Eocursor: ornithischian dinosaurs

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Eocursor (lat.: Eocursor, “early runner”) is a genus of very early and primitive dinosaurs from the order Ornithischians (lat.: Ornithischia).

The fossilized remains of the only individual of this dinosaur at the moment were recovered in 1993 in South Africa from the layer of the Lower Elliot Formation (Eng.: Lower Elliot formation), related to the Upper Triassic period (to the upper part of the Norian stage or the Rhaetian stage).

Based on this specimen of the remains, which includes several skull bones as well as several postcranial bones (t.e. the rest of the skeleton without a skull), in 2007 the first scientific description of the so far only known species of eocursor, called Eocursor parvus, was compiled.

Even though fragmentary, these fossils represent the best-preserved skeleton of an ornithischian dinosaur from the Triassic period.

Very early ornithischians are still known mainly from very few finds, so the eocursor is of great scientific importance for understanding the early stage of evolution of this group of dinosaurs.

Name etymology

The Latin generic name Eocursor is derived from the Greek word “eos” (“predawn twilight” or “dawn”) and the Latin word “cursor” (“runner”) and can be translated into Russian as “predawn, or early, runner”.

The Latin specific epithet parvus means “small”. The full name of the species Eocursor parvus (“small early runner”) indicates the position occupied by this animal in the history of evolution (eos; “early”), its ability to run fast (cursor; “runner”) and small body size (parvus; “small “”).

Description

Eocursor was a “bipedal” dinosaur of light build. According to scientists, the length of his body was about 1 meter, and the height of the hips was about 30 centimeters. It is assumed that the dinosaur ran fast, as indicated by the proportions of the bones of its hind (lower) limbs.

According to the general structure of the body, the eocursor resembles ornithischian dinosaurs of the Lower Jurassic period, such as Lesothosaurus (lat.: Lesothosaurus) and Scutellosaurus (Scutellosaurus), which in turn only slightly differed in appearance from the modern lizard dinosaurs (Saurischia). True, the hand of the forelimb of the eocursor was relatively large and elongated and therefore resembled the hand of heterodontosaurids (lat.: Heterodontosauridae), relative to a specialized group of basal ornithischian dinosaurs.

The morphology of triangular teeth indicates that the basis of the diet of this animal, at least a certain part of it, was plants.

A backward and downward pubic bone (opisthopubic pelvis) and a distinct prepubis, t.e. forward-facing process of the upper (proximal) end of the pubic bone, are the key features of ornithischian dinosaurs inherent in the eocursor.

History of the find

The only known remains of this dinosaur were discovered in a three-meter massive horizon of dark red-brown siltstone in the uppermost part of the Late Triassic Lower Elliot Formation, belonging to the Karoo Supergroup (Eng.: Karoo Supergroup. At the same time, all sedimentary rocks of the Elliot Formation are alluvial deposits formed in a dry and warm climate.

The exact age of the layer in which the eocursor fossils were found is given as Norian. However, such a determination of the age of this layer is based on the outdated chronostratigraphic division of the Upper Triassic, so that not only the very top of the Norian stage, but also the Rhaetian stage can be considered as the period of formation of these deposits.

The find site is located in the southern part of the South African province of the Free State (Eng.: Free State, African.: Vrystaat) on the territory of the farm Damplaats 55 (Africa.: Damplaats 55), belonging to the municipality of Mantsopa (Mantsopa).

The bone material of an eocursor specimen, found in an anatomically disjointed state, includes various bones of the skull, vertebrae, scapula and bones of the fore (upper) limbs, pelvis, and bones of the lower limbs. It is in the collection of the South African Museum of Art.: Iziko South African Museum) in Cape Town under inventory number SAM-PK-K8025.

Classification

Eocursor is an early and primitive member of the order Ornithischidae. The result of the analysis of kinship, carried out when compiling the first scientific description, shows that the genus Eocursor is the basal, but not the most ancient representative of this order, and at the same time is a sister group in relation to the entire Genasaurus group (lat.: Genasauria), uniting “more highly developed” ornithischian dinosaurs.

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