Discoveries and naming
Liaoceratops was discovered in the famous Liaoning Province of China, where several fossils of feathered dinosaurs have also been collected. The type species Liaoceratops yanzigouensis was in 2002 named and described by Xu Xing, Peter Makovicky, Wang Xiaolin, Mark Norell and You Hailu. [2] The generic name is derived from Liaoning and the Greek keras, "horn" and ops, "face". The specific name refers to the town Yanzigou.
The holotype IVPP V12738 has been found in the Yixian Formation dating from the Barremian. These beds have also yielded fossil insects, fossils of ginkgo trees, and many other dinosaurs, including the early troodontid Sinovenator , also described by Makovicky later in 2002. [3]
"This area is yielding extremely important information on the evolution of dinosaurs, mammals, insects, and flowering plants. I hope to find even more primitive specimens than Liaoceratops," Peter Makovicky said.
The holotype consists of an almost complete skull. As paratype specimen IVPP V12633 has been referred, the skull of a juvenile. In 2007 another skull, CAGS-IG-VD-002, of an even younger individual was referred. This lacked the skull roof, which has been explained as the result of a predator opening the braincase to eat the contents. [4]
Description and classification
Liaoceratops was a relatively small dinosaur, reaching 50 cm (1.6 ft) in length and 2 kg (4.4 lb) in body mass. [5] The holotype skull measures of 154 millimetres in length, weighing an estimated seven pounds and possessing only jugal horns and a small skull frill, lacking the orbital horns and true neck shield that characterized later ceratopsians. However, these features help understand a major split in the evolution of ceratopsians. Long before the familiar Triceratops evolved in North America, the ceratopsian lineage branched into two lines: the neoceratopsians, the main lineage that includes the recognizable horned and frilled forms, and of which Liaoceratops in 2002 was the most basal known member, and the Psittacosauridae, a radiation of smaller, parrot-beaked dinosaurs.
"Liaoceratops gives us a great window on the early evolution of horned dinosaurs and tells us that Triceratops and its relatives evolved from very small Asian ceratopsians. This small, primitive dinosaur is actually more interesting to science in many ways than its larger, more famous relatives because it teaches us more about evolution. Basal dinosaurs are critical because they help us to tie different groups of dinosaurs together and map out evolutionary patterns," said Peter Makovicky, Curator of Dinosaurs at the Field Museum in Chicago and a co-author of the paper describing the dinosaur.
"Liaoceratops establishes that this split occurred no later than the earliest part of the Cretaceous Period. Also, it indicates that ceratopsians acquired some of their distinctive features earlier and more rapidly than was previously recognized," Makovicky said.
Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil discoveries of complete and articulated specimens, have helped to increase understanding about this group. Anatomical studies, particularly studies of the most primitive troodontids, like Sinovenator, demonstrate striking anatomical similarities with Archaeopteryx and primitive dromaeosaurids, and demonstrate that they are relatives comprising a clade called Paraves.
Psittacosaurus is a genus of extinct ceratopsian dinosaur from the Early Cretaceous of what is now Asia, existing between 126 and 101 million years ago. It is notable for being the most species-rich non-avian dinosaur genus. Up to 12 species are known, from across China, Mongolia, Russia, and Thailand. The species of Psittacosaurus were obligate bipeds at adulthood, with a high skull and a robust beak. One individual was found preserved with long filaments on the tail, similar to those of Tianyulong. Psittacosaurus probably had complex behaviours, based on the proportions and relative size of the brain. It may have been active for short periods of time during the day and night, and had well-developed senses of smell and vision.
Byronosaurus is a genus of troodontid dinosaur from the Late Cretaceous Period of Mongolia.
Jinfengopteryx is a genus of maniraptoran dinosaur. It was found in the Qiaotou Member of the Huajiying Formation of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.
Sinornithoides is a genus of troodontid theropod dinosaurs containing the single species Sinornithoides youngi. S. youngi lived during the Early Cretaceous. It measured approximately one meter long (3.3 ft). It lived in Inner Mongolia, China, and probably ate invertebrates and other small prey. They lived in what is now Mongolia, which was part of Laurasia.
Bagaceratops is a genus of small protoceratopsid dinosaurs that lived in Asia during the Late Cretaceous, around 72 to 71 million years ago. Bagaceratops remains have been reported from the Barun Goyot Formation and Bayan Mandahu Formation. One specimen may argue the possible presence of Bagaceratops in the Djadochta Formation.
Xuanhuaceratops is a genus of dinosaur from the Late Jurassic Period. The genus was in 2006 dated to the Tithonian, 150.8-145.5 million years ago. A member of the family Chaoyangsauridae, it was one of the earliest ceratopsians. The fossils were found in the Houcheng Formation of Hebei Province, northeastern China.
Sinovenator is a genus of troodontid dinosaur from China. It is from the early Cretaceous Period.
Sinusonasus is a genus of dinosaurs from the Early Cretaceous Period, recovered from the Yixian Formation. It lived in what is now the Liaoning Province of China. Sinusonasus was a theropod, specifically a troodontid dinosaur.
Jeholosaurus is a genus of neornithischian dinosaur from the Early Cretaceous Period. It is thought to have been a herbivorous small ornithopod.
Graciliraptor is a genus of theropod dinosaur from the early Cretaceous Period. It is a microraptorine dromaeosaurid.
Linheraptor is a genus of dromaeosaurid dinosaur which lived in what is now China in the Late Cretaceous. It was named by Xu Xing and colleagues in 2010, and contains the species Linheraptor exquisitus. This bird-like dinosaur was less than 2 m (6.5 ft) long and was found in Inner Mongolia. It is known from a single, nearly complete skeleton.
Jinfengopteryginae is a subfamily of bird-like theropod dinosaurs known from the Cretaceous of Eurasia. This group includes relatively few genera, with members discovered in 2005 but the name erected in 2012. Like other troodontids, this group of dinosaurs resided in the Paraves potentially close to the Avialae.
This timeline of troodontid research is a chronological listing of events in the history of paleontology focused on the troodontids, a group of bird-like theropod dinosaurs including animals like Troodon. Troodontid remains were among the first dinosaur fossils to be reported from North America after paleontologists began performing research on the continent, specifically the genus Troodon itself. Since the type specimen of this genus was only a tooth and Troodon teeth are unusually similar to those of the unrelated thick-headed pachycephalosaurs, Troodon and its relatives would be embroiled in taxonomic confusion for over a century. Troodon was finally recognized as distinct from the pachycephalosaurs by Phil Currie in 1987. By that time many other species now recognized as troodontid had been discovered but had been classified in the family Saurornithoididae. Since these families were the same but the Troodontidae named first, it carries scientific legitimacy.
This timeline of ceratopsian research is a chronological listing of events in the history of paleontology focused on the ceratopsians, a group of herbivorous marginocephalian dinosaurs that evolved parrot-like beaks, bony frills, and, later, spectacular horns. The first scientifically documented ceratopsian fossils were described by Edward Drinker Cope starting in the 1870s; however, the remains were poorly preserved and their true nature was not recognized. Over the next several decades, Cope named several such genera and species. Cope's hated rival, Othniel Charles Marsh, also described ceratopsian remains. In 1887, Marsh mistook a Triceratops horn for one belonging to a new species of prehistoric Bison. Marsh also named the eponymous genus Ceratops in 1888. The next year, he named the most famous ceratopsian, Triceratops horridus. It was the discovery of Triceratops that illuminated the ceratopsian body plan, and he formally named the Ceratopsia in 1890.
Mosaiceratops is a genus of ceratopsian, described by Zheng, Jin & Xu in 2015 and found in the Xiaguan Formation of Neixiang County. Mosaiceratops lived in the upper Cretaceous in what is now the Henan Province of China.
Jianianhualong is a genus of troodontid theropod dinosaur from the Early Cretaceous of China. It contains a single species, Jianianhualong tengi, named in 2017 by Xu Xing and colleagues based on an articulated skeleton preserving feathers. The feathers at the middle of the tail of Jianianhualong are asymmetric, being the first record of asymmetrical feathers among the troodontids. Despite aerodynamic differences from the flight feathers of modern birds, the feathers in the tail vane of Jianianhualong could have functioned in drag reduction whilst the animal was moving. The discovery of Jianianhualong supports the notion that asymmetrical feathers appeared early in the evolutionary history of the Paraves.
Daliansaurus is a genus of small troodontid theropod dinosaur, measuring approximately 1 metre long, from the Early Cretaceous of China. It contains a single species, D. liaoningensis, named in 2017 by Shen and colleagues from a nearly complete skeleton preserved in three dimensions. Daliansaurus is unusual in possessing an enlarged claw on the fourth digit of the foot, in addition to the "sickle claw" found on the second digit of the feet of most paravians. It also has long metatarsal bones, and apparently possesses bird-like uncinate processes. In the Lujiatun Beds of the Yixian Formation, a volcanically-influenced region with a cold climate, Daliansaurus lived alongside its closest relatives - Sinovenator, Sinusonasus, and Mei, with which it forms the group Sinovenatorinae.
Liaoningvenator is a genus of troodontid theropod dinosaur from the Early Cretaceous of China. It contains a single species, L. curriei, named after paleontologist Phillip J. Currie in 2017 by Shen Cai-Zhi and colleagues from an articulated, nearly complete skeleton, one of the most complete troodontid specimens known. Shen and colleagues found indicative traits that placed Liaoningvenator within the Troodontidae. These traits included its numerous, small, and closely packed teeth, as well as the vertebrae towards the end of its tail having shallow grooves in place of neural spines on their top surfaces.
