Thaumastognathus is an extinct genus of Paleogene artiodactyls within the Choeropotamidae family. It was endemic to western Europe and lived from the Middle to Late Eocene. The genus and its only species T. quercyi were first described by French palaeontologist Henri Filhol in 1890. Thaumastognathus is best known from several mandibles with largely complete dental sets, with one larger mandible probably being an intraspecific variation. Although it was large in size in relation to its family, it was smaller than Choeropotamus and differed from it by several traits like thinner tooth enamel and longer diastemata; both genera share traits such as a caniniform first premolar.
Taxonomy
In 1890, French palaeontologist Henri Filhol stated that he was to introduce a new genus of mammal from the phosphorite deposits of Quercy, represented by a partial left mandible with a canine, premolars, and molars. He pointed out that the incisors increased in size from the first to the third in a row. He compared its dentition with those of other fossil artiodactyls, suggesting that it was distinct from most of them but that the premolars were somewhat similar to those of anthracotheres like Microbunodon. Filhol stated that given that it did not seemingly have a close analogue among artiodactyl groups like ruminants, he designated it the genus name Taumastognatus and the species name Taumastognathus Quercyi (the genus name being spelled differently). The genus name, for unclear reasons, was subsequently emended to Thaumastognathus starting from later 19th century taxa indexes onward. In 1908, Swiss palaeontologist Hans Georg Stehlin confirmed the validity and spelling of the genus Thaumastognathus, suggesting that it is related to the other artiodactyls Haplobunodon and Lophiobunodon. He additionally described a less complete right mandible from the Quercy phosphorites that were held in a Basel fossil collection. Stehlin suggested that a caniniform tooth being similar to that of the ruminant Bachitherium means that it was actually a first premolar rather than a canine.
Classification
Thaumastognathus is classified within the Choeropotamidae, a Palaeogene artiodactyl family endemic to western Europe that lived from the Middle Eocene to the Early Oligocene. Choeropotamidae had a particularly complicated taxonomic history, as many genera now classified in the family, other than Choeropotamus, were not originally recognized as such in the 20th century. In particular, many genera like Haplobunodon, Lophiobunodon, and Rhagatherium were classified in a separate family called the "Haplobunodontidae". As a result, Choeropotamidae had, by some sources, been considered a monotypic family, meaning that Choeropotamus was the only genus classified in it. However, the Haplobunodontidae had been synonymized by later taxonomists, its genera being reclassified into the Choeropotamidae. However, some authors have suggested that the Haplobunodontidae should be revived due to questions relating to the polyphyly of the Choeropotamidae. The Choeropotamidae as currently defined is polyphyletic. This is because cladistic analyses of "choeropotamids" based on dental anatomy reveal that not all genera share close synapomorphies (or traits of the latest common ancestor) to prove close relations between them. However, disagreements remain on whether or not Haplobunodon lies within the Choeropotamidae sensu stricto (in a strict sense) to justify a separate Haplobunodontidae family. Because the definition of the Choeropotamidae is polyphyletic and not agreed upon, the Choeropotamidae requires further analyses. Regardless of taxonomic problems, the Choeropotamidae has been well-defined as one of the endemic European Palaeogene artiodactyl groups that lived primarily during the Eocene. The Choeropotamidae itself from the middle Eocene up to the earliest Oligocene. Masillabune, arguably the oldest choeropotamid, made its first appearance during the unit MP11 of the Mammal Palaeogene zones. It was followed by the likes of Haplobunodon and Amphirhagatherium in MP12 and Hallebune in MP13. Two of the latest-appearing choeropotamids, Choeropotamus and Thaumastognathus, made their first appearances in MP16. Both Choeropotamus and Amphirhagatherium, the latest-surviving choeropotamids, extended up to MP20, coinciding with the Grande Coupure extinction event in western Europe. They are generally regarded as close relatives of the Cebochoeridae, another endemic European artiodactyl family. One phylogenetic tree example of the Choeropotamidae and Haplobunodontidae being defined as separate families according to Vincent Luccisano et al. in 2020 is shown below:
In 2022, Weppe conducted a phylogenetic analysis in his academic thesis regarding Palaeogene artiodactyl lineages, focusing most specifically on the endemic European families. One monophyletic set consisted of the Dichobuninae, Cebochoeridae, and two clades of the polyphyletic Choeropotamidae. He suggested that Cuisitherium and Lophiobunodon were not very closely related to the true clade of choeropotamids, consisting of Thaumastognathus, Choeropotamus, Amphirhagatherium, Rhagatherium, and the polyphyletic Haplobunodon; his analysis disagrees with other sources suggesting that some genera like Haplobunodon were not closely related to Choeropotamus and states that the Haplobunodontidae is therefore not valid. More specifically, he defined Thaumastognathus, Choeropotamus, Haplobunodon lydekkeri, and "H." solodurense as forming one specific clade of the Choeropotamidae sensu stricto.
Description
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