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| [花之故都] |
[恐龙之乡] |
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| [鸟类的祖籍] |
[昆虫王国]] |
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| [鱼类乐园 |
[哺乳动物摇篮] |
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Four-winged dinosaurs
from China
Xing Xu*, Zhonghe Zhou*, Xiaolin Wang*,
Xuewen Kuang?, Fucheng Zhang*
& Xiangke Du?
* Institute of Vertebrate Paleontology and Paleoanthropology,
Chinese
Academy of
Sciences, P.O. Box 643, Beijing 100044, China
? Tianjin Museum of Natural History, Tianjin 300074, China
? Radiological Department, People’s Hospital, Beijing University,
Beijing 100044, China
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Although the dinosaurian hypothesis of bird origins is widely
accepted,
debate remains about how the ancestor of birds first learned
to fly.
Here we provide new evidence suggesting that basal dromaeosaurid
dinosaurs were four-winged animals and probably could glide,
representing
an intermediate stage towards the active, flapping-flight stage.
The new
discovery conforms to the predictions of early hypotheses that
proavians
passed through a tetrapteryx stage. For the past few decades,
the
theropod hypothesis of bird origin has been strongly corroborated
by fossil evidence1–9 and systematic work10–15. Dromaeosaurids,
one of the most distinctive theropod groups, have attracted
particular
attention since the description of Deinonychus1, owing to its
pivotal
role in supporting a theropod origin of birds. They, either
by
themselves or with troodontids7,10,11,13
–16, have been regarded as most closely related to birds.
A better understanding of these animals is therefore crucial
in
reconstructing the evolutionary transition towards birds. Recent
discoveries from the Jehol Group of western Liaoning, China,
suggest that basal dromaeosaurs are small, feathered animals
with
forelimbs similar to those of Archaeopteryx, and feet showing
features comparable to those of arboreal birds7,8,17. In 2001
and
2002, we obtained six new basal dromaeosaurid specimens from
the
Lower Cretaceous Jehol Group at a few localities in Chaoyang
Basin,
western Liaoning, China. IVPP (The Institute of Vertebrate Paleontology
and Paleoanthropology) V13352 and V13320 were identified
as a new species of Microraptor, TNP00996 (Tianjin Museum of
Natural History), IVPP V13351 and IVPP V13476 as Microraptor
sp., and IVPP V13477 as Dromaeosauridae gen. et sp. indet. These
specimens provide new information on the morphology and
distribution of feathers on non-avian dromaeosaurids. Here we
describe the new dromaeosaurid species and in particular the
morphology and distribution of feathers on the newly collected
dromaeosaurid specimens.
Theropoda Marsh, 1881
Maniraptora Gauthier, 1986
Dromaeosauridae Matthew & Brown, 1922
Microraptor Xu, Zhou & Wang, 2000
Microraptor gui sp. nov.
Etymology. The specific name is in honour of Gu Zhiwei, a
distinguished palaeontologist who contributed greatly to the
study of Jehol biota.
Material. IVPP V13352 (holotype) and V13320 (referred specimen),
both represented by an almost complete skeleton.
Locality and horizon. Dapingfang, Chaoyang County, western
Liaoning (30 km southwest of Chaoyang City); Jiufotang Formation18
(Early Cretaceous).
Diagnosis. Distinguishable from Microraptor zhaoianus in having
prominent biceps tuberocity on radius, much shorter manual digit
I, strongly curved pubis, and bowed tibia.
Description. Microraptor gui is a small animal, the holotype
being
approximately 77 cm in total length (Fig. 1a). Little can be
said
about the cranial morphology but a tri-radiate postorbital is
identifiable. As in M. zhaoianus8, the basal troodontid Sinovenator15,
and the basal oviraptorosaur Caudipteryx19, M. gui has a relatively
short trunk length, which is 44–50% of hindlimb length (according
to the method of ref. 19). The tail is long (Fig. 1a) but has
relatively
few vertebrae (approximately 26). The middle and posterior caudals
are significantly elongate as in other basal dromaeosaurs, basal
troodontids and Archaeopteryx20. The sternum is a single, flat
and
large bone (Fig. 1a), different from the condition in other
dromaeosaurids7,21
where two unfused sternal plates are present. At
least seven pairs of slender uncinate processes are present.
The
anterior uncinate processes cover three ribs and the posteriormost
one is short and does not reach the succeeding rib. The fused
scapula
and coracoid are similar to those of Sinornithosaurus and
M. zhaoianus in the following features: scapula shorter than
humerus; glenoid fossa laterally faced; angle between scapula
and
coracoid less than 908; and large supracoracoid fenestra present
on
coracoid20. The forelimb is approximately 2.7 times the femoral
length. The ulna is bowed and the radius is much thinner than
the
ulna (Fig. 1). Metacarpal I is about one-quarter of metacarpal
II in
length and metacarpal III is slender and bowed laterally. Manual
digit II, particularly phalanx II-1, is thick. The pelvis displays
the
following derived features as in M. zhaoianus, Sinornithosaurus,
Sinovenator and basal birds5,7,15: postacetabular process of
the ilium
tapered; pubis retroverted; and ischium short, with a distally
located
obturator process and two dorsal processes. The tibia is variably
bowed,more so in the referred specimen than the holotype. The
pes is
similar to that of M. zhaoianus in showing a sub-arctometatarsalian
Table 1 Measurements of femoral length and the length and asymmetry
ratio
of feathers from the forelimb, hindlimb and tail Specimen Femoral
length
A distal primary feather
A middle secondary
feather
A proximal secondary
feather
A distal metatarsus
feather
A proximal metatarsus
feather
A distal tail
feather
......................................................................
IVPP V13352 97 222/1.94* (7)? 95*/1.52 (10)? 81/1.0 (15)? 194/?
(2)? 104/1.33 (13)? 120/? (2)?
TNP00996 63 ?/? ?/? ?/? 121/1.56* (1)? 72/1.1 (13)? 100/2.1*
(1)?
IVPP V13477 72 ?/? ?/? ?/? 113/3.08 (2)? ?/? ?/?
IVPP V13351 81 ?/? ?/? ?/? 190/? (4)? ?/? 185/? (1)?
IVPP V13320 61 186/1.5* (10)? ?/? ?/? ?/2.4 (1)? 130/? (10)?
?/?
IVPP V13476 94* ?/? ?/? ?/? 175/? (1)? ?/? ?/?
......................................................................
Length measurements are given in millimetres. Asymmetry ratio
is measured
based on the method of ref. 46. Numbers in parentheses
indicate the anatomical positions of the feathers (the metatarsal
feathers are numbered from distal).
* Incomplete measurements.
?Estimation.
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