Liaoningvenator Temporal range: Barremian, | |
---|---|
![]() | |
Life reconstruction with hand for scale | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Theropoda |
Family: | † Troodontidae |
Genus: | † Liaoningvenator Shen et al., 2017 |
Type species | |
†Liaoningvenator curriei Shen et al., 2017 |
Liaoningvenator (meaning "Liaoning hunter") 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.
Within the Troodontidae, the closest relative of Liaoningvenator was Eosinopteryx , and it was also closely related to Anchiornis and Xiaotingia ; while these have traditionally been placed outside the Troodontidae, the phylogenetic analysis conducted by Shen and colleagues offered evidence supporting the alternative identification of these paravians as troodontids. Compared to its close relatives, however, Liaoningvenator had relatively long legs, in particular the femora. As the fifth troodontid known from geographically and temporally comparable strata, Liaoningvenator increases the diversity of Chinese troodontids.
With a total body length (estimated lengths of the skull, neck, trunk, and tail combined) of approximately 69 cm (27 in), Liaoningvenator is a small troodontid. [1]
Liaoningvenator possesses a long, narrow, and triangular skull that measured 9.8 cm (3.9 in) long. At the front of the snout, like Sinovenator and Xixiasaurus , the premaxilla excludes the maxilla from the rim of the nostril. There are three openings on the surface of the maxilla, the premaxillary, maxillary, and antorbital fenestrae. Below, the maxilla forms the secondary palate as in Byronosaurus , Gobivenator , and Xixiasaurus. Uniquely among troodontids, the postorbital bone is slender and radiates into three processes. Like Zanabazar , there is a pneumatic diverticulum in the jugal bone where an air sac was present within the bone; there is also a pneumatic opening on the rear side of the quadrate bone, as in other troodontids. [2] Unlike Sauronithoides, Zanabazar, and Stenonychosaurus , the crest separating the parietal bones does not participate in the border of the supratemporal (upper) temporal fenestra at the back of the skull. [1]
Characteristic of troodontids, [2] Liaoningvenator has a pitted groove on the outer edge of its shallow and triangular lower jaw. The bottom margin of the jaw is slightly convex; in Sinornithoides , it is straight. The dentary and angular bones may have formed a flexible joint within the jaw - that is, an intramandibular joint. [3] Unlike Xiaotingia , the dentary and maxilla terminate at the same position in the jaw. Also like other troodontids (with Sinusonasus being an exception), Liaoningvenator has a number of small, closely spaced teeth, with at least 15 in the upper jaw and 23 in the lower jaw. The teeth towards the rear of the lower jaw are serrated, unlike a number of basal troodontids. The tooth row of the maxilla terminates below the front margin of the antorbital fenestra, whereas it terminates further forward - below the rear of the maxillary fenestra - in Jinfengopteryx . [1]
There are ten cervical vertebrae, twelve dorsal (trunk) vertebrae, and at least sixteen caudal (tail) vertebrae in Liaoningvenator. Out of the cervicals, the third to eighth are elongated, with the fifth being the longest; among the articular processes known as prezygapophyses, the fifth cervical also has the longest. In the third and fourth cervicals, the latter like other derived troodontids, the prezygapophyses are longer than another set of processes known as the postzygapophyses. In the dorsals, the pneumatic pitting is simplified relative to Anchiornis. In the tail, the transition point - the point where the sides of the caudals become more compressed such that they are sub-triangular instead of rectangular - occurs at the seventh caudal, further forward than Sinornithoides and Mei (where it occurs at the ninth). [4] [5] The longest of the caudals is the fourteenth, which is almost twice the length of the sixth. On the underside of the caudals, the chevrons are slightly curved and directed backwards, as is seen in Deinonychus . [1]
The acromion process on the scapula of Liaoningvenator is poorly developed, as in basal troodontids. Unlike basal troodontids, however, the glenoid - the arm socket - is directed vertically downwards instead of to the side. On the humerus, the deltopectoral crest extends for 40% of the bone's length, and terminates halfway down the bone. The humerus is shorter, relative to the femur, in Liaoningvenator (59% length) than in Eosinopteryx (80% length). [6] Further below, the three-digited hand is unique in that the first phalanx of the first digit is longer than the second metacarpal, at 1.49 times the length of the latter. [1]
As in Mei , the top of the ilium has a curved sinusoidal shape in Liaoningvenator. There is no crest over the acetabulum (hip socket) of Liaoningvenator, unlike Anchiornis. The rear portion of the ilium (the postacetabular process) also has a shorter bottom edge than both Anchiornis and Eosinopteryx. Uniquely, there is no process on the top end at the tip of the ischium, and the bone also has a slender obturator process. The pubis points forwards in Liaoningvenator, but backwards in Mei. [5] Additionally, the hindlimb of Liaoningvenator is twice the length of the torso, while in Mei it is 2.8 times the length of the torso. Unlike Sinovenator, Liaoningvenator has a fourth trochanter on its femur. The tibia is slender and 1.4 times the length of the femur, like Sinornithoides. The four-digited foot is highly compacted, with a tarsus that narrows toward the bottom. The third metatarsal is offset from the second and fourth, forming a trough between the latter two that is deeper than in other troodontids. Proportionally, the first phalanx of the second digit is shorter relative to the second phalanx in Liaoningvenator (135% length) than in Sinovenator (150% length). [1] [7]
Liaoningvenator is known from a single specimen, a nearly complete and well-preserved skeleton with most bones preserved in their original articulated positions. It was found in the Lujiatun Beds of the Yixian Formation in Shangyuan, Beipiao, Liaoning, China; currently, it is stored at the Dalian Natural History Museum (DNHM) in Dalian, Liaoning under the accession number DNHM D3012. Some of the specimen's snout bones are incomplete and some toe phalanges have been added by illegal fossil traders; asides from this, it is one of the most complete troodontid fossils ever found. Its head is curved forward, and its limbs are tucked in; this differs from both the classic death pose (where the head is flexed backwards), as well as the sleeping posture of Mei and Sinornithoides. [1]
In 2017, DNHM D3012 was named as the type specimen of the new genus and species Liaoningvenator curriei by Shen Caizhi, Zhao Bo, Gao Chunling, Lü Junchang, and Martin Kundrát. The genus name Liaoningvenator combines Liaoning with the suffix -venator, meaning "hunter" in Latin; the specific name curriei honors the contributions of Canadian paleontologist Philip John Currie to the research of small theropods. [1]
Shen and colleagues identified Liaoningvenator as a member of the Troodontidae based on its numerous, closely spaced teeth that are constricted below the crown; the pneumatic opening on the rear of its quadrate; the oval shape of its foramen magnum; the replacement of neural spines by shallow midline grooves in the vertebrae towards the end of its tail; the tall ascending process on its astragalus; and its asymmetrical and subarctometatarsal (i.e. where the third metatarsal is somewhat pinched by the neighboring metatarsals) foot. [2] [8] They further placed it in the "higher troodontid clade" based on the lack of a bulbous capsule-like structure on the parasphenoid of its palate, and the presence of the promaxillary fenestra on its skull. [1]
Based on a phylogenetic analysis modified from a prior analysis by Takanobu Tsuihiji and colleagues in 2016, which was in turn modified from the modification by Gao and colleagues in 2012 of an analysis by Xu Xing and colleagues in 2012, [9] Shen and colleagues found that Liaoningvenator formed a unified group, or clade, with Eosinopteryx, Anchiornis, and Xiaotingia , thus offering contrary evidence to the traditional placement of these taxa as non-troodontid members of the Paraves. They are united by the teeth being flattened and recurved, with the crowns in the middle of the tooth row having heights smaller than twice their widths; the front edge of the acromion being outturned; the presence of a pronounced notch between the acromion and the coracoid; the presence of a flange on the first phalanx of the second digit on the finger; and the backward-projecting pubis. [1]
Within this clade, which Shen and colleagues did not name, Liaoningvenator formed a group with Eosinopteryx while Anchiornis formed a group with Xiaotingia. The former two are united by the lack of serrated teeth at the front of the jaw; the skull being more than 90% of the length of the femur; the cervical ribs having slender shafts and being longer than their corresponding vertebrae; and the front end of the ilium being "gently straight". Meanwhile, the latter two share the tips of the neural spines on the dorsals being fan-shaped; the coracoid being sub-triangular; the claw on the first digit of the hand being strongly arched, being higher than the top of the articulating surface; the presence of a "lip" at the top end of the claws on the second and third digits; the front edge of the pubic shaft being convex; and the claws on the third and fourth digits of the foot being strongly curved. The results of the phylogenetic analysis are reproduced in the below phylogenetic tree. [1]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Thin sections from the tibia of the holotype specimen of Liaoningvenator indicate that the cortical bone is 1.5 mm (0.059 in) thick. The cortex is divided into four zones by lines of arrested growth (LAGs), which indicates that the animal was at least four years old when it died (further LAGs may have been obliterated by the expansion of the medullary cavity). Shen and colleagues suggested, based on the thinness of the innermost zone 1 compared to zone 2, that it had partially eroded away. However, the complete zone 3 is even thinner, being only a quarter of the width of zone 2, and zone 4 is even thinner (albeit incomplete). This indicates that growth had slowed substantially by the end of the third year. [1]
Each LAG is surrounded by two bands of dense avascular (i.e. lacking openings for blood vessels) bone, which Shen and colleagues termed the "pre-annular" and "post-annular" bands. The first LAG differs from the others in that it consists of two LAGs, one weaker than the other, indicating that growth mildly slowed before the resumption of bone growth. There is no external fundamental system (EFS) on the outer rim of the bone, indicating that the holotype was still growing at the time of death. However, the decreasing thinness of zones, the presence of avascular bone in the outer layers, and evidence of bone remodeling collectively suggest that it was close to skeletal maturity. [1]
According to Shen and colleagues, Liaoningvenator is one of eleven troodontids known from China, and the fifth Early Cretaceous Chinese troodontid after Sinovenator, Sinusonasus, Mei, and Jinfengopteryx. [1] In a separate 2017 publication for which Shen was also the lead author, an additional troodontid was described, Daliansaurus , which forms the Sinovenatorinae with the former three. [10] With the exception of Jinfengopteryx, all of these troodontids lived in the Lujiatun Beds. While Shen and colleagues assigned the Lujiatun Beds to the Hauterivian epoch, newer date estimates published by Chang Su-chin and colleagues suggested a younger age of ~126 Ma for the Lujiatun Beds, which dates to the Barremian epoch. [11]
Contemporaneous dinosaurs included the microraptorine dromaeosaurid Graciliraptor ; the oviraptorosaur Incisivosaurus ; the ornithomimosaurs Shenzhousaurus [12] and Hexing ; [13] the proceratosaurid tyrannosauroid Dilong ; [12] the titanosauriform sauropod Euhelopus ; [14] the ornithopod Jeholosaurus ; and ceratopsians such as the ubiquitous Psittacosaurus [15] as well as Liaoceratops . [12] Mammals present included Acristatherium , [16] Gobiconodon , Juchilestes , Maotherium , Meemannodon , and Repenomamus . [17] [18] [19] Other tetrapods included the frogs Liaobatrachus [20] and Mesophryne ; [21] and the lizard Dalinghosaurus . [22] The Lujiatun Beds consist of fluvial and volcaniclastic deposits, indicating a landscape of rivers bearing volcanoes, [1] which may have killed the preserved animals by lahar. [19] Mean annual air temperatures in the region reached a minimum of 10 °C (50 °F). [23]
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.
Mei is a genus of duck-sized troodontid dinosaur first unearthed by paleontologists from the Yixian Formation in Liaoning, China in 2004. Mei lived during the Early Cretaceous period. The binomial name of its only species, Mei long, means sleeping dragon.
Oviraptorosaurs are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or without bony crests atop the head. They ranged in size from Caudipteryx, which was the size of a turkey, to the 8-meter-long, 1.4-ton Gigantoraptor. The group is close to the ancestry of birds. Some researchers such as Maryanska et al (2002) and Osmólska et al. (2004) have proposed that they may represent primitive flightless birds. The most complete oviraptorosaur specimens have been found in Asia. The North American oviraptorosaur record is sparse.
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.
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.
Hesperornithoides is a genus of troodontid theropod dinosaur that lived in North America during the Late Jurassic period.
Dongbeititan is a genus of sauropod dinosaur from the Early Cretaceous-age Yixian Formation of Beipiao, Liaoning, China. It is based on holotype DNHM D2867, a partial postcranial skeleton including bones from the limbs, shoulder and pelvic girdles, and vertebrae, which was described in 2007. Its describers suggested it was as a basal titanosauriform, not as derived as Gobititan or Jiutaisaurus, but more derived than Euhelopus, Fusuisaurus, and Huanghetitan. The type species is D. dongi, and it is the first named sauropod from the Yixian Formation, which is part of the well-known Jehol Group. The genus name refers to the region Dongbei and to Greek titan, "giant". The specific name honours the Chinese paleontologist Dong Zhiming. Like other sauropods, Dongbeititan would have been a large quadrupedal herbivore.
Anchiornis is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species Anchiornis huxleyi, named for its similarity to modern birds. The Latin name Anchiornis derives from a Greek word meaning "near bird", and huxleyi refers to Thomas Henry Huxley, a contemporary of Charles Darwin.
Xixiasaurus is a genus of troodontid dinosaur that lived during the Late Cretaceous Period in what is now China. The only known specimen was discovered in Xixia County, Henan Province, in central China, and became the holotype of the new genus and species Xixiasaurus henanensis in 2010. The names refer to the areas of discovery, and can be translated as "Henan Xixia lizard". The specimen consists of an almost complete skull, part of the lower jaw, and teeth, as well as a partial right forelimb.
Xiaotingia is a genus of anchiornithid theropod dinosaur from Middle Jurassic or early Late Jurassic deposits of western Liaoning, China, containing a single species, Xiaotingia zhengi.
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.
Eosinopteryx is an extinct genus of theropod dinosaurs known to the Late Jurassic epoch of China. It contains a single species, Eosinopteryx brevipenna.
Gobivenator is an extinct genus of troodontid theropod dinosaur known from the late Campanian Djadokhta Formation of central Gobi Desert, Mongolia. It contains a single species, Gobivenator mongoliensis. G. mongoliensis is known from a single individual, which represents the most complete specimen of a Late Cretaceous troodontid currently known.
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.
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.
Anchiornithidae is a family of eumaniraptorans which could be the basalmost family of birds in the clade Avialae. Anchiornithids have been classified at varying positions in the maniraptoran tree, with some scientists classifying them as a distinct family, a basal subfamily of Troodontidae, members of Archaeopterygidae, or an assemblage of dinosaurs that are an evolutionary grade within Avialae or Paraves.