Zhenyuanlong

Credit: Chuang Zhao.

"Zhenyuanlong" is a naked genus of dromaeosaurid dinosaur that lived in China during the Early Cretaceous*.*

## History

—Steve Brusatte in "The Rise and Fall of the Dinosaurs".

Near Sihedang, Liaoning, JPM-0008, the holotype, was discovered and sent to the Jinzhou Paleontological Museum by Zhenyuan Sun. Stephen Brusatte and Junchang Lü were flown in to help study the specimen, who had the belief that it may represent a new taxon and was a "holy grail fossil". It was named "Zhenyuan Sun's dragon" with the specific epithet derived from Sun. It is Aptian-aged and a near-complete, articulate subadult preserving integument. It is compressed on a slab, with an absent counterplate.

## Description

Zhenyuanlong is medium-sized and most comparable to *Tianyuraptor*, which it may be a synonym of. It is complete but lacks half of the tail, with a preserved length of 122.6 centimeters. It was likely about 165 centimeters long in life, based on *Tianyuraptor*, and probably 2 meters long if the integument is included. The skull is well-preserved and very similar to *Tianyuraptor* and *Sinornithosaurus*. The sacrum has 6 vertebrae, with 4 fused and a tail supported by bony rods. The mid-caudals are somewhat more elongate. Both pectoral girdles are present and suggest unfused sternal plates. The proportions are similar to close relatives. The tibiotarsus is longer than the femur, having a 1:20 ratio typical of Liaoning dromaeosaurs but atypical of other dromaeosaurs. The forearms are short with the shortest arm/leg ratio of any dromaeosaur except *Mahakala* and *Austroraptor*. The radius is the thinnest of any theropod except for some basal coelurosaurs and alvarezsaurs. The second metacarpal is shorter than the first metacarpal and the first innermost finger bone combined.

A simple hair-like integument spans most of the body and large vaned feathers sit at the arms and tail. Small imprints around the holotype indicate the existence of these. Around the front and back of the neck sit >1 millimeter-thick and 30-millimeter-long filament that are are poorly preserved, so it is unknown if they were complex or not. The arm feathers are more than 2x the length of the humerus. These formed broad wings that had a surface area of 1 meter/wing. Distortion during fossilization makes it impossible to know their true shape. The right wing has an overlapping complex of primaries, secondaries and coverts. The wings are similar in form to *Microraptor*, *Changyuraptor*, *Anchiornis*, *Eosinopteryx* and basal avialans such as *Archaeopteryx*. The coverts are similar in size and shape to modern birds. ~30 feathers of consistent, small size perpendicularly attach to the ulna and third metacarpal and make a row. The primaries were longer than the secondaries, with ~10 primaries and ~20 secondaries (estimation). These may have asymmetric shape, similar to modern birds, but distortion makes this difficult to tell.

Vaned feathers line the tail and project at a 45° angle from the vertebrae. These appear to be similar to the tails of other taxa, but it is difficult to tell symmetry from the specimen. However, it is different from *Microraptor* and *Changyuraptor*. It is impossible to rule out the presence of a tail fan. Given it's close relations to dromaeosaurs with wings on their legs, they are absent in Zhenyuanlong. However, it has been hypothesized that the "leg wings" may be due to preservation bias or faulty preparation. Thus, this feature may not be ruled out truly. Zhenyuanlong was likely unable to fly sue to it's size and stress that biomechanical studies would be needed to test this. It is one of the largest non-avian dinosaurs with complex wings. They question what such a large animal with short limbs and complex wings would have used their wings for. They suggest it is secondarily flightless, since it has shared ancestry of microraptorians, using it's wings to gain flight through inertia or for other reasons. Others include display, protecting eggs or maybe arboreal gliding. It may have had wing-assisted incline running, flapping their wings while sprinting up steep surfaces. Sexual display or a warning to rivals may be one of the most viable hypotheses. If Zhenyuanlong is distinct, it may gain insight to contemporaneous long-armed and short-armed forms in the Jehol biota.

## Classification

"Z. suni" lacks a ZooBank entry, so it is considered a nomen nudum. Additionally, the differences between it and *Tianyuraptor* have differences explainable as individual variation. It was recovered in a polytomy with related taxa upon naming, seen here:

## References

1. ↑ https://www.goodreads.com/book/show/35820369-the-rise-and-fall-of-the-dinosaurs

	* http://news.sciencemag.org/biology/2015/07/big-bird-dino-researchers-discover-largest-ever-winged-dinosaur
	* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4504142
	* http://blogs.plos.org/paleocomm/2016/01/06/the-open-access-dinosaurs-of-2015/
	* https://www.bbc.com/news/science-environment-33510288
	* http://time.com/3961931/science-dinosaur-velociraptor-feather/
	* https://www.reuters.com/article/us-science-dinosaur-idUSKCN0PQ1EJ20150716
	* https://www.theguardian.com/science/2015/jul/16/zhenyuanlong-suni-biggest-ever-winged-dinosaur-discovered-china
3. ↑ https://www.theropoddatabase.com/Dromaeosaurs.htm#Tianyuraptorostromi