Kulindadromeus

Kulindadromeus Temporal range: Middle Jurassic to Late Jurassic, 169–144Ma PreꞒ Ꞓ O S D C P T J K Pg N
Reconstruction of Kulindadromeus zabaikalicus showing integument patterns preserved on the fossils.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Order:	†Ornithischia
Clade:	†Neornithischia
Genus:	†Kulindadromeus
Type species
†Kulindadromeus zabaikalicus Godefroit et al., 2014

Kulindadromeus is a feathered, herbivorous dinosaur, a basal neornithischian from the Jurassic of Russia. Its integument is evidence for the trait being basal to Dinosauria as a whole, rather than just to Coelurosauria, as previously suspected.

Discovery and naming

In 2014, the type species Kulindadromeus zabaikalicus was named and described by Pascal Godefroit, Sofia Sinitsa, Danielle Dhouailly, Yuri Bolotsky, Alexander Sizov, Maria McNamara, Michael Benton, and Paul Spagna. The generic name is derived from the Kulinda sites and a Classical Greek δρομεύς, dromeus, "runner". The specific name refers to the Zabaikal region.^[1]

The holotype, INREC K3/109, was found in a layer of the Ukureyskaya Formation dating from the Middle to Late Jurassic, Bajocian-Tithonian. It consists of a partial skull with lower jaws. The volcanic ash layers of the formation form a Konservat-Lagerstätte with an exceptional preservation. From 2010 onwards, the area has brought forth considerable amounts of additional fossil material, including subadult and juvenile individuals.^[1] Earlier in 2014, based on fossils from this material, the genera Kulindapteryx and Daurosaurus were named.^[2] According to Godefroit, this publication was based on stolen specimens, and should be ignored.^[3] The material consists of six skulls,^[4] and hundreds of disarticulated skeletons found in two bone beds. Each skeletal element shows but a single morphotype and Godefroit e.a. concluded, contrary to the earlier publication, that the bone beds are monospecific, containing but a single species.^[1]

Description

Like other early neornithischians, Kulindadromeus was a bipedal runner, approximately 1.5 meters in length.^[4] It had a short head, short forelimbs, long hindlimbs and a long tail.^[1]

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.^[1]

Kulindadromeus is significant in that the various specimens 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.^[5] The feather remains discovered are of three types, adding a level of complexity to the evolution of feathers in dinosaurs.^[4] 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 up to 1.5 centimetres long filaments, together 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.^[1]

Godefroit et al. concluded that the filaments earlier reported in Ornithischia, with Psittacosaurus and Tianyulong, could be homologous to the "protofeathers" found in non-avian theropods. With known feather-like structures in pterosaurs, there is evidence for it being basal to Ornithodira. Furthermore, evidence from dormant feather genes in alligators^[6] shows the trait may be basal to Archosauria, and possible to have appeared as far back as basal archosauromorphs, as some distinctive archosaurian integument features have appeared this far back. Evidence currently, however, only likely points to basal Ornithodira or Archosauria.^[1]

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.^[1]

Phylogeny

According to a cladistic analysis performed by the describing authors, Kulindadromeus is a basal member of the Neornithischia, placed just above Hexinlusaurus in the evolutionary tree. It is the sister species of the Cerapoda.^[1]

References