Damocles serratus, Lund, 1986

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 : 96-97

DAMOCLES SERRATUS Lund, 1986

MATERIAL EXAMINED: MV 5449, complete small individual lacking a dorsal spine, with the head in ventrolateral view, and a twisted caudal skeleton, part and counterpart; MV 6158, dorsal spine in lateral view, associated with scattered dermal denticles, part and counterpart; MV 7685, small curled skeleton with well-preserved head and detached dorsal spine lying across caudal fin, part and counterpart; all from Fergus County, Montana; Bear Gulch Limestone, Bear Gulch member, Heath formation, Upper Chesterian, Namurian E2b, Upper Mississippian.

GENERAL REMARKS: Damocles serratus is the second falcatid symmoriiform described from the Bear Gulch Limestone of Montana ( Lund, 1986). Fewer specimens are known than for Falcatus falcatus and its skeletal anatomy is less completely known. No females have been identified satisfactorily, although one specimen of uncertain gender lacks a dorsal spine ( MV 5449). Where present, the spine resembles that of Falcatus , but it is not associated with a Stethacanthus -like ‘‘brush’’ or a Falcatus - like dorsal rod (although this could be fused to the distal part of the spine). Lund (1986) described the teeth of D. serratus as similar to those of F. falcatus , although they may have a shallower lingual torus. Damocles teeth may also lack an apical button (as in Stethacanthulus ), but it has not been determined whether this feature was absent or present in Falcatus .

DESCRIPTION: The braincase in Damocles serratus is known from only a few specimens, all of which are preserved in lateral or ventrolateral views (fig. 57). The postnasal wall is short and poorly calcified. As in Falcatus falcatus , ringlike denticles mark the course of the cephalic sensory line system and reveal that the snout extended a considerable distance in front of the jaws although there is no evidence of cartilage mineralization in the rostrum ( Lund, 1986: fig. 5). There is a large, round orbit and the otic region is short. No features of the orbital wall are known, but a large sclerotic ring is present and consists of numerous small plates as in F. falcatus . The postorbital arcade is delicate and short anteroposteriorly. Lund (1986) suggested that variation in the length of the otic region in D. serratus may be growth related, although in MV 7685 and CM 35472 (which are apparently closely matched in size) there is considerable discrepancy in the relative length of the otic region. The occipital arch was short. It is unknown whether there was a persistent otico-occipital fissure.

Articulated specimens of Damocles show that the otic process of the palatoquadrate made extensive contact with the postorbital arcade, suggesting that the jaw firmly attached by ligaments and other connective tissue although the postorbital articulation (on the ventrolateral surface of the arcade) was quite small. Lund (1986: fig. 4) reconstructed the orbital attachment of the palatoquadrate as robust as in Falcatus .

ORDER CLADOSELACHIDA DEAN 1909 FAMILY CLADOSELACHIDAE DEAN 1894