Was Xenodens calminechari described from a fake fossil?

Humans have been taking an interest in fossils for a long time—perhaps since the days of the Neanderthals. Ever since the interest of more and more people in owning a piece of the deep past gave rise to a market for fossils in the early 19th century, fakes and forgeries have been circulating among authentic specimens. The earliest historical evidence documents fossil forgery in Verona (Italy) in 1827. With the boom of the fossil market in recent decades and especially recent years, the commercial incentive to manipulate specimens to fetch higher prices at mineral shows or auctions has never been higher.

Palaeontologists have long recognised such practices as harmful to science—and linked it to the issue of illicit fossil trafficking. And yet, instances continue to be reported where specimens of at least doubtful provenance turn out to have been tampered with. The lastest example: Xenodens calminechari.

A new, strangely-toothed mosasaur

In 2021, X. calminechari was described as a new genus and species of mosasaurid from the upper Maastrichtian of Morocco. The authors, under the lead of Nicholas Longrich, named the genus after the type specimen's most striking feature: its strange teeth. X. calminechari had highly unusual, shark-like teeth, which was something never before seen in other mosasaur species and even squamates and tetrapods in general. Furthermore, the authors declared that the fossil of the type specimen had come out of the Sidi Chennane phosphate mine and "was collected by locals working in the mines, rather than by paleontologists, complicating attempts to constrain stratigraphy and provenance." The fossils are kept in the collections of the Muséum d’Histoire naturelle de Marrakech.

Not a new, strangely-toothed mosasaur?

The authenticity of the specimen was challenged on 16 December 2024 when a group of researchers published a reassessment of the holotype specimen. One of the authors was Michael Caldwell who already lead another reassessment study in 2021, that time for the fossil of Tetradophis amplectus, an alleged four-legged snake which had been smuggled from Brazil. Together with his co-authors, he suggests that the holotype of X. calminechari had been manipulated, and possibly wrongly interpreted as well.

It was the dentition which made them suspicious. Longrich et al. (2021) had reported that four teeth seem to have only two roots. The authors of the reassessment study suggest, however, that the teeth have been glued in place. Since they were not given access to the holotype, they used different fossils which are known to be forgeries to demonstrate how a CT scan can determine whether adhesive was used. They also encourage Longrich et al. to perform such an analysis. This, the authors emphasise, is even more necessary in light of the provenance of the holotype specimen.

Moreover, the authors suggest that X. calminechari might not be a new genus and species after all but rather a juvenile form of another mosasaur (perhaps Carinodens).¹ Its teeth had been its more striking feature when X. calminechari was described in 2021 but Longrich et al. might have insufficiently considered how much the teeth of lizards can vary even within the same species. In their view, X. calminechari is a nomen dubium, i.e., a scientific name of uncertain validity.

Legal and ethical concerns

The case of X. calminechari brings together different aspects that are currently not going right in palaeontology: the lack of care about the legal provenance of fossils, the access to specimens, and the description of new species even from insufficient materials.

Legal fossil collection and due diligence in publishing

First, there are pressing legal questions which nobody in the publication process for the description of the new species seems to have bothered to address. Admittedly, the frequent issue of illicit trafficking does not concern us here since the fossil remains in its country of origin. However, Article 116 of Morocco’s 2015 Mining Code provides that fossils may only be collected and commercialised with a permit.

Therefore, it is entirely unclear whether the fossil of X. calminechari was obtained in compliance with the legal requirements of the Mining Code.

This does not seem to have bothered the authors but neither the reviewers nor the editors of the study appear to have done their due diligence regarding the legal provenance of the studied material.

Fossil access and reproducibility

Second, the case raises concerns about access to scientific materials and, ultimately, reproducibility. This is a core pillar of good science: researchers need to be able to run the same tests as their colleagues to determine whether they come to the same result. To that end, access to scientific data is crucial. In the context of studies on physical fossil material the imperative of reproducibility will in many cases demand physical access to specimens, and the reassessment study is precisely such an example: its authors could only have performed the CT scan which they consider necessary on the actual specimen. That Longrich et al. did not make this possible for them, seemingly without giving any reason, is therefore problematic from a research ethics point of view. Such behaviour stands in the way of scientific progress. Interestingly, the issue of access to specimens is typically discussed when fossils are in private collections but the case of X. calminechari shows how this can affect specimens in public collections, too.

Premature description of new species

Third and last, the reassessment study effectively charges Longrich et al. with sensationalism in their taxonomic work, claiming that tried to describe a new genus and species where there was insufficient scientific evidence for it. Especially in the context of squamates, they criticise the practice of naming new species from tooth-based holotypes since the teeth of these animals might considerably converge across different species and diverge within the same species.

To me, this reads like a valid criticism but I am not a scientist and will therefore not make myself the judge of this dispute. The same way I do not appreciate palaeontologists trying to explain what the law says, I will not try and tell them what science says.

What I will say is that I deeply respect reassessment studies such as the most recent one for X. calminechari or the one for the “four-legged snake.” To my mind, these form a crucial institution of scientific quality control—instead of chasing the next gen. et spec. nov.