The Little Placoderm Who Could

Bothriolepis

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When one considers the placoderms, the image of Dunkleosteus terrelli probably comes to mind. However, the class is much more diverse than the arthrodires, with a myriad of body forms arising over the group’s fifty million year run. Bothriolepis is a good example of this. Though they share armor plating, the similarities between these general seem to end there. Size, for instance, provides a stark contrast. Dunkleosteus grew to between twenty and thirty feet long, with a head up to four feet wide, whereas the diminutive Bothriolepis had a head only four inches wide (Waggoner, 2000).

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Bothriolepis lacks the craniovertebral joint of the arthrodires that allowed its chondrocranium to rise as its splanchnocranium drops. However, this may have allowed for a larger braincase in this benthic creature (Young, 1984). This genus, along with the rest of the placoderms, went extinct in the Mississippian Period with no modern relatives. The reason for placoderm extinction, especially when members of Class Chondrichthyes survive today, is mysterious.
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Young, G.C. (1984). “Reconstruction of the Jaws and Braincase in the Devonian Placoderm Fish, Bothriolepis .” Palaeontology, Vol. 27 (3), 635-661.
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Waggoner, B. (2000). “Introduction to the Placodermi.” Retrieved 29 Mar 2008 from http://www.ucmp.berkeley.edu/vertebrates/basalfish/placodermi.html.