Azilestes

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Azilestes
Temporal range: 70–66  Ma
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Family: Zhelestidae
Genus: Azilestes
Gheerbrant & Teodori, 2021
Species:
A. ragei
Binomial name
Azilestes ragei
Gheerbrant & Teodori, 2021

Azilestes ("Mas-d'Azil robber") is a genus of probable zhelestid eutherian mammal, a family consisting of small herbivores, that was discovered in the early Maastrichtian Grès de Labarre Formation of France. [2] It is a monotypic genus, with only type species A. ragei being known. Only one specimen, the holotype described in 2021, is known. It consists of a partial dentary with teeth. [2]

Contents

Certain aspects of Azilestes's dental anatomy are convergent with later groups of herbivorous mammals, including Glires, though phylogenetic analysis strongly suggests a position within the Zhelestidae. [2] It possesses bunodont molars, enlarged postfossids and hypoconids, an interradicular crest and radicular grooves, a unique combination among Cretaceous eutherians. [2]

History of discovery

The sole specimen and holotype of Azilestes, a partial dentary with teeth, was discovered in the Grès de Labarre Formation of the northern Pyrenees, near the Mas-d’Azil of the Ariège department in Occitanie region, France. [2] The specimen was found in the northeastern outcrops of the Grès de Labarre levels, northeast of the Mas-d’Azil, by surface prospecting in the area. The vertebrate-bearing level where it was found is a fossiliferous hard limestone, belonging to the upper unit of the Grès de Labarre which overlies the Marnes d’En locality. [2] Together with the overlying "Marnes Rouges Inférieures" formation, an eastern lateral equivalent of the Marnes d'Auzas, it comprises the last Cretaceous deposits of the Sub-Pyrenean zone. [2]

Azilestes was described by Emmanuel Gheerbrant and Dominique Teodori in 2021, and much of its anatomy was mapped using CT scanning. [2] It was named for Mas-d'Azil, the type locality, and the Greek λῃστήσ, or lestes ("robber"). The specific epithet is after Jean-Claude Rage, in tribute to his major contribution to the study of Cretaceous microvertebrates from Europe. [2]

Description

Though damaged and fragmentary, the sole specimen of Azilestes, dated to the early Maastrichtian, [2] is one of the most complete jaw remains of a eutherian reported from the Late Cretaceous of Europe. It preserves only part of the mandibular corpus, including the posterior part of the mandibular symphysis. [2] The symphysis extends far posteriorly, close to the level of the alveolus of the fourth upper molar, and is very compact. The mandibular corpus is dorso-ventrally high, and labially inflated. [2] It is convex below the molars, but below the premolars and the symphysis, it is concave. Its dorso-ventral depth decreases drastically at the length of the symphysis. [2]

The posterior mental foramen is rather large and located ventro-labially below and between the two roots of the fifth upper molar, as in most Cretaceous eutherians. [2] The dentary preserves two damaged molars and four well-developed empty anterior alveoli, interpreted as corresponding to two-rooted fifth upper molar, and a single-rooted fourth upper molar and canine. [2] Among Cretaceous eutherians, the molar morphology of the holotype most closely resembles the family Zhelestidae, to which it is tentatively assigned. [2] Zhelestids were non-placental eutherians, and were specialized for a herbivorous diet. [3]

The bunodont cusps and crowns, a shortened, robust dentary with reduced premolar formula, a small hypolophid and cingular-like postcristid and hypoconulid are unique among Cretaceous eutherians. [2] The closest eutherian to Azilestes, assuming a zhelestid identity, is Valentinella . However, the comparison of these two genera is limited due to the latter's poor preservation. Shared attributes include a possible hypocone, bunodont molar crowns with bulbous cusps, and a robust and deep mandibular corpus that is laterally convex. [2]

Taxonomy

Phylogenetic analyses within the paper variably suggest Azilestes to be part of a zhelestid polytomy which includes solenodons, a monophyletic Zhelestidae, or a basal member of Glires, though all but the latter recover it as the sister genus to Valentinella, and in one phylogeny, they are part of the Lainodontinae. [2] While a position within the Zhelestidae is most likely, Gheerbrant and Teodori (2021) assume a basal position within the Eutheria. [2]

Below is a phylogeny from Gheerbrant & Teodori (2021): [2]

Palaeoecology

The bunodont molars, the large postfossid and hypoconid, wear patterns, and the development of an interradicular crest and radicular grooves indicate a crushing-grinding function for Azilestes's teeth, possibly suggesting a durophagous lifestyle. [2]

Only three non-avian dinosaurs are known to have coexisted with Azilestes. These are the rhabdodontid Rhabdodon , cf. Ampelosaurus atacis, and an indeterminate nodosaurid. [4] [1]

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References

  1. 1 2 Fossilworks: Maison Varin, Dreuilhe fossilworks.org. Retrieved 2021-03-29.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Gheerbrant E. & Teodori D. 2021. — An enigmatic specialized new eutherian mammal from the Late Cretaceous of Western Europe (Northern Pyrenees), in Folie A., Buffetaut E., Bardet N., Houssaye A., Gheerbrant E. & Laurin M. (eds), Palaeobiology and palaeobiogeography of amphibians and reptiles: An homage to Jean-Claude Rage. Comptes Rendus Palevol 20 (13): 207-223. https://doi.org/10.5852/cr-palevol2021v20a13
  3. L. A. Nessov, J. D. Archibald, and Z. Kielan-Jaworowska. 1998. Ungulate-like mammals from the Late Cretaceous of Uzbekistan and a phylogenetic analysis of Ungulatomorpha. Bulletin of Carnegie Museum of Natural History 34:40-88
  4. Weishampel, David B; et al. (2004). "Dinosaur distribution (Late Cretaceous, Europe)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 588-593. ISBN   0-520-24209-2.