Coparion: small theropod dinosaurs from the Coelurosaur group

Koparion (dr. Greek.: κοπάριον; lat.: Koparion) is a genus of small theropod dinosaurs from the Coelurosaur group (lat.: Coelurosauria), probably belonging to the Troodontidae family (Troodontidae) and living in the territory of the modern American state of Utah in the late Jurassic period (in the Kimmeridgian stage).

This genus includes only one species, Koparion douglassi, known from a single tooth.

History of the find and name

In 1993, paleontologists Daniel Chur.: Daniel Chure and Brooks Britt reported the discovery of a fragment of a small theropod found while washing large volumes of soil on grids in Rainbow Park near Dinosaur National Monument in Winta County, Utah.

In 1994, Chur described a single tooth as the type specimen of a new species, Koparion douglassi. The Latin generic name Koparion comes from the ancient Greek word κοπάριον (“small surgical knife”), which the scientist used to emphasize the tiny size of the tooth.

The species epithet douglassi was given to the dinosaur in honor of American paleontologist Earl Douglas.: Earl Douglass), who excavated in the early 20th century at the very site that was later declared a National Monument.

Holotype no. DINO 3353 was found in a sedimentary stratum of the Brushy Basin Basin.: Brushy Basin Member of the Morrison Formation. The age of this layer is about 151 million years. Thus, this taxon is present in the 6th stratigraphic zone of the Morrison Formation.

Description

The holotype consists of the crown of a single maxillary tooth (the root of the tooth is missing). In this case, it is impossible to determine whether the found tooth belongs to the left or right side of the jaw.

Tooth height is only 2mm. It is distinguished by a strongly convex leading edge and an almost vertical trailing edge. The tooth has a dense structure. Its maximum length from front to back is 1.9 mm. There are slightly protruding rectangular teeth on the leading and trailing edges. At the same time, the 12 teeth of the rear edge of the tooth protrude much more than the 14 teeth of the leading edge, which are distributed only on its almost horizontal upper part.

The base of the tooth is very long, but narrow. It is asymmetrical, its right side is much more convex than the left; but, since it is not known whether it is a left tooth or a right one, it is impossible to determine where it has the inside and where the outside.

By analogy with edged weapons, the teeth of the edges of the tooth are separated from each other by “grooves for the outflow of blood”, and in addition, there are “deepenings for blood” on the tooth. In this case, the teeth of the trailing edge are directed obliquely upwards, but do not have hook-shaped upper corners.

Classification

Daniel Chur included the genus Coparion in the Troodontidae family, guided by the anatomical structure of his tooth. At that time, it was the oldest troodontid known to science, moreover, it became the first representative of this family found dating back to the Jurassic period.

The existence of troodontids in the Jurassic was predicted by the standard theory of the origin of birds, which states that birds and troodontids are closely related (Chur suggested that they could even be sister taxa, although this assumption is not currently supported).

In this context, the coparion could be used to refute the temporal paradox argument that such a close relationship was improbable because the oldest known bird, Archeopteryx, lived much earlier than Deinonychosaurs (lat.: Deinonychosauria), i.e. dromaeosaurids (Dromaeosauridae) and troodontids.

Be that as it may, later there was a report about the discovery in China of unfragmented bone material of another troodontid of the Jurassic period.

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