Symmorium reniforme, COPE, 1893

Maisey, John G., 2007, The Braincase In Paleozoic Symmoriiform And Cladoselachian Sharks, Bulletin of the American Museum of Natural History 2007 (307), pp. 1-122 : 77-80

SYMMORIUM RENIFORME COPE, 1893

MATERIAL EXAMINED: Holotype FMNH UF 574, plus X-rays; Court Creek, NE of Knoxville, Illinois; Mecca Quarry Shale, Liverpool cyclothem, Des Moines series, Westphalian Upper C, Pennsylvanian. Collected by F. R. Jelliffe, described by Cope (1893) and by Williams (1985); FMNH PF 2582, chondrocranium with rostrum; FMNH PF 2633, chondrocranium with rostrum, plus partial pectoral skeleton (both specimens Xrays only); Logan Quarry, Parke County, Indiana ( Zangerl and Richardson, 1963); Logan Quarry Shale, Lower Wiley cyclothem (Staunton formation), Des Moines Series, Westphalian Upper C, Pennsylvanian; FMNH PF 8274, chondrocranium (X-ray only); Hajji Hollow, Wabash Township, Parke County, Indiana; Logan Quarry Shale, Lower Wiley cyclothem (Staunton formation), Des Moines Series, Westphalian Upper C, Pennsylvanian.

GENERAL REMARKS: This genus and species is founded on the disarticulated anterior part of a skeleton, plus numerous teeth clustered around the jaws ( Cope, 1893).

(same specimen as ventral view shown in fig. 37). Scale bar 5 10 mm.

Williams (1985) referred several additional specimens to this species, although they differ from the holotype in overall tooth size and shape ( Ginter, 2002). Nevertheless, morphologically intermediate teeth have now been found and these differences are now considered to be growth-related (M. Ginter, personal commun., Feb. 2006). Some large isolated teeth were also referred to Symmorium reniforme by Williams (1985), but these differ profoundly from the teeth in the holotype and are now referred to the ctenacanthiform genus Glikmanius ( Ginter, 1998, 1999, 2002; Ginter et al., 2005), a form considered closely related to Cladodus (sensu Duffin and Ginter, 2006). The teeth in S. reniforme lack apical buttons, labiobasal projections, and a median labial concavity; instead, the upper side of the kidney-shaped tooth base has a long, low, crescent-shaped lingual ridge, the main cusp is flattened labiolingually, and there is a corresponding shallow, curved basal concavity. By contrast, Glikmanius teeth have a lingually directed base with two widely separated apical buttons, two corresponding labiobasal projections, and a median labial concavity between the projections.

DESCRIPTION: The braincase in Symmorium reniforme is not preserved in the holotype and can be observed only in X-rays of other specimens (listed above). In the most complete specimen (FMNH PF 2428), the head is preserved intact and has been compressed dorsoventrally, but the braincase cannot be distinguished from the underlying visceral skeleton. Williams (1985: 104) noted only that the otic region is short (approximately one-third the braincase length), that there is ‘‘a short, but well developed rostrum’’, and that the posterior process is ‘‘a stout, triangular projection and bears a thickened, transverse keel on its posterior border’’. As far as can be determined, however, the braincase resembles that of ‘‘ Cobelodus ’’ and may also have been tropibasic (especially since the palatoquadrate otic process is equally deep). Unfortunately, no direct indication of eye size can be established, because sclerotic cartilages are not preserved and the braincases are all dorsoventrally compressed. Consequently, it is not possible to confirm the presence of an interorbital septum (although one was probably present). No reconstruction of the braincase in S. reniforme will be presented here.

STETHACANTHULUS MECCAENSIS