Liaoningvenator
Liaoningvenator | |
---|---|
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
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Liaoningvenator (meaning "
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.
Description
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]
Skull and jaws
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]
Vertebrae
There are ten
Limbs
The
As in
Discovery and naming
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
In 2017, DNHM D3012 was named as the
Classification
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]
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Paleobiology
Histology
Thin sections from the
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]
Paleoecology
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
See also
References
- ^ .
- ^ a b c Makovicky, P.J.; Norell, M.A. (2004). "Troodontidae". In Weishampel, D.B.; Dodson, P.; Osmólska, H. (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 184–195.
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