Teleocrater (meaning "completed basin", in reference to its closed acetabulum) is a genus of avemetatarsalian archosaur from the Middle Triassic Manda Formation of Tanzania. The name was coined by English paleontologist Alan Charig in his 1956 doctoral dissertation, but was only formally published in 2017 by Sterling Nesbitt and colleagues. The genus contains the type and only species T. rhadinus. Uncertainty over the affinities of Teleocrater have persisted since Charig's initial publication; they were not resolved until Nesbitt et al. performed a phylogenetic analysis. They found that Teleocrater is most closely related to the similarly enigmatic Yarasuchus, Dongusuchus, and Spondylosoma in a group that was named the Aphanosauria. Aphanosauria was found to be the sister group of the Ornithodira, the group containing dinosaurs and pterosaurs. A carnivorous quadruped measuring 7–10 feet (2.1–3.0 m) long, Teleocrater is notable for its unusually long neck vertebrae. The neural canals in its neck vertebrae gradually become taller towards the back of the neck, which may be a distinguishing trait. Unlike the Lagerpetidae or Ornithodira, the hindlimbs of Teleocrater are not adapted for running; the metatarsal bones are not particularly elongated. Also unlike lagerpetids and ornithodirans, Teleocrater inherited the more flexible ankle configuration present ancestrally among archosaurs, suggesting that the same configuration was also ancestral to Avemetatarsalia but was lost independently by several lineages. Histology of the long bones of Teleocrater indicates that it had moderately fast growth rates, closer to ornithodirans than crocodilians and other pseudosuchians.
Description
In life, Teleocrater would have been a long-necked and carnivorous quadruped that measured some 7–10 feet (2.1–3.0 m) in length.
Skull Carnivory can be inferred for Teleocrater from the single tooth that was preserved, which is compressed, recurved, and bears serrations on both edges. Like other members of the Archosauria, the recess in the maxilla in front of the antorbital fenestra (the antorbital fossa) extends onto the backward-projecting process of the bone, and the palatal projection of the two maxillae contacted each other. Additionally, like early dinosaurs, there is a depression on the frontal bone in front of the supratemporal fenestra (the supratemporal fossa).
Axial skeleton The cervical vertebrae of Teleocrater from the front half of the neck are quite long, up to 3.5 times as long as they are high; they are among the longest of Triassic avemetatarsalians. Proportionally, they are longer than either the rest of the cervical vertebrae or any of the vertebrae from the front of the trunk. On the cervical vertebrae, the tops of the neural spines are blade-like, but are accompanied by rounded and roughened projections; the front portions of the neural spines strongly overhang the preceding vertebrae; and the cervical vertebrae from the back of the neck have an additional projection above the parapophysis, previously identified by Nesbitt as part of a "divided parapophysis". These are shared characteristics of the Aphanosauria. In contrast to most other archosauriforms, the openings of the cervical neural canals in Teleocrater are large, subelliptical, and transition from being wider than they are tall at the front of the neck to being taller than they are wide at the back of the neck; this may be unique to the genus. The epipophyses from the front and middle cervical vertebrae project backwards, and, as in Yarasuchus and some pseudosuchians, the back cervical vertebrae appear to have supported three-headed ribs. On the dorsal vertebrae, the accessory articulations known as the hyposphene-hypantrum articulations are well-developed. Like other aphanosaurians, there are pits located on the side of the base of the dorsal vertebrae. Two vertebrae are associated with the sacrum in Teleocrater; there are three such vertebrae in Nyasasaurus. The ribs associated with the latter sacral vertebra bear processes that project backward and outward, which is only otherwise seen in Yarasuchus, Spondylosoma, and members of the dinosauriforms. There were no bony osteoderms preserved in association with the specimen, which indicates that Teleocrater probably lacked osteoderms, unlike pseudosuchians.
Appendicular skeleton Like other archosaurs as well as the proterosuchids, Teleocrater has a distinct acromion process on the scapula, and like silesaurids there is a thin ridge on the back of the bone. The socket of the scapula is oriented downwards and backwards, more so than that of Yarasuchus. On the humerus, there is a long deltopectoral crest that stretches for about 30% of the bone's length, as with other aphanosaurians; such a long crest is also seen in Nyasasaurus and dinosaurs, but not pterosaurs or silesaurids. Another aphanosaurian characteristic is the wide bottom end of the humerus, which is about 30% of the bone's length. The hand was apparently quite small. Teleocrater is named after its mostly-closed acetabulum, or hip socket (the eponymous "basin"). There is a small and concave notch on the bottom edge of the part of the ilium that extends to meet the ischium, which suggests a small perforation within the acetabulum. This is not a unique characteristic; Asilisaurus and Silesaurus both also possess it. The inner surface of the ilium in front of the acetabulum curves inwards, forming a pocket. Like both Asilisaurus and Marasuchus, the front portion of the ilium is separated from the rest of the bone by a ridge that rises vertically from the top rim of the acetabulum. As in other aphanosaurians, the ischia contact each other extensively along the midline, but less so near the tops of the bones; the bottom back portion of each ischium is rounded, and the top of the shaft of each ischium bears a longitudinal groove.
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