The first articulated specimen of the Cretaceous mackerel shark Haimirichia amonensis gen. nov. (Haimirichiidae fam. nov.) reveals a novel ecomorphological adaptation within the Lamniformes (Elasmobranchii)

International audienceThe first shark from the early Late Cretaceous Konservat Lagerstätte of Agoult (south-eastern Morocco) is described. The specimen consists of the anterior part of an articulated skeleton including the cephalic and branchial regions, anterior vertebrae and one pectoral fin. The well-preserved dentition of this specimen indicates that it corresponds to the fossil lamniform originally described as Odontaspis amonensis Cappetta & Case, 1975, a purported odontaspidid species of unclear affinities. The new material provides crucial anatomical data for this taxon, such as head shape, cranial structure, tooth formula, organization of the ampullary system and type of vertebra. Based on these features, this short-snouted, broad-headed shark is confirmed as a member of Lamniformes but is clearly not assignable to any of the known living and fossil genera, and is thus described as Haimirichia amonensis gen. nov. Moreover, this unique set of features, including several autapomorphies, differs sufficiently from those of odontaspidids and other lamniform families (both living and extinct) that it requires the erection of the family Haimirichiidae fam. nov. The articulated specimen of H. amonensis reveals a novel ecomorphological specialization within the Lamniformes, adding to the high disparity observed within this order. During the Cenomanian, H. amonensis was a common, widely distributed species that likely had a lifestyle similar to that of some living medium-sized coastal pelagic carcharhiniform sharks with a comparable overall morphology, such as the whitetip reef shark Triaenodon obesus