The genus Heterodontus in the Early Paleogene of the North Sea Basin and the Landes, France

Type material of the four nominal Palaeocene-Eocene species of 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 realization 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 literature but I refrain 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.

 Keywords: North Sea Basin, Palaeocene, Eocene, Heterodontidae, Heterodontiformes, Heterodontus vincenti, Heterodontus lerichei, Heterodontus adneti nov. sp., tooth morphology, Heterodonty, basal ornamentation, Egem, Erquelinnes, Dormaal.

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

General paleogeographic overview and sedimentationof 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