Palaeo Ichthyologica, Volume 17 [English] The Genus Heterodontus in the Early Paleogene of the North Sea Basin and the Landes, France

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Language: English

Type material of the four nominal Palaeocene-Eocene species of the bullhead shark genus Heterodontus from the North Sea Basin, H. lerichei Casier, 1943b, Heterodontus vincenti (Leriche, 1905), Heterodontus wardenensis Casier, 1966 and Heterodontus woodwardi Casier, 1946 is restudied, based on a very detailed analysis of H. vincenti specimens recovered from the Ypresian of Egem (Belgium) and on morphological, stratigraphical and environmental considerations and on intraspecific and interspecific conclusions from a study on the extant species Heterodontus mexicanus Taylor & Castro-Aguirre, 1972 and Heterodontus quoyi (Frémenville, 1840) (see Migom & Hoedemakers, 2023).

This led to the realisation that several of the above fossil species represent, in fact, different ontogenetic stages of the same species. In this work, a specimen from the original type series of H. vincenti is formally designated as lectotype and other specimens are designated as paralectotypes. Dignathic and gynandric heterodonty is observed in H. vincenti, and interspecific heterodonty with this species is demonstrated through a comparison with the above Recent species. A partial overview of the ontogenetic characteristics of the Palaeocene H. lerichei is presented. Heterodontus adneti nov. sp. is defined for specimens formerly described as Heterodontus cf. vincenti, sensu Adnet (2006). Figured specimens in Adnet (2006) are designated as holotype and paratype.

Other putative Heterodontus species are identified from the literature, but the author refrains from formally describing them as these specimens were not studied. Finally, a new set of characteristics, based amongst others on interspecific differences with the above-mentioned extant species, is suggested to identify H. vincenti and H. lerichei.

Contents

Introduction   5
Material and methods   5
Terminology   5
Abbreviations   6
Measurements   6

General paleogeographic overview and sedimentation of the NSB and limitrophe areas   7

Analysis of the dental morphology of Heterodontus in the Early Paleogene of the NSB   9
      Heterodontus vincenti (Leriche, 1905)   9
      Material studied   10
      Lectotype (here designated)   10
      Paralectotypes (here designated)   10
      Other comparative material   10
      Type locality and age   10

      Descriptions of H. vincenti from the Egem quarry   10
      Analysis of teeth of H. vincenti from the Egem quarry and comparison with teeth of the extant species H. mexicanus and H. quoyi   10

      Analysis of the types H. vincenti, H. woodwardi and H. wardenensis   16
      Lectotype of H. vincenti (Leriche, 1905)   16
      Paralectotypes of H. woodwardi Casier (1946)   18
      Paralectotypes of H. wardenensis Casier (1966)   20

      Heterodontus lerichei Casier, 1943   23
      Material studied   23
      Holotype   23
      Other material from Dormaal   23
      Type locality and age   23

      Description of the holotype mediolateral tooth of H. lerichei Casier, 1943b   24
      Descriptions of teeth of H. lerichei Casier, 1943b from Dormaal   24
      Adult dentition   24
      Juvenile dentition   29

      Heterodontus sp. (IRSNB P.00100)   32
      Analysis of teeth of H. lerichei   32

Heterodontus in the Eocene of the Landes, France   39
      Material studied   39
      Heterodontus adneti nov sp.   39
      Description of the tooth SG26 (Adnet, 2006)   39
      Description of the tooth SG27 (Adnet, 2006)   39
      Analysis and discussion of teeth of H. adneti nov. sp.   39

Discussion   41
      Earlier studies   41
      Palaeogeographic and stratigraphic distribution (earlier studies)   46
      Bathymetry (earlier studies)   48

Conclusions   50
      Conclusions on teeth of H. vincenti   50
      Conclusions on teeth of H. lerichei   53
      Conclusions on teeth of H. adneti nov. sp.   54
      Conclusions on Earlier Studies   54

Acknowledgements   55
Appendix   56
References   58

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