A new giant pterosaur with a robust skull from the latest Cretaceous

Naturwissenschaften (2002) 89:180–184
DOI 10.1007/s00114-002-0307-1
S H O R T C O M M U N I C AT I O N
E. Buffetaut · D. Grigorescu · Z. Csiki
A new giant pterosaur with a robust skull
from the latest Cretaceous of Romania
Received: 29 August 2001 / Accepted: 14 January 2002 / Published online: 26 February 2002
© Springer-Verlag 2002
Abstract A new giant pterosaur, Hatzegopteryx thambema, nov.gen., nov.sp., from the Maastrichtian DensuşCiula Formation of Romania is remarkable for its very
large size (estimated wing span ≥12 m) and for the robustness of its large skull, which may have been nearly
3 m long. The stout skull bones contrast with the usually
thin and slender skull elements of other pterosaurs, and
raise the question of how the weight of the skull was reduced in order to make flight possible. The answer probably lies in the very peculiar internal structure of the
bones, which consists of a dense network of very thin
trabeculae enclosing small alveoli. This structure is reminiscent of expanded polystyrene and, like it, probably
combined strength with lightness.
The Maastrichtian continental deposits of Transylvania,
in western Romania, are well known for their rich and
diverse vertebrate fauna (Weishampel et al 1991;
Grigorescu 1992). So far, however, only a few pterosaur
remains of moderate size and uncertain affinities have
been reported from there (Nopcsa 1923; Jianu et al
1997). A new taxon of giant pterosaur described below
is based on elements of a single individual from the
Densuş-Ciula Formation at Vǎlioara, in the Haţeg
(or Hatzeg) basin of Transylvania. The Densuş-Ciula
Formation is referred to the late Maastrichtian on
stratigraphic and palaeontological grounds (Grigorescu
1992).
Taxonomy
Pterosauria (Kaup, 1834)
Pterodactyloidea (Plieninger, 1901)
Azhdarchidae (Nesov, 1984)
Hatzegopteryx thambema nov.gen., nov.sp.
Derivatio nominis
Generic name from the Hatzeg (or Haţeg) basin of Transylvania, where the type specimen was collected, and
pteryx, Greek for wing. Specific name from thambema,
Greek for monster, alluding to the monstrous size of this
pterosaur.
Holotype
Associated skull elements (occiput, right suspensorium),
incomplete left humerus and unidentified bone fragments
from a single individual. Palaeontological Collection of
the Faculty of Geology and Geophysics of the University
of Bucharest, no. FGGUB R1083.
Stratum typicum
Chocolate-coloured siltstones of the late Maastrichtian
Densuş-Ciula Formation.
Locus typicus
E. Buffetaut (✉)
Centre National de la Recherche Scientifique (CNRS),
16 cour du Liégat, 75013 Paris, France
e-mail: [email protected]
Tel.: +33-1-45848145, Fax: +33-1-45848145
D. Grigorescu · Z. Csiki
Laboratory of Palaeontology, Faculty of Geology and Geophysics,
University of Bucharest, bd. N Balcescu no. 1,
70111 Bucharest, Romania
Vǎlioara, northwestern Haţeg Basin, Transylvania, Romania.
Diagnosis
A very large azhdarchid pterosaur with a robustly built
and posteriorly broad skull. Helical articulation of the
181
Fig. 1 Hatzegopteryx thambema, holotype (FGGUB R 1083).
Proximal part of left humerus in ventral view, showing unwarped
deltopectoral crest. Scale bar 50 mm. Insert shows position of the
specimen on an azhdarchid humerus
quadrate with the mandible massive, with smoothly
rounded rather than angular condyles, and no notch posterior to the lateral condyle.
Referred material
A 385-mm-long femur (FGGUB R1625), lacking both
articular ends, from the Densuş-Ciula Formation at
Tuştea (Haţeg Basin) may belong to Hatzegopteryx
thambema.
Description and discussion
Fig. 2a, b Hatzegopteryx thambema, holotype (FGGUB R 1083).
a Posterior view of occiput; bo basioccipital, oc occipital condyle,
po paroccipital process of exoccipital, ptf post-temporal fenestra,
so supraoccipital. b Right part of palate and suspensorium; c choana, j jugal, pt pterygoid, q quadrate, qj quadratojugal. Scale bars
50 mm. Insert shows position of the palatal elements on a pterosaur skull (ventral view)
The type of the new taxon is a group of uncrushed bones
found in association, unmixed with other fossils, including the proximal half of a left humerus, the occipital region of the skull, the right suspensorium with part of the
palate attached, and unidentified bone fragments. Because of their size, the skull elements from Vǎlioara were
previously misidentified as those of a large theropod dinosaur (Weishampel et al 1991). However, the humerus
(Fig. 1) is clearly pterosaurian, showing a large wingshaped deltopectoral crest, the base of the medial process, and, as a separate fragment, the articular head. The
skull bones (Fig. 2), including parts of the right quadrate,
pterygoid, quadratojugal and jugal, and the posterior part
of the braincase, also show distinctive pterosaur features.
The articular area for the mandible on the quadrate is he-
lical, with an oblique groove separating two offset,
rounded condyles. This peculiar type of jaw articulation
is known in various pterosaurs (Wellnhofer 1980), notably Pteranodon (Plieninger 1901; Eaton 1910; Bennett
2001) and apparently allowed a very wide opening of the
jaws. Although in theropods the quadrate may also show
a helical jaw joint, the quadrate from Vǎlioara clearly
differs from theropod quadrates in the lack of a winglike anteromedial flange. Lateral to the quadrate articulation, the quadratojugal and part of the jugal are preserved; the jugal forms part of the ventral edge of a very
large infratemporal fenestra. Medial to the jaw articulation, the pterygoid process of the quadrate merges into
the pterygoid; no suture is visible, as the bones are very
182
firmly fused, The pterygoid forms a robust rod of bone,
some 45 mm in diameter, which is bifurcated anteromedially to form the bevelled posterior border of the choana. The posterior part of the palate is highly vaulted. The
individual bones of the remarkably massive occiput,
which was probably steeply inclined as in all pterosaurs,
are completely fused together. The occipital condyle is
hemispherical and its diameter (55 mm) is greater than
that of the foramen magnum (43 mm). Ventrally, the basioccipital forms a transversely concave rugose plate,
which provided an insertion for strong neck muscles.
The supraoccipital bears a median ridge also indicating
the insertion of powerful muscles. Above the strong paroccipital process, there is a large post-temporal opening,
as usual in pterosaurs. In dinosaurs, the post-temporal fenestra is reduced (Romer 1956); the occurrence of a
large opening in the specimen from Vǎlioara shows that,
contrary to a previous interpretation (Weishampel et al.
1991), it does not belong to a theropod dinosaur.
To determine the systematic position of Hatzegopteryx, comparisons were made with two groups of very
large Late Cretaceous pterosaurs. The giant azhdarchids
of the terminal Cretaceous, with wing spans reaching or
exceeding 10 m, were the largest known flying creatures.
Specimens from the Maastrichtian of North America
(Lawson 1975; Langston 1981), western Asia (Arambourg 1959; Martill et al 1998) and Europe (Buffetaut et
al. 1997) are usually fragmentary, consisting mainly of
cervical vertebrae and limb bones. Relatively complete
skull material was hitherto known only in Quetzalcoatlus
sp. (Kellner and Langston 1996), from Texas, a “small”
species with a wing span of about 5.5 m (the skull of the
much larger Quetzalcoatlus northropi is unknown). The
skull is better known in the earlier (mainly SantonianCampanian) pteranodontids (Eaton 1910; Bennett 2001),
which were very large pterosaurs, but did not reach the
huge size of some azhdarchids (the largest estimated
wing span listed by Bennett (2001) for a Pteranodon
specimen is 7.25 m).
The humerus of Hatzegopteryx resembles that of
Quetzalcoatlus, with a long and gently curved deltopectoral crest unlike the distinctly warped crest of the Pteranodontidae (Bennett 1989). As in azhdarchids (Padian
and Smith 1992), the distal end of the deltopectoral crest
shows no bulbous expansion; the articular head, represented by a large fragment with no direct contact with
the rest of the specimen, is thickened as in azhdarchids
and morphologically very similar to the corresponding
part of Q. northropi. Because of these shared derived
characters, Hatzegopteryx thambema can be assigned to
the Azhdarchidae. The only azhdarchid in which some
parts or the posterior region of the skull are known and
which can be compared with the Romanian form is
Quetzalcoatlus sp. (Kellner and Langston 1996), which
is perhaps only a third as large as the Vǎlioara specimen.
In Quetzalcoatlus sp., the skull is much more lightly
built, and the articular surfaces of the lateral condyle of
the quadrate are set at a marked angle, unlike the condition in the Vǎlioara specimen. In the latter, the helical
condyles of the quadrate are more reminiscent of the
condition in Pteranodon (Plieninger 1901; Eaton 1910;
Wellnhofer 1980; Bennett 2001), but they are even more
smoothly rounded. In Quetzalcoatlus sp. there is a deep
notch posterior to the lateral condyle, for the reception of
a process on the posterolateral edge of the glenoid fossa
of the mandible (Kellner and Langston 1996). No such
notch is present on the specimen from Vǎlioara. The Romanian pterosaur thus appears to be a very large azhdarchid with a jaw articulation markedly different from that
of Quetzalcoatlus, which justifies the erection of a new
taxon.
The preserved proximal part of the humerus is
236 mm long, with a maximum shaft diameter of 90 mm.
As apparently less than half the bone is preserved, the
humerus of H. thambema may have been slightly longer
than that of the type of Q. northropi (TMM 41450-3),
which is 544 mm long (W. Langston, personal communication). Wing span estimates for the latter range from 11
or 12 m (Langston 1981) to 15 and even 20 m (Lawson
1975). A conservative estimate of the wing span of
H. thambema would thus be about 12 m, if its humerus
was indeed somewhat longer than that of Q. northropi.
How large the skull was by comparison with other pterosaurs is shown by the width of the quadrate articulation
for the mandible, which is 100 mm in Hatzegopteryx,
versus 25 mm in Quetzalcoatlus sp. (Kellner and
Langston 1996), 20 mm in Pteranodon longiceps (Eaton
1910), and 10 mm in Nyctosaurus gracilis (von Huene
1914). The width of the skull at the level of the jaw articulation, estimated from the available specimen which
corresponds to the right half of the palate, was about
500 mm. Assuming that H. thambema was a long-snouted form, like other azhdarchids (and more generally
other Late Cretaceous pterosaurs), the length of its skull
can be roughly estimated on the basis of the width/length
ratio of other pterosaur skulls. An estimate based on the
proportions of a Nyctosaurus gracilis skull from Kansas
(von Huene 1914), which is one of the very few uncrushed pterosaur skulls known from the Late Cretaceous, suggests that the skull was about 2.9 m in length.
On the basis of the Early Cretaceous Anhanguera santanae, which had a relatively shorter skull (Wellnhofer
1985), the estimated skull length is 2.75 m. Estimates
based on the ratio between the width of the quadrate articulation and the total length of the skull in various
pterosaurs give even higher values, but may be less reliable because of the great discrepancy in absolute size between quadrate width and total length. It thus appears
that the skull of H. thambema was nearly 3 m in length.
The size of the skull of Q. northropi can only be estimated by scaling up the dimensions of Quetzalcoatlus sp.;
this suggests a minimum width of 24 cm at the level of
the jaw joint for Q. northropi (W. Langston, personal
communication). It would thus seem that Hatzegopteryx
had a broader skull than Q. northropi, and possibly was
larger overall. Be that as it may, H. thambema probably
had one of the longest skulls in any non-marine vertebrate.
183
1 mm in thickness. Inside, the bones consist of very numerous, closely packed, elongated alveoli, usually a few
millimetres in width and up to more than 10 mm in
length, separated from one another by a dense network
of extremely thin bony trabeculae. A similar structure
occurs in the proximal part of the humerus. This is quite
different from the much larger and more irregular vacuities described in the Brazilian skulls. This unusual structure is rather reminiscent of expanded polystyrene and,
like it, probably provided a very light but rigid material
capable of forming robust, strain-resistant bones without
inducing excessive weight. Apparently, this peculiar
structure sufficiently reduced the weight of the skull to
make flight possible for an animal with such an enormous head as H. thambema.
Fig. 3 Close-up of bone structure in a bone fragment from the holotype of Hatzegopteryx thambema, showing the thin outer cortex
(upper right) and the inner network of bony trabeculae enclosing
elongated alveoli. Scale bar 30 mm
Whereas pterosaur skulls are usually very lightly
built, consisting of thin bony struts and plates, the skull
of H. thambema was robustly built, with stout bones
bearing strong ridges for muscle insertions. It was doubtless made lighter by large openings, but the elements of
the palate and occiput are remarkably large and robust,
especially by comparison with other large pterosaurs
such as pteranodontids and Quetzalcoatlus sp. It is frequently accepted that very large pterosaurs such as Pteranodon were able to fly because the combination of a
lightly built skeleton and a vast wing span resulted in
low wing loading (Bramwell and Whitfield 1974;
McNeill Alexander 1989), although alternative views
have been expressed (Brower 1983). H. thambema had a
much more robust skull than Pteranodon, and the weight
of its huge skull must somehow have been reduced to enable it to take off (a possible alternative would be that
Hatzegopteryx was a flightless pterosaur, but this seems
unlikely because its humerus is very similar to that of
normal flying pterosaurs). As this was not done by reducing the volume of the bones, the answer probably lies
in their internal structure. Many elements of the pterosaur skeleton were pneumatic. Extensive pneumatisation
has been described in uncrushed Early Cretaceous pterosaur skulls from Brazil (Kellner 1996). In Late Cretaceous pterosaurs, pneumatisation of post-cranial elements is fairly well known (Frey and Martill 1996), but
details of skull pneumatisation are usually obscured by
the widespread crushing affecting most cranial remains
(Williston 1898) and little is known beyond the fact that
the skull bones of pteranodontids “consist of thin plates
with internal reticulate reinforcing ridges” (Bennett
2001). In the uncrushed skull elements of Hatzegopteryx,
although the vacuities are now filled with matrix, the internal structure is well preserved, and visible wherever
the outer surface of the bones is damaged (Fig. 3). The
outer layer is a thin compact cortex, usually less than
Acknowledgements This work was supported by an exchange
programme of the Centre National de la Recherche Scientifique
(Paris) and the Romanian Academy of Sciences (Bucharest). We
thank Dino Frey (Karlsruhe, Germany) for advice and access to
comparative material, and Wann Langston (Austin, Texas) and
Chris Bennett (Bridgeport, Connecticut) for useful reviews of the
manuscript.
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