary teeth in acrodontans are still replaced during post-embryonic ontogeny, but even among those, tooth replacement ceases during early ontogeny (Cooper et al 1970, Cooper and Poole 1973). There is no tooth replacement at all during post-embryonic life, such as in the agamids Calotes (Edmund 1960) and Uromastyx (Cooper and Poole 1973). It has been identified that in agamids and chameleons the cessation of replacement occurs due to a dramatic reduction in the size of the successional lamina (which becomes vestigial), not producing any tooth germs for replacement tooth generations (Richman and Handrigan 2011, Buchtová et al 2013)
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