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Priscansermarinus barnetti, a Probable Lepadomorph Barnacle from the Middle Cambrian Burgess Shale of British Columbia

Desmond Collins and David M. Rudkin
Journal of Paleontology
Vol. 55, No. 5 (Sep., 1981), pp. 1006-1015
Stable URL: http://www.jstor.org/stable/1304526
Page Count: 10
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Priscansermarinus barnetti, a Probable Lepadomorph Barnacle from the Middle Cambrian Burgess Shale of British Columbia
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Abstract

Priscansermarinus barnetti n.gen., n.sp., from the Middle Cambrian Burgess Shale of British Columbia is probably a lepadomorph cirriped. If so, it is the oldest barnacle known, pushing back the known age of the cirripeds 140 million years. Priscansermarinus has a remarkably modern aspect with a rounded, irregularly ovoid capitulum and a smooth, thick peduncle ending in a thickened collar or attachment disc. The capitulum appears to have a thick, leathery wall with two large tear-drop shaped chitinous plates similar in shape to the scuta of Lepas. The apparent presence of chitinous plates on Priscansermarinus supports the proposal of Newman, Zullo and Withers (1969) that the lepadomorph ancestor was of the Cyprilepas grade of construction with a chitinous shell, rather than that of Foster (1978) who proposed a non-shelled lepadomorph ancestor. The similarity in size and shape of the Priscansermarinus capitular plates to the scuta of Lepas suggests that in the phylogeny of the lepadomorph barnacles the scuta appeared before the terga and carina. Because barnacles are so highly modified compared to other crustaceans, a considerable length of time was needed for them to evolve from the ancestral crustacean. It is evident, therefore, that the presence of a probable lepadomorph barnacle in the Middle Cambrian, particularly one of such modern aspect, demonstrates that crustacean diversification began well before the Middle Cambrian, most likely during the late Precambrian arthropod radiation postulated by Whittington (1979).

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