RESEARCH PAPER

New observations on the skull of Archaeopteryx

Oliver W. M. Rauhut

Received: 18 January 2013 / Accepted: 14 May 2013 / Published online: 8 June 2013

� Springer-Verlag Berlin Heidelberg 2013

Abstract Although skeletal remains of the iconic oldest

known avialian Archaeopteryx have been known for almost

150 years, several aspects of the cranial anatomy of this

taxon have remained enigmatic, mainly because of the

strongly flattened and often fractured and incomplete nat-

ure of available skull materials. New investigation of the

skulls of the recently described, excellently preserved tenth

(Thermopolis) and the seventh (Munich) specimens

revealed several previously unrecognized characters and

helps to resolve some problematic issues. Thus, the nasal of

Archaeopteryx shows a lateral notch for the lacrimal, as is

found in many other saurischian dinosaurs, the maxilla

clearly participates in the margin of the external nares, and

there seems to be a pneumatic foramen in the lacrimal,

comparable to the lacrimal fenestra found in many non-

avian theropods. In the braincase, Archaeopteryx shows

pneumatic features reminiscent of non-avian theropods,

including a ventral basisphenoid recess and an anterior

tympanic recess that is laterally incised into the basisphe-

noid/prootic. Most importantly, however, the postorbital

process of the jugal shows a facet for the suture with the

postorbital, thus resolving the question of whether

Archaeopteryx had a closed postorbital bar. A new recon-

struction of the skull of Archaeopteryx is presented, mak-

ing the skull of this taxon even more theropod-like than

previously recognized. Furthermore, the closed postorbital

bar and the configuration of the bones of the skull roof cast

serious doubt on claims that an avian-style cranial kinesis

was present in this taxon.

Keywords Archaeopteryx � Upper Jurassic � Avialae �Cranial osteology � Cranial kinesis

Kurzfassung Obwohl Skelettreste des altesten be-

kannten Vogels Archaeopteryx seit nun 150 Jahren be-

kannt sind, sind einige Aspekte der Schadelanatomie

dieses Taxon weiter ungewiss, vor allem da die meisten

bekannten Schadelreste stark komprimiert und meist

zerbrochen und unvollstandig sind. Neue Untersuchun-

gen am Schadel des kurzlich beschriebenen und her-

vorragend erhaltenen 10. (Thermopolis) und des 7.

(Munchener) Exemplares zeigen einige bisher un-

erkannte Merkmale der Schadelanatomie und helfen,

andere bisher umstrittene Fragen zu losen. So zeigt das

Nasale von Archaeopteryx einen lateralen Einschnitt fur

die Sutur mit dem Lacrimale, wie er bei vielen Saurischia

vorhanden ist, das Maxillare hat Anteil am Rand der

externen Nares und das Lacrimale hat offenbar ein gro-

ßes, pneumatisches Foramen, das in seiner Position dem

Lacrimal-Fenster vieler basalerer Theropoden entspricht.

Im Hirnschadel zeigt Archaeopteryx Merkmale die an

jene basalerer Theropoden erinnern, so etwa einen Re-

zessus basisphenoidalis und einen anterioren tympani-

schen Rezessus, der von lateral in das Basisphenoid und

das Prooticum einschneidet. Insbesondere zeigt jedoch

der Postorbital-Fortsatz des Jugale eine Facette fur die

Sutur mit dem Postorbitale, was die Frage klart, ob

Archaeopteryx eine geschlossene Postorbital-Spange

besass. Eine neue Rekonstruktion des Schadels von

Archaeopteryx macht diesen noch Theropoden-ahnlicher

als bisher angenommen. Zudem stellt die geschlossene

Postorbital-Spange und die Konfiguration der Knochen

des Schadeldaches die angenommene Vogel-ahnliche

Schadel-Kinetik bei Archaeopteryx in Frage.

O. W. M. Rauhut (&)

Bayerische Staatssammlung fur Palaontologie und Geologie

and Department of Earth and Environmental Sciences, LMU

Munich, Richard-Wagner-Str. 10, 80333 Munich, Germany

e-mail: o.rauhut@lrz.uni-muenchen.de

123

Palaontol Z (2014) 88:211–221

DOI 10.1007/s12542-013-0186-0

Schlusselworter Archaeotperyx � Oberer Jura � Avialae �Schadel-Osteologie � Schadel-Kinetik

Introduction

Ever since the discovery of the first skeletal remains in

1861 (von Meyer 1861), just 2 years after the publication of

Darwin’s ‘‘Origin of Species’’ (Darwin 1859), the oldest

known ‘‘bird’’ Archaeopteryx has played a pivotal role in

the scientific discussion of the origin of birds (e.g., Huxley

1868; Heilmann 1926; Ostrom 1973, 1976). Thus, despite

the important discoveries of numerous bird-like non-avian

theropod dinosaurs and basal birds in the past decades in

China (see Xu and Norell 2006 and Zhou and Zhang 2006

for recent reviews) and recent claims that the taxon is not

placed on the immediate lineage leading toward birds (Xu

et al. 2011), Archaeopteryx can still be regarded as the

‘‘yardstick’’ of bird evolution, and new insights into the

anatomy and biology of this animal are published frequently

(e.g., Dominguez Alonso et al. 2004; Mayr et al. 2005, 2007;

Tischlinger 2005, 2009; Wellnhofer 2008; Erickson et al.

2009; Bergmann et al. 2010; Longrich et al. 2012).

For more than 100 years after the first discoveries, the

cranial structure of Archaeopteryx has been known only

from the very incomplete and/or strongly damaged remains

of the London and Berlin specimens (see Dames 1884;

Heilmann 1926; De Beer 1954). With the discovery of the

fifth (Eichstatt) specimen, a first well-preserved skull of

this animal became available, and study of this specimen

led to important new insights into the cranial anatomy of

the earliest known bird (Wellnhofer 1974). Further prepa-

ration of the skull of the London specimen and the dis-

covery of the Munich specimen provided new data,

especially on the structure of the braincase, palate, and

lower jaw of this taxon in the following 25 years (Whet-

stone 1983; Walker 1985; Wellnhofer 1993; Elzanowski

and Wellnhofer 1996). In the past decade, the application

of new techniques, such as computed tomography and new

methods in UV photography, have led to additional insights

into several anatomical details (Dominguez Alonso et al.

2004; Tischlinger and Unwin 2004; Tischlinger 2005).

Finally, the discovery of a new specimen with a beautifully

preserved skull and skeleton provided important new

information on many aspects of the anatomy of Archae-

opteryx (Mayr et al. 2005, 2007). Nevertheless, many

details of the skull anatomy of this taxon, especially the

configuration of the temporal region and the braincase,

have remained enigmatic.

The aim of this article is not to present a full description

of the cranial osteology of Archaeopteryx, but to help

clarify some details of its cranial anatomy and to provide a

new reconstruction of the skull. For more general accounts

of the osteology of this taxon, the reader is referred to the

excellent descriptions of Wellnhofer (1974, 2008), Elza-

nowski and Wellnhofer (1996), and Elzanowski (2002),

and to the numerous other contributions that have helped

clarify the cranial structure of this taxon (e.g., Dames 1884;

Heilmann 1926; Whetstone 1983; Walker 1985; Domin-

guez Alonso et al. 2004; Tischlinger 2005; Mayr et al.

2007).

For this study, the skulls of mainly two specimens were

studied in detail, the 7th (Munich) and the 10th (Ther-

mopolis) specimens. The Eichstatt, Berlin, Solnhofen, and

Daiting (8th) specimens were also examined first hand, as

were a large number of non-avian theropod specimens.

Comparative information for basal birds was mainly taken

from the literature.

The specimens were examined using a binocular

microscope and high-resolution UV photographs, gener-

ously provided by Helmut Tischlinger.

Institutional abbreviations

BSPG Bayerische Staatssammlung fur Palaontologie und

Geologie, Munich, Germany; IGM Institute of Geology,

Ulan Bataar, Mongoloia; MB Museum fur Naturkunde

Berlin, Germany; WDC Wyoming Dinosaur Center, Ther-

mopolis, Wyoming, USA.

Configuration of the skull roof

The 10th (Thermopolis) specimen (WDC-CSG-100) has

the dorsal skull roof preserved in exquisite detail (Fig. 1).

Many of the important characters have already been

reported by Mayr et al. (2007), so only a few details will be

pointed out here.

The premaxilla has a long anterior body, in which all

tooth positions are placed anterior to the external nares

(Fig. 1a). At the anterior end of the premaxilla, an

enlarged, anteriorly facing foramen is present, as in many

theropod dinosaurs (e.g., Rauhut et al. 2010). As mentioned

by Mayr et al. (2007: 101), another large foramen is present

anterodorsal to the anteriormost end of the external nares.

This foramen is connected to the anterodorsal margin of the

external nares by an elongate furrow and thus opens pos-

terolaterally (Figs. 1a, 5). Such a foramen is also present in

the Eichstatt specimen (pers. obs.), but not the London

(Wellnhofer 2008: Fig. 5.26), Solnhofen (pers. obs.), and

Berlin specimens (Tischlinger 2005: Fig. 10; Wellnhofer

2008: Fig. 5.48 b). The Thermopolis specimen further

confirms the reconstruction of the relation among the

premaxilla, maxilla, and nasal in Archaeopteryx by

Wellnhofer (1974, 2008). Thus, the dorsal nasal process of

212 O. W. M. Rauhut

123

the premaxilla is approximately 175 % of the length of the

main premaxillary body and almost reaches the posterior

end of the external nares. The ventral posterior process of

the premaxilla is much shorter than the dorsal process and

flanks the ventral margin of the nares for approximately

half of its length. However, it is slightly longer than the

premaxillary body, slender, and rod-like, and not as

abbreviated as illustrated by Elzanowski (2001). Although

the nasal has a slender anterior subnarial process, the latter

is clearly separated from the ventral posterior process of

the premaxilla so that the maxilla forms part of the ventral

margin of the nares, as argued by Wellnhofer (1974, 2008).

On the lateral side of the skull roof, the configuration of

the contacts among the nasal, lacrimal and maxilla largely

conforms to the situation found in basal theropods (Fig. 1b,

c). As in Zupaysaurus (Ezcurra 2007), Allosaurus (Madsen

1976), Sinraptor (Currie and Zhao 1994a), and other taxa,

but in contrast to the reconstructions of Elzanowski (2001)

and Wellnhofer (2008), the posterior end of the ascending

process of the maxilla is forked to receive a pointed

Fig. 1 Cranial anatomy of the 10th (Thermopolis) specimen of

Archaeopteryx (WDC-CSG-100). a Photograph of skull under

ultraviolet light, with indications of enlarged areas. b Enlargement

of lateral edge of left nasal, showing lateral process of the nasal.

c Enlargement of the contact between right maxilla, nasal, and

lacrimal. d Enlargement of the lacrimal fenestra. e Enlargement of the

ascending process of the jugal. en external nares, f frontal, fo foramina

in the premaxilla, j jugal, l lacrimal, lf lacrimal fenestra, lp lateral

process of nasal, m maxilla, mf maxillary fenestra, mu manual ungual,

n nasal, pa parietal, pm premaxilla, pof postorbital facet on the

ascending process of the jugal, pro premaxillary foramen, sc scleral

ring. Scale bar in a is 5 mm

Skull of Archaeopteryx 213

123

anterior process of the lacrimal (Fig. 1c). Furthermore, the

lateral margin of the nasal has a small posterolateral pro-

cess that embraced the anterior end of the dorsal surface of

the lacrimal (Fig. 1b), as is present in Syntarsus (Bristowe

and Raath 2004), Allosaurus (Madsen 1976), Sinraptor

(Currie and Zhao 1994a: Fig. 3a), and many basal saur-

opodomorphs (e.g., Yates 2003: Fig. 10b).

The Thermopolis specimen also helps to clarify some

aspects of the paranasal sinus system. Although Wellnhofer

(1974) identified both a maxillary fenestra and a large,

laterally facing promaxillary fenestra in the Eichstatt

specimen, Elzanowski (2001, 2002) argued that the dorsal

part of the ascending process of the maxilla represented a

nasal capsule, representing a rostral ethmoid ossification,

and thus reconstructed the skull without maxillary fenestra.

Wellnhofer (2008) again reconstructed the skull with both

a maxillary and promaxillary fenestra, but figured the two

considerably smaller than in his 1974 reconstruction. As

noted by Mayr et al. (2007) [see also Xu et al. 2011)], the

Thermopolis specimen confirms the interpretation of

Wellnhofer (1974), in that Archaeopteryx had a large,

semicircular maxillary fenestra and a more anteriorly

placed and smaller, laterally facing promaxillary foramen

(Fig. 1a). It is thus similar to Anchiornis (Hu et al. 2009)

and Compsognathus (BSPG AS 563), whereas in most

coelurosaurs, the premaxillary fenestra is concealed in the

lateral view (e.g., tyrannosaurids: Currie 2003; Carr and

Williamson 2004; ornithomimosaurs: Osmolska et al.

1972; Ji et al. 2003; oviraptorosaurs: Clark et al. 2002;

troodontids: Norell et al. 2009). In many dromaeosaurs, the

premaxillary fenestra is small and at least partially exposed

laterally (e.g., Ostrom 1969; Barsbold and Osmolska 1999;

Xu and Wu 2001; Burnham 2004; Norell et al. 2006), but it

is placed anteroventral to the maxillary fenestra and is

relatively smaller than in Archaeopteryx.

In the Thermopolis specimen, the lacrimal shows a large

recess in the posterodorsal corner laterally (Fig. 1d). The

recess is filled with matrix, so nothing can be said about its

medial extent, but it is in the same position as the lacrimal

fenestra in basal tetanurans such as Allosaurus (Madsen

1976) and Sinraptor (Currie and Zhao 1994a). In paravian

theropods, a lacrimal recess has otherwise only been men-

tioned, but not yet been described in detail, in Deinonychus

(Witmer 1997a).

One of the most significant new observations concerns

the configuration of the temporal region of Archaeopteryx.

In the Thermopolis specimen, no postorbital is preserved,

but the short dorsal process of the jugal is present and

shows a slightly depressed facet on the anterior side of its

dorsal part (Fig. 1e). This facet is slightly offset from

the ventral part of the anterior margin of the process and

slopes more strongly posterodorsally than the latter. A very

similar though not as conspicuous facet is also visible in

the medially exposed left jugal of the Munich specimen

(BSPG 1999 I 50). This facet fits the jugal facet for the

connection with the postorbital in non-avian theropods in

both its position and the details of its morphology (angu-

lation of the facet in relation to the ascending process of the

jugal; facet facing more laterally than medially) and thus

clearly indicates that a jugal-postorbital contact was pres-

ent in Archaeopteryx.

Finally, the area identified as the quadrate cotyle in the

squamosal of the Munich specimen by Elzanowski and

Wellnhofer (1996) most probably represents a slightly

depressed facet for the contact with the paroccipital process

of the braincase on a rather long posterior process (Fig. 2),

as is also present in dromaeosaurids (e.g., Ostrom 1969;

Barsbold and Osmolska 1999).

Braincase

The dorsal parts of the braincase of Archaeopteryx are

preserved in the London specimen and have been

described by de Beer (1954), Whetstone (1983), Walker

(1985) and Dominguez Alonso et al. (2004). The ventral

and lateral parts of the braincase are preserved in the

Munich specimen (BSPG 1999 I 50) and have been

described by Wellnhofer (1993) and Elzanowski and

Wellnhofer (1996). This specimen is redescribed here,

since detailed investigation of the braincase under both

normal and UV light led to some re-interpretations of

structures (Figs. 2, 3).

Elzanowski and Wellnhofer (1996) considered the cra-

nial base of the Munich specimen to be exposed in lateral

view. However, re-examination of the specimen indicates

that the basisphenoid and basioccipital are exposed in the

ventrolateral view (Fig. 3). Thus, the ventral side of both

bones and both left and right basal tubera and basipterygoid

processes are visible, though the left basipterygoid process

is broken and partially preserved on the counterslab

(Fig. 2). The occipital condyle is almost aligned with the

ventral surface of the basisphenoid and only slightly offset

dorsally, in contrast to most theropods, although this might

be partially due to preservation, as noted by Elzanowski

and Wellnhofer (1996). The posteroventral side of the

basioccipital anterior to the condyle is flat, with a very

shallow longitudinal groove extending along the midline

from the occipital condyle to the basioccipital-basi-

sphenoid suture. The basal tubera are small, placed far

laterally, and separated by a wide, U-shaped incision.

The ventral side of the basisphenoid is elongate, its

length between the basal tubera and the basipterygoid

processes being approximately 1.8 times the minimal

width. Posteriorly, the basisphenoid forms the anterior

half of the basal tubera. Immediately anterior to the

214 O. W. M. Rauhut

123

basioccipital-basisphenoid suture there is an elongate oval

depression on the ventral side of the basisphenoid, repre-

senting the basisphenoid recess (Fig. 3), as in other non-

avian theropods. Thus, the basisphenoid pneumaticity was

ventrally open in Archaeopteryx, as in most non-avian

theropods, but in contrast to the situation in therizino-

saurids (Clark et al. 1994) and troodontids (Currie 1985;

Currie and Zhao 1994b; Makovicky et al. 2003), which

have a highly pneumatized basisphenoid without a ventral

opening. Unfortunately, the recess is partially covered by

an unidentified bone fragment, so nothing can be said about

its depth or internal extent. The recess is bordered laterally

by transversely rounded edges rather than sharp cristae

ventrolateralis, as is the case in some other theropods (e.g.,

Proceratosaurus: Rauhut et al. 2010) and ends anteriorly

well posterior to the level of the basipterygoid processes,

thus covering the posterior two-thirds of the ventral side of

the basisphenoid. The basipterygoid processes are well

separated and directed ventrolaterally and slightly anteri-

orly. They are anteroposteriorly elongate (their length

being approximately 60 % of the length of the ventral

basisphenoid between the tubera and the base of the pro-

cesses) and dorsoventrally low. The articular facet of the

process faces anteroventrally and is lower anteriorly than

posteriorly. The left basipterygoid process is broken at its

base and preserved on the counterslab in partial articulation

with the pterygoid (Fig. 2). At the break, the bone is

transversely thin, and there obviously was a deep lateral

depression at the base of the basipterygoid process (Fig. 3).

This depression most probably corresponds to the basip-

terygoid recess, as is also found in the dromaeosaurids

Velociraptor (Barsbold and Osmolska 1999), the basal

troodontid Sinovenator (Xu et al. 2002), and several other

theropods.

Only a small part of the lateral side of the occiput can be

seen. On the lateral side of the occipital condyle, two large,

dorsoventrally elongate foramina are visible, probably for

the passages of cranial nerves IX, XI, and XII, and prob-

ably X. Anteriorly, these foramina are bordered by a well-

developed, slender crista metotica that extends from the

basal tubera to the ventral side of the paroccipital process.

The middle ear is situated anterior to the crista metotica

(Fig. 3). In contrast to the situation figured by Elzanowski

and Wellnhofer (1996): Fig. 2a), the middle ear is not

narrow and slit-like, but represents one of the largest

openings in the lateral brain wall, as in the London spec-

imen (Whetstone 1983; Walker 1985). As in the latter, the

middle ear cavity is subdivided by an oblique crista

Fig. 2 Cranial anatomy of the 7th (Munich) specimen of Archaeop-

teryx (BSPG 1999 I 50). Posterior skull remains on the counterslab

under ultraviolet light. cp cultriform process of the parasphenoid,

f frontal, j jugal, lbpt left basipterygoid process, lpt left pterygoid, pa

parietal, po postorbital, q quadrate, rpt right pterygoid, sq squamosal.

Question marks indicate unidentified elements. Scale bar is 5 mm

Skull of Archaeopteryx 215

123

interfenestralis (only the dorsal base of which is preserved;

Fig. 3) into the slightly smaller foramen ovale anterodor-

sally and the foramen pseudorotunda posteroventrally, thus

confirming the configuration of this region as reconstructed

by Walker ( 1985: Fig. 4). The left paroccipital process has

been sheared off and displaced dorsally, as noted by

Elzanowski and Wellnhofer (1996), so that its anteroventral

side is exposed (Fig. 3). As in most theropods, a shallow

stapedial groove extends along the anteroventral side of the

process distally. Proximally, a large, oval opening is present

at the base of this groove, as is also found in the base of the

paroccipital process of the London specimen (Whetstone

1983; Walker 1985); this opening corresponds to the

entrance of the posterior tympanic recess in other coeluro-

saurs (e.g., Clark et al. 1994; Norell et al. 2006).

The prootic of the Munich specimen has been well

described and figured by Elzanowski and Wellnhofer

(1996). However, the separate bone identified as the broken

prootic wing by these authors most probably rather repre-

sents the laterosphenoid (Fig. 3), as originally suggested by

Wellnhofer (1993). Thus, the prootic pendant (Sampson

and Witmer 2007; ‘‘prootic wing’’ of Elzanowski and

Wellnhofer 1996) is considerably smaller than recon-

structed by Elzanowski and Wellnhofer (1996) and

directed ventrally (Figs. 3, 4), as in other theropods, rather

than anteroventrally. The laterosphenoid is a subquadran-

gular element with a stout lateral process anterodorsally for

Fig. 3 Cranial anatomy of the 7th (Munich) specimen of Archaeop-

teryx (BSPG 1999 I 50). Posterior skull elements and braincase on the

main slab. a Photograph under ultraviolet light. b Interpretative

drawing. at anterior tympanic recess, boc basioccipital, bpt basip-

terygoid process, bptr basipterygoid recess, bs basisphenoid, bsr

basisphenoid recess, bt basal tubera, cif crista interfenestralis, cm

crista metotica, dtr dorsal tympanic recess, ec ectopterygoid fragment,

epi epipterygoid, f frontal, fo fenestra ovale, fp fenestra pseudoro-

tunda, ls laterosphenoid, oc occipital condyle, pa parietal, pap

paroccipital process, pro prootic, pt pterygoid, ptr posterior tympanic

recess, qw quadrate wing of the pterygoid, sa surangular, sg stapedial

groove. Roman numerals denote cranial nerves; question marks

indicate unidentified elements. Scale bar is 5 mm

Fig. 4 Schematic reconstruction of the braincase of Archaeopteryx,

based on the 7th specimen. Note that most sutures are conjectural,

since the elements are partially disarticulated and damaged, so their

courses should not be used for phylogenetic coding. Abbreviations as

in Figs. 2 and 3; op opisthotic, pp preotic pendant

216 O. W. M. Rauhut

123

the contact with the frontal and, possibly, the postorbital, as

in other theropods. However, the element has been flat-

tened into the bedding plane, so that the orientation of this

process is not as obvious, but the lateral convexity of the

main laterosphenoid body and the concavity at the base of

the lateral process are still visible (Fig. 3a). In the London

specimen, only the lateral process of the laterosphenoid

seems to be preserved (Whetstone 1983). The laterosphe-

noid is not pierced by any foramina in its lateral part,

indicating that the exit for the ophthalmic branch of the

trigeminal nerve was not separate from the maxillary and

mandibular branches, as is the case in Troodon (Currie and

Zhao 1994b).

Thus, the trigeminal foramen in Archaeopteryx seems to

be somewhat smaller than reconstructed by Walker (1985)

and Elzanowski and Wellnhofer (1996). The laterosphe-

noid in the Munich specimen is displaced ventrally, and the

margin that probably contacted the prootic is partially

covered by unidentified bone fragments, but the incision

for the trigeminal opening in this bone, if present, seems to

have been rather small. Whetstone (1983) figured a small

incision in the posterodorsal rim of this opening and ten-

tatively identified it as the trigeminal foramen. The same

feature was refigured, but not discussed by Elzanowski and

Wellnhofer ( 1996: 5B), but Walker (1985) argued that the

posterior margin of the trigeminal foramen was incomplete

and identified this incision as part of a pneumatic recess. In

many saurischians, the exit of the mid-cerebral vein is

separated from the exit of the trigeminal nerve and is

developed as a small foramen in the dorsal margin of the

trigeminal opening or somewhat more dorsally (Rauhut

2003). Interestingly, this opening is positioned on the

prootic-latereosphenoid suture in some taxa (e.g., Drom-

aeosaurus: Currie 1995) or entirely in the laterosphenoid

(e.g., Troodon: Rauhut 2003), but it is entirely within the

prootic, at the posterodorsal rim of the trigeminal foramen,

and thus in a very similar position to this incision in

Plateosaurus (MB.R. 5586.1). Thus, this incision might

represent the exit of the mid-cerebral vein. In the Munich

specimen, there is a posterior rim around the trigeminal

foramen (Fig. 3), as figured for the London specimen by

Walker ( 1985: Fig. 4), and there seems to be a matrix-

filled depression or opening in the elevated posterodorsal

margin of this depression. This depression or opening is in

the same position as the incision figured by Whetstone

(1983) in the London specimen, thus supporting Walker’s

interpretation that the posterior rim of the trigeminal

foramen is broken in this specimen, and the opening might

represent a small separate foramen rather than an incision

branching off the trigeminal foramen.

Below the opening for the seventh cranial nerve, a large

depression is present on the ventral side of the prootic, as in

the London specimen (Whetstone 1983; Walker 1985).

Wellnhofer (1993) identified this matrix-filled structure as

the fenestra ovalis, but Walker (1985) argued that pneu-

matic openings were located within this depression.

Indeed, the depression is in exactly the position covered by

the anterior tympanic recess in non-avian theropods (e.g.,

Raath 1985; Currie and Zhao 1994b; Witmer 1997b;

Makovicky et al. 2003; Rauhut 2004; Paulina-Carabajal

and Currie 2012) and thus most probably represents this

structure. This recess is partially covered by a broken,

plate-like bone, which probably represents remains of the

quadrate wing of the pterygoid. At the level of the anterior

end of the prootic, a slender, triangular bone sits laterally

on this bony plate (Fig. 3). This bone tapers dorsally and

reaches approximately the level of the dorsal margin of the

trigeminal foramen. In position and shape, it is similar to

the epipterygoid in other theropods (e.g., Clark et al. 2002;

Eddy and Clarke 2011; Brusatte et al. 2012a) and might

thus represent this element.

Discussion

The observations presented here help to clarify some

details of the cranial anatomy of Archaeopteryx that might

be of interest for both functional and phylogenetic studies.

The configuration of the dorsal skull roof, especially the

detailed sutures between the nasal, lacrimal, and maxilla,

corresponds well to the situation in basal tetanuran thero-

pods in which the anterior process of the lacrimal slots into

the forked posterior end of the ascending process of the

maxilla and the dorsal surface of the lacrimal is braced

anteriorly by a posterolaterally directed lateral process of

the nasal (e.g., Allosaurus: Madsen 1976; Sinraptor: Currie

and Zhao 1994a). Interestingly, most reconstructions of

skulls of paravian theropods show the anterior end of the

lacrimal overlapping the posterior end of the ascending

process of the maxilla dorsally and lack a lateral process of

the nasal (e.g., Barsbold and Osmolska 1999; Xu and Wu

2001; Burnham 2004; Xu et al. 2011). More detailed

studies of the cranial sutures in paravian theropods are

necessary to decide whether this indicates a remarkable

retention of the plesiomorphic condition in Archaeopteryx

or if this might simply reflect lack of detail in available

reconstructions; the fact that the skull of the ‘‘fighting

dinosaur’’ specimen of Velociraptor (IGM 100/25) seems

to show a slender anterior end of the lacrimal that slots into

the forked posterior end of the ascending process of the

maxilla (Barsbold and Osmolska 1999: Fig. 1a; Norell

et al. 2006: Fig. 6b) indicates that the latter might at least

account for some of this apparent variation. However, the

dorsal view of the same specimen does not show any

evidence of a lateral process of the nasal (Barsbold and

Osmolska 1999: Fig. 2b).

Skull of Archaeopteryx 217

123

One of the most significant findings is that of an articular

facet for the postorbital on the ascending process of the

jugal (Fig. 1e), presenting evidence for a closed postorbital

bar, as originally hypothesized by Wellnhofer (1974) and

Elzanowski and Wellnhofer (1996) on the basis of the

presence of a postorbital process of the jugal. Several

previous analyses of the available skull material of

Archaeopteryx failed to recognize a postorbital, resulting in

the hypothesis that this element was absent and the orbit

open posteriorly, as in recent birds, by Buhler (1985),

Martin (1991) and Elzanowski (2001, 2002). This alleged

absence of a postorbital bar was one of the key arguments

that led Buhler (1985) to propose a bird-like cranial kinesis

in Archaeopteryx. Even if a complete absence of a post-

orbital was not assumed and after UV analyses by Tisch-

linger (2005) unequivocally showed a postorbital to be

present in this taxon, many authors retained an open

postorbital bar in their reconstruction to allow for cranial

kinesis (e.g., Chiappe 2007; Wellnhofer 2008). Wellnhofer

(2008: Fig. 6.3) proposed that, in a prokinetic movement,

the nasal might move over the frontals in Archaeopteryx.

The presence of a theropod-like articular facet on the

ascending process of the jugal for the postorbital calls the

interpretation of a prokinetic skull in Archaeopteryx into

question. According to this hypothesis, the streptostylic

quadrate would move the anterior part of the skull via the

jugal bar (see Buhler 1985; Wellnhofer 2008). However, a

closed postorbital bar would severely hamper any antero-

posterior movement of the jugal and thus the mechanism

by which the snout is allegedly raised. Furthermore, the

sutures between the jugal and postorbital, and, as far as can

be said, between the nasal and frontal (based on the

Thermopolis and Eichstatt specimens) correspond well to

the situation in other theropods, and there is no indication

for either a flexible overlap between the nasal and frontal

nor for a flexible bending zone within the nasal (as

hypothesized by Buhler, 1985). Thus, the situation is

comparable to that in non-avian theropods, for which

Holliday and Witmer (2008) concluded that there is little

evidence for any sophisticated kinesis. These findings are

also in agreement with the skull configuration reported in

the more advanced basal avialian Confuciusornis, which

also has a closed postorbital bar (Peters and Ji 1998; Chi-

appe et al. 1999; Hou et al. 1999), and the possibility that at

least some Enantiornithes still retained a postorbital-jugal

contact (Wang et al. 2010). This indicates that the opening

of the postorbital bar and the development of the cranial

kinesis typical for modern birds happened later in avialian

evolution.

The new interpretation of the braincase of Archaeop-

teryx indicates that this structure is closely comparable to

that in other non-avian maniraptorans (Fig. 4). The

description of the middle ear cavity largely confirms the

interpretation of Walker (1985) and shows close similarity

to deinonychosaurs, such as Byronosaurus (Makovicky

et al. 2003). The lateral braincase wall is closely compa-

rable to that of dromaeosaurids, in both the position of

nerve foramina and the presence and position of an anterior

tympanic recess and a basipterygoid recess (e.g., Barsbold

and Osmolska 1999). The braincase differs from that of

troodontids in that the basisphenoid recess is ventrally open

and the exit for the trigeminal nerve is not subdivided,

Fig. 5 Revised reconstruction of the skull of Archaeopteryx, mainly

based on the Eichstatt and Thermopolis specimens. A angular, aof

antorbital fenestra, ar articular, d dentary, en external nares, f frontal,

fao fossa antorbitalis, fo foramen, itf infratemporal fenestra, j jugal,

l lacrimal, lf lacrimal fenestra, m maxilla, mf maxillary fenestra,

n nasal, o orbit, pa parietal, pap paroccipital process, pm premaxilla,

po postorbital, pro premaxillary foramen quadrate, qj quadratojugal,

sa surangular, sq squamosal. Modified from Rauhut (2003). Scale bar

is 10 mm

218 O. W. M. Rauhut

123

indicating that the ‘‘inflated’’ basisphenoid without a ven-

tral recess and subdivided trigeminal foramen in birds

arose independently from the situation in that clade. With

the presence of anterior, posterior, and dorsal tympanic

recesses, a basisphenoid recess and basipterygoid recesses,

basicranial pneumaticity is also closely comparable to that

in many coelurosaurs (Witmer 1997b).

Conclusions

Detailed re-examinations of the skulls of two specimens of

Archaeopteryx show that the skull of this primeval bird is

more theropod-like than previously recognized (Fig. 5).

The detailed sutures between the nasal, lacrimal and

maxilla are closely comparable to those in more basal

theropods. These findings contrast with the reconstructions

of the skulls of other advanced coelurosaurians, which,

however, might be due to the lack of detail in at least some

available reconstructions. Given that the exact position and

morphology of cranial sutures is important for interpreta-

tions of cranial function (e.g., Weishampel 1984; Rayfield

2005), landmark-based analyses of cranial shape (e.g.,

Brusatte et al. 2012b; Foth and Rauhut (2013), and phy-

logenetic analyses, more detailed anatomical studies of

cranial sutures in coelurosaurs and basal birds and inves-

tigations of the evolution of these structures are needed.

An articular facet on the ascending process of the jugal

is closely comparable to the postorbital articulation in non-

avian theropods, indicating a closed postorbital bar.

Together with the lack of indications for a preorbital

bending zone in the dorsal skull roof, this makes the

presence of a bird-like prokinetic skull in Archaeopteryx

unlikely.

Cranial pneumaticity in Archaeopteryx conforms to that

seen in non-avian coelurosaurs. This applies to both para-

nasal pneumaticity, with the development of a maxillary

fenestra, premaxillary foramen, and lacrimal fenestra (see

Witmer 1997a), and basicranial pneumaticity. The latter

includes three tympanic recesses (anterior, posterior and

dorsal), basipterygoid recesses, and a basisphenoid recess.

All of these pneumatic features are in the same position and

show the same development as in many non-avian coel-

urosaurs, such as dromaeosaurids.

Acknowledgments This article resulted from the Archaeopteryx

event during the Munich Mineralientage in 2009, during which six of

the original Archaeopteryx specimens were gathered together. Special

thanks are therefore due to Christoph Keilmann, who made this event

possible, and the institutions and private individuals who made their

specimens of the Urvogel available during the event. Very special

thanks are furthermore due to Burkhard Pohl for the loan of the

Thermopolis specimen after the event and to Helmut Tischlinger for

UV photography. The article benefited from discussions with Chris-

tian Foth, Xu Xing, and Adriana Lopez-Arbarello, and from financial

support by the Volkswagen Foundation under grant AZ I/84 640.

Gerald Mayr is thanked for a critical review of the manuscript.

References

Barsbold, R., and H. Osmolska. 1999. The skull of Velociraptor

(Theropoda) from the Late Cretaceous of Mongolia. Acta

Palaeontologica Polonica 44(2): 189–219.

Bergmann, U., R.W. Morton, P.L. Manning, W.I. Sellers, S. Farrar,

K.G. Huntley, R.A. Wogelius, and P. Larson. 2010. Archaeop-

teryx feathers and bone chemistry fully revealed via synchrotron

imaging. Proceedings of the National Academy of Sciences

107(20): 9060–9065.

Bristowe, A., and M.A. Raath. 2004. A juvenile coelophysoid skull

from the Early Jurassic of Zimbabwe, and the synonymy of

Coelophysis and Syntarsus. Palaeontologia Africana 40: 31–41.

Brusatte, S.L., T.D. Carr, and M.A. Norell. 2012a. The osteology of

Alioramus, a gracile and long-snouted tyrannosaurid (Dinosau-

ria: Theropoda) from the Late Cretaceous of Mongolia. Bulletin

of the American Museum of Natural History 366: 1–197.

Brusatte, S.L., S. Manabu, S. Montanari, and W.E.H. Harcourt Smith.

2012b. The evolution of cranial form and function in theropod

dinosaurs: insights from geometric morphometrics. Journal of

Evolutionary Biology 25: 365–377.

Buhler, P. 1985. On the morphology of the skull of Archaeopteryx. In

The beginning of birds, ed. M.K. Hecht, J.H. Ostrom, G. Viohl,

and P. Wellnhofer, 135–140. Eichstatt: Freunde des Jura

Museums.

Burnham, D.A. 2004. New information on Bambiraptor feinbergi

(Theropoda: Dromaeosauridae) from the Late Cretaceous of

Montana. In Feathered dragons. Studies on the transition from

dinosaurs to birds, ed. P.J. Currie, E.B. Koppelhus, M.A.

Shugar, and J.L. Wright, 67–111. Bloomington & Indianapolis:

Indiana University Press.

Carr, T.D., and T.E. Williamson. 2004. Diversity of late Maastrich-

tian Tyrannosauridae (Dinosauria: Theropoda) from western

North America. Zoological Journal of the Linnean Society 142:

479–523.

Chiappe, L.M. 2007. Glorified dinosaurs: the origin and early

evolution of birds. London: Wiley-Liss.

Chiappe, L.M., S.-A. Ji, Q. Ji, and M.A. Norell. 1999. Anatomy and

systematics of the Confucuisornithidae (Theropoda: Aves) from

the Late Mesozoic of northeastern China. Bulletin of the

American Museum of Natural History 242: 1–89.

Clark, J.M., M.A. Norell, and T. Rowe. 2002. Cranial anatomy of

Citipati osmolskae (Theropoda, Oviraptorosauria), and a rein-

terpretation of the holotype of Oviraptor philoceratops. Amer-

ican Museum Novitates 3364: 1–24.

Clark, J.M., A. Perle, and M.A. Norell. 1994. The skull of

Erlicosaurus andrewsi, a Late Cretaceous ‘‘segnosaur’’ (Thero-

poda: Therizinosauridae) from Mongolia. American Museum

Novitates 3115: 1–39.

Currie, P.J. 1985. Cranial anatomy of Stenonychosaurus inequalis

(Saurischia, Theropoda) and its bearing on the origin of birds.

Canadian Journal of Earth Sciences 22: 1643–1658.

Currie, P.J. 1995. New information on the anatomy and relationships

of Dromaeosaurus albertensis (Dinosauria: Theropoda). Journal

of Vertebrate Paleontology 15(3): 576–591.

Currie, P.J. 2003. Cranial anatomy of tyrannosaurid dinosaurs from

the Late Cretaceous of Alberta. Canada. Acta Palaeontologica

Polonica 48(2): 191–226.

Currie, P.J., and X.-J. Zhao. 1994a. A new carnosaur (Dinosauria,

Theropoda) from the Jurassic of Xinjiang, People’s Republic of

China. Canadian Journal of Earth Sciences 30: 2037–2081.

Skull of Archaeopteryx 219

123

Currie, P.J., and X.-J. Zhao. 1994b. A new troodontid (Dinosauria,

Theropoda) braincase from the Dinosaur Park Formation

(Campanian) of Alberta. Canadian Journal of Earth Sciences

30: 2231–2247.

Dames, W. 1884. Ueber Archaeopteryx. Palaeontologische Abhandl-

ungen 2(3): 119–196.

Darwin, C. 1859. On the origin of species by means of natural

selection. London: Murrey.

De Beer, G. 1954. Archaeopteryx lithographica. A study based on the

British Museum specimen. London: British Museum (Natural

History).

Dominguez Alonso, P., A.C. Milner, R.A. Ketcham, M.J. Cookson,

and T.B. Rowe. 2004. The avian nature of the brain and inner ear

of Archaeopteryx. Nature 430: 666–669.

Eddy, D.R., and J.A. Clarke. 2011. New information on the cranial

anatomy of Acrocanthosaurus atokensis and its implications for

the phylogeny of Allosauroidea (Dinosauria: Theropoda). PLoS

ONE 6(3): e17932.

Elzanowski, A. 2001. A novel reconstruction of the skull of

Archaeopteryx. Netherlands Journal of Zoology 51(2): 207–215.

Elzanowski, A. 2002. Archaeopterygidae (Upper Jurassic of Ger-

many). In Mesozoic birds. Above the heads of dinosaurs, ed.

L.M. Chiappe, and L.M. Witmer, 129. Berkeley: University of

California Press.

Elzanowski, A., and P. Wellnhofer. 1996. Cranial morphology of

Archaeopteryx: evidence from the seventh skeleton. Journal of

Vertebrate Paleontology 16(1): 81–94.

Erickson, G.M., O.W.M. Rauhut, Z. Zhou, A.H. Turner, B.D. Inouye,

D. Hu, and M.A. Norell. 2009. Was dinosaurian physiology

inherited by birds? Reconciling slow growth in Archaeopteryx.

PLoS ONE 4(10): 1–9.

Ezcurra, M.D. 2007. The cranial anatomy of the coelophysoid

theropod Zupaysaurus rougieri from the Upper Triassic of

Argentina. Historical Biology 19(2): 185–202.

Foth, C., and O.W.M. Rauhut. 2013. Macroevolutionary and

morphofunctional patterns in theropod skulls: a morphometric

approach. Acta Palaeontologica Polonica 58(1): 1–16.

Heilmann, G. 1926. The origin of birds. London: Witherby.

Holliday, C.M., and L.M. Witmer. 2008. Cranial kinesis in dinosaurs:

intracranial joints, protractor muscles, and their significance for

cranial evolution and function in diapsids. Journal of Vertebrate

Paleontology 28(4): 1073–1088.

Hou, L., L.D. Martin, Z. Zhou, A. Feduccia, and F. Zhang. 1999. A

diapsid skull in a new species of the primitive bird Confuciu-

sornis. Nature 399: 679–682.

Hu, D., L. Hou, L. Zhang, and X. Xu. 2009. A pre-Archaeopteryx

troodontid theropod from China with long feathers on the

metatarsus. Nature 461: 640–643.

Huxley, T.H. 1868. On the animals which are most nearly interme-

diate between birds and reptiles. Annals and Magazin of Natural

History 4: 66–75.

Ji, Q., M.A. Norell, P.J. Makovicky, K.-Q. Gao, S. Ji, and C.-X. Yuan.

2003. An early ostrich dinosaur and implications for ornithomi-

mosaur phylogeny. American Museum Novitates 3420: 1–12.

Longrich, N.R., J. Vinther, Q. Meng, Q. Li, and A.P. Russell. 2012.

Primitive wing feather arrangement in Archaeopteryx litho-

graphica and Anchiornis huxleyi. Current Biology 22:

2262–2267.

Madsen, J.H. 1976. Allosaurus fragilis: a revised osteology. Utah

Geological and Mineralogical Survey Bulletin 109: 3–163.

Makovicky, P.J., M.A. Norell, J.M. Clark, and T. Rowe. 2003.

Osteology and relationships of Byronosaurus jaffei (Theropoda:

troodontidae). American Museum Novitates 3402: 1–32.

Martin, L.D. 1991. Mesozoic birds and the origin of birds. In Origins

of higher groups of tetrapods, ed. H.-P. Schultze, and L. Trueb,

485–540. Ithaka and London: Comstock Publishing Associate.

Mayr, G., B. Pohl, S. Hartman, and D.S. Peters. 2007. The tenth

skeletal specimen of Archaeopteryx. Zoological Journal of the

Linnean Society 149: 97–116.

Mayr, G., B. Pohl, and D.S. Peters. 2005. A well-preserved

Archaeopteryx specimen with theropod features. Science 310:

1483–1486.

Norell, M.A., J.M. Clark, A.H. Turner, P.J. Makovicky, R. Barsbold,

and T. Rowe. 2006. A new dromaeosaurid theropod from Ukhaa

Tolgod (Omnogov, Mongolia). American Museum Novitates

3545: 1–51.

Norell, M.A., P.J. Makovicky, G.S. Bever, A.M. Balanoff, J.M. Clark,

R. Barsbold, and T. Rowe. 2009. A review of the Mongolian

Cretaceous dinosaur Saurornithoides (Troodontidae: Thero-

poda). American Museum Novitates 3654: 1–63.

Osmolska, H., E. Roniewicz, and R. Barsbold. 1972. A new dinosaur,

Gallimimus bullatus n. gen., n. sp. (Ornithomimidae) from the Upper

Cretaceous of Mongolia. Palaeontologia Polonica 27: 103–143.

Ostrom, J.H. 1969. Osteology of Deinonychus antirrhopus, an

unusual theropod from the Lower Cretaceous of Montana.

Bulletin of the Peabody Museum of Natural History 30: 1–165.

Ostrom, J.H. 1973. The ancestry of birds. Nature 242: 136.

Ostrom, J.H. 1976. Archaeopteryx and the origin of birds. Biological

Journal of the Linnean Society 8: 91–182.

Paulina-Carabajal, A., and P.J. Currie. 2012. New information on the

braincase of Sinraptor dongi (Theropoda: allosauroidea): eth-

moidal region, endocranial anatomy, and pneumaticity. Verte-

brata Palasiatica 50(2): 85–101.

Peters, S., and Q. Ji. 1998. The diapsid temporal construction of the

Chinese fossil bird Confuciusornis. Senckenbergiana Lethaea

78: 155–158.

Raath, M.A. 1985. The theropod Syntarsus and its bearing on the

origin of birds. In The beginning of birds, ed. M.K. Hecht, J.H.

Ostrom, G. Viohl, and P. Wellnhofer, 219–227. Eichstatt:

Freunde des Jura Museums.

Rauhut, O.W.M. 2003. The interrelationships and evolution of basal

theropod dinosaurs. Special Papers in Palaeontology 69: 1–213.

Rauhut, O.W.M. 2004. Braincase structure of the Middle Jurassic

theropod dinosaur Piatnitzkysaurus. Canadian Journal of Earth

Sciences 41(9): 1109–1122.

Rauhut, O.W.M., A.C. Milner, and S.C. Moore-Fay. 2010. Cranial

osteology and phylogenetic position of the theropod dinosaur

Proceratosaurus bradleyi (Woodward, 1910) from the Middle

Jurassic of England. Zoological Journal of the Linnean Society

158: 155–195.

Rayfield, E.J. 2005. Using Finite-Element Analysis to investigate

suture morphology: a case study using large carnivorous

dinosaurs. Anatomical Record A 283A: 349–365.

Sampson, S.D., and L.M. Witmer. 2007. Craniofacial anatomy of

Majungsaurus crenatissimus (Theropoda: abelisauridae) from

the Late Cretaceous of Madagascar. Society of Vertebrate

Paleontology, Memoir 8: 32–102.

Tischlinger, H. 2005. Neue Informationen zum Berliner Exemplar

von Archaeopteryx lithographica H. v. Meyer 1861. Archaeop-

teryx 23: 33–50.

Tischlinger, H. 2009. Der achte Archaeopteryx–das Daitinger Exem-

plar. Archaeopteryx 27: 1–20.

Tischlinger, H., and D.M. Unwin. 2004. UV-Untersuchungen des

Berliner Exemplars von Archaeopteryx lithographica H. v.

Meyer 1861 und der isolierten Archaeopteryx-Feder. Archaeop-

teryx 22: 17–50.

von Meyer, H. 1861. Archaeopteryx lithographica und Pterodactylus.

Neues Jahrbuch fuer Mineralogie, Geognosie, Geologie und

Petrefaktenkunde 1861: 678–679.

Walker, A. 1985. The braincase of Archaeopteryx. In The beginning

of birds, ed. M.K. Hecht, J.H. Ostrom, G. Viohl, and P.

Wellnhofer, 123–134. Eichstatt: Freunde des Jura Museums.

220 O. W. M. Rauhut

123

Wang, X., J.K. O’Connor, B. Zhao, L.M. Chiappe, C. Gao, and X.

Cheng. 2010. New species of Enantiornithes (Aves: ornithotho-

races) from the Qiaotou Formation in northern Hebei, China.

Acta Geologica Sinica 84: 247–256.

Weishampel, D.B. 1984. Evolution of jaw mechanisms in ornithopod

dinosaurs. Advancements in Anatomy, Embryology and Cell

Biology 87: 1–110.

Wellnhofer, P. 1974. Das funfte Skelettexemplar von Archaeopteryx.

Palaeontographica A 147(4–6): 169–216.

Wellnhofer, P. 1993. Das siebte Exemplar von Archaeopteryx aus den

Solnhofener Schichten. Archaeopteryx 11: 1–47.

Wellnhofer, P. 2008. Archaeopteryx. Der Urvogel von Solnhofen.

Munich: Dr. Friedrich Pfeil.

Whetstone, K.N. 1983. Braincase of Mesozoic birds: I. New

preparation of the ‘‘London’’ Archaeopteryx. Journal of Verte-

brate Paleontology 2(4): 439–452.

Witmer, L.M. 1997a. The evolution of the antorbital cavity of

archosaurs: a study in soft-tissue reconstruction in the fossil

record with an analysis of the function of pneumaticity. Society

of Vertebrate Paleontology, Memoir 3: 1–73.

Witmer, L.M. 1997b. Craniofacial air sinus systems. In Encyclopedia

of dinosaurs, ed. P.J. Currie, and K. Padian, 151–159. San

Diego: Academic Press.

Xu, X., and M.A. Norell. 2006. Non-avian dinosaur fossils from the

Lower Cretaceous Jehol Group of western Liaoning, China.

Geological Journal 41: 419–437.

Xu, X., M.A. Norell, X.-L. Wang, P.J. Makovicky, and X.-C. Wu.

2002. A basal troodontid from the early Cretaceous of China.

Nature 415: 780–784.

Xu, X., and X.-C. Wu. 2001. Cranial morphology of Sinornithosaurus

millenii Xue et al. 1999 (Dinosauria: Theropoda: Dromaeosau-

ridae) from the Yixian Formation of Liaoning, China. Canadian

Jorunal of Earth Sciences 38: 1739–1752.

Xu, X., H.-L. You, K. Du, and F. Han. 2011. An Archaeopteryx-like

theropod from China and the origin of Avialae. Nature 475: 465–470.

Yates, A.M. 2003. The species taxonomy of the sauropodomorph

dinosaurs from the Lowenstein Formation (Norian, Late Trias-

sic) of Germany. Palaeontology 46(2): 317–337.

Zhou, Z., and F. Zhang. 2006. Mesozoic birds of China: A synoptic

review. Vertebrata Palasiatica 44(1): 74–98.

Skull of Archaeopteryx 221

123