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. 2021 May 11:9:e11362.
doi: 10.7717/peerj.11362. eCollection 2021.

Durnonovariaodus maiseyi gen. et sp. nov., a new hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of England

Affiliations

Durnonovariaodus maiseyi gen. et sp. nov., a new hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of England

Sebastian Stumpf et al. PeerJ. .

Abstract

A partial skeleton of a hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of Dorset, England, is described and designated as a new genus and species, Durnonovariaodus maiseyi gen. et sp. nov. The holotype and only known specimen, which is represented by disarticulated splanchnocranial elements with associated teeth, a single dorsal fin spine, the pelvic girdle, as well as unidentifiable cartilage fragments, plus countless dermal denticles, exhibits a puzzling combination of dental and skeletal features, providing important new insights into the morphological and ecological diversity of hybodontiforms. Durnonovariaodus gen. nov. displays a unique set of dental characters, showing close morphological resemblance to Secarodus from the Middle Jurassic of England, which was erected for distinctive, strongly labio-lingually compressed multicuspid cutting teeth originally described as Hybodus polyprion. Skeletally, Durnonovariaodus gen. nov. resembles Hybodus and Egertonodus in having a palatoquadrate with a palatobasal process and an ethmoidal articular surface, combined with the possession of dorsal fin spines ornamented with costae. Therefore, and given the absence of any conclusive phylogenetic framework, Durnonovariaodus maiseyi gen. et sp. nov. is here tentatively referred to Hybodontidae until more complete material becomes available in order to enable a more reliable suprageneric identification. The holotype of Durnonovariaodus maiseyi gen. et sp. nov. contains two separate pelvic half-girdles, a feature previously considered as evolutionarily primitive among hybodontiforms. However, unfused pelvic half-girdles also occur in the supposedly closely related species Hybodus hauffianus and may in fact have been more widely distributed among hybodontiforms than previously thought, thus rendering the phylogenetic utility of separated pelvic half-girdles for inferring hybodontiform interrelationships difficult and unresolved.

Keywords: Chondrichthyes; England; Hybodontiformes; Kimmeridge Clay Formation; Late Jurassic; Mesozoic; Taxonomy.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Location map.
Rough palaeogeographic reconstruction of the western Tethys during the early Tithonian (modified from Thierry et al., 2000) showing the type locality Durnonovariaodus maiseyi gen. et sp. nov. near Freshwater Steps, Encombe, Dorset, England (indicated by a star).
Figure 2
Figure 2. Durnonovariaodus maiseyi gen. et sp. nov., MJML K1624, holotype, from the Upper Jurassic Kimmeridge Clay Formation (early Tithonian) near Freshwater Steps, Encombe, Dorset, England.
(A) Slab containing specimen. (B) Interpretative line drawing (dashed box indicates splanchnocranial elements shown in Fig. 3).
Figure 3
Figure 3. Durnonovariaodus maiseyi gen. et sp. nov., MJML K1624, holotype, from the Upper Jurassic Kimmeridge Clay Formation (early Tithonian) near Freshwater Steps, Encombe, Dorset, England.
(A) Splanchnocranium; (B) Interpretative line drawing. Anatomical abbreviations: af, adductor fossa; artcot, articular cotylus; br, branchial element; brr, branchial rays; ch, ceratohyal; dgr, dental groove; eart, ethmoidal articulation; hym, hyomandibular; l, left (in parentheses); Mc, Meckel’s cartilage; mqj, medial quadratomandibular joint; pbpr, palatobasal process; pq, palatoquadrate; qf, quadrate flange; r, right (in parentheses).
Figure 4
Figure 4. Durnonovariaodus maiseyi gen. et sp. nov., MJML K1624, holotype, from the Upper Jurassic Kimmeridge Clay Formation (early Tithonian) near Freshwater Steps, Encombe, Dorset, England.
Overview of dentition (for anatomical abbreviations see caption to Fig. 3).
Figure 5
Figure 5. Durnonovariaodus maiseyi gen. et sp. nov., MJML K1624, holotype, from the Upper Jurassic Kimmeridge Clay Formation (early Tithonian) near Freshwater Steps, Encombe, Dorset, England.
Close-up view of teeth. (A–D) Anterior teeth in labial views. (E) Antero-lateral tooth in lingual view. (F) Lateral tooth in labial view. (G–I) Lateral teeth in lingual aspects (J) Postero-lateral teeth in labial views (K) Postero-lateral tooth in lingual view. (L, M) Extreme posterior teeth in (L) labial and (M) lingual aspect.
Figure 6
Figure 6. Durnonovariaodus maiseyi gen. et sp. nov., MJML K1624, holotype, from the Upper Jurassic Kimmeridge Clay Formation (early Tithonian) near Freshwater Steps, Encombe, Dorset, England.
(A) Dorsal fin spine. (B) Interpretative line drawing of complete specimen. (C, D) Pelvic girdle. (E) Close-up view of dermal denticles. (F, G) Simplified sketch drawing of dermal denticle in (F) lateral and (G) anterior view. Anatomical abbreviations: bp, basal plate; df, diazonal nerve foramina; pvg, pelvic half-girdle.
Figure 7
Figure 7. Separate pelvic half-girdles (pvg) in hybodontiforms.
(A, B) Male specimen of Hybodus hauffianus Fraas, 1895, SMNS 10060, from the Lower Jurassic Posidonienschiefer Formation of Holzmaden, Baden-Württemberg, Germany, in (A) total view and (B) close-up view of pelvic girdle. (C, D) Female specimen of H. hauffianus, SMNS 15150, from the Posidonienschiefer Formation of Holzmaden in (C) total view and (D) close-up view of pelvic girdle. (E) Hybodontiformes gen. et sp. indet., NHMUK PV P 339, from the Lower Jurassic of Lyme Regis, Dorset, England, showing pelvic girdle and associated clasper complex.

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