Sciency Thoughts: Zhenyuanlong suni: A large feathered Dromaeosaur from the Jehol Biota.

Dromaeosaurid Dinosaurs are among the closest non-Avian relatives of the Birds and show many similarities to the earliest members of that group, making understanding Dromaeosaurs important for understanding the origin of Birds. In particular many Dromaeosaur specimens from the Early Cretaceous of Liaoning Province, China, have been shown to possess extremely Bird-like feather coats, and in several cases feathered wings which may have allowed them to fly. This is particularly interesting as the Liaoning specimens are not thought to represent a tight monophyletic group (i.e. a group of species more closely related to one-another than anything else), but rather a diverse group of Dromaeosaurs with exceptional preservation, part of the Jehol Biota of exceptionally well preserved Early Cretaceous fossils, suggesting that feathers were also present in Dromaeosaurs from other locations even if they have not been preserved. The smallest and most numerous Liaoning Dromaeosaurs are placed in the genus Microraptor and may (or may not) represent several species of small (cat-sized) Dinosaurs fully capable of flight, while the largest, Tianyuraptor, is a much larger animal with reduced fore-limbs highly unlikely to have been capable of supporting it in flight. Unfortunately Tianyuraptor is known only from a single specimen lacking feathers; it is impossible to determine whether this species was truly featherless from a single specimen, nor to speculate about what sort of feathers it may have possessed.

In a paper published in the journal Nature Scientific Reports on 16 July 2015, Junchang Lü of the Institute of Geology of the Chinese Academy of Geological Sciences and the Key Laboratory of Stratigraphy and Paleontology of the Ministry of Land and Resources of China and Stephen Brusatte of the School of GeoSciences at the University of Edinburgh, describe a new species of Dromaeosaur from the Yixian Formation of Jianchang County in Liaoning Province.

The new species is named Zhenyuanlong suni, honouring Zhenyuan Sun who discovered the specimen; the suffix ‘-long’ means ‘Dragon’ in Chinese, making ‘Zhenyuanlong suni’ ‘Zhenyuan Sun’s Dragon’. The specimen comprises an almost complete specimen preserved on in two dimensions on three separate blocks, with only the end part of the tail missing. The specimen is 126.6 cm in length, but it is thought to have been about 165 cm long in life. Not all of the vertebrae fused in adult Dinosaurs are fully fused in this specimen, leading Lü and Brusatte to conclude it was a subadult at the time when it died.

The holotype of the large-bodied Liaoning Dromaeosaurid Zhenyuanlong suni. Lü & Brusatte (2015).

Like Tianyuraptor, Zhenyuanlong suni has relatively small forelimbs for the size of its body, however unlike Tianyuraptor an extensive feather coating is preserved on all of Zhenyuanlong suni except its hindlimbs (these are preserved on a separate block which does not contain any feathers, making it hard to assess whether feathers were originally present on the hindlimbs; feathered hindlimbs are common in both smaller Dromaeosaurs and early Birds). Notably these show layered feathers similar to those seen in modern Birds and Microraptor.

The integument of the large-bodied, short-armed Liaoning Dromaeosaurid Zhenyuanlong suni. (A) Overview of the skeleton with regions of integument indicated with grey highlight; (B) proximal tail; (C) left forearm; (D) right forearm; (E) closeup of coverts on right forearm. Lü & Brusatte (2015).

Without a full biomechanical analysis (which has not been carried out for Zhenyuanlong suni at the time of writing) it is impossible to say whether or not it was capable of flying or gliding, but the combination of a large body size and small forelimbs makes this seem somewhat unlikely, leading to support for the alternative theory that feathered wings were first developed for some other purpose in Bird-like Dinosaurs and later co-opted for flight in Birds and possibly some small Dromaeosaurs. This is not uncommon as evolution does not plan ahead, and major biological revolutions often come about when organs or metabolic pathways adapted to one purpose are then used for another.

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Saturday, 25 July 2015

Zhenyuanlong suni: A large feathered Dromaeosaur from the Jehol Biota.