The Ground Sharks, Carcharhiniformes, are the largest extant Shark group today, comprising over 280 species, which are variously refereed to as Requiem Sharks, Weasel Sharks, Houndsharks, Catsharks and Hammerheads. They have a fossil record which dates back to the Middle Jurassic, though, as with other Shark groups, this comprises almost entirely of teeth, due to the lack of a mineralised skeleton.
In a paper published in the Journal of Vertebrate Paleontology on 3 May 2019, Sebastian Stumpf of the Department of Palaeontology at the University of Vienna, Udo Scheer of Sat Mătăsaru in Romania, and Jürgen Kriwet, also of the Department of Palaeontology at the University of Vienna, describe a new species of Ground Shark from the Late Cretaceous Hesseltal Formation of Lower Saxony in northeast Germany.
The Hesseltal Formation comprises a sequence of organic-rich laminated marlstones with organic carbon alternating with light and sometimes red limestone and marl beds, associated with a time of rapid global warming, rising sea levels and repeated incidents of ocean anoxia, known as the Cenomanian–early Turonian Oceanic Anoxic Event 2.
The new species is named Diprosopovenator hilperti, where 'Diprosopovenator' means 'two-faced hunter', in reference to the fact that the specimen is preserved in two slabs as part and counterpart, and 'hilperti' honours fossil collector Karl-Heinz Hilpert, who found rhe specimen from which the species is described and donated it to the Ruhr Museum in Essen. One of the slabs preserves part of the neuro- and splanchocranium, including part of the upper and lower mandibular arch with associated dentition, as well as a patch of densely packed placoid scales posterior to the cranium, the other remains of the lower mandibular arch plus associated dentition, part of the anterior vertebral column comprising nine vertebral centra, as well as part of the dermis. All are somewhat compressed and distorted.
The teeth of Diprosopovenator hilperti resemble those of modern Catsharks, Scyliorhinidae, a group currently considered to date back to the Middle Jurassic. However recent mollecular studies have suggested that the Scyliorhinidae is a paraphyletic group (i.e. does not contain all the descendents of their most recent common acestot), which makes the inclusion of ancient fossils in the group difficult, for which reason Stumf et al. recomend that all fossil species currently assigned to the Scyliorhinidae, should be considered to be unplaced members of the Carcharhiniformes until they are better understood. Having said this, they note that Diprosopovenator hilperti does appear to be closely related to the previously desctibed Pseudoscyliorhinus reussi and Pseudoscyliorhinus schwarzhansi, and therefore place the three species together in a new family, the Pseudoscyliorhinidae.
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The new species is named Diprosopovenator hilperti, where 'Diprosopovenator' means 'two-faced hunter', in reference to the fact that the specimen is preserved in two slabs as part and counterpart, and 'hilperti' honours fossil collector Karl-Heinz Hilpert, who found rhe specimen from which the species is described and donated it to the Ruhr Museum in Essen. One of the slabs preserves part of the neuro- and splanchocranium, including part of the upper and lower mandibular arch with associated dentition, as well as a patch of densely packed placoid scales posterior to the cranium, the other remains of the lower mandibular arch plus associated dentition, part of the anterior vertebral column comprising nine vertebral centra, as well as part of the dermis. All are somewhat compressed and distorted.
Diprosopovenator hilperti, RE A 4872/1, holotype. (A) interpretative composite drawing combining RE A 4872/1 (dark gray) and RE A 4872/2 (light gray). (B)–(E), RE A 4872/1. (B), under normal light; (C), close-up view of placoid scales; (D), interpretative drawing; (E), under ultraviolet light. Abbreviations: ao.w, antorbital wall; d, dermis; hym, hyomandibula; l, left (in parentheses, e.g., ‘M.c(l)’); M.c, Meckel’s cartilage; nc, neurocranium; ot.cap, otic capsule; pl.sc; placoid scales; po.pr, postorbital process; po.w, postorbital wall; pq, palatoquadrate; r, right (in parentheses, e.g., ‘M.c(r)’); so.cr, supraorbital crest; spt.r, sphenopterotic ridge; t, teeth; v.c, vertebral centra. Stumf et al. (2019).
The teeth of Diprosopovenator hilperti resemble those of modern Catsharks, Scyliorhinidae, a group currently considered to date back to the Middle Jurassic. However recent mollecular studies have suggested that the Scyliorhinidae is a paraphyletic group (i.e. does not contain all the descendents of their most recent common acestot), which makes the inclusion of ancient fossils in the group difficult, for which reason Stumf et al. recomend that all fossil species currently assigned to the Scyliorhinidae, should be considered to be unplaced members of the Carcharhiniformes until they are better understood. Having said this, they note that Diprosopovenator hilperti does appear to be closely related to the previously desctibed Pseudoscyliorhinus reussi and Pseudoscyliorhinus schwarzhansi, and therefore place the three species together in a new family, the Pseudoscyliorhinidae.
Diprosopovenator hilperti, RE A 4872/2, holotype, (A) under normal light; B, close-up view of vertebral column; (C) under ultraviolet light. Abbreviations: l, left (in parentheses); M.c, Meckel’s cartilage; r, right (in parentheses). Stumf et al. (2019).
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