Vol 461 | 1 October 2009 | doi:10.1038/nature08322
LETTERS
A pre-Archaeopteryx troodontid theropod from China
with long feathers on the metatarsus
Dongyu Hu1, Lianhai Hou1,2, Lijun Zhang1,3 & Xing Xu1,2
600–2,890m
176–2,624m
Ber
Jehol Group
Tuchengzi
Formation
~125 Myr
~155 Myr
Haifanggou
Formation
104–580m
Aal-Tit
Tiaojishan
Formation
230–1,800m
Jurassic
Cretaceous
on the lateral surface near the junction of the neural arch and centrum
(Fig. 3b), and the coracoid bears a laterally located coracoid tubercle
(Fig. 3c). The ischium is strongly curved posteriorly, with an obturator
Basalt
Plb-Toa
Beipiao
Formation
500–1,300m
Andesite
Siltstone
Mudstone
Conglomerate
Sandstone
Tuff
Het-Sin
Xinglonggou
Formation
130–500m
The early evolution of the major groups of derived non-avialan
theropods is still not well understood, mainly because of their poor
fossil record in the Jurassic. A well-known result of this problem is
the ‘temporal paradox’ argument that is sometimes made against
the theropod hypothesis of avian origins1. Here we report on an
exceptionally well-preserved small theropod specimen collected
from the earliest Late Jurassic Tiaojishan Formation of western
Liaoning, China2. The specimen is referable to the Troodontidae,
which are among the theropods most closely related to birds. This
new find refutes the ‘temporal paradox’1 and provides significant
information on the temporal framework of theropod divergence.
Furthermore, the extensive feathering of this specimen, particularly the attachment of long pennaceous feathers to the pes, sheds
new light on the early evolution of feathers and demonstrates the
complex distribution of skeletal and integumentary features close
to the dinosaur–bird transition.
Anchiornis huxleyi has been recently described, based on an incomplete specimen, as a basal avialan filling the morphological gap
between non-avian and avian dinosaurs3. A nearly complete, extensively feathered specimen (LPM-B00169, housed in Liaoning Paleontological Museum) referable to Anchiornis huxleyi (Supplementary Information) has now been recovered from the Tiaojishan
Formation at the Daxishan locality, Jianchang County. The
Tiaojishan Formation has traditionally been regarded as Middle
Jurassic but was recently dated to between 161 and 151 Myr (ref. 2)
(Fig. 1; Supplementary Information). It is therefore older than the
Archaeopteryx-bearing strata near Solnhofen, Germany, which date
to less than 150 Myr (ref. 4).
The new specimen exhibits a sub-triangular skull in lateral view
and a large surangular foramen, as in other paravians and deinonychosaurs, respectively5–7 (Figs 2 and 3a). It has a large maxillary
fenestra separated from the antorbital fenestra by a narrow interfenestral bar, a dorsoventrally flattened internarial bar, a distinct, posteriorly widening groove on the labial surface of the dentary housing
the neurovascular foramina, and closely packed premaxillary and
dentary teeth in the symphyseal region, derived features shared with
other troodontids5,7–9. Furthermore, Anchiornis resembles Mei in
having a large external naris extending posteriorly well beyond the
anterior border of the antorbital fossa5, a longitudinal groove along
the dorsomedial margin of the slender sub-orbital ramus of the jugal,
a maxillary tooth row that approaches the preorbital bar posteriorly5
and unserrated teeth (also seen in the troodontid Byronosaurus8). A
large paraquadrate foramen is present, in contrast to other troodontids but in agreement with dromaeosaurs6.
Postcranially, Anchiornis also possesses a few troodontid features,
including relatively long and slender transverse processes on the dorsal
vertebrae and anterior-most caudal vertebrae8. As in Archaeopteryx4,
the middle and posterior caudal vertebrae each bear a distinct groove
Agglomerate
Shale
Breccia
Coal measures
Figure 1 | Stratigraphic column of Jurassic and Lowest Cretaceous strata in
western Liaoning, showing horizons from which feathered dinosaurs have
been described. Two major horizons have produced such specimens: the
Tiaojishan Formation has yielded Anchiornis huxleyi LPM-B00169 and
dates to about 155 Myr, whereas the Jehol Group has yielded Microraptor
and other feathered dinosaurs and dates to about 125 Myr.
1
Paleontological Institute, Shenyang Normal University, 253 North Huanghe Street, Shenyang 110034, China. 2Key Laboratory of Evolutionary Systematics of Vertebrates, Institute of
Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xiwai Street, Beijing 100044, China. 3Shenyang Institute of Geology and Mineral Resources, 25
Beiling Street, Shenyang 110032, China.
640
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LETTERS
NATURE | Vol 461 | 1 October 2009
a
a
f
g
b
c
h
i
j
d
k
l
m
e
b
sk
lp
lm
lt
ma
lu
ril sy
dv
lil
cav
lh
ls
lfe
ga
fu dr
rc
f
Figure 3 | Selected skeletal elements and associated feathers of LPMB00169. a, Skull and mandible. b, Middle caudal vertebrae. c, Furcula and
right scapulocoracoid. d, Left forelimb. e, Right forelimb. f, Left hindlimb.
g, Right pes. h, Feathers near skull. i, Feathers near pectoral region.
j, Distalmost primary remiges. k, Middle primary remiges. l, Secondary
primary remiges. m, Pennaceous feathers attached to metatarsus. Arrows
indicate the boundary of the soft tissue. Scale bars: a, b, d–g, 2 cm; c, 1 cm;
h, k, l, 2 mm in; i, j, m, 1 mm.
lfi
lr
cev
lis
pu
rs
rfe rt
f
rp
rr
f
rh
ru
rm
Figure 2 | Anchiornis huxleyi LPM-B00169. a, Photograph and b, line
drawing of LPM-B00169 A (slab). Abbreviations: cav, caudal vertebra; cev,
cervical vertebra; dr, dorsal rib; dv, dorsal vertebra; f, feather; fu, furcula; ga,
gastralia; lfe, left femur; lfi, left fibula; lh, left humerus; lil, left ilium; lis, left
ischium; lm, left manus; lp left pes; lr, left radius; ls, left scapula; lt, left
tibiotarsus; lu, left ulna; ma, mandible; pu, pubis; rc, right coracoid; rfe, right
femur; rh, right humerus; ril, right ilium; rm, right manus; rp, right pes; rr,
right radius; rs, right scapula; rt, right tibiotarsus; ru, right ulna; sk, skull; sy,
synsacrum. Scale bar, 5 cm.
process located close to the midpoint of the ischial shaft as in the
dromaeosaurid Buitreraptor10. As in Mei and some dromaeosaurids11,
the distal articulation of metatarsal II is about as wide as that of
metatarsal III.
There are about ten large pennaceous feathers attached to the
forearm, 11 to the manus (Fig. 3d, e), 12–13 to the crus (Fig. 3f)
and 10–11 to the metatarsus (Fig. 3g). The primary and secondary
remiges are similar in size and morphology (Fig. 3j–l). The longest
remiges, located near the distal end of the forearm and the proximal
end of the manus, are about 150% of the humeral length. Because the
longest wing feathers are close to the wrist, the broadest part of the
wing is relatively proximal, in contrast to the basal dromaeosaurid
Microraptor and basal avians such as Archaeopteryx12. The distal
primary remiges resemble those of Microraptor and basal avians4,12,13
in having curved rachides, but the remiges are relatively small, with
thin rachides, symmetrical vanes, and blunt ends. In Microraptor and
basal avians12, the primary remiges are not only significantly longer
than the secondary ones but also possess prominent rachides, asymmetrical vanes and somewhat pointed tips. Large pennaceous
feathers also cover nearly the whole length of the lower leg of
Anchiornis (Fig. 3m). The crural feathers are longer than the metatarsal feathers, which are nearly perpendicular to the long axis of the
metatarsus. Much shorter feathers also attach to the pedal phalanges,
apart from the unguals. These feathers appear to be pennaceous, a
condition previously unknown in any fossil taxon.
Two types of plumulaceous feather can be distinguished, corresponding to types previously identified in the dromaeosaurid
Sinornithosaurus14. Feathers of the first type are each composed of a
bundle of filaments that are joined together proximally and remain
nearly parallel as they pass distally (Fig. 3h). Feathers of the second
type each consist of a series of filaments branching laterally from a
slender central rachial filament (Fig. 3i).
Anchiornis huxleyi is posited as a basal troodontid by our phylogenetic analysis (Fig. 4) but also possesses several salient features of
the Avialae and Dromaeosauridae, further blurring distinctions
among the three major paravian groups (Supplementary Information). In particular, the forelimbs of Anchiornis are proportionally
much longer than those of other troodontids, but similar in length to
those of basal avialans and dromaeosaurids. Anchiornis huxleyi even
exceeds Microraptor in the length of the forelimbs3, a feature often
641
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LETTERS
Aptian
121
Barremian
Hauterivian
Valanginian
Berriasian
144
Kimmeridgian
Middle
Jurassic
Oxfordian
159
Callovian
Bathonian
Bajocian
Aalenian
190
Other avians
Coelophysoidea
Late
Tithonian
Scansoriopterygidae
Archaeopteryx
Early
Albian
Mei long
99
Sinovenator changii
Cretaceous
Cenomanian
Anchiornis huxleyi
Santonian
Coniacian
Turonian
Compsognathidae
Late
Campanian
Ornitholestes hermanni
Basal tetanurans
Maastrichtian
Other troodontids
Dromaeosauridae
Therizinosauroidae
Alvarezsauroidea
Oviraptorosauria
Ceratosauria
Tyrannosauroidea
Ornithomimosauria
NATURE | Vol 461 | 1 October 2009
Early
Toarcian
Pliensbachian
Sinemurian
Late
Triassic
Hettangian
Rhaetian
206
Norian
Carnian
227
Figure 4 | Temporally calibrated phylogeny of the Theropoda. (See
Supplementary Information for details.) The known temporal durations
(solid bars) of the major theropod groups, based on well-corroborated fossil
occurrences, indicate that the major tetanuran theropod groups diverged
rapidly in the Middle Jurassic to earliest Late Jurassic.
regarded as an indicator of aerial capability. However, the remiges of
Anchiornis are not obviously flight-adapted as in Microraptor and
basal avians12. Furthermore, the extreme elongation of the lower legs
in Anchiornis huxleyi suggests strong cursorial capability3, but their
long and extensive plumage is not common among cursorial animals:
in cursorial birds and mammals, the lower legs tend to show reduction or even complete loss of the feathers or hair, respectively.
Similarly, the recently reported Jurassic basal avialan Epidexipteryx
hui closely resembles basal birds in various skeletal features usually
interpreted as being related to aerial capability, but lacks pennaceous
feathers that would facilitate aerial locomotion15. Collectively, these
data point to a complex pattern of morphological evolution at the
base of the Paraves.
The distribution of large pennaceous feathers, both phylogenetic
and anatomical, implies that these structures first evolved on the distal
portions of the forelimbs and tail in maniraptoran theropods and only
spread proximally at a subsequent stage in theropod evolution12.
Interestingly, such a distal-first pattern seems also to apply to the
evolution of pennaceous feathers on the hindlimbs of paravians.
Large pennaceous feathers are now known to occur on the lower leg
and particularly the metatarsus of at least one basal member of each of
the three major paravian groups, namely the basal troodontid
Anchiornis, the basal avialan Pedopenna and the basal dromaeosaurid
Microraptor13,16. Furthermore, many basal avians have proportionally
large pennaceous feathers on the lower leg13,17, which are reduced in
more derived birds. This suggests that large pennaceous feathers first
evolved distally on the hindlimbs, as on the forelimbs and tail. This
distal-first development led to a four-winged condition at the base of
the Paraves. Whereas the large feathers of the forewing developed
further in subsequent avian evolution, the large hindwing feathers
were reduced and even lost12. This suggests that extensive feathering
of the pes was a critical modification in the transition to birds and that
the pedal scales of extant birds might be secondarily derived structures, a possibility also supported by some developmental studies18.
Extensive feathering of the pes is also seen in some modern birds,
and serves an insulating or protective function19. In most cases the
feathers are not organized into a coherent planar surface as in
Microraptor, Pedopenna and Anchiornis20, which indicates that the
pedal feathers of these fossil taxa may have differed from those of
extant birds in having an aerodynamic function. This would imply
that a four-winged condition played a role in the origin of avian
flight, as suggested by previous studies12,17, although this conclusion
is not universally accepted21. However, the significant differences
noted above between the large pedal feathers of Anchiornis and those
of Microraptor suggest that these feathers might have been less aerodynamically effective in Anchiornis than in Microraptor.
The poor fossil record of derived non-avialan theropods has hindered
understanding of early coelurosaurian theropod evolution, and has
created an apparent discrepancy between stratigraphy and phylogeny
that has sometimes been used to argue against the theropod hypothesis
of bird origins1. Although derived theropods including troodontids
have been reported in the Jurassic, all have been based on fragmentary
material22–25. Anchiornis huxleyi is probably Oxfordian in age, and
unquestionably represents the oldest troodontid reported so far7. The
presence of a troodontid in the earliest Late Jurassic indicates that all
groups of derived theropods had originated by this time. A calibrated
theropod phylogeny based only on well-corroborated fossil occurrences
suggests that all major tetanuran groups, including Aves, might have
originated and diversified rapidly in the Middle to earliest Late
Jurassic (Fig. 4). This rapid divergence event would have coincided with
documented palaeogeographical changes that took place around the
same time. Alternatively, a calibrated theropod phylogeny incorporating
fragmentary material suggests that tetanurans have a much longer
evolutionary history, and that great potential exists for discovering
derived theropod fossils, even in the Triassic24.
Received 29 April; accepted 27 July 2009.
1.
Feduccia, A. Birds are dinosaurs: simple answer to a complex problem. Auk 119,
1187–1201 (2002).
2. Xu, K. et al. Jurassic System in the North of China (VII): The Stratigraphic Region of
Northeast China (Petroleum Industry Press, 2003).
3. Xu, X. et al. A new feathered maniraptoran dinosaur fossil that fills a
morphological gap in avian origin. Chin. Sci. Bull. 54, 430–435 (2009).
4. Wellnhofer, P. Archaeopteryx—Der urvogel von Solnhofen (Friedrich Pfeil, 2008).
5. Xu, X. & Norell, M. A. A new troodontid from China with avian-like sleeping
posture. Nature 431, 838–841 (2004).
6. Norell, M. A. & Makovicky, P. J. in The Dinosauria 2nd edn (eds Weishampel, D. B.,
Dodson, P. & Osmolska, H.) 196–209 (Univ. California Press, 2004).
7. Makovicky, P. J. & Norell, M. A. in The Dinosauria 2nd edn (eds Weishampel, D. B.,
Dodson, P., Osmolska, H.) 184–195 (Univ. California Press, 2004).
8. Makovicky, P. J., Norell, M. A., Clark, J. M. & Rowe, T. Osteology and relationships of
Byronosaurus jaffei (Theropda: Troodontidae). Am. Mus. Novit. 3402, 1–32 (2003).
9. Currie, P. J. Bird-like characteristics of the jaws and teeth of troodontid theropods
(Dinosauria: Saurischia). J. Vert. Paleontol. 7, 72–81 (1987).
10. Makovicky, P. J. Apesteguı́a, S. & Agnolı́n, F. L. The earliest dromaeosaurid
theropod from South America. Nature 437, 1007–1011 (2005).
11. Xu, X. & Wang, X.-L. A new dromaeosaur (Dinosauria: Theropoda) from the Early
Cretaceous Yixian Formation of western Liaoning. Vert. PalAsia. 42, 111–119 (2004).
12. Xu, X. et al. Four-winged dinosaurs from China. Nature 421, 335–340 (2003).
642
©2009 Macmillan Publishers Limited. All rights reserved
LETTERS
NATURE | Vol 461 | 1 October 2009
13. Zhang, F.-C. & Zhou, Z.-H. Leg feathers in an Early Cretaceous bird. Nature 431,
925 (2004).
14. Xu, X., Zhou, Z.-H. & Prum, R. O. Branched integumental structures in
Sinornithosaurus and the origin of feathers. Nature 410, 200–204 (2001).
15. Zhang, F.-C., Zhou, Z.-H., Xu, X., Wang, X.-L. & Sullivan, C. A bizarre Jurassic
maniraptoran from China with elongate ribbon-like feathers. Nature 455,
1105–1108 (2008).
16. Xu, X. & Zhang, F.-C. A new maniraptoran with long metatarsalian feathers from
China. Naturwissenschaften 92, 173–177 (2005).
17. Longrich, N. R. Structure and function of hindlimb feathers in Archaeopteryx
lithographica. Paleobiology 32, 417–431 (2006).
18. Sawyer, R. H. & Knapp, L. W. Avian skin development and the evolutionary origin
of feathers. J. Exp. Zool. 298B, 57–72 (2003).
19. Weidensaul, S. Raptors—The Birds of Prey (Lyons & Burford, 1995).
20. Xu,X.etal.Originofflight:couldfour-wingeddinosaursfly?Nature438,E3–E4(2005).
21. Padian, K. Four-winged dinosaurs, bird precursors, or neither? Bioscience 53,
450–452 (2003).
22. Jensen, J. A. & Padian, K. Small pterosaurs and dinosaurs from the Uncompahgre
Fauna (Brushy Basin Member, Morrison Formation: ?Tithonian), Late Jurassic,
western Colorado. J. Paleontol. 63, 364–373 (1989).
23. Chure, D. J. Koparion douglassi, a new dinosaur from the Morrison Formation
(Upper Jurassic) of Dinosaur National Monument: the oldest troodontid
(Theropoda: Maniraptora). Brigham Young Univ. Geol. Stud. 40, 11–15 (1994).
24. Xu, X., Zhao, X.-J. & Clark, J. M. A new therizinosaur from the Lower Jurassic
Lufeng Formation of Yunnan, China. J. Vert. Paleontol. 21, 477–483 (2001).
25. Evans, S. E. & Milner, A. R. in In the Shadow of the Dinosaurs (eds Fraser, N. C. &
Sues, H.-D.) 303–321 (Cambridge Univ. Press, 1985).
Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements We thank S. Zheng for help with the fieldwork, T. Yu for
preparing the specimen, C. Sullivan for editing and commenting on the manuscript,
G. Sun, P. Cheng and F. Jin for discussions and comments, and J. Huang for
Supplementary Fig. 4i. The fieldwork was supported by grants from the Education
Bureau of Liaoning Province (numbers 20060805 and 2008S214) and the Special
Fund of Shenyang Normal University. This study was also supported by grants to
X.X. from the Chinese Academy of Sciences, the National Natural Science
Foundation of China, and Major Basic Research Projects of the Ministry of Science
and Technology, China.
Author Contributions D.-Y.H and X.X. designed the project. D.-Y.H., X.X., L.-H.H
and L.-J.Z. performed the research. X.X. and D.-Y.H. wrote the manuscript.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. Correspondence and requests for materials should be
addressed to X.X. (xingxu@vip.sina.com) or D.-Y.H. (hudongyu@synu.edu.cn).
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