Teleocrater
Teleocrater | |
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Replica of hindlimb at the Field Museum of Natural History | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Avemetatarsalia |
Clade: | †Aphanosauria |
Genus: | †Teleocrater Nesbitt et al., 2017 |
Type species | |
†Teleocrater rhadinus Nesbitt et al., 2017
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Teleocrater (meaning "completed basin", in reference to its closed
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
![](http://upload.wikimedia.org/wikipedia/commons/thumb/a/a6/Teleocrater_v1.png/220px-Teleocrater_v1.png)
In life, Teleocrater would have been a long-necked and carnivorous[1] quadruped that measured some 7–10 feet (2.1–3.0 m) in length.[2]
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
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.[1][3][6]
On the
Appendicular skeleton
Like other archosaurs as well as the proterosuchids,[6] 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[7] and dinosaurs,[8] 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.[1]
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[9] and Silesaurus[10] both also possess it. The inner surface of the ilium in front of the acetabulum curves inwards, forming a pocket. Like both Asilisaurus[9] and Marasuchus,[11] 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.[1]
Hindlimb
In terms of hindlimb proportions, Teleocrater is more similar to silesaurids, pseudosuchians, and early archosaurs than
The femur of Teleocrater shows a combination of diverse characteristics. Like other aphanosaurians, the top end of the femur bears a transverse groove, and also bears a scar for the attachment of the iliofemoralis externus muscle that is connected to the intermuscular line; the same condition is seen with the anterior trochanter in dinosaurmorphs, yet the scar is clearly separated from that of the iliotrochantericus caudalis as it is in Dongusuchus, Yarasuchus, and early archosaurs.[3] An additional aphanosaurian trait is that the bottom articulating surface of the femur is concave. On this articulating surface, the back of the medial condyle bears a vertical scar, also seen in dinosauromorphs. The femur is overall quite similar to that of Dongusuchus; however, in Teleocrater, the sides of the top end are more rounded and the inner surface is concave, the posteromedial tuber on the top end is convex instead of flat, and the length relative to midshaft width is shorter.[1]
Unlike either proterochampsids or dinosauromorphs,[3][6] the tibia of Teleocrater does not bear a cnemial crest. The fibula bears a long, twisted crest for the attachment of the iliofibularis, and the front edge of the top of the bone is expanded outwards. Additional features shared by aphanosaurians, silesaurids (namely Asilisaurus and Lewisuchus[9]), and pseudosuchians occur in the calcaneum. It has a convex-concave joint with the astragalus that allows for free movement, a tuber on its surface that is tall, broad, and directed backwards, and its articulation with the fibula is distinctly rounded. Meanwhile, lagerpetids and pterosaurs both lack the tuber (lagerpetids also lack the rounded fibular articulation), and dinosaurs lack the convex-concave joint.[1]
Discovery and naming
The holotype specimen of Teleocrater, NHMUK PV R6795, was found by
Alan J. Charig described the remains of Teleocrater in his 1956 PhD thesis for the University of Cambridge.[2] He was the first to apply the name Teleocrater, derived from Greek teleos ("finished", "complete") and krater ("bowl", "basin"), in reference to the closed acetabulum of the animal.[1] His initial thesis listed tanyura as the specific name of Teleocrater; later, in a 1967 overview of reptiles, he revised it to rhadinus, from Greek rhadinos ("slender", in reference to the bodyplan of the animal). However, given that it was never formally published, it remained an invalid nomen nudum.[14]
In 2015, a bonebed designated as Z183 was discovered within 1 kilometre (0.62 mi) of the approximate location described by Parrington. This bonebed contained at least three individuals of different sizes, represented by 27 bones, all of which were mixed in with the remains of an
Bonebed Z183 belongs to the lower portion of the Lifua Member of the
Classification
Prior to the formalization of the definitions of these groups by
Nesbitt et al. utilized two phylogenetic datasets to analyze the affinities of Teleocrater: one published by Nesbitt himself in 2011,
Archosauriformes |
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The inclusion of Scleromochlus altered the topology obtained to varying extents, although both analyses recovered it as an avemetatarsalian. In the Nesbitt dataset, Scleromochlus collapsed Avemetatarsalia into a polytomy containing itself, Spondylosoma, the other aphanosaurians, pterosaurs, lagerpetids, and dinosauriforms. Meanwhile, in the Ezcurra dataset, Scleromochlus formed a polytomy with lagerpetids and dinosauriforms. Nesbitt et al. emphasized that characteristics of pelvic and leg anatomy could not be assessed for Scleromochlus due to conflicting descriptions[19][20] and poor quality of skeletal casts; these characteristics play a substantial role in the topology of basal avemetatarsalians.[1][3][6][17][19][20][21]
Traditionally, the "crocodile-normal" and "advanced mesotarsal" ankle arrangements have been considered as a dichotomy among archosaurs: early archosaurs and pseudosuchians possess the more mobile "crocodile-normal" configuration, while pterosaurs and dinosauromorphs (including birds) possess the stiffer "advanced mesotarsal" configuration.
Paleobiology
Histology and growth
Nesbitt et al. examined cross-sections from the fibula of Teleocrater. The
Similar results were reached by Ricqlès et al., who analyzed a cross-section from a metatarsal. The cortex likewise consists entirely of the primary layer, with the vascular canals consisting of longitudinal osteons that are less dense in the peripheries of the cortex. The interior medullary cavity of the bone is occupied by dense spongy endosteum; the trabecula is missing.[18] Overall, histology suggests that specimens of Teleocrater were rapidly growing at time of death. The dense vasularization, anastomosis in the humerus, and disorganization of osteocytes indicates a growth rate higher than more basal archosaurs[24] and comparable to silesaurids,[25][26] but less than that of Nyasasaurus,[7] pterosaurs, and dinosaurs.[1][27][28]
Paleoecology
In Bonebed Z183, from where the newer specimens of Teleocrater (and possibly the type specimen) are known, the fauna can generally divided into two types. Larger bones originate from the
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