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New Petalodonts (Chondrichthyes) from the Upper Mississippian Bear Gulch Limestone (Namurian E₂b) of Montana

Richard Lund
Journal of Vertebrate Paleontology
Vol. 9, No. 3 (Sep. 28, 1989), pp. 350-368
Stable URL: http://www.jstor.org/stable/4523270
Page Count: 19
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New Petalodonts (Chondrichthyes) from the Upper Mississippian Bear Gulch Limestone (Namurian E₂b) of Montana
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Abstract

Five new petalodonts are described from the Bear Gulch Limestone (Namurian) of Montana. Belantsea montana and Netsepoye hawesi (Family Belantseidae, nov.) are holomorphs with complete heterodont dentitions and a body form never seen before among chondrichthyans. Siksika ottae (Family Pristodontidae) consists of a braincase and associated teeth, Petalorhynchus beargulchensis (Family Pristodontidae) is a very small anterior part of a fish with one well preserved tooth and parts of several others, and Janassa clarki (Family Janassidae) is known from an isolated tooth. Heterodonty prevents attribution of most isolated petalodont tooth taxa to a classification scheme, but permits determination of the apomorphous characters of the order and exclusion of several taxa previously considered to be petalodonts. The dental morphology and histology of the clade containing Tanaodus, Harpacodus, and Lisgodus support a hypothesis of sister group relationships with the Petalodontiformes as restricted. The evolution of differential dental developmental pathways is seen as a driving mechanism of evolution both within the Petalodontiformes and in the proposed sister clade.

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