Tetraceratops insignis ("four-horned face emblem") is an extinct synapsid from the Early Permian that was formerly considered the earliest known representative of Therapsida, a group that includes mammals and their close extinct relatives.
Description
Tetraceratops is known from a single
skull discovered in Texas in the early 1900s. Contrary to its
genus name,
Tetraceratops actually has six horns, one pair being on the
premaxilla bones, one pair on the
prefrontal bone bones, and one pair on the angular processes of the
mandible. When it was discovered and described in 1908, the skull was still embedded in a matrix, and only the premaxilla and prefrontal pairs were visible. In life, thus, it would have resembled a large lizard with four horns on its snout, and a pair of large spines emanating from the corners of its jaw.
In addition to horns, Tetraceratops also had an impressive set of teeth. The second pair of teeth on the bones were large and fang-like. Likewise the first teeth in the upper jaw were long and dagger-like.
Classification
Tetraceratops was originally identified as a member of a group called
Pelycosauria, an evolutionary grade of synapsids more basal than therapsids. It has been variously grouped in the family
Sphenacodontidae, which is closely related to Therapsida, and
Eothyrididae, which is more distantly related. Recent
phylogenetic studies classify it as either a pelycosaur-grade synapsid or the basalmost therapsid, rendering its exact phylogenetic placement unclear.
However, a recent study by Spindler concluded that no convincing morphological evidence could be made for a therapsid placement of
Tetraceratops and that this genus was better placed as a basal sphenacodontian.
See also
-
List of synapsids
-
Evolution of mammals
External links
