Thursday, April 23, 2020

[PaleoMammalogy • 2019] Cartierodon egerkingensis • A Large Hyaenodont from the Lutetian of Switzerland expands the Body Mass Range of the European Mammalian Predators during the Eocene

Cartierodon egerkingensis
Solé & Mennecart, 2019

We here present a new hyaenodont genus and species from the Lutetian locality of Egerkingen γ (Switzerland; MP13?): Cartierodon egerkingensis gen. et sp. nov. The new taxon is represented by numerous dental elements, mostly isolated teeth. The molars show typical features of a hypercarnivorous predator such as the strong reduction of the crushing (talonid/protocone) and puncturing (metaconid) structures. The calculation of several dental indices indicates that this hyaenodont may have been a bone-cracking predator. The new taxon differs from all the hyaenodonts previously known in Europe during the Ypresian and Lutetian by its larger size, with an estimated mass of almost 29 kg (the size of the extant African wild dog, Lycaon pictus). Other hyaenodonts known for this period do not exceed 20 kg. Previous authors proposed the hypothesis of an ecological limitation of the body mass, but the description of Cartierodon egerkingensis indicates instead that the European hyaenodonts continuously increased in size throughout the Eocene. We also performed a phylogenetic analysis in order to test the relationships of this new taxon: the new hyaenodont appears to be closely related to the Lutetian hyaenodont Prodissopsalis eocaenicus.

Key words: Mammalia, Hyaenodonta, Cartierodon, ecology, phylogeny, Eocene, Switzerland.

Hyaenodontid mammal Cartierodon egerkingensis gen. and sp. nov. from Switzerland, Egerkingen γ (MP13?, Lutetian, Eocene)

Systematic palaeontology 
Hyaenodonta Van Valen, 1967 
Hyaenodontoidea Leidy, 1869 
Hyaenodontidae Leidy, 1869 

Genus Cartierodon nov. 
Type species: Cartierodon egerkingensis sp. nov.; monotypic, see below. 

Etymology: Dedicated to Pastor Robert Cartier, who excavated the infilling of Egerkingen γ from 1840 to 1884 and gave his collection to the Naturhistorisches Museum Basel; combined with Greek odon, tooth. 

Cartierodon egerkingensis sp. nov.

Etymology: Refers to the type locality, the filling of Egerkingen γ. 
Holotype: NMB.Em.11, right mandible bearing p2, p3, p4, the trigonid of m1, and the alveoli of p1. 

Type locality: Egerkingen γ, Gaü, Solothurn, Switzerland. 

Type horizon: Unnamed unit of karst fillings in an aberrant siderolitic facies; MP13?, Lutetian, Eocene.

Diagnosis.— Differs from all contemporaneous European hyaenodont genera (Oxyaenoides, Proviverra, Cynohyaenodon, Eurotherium, Prodissopsalis, Leonhardtina, Allopterodon, Alienetherium, and Praecodens) by its larger size. It differs from Oxyaenoides by the presence of a metaconid on molars and transversally enlarged premolars. It also differs from Proviverra, Cynohyaenodon, Eurotherium, Leonhardtina, Allopterodon, Alienetherium, and Praecodens by a poorly developed metaconid on molars. It differs from Quer cytherium, with which it shares transversally enlarged premolars, by its larger size, poorly developed metaconid on molars, and less squared p2 and p3. It differs from Prodissopsalis eocaenicus, its closest hyaenodont relative, by a second foramen located below the anterior root of the p4, wider lower premolars, mesiodistally shorter talonid on m3, and a protocone area more developed on P3.

Taxonomy.— Modifications to the Borths and Stevens (2017b) matrix grouped almost all “proviverrine” taxa sensu Solé (2013) in the same clade (see below). However, hyaenodontines are still included in the “proviverrine” clade, as in previous analyses. This result refutes the monophyly of “Proviverrinae” sensu Solé (2013), resolving “proviverrines” as part of hyaenodontine stem lineages. Because our results agree with those of Borths et al. (2016), we propose to consider the Proviverrinae as a clade that includes the last common ancestor of Proviverra and Parvagula. We here propose to name Hyaenodontoidea the clade that includes the last common ancestor of Proviverra and Hyaenodon. This results in grouping Hyaenodontidae and Proviverrinae among Hyaenodontoidea.

The description of Cartierodon egerkingensis based on fossils from Egerkingen γ (MP13?) importantly improves our knowledge of the ecology of the Lutetian hyaenodonts. This taxon likely represents a bone-cracking hypercarnivore. Moreover, it is the largest hyaenodont from the Lutetian. 
Its body mass clearly shows that the maximum body mass of the European hyaenodontoids increased throughout the Ypresian and Lutetian, possibly in response to the vacated large-size predator niche after the disappearance of oxyaenids (Palaeonictis and Oxyaena) and mesonychids (Dissacus and Pachyaena) during the Ypresian. 
However, one can still wonder why European hyaenodonts did not reach 150 kg during the Eocene as some Pachyaena species did during the early Ypresian of Europe. This question needs future study, including the analysis of available prey body masses.

Floréal Solé and Bastien Mennecart. 2019. A Large Hyaenodont from the Lutetian of Switzerland expands the Body Mass Range of the European Mammalian Predators during the Eocene. Acta Palaeontologica Polonica. 64(2); 275-290. DOI: 10.4202/app.00581.2018