Original paper
The Late Jurassic shark Palaeocarcharias (Elasmobranchii, Selachimorpha) – functional morphology of teeth, dermal cephalic lobes and phylogenetic position
Landemaine, Olivier; Thies, Detlev; Waschkewitz, Jens
Palaeontographica Abteilung A Band 312 Lieferung 5-6 (2018), p. 103 - 165
published: Nov 1, 2018
Abstract
New remains of the Late Jurassic selachimorph elasmobranch Palaeocarcharias stromeri de Beaumont, 1960, comprising one holomorphic specimen and seven isolated oral teeth are described. The articulated specimen is from the Early Tithonian of Southern Germany and shows dermal cephalic lobes, a character which is so far regarded as an autapomophy of the Recent Orectolobidae (nurse sharks). Together with the similar isolated teeth from Southwest France, which are also Earliest Tithonian in age, it reveals the morphology of the lateral and posterolateral teeth, which were previously unknown in this shark. A new order Palaeocarchariiformes and a new family Palaeocarchariidae are introduced for P. stromeri. With respect to biostratigraphy and paleobiogeography, unambiguous remains of Palaeocarcharias are known from the Kimmeridgian to the Early Tithonian of the Eastern Central Atlantic and the north margin of the "Mediterranean Tethys”. Questionable remains are reported from the Tithonian of the south margin of the "Mediterranean Tethys” and the Middle Volgian of the Russian Boreal Realm. The tooth architecture of some orectolobiforms (e.g. Orectolobidae) and stem-lamniforms characterizes the orectoloboid and lamnoid tooth designs, respectively. An analysis of structural and functional morphology of anterior teeth of Palaeocarcharias shows that they agree much better with the lamnoid design than with that of the orectolobiform teeth from which they are derived. The surface of the elasmobranch tooth root is covered by smaller pores and larger foramina. The fixation (anchoring and linking) pores are the imprints on the root surface of collagen fiber bundles attaching the tooth firmly into the connective tissue of the oral mucosa or interconnecting successive teeth in the same file. Foramina are the holes (or openings) left by the internal vascularization system of the tooth. The arrangement of linking pores on the Palaeocarcharias teeth also matches the lamnoid design. A Bayesian analysis shows Palaeocarchariiformes nov. ord. as the sister-group of Lamniformes/Carcharhiniformes, with both clades forming a sister-group relationship to the Orectolobiformes. The Palaeocarchariiformes possibly begin in the Middle Jurassic as indicated by the geological age of its sister-group Lamniformes/Carcharhiniformes. P. stromeri is morphologically intermediate between the orectolobiforms and lamniforms. This illustrates a possible evolutionary scenario that demonstrates the way by which lamniforms could have developed from Jurassic Orectolobiformes.
Keywords
Chondrichthyes •
Elasmobranchii •
Palaeocarcharias
•
Jurassic •
lithographic limestones