On a dorsal dermal spine of the hylæosaurus recently discovered in the strata of Tilgate forest

Abstract

In the first discovered specimen of the remains of the fossil reptile named Hylæosaurus by the author, there were associated with the recognizable parts of the skeleton a series of thin, long angular processes, six or seven of which extended in a line nearly parallel with the upper part of the vertebral column: these bones are from four to seventeen inches in length. There are also several imbedded in various parts of the same block of stone; and in another specimen of this reptile, consisting of a considerable portion of the distal part of the vertebral column, similar angular bones are associated with the spine. The true nature of these processes, from their great size and osseous character, was deemed very problematical: Dr. Mantell, in his original memoir in 1832, regarded them as dorsal dermal spines that had formed a serrated crest which extended along the back of the Hylæosaurus, in the same manner as the horny dermal fringe in many species of Iguana, Cyclura, &c. Professor Owen, in his reports on British fossil reptiles, expressed his dissent from this opinion, and considered it more probable that the bones in question were abdominal ribs. In a memoir on the Iguanodon and Hylæosaurus (Phil. Trans. 1849), Dr. Mantell states that he had been able to obtain slices of one of these spines for microscopical examination, and that their internal structure was identical with that of the acknowledged dermal scutes of the same reptile. Still the true form of the articulating surface of the base of these spines was unknown, every specimen being imperfect in this respect. At length, after the lapse of eighteen years, Dr. Mantell obtained, through the liberality of Mr. Peter Fuller of Lewes, from the very quarry in which the original specimen of Hylæosaurus was found, the spine figured and described in this communication, in which the base is sufficiently entire to show that the mode of implantation in the skin was identical with that of the true dermal scutes; thus confirming the authors original interpretation of these remarkable appendages having constituted a serrated crest along the back of the Hylæosaurus. The specimens, and the microscopical sections, were exhibited to the Society.