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Kulindadromeus
Kulindadromeus by Tom Parker.png
Scientific classification
Subkingdom: Animalia
Infraphylum: Chordata
Genus: Kulindadromeus
Type species
Kulindadromeus zabaikalicus
Kulindadromeus, a basal neornithiscian, is one of the first ornithischians preserved with some sort of integument. This is evidence that feathers may have evolved earlier in the dinosaur lineage although it is still being debated whether or not it is homologous with the proto-feathers found on coelurosaurs.

Description

Like other early neornithischians, Kulindadromeus was a bipedal runner, approximately 1.5 meters in length.[2] It had a short head, short forelimbs, long hindlimbs and a long tail.

The describers of Kulindadromeus established some distinguishing traits. The front ascending branch of the maxilla is much lower than the rear ascending branch. The fenestra maxillaris is larger than the antorbital fenestra, the usually more extensive skull opening in the snout side. The branch of the jugal towards the postorbital is notched. The postorbital has a rear branch that is vertically expanded. The rear blade of the ilium is slender in side view. The second, third and fourth metatarsals have deep grooves for the tendons of the extensor muscles.

Various specimens of Kulindadromeus show large parts of its integument. This includes imbricated rows of scales on top of its tail and also a covering of scales branching into feather-like structures, which until its discovery were thought to be exclusive to the Theropoda, of the saurischian line. The feather remains discovered are of three types, adding a level of complexity to the evolution of feathers in dinosaurs. The first type consists of hair-like filaments covering the trunk, neck and head. These are up to three centimetres long and resemble the stage 1 "dino-fuzz" already known from theropods like Sinosauropteryx. The second type is represented by groups of six or seven downwards-projecting filaments up to 1.5 centimetres long, originating from a base plate. These are present on the upper arm and thigh. They resemble the type 3 feathers of theropods. The base plates are ordered in a hexagonal pattern but do not touch each other. The third type is unique. It was found on the upper lower legs and consists of bundles of six or seven ribbon-like structures, up to two centimetres long. Each ribbon is constructed from about ten parallel filaments up to 0.1 millimetres wide.

There are also three types of scales. Overlapping hexagonal scales, up to 3.5 millimetres in diameter, are present on the lower shins. Small round non-overlapping scales, less than one millimetre in cross-section, cover the hands, ankles and feet. The top of the tail is covered by five longitudinal rows of arched rectangular scales, measuring up to one by two centimetres. With these scales the trailing edge of each scale slightly overlaps the front edge of the scale behind it. In the middle, to the contrary, a small spur projects forward, covering the trailing edge of the preceding scale. This way an imbricated row is formed. The scale surface is smooth and the thickness is limited, less than 0.1 millimetres. The authors considered it unlikely these structures were ossified scutes or osteoderms. Towards the rear of the tail, the scales become smaller and more rounded; they then no longer overlap each other.

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