Zhenyuanlong
| Zhenyuanlong | ||||||||||||
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Zhenyuanlong suni ( holotype ) |
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| Temporal occurrence | ||||||||||||
| Lower Cretaceous ( Aptium ) | ||||||||||||
| 126.3 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Zhenyuanlong | ||||||||||||
| Lü & Brusatte , 2015 | ||||||||||||
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Zhenyuanlong is a genus of theropod dinosaur in the Dromaeosauridae family. The only known species from time to time is Zhenyuanlong suni , which appeared in the early Cretaceous (Aptium, approx. 125 mya ). The holotype exhibits notable plumage features, including highly developed feathers and wings, but was not capable of flight.
etymology
The generic name “Zhenyuanlong” and the specific epithet “suni” honor Mr. Zhenyuan Sun, who secured the discovery of the holotype for the first description . The term "long", from the Chinese pinyin, 龙 lóng, means dragon.
features
Zhenyuanlong is known so far (as of 2020) only from one copy. There is a nearly complete skeleton, including the skull and mandible (lower jaw). The animal was subadult, the skeleton measures 126.6 cm in length, with the rear half of the tail missing. Overall a length of about 165 cm is assumed (without feathers). Typical features quickly reveal the relationship to long-known predatory dinosaurs such as Velociraptor : steak knife-like teeth, pointed claws and a long tail. The legs are long and resemble a heron. The body mass was around 10 kg.
skull
In the upper jaw, the antorbital fossa (fossa - pit-like indentation) is ventrally limited by sharp edges. A series of pits below the fenestra antorbitalis is typical of Liaoning dromaeosaurids . At Zhenyuanlong suni , however, these pits are poorly developed. The promaxillary fenestra , another opening in the upper jawbone, is very large. The tear bone is T-shaped and has a cavity on the side surface. The quadratojugale has a thin, dorsal ramus . Above the nasal bone and the frontal bone, a ridge forms the lateral edge of the skull. The frontals are elongated, the supratemporal fossa extends far forward onto the dorsal bone surface. The parietals (parietal bones) of the holotype are broken, but the left and right parietals in Zhenyuanlong seem to grow together during growth. This feature is unusual for dromaeosaurids, but has also been found in Tianyuraptor and Sinornithosaurus .
The lower jaw has a series of large openings ( foramina ) in the middle of the lateral dentals (tooth-bearing lower jaw). The external lower jaw has a large window. The posterior surangular has a small foramen anteroventral to the glenoid . The hyoid bone is long and thin.
Postcranium
Limb
The forelimbs are reduced, their length is about half the length of the hind limbs; Zhenyuanlong suni has an extremely short forearm. The femur (thigh bone) of Zhenyuanlong is 193.4 mm long. The humerus (upper arm bone) carries a groin; However, anatomical details are not recognizable on the holotype. The ulna is robust and curved, the olecranon , a proximal protrusion of the ulna, is small and clearly defined. One of the most distinctive features of Zhenyuanlong suni is the radius bone: Zhenyuanlong suni has an extremely slim radius (spoke), the shaft of which is thinner than the shaft of the phalanx I-1 of the finger bones . The latter characteristic is atypical for theropods; the ratio of the diameter of the radius to the hand phalanx I-1 is unique among the dromaeosaurids and has only been documented for alvarez sauroids and a few basal coelurosaurs . The second metacarpal bone measures 55 mm and is therefore shorter than the length of the metacarpal bone I and the first phalanx I combined (60 mm). The metacarpal II (a metacarpal bone ) is shortened. The metatarsal is elongated; the three middle metatarsals are close together and have large, curved claws; the claw of the second toe is designed as a sickle claw. A fourth toe is greatly reduced in size.
The proportional proportions of the limbs of Zhenyuanlong suni can only be compared with Tianyuraptor among the dromaeosaurids from Liaoning . In Zhenyuanlong suni , the humerus to femur ratio is <0.65, the ulna (ulna) to femur ratio <0.55 and the manus (hand) to femur ratio <0.9.
With reference to the fossil record at the time of description (2015), the following differences between Zhenyuanlong and Tianyuraptor arise in terms of proportions: in Zhenyuanlong suni , the fore limb is shorter in relation to the hind limb (ratio 0.48 compared to 0.53) and the hand is shorter in relation to the femur (ratio 0.76 vs. 0.86). Regarding the reliability of these features as diagnostic criteria, however, the small number of fossil records and the possibility of variations due to taphonomic distortions (e.g. due to geological processes) must be taken into account. In related genera (e.g. Microraptor ), the difference in the ratio of fore limbs to hind limbs lies within the range of intraspecific variation; that is, such differences in the proportions of the limbs also occur there within the same species or genus.
Trunk and tail
The spine has six sacral vertebrae ; there may be other non-fused sacral vertebrae. In the holotype, the neural arches of some anterior thoracic vertebrae and parts of the sacral vertebrae are not yet completely fused, which is why the specimen is considered to be subadult. The fact that the posterior sacral fused and the neural arches of the cervical , caudal and some thoracic vertebrae are fused, however, indicates that it is a relatively mature specimen.
The neural arches of the cervical spine are X-shaped with widely spaced zygapophyses (articular processes). The thoracic vertebrae have upwardly elongated spinous processes ; the thorn processes lack a swelling at the dorsal edges, which Zhenyuanlong suni has in common with Tianyuraptor and Microraptor , but is altogether untypical for dromaeosaurids.
There are six vertebrae in the sacrum, four of which are clearly fused together. A tail stiffened by mechanical connecting elements (prezygapophyses; see: vertebral arch ) is characteristic of dromaeosaurids including Zhenyuanlong suni . The prezygapophyses extend as a complex network proximally almost to the base of the tail. The middle caudal vertebrae are about three times as long as the dorsal vertebrae, but proportionally longer than most other dromaeosaurids.
The left and right sides of the bony sternum are not fused together. The shoulder blade is long and straight, similar to Sinornithosaurus (in other Dromaeosauriden mostly curved dorsoventrally).
feathers
The size and orientation of the feathers largely correspond to those of other coelurosaurs (e.g. Sinornithosaurus , Jinfengopteryx ) and presumably mark taxa that are closely associated with the evolution of birds. The tail of Zhenyuanlong suni has large feathers dorsally. It is unclear whether these were symmetrical or asymmetrical. The rhachids (feather shafts) have been preserved; at an angle of about 45 °, these are directed backwards from the tail. They measure 1 mm in diameter and up to 8 mm in height. The front tail rhachids appear to be longer than those of Microraptor and Changyuraptor ; their feathers became larger and more complex towards the rear, towards the distal end of the tail, and formed a fan. Since the distal tail is absent from the Zhenyuanlong suni holotype , the possible presence of such a fan cannot sometimes be assessed.
Other feathers can be seen on the back and neck. Threaded structures about 1 mm thick and 30 mm long were preserved. It is not clear whether the filaments were simple filaments or more developed feathers with lateral secondary rays. In contrast to relatives like Microrapor , Zhenyuanlong suni has no evidence of feathers or even wings on the legs. However, it cannot be completely ruled out that corresponding features have been lost in fossil form.
wing
Zhenyuanlong suni has remarkably well developed plumage and is the largest winged dinosaur found to date. Large feathers with a central rachis (feather shaft) and hooked secondary rays form broad wings. The wing area of the holotype is about 800 cm 2 (right wing) or 1120 cm 2 (left wing).
On the right wing of the forearm of Zhenyuanlong suni there is a row of about 30 small coverts (25–35 mm long) that attach to the ulna and metacarpal bone III. Most of these cover feathers are arranged perpendicular to the ulna; the springs, which attach to metacarpal III, are arranged obliquely and parallel to the longitudinal axis of the hand. The rear wing springs are mainly represented by weak imprints of the spring shafts. There appear to be ten handwings and twenty armwings . As with microraptors and modern birds, the hand and arm wings are more than twice as long as the upper arm; the hand wings are longer than the arm wings. The wings of the arm are arranged perpendicular to the ulna, the wings of the hand are at an acute angle from the hand. The feathers of the wings seem to have been shaped asymmetrically, however, due to the condition of the holotype, an assessment cannot be made with certainty. There are no signs of the formation of an alula .
The plumage of the wings is comparable to Microraptor and basal Avialae like Archeopteryx . Sinornithosaurus, however, had smaller wings and more simply constructed feathers according to the current state of knowledge. Investigations into the aerodynamic properties of the wings of Zhenyuanlong suni are still pending ; however, function for gliding is considered unlikely and the general physique is not optimized for flight. The short arms, the relatively large body mass and the lack of massive chest muscles, as they are also present in modern birds, speak against a purpose as a flying tool. Their purpose may have been to isolate the animals and keep them warm. The use of colored plumage for ornamental and communication purposes is also conceivable, for example for courtship , to ward off enemies or for territorial behavior . Furthermore, the use for breeding purposes (warming the eggs) is discussed.
Paleoecology
The habitat of Zhenyuanlong suni was densely forested and showed high biodiversity . In the Yixian rock formations, in addition to various dinosaurs, including various other dromaeosaurids and feathered species, evidence of amphibians and mammals was found. Zhenyuanlong suni probably shared its habitat with Repenomamus , a predatory mammal genus.
It is not clear which Liaoning dromaeosaurids coexisted. However, it can be assumed that not all six of the currently known species occurred together. From the point of view of today's ecosystems, which colonize numerous bird species side by side, simultaneous occurrence in the same habitats is quite conceivable if the existence of all species had overlapped spatially and temporally.
Zhenyuanlong suni ate carnivore .
Systematics
The taxon was established in 2015 by Lü Junchang and Stephen L. Brusatte . The holotype (JPM-0008) was found in the Chinese Yixian Formation ( Jianchang , Liaoning Province ) and is kept in the Jinzhou Palaeontological Museum.
Among the dromaeosaurids from the sites in Liaoning - five genera were known up to 2015 - there were numerous specimens of small to medium body size, at most comparable with dogs of medium size, long forelimbs and contour or flight feathers. Only in the up to two meters long Tianyuraptor were there reduced forelimbs, but no evidence of a comparable plumage or other imprints of the integument . The somewhat smaller holotype of Zhenyuanlong is sufficiently delimited from Tianyuraptor by proportionally shorter forelimbs and other features to support the description as a new species. At the same time, compared to other species with well-developed plumage, it is a large specimen with reduced forelimbs and easily recognizable feather morphology, which reveals broad forewings with feathers (presumably asymmetrical contour feathers) and other presumed contour feathers on the tail. Due to their mostly long forelimbs, the dromaeosaurids are usually regarded as an intermediate form in the evolution of long-armed birds from the mostly short-armed theropods. Zhenyuanlong and Tianyuraptor, however, stand out from other dromaeosaurids due to their forelimbs , which are differently shortened.
This combination of characteristics is remarkable, long-armed and short-armed dromaeosaurids existed at the same time. In connection with the other dromaeosaurid finds in Liaoning, the investigation by Zhenyuanlong suggests that the Liaoning taxa are probably not a separate clade and that common features may have developed partly independently of each other ( convergent evolution ). The better preserved topology of the Zhenyuanlong holotype compared to older dromaeosaurid finds from Liaoning provides new insights into the systematics. Previously, the Liaoning dromaeosaurids were listed within the Microraptorinae , a sister taxon of the Dromaeosaurinae and Velociraptorinae.
| Dromaeosauridae cladogram (Cau et al., 2017) | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Position of Zhenyuanlong within the Dromaeosauridae according to Cau et al. (2017); Fig. Strict consensus of the shortest trees found by the analysis of first dataset a, Non-paravian taxa. b, paraves . |
Forcing a clade of the six Liaoning dromaeosaurids results in MPTs ( most-parsimonious trees , see: Maximum parsimony , principle of maximum thrift) that are one step longer than the shortest pedigrees of an unrestricted analysis. In some of the most economical family trees, the Liaoning dromaeosaurids form a clade, but in others different species are more closely related to the group of dromaeosaurins and velociraptorins. Likewise, Zhenyuanlong and Tianyulong are sister taxas to some of the most economical trees, but not to others. These uncertainties are due in particular to a high level of homoplasia due to the addition of zhenyuanlong , i.e. features that have evolved independently of one another in several species. Zhenyuanlong and Tianyuraptor do not represent an independent clade despite some common features, especially the anatomical proportions.
The Liaoning dromaeosaurids including Zhenyuanlong are initially listed by Lü & Brusatte (2015) as a basal polytomy together with the Dromaeosaurinae and Velociraptorinae within the Dromaeosauridae. Thus, Zhenyuanlong is more closely related to other Liaoning dromaeosaurids ( Graciliraptor , Changyuraptor , Microraptor , Sinornithosaurus , Tianyuraptor ) and Laurasian Dromaeosarinae and Velociraptorinae than to representatives of the Unenlagiinae or Mahakala .
All in all, the Zhenyuanlong find is an important event in the history of paleontological research; however, it also raises other questions regarding the phylogeny of the dromaeosaurids.
Cau et al. (2017) suggest a different cladistics in their revision of the system, in which Zhenyuanlong is classified basally before the Microraptorinae. The polytomy under Microraptorinae includes six types; Tianyuraptor is placed basal at the transition to Eudromaeosauria.
Individual evidence
- ↑ a b Lü, J .; Brusatte: Paleontology: The Puzzle of Bird Evolution on: Spectrum Biology , August 18, 2017 ( Link , accessed March 25, 2020)
- ↑ a b Jelting, Uwe: Zhenyuanlong suni Lü & Brusatte, 2015 on: Dinodata.de ( Link , accessed on: March 25, 2020)
- ↑ a b Lingenhöhl, Daniel: Dinosaurier: So far the largest dinosaur with wings found on: Spektrum Biologie , July 17, 2015 ( Link , accessed March 24, 2020)
- ↑ Cau, A. et al. (December 6, 2017). Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs . Cladogram accessed via ResearchGate ( Link , accessed on: March 29, 2020)
literature
The information in this article was largely taken from the first scientific description by Lü & Brusatte (2015) , unless supported by individual references :
- Lü, J .; Brusatte, S .: A large, short-armed, winged dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous of China and its implications for feather evolution in: Scientific Reports 5, 11775 (2015). ( PDF )
Left
- Prehistoric Wildlife: Zhenyuanlong