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Neuroanatomical reconstructions of extinct animals have long been recognized as powerful proxies for palaeoecology, yet our understanding of the endocranial anatomy of dromaeosaur theropod dinosaurs is still incomplete. Here, we used X-ray computed microtomography (µCT) to reconstruct and describe the endocranial anatomy, including the endosseous labyrinth of the inner ear, of the small-bodied dromaeosaur, Velociraptor mongoliensis. The anatomy of the cranial endocast and ear were compared with non-avian theropods, modern birds, and other extant archosaurs to establish trends in agility, balance, and hearing thresholds in order to reconstruct the trophic ecology of the taxon. Our results indicate that V. mongoliensis could detect a wide and high range of sound frequencies (2,368–3,965 Hz), was agile, and could likely track prey items with ease. When viewed in conjunction with fossils that suggest scavenging-like behaviours in V. mongoliensis, a complex trophic ecology that mirrors modern predators becomes apparent. These data suggest that V. mongoliensis was an active predator that would likely scavenge depending on the age and health of the individual or during prolonged climatic events such as droughts.
Journal of Anatomy. 2020;00:1–9.
Velociraptor mongoliensis Osborn, 1924 is a velociraptorine dro-
maeosaur found in Late Cretaceous formations of China and
Mongolia (Osborn, 1924; Godefroit et al., 2008) that has been
made famous in recent years thanks to its portrayal in numer-
ous Holly wood movies. V. mongoliensis has also been the subject
of a number of cranial and postcranial publications (Sues, 1977;
Norell et al., 1997; 2004; Barsbold and Osmólska, 1999; Turner
et al., 2007; Manning et al., 20 09), with the cranial osteolog y,
including the braincase, being well-known thanks to the excep-
tionally preser ved specimens found in Mongolia (Barsbold and
Osmólska, 1999). Despite this heightened attention, the endo-
cranial anatomy of V. mongoliensis has not yet been described.
Indeed, the endocranial anatomy of Dromaeosauridae as a whole
is still relatively poorly known despite the initial osteological
description of Dromaeosaurus having occurred almost a centur y
ago (Matthew and Brown, 1922). Since that time, the endocast
Received: 10 Januar y 2020 
  Revised: 30 April 2020 
  Accepted: 22 M ay 2020
DOI: 10.1111/joa.13253
The endocranium and trophic ecology of Velociraptor
J. Logan King1| Justin S. Sipla2| Justin A. Georgi3| Amy M. Balanoff4,5|
James M. Neenan6
This is an op en access article under t he terms of the Creat ive Commons Attributio n License, which permits use, dist ribution and reproduc tion in any medium,
provide d the orig inal work is proper ly cited .
© 2020 The Authors . Journa l of Anatomy publishe d by John Wiley & Sons Ltd on behalf of Anatomical Society
1School of Earth Science s, University of
Bristol, Bristol, UK
2Depar tment of A natomy and Cell Biology,
University of Iow a, Iowa City, IA, USA
3Depar tment of A natomy, Midwe stern
University, Glen dale, A Z, USA
4Divisio n of Paleontology, America n
Museum of N atural H istor y, New York, NY,
5Depar tment of P sychological and Brain
Science s, Johns Hopkins University,
Baltim ore, MD, USA
6Oxford University Mus eum of Natural
Histor y, University of Ox ford, Ox ford, U K
James M. Neenan, Oxford University
Museum of N atural H istor y, University of
Oxford, Oxford OX1 3PW, UK.
Funding information
Leverhulme Trust, G rant/Award Number :
Neuroanatomical reconstructions of extinct animals have long been recognized as
powerful proxies for palaeoecology, yet our understanding of the endocranial anat-
omy of dromaeosaur theropod dinosaurs is still incomplete. Here, we used X-ray
computed microtomography (µCT) to reconstruct and describe the endocranial
anatomy, including the endosseous labyrinth of the inner ear, of the small-bodied
dromaeosaur, Velociraptor mongoliensis. The anatomy of the cranial endocast and ear
were compared with non-avian theropods, modern birds, and other extant archo-
saurs to establish trends in agility, balance, and hearing thresholds in order to recon-
struct the trophic ecology of the taxon. Our results indicate that V. mongoliensis could
detect a wide and high range of sound frequencies (2,368–3,965 Hz), was agile, and
could likely track prey items with ease. When viewed in conjunction with fossils that
suggest scavenging-like behaviours in V. mongoliensis, a complex trophic ecology that
mirrors modern predators becomes apparent. These data suggest that V. mongoliensis
was an active predator that would likely scavenge depending on the age and health of
the individual or during prolonged climatic events such as droughts.
Dinosauria, Dromaeosauridae, endosseous labyrinth, neuroanatomy, sensory anatomy,
   KING et al.
for Bambiraptor feinbergi (Burnham, 2004) has been partially
described and portions of the endocast of Saurornitholestes
langstoni, V. mongoliensis, Tsaagan mangas, and Deinonychus an-
tirrhopus have been measured for quantitative analysis or other-
wise imaged (Witmer and Ridgely, 2009; Zelenitsky et al., 2011;
Balanoff et al., 2013). There is, however, a distinct lack of de-
scribed endocasts with which to expand the palaeobiology of
dromaeosaurs in the formal literature to date. Although a few
publications have noted and discussed the implications of the
large endocranial space in dromaeosaurs (Hopson, 1977; Currie,
1995; Norell et al., 2004), relating the endocranial anatomy of
velociraptorine dromaeosaurs to their trophic ecology has yet to
be done in any c apacit y.
Evidence for the trophic ecology of V. mongoliensis, or at least
velociraptorine dromaeosaurs, is provided by a few different
sources. The most famous of these, the ‘fighting dinosaurs’ of
Inner Mongolia, preserves a glimpse into the predator–prey rela-
tionship between V. mongoliensis (IGM 100/25) and Protoceratops
andrewsi (IGM 100/512) (Carpenter, 1998). However, two other
V. mongoliensis specimens indicate what may be considered scav-
enging behaviour (Hone et al., 2010; 2012). Several previous
studies have explored the connection between endocranial anat-
omy, palaeoecology, and behaviour within theropod dinosaurs.
Medium- and large-bodied carnivorous theropods (e.g. tyranno-
saurids ( Witmer and Ridgely, 2009; Bever et al., 2011; Brusatte
et al., 2016; Kundrát et al., 2018; McKeown et al., 2020), abe-
lisaurids (Carabajal and Succar, 2015), carcharodontosaurids
(Franzosa and Rowe, 2005; Brusatte and Sereno, 2007; Carabajal
and Canale, 2010), megaraptorans (Carabajal and Currie, 2017),
and allosaurids (Rogers, 1999; Gleich et al., 2005)) as well as small
and medium-sized maniraptorans—e.g. oviraptorosaurs (Kundrát,
2007; Balanof f et al., 2018), therizinosaurs (Lautenschlager et al.,
2012), and others (Walsh et al., 2009; Zelenitsky et al., 2011)—
have been the focus of neurosensory studies. These studies often
are able to utilize structures reflected in the endocasts such as the
olfactory apparatus, cochlear ducts, and optic lobes to reconstruct
the posture and sensory capabilities for these extinct taxa. For
instance, quantitative and comparative analyses of tyrannosaurids
have found that they had the sensor y requirements for an active
predatory lifestyle (Witmer and Ridgely, 2009), and semicircular
canal morphologies have been found to correspond to quadru-
pedal and bipedal locomotor modes in dinosaurs (Georgi et al.,
2013). Even in herbivorous theropods, such as Erlikosaurus, strong
senses of smell, agility, eyesight, and hearing have been estimated
(Lautenschlager et al., 2012).
With this in mind, we explored the neuroanatomy of V. mongo-
liensis (IGM 100/976) in order to better estimate the trophic ecolog y
and sensory aptitude of this species—thus providing much needed
sensory and behavioural data for dromaeosaurs. Here, we describe
the anatomy of the hindbrain and inner ear of V. mongoliensis using
cranial endocasts and compare its neuroanatomy to extant reptil-
ian (including birds) taxa in order to place its sensor y abilities into a
broad palaeoecological context.
IGM 100/976 was collected as a part of the 1991 Joint Expedition
of the Mongolian Academy of Sciences and American Museum of
Natural History. This specimen was recovered from the Djadokhta
Formation at Tugrugeen Shireh, Mongolia (Norell et al., 1997) and
consists of a partial skeleton, including an incomplete braincase that
is missing the bones anterior to the basisphenoid and supraoccipitals
(Figure 1a,b). The braincase is comprised of a few incomplete ele-
ments—the exoccipitals, supraoccipital, and basioccipital. These four
element s are fused to form an incomplete adult endocranial space
where the sutures are obliterated along the surface (Norell et al.,
2004). Because of its incomplete nature, the endocast preserves the
entire hindbrain but only a featureless portion of the midbrain.
IGM 100/976 was scanned at the University of Texas High-
Resolution X-ray CT Facility in Austin, Texas, USA, producing
1024 × 1024 16-bit TIFF images. Scan parameters were as follows:
210 kV, 0.11 mA, intensity control on, high-power mode, no filter,
air wedge, no of fset, slice thick ness 1 line (0.08506 mm), source-ob-
ject distance 245 mm, 1,400 views, two samples per view, inter-slice
spacing 1 line (0.08506 mm), field of reconstruction 81 mm (max-
imum field of view 81.8084 mm), reconstruction of fset 8,700, re-
construction scale 4,000. Acquired with 31 slices per rotation and
25 slices per set. Ring-removal processing based on correction of
raw sinogram data using IDL routine ‘RK_SinoRingProcSimul’ with
parameter ‘bestof5 = 11’. Reconstruc ted with beam-hardening co-
efficients (0.0, 0.6, 0.1, 0.05), and a rotation of 4 degrees. Total final
slices = 450. Segmentation, reconstruction, and measurement col-
lection were conducted in Avizo Lit e (Thermo Fisher Scientific, 9.7.0)
and Amir A 2019.1 (Thermo Fisher Scientific).
The mean and high hearing frequencies for IGM 100/976 were
calculated following the method outlined in Walsh et al. (2009). To
accomplish these reconstructions, we took measurements from the
anterior-most extent of the basisphenoid to the posterior-most mar-
gin of the occipital condyle along with the length of the cochlear
duct (Table 1). The two measurement s were then used to calculate
a cochlear duct-basisphenoid ratio and then logarithmically trans-
formed. This normalized value was placed into pre-calculated formu-
lae found in Walsh et al. (2009).
Institutional abbreviations: IGM—Institute of Geology in Ulaan
Baatar, Mongolia; IVPP—Institute of Vertebrate Paleontolog y
and Paleoanthropology, Beijing, China; MPC-D—Paleontological
Laboratory of the Paleontological Center, Ulaan Baatar, Mongolia.
3.1 | Cranial endocast
The identifiable regions of the brain preserved in the specimen are
limited to the hindbrain: the medulla and cerebellum, including its
floccular lobes. The flocculi are situated posterolaterally and orien-
tated posteriorly at 123° (Figure 1c,f) The bodies of the floccular
KING et a l.
lobes are elongate, roughly circular in cross-section, and fill most of
the space between the anterior and posterior semicircular canals.
Each lobe extends well beyond the posterior margin of the anterior
canal and almost through the posterior semicircular canal of the en-
dosseous labyrinth. The flocculi together account for approximately
7% of the total hindbrain volume (Table 1).
The medulla is wider than tall and forms an almost oval shape
at the foramen magnum. As seen in most other maniraptorans, the
medulla is antero-posteriorly short and narrower than the rest of the
hindbrain (Kundrát, 2007; Balanoff et al., 2009; Lautenschlager et al.,
2012) (Table 1). Anteriorly, the medulla exhibits a gentle dorsolat-
eral constric tion between it and the cerebellum. Anteriorly, there is
a 132.94° angle between the hindbrain and midbrain. This pontine
flexure ( Table 1) implies that the brain exhibited a gentle curvature
and was not all located along the same horizontal plane. This cur va-
ture is unsurprising due to its presence in many non-maniraptoran
theropods (Sampson and Witmer, 2007; Witmer and Ridgely, 2009),
basal therizinosaurs (Lautenschlager et al., 2012), and oviraptoro-
saurs (Kundrát, 20 07; Balanoff et al., 2014).
As a whole, few anatomical structures are preserved on the en-
docast of the cerebellum. The hindbrain lacks a prominent dorsal
dural peak overlying the cerebellum that is found in some other man-
iraptorans such as Conchoraptor (Kundrát, 2007) and large-bodied
derived t yrannosaurs (Osborn, 1912; Witmer and Ridgely, 2009;
Bever et al., 2011; Brusat te et al., 2016). The absence of a large
dural peak is consistent with another velociraptorine dromaeosaur,
FIGURE 1 The braincase and
endocranium of Velociraptor mongoliensis
IGM 100/976. (a) Partial braincase in
anterolateral view. (b) Braincase rendered
transparent, revealing the in situ endocast
in anterolateral view. The labelled
endocast is presented in the right, (c), and
left (d) lateral, dorsal (e), and posterior
(f) views. Brain endocast is shown in
blue, veins in dark blue, cranial nerves in
yellow, and endosseous labyrinth in pink.
Scale bars: 5 mm. cb, cerebellum; pvcm,
posterior middle cerebral vein; fl, floccular
lobes; V, trigeminal nerve; VI, abducens
nerve; VII, facial nerve; X–XI, shared
foramina for the vagus and accessory
TABLE 1 Measurements taken from the endocast of IGM
100/976. Volumes do not account for vascularization, endosseous
labyrinths or cranial nerves.
Element measured
Minimum width 14.4 4 mm
Maximum width 28.49 mm
Cerebellum height 26.13 mm
Cerebellum width 15.75 mm
Total endocast length 22.79 mm
Pontine flexure angle 132.94°
Floccular lobe length 9.59 mm
Angle of floccular lobe orientation 123°
Total floccular volume 0.4 0 g/mm3
Total volume 5.73 g/mm3
Cochlear duct length 11.15 mm
Basisphenoid length 34.71 mm
   KING et al.
T. manga s (personal observation by the authors) and basal tyranno-
saurs (Kundrát et al., 2018); however, it is possible that this portion
of the endocast was not preser ved.
3.2 | Cranial nerves and vasculature
Both trigeminal ner ves (CN V) are preserved; each exiting the lateral
portions of the anteriormost endocast. The trigeminal is preserved
as a single nerve that likely diverged into its component branches
outside of the braincase as it does in other non-avian maniraptorans
(Figure 1c,d) (Currie, 1995). The abducens nerve (CN VI) is located
ventromedial to CN V (Figure 1c,d) and has an anterior trajec tory.
The endocasts of the abducens nerves are incomplete and project
anteriorly only a few millimetres before reaching the anterior limit of
the braincase. A short canal for the facial nerve (CN VII) lies on the
medulla at the level of the anterior edge of the endosseous labyrinth,
just posterolateral to CN V. Both the vagus and accessory nerves
(CN X–XI, respectively) exit a single ventrolaterally located foramen
along the posterior portion of the braincase (Figure 1e,f). While it is
located laterally near the posteriormost par t of the braincase, the
hypoglossal (CN XII) could not be reliably reconstruc ted even though
the CN XII foramina are visible on the external braincase (Norell
et al., 2004).
Norell et al. (2004) initially described the presence of vascula-
ture along the interior surfaces of the braincase in this specimen of
Velociraptor, although these could not be reconstructed digitally. The
occurrence of small veins in Velociraptor would not be surprising con-
sidering birds and their close relatives have a thin dural envelope and
a majority of their braincase filled with neural tissue (Norell et al.,
2004; Evans, 2005). Little of the venous architecture is preserved—
only the posterior middle cerebral veins are obser vable along the
posterodorsal surface of the cerebellum (Figure 1e).
3.3 | Endosseous labyrinth
Both endo sseous labyrint hs are preserve d in IGM 100/976 (Figure 2),
although the posterior por tion of the left labyrinth, i.e. where the
posterior semicircular canal meets the lateral canal, is not preserved
(Figure 2f ). In many respects, the vestibular anatomy of V. mo n-
goliensis is similar to that of other non-avian theropods (Balanoff
et al., 2009; Witmer and Ridgely, 2009; Lautenschlager et al., 2012).
Overall, the labyrinth has a somewhat triangular aspect in lateral
view, with all semicircular canals being approximately orthogonal to
each other. The anterior canal is taller than the posterior one and ex-
hibits only a slight curvature until it cur ves sharply ventrally to help
form the crus communis. The course of the anterior vertical canal
FIGURE 2 The endosseous labyrinth
of IGM 100/976. (a) Labelled right
labyrinth in lateral (left) and dorsal
(right) views. The right (b–e) and left
(f–i) labyrinths of IGM 100/976 shown
in lateral (b,f), posterior (c,g), anterior
(d,h), and dorsal (e,i) views. Scale bars:
5 mm. asc, anterior semicircular canal;
asca, ampulla of the anterior semicircular
canal; cc, crus communis; ecd, endosseous
cochlear duct; f v/fc, fenestra vestibuli and
fenestra cochleae (the division between
the two cannot be identified); lsc, lateral
semicircular canal; lsca, ampulla of the
lateral semicircular canal; psc, posterior
semicircular canal
cc asc
KING et a l.
is planar and has a roughly uniform lumen thickness along its entire
length, except at the anterior ampulla where it meets the vestibule
(Figure 2).
The posterior and lateral canals are approximately equal in
length. The posterior canal deviates from planarity by exhibiting a
slight sinusoidal curvature along its course. Although the posterior
and lateral endosseous canals both appear to terminate posteriorly
in a confluence (Figure 2), the posterior semicircular duct of the
membranous labyrinth would have continued ventromedially and
expanded into its component ampulla (as discussed in Neenan et al.,
2018; Evers et al., 2019), and the lateral duct would have continued
medially to meet the vestibule. Similar to palaeognath birds, but
previously unknown in non-avian theropods, the medial extremity
of the posterior canal curves sharply ventrally and meet s the crus
communis in a position more anterolateral than the anterior canal
(Carabajal and Succar, 2015; Benson et al., 2017).
The lateral canal emerges anteriorly from a large but dorsoven-
trally compressed ampulla. Its course is planar and highly curved in
dorsal view, appearing to meet the vestibule at its posterior extreme
just anterior to the posterior vertical canal (Figure 2a,e,i). As men-
tioned above, however, the membranous duct would have continued
its loop medial to the posterior canal to meet the vestibule (e.g. Evers
et al., 2019).
The cochlear duct , which would have housed the basilar papilla,
the receptor organ for hearing, is relatively long in V. mongoliensis
compared with most non-avian theropods. It is also relatively wide
and follows a similar anteriorly orientated course as the crus com-
munis. The separation between the fenestra vestibuli and fenestra
cochleae (oval and round windows, respectively) cannot be dif feren-
tiated in this scan (Figure 2a,b,f).
4.1 | Sensory abilities of Velociraptor
Floccular lobes are used to maintain head and eye stability during
movement within vertebrates and, as such, are frequently linked to
the agility of an organism (Witmer and Ridgely, 2009). As pointed
out in Walsh et al. (2013) and Ferreira-Cardoso et al. (2017), how-
ever, the size of the reconstructed flocculi do not necessarily reflec t
the actual volume of the lobes in life, as other anatomy (e.g. blood
vessels) may have also resided within the floccular fossae, making
them generally a poor indicator of flight style and ecology in birds
(e.g. powered flight vs. gliding). Nevertheless, relatively large floc-
cular fossae likely correlate with large flocculae despite extraneous
anatomical structures, and Walsh et al. (2013) further postulate that
enlarged flocculi in terrestrial birds could be an adaptation found
in bipeds to help stabilize the unstable nature of bipedalism. It is
therefore logical to interpret the floccular size in terrestrial, bipedal
maniraptorans, such as dromaeosaurs, as relating to balance—with
enlarged lobes corresponding to species that necessitated stable
bipedal movement. The flocculi of IGM 100/976 are massive and
suggest that quick movements and a stable gaze were essential to its
everyday life (Figure 1). This interpretation fits well with the current
idea that V. mongoliensis was a nimble predator that relied heavily on
its agility while pursuing and attacking prey. Moreover, as enlarged
floccular lobes have also been proposed to be indicative of strong
vestibulo-ocular (VOR) and vestibulocollic (VCR) reflexes (Hopson,
1977; Witmer and Ridgely, 2009), it can be reasoned that V. mongo-
liensis was able to track moving objects easily. With that being said,
because the optic lobes were not preser ved it is impossible to say at
this point to what degree IGM 100/976 relied on sight rather than
other senses. Based on the enlarged floccular lobes, elongated semi-
circular canals, and large orbit size of the species, it can be assumed
that the visual acuit y and field of view of V. mongoliensis was high
(Stevens, 20 06; Schmitz and Motani, 2011; Torres and Clarke, 2018).
This heightened optical sensitivity is not surprising considering the
hypothesized predatory lifestyle of V. mongoliensis. When combined
with its large flocculi and potentially sensitive VOR and VCR, it is
likely that V. mongoliensis was easily able to track and pursue its prey
smoothly based on its sensory neuroanatomy and stereoscopic vi-
sion (as determined from the position of the orbits).
In life, the endosseous cochlear duct of V. mongoliensis would
have housed the basilar papilla—the auditory organ of tetrapods
(Gleich et al., 2005; Walsh et al., 2009). As the length of the cochlear
duct has been interpreted as a rough measurement of the basilar
papilla, the length of the duc t can be used as an estimator of hear-
ing frequencies in non-avian dinosaurs (Witmer and Ridgely, 2009;
Lautenschlager et al., 2012). Moreover, the relationship between
the length of the cochlear duc t and the basisphenoid has also been
shown to correlate with hearing frequencies in modern archosaurs
(Walsh et al., 20 09), thus providing a way to calculate mean and high
frequencies of non-avian dinosaurs. A recent study using extant
turkeys demonstrated that a shape analysis of a single endosseous
labyrinth can be used to represent an entire population (Cerio and
Witmer, 2019); we therefore suggest that the hearing frequencies
calculated in this study can be used as proxies for high and average
hearing frequencies for V. mongoliensis. By measuring and logarith-
mically transforming the ratio between the cochlear duct leng th and
the total length of the basisphenoid, a mean hearing range (2,368 Hz)
and high-frequency hearing limit (3,965 Hz) was calculated for IGM
100/976—a range that is comparable to birds such as the common
raven (Corvus corax) and the African penguin (Spheniscus demersus)
(Walsh et al., 2009). Unsurprisingly, the scaled anteroposterior width
and length of the cochlear duct were much more similar to birds—
specifically neognaths such as budgerigars (Melopsittacus undulatus),
storks (Ciconia ciconia), and mute swans (Cygnus olor) —than to more
basal archosaurs and other reptiles (Figure 3).
Our results indicate that V. mongoliensis could hear, hunt, and
perhaps vocalize most efficiently in the range of 2,400 Hz. When
compared with other maniraptorans for which data are available,
the mean hearing frequency of V. mongoliensis is high. For instance,
the mean and high hearing frequencies estimated for the basally di-
verging therizinosaur Falcarius utahensis are 1,630 Hz and 4,0 00 Hz,
respectively (Lautenschlager et al., 2012). Similarly, the frequency
   KING et al.
range of the more derived therizinosaurid Erlikosaurus andrewsi has
a high range between 1,600 and 4,000 Hz (Lautenschlager et al.,
2012). Although the mean frequency range of V. mongoliensis is no-
tably higher than that of therizinosaurs, the high-frequency values
are roughly the same.
The elongate nature of the cochlear duct support s the hypoth-
esis that V. mongoliensis was capable of detecting a wide range of
sounds, indicating that hearing was likely an impor tant sensory
system in this taxon (Manley, 1990; Walsh et al., 2009; Witmer
and Ridgely, 2009; Brusatte et al., 2016; Carabajal et al., 2016).
In fact, IGM 100/976 plots closest to the social vocal learner
Melopsittacus undulatus (budgerigar), making it feasible that
V. mongoliensis utilized hearing in social interactions as well as ac-
tive predation (Figure 3).
4.2 | The trophic ecology of Velociraptor
Dinosaur feeding styles, such as predation vs. scavenging, have
been a topic of popular interest in the past but remain difficult
to diagnose in the fossil record (Holtz, 2008). Our current un-
derstanding of the trophic ecology of V. mongoliensis is provided
by several sources. The most famous of these, the ‘fighting di-
nosaurs’ (IGM 100/25) of Mongolia, preserves what has been
interpreted by some palaeontologists as a predation attempt of
a Velociraptor on a Protoceratops (Carpenter, 1998). However,
further evidence has emerged in recent years suggesting that
V. mongoliensis was not an obligate predator. This includes
Velociraptor tooth marks on bones, which have been interpreted
as late stage scavenging, and the preser ved gut contents of a
subadult individual (Hone et al., 2010; 2012). Each of these spec-
imens indicate that scavenging was a part of the trophic ecology
of V. mongoliensis. The neuroanatomical results described in this
study help flesh out the degree to which scavenging contributed
to the diet of V. mongoliensis.
Our current understanding of the neuroanatomy of V. mongolien-
sis suggests that predation likely made up a large part of its diet.
As with therizinosaurs and oviraptorosaurs, IGM 100/976 possesses
relatively enlarged flocculi (Figure 1c,e; Lautenschlager et al., 2012;
Balanoff et al., 2018). However, the flocculi of IGM 100/976 surpass
those of observed therizinosaurs and almost completely fill the in-
terior space between the semicircular canals. Enlarged flocculi have
been used to predict prey tracking capabilities and may imply that
the species had an acute vestibulo-ocular reflex (Walsh et al., 2013).
This evidence in conjunction with the wide field of binocular vision,
extended hearing range (as determined from this study), and skeletal
morphology indicates that rather than being equally or more reli-
ant on scavenging, V. mongoliensis was well-equipped to be an ac tive
pr ed at or.
The fossil record, however, indicates that scavenging was at
least a small part of the diet in V. mongoliensis (Hone et al., 2010,
2012). Opportunistic scavenging is supported by gut contents re-
covered from MPC-D100/54 that include a 75-mm-long bone of an
unidentified pterosaur. Whether this represents an act of osteoph-
agy or scavenging due to an injury or its small size, it is probable that
the pterosaur was dead prior to being eaten, given its incomplete
nature. In the case of IVPP V16137, a probable Protoceratops, multi-
ple bone fragment s including a dentary, exhibited bite marks char-
acteristic of velociraptorine dromaeosaurs. Velociraptorine teeth
(IVPP V16138) were also found in association with IVPP V16137,
further indicating that a velociraptorine dromaeosaur was feeding
on the carcass of IVPP V16137. Some of these tooth drag marks
found along the anterior portion of the dentary suggest that this
was an instance of late-stage scavenging by V. mongoliensis due to
the lack of significant muscle mass located along a dentary during
life. While this evidence for scavenging can be interpreted as being
somewhat circumstantial, we accept that the specimens neverthe-
less show enough evidence to be considered acts of scavenging
rather than active predation based on the conclusions of previous
studies (Hone et al., 2010; 2012).
This type of flexible hunting strateg y is not surprising given
that modern predator diets are a spectrum rather than an ‘either/
or’ scenario in which seasonality, fitness, and other ecological con-
straints are the primary drivers (Mattisson et al., 2016). Here we
propose the fossil evidence indicates a scavenging behaviour that
complimented an active predatory lifestyle—similar to what can be
found in the modern biota. Modern predators, including predatory
FIGURE 3 Scaled endosseous cochlear duct (ECD) length
against scaled ECD anteroposterior width, with some taxa
highlighted. Velociraptor mongoliensis grouped more closely with
birds rather than wiith Crocodyliformes and non-archosaurs. The
scaled measurements of IGM 100/976 most closely resembled
the upper range of vocal/social neognath birds. A.n, Ahaetulla
nasuta; C.j, Crocodylus johnstoni; C.n, Ciconia nigra; C.o, Cygnus olor;
C.s, Chelydra serpentina; Ci.c, Ciconia ciconia; Co.c, Corvus corax;
D.n, Dromaius novaehollandiae; G.g, Gymnodactylus geckoides; L.m,
Luscinia megarhynchos; M.u, Melopsittacus undulatus; P.e, Psittacus
erithacus; S.c, Struthio camelus; S.p, Sphenodon punctatus; T.a,
Tyto alba; T.s , Tomistoma schlegelii; V.m, Velociraptor mongoliensis.
Modified from Walsh et al. (20 09)
0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45
Scaled ECD anteroposterior width
Scaled ECD length
Aves - Neognathae
Aves - Palaeognathae
Squamata excl. Serpentes
KING et a l.
birds such as Aquila chrysaetos, often resort to changes in hunting
behaviour, or even scavenging, when prolonged weather patterns,
injury or ontogenetic stage forces them to find alternative food
sources (Tjernberg, 1981; Marchetti and Price, 1989; Wilmers
et al., 2003; Mattisson et al., 2016). It follows that the neuroanat-
omy of V. mongoliensis suggests a behaviour that is adapted for
active predation (C arpenter, 1998); however, young or injured in-
dividuals and those experiencing diet ary constraints brought on
by local climate would have actively sought out carcasses for an
easy meal.
The neuroanatomy and sensory capabilities of V. mongoliensis are
described here for the first time and are subsequently used to put
this taxon into a larger palaeobiological context. Evidence from the
hindbrain and labyrinth of IGM 100/976 suggests that V. mongolien-
sis had an average hearing range near 2,400 Hz (similar to modern
social birds such as ravens and penguins), highly sensitive vestib-
ulo-ocular and vestibulocollic reflexes, and a fine-tuned sense of
balance—all of which would have been advantageous as an active
predator. Although previous studies have used gut contents and
tooth marks on Protoceratops mandibles to provide evidence that
scavenging was a part of V. mongoliensis trophic ecology, most evi-
dence, including the neuroanatomy, suggests an active predatory
lifestyle. Therefore, we interpret the presence of scavenging as a
facet of the trophic ecology for V. mongoliensis. Based on the behav-
iour of modern bird taxa, our better understanding of velocirapto-
rine senses, the apparent case of a predation event in the ‘fighting
dinosaurs’, and the age/health/environment of the scavenging indi-
viduals, it is likely that V. mongoliensis was an active predator that
would readily rely on carrion in the event that a ready source of
prey items was not available.
We thank Mark Norell (AMNH) for granting access to the specimen
and Matthew Colbert (University of Texas at Austin) for conduct-
ing the scanning. Additionally, we would like to thank Steve Brusatte
(University of Edinburgh) and Stig Walsh (National Museums
Scotland) for kindly reviewing the manuscript. Duncan Murdock and
Imran Rahman (both University of Oxford) are also thanked for fruit-
ful discussions. This project was funded by a Leverhulme Trust Early
Career Fellowship (ECF-2017-360) awarded to J.M.N.
The authors declare no conflict of interest.
J.L.K. and J.M.N conceived the study. J.L.K reconstructed the 3D
brain endocast, performed the sensory calculations, and drafted/
revised the manuscript. J.M.N reconstructed and described the
labyrinths and assisted in writing the manuscript. J.S.S. and J.A.G.
provided the CT data, gave anatomical considerations for the pro-
ject, and edited the initial drafts of the manuscript. A.M.B. provided
expert knowledge and edited the final drafts of the paper.
The 3D models produced in this study are openly available from
MorphoSource at
J. Logan King
Justin S. Sipla
Justin A. Georgi
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How to cite this article: King JL, Sipla JS, Georgi JA, Balanoff
AM, Neenan JM. The endocranium and trophic ecology of
Velociraptor mongoliensis. J. Anat. 2020;00:1–9. ht t p s :// d oi .
org /10.1111/j oa.13253
... Broadly, the inner ear morphology resembles that in other paravians such as Velociraptor (King et al. 2020; Choiniere et al. 2021). The labyrinth is roughly triangular like that in Velociraptor (King et al. 2020) though it bulges more anteriorly due to the larger anteroposterior shape of the anterior semicircular canal. All of the semicircular canals are roughly orthogonal to each other. ...
... When compared to the vestibular portion of the endosseous labyrinth, the cochlear duct is approximately the same length with no evidence of twisting or further curvature beyond its medial de ection. The cochlear duct is also thick as is the case in Velociraptor (King et al. 2020). Both the left and right cochlear ducts are similar in size, shape, and angle. ...
... Both the left and right cochlear ducts are similar in size, shape, and angle. Laterally, the fenestra vestibuli and fenestra cochleae are not visible but do not seem to have created a small pro le that took do not seem to have taken up a large area -unlike those found in Velociraptor (King et al. 2020) Geometric Morphometric Analysis Prior to collection of landmark data from Sinovenator, the endocast was virtually mirrored to enable collection of arti cially 'left' sided landmarks, then subsequently retrodeformed using median and several pairs of bilaterally symmetric landmarks. While the retrodefomed virtual endocast still exhibited some deformation, we conducted shape analysis on clearly identi able landmarks that characterize the overall con guration of the neuroanatomical regions. ...
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Multiple modifications to the skull and brain anatomy occurred along the lineage encompassing bird-line theropod dinosaurs and modern birds. Anatomical changes to the endocranium include an enlarged endocranial cavity, relatively larger optic lobe that implies elevated visual acuity, and proportionately smaller olfactory bulbs that suggests reduced olfaction. Here, we use micro-computed tomographic (CT) imaging to reconstruct the endocranium and its brain structures from an exceptionally well-preserved skull of Sinovenator changii (Troodontidae, Theropoda). While its overall morphology resembles the typical endocranium of other troodontids, Sinovenator also exhibits unique endocranial features that are similar to other paravian taxa and non-maniraptoran theropods. Landmark-based geometric morphometric analysis on endocranial shape of non-avialan and avian dinosaurs points to the overall brain morphology of Sinovenator most closely resembling that of Archaeopteryx, thus indicating convergent evolution of avialan brain morphology in troodontids and wide existence of such architecture in Maniraptora. Institutional abbreviations: IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China. PMOL, Paleontological Museum of Liaoning, Shenyang 110034, China.
... Although the mediolateral width of the lagena does not appear to be associated with auditory capabilities (Walsh et al., 2009), the lagena of Europasaurus is conspicuously thick mediolaterally, especially when compared to its anteroposterior slenderness ( Figure 6). The calculated auditory capacities (based on Walsh et al., 2009) impute Europasaurus a relatively wide hearing range with a high upper frequency limit (among non-avian dinosaurs; Lautenschlager et al., 2012;King et al., 2020;Sakagami and Kawabe, 2020). Walsh et al., 2009, demonstrate a certain correlation between hearing range, complexity of vocalization, and aggregational behaviour in extant reptiles and birds (see also Gleich et al., 2005;Hanson et al., 2021). ...
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Macronaria, a group of mostly colossal sauropod dinosaurs, comprised the largest terrestrial vertebrates of Earth's history. However, some of the smallest sauropods belong to this group as well. The Late Jurassic macronarian island dwarf Europasaurus holgeri is one of the most peculiar and best-studied sauropods worldwide. So far, the braincase material of this taxon from Germany pended greater attention. With the aid of micro-computed tomography (microCT), we report on the neuroanatomy of the nearly complete braincase of an adult individual, as well as the inner ears (endosseous labyrinths) of one other adult and several juveniles (the latter also containing novel vascular cavities). The presence of large and morphologically adult inner ears in juvenile material suggests precociality. Our findings add to the diversity of neurovascular anatomy in sauropod braincases and buttress the perception of sauropods as fast-growing and autonomous giants with manifold facets of reproductive and social behaviour. This suggests that - apart from sheer size - little separated Europasaurus from its large-bodied relatives.
... The specimen's skull was scanned using computed tomography (CT scanning) to study its internal and external structures in silico. Many subsequent studies applied CT scanning to dinosaur cranial material, focusing mainly on both the braincase and bony labyrinth (Knoll et al., 2006(Knoll et al., , 2012Sereno et al., 2007;Witmer and Ridgely, 2009;Neenan et al., 2019;King et al., 2020;Sakagami and Kawabe, 2020). Recently, an increasing number of studies have focused on the rostral neurovascular anatomy of extant (e.g., Witmer et al., 2008;Leitch and Catania, 2012;Porter andWitmer, 2015, 2016;Jones et al., 2019;Lessner et al., 2019;Lessner and Holliday, 2020) and extinct amniote taxa, including therapsids (Benoit et al., 2016a(Benoit et al., , 2016b(Benoit et al., , 2017b(Benoit et al., , 2019Pusch et al., 2019;Wallace et al., 2019;Pusch et al., 2020;Benoit et al., 2021b;Ekdale and Deméré, 2021), plesiosaurs (Foffa et al., 2014), and archosauromorphs (Lessner et al., 2016;Lessner and Stocker, 2017;Serrano-Martínez et al., 2020;Benoit et al., 2021a), including theropod dinosaurs (Ibrahim et al., 2014(Ibrahim et al., , 2014Barker et al., 2017;Cau, 2020;Cerroni et al., 2020;Porter and Witmer, 2020;Kawabe and Hattori, 2021). ...
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The study of the rostral neurovascular system using CT scanning has shed new light on phylogenetic and palaeobiological reconstructions of many extinct tetrapods. This research shows a detailed description of the rostral neurovascular canals of Tyrannosaurus rex including the nasal, maxillary (dorsal alveolar), and mandibular (ventral alveolar) canals. Extensive comparisons with published descriptions show that the pattern of these canals in Tyrannosaurus is not unusual for a non-avian theropod. As in the non-avian theropod Neovenator, the maxillary canal shows several anasto-moses of its branches. Differences from the plesiomorphic sauropsid condition are concentrated within the canal for the maxillary neurovasculature, which is primitively horizontal, tubular, and connected to a single row of supralabial foramina, whereas in Tyrannosaurus the main trunk of the canal is oriented more obliquely and dorsally dis-placed to give room to the deep tooth alveolae. As a result, the lateral branches that provide innervation and blood supply to the skin are dorsoventrally elongated com-pared to non-theropod taxa, and multiple rows of supralabial foramina are present. An overview of the literature suggests that the evolution of the trigeminal canals among sauropsids only weakly supports previous hypotheses of crocodile-like facial sensitivity in non-avian theropods (except, maybe, in semiaquatic taxa). More systematic studies of the rostral neurovascular canals in non-avian theropods may help answer the question of whether lips were present or not.
... In Alioramus, Dilong, and other coelurosaurs in general, the flocculus is oval and subcircular in cross section, and extends well past the anterior semicircular canal and into the loop of the posterior semicircular canal (Currie and Zhao 1993b;Lautenschlager et al. 2012;Bever et al. 2013;Balanoff et al. 2014;King et al. 2020;Kundrát et al. 2020). Generally, the relative size of the flocculus negatively correlates with body size among theropods. ...
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... ambush predators, amphibious predators, scavengers) and diet breadth (e.g. birds, insects, lizards) [98][99][100][101][102][103][104][105][106] . Our analyses did not detect interactions between carnivorous families, which agrees with evidence from stable isotopes that theropods had different niches within the predator guild, suggesting plausible means by which ecospace was divided among the predatory dinosaurs 107,108 . ...
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The question why non-avian dinosaurs went extinct 66 million years ago (Ma) remains unresolved because of the coarseness of the fossil record. A sudden extinction caused by an asteroid is the most accepted hypothesis but it is debated whether dinosaurs were in decline or not before the impact. We analyse the speciation-extinction dynamics for six key dinosaur families, and find a decline across dinosaurs, where diversification shifted to a declining-diversity pattern ~76 Ma. We investigate the influence of ecological and physical factors, and find that the decline of dinosaurs was likely driven by global climate cooling and herbivorous diversity drop. The latter is likely due to hadrosaurs outcompeting other herbivores. We also estimate that extinction risk is related to species age during the decline, suggesting a lack of evolutionary novelty or adaptation to changing environments. These results support an environmentally driven decline of non-avian dinosaurs well before the asteroid impact.
Theropod dinosaurs have captured the imagination of the public and paleontologists alike. Histology of the bones of theropods has revealed much about dinosaur physiology, behavior, and growth. Histology and ultraviolet fluorescence (UVFL) microscopy of one controversial dinosaur, Nanotyrannus lancensis, reveals the presence of blood clots in post-fixed vessel canals of claw, vertebra, and other isolated post-cranial elements collected at Hell Creek, MT. These clots are thicker, more closely adherent to canal walls, and more reactive to 347 nm UVFL incident light than unfixed specimens. Theropod histology images in the literature display similar clots, and those should be subjected to UVFL for confirmation. In addition, nematodes are evidently preserved in vessel canals of dinosaurs.
This chapter aims to provide an overview of the state of knowledge on non-avian dinosaur paleoneurology, throughout the history and synthesis of recent advances in the field. Today, the endocranial morphology of approximately 150 dinosaur taxa has been described using natural or artificial cranial endocasts. They represent all major clades, although there is a bias towards Cretaceous -and more derived- forms. From this sample more than a half of the publications were made in the last 20 years, hand in hand with the use of non-invasive technologies. This larger amount of anatomical data opened the door to more comprehensive analyses (quantitative methods), allowing us to better understand the evolution of the dinosaur brain pattern and sense biology through deep time.
Dromaeosaurids (Theropoda: Dromaeosauridae), a group of dynamic, swift predators, have a sparse fossil record, particularly at the end of the Cretaceous Period. The recently described Dineobellator notohesperus, consisting of a partial skeleton from the Upper Cretaceous (Maastrichtian) of New Mexico, is the only diagnostic dromaeosaurid to be recovered from the latest Cretaceous of the southwestern United States. Reinterpreted and newly described material include several caudal vertebrae, portions of the right radius and pubis, and an additional ungual, tentatively inferred to be from manual digit III. Unique features, particularly those of the humerus, unguals, and caudal vertebrae, distinguish D. notohesperus from other known dromaeosaurids. This material indicates different physical attributes among dromaeosaurids, such as use of the forearms, strength in the hands and feet, and mobility of the tail. Several bones in the holotype exhibit abnormal growth and are inferred to be pathologic features resulting from an injury or disease. Similar lengths of the humerus imply Dineobellator and Deinonychus were of similar size, at least regarding length and/or height, although the more gracile nature of the humerus implies Dineobellator was a more lightly built predator. A new phylogenetic analysis recovers D. notohesperus as a dromaeosaurid outside other previously known and named clades. Theropod composition of the Naashoibito Member theropod fauna is like those found in the more northern Late Cretaceous North American ecosystems. Differences in tooth morphologies among recovered theropod teeth from the Naashoibito Member also implies D. notohesperus was not the only dromaeosaurid present in its environment.
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Macronaria, a group of mostly colossal sauropod dinosaurs, comprised the largest terrestrial vertebrates of Earth’s history. However, some of the smallest sauropods belong to this group as well. The Late Jurassic macronarian Europasaurus holgeri is one of the best-known sauropods worldwide. So far, the braincase material of this taxon from Germany pended greater attention. With the aid of microCT, we report on the neuroanatomy of the almost complete braincase of an adult individual, as well as the inner ears of one other adult and several juveniles (also containing so far unknown vascular cavities). The presence of large and morphologically adult inner ears in juvenile material suggests precociality. Our findings add to the diversity of neurovascular anatomy in sauropod braincases and buttress the perception of sauropods as fast-growing and autonomous giants with manifold facets of reproductive and social behavior. This suggests that – apart from sheer size – little separated the island dwarf Europasaurus from its large-bodied relatives.
The endocranial structures of the sebecid crocodylomorph Zulmasuchus querejazus (MHNC 6672) from the Lower Paleocene of Bolivia are described in this article. Using computed tomography scanning, the cranial endocast, associated nerves and arteries, endosseous labyrinths, and cranial pneumatization are reconstructed and compared with those of extant and fossil crocodylomorphs, representative of different ecomorphological adaptations. Z. querejazus exhibits an unusual flexure of the brain, pericerebral spines, semicircular canals with a narrow diameter, as well as enlarged pharyngotympanic sinuses. First, those structures allow to estimate the alert head posture and hearing capabilities of Zulmasuchus. Then, functional comparisons are proposed between this purportedly terrestrial taxon, semi-aquatic, and aquatic forms (extant crocodylians, thalattosuchians, and dyrosaurids). The narrow diameter of the semicircular canals but expanded morphology of the endosseous labyrinths and the enlarged pneumatization of the skull compared to other forms indeed tend to indicate a terrestrial lifestyle for Zulmasuchus. Our results highlight the need to gather new data, especially from altirostral forms in order to further our understanding of the evolution of endocranial structures in crocodylomorphs with different ecomorphological adaptations.
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Chelonioid turtles are the only surviving group of reptiles that secondarily evolved marine lifestyles during the Mesozoic Early chelonioid evolution is documented by fossils of their stem group, such as protostegids, which yield insights into the evolution of marine adaptation. Neuroanatomical features are commonly used to infer palaeoecology owing to the functional adaptation of the senses of an organism to its environment. We investigated the neuroanatomy and carotid circulation of the early Late Cretaceous protostegid Rhinochelys pulchriceps based on micro-computed tomography data. We show that the trigeminal foramen of turtles is not homologous to that of other reptiles. The endosseous labyrinth of R. pulchriceps has thick semicircular canals and a high aspect ratio. Comparisons among turtles and other reptiles show that the endosseous labyrinth aspect ratio is not a reliable predictor of the degree of aquatic adaptation, contradicting previous hypotheses. We provide the first models of neuroanatomical soft tissues of an extant turtle. Turtle brain morphology is not reflected by the brain cavity, and the endosseous labyrinth provides an incomplete reflection of membranous semicircular duct morphology. Membranous labyrinth geometry is conserved across gnathostomes, which allows approximate reconstruction of the total membranous labyrinth morphology from the endosseous labyrinth despite their poor reflection of duct morphology.
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The cochlea and semicircular canals (SCCs) of the inner ear are vital neurosensory devices. There are associations between the anatomy of these sensorineural structures, their function, and the function of related biological systems, for example, hearing ability, gaze stabilization, locomotor agility, and posture. The endosseous labyrinth is frequently used as a proxy to infer the performance of the hearing and vestibular systems, locomotor abilities, and ecology of extinct species. Such fossil inferences are often based on single specimens or even a single ear, representing an entire species. To address whether a single ear is representative of a population, we used geometric morphometrics to quantitatively assess the variation in shape and symmetry in a sample of endosseous labyrinths of wild turkeys Meleagris gallopavo of southern Ohio. We predicted that ears would be symmetrical both within individuals and across the sample; that labyrinth shape and size would covary; that labyrinth shape would vary with the size of the brain, measured as width of the endocranium at the cerebellum; and that labyrinths would be morphologically integrated. To test these predictions, we microCT-scanned the heads of 26 cadaveric turkeys, digitally segmented their endosseous labyrinths in Avizo, and assigned 15 manual landmarks and 20 sliding semilandmarks to each digital model. Following Procrustes alignment, we conducted an analysis of bilateral symmetry, a Procrustes regression analysis for allometry and other covariates including side and replicate, and analyses of global integration and modularity. Based on Procrustes distances, no individual’s left and right ears were clearly different from each other. When comparing the ears of different specimens, statistically clear differences in shape were found in only 66 of more than 1,300 contrasts. Moreover, effects of both directional and fluctuating asymmetry were very small—generally, two orders of magnitude smaller than the variance explained by individual variation. Statistical tests disagreed on whether these asymmetric effects crossed the threshold of significance, possibly due to non-isotropic variation among landmarks. Regardless, labyrinths appeared to primarily vary in shape symmetrically. Neither labyrinth size nor endocranial width was correlated with labyrinth shape, contrary to our expectations. Finally, labyrinths were found to be moderately integrated in a global sense, but four weakly separated modules—the three SCCs and cochlea—were recovered using a maximum-likelihood analysis. The results show that both fluctuating and directional asymmetry play a larger role in shape variation than expected—but nonetheless, endosseous labyrinths are symmetrical within individuals and at the level of the population, and their shape varies symmetrically. Thus, inferences about populations, and very possibly species, may be confidently made when only a single specimen, or even a single ear, is available for study.
Tyrannosaurus rex and other tyrannosaurid dinosaurs were apex predators during the latest Cretaceous, which combined giant size and advanced neurosensory systems. Computed tomography (CT) data have shown that tyrannosaurids had a trademark system of a large brain, large olfactory bulbs, elongate cochlear ducts, and expansive endocranial sinuses surrounding the brain and sense organs. Older, smaller tyrannosauroid relatives of tyrannosaurids developed some, but not all, of these features, raising the hypothesis that tyrannosaurid‐style brains evolved before the enlarged tyrannosaurid‐style sinuses, which might have developed only with large body size. This has been difficult to test, however, because little is known about the brains and sinuses of the first large‐bodied tyrannosauroids, which evolved prior to Tyrannosauridae. We here present the first CT data for one of these species, Bistahieversor sealeyi from New Mexico. Bistahieversor had a nearly identical brain and sinus system as tyrannosaurids like Tyrannosaurus, including a large brain, large olfactory bulbs, reduced cerebral hemispheres, and optic lobes, a small tab‐like flocculus, long and straight cochlear ducts, and voluminous sinuses that include a supraocciptal recess, subcondyar sinus, and an anterior tympanic recess that exits the braincase via a prootic fossa. When characters are plotted onto tyrannosauroid phylogeny, there is a two‐stage sequence in which features of the tyrannosaurid‐style brain evolved first (in smaller, nontyrannosaurid species like Timurlengia), followed by features of the tyrannosaurid‐style sinuses (in the first large‐bodied nontyrannosaurid tyrannosauroids like Bistahieversor). This suggests that the signature tyrannosaurid sinus system evolved in concert with large size, whereas the brain did not. Anat Rec, 2020. © 2020 American Association for Anatomy
The recently extinct Malagasy elephant birds (Palaeognathae, Aepyornithiformes) included the largest birds that ever lived. Elephant bird neuroanatomy is understudied but can shed light on the lifestyle of these enigmatic birds. Palaeoneurological studies can provide clues to the ecologies and behaviours of extinct birds because avian brain shape is correlated with neurological function. We digitally reconstruct endocasts of two elephant bird species, Aepyornis maximus and A. hildebrandti, and compare them with representatives of all major extant and recently extinct palaeognath lineages. Among palaeognaths, we find large olfactory bulbs in taxa generally occupying forested environments where visual cues used in foraging are likely to be limited. We detected variation in olfactory bulb size among elephant bird species, possibly indicating interspecific variation in habitat. Elephant birds exhibited extremely reduced optic lobes, a condition also observed in the nocturnal kiwi. Kiwi, the sister taxon of elephant birds, have effectively replaced their visual systems with hyperdeveloped olfactory, somatosensory and auditory systems useful for foraging. We interpret these results as evidence for nocturnality among elephant birds. Vision was likely deemphasized in the ancestor of elephant birds and kiwi. These results show a previously unreported trend towards decreased visual capacity apparently exclusive to flightless, nocturnal taxa endemic to predator-depauperate islands. © 2018 The Author(s) Published by the Royal Society. All rights reserved.
The recently extinct Malagasy elephant birds (Palaeognathae, Aepyornithiformes) included the largest birds that ever lived. Elephant bird neuroanatomy is understudied but can shed light on the lifestyle of these enigmatic birds. Palaeoneurological studies can provide clues to the ecologies and behaviours of extinct birds because avian brain shape is correlated with neurological function. We digitally reconstruct endocasts of two elephant bird species, Aepyornis maximus and A. hildebrandti, and compare them with representatives of all major extant and recently extinct palaeognath lineages. Among palaeognaths, we find large olfactory bulbs in taxa generally occupying forested environments where visual cues used in foraging are likely to be limited. We detected variation in olfactory bulb size among elephant bird species, possibly indicating interspecific variation in habitat. Elephant birds exhibited extremely reduced optic lobes, a condition also observed in the nocturnal kiwi. Kiwi, the sister taxon of elephant birds, have effectively replaced their visual systems with hyperdeveloped olfactory, somatosensory and auditory systems useful for foraging. We interpret these results as evidence for nocturnality among elephant birds. Vision was likely deemphasized in the ancestor of elephant birds and kiwi. These results show a previously unreported trend towards decreased visual capacity apparently exclusive to flightless, nocturnal taxa endemic to predator-depauperate islands.
In extinct archosaurs, brain proportions have been inferred from the morphology of fossilized endocasts. Here we provide the first neurocranial and paleoneurological description of the basal, small-bodied tyrannosauroid Dilong paradoxus compared with larger tyrannosaurids, like Tyrannosaurus rex. Dilong differs from other tyrannosauroids in the proportions of cerebral and cerebellar regions, morphology of venous sinuses, and superimposed position of the forebrain relative to the rest of the endocast. Whereas endocasts of Tyrannosaurus show a more linear configuration and likely contained within a thick intersticial space, the endocast of Dilong indicates an S-shaped brain protected by thinner meninges. Based on our statistic analysis and comparisons with modern crocodilians, we hypothesize that increased body size likely imposed a new spatial configuration for development of the central nervous system during the evolution of gigantism in tyrannosaurs.
Unraveling the origins of the character complexes diagnosing major crown clades is one of the greatest challenges in evolutionary biology. These origination events tend to optimize along extraordinarily long stem lineages where the comparative biology of extant lineages is relatively weak in its heuristic power. Here we add to a growing paleontological literature on the evolutionary origins of the modern avi an brain by describing the endocranial casts of two oviraptorosaur dinosaurs, Citipati osmolskae and Khaan mckennai. These fossil data confirm the antiquity of several avian features, including the expanded cerebrum. They also extend our appreciation of both the inherent variability in the brain-skull relationship along the avian stem and the dynamic nature of these crown characters in the earliest history of their expression.
The bony labyrinth of vertebrates houses the semicircular canals. These sense rotational accelerations of the head and play an essential role in gaze stabilisation during locomotion. The sizes and shapes of the semicircular canals have hypothesised relationships to agility and locomotory modes in many groups, including birds, and a burgeoning palaeontological literature seeks to make ecological interpretations from the morphology of the labyrinth in extinct species. Rigorous tests of form–function relationships for the vestibular system are required to support these interpretations. We test the hypothesis that the lengths, streamlines and angles between the semicircular canals are related to body size, wing kinematics and flying style in birds. To do this, we applied geometric morphometrics and multivariate phylogenetic comparative methods to a dataset of 64 three-dimensional reconstructions of the endosseous labyrinth obtained using micro-computed tomography scanning of bird crania. A strong relationship between centroid size of the semicircular canals and body size indicates that larger birds have longer semicircular canals compared with their evolutionary relatives. Wing kinematics related to manoeuvrability (and quantified using the brachial index) explain a small additional portion of the variance in labyrinth size. We also find strong evidence for allometric shape change in the semicircular canals of birds, indicating that major aspects of the shape of the avian labyrinth are determined by spatial constraints. The avian braincase accommodates a large brain, a large eye and large semicircular canals compared with other tetrapods. Negative allometry of these structures means that the restriction of space within the braincase is intense in small birds. This may explain our observation that the angles between planes of the semicircular canals of birds deviate more strongly from orthogonality than those of mammals, and especially from agile, gliding and flying mammals. Furthermore, we find little support for relationships between labyrinth shape and flying style or wing kinematics. Overall, our results suggest that the topological problem of fitting long semicircular canals into a spatially constrained braincase is more important in determining the shape of the avian labyrinth than the specifics of locomotory style or agility. Our results tentatively indicate a link between visual acuity and proportional size of the labyrinth among birds. This suggests that the large labyrinths of birds compared with other tetrapods may result from their generally high visual acuities, and not directly from their ability to fly. The endosseous labyrinths of extinct birds and their close dinosaurian relatives may allow broad inferences about flight or vision, but so far provide few specific insights into detailed aspects of locomotion.