The Function of the Cranial Crest
and Jaws of a Unique Pterosaur
from the Early Cretaceous of Brazil
Alexander W. A. Kellner
*† and Diogenes de Almeida Campos
The discovery of a previously undescribed pterosaur, Thalassodromeus sethi, yields
information on the function of cranial crests and the feeding strategy developed
by these extinct ﬂying reptiles. The material consists of a large skull (length: 1420
millimeters, including the crest) with a huge bony crest that was well irrigated by
blood vessels and may have been used for regulation of its body temperature. The
rostrum consists of two bladelike laminae, the arrangement of which is anal-
ogous to the condition found in the bird Rynchops, which skims over the water
to catch food, indicating that T. sethi also may have been a skimmer.
Despite being studied for over 200 years, the
overall knowledge of pterosaur diversity and
biology is rather slim, mainly due to uneven
sampling and the generally poor preservation
of specimens (1, 2). Moreover, because ptero-
saurs are extinct, their biological habits and
functions of anatomical features are difficult
to establish, and most interpretations have
relied on comparisons with modern analogs
such as birds. Here, we report a previously
undescribed pterosaur that shows a distinct
morphology of the skull, providing informa-
tion on the function of cranial crests and
feeding strategy. The specimen comes from
the Romualdo Member of the Santana For-
mation (3), in the Araripe Basin, in northeast-
ern Brazil, which is one of the few deposits
where pterosaurs are found in large numbers
with good preservation.
The sedimentary rocks of the Santana For-
mation were deposited during the Early Cre-
taceous (Aptian/Albian) and represent two
distinct lagerstatten, formed by the lacustrine
limestone layers of the Crato Member at the
base and the lagoonal limestone concretions
embedded in shales of the Romualdo Mem-
ber at the top (4, 5). Although pterosaurs have
been found in the lower layers (2, 6–8), the
deposits in the Romualdo Member contain
better-preserved specimens (9–12). The ma-
terial described here was preserved in a cal-
careous nodule from this deposit and consists
of an almost complete skull (Fig. 1), repre-
senting a new species.
Pterosauria Kaup, 1834
Pterodactyloidea Plieninger, 1901
Tapejaridae Kellner, 1989
Thalassodromeus nov. gen.
T. sethi nov. sp.
Etymology: Thalassodromeus from the
Greek tha´lassa (⫽ sea) ⫹ dromeu´s (runner)
meaning the “sea runner”; sethi for the an-
cient Egyptian god Seth.
Holotype: skull (total length, 1420 mm;
length from the squamosal to the tip of the
premaxilla, 798 mm) and lower jaw (length:
preserved, 635 mm; estimated, 710 mm) de-
posited at the Museu de Cieˆncias da Terra/
Departamento Nacional de Produc¸a˜o Mineral
(DGM 1476-R) (Figs. 1 to 3); cast at the
Museu Nacional (MN)/Universidade Federal
do Rio de Janeiro (UFRJ) (MN 6678-V).
Horizon and locality: The specimen was
collected in 1983 at the outcrops of the Ro-
mualdo Member [Albian (3, 5)], in the Santana
Formation, near the town of Santana do Cariri,
in the state of Ceara´, northeastern Brazil.
Diagnosis: Tapejarid with developed cranial
crest composed of premaxillae, frontal, parietal,
and supraoccipital, starting at the tip of the skull
and extended posteriorly, well behind the oc-
cipital region; posterior end of the cranial crest
V-shaped; suture between premaxillae and
frontoparietal portion of the crest rectilinear;
anterior portion of the premaxillae and dentary
with sharp dorsal and ventral edges; palatines
before palatal crest strongly concave; posterior
(occipital) region broader than in other tapeja-
rids (width over quadrates, 20% of squamosal
to premaxilla length).
With the exception of two segments from
the ventral part of the skull plus the mandible
and the distal tip of the lower jaw, the mate-
rial is complete and all bones are preserved in
three dimensions. The only signs of compac-
tion are found in the region of the left jugal
and in the right mandibular ramus, which are
slightly pushed inward.
As is typical of derived pterosaurs (mem-
bers of the clade Pterodactyloidea), T. sethi
has an elongated skull (Fig. 1). The orbit is
positioned lower than the dorsal rim of the
antorbital fenestra, a feature only present in
the azhdarchids [e.g., Quetzalcoatlus sp.
Paleovertebrate Sector, Department of Geology and
Paleontology, Museu Nacional/Universidade Federal
do Rio de Janeiro, Quinta da Boa Vista, Sa˜o Cristo´va˜o,
Rio de Janeiro, RJ, 20940 –040, Brazil.
Cieˆncias da Terra/Departamento Nacional de Produ-
c¸a˜o Mineral, avenida Pasteur 404, Rio de Janeiro, RJ,
*The authors are fellows at Conselho Nacional de
Desenvolvimento Cientı´ﬁco e Tecnolo´gico and asso-
ciate researchers at the American Museum of Natural
†To whom correspondence should be addressed. E-
www.sciencemag.org SCIENCE VOL 297 19 JULY 2002 389
(13)] and tapejarids [Tapejara wellnhoferi
(14, 15)]. The nasoantorbital fenestra is very
large (390 mm), comprising about half of the
cranial length between the squamosal and the
tip of the premaxilla. Starting at the anterior
end of the premaxillae, T. sethi exhibits a
large sagittal crest that extends above the
nasoantorbital fenestra and well behind the
occipital region. This cranial structure is
formed by frontals, parietals, and premaxil-
lae, which fuse in the midline, and by the
supraoccipital, which builds the ventral edge
right behind the occipital region. Despite its
size, the crest is lightly built, with the bones
united by a well-developed trabecular sys-
tem. The premaxillae contribute to most of it
and differ from those of other crested ptero-
saurs [e.g., Pteranodon (16, 17) and Dsun-
garipterus (18)], because they extend to the
most posterior portion of the crest, terminat-
ing in a V-shaped structure. The frontals and
parietals form the base of the posterior part of
the crest, and their contact with the premax-
illae is straight. This crest is essentially hol-
low, internally supported by a well-devel-
oped system of trabeculae, and varies in
thickness (from 1.0 to 10.5 mm) along the
region where it connects to the skull. Above
the skull roof, it thickens at the contact be-
tween the premaxilla and frontal and gets
gradually thinner toward the top and back,
except for the ventral part directly behind the
occiput (formed by the supraoccipital), where
it has a thick base (7.5 mm) and shows
several ridges for muscle attachment.
On the basis of the large sagittal crest and
the extended nasoantorbital fenestra, T. sethi
can be allocated to the Tapejaridae (19). Two
other genera, Tapejara (7, 14 ) and Tupuxu-
ara (20, 21), each with two species, have
been grouped in this clade. Thalassodromeus
is easily set apart from Tapejara, which
are comparatively short-faced pterosaurs.
Thalassodromeus shares with Tupuxuara a
palatal crest but has the anterior portion of the
palatal region turned into a bladelike lamina
instead of the flat condition found in Tupuxu-
ara. Furthermore, the palate posterior to the
palatal crest of the new taxon is concave
instead of having the convex condition found
in Tupuxuara (20). Thalassodromeus also has
a proportionally higher premaxillary sagittal
crest, particularly above the nasoantorbital
fenestra. A briefly mentioned skull of Tu-
puxuara (22) shows that the occipital region
of Thalassodromeus is comparatively broad-
er. Some fragmentary pterosaur remains from
Maastrichtian strata of Romania include a
large occiput (23), but the material lacks the
anterior portion of the skull, impeding de-
tailed comparisons with Thalassodromeus.
With the exception of Tapejara imperator
(7), T. sethi has the proportionally largest
crest known in any vertebrate (fossil or re-
cent), which makes up about 75% of the
Fig. 1. (A) T. sethi (DGM 1476-R) skull in left lateral view. (B) Drawing showing the contact of
the cranial bones. Art, articular; f, frontal; d, dentary; j, jugal; l, lacrimal; ltf, lower temporal
fenestra; m, maxilla; naof, nasoantorbital fenestra; n, nasal; np, nasal process; or, orbit; p,
parietal; pm, premaxilla; q, quadrate; san, surangular; soc, supraoccipital; sq, squamosal; utf,
upper temporal fenestra. Scale bar, 200 mm.
Fig. 2. (A) Detail of the crest of T. sethi (DGM
1476-R), showing channels on the bone surface,
interpreted as the imprints of blood vessels. (B)
Drawing showing the preferential orientation
of the interpreted blood vessels (only the larger
ones are illustrated here). The stippled area
indicates sedimentary rock. Naof, nasoantor-
bital fenestra; np, nasal process. Scale bar, 100
19 JULY 2002 VOL 297 SCIENCE www.sciencemag.org390
cranial lateral surface. The crest in T. sethi
differs from the one in T. imperator, because
it is fully ossified, with some darker areas
suggesting that it had a horny covering, par-
ticularly on the top and posterior end. A
system of channels of different sizes and
thicknesses is present on the external bone
surface (Fig. 2A). This feature, observed for
the first time in a pterosaur cranial crest, is
interpreted as the impression of blood ves-
sels. A main central channel rises vertically
from above the orbit and is divided into large
channels directed anteroposteriorly at the
basal portion of the crest. From those, other
channels branch off, curve upward, and tend
to be parallel to each other, giving rise to
smaller ones that form a complex pattern
(Fig. 2, A and B). This network of vascular
supply indicates that this crest was extensive-
ly irrigated by blood vessels and is consistent
with the notion of it having been used in
thermoregulation, as has been argued for
some dinosaurs (24, 25). In Thalasso-
dromeus, this cranial structure might have
been more useful for cooling, with the crest
used as a heat dissipater enabling the animal
to lose excess metabolic heat to the environ-
ment through convection. The large size of
the crest increased the surface area for that
purpose, but the heat transfer effectiveness
must have been controlled by, and been de-
pendent on, the ability of the circulatory sys-
tem to pump blood to the crest, for which a
well-developed network of vascular supply
was necessary. To be able to control the body
temperature might have been particularly
useful when the animal was most active, as,
for example, during hunting, when it would
dump excess metabolic heat into the environ-
ment, with the crest having a wind-aligned
orientation, with effectiveness being eventu-
ally increased by restricted intentional lateral
movement of the head.
It should be noted that a thermoregulatory
function of the crest would not preclude this
structure from having had other functions,
such as species recognition, with the particu-
lar form (including the V-shaped end), in
conjunction with colors, allowing members
of T. sethi to recognize their kin. Sexual
dimorphism is also a possibility and has been
argued for Pteranodon [all having cranial
crests (26, 27 )], but the limited information
on tapejarid postcranials makes this last hy-
pothesis complicated to test. Although the
function of cranial crests in pterosaurs is
difficult to determine (14, 17, 18, 26–29), all
evidence suggests that, in T. sethi, this struc-
ture had multiple functions, interfering with
aerodynamics (because of its large size),
helping in thermal regulation, and function-
ing as a display structure.
The palatal and rostral configuration of T.
sethi is also unusual and is related to its feeding
habit. A strong concavity formed by the pala-
tines and bordered laterally by the maxillae is
present under the anterior half of the nasoantor-
bital fenestrae. Anterior to this concavity, the
palate is convex, forming a short ventral keel
that turns into a sharp blade anteriorly. The
fused dentaries form a perfect counterpart to the
palate, with a developed concavity, followed by
a short, deep groove (that during occlusion
encases the palatal keel, forming a strong inter-
locking mechanism) and an anterior sharp bony
blade (Fig. 3A). Between both blades there is a
gap. The whole skull, particularly the rostral
portion, is streamlined.
The only modern analog with such a rostral
end is found in the avian genus Rynchops (Lari-
dae; Rynchopini). Popularly known as skim-
mers, the members of this taxon have laterally
compressed upper and lower jaws with a blade-
like horny covering (rhamphotheca) and a pro-
truding lower jaw, giving it, in lateral view, an
asymmetric scissors-like aspect (Fig. 3B). Ryn-
chops, whose wing span is generally less than 1
meter, skims over the surface and dips its lower
jaw into the water to catch small pelagic fishes
and crustaceans (30). In addition to the rostrum,
these birds have other structural adaptations for
skimming, among which are curved tomia (the
cutting edge of the rhamphotheca) of the upper
jaw, broad quadrate condyles, large palatines,
large neck musculature, large adductor man-
dibula complex musculature, and greater blood
supply and enervation of the tips of the jaws,
particularly the lower one (30).
The palatines of T. sethi are enlarged too,
but unlike those of Rynchops and other ptero-
saurs, they are concave, constituting a possi-
ble adaptation for momentarily storing food.
The occipital region of T. sethi is more de-
veloped (width between opisthotics ⫽ 113.6
mm) than in other pterosaurs, with strong
muscle scars in several parts and a well-
developed supraoccipital crest, suggesting
the presence of powerful neck muscles. Sev-
eral ridges that reach the base of the basal
portion of the sagittal crest behind the occip-
ital region are observed above the temporal
opening, indicating that the adductor muscu-
lature was well developed. Lastly, there are
several small foramina on the tip of the pre-
maxillae (the tip of the dentary is not pre-
served) indicating that this region was well
irrigated by blood vessels (and likely well
supplied by nerves). The morphology of the
specimen supports the hypothesis that T. sethi
was also a skimmer. As in Rynchops, the
specialized scissors-like bill of Thalasso-
dromeus almost precludes any other method
of capturing prey, such as swooping toward
the water and taking the prey with a single
downward nod of the head, as observed in
several birds [e.g., gull-billed tern (30)]. Be-
cause of the large but thin crest, it is also
unlikely that Thalassodromeus plunged in the
water for fish, as observed, for example, in
the royal tern (30).
Although the fishing technique of T. sethi is
difficult to reconstruct, we have used detailed
reports of the skimming technique of Rynchops
(30) to develop a model, which also takes into
account the differences between the basic avian
and pterosaurian skeletons (figs. S1 and S2).
Whenever striking an object during skimming,
the upper jaw of Rynchops clamps down, while
the head moves down and back, sometimes
becoming completely submerged. The ptero-
saur neck is formed usually by nine cervicals (1,
12, 17 ) [compared to the 15 cervicals of Ryn-
chops (30)], limiting its mobility, as compared
to Rynchops. Therefore, although the general
downward movement of the head of Thalasso-
dromeus was similar to that of Rynchops, the
backward motion was more limited. Further-
more, the size of the crest would impede a
complete submersion of the skull, contrary to
what occasionally happens in Rynchops. Dur-
ing skimming, this bird maintains its body in a
horizontal or only slightly tilted position rela-
tive to the water surface, alternately gliding or
flapping rapidly with regular beats (30). Based
on its large wing surface, Thalassodromeus
probably used more gliding power during skim-
ming, occasionally flapping its wings, particu-
larly after catching prey.
The rostral configuration of T. sethi is
unique among pterosaurs. The most similar
condition is found in some species of Rham-
phorhynchus from the Late Jurassic Soln-
hofen limestone (31), which have a small
anterior projection on the tip of the lower jaw
and have been regarded as “casual skimmers”
Fig. 3. The skull of T. sethi (A) and Rynchops (B).
Note the extreme lateral-compressed and scis-
sors-like upper and lower jaws of both (not
drawn to scale).
www.sciencemag.org SCIENCE VOL 297 19 JULY 2002 391
(1). The rostral portion of the Rhamphorhyn-
chus species differs from that of Thalasso-
dromeus because it is toothed, is compara-
tively reduced, and has a less sharp and
smaller anterior rostral projection. Further-
more, the skull in Rhamphorhynchus lacks
the adaptations for skimming activity dis-
cussed above and might have had only crude
and limited skimming behavior. Another dif-
ference between both is size. Although most
Rhamphorhynchus specimens have a wing-
span ranging from 500 to 1200 mm [the
largest one being 1750 mm (31)], the estimat-
ed length represented by the type material of
Thalassodromeus sethi [based on other tape-
jarid specimens (8, 22)] varies between 4200
and 4500 mm, making it a large volant crea-
ture that got its nourishment by skimming the
Araripe lagoon and the nearby ocean 110
million years ago.
References and Notes
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32. We thank V. Arraes de Alencar Gervaiseau, P. Nuvens,
. Saravaia (Universidade Regional do Cariri), and A.
Andrade (Departamento Nacional de Produc¸a˜o Min-
eral, Crato) for supporting ﬁeldwork at the Araripe
Basin; J. de Alencar (Crato) for assisting D.A.C. during
ﬁeld activities; J. G. Maisey, G. Leonardi, G. Ligabue,
and P. Taquet for discussions about this specimen; H.
Silva and M. Craik (MN/UFRJ) for helping with the
preparation of the material; and M. Oliveira (MN/
UFRJ) for the drawings used in this paper. Partially
funded by the Fundac¸a˜o Carlos Chagas de Amparo a`
Pesquisa do Rio de Janeiro.
Supporting Online Material
Figs. S1 and S2
23 April 2002; accepted 14 June 2002
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