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.
See also…
The Dromaeosaurid (a type of small Theropod Dinosaur closely related to Birds and Troodontids) Saurornitholestes langstoni was first...
In December 2000 Xing Xu, Zonghe Zhou and Xioalin Wang of the Institute of Vertebrate Paleontologyand Paleoanthropology of the Chinese Academy of...
Dromaeosaurs were small Therapod Dinosaurs, thought to have been the group most closely related to...
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