Antaeusuchus

''Antaeusuchus taouzensis'' is a species of peirosaurid notosuchian from the Late Cretaceous Kem Kem Group of Morocco. It was described in 2021, and it is the only species in the genus ''Antaeusuchus''. It is the fourth notosuchian described from the region and the second Kem Kem peirosaurid after ''Hamadasuchus''.

Discovery and naming

''Antaeusuchus'' is known from two specimens: the holotype NHMUK PV R36829, consisting of paired mandibles, and the paratype NHMUK PV R36874, a partial right mandible. Both specimens were commercially collected and recovered from unspecified beds of the Kem Kem Group near Jebel Beg'aa, Taouz township in the Errachidia Province of Morocco. Both fossils are preserved without distortion and in good condition, with damage mostly restricted to the teeth.

The generic name derives from Antaeus, a giant from Greek and Berber mythology said to be buried in northern Morocco and the Ancient Greek σοῦχος, soukhos meaning crocodile. The species name refers to the township Taouz where both specimens had been found.

Description

The anterior region of the mandible is characterized by a broad ’U’-shaped symphysis. Each mandibular ramus diverges at an 22° angle from the midline and remains mostly straight for most its preserved length, curving slightly medially towards the fossil's posterior. The anterior of the dorsal margin of the mandible is characterized by two 'waves', the first of which spanning the dentary teeth 1 to 6. The second wave rises from the 9th to 15th tooth. These 'waves' reach their peak at the 4th and 13th dentary tooth respectively. Other than a series of foramina adjacent to the tooth row, this part of the bone shows little ornamentation. The holotype dentary preserves 18 alveoli, the first 16 of which preserving partial or complete teeth, all of which are closely spaced. The posterior half of the dorsal margin remains largely straight and is strongly sloping. The mandibular fenestra is not fully preserved in either specimen, but can be inferred to be large in size and anteroventrally-posterodorsally elongated.

The first alveoli are circular in shape, suggesting the anterior teeth to be roughly conical while from the 10th dentary alveoli onward become more labiolingually compressed, more extreme flattening is present at the anterior and posterior margin of the preserved teeth. These margins are adorned with denticulated carinae which form the cutting edge of the teeth. These denticles are small in size and show no significant variation in size.

In ''Antaeusuchus,'' the mandibular rami diverge at a much broader angle (43 to 44°) than in ''Hamadasuchus'' (between 20 and 30° depending on the specimen), meaning that it had a broader rostrum than its relative. The surface of the mandible in ''Antaeusuchus'' is covered in shallow pits and groves different from the deeper ornamentation of ''Hamadasuchus''. The posterior teeth of the ''Hamadasuchus'' holotype are lanceolate in shape, which is not seen in ''Antaeusuchus''. Furthermore the teeth of the ''Antaeusuchus'' holotype, while slightly pointed at their apices, they are not comparable to the almost triangular teeth seen in the holotype of ''Hamadasuchus''. The 10th to 14th teeth in referred specimen NHMUK PV R36874 are angular, but their anterior and posterior margin run parallel for most of their length and only converge to a point at the apex of the crown.

''Antaeusuchus'' was significantly larger than ''Hamadasuchus'', almost twice the size of the later. While size is not a distinguishing character on its own, it adds to the already present morphological differences between the two genera. Furthermore, Nicholl ''et al.'' argue that the features present in ''Antaeusuchus'' are not compatible with the ontogenetic series known for ''Hamadasuchus'', which already includes specimen presumed to be 'adult'.

Phylogeny

For the phylogenetic analysis both specimens were combined as one operational taxonomic unit and inserted into a character-taxon matrix based on that of Pol ''et al.'' 2014. This matrix was subsequently used as a basis for multiple further studies running parallel to one another, resulting in numerous 'daughter' matrices, which were united for the phylogeny of Nicholl ''et al.'' 2021. The sampling was also expanded by the inclusion of the putative peirosaurids ''Rukwasuchus yajabalijekundu'' from Tanzania and ''Miadanasuchus oblita'' from Madagascar. The resulting strict consensus tree under equal weighting of characters can be seen below:

The resulting phylogeny recovered peirosaurids and mahajangasuchids grouping together, forming a sister clade to uruguaysuchids. Internally, ''Antaeusuchus'' was recovered as a sister taxon to ''Hamadasuchus'' from the Kem Kem Group, the two taxa clade together with ''Bayomesasuchus'' as their sister, which in turn forms a sister clade to all other peirosaurids. ''Peirosaurus torminni'' was not included in the analysis, however its close relative ''Uberabasuchus terrificus'' has been consistently recovered as a close relative or possible junior synonym, consequently ''Uberabasuchus

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