Monday, February 8, 2016

[PaleoIchthyology • 2016] 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)


Haimirichia amonensis
Vullo, Guinot & Barbe, 2016

Figure 1.
General view of the articulated specimen (UM AGT 1) of Haimirichia amonensis from Agoult, Morocco.
  A, ventral part in dorsal view (slab UM AGT 1a) and interpretative line drawing; B, dorsal part in ventral view (counterslab UM AGT 1b) and interpretative line drawing.
Scale bar = 10 cm.  DOI:  10.1080/14772019.2015.1137983  

Abstract

The 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.

Keywords: lamniform sharks, Haimirichiidae fam. nov., Haimirichia gen. nov., ecomorphology, Upper Cretaceous, Morocco


Conclusions
The lamniform shark Haimirichia amonensis was previously known only from isolated teeth and was thought tobelong to the lamniform family Odontaspididae (sandtiger sharks). By revealing unique morphological features, anatomical study of the new, articulated specimen of H. amonensis demonstrates that this species is not an odontaspididmember and must be assigned to a new genus andfamily within the order Lamniformes. The shape and positionof the orbital processes and the specialized type of dermal denticle directly associated with the electrosensory ampullary system are two of the peculiar, autapomorphic features of Haimirichia.

The new articulated specimen shows that H. amonensis was one of the major components of the mid-Cretaceous morphological and ecological lamniform diversification. Haimirichia represents a novel, unique ecomorphotype within lamniforms, and reaffirms the high disparity observed within this order through Late Cretaceous and Cenozoic time (Cappetta 2012, p. 33). The morphological features and occurrences of H. amonensis suggest that this tropical-subtropical shark had life habits and a feeding behaviour similar, at least in part, to those of some extant carcharhiniforms such as Triaenodon obesus and Sphyrna tiburo. As with the extinct anacoracid Squalicorax and the extant carcharhinids Carcharhinus and Galeocerdo (Cappetta 2012, pp. 33, 246), this is another case of parallel evolution between a Cretaceous lamniform taxon and Cenozoic and/or living carcharhiniforms.


 Romain Vullo, Guillaume Guinot and Gérard Barbe. 2016.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). Journal of Systematic Palaeontology .  DOI:  10.1080/14772019.2015.1137983     

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