Ammitocyon
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| Ammitocyon Temporal range: Late Miocene, 9.1 Ma | |
|---|---|
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Suborder: | Caniformia |
| Family: | †Amphicyonidae |
| Subfamily: | †Thaumastocyoninae |
| Genus: | †Ammitocyon Morales et al., 2021 |
| Type species | |
| †Ammitocyon kainos Morales et al., 2021 | |
Ammitocyon is a genus of large sized carnivoran mammals, belonging to the Amphicyonidae ("bear dogs"), that lived during the Late Miocene in what is now Spain. It is notable for its extreme adaptations towards hypercarnivory, its extremely robust skeleton, and was one of the last surviving members of its family.
Ammitocyon was described in the year 2021 by Morales et al. based on comparatively complete remains, originally referred to Thaumastocyon,[1] enabling a greater understanding of the subfamily Thaumastocyoninae, hitherto only known from fragmentary material. Holotype is the pair of hemimandibles BAT-3'09.1239 and BAT-3'08.604, which belong to the same individual. BAT-3'10.1689 (a skull with strong signs of corrosion, especially in the dorsal region, belonging to a senile individual) and BAT-3'11.453 (a complete mandible belonging to the same individual), as well as the isolated left m2 BAT-3'09.1124, have been designated as paratypes. Furthermore, postcranial remains are known and await a closer description.[2]
The name Ammitocyon is a combination of "Ammit", an ancient Egyptian goddess, chosen as her mix of crocodile, hippopotamus, and lion features reminded the authors of the fossil species, and the Ancient Greek κύων (kúōn, "dog"). The species καινός (kainós) name also derives from Ancient Greek, and translates to "of a new kind".[2]
Geographical and temporal distribution
The type and so far only locality of the genus is Batallones-3, part of the Cerro de los Batallones site complex located in Madrid, Spain. BAT-3 is the most recent deposit of the series, dating to the late Vallesian, MN10, dating to circa 9.1 Ma.[2]
The Batallones are a complex of cavities, which held water even in harsh droughts, trapping herbivores that came down to drink. Their carcasses then attracted a large variety of carnivores, which then got stuck themselves. As a result, over 90% of mammalian fossils in BAT-3 are remains of carnivorans.[3]
Description
Ammitocyon was a lion-sized taxon, with its weight estimated at 231 kg. It is characterized by its extremely robust build, with powerful legs, almost unmatched among caniforms, and adaptations to hypercarnivory. Its chin and muzzle are sturdy, and its snout is huge, with a wide nasal aperture. The dentition is sectorial. The reduction of its premolars, typical for thamastocyonines, is taken to an extreme - it has completely lost P2/P3 and p1-3, as well as its third molars (M3 and m3).[2]
It possesses a premaxilla more robust than that found in Magericyon. Both the frontal and jugal possess well-developed postorbital processes, resulting in a relatively large eye socket, which is more enclosed than that of similarly sized arctoid carnivorans. The Bulla is large and somewhat inflated and the sagittal crest well-developed and convex, stretching from the post-orbital constriction to the nuchal crests.[2]
Like in Ysengrinia americana and some temnocynines the palate is cadually expanded beyond the molars. The mandible is long and robust, with strong symphysis, it is dorsoventrally slender between the canine and p4, and buccolingually thick under m1 and m2. In typical amphicyonids, including thaumastocyonines, the depth of masseteric fossa surpasses basal level of postcanine row, while in Ammitocyon it does not exceed the depth of margo alveolaris. A relatively deep rim encloses it completely in its ventral region, separating the fossa from the unique flat region in a premasseteric position. Another unique feature is the broad concavity in the ventral margin, extending from the genial tuberosity to the mesial base of the ascending ramus.[2]
The dental formula of A. kainos is .
The upper canine is robust and shows buccolingual compression, while its large and curved lower canines are buccolingually elongated and have broad roots, relative to the height of their crown. The P4 is elongated, possessing a large parastyle and a well-developed lingual root for the protocone. The M1 and M2 meanwhile are reduced, showing a triangular outline in combination with P4, and the incisor battery is extremely wide, each one being well separated from the other, similar to that of barbourofelids. The I3 is considerably larger than the I2, which seems to be larger than the not yet recovered I1. Their most striking feature is the buccolingual width, which is much more developed than in any other carnivoran studied. In comparison to the M1, the P4 is large. The m2 is elongated, possessing a much larger paraconid than that of other thaumastocyonines, and the species lacks an M3.[2]
Its scapula is robust and almost square-shaped and possesses a large subscapular fossa and scapular spine, which occupies almost its whole length, while the dorsally developed acromion does not go past the glenoid cavity. The robust humerus possesses a long wide deltoid tuberosity and a large lateral supracondylar crest, but no entepicondylar foramen. The distal epiphysis is wide. Both its radius and ulna are short and robust, with large muscular attachments along the diaphysis.[2]
The manus is robust and short, especially towards the distal segments. Both the carpals and metapodials are short and robust, with the latter possessing a flattened distal epiphyse. The phalanxes are extremely robust, with an almost rounded cross-section. The pelvis and femur are both robust but fragmentary, with the latter being relatively short. The robust tibia possesses a wide proximal epiphysis and short diaphysis, the triangular cross-section of its distal diaphysis possessing relatively oblique, deep, and reinforced articulation sulci for the astragalus.[2]
Its pes is wide and short, particularly towards the distal segments, while the robust tarsals have few contact facets. The short calcaneus has solid articulation facets for the astragalus and a concave distal one for the cuboid. Almost no distal neck is present at the astragalus, but it has a convex articular facet for the navicular. The articulation facet between the cuboid and navicular is absent. Articulations gradually become less mobile towards the distal parts of the limb, with some being ankylosed or completely immobile. It possesses short and robust metatarsals, with flattened distal epiphyses, as well as short and extremely robust phalanxes, with an almost rounded cressection and a short and thickened claw.[2]
Phylogeny and evolution
Ammitocyon belongs to the subfamily Thaumastocyoninae, originally erected by Hürzeler (1940), which is defined by the complete suppression of m1 metaconid, reduction of the premolars, except the p4, which is reinforced, and the oblique abrasion of the teeth, and possesses hypercarnivorous tendencies.[1] Within the subfamily its sister taxon is Thaumastocyon.
Below is the cladogram based on cranial, mandibular, and dental characters, after Morales et al., 2021:[2]
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