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Mosasaur and crocodylian tooth histology from Cretaceous of Sweden



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Johan A. Gren and Johan Lindren (2013)
Dental histology of mosasaurs and a marine crocodylian from the
Campanian (Upper Cretaceous) of southern Sweden: incremental growth
lines and dentine formation rates.
Geological Magazine (advance onlinen publication)
DOI: http://dx.doi.org/10.1017/S0016756813000526
http://128.232.233.5/action/displayAbstract?fromPage=online&aid=8970382&fulltextType=RA&fileId=S0016756813000526




Mosasaurs are an extinct group of secondarily adapted aquatic lizards
that became the dominant marine tetrapods in the Late Cretaceous
oceans. They continuously shed and replaced their teeth in order to
maintain a functional dentition at all times; however, the process of
tooth development in mosasaurs is still incompletely known. Based on
incremental line width measurements and growth line counts, we assess
dentine formation rates in three mosasaur taxa (Dollosaurus, cf.
Platecarpus and Tylosaurus) and one genus of marine crocodylian
(Aigialosuchus), all from the lower Campanian (Upper Cretaceous) of
southernmost Sweden. Two sets of periodic dentinal markings
characterized by concentric, alternating opaque and transparent
laminae are recognized: one set comprising thin bands situated 6-34 μm
apart (depending on taxon), which is superimposed onto a second set of
coarser bands where spaces vary between 102 and 275 μm. Assuming that
the finer striations represent daily increments (i.e. lines of von
Ebner), it is estimated that the deposition of dentine at the
sectioned level of the tooth-crowns took 342 (cf. Platecarpus), 426
(Dollosaurus), 487 (Tylosaurus) and 259 (Aigialosuchus) days,
respectively. The coarser bands contain between 11 and 13 thin
striations each, and are thus considered to be homologous to similar
periodic dentinal markings in extant vertebrates, i.e. Andresen lines.
Prolonged tooth development times in large-toothed taxa, such as
Tylosaurus, presumably increased the risk of long-term incapacity to
capture prey after dental trauma, an evolutionary trade-off which may
have been compensated for by allometric modifications of the teeth.