Graciliceratops

*Graciliceratops mongoliensis*

***Graciliceratops*** (meaning "slender horn") is a genus of neoceratopsian dinosaurs that lived in Asia during the Late Cretaceous period.

## Discovery and naming

The holotype, ZPAL MgD-I/156, was discovered at the Bayan Shireh Formation in Mongolia, coming from the Sheeregeen Gashoon locality near Sainshand. The discoveries were made during field exploration by the Polish-Mongolian Palaeontological Expedition, in 1971. Four years later, in 1975, the specimen was described by Teresa Maryańska and Halszka Osmólska and referred to the genus *Microceratops*. However, Paul Sereno noted that the referral for this specimen was injustified and overall, the genus lacked diagnosis, therefore, *Microceratops* (now named *Microceratus*) was considered a nomen dubium. The referred specimen was redescribed by him, creating a new genus and species: *Graciliceratops mongoliensis*.

The holotype is fragmentary, consisting of a very fragmented skull with mandibles; vertebrae, four cervicals, twelve dorsals and seven sacrals; right scapula; proximal end of left scapula; left coracoid; right humerus, radius and fragmentary ulna; proximal and distal end of left humerus; proximal fragments of both pubis; fragments of both illium and fragment of right ischium; right femur, tibia and nearly complete pes; distal part of left tibia, fragmentary left pes; tarsals and isolated ribs. The generic name, *Graciliceratops*, is derived from the Latin *gracilis* (meaning slender) and the Greek κέρας (kéras, meaning horn) in reference to its fragile build. Lastly, the specific name, *mongolienses*, is to emphasize the place of its discovery: Mongolia.

## Description

Although very damaged, the skull measures approximately 20 cm (200 mm), the arches and centra of the sacral vertebrae are not fused, which indicates that this specimen was not fully grown when it died, probably a juvenile individual. Its size is estimated at 60 cm (2.0 ft) long with a weight between 2.27 to 9.1 kg (5.0 to 20.1 lb). However, due to the immature nature of the specimen, the adult size is estimated around 2 m (6.6 ft), or similar to *Protoceratops*. The frill has large fenestrae bounded by very slender struts. This structure is very similar to that of the later *Protoceratops*. *Graciliceratops* is recognised by the fragile frill and characteristic tibial-femoral ratio (1.2:1); the frill is also briefly elongated with well developed squamosal processes. Seven sacral vertebrae were identified and not fused. The scapula is very gracile in constitution but thicker at the glenoid, with a relatively large coracoid; the humerus is also very slender. The femur measures 9.5 cm (95 mm), it is lightly curved and has a large head; the fourth trochanter is fragile and place above the midlength of the femoral end. Being larger than the femur, the tibia measures 11 cm (110 mm) and its proximal articulation is more developed than distally. The right pes is virtually complete, only lacking the distal end of the IV metatarsal. The pedal unguals are dorsoventrally flattened and somewhat sharply-developed.

## Classification

During the description of *Aquilops* in 2014, an extensive Ceratopsia phylogenetic analysis was conducted. *Graciliceratops* was found to be a basal neoceratopsian. Below are the results obtained for the Neoceratopsia:

## Paleoecology

Caliche, fluvial and lacustrine sediments from Bayan Shireh suggest the environments had rivers and large lakes. It was contemporaneous with *Achillobator*, *Alectrosaurus*, *Erlikosaurus*, *Segnosaurus*, *Amtocephale*, *Talarurus*, *Tsagantegia*, *Erketu*, *Gobihadros*, azhdarchids, *Paralligator*, *Lindholmemys* and *Hybodus*.