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Ciampaglio, C. N., G. A. Wray, and B. H. Corliss. 2005. A toothy tale
of evolution: convergence in tooth morphology among marine
Mesozoic-Cenozoic sharks, reptiles, and mammals. The Sedimentary
Record 3(4):4-8.
ABSTRACT: Although mechanisms of niche replacement are discussed
thoroughly in the evolutionary paleontological literature (i.e.,
extinctions, competition, evolution of new adaptive morphologies),
actual studies involving quantitative analyses are not common. In this
study, morphological features of dentition in Late Cretaceous and
Cenozoic marine vertebrate predators were analyzed.The analysis
included species of Late Cretaceous and Cenozoic sharks, Late
Cretaceous marine reptiles, and Cenozoic marine mammals. Dental
characters used in the study were both discrete and continuous.
Species included in the analysis were originally collected from Late
Cretaceous and Cenozoic rocks from the south-central, southeastern,
and the mid-Atlantic regions of the United States, as well as Europe
and the Pacific Rim.
A morphometric "tooth space" was constructed using the
eigenvectors generated from Principal Component Analysis of the dental
character data.The results of the analysis show that Mesozoic marine
reptiles occupied a small, discrete region of the tooth morphospace,
whereas Cretaceous sharks occupied a much larger, diffuse region of
the morphospace. During the Paleogene a profusion of shark tooth
morphologies occurred and then expanded into new areas of tooth
morphospace.Yet, no overlap with the morphospace previously occupied
by Mesozoic marine reptiles occurred.A large number of novel tooth
morphologies evolved with the evolution of marine mammals during the
Cenozoic. Remarkably, many of the tooth forms converged on the
Mesozoic marine reptile designs, and hence a major overlap of marine
mammal tooth morphospace with the previously occupied Mesozoic marine
reptile morphospace occurred.Additionally, the shift from heterodonty
(teeth of different types) to homodonty (teeth of similar types)
occurred in several members of both the Mesozoic marine reptiles and
the Cenozoic marine mammals.
Based on dental morphology, this study indicates that following
the extinction of the Mesozoic marine reptiles during the Late
Cretaceous, Cenozoic sharks failed to occupy the vacated niches, yet
Cenozoic marine mammal dentition converged on the previous Mesozoic
marine reptile tooth designs.Apparently, Cenozoic marine mammals occupied
the vacated Mesozoic marine reptile dietary niches.
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Jerry D. Harris
Director of Paleontology
Dixie State College
Science Building
225 South 700 East
St. George, UT 84770 USA
Phone: (435) 652-7758
Fax: (435) 656-4022
E-mail: jharris@dixie.edu
and dinogami@gmail.com
http://cactus.dixie.edu/jharris/
"Actually, it's a bacteria-run planet, but
mammals are better at public relations."
-- Dave Unwin