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| Xenodens calminechari be considered a nomen dubium in Sharpe, Powers et Caldwell, 2024. |
Abstract
Xenodens calminechari is a mosasaurid taxon named by Longrich et al. (2021) based on the holotype MHNM.KH.331, a left maxilla with several teeth. This holotype was obtained nonscientifically (without technical supervision) from an area in Morocco that yields many manipulated or forged specimens. Examination of Longrich et al. (2021) reveals four tooth crowns occupy what appear to be two alveoli in MHNM.KH.331, and there is potential adhesive connecting the tooth crowns to the maxilla on their lateral sides. We argue that the articulated tooth crowns of this taxon were artificially placed in the maxilla, rendering at least two apomorphies of this taxon the product of forgery. Longrich et al. (2021)'s claims of fused tooth ‘roots' in MNHM.KH.331 are instead calcified periodontal ligament and alveolar bone that have ankylosed, resembling the typical mosasaurid condition. Differing tooth crown morphology does not preclude the referral of the teeth of this specimen to a younger ontogenetic stage of another mosasaur (possibly Carinodens) because many extant lizard species show drastic ontogenetic changes in the dentition. We argue that Xenodens calminechari represents a nomen dubium. This specimen constitutes a confluence of two persistent problems in vertebrate paleontology: material sourced from commercial excavations that has not been adequately tested for forgery, and taxa named from tooth-based holotypes that ignore the potential for intraspecific dental variation and interspecific convergence in dental characters, as are common in squamates. We suggest that Longrich et al. CT scan MHNM.KH.331, and we supply CT examples for identifying artificially added tooth crowns to Moroccan mosasaur jaws. Finally, we provide recommendations for the designation of mosasaurid holotypes.
Keywords: dentition, mosasaur, paleontology, squamate, taxonomy
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| (a) MHNM.KH.331, holotype of Xenodens calminechari in lateral view in matrix, photograph adapted from Longrich et al., 2021; (b) fake mosasaurid jaw (UALVP unlisted) from Morocco showing tooth crowns artificially attached to unrelated bone fragments, ‘in matrix’; (b) close-up of tooth crowns in lateral view of MHNM.KH.331, photograph adapted from Longrich et al. (2021); (d) close-up of (c) showing tooth crown-‘jaw’ intersection; (e) close-up of Halisaurus arambourgi UALVP 56123 showing forged tooth-jaw intersection. |
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| Left maxilla of Xenodens calminechari, MHNM.KH.331: All photographs adapted from Longrich et al. (2021). (a) Maxilla in ventral view, showing irregular proposed tooth spacing in posterior tooth row; (b) close-up of (a) showing nonfusion of tooth roots due to separation of alveoli (marked by asterisks) by alveolar bone; (c) maxilla in medial view showing a disjunct arrangement of tooth crowns and resorption pits (which indicate alveolar spacing); (d) close-up of tooth crowns in medial view showing the irregular junction of tooth crowns and basal tissue; (e) close-up of tooth crowns in lateral view showing potential adhesive connecting tooth crowns to maxilla. |
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| CT scan example for recognizing falsely attached teeth in mosasaur fossils from Morocco. (a, b) Anterior portion of left dentary of Halisaurus arambourgi UALVP 56123 from type locality of Xenodens calminechari |
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| Issues with tooth-based holotypes in vertebrate paleontology, using three hypothetical species of mosasaurids as an example. Holotype 1 was established using an anterior adult tooth of species 2, and holotype 2 was established using a juvenile posterior tooth from species 1. Neither holotype adequately represents the anatomy of its target taxon. |
Henry S. Sharpe, Mark J. Powers and Michael W. Caldwell. 2024. Reassessment of Xenodens calminechari with A Discussion of Tooth Morphology in Mosasaurs. The Anatomical Record. DOI: doi.org/10.1002/ar.25612
