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This chapter addresses the tooth-bearing bones and dental battery of Nigersaurus taqueti and provides an initial cranial reconstruction. It also reviews the feeding specializations common to diplodocoids and how these were modified within rebbachisaurids. The skull and neck of the holotypic specimen of N. taqueti were found in close association. The premaxillary, maxillary, and dentary teeth are explained. The tooth battery of Nigersaurus is quite different from that in ornithischians. In Nigersaurus, the teeth are restricted to the transverse portion of the anterior end of the skull, and at least the lower tooth row extends lateral to the parasagittal plane of the lower jaw. Unlike the parasagittal dental batteries of ornithischians, the dental battery in Nigersaurus is oriented transversely and may have been used for cropping rather than prolonged oral processing. Dental batteries evolved three times independently within Dinosauria—in euornithopod and neoceratopsian ornithischians and in rebbachisaurid sauropods.
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uring the jurassic, sauropod
dinosaurs rose to predominance among
vertebrate herbivores, in terms of both species di-
versity and biomass (e.g., Romer 1966; McIntosh
1990). Their perceived decline on northern land-
masses during the Cretaceous has been linked to
the evolution of tooth batteries in ornithischian
herbivores (e.g., Lull and Wright 1942; Ostrom
1961; Bakker 1978; Lucas and Hunt 1989). On
southern landmasses, in contrast, sauropod di-
versity increased during the Cretaceous
(Weishampel 1990; Hunt et al. 1994), and a
newly discovered southern sauropod, the reb-
bachisaurid Nigersaurus taqueti, is now known to
have evolved a complex tooth battery (Sereno et al.
Rebbachisaurids are a poorly known sauro-
pod clade, reported thus far only from Cretaceous
rocks in South America (Calvo and Salgado
1995; Bonaparte 1996; Apestiguía et al. 2001;
Lamanna et al. 2001), Africa (Lavocat 1954;
Taquet 1976; Sereno et al. 1999), and Europe
(Dalla Vecchia 1998; Pereda-Suberbiola et al.
2003). Many of these are fragmentary finds,
leaving much of the skeletal anatomy of this
group in question, especially the skull. In this
chapter, we describe the tooth-bearing bones
and dental battery of Nigersaurus taqueti and pro-
vide an initial cranial reconstruction. We outline
the feeding specializations common to diplo-
docoids and how these were modified within
Institutional Abbreviation: MNN, Musée
National du Niger, Niamey.
TYPE SPECIES: Nigersaurus taqueti Sereno et
al. 1999.
AGE: Early Cretaceous (Aptian–Albian).
DISCUSSION: Nigersaurus taqueti is the most
common sauropod and one of the most common
species recovered in the rich vertebrate fauna
described from Gadoufaoua, Niger Republic
Structure and Evolution
of a Sauropod Tooth Battery
Paul C. Sereno and Jeffrey A. Wilson
(Taquet 1976; Sereno et al. 1998, 1999, 2001,
2003; Larsson and Gado 2000). Nevertheless,
because the skull and skeleton are delicately con-
structed and highly pneumatic, there are no com-
plete skulls and only a few partially articulated
skeletons. Nigersaurus taqueti was named and
identified as a rebbachisaurid by Sereno et al.
(1999). An earlier report from the same beds of a
dicraeosaurid allied with titanosaurs (Taquet
1976:53) very likely pertains to the same species.
(FIGS. 5.1, 5.3–5.8)
HOLOTYPE:MNN GDF512, partial disarticu-
lated skull and partially articulated neck pre-
served in close association on 1 m2of sandstone
outcrop. Sereno et al. (1999:1346) also list a
“scapula, forelimbs, and hind limbs” as part of
the holotype. These and other bones, which we
regard as referable to this species, were found
at some distance from the skull and neck and
cannot be reliably associated with the holotypic
specimen. The partial skeleton described by
Taquet (1976) also was discovered in the vicin-
ity of the holotype and may pertain to the same
27´N, 9°8´´E), eastern edge of the Ténéré Desert,
Niger Republic; Elrhaz Formation.
crown. Additional skeletal and dental material
is described elsewhere.
REVISED DIAGNOSIS:Rebbachisaurid sauro-
pod characterized by five accessory fenestrae in
the jugal, surangular, and angular; tooth num-
ber increased to 20 and to 34 in the maxilla and
dentary, respectively; tooth replacement
increased to as many as 10–12 in a single col-
umn; premaxilla and dentary lacking alveolar
septa; maxilla with oval (vertically elongated)
replacement foramina; extension of the dentary
tooth row lateral to the sagittal plane of the
FIGURE 5.1. Preliminary reconstruction of the skull of Nigersaurus taqueti based on MNN GDF512. (A) Skull in left lateral
view. (B) Left lower jaw in dorsal view with tooth batteries removed. 1–5, accessory cranial fenestrae; a, angular; altr, alveolar
trough; antfe, antorbital fenestra; ar, articular, br, buccal ridge; cp, coronoid process; d, dentary; d1–d34, replacement foram-
ina for dentary tooth positions 1–34; emf, external mandibular fenestra; en, external naris; f, frontal, fo, foramen; j, jugal; ltf,
laterotemporal fenestra; m, maxilla; mc, Meckel’s canal; nf, narial fossa; pm, premaxilla; po, postorbital; popr, paraoccipital
process; ps, parasphenoid; q, quadrate; qfo, quadrate fossa; qj, quadratojugal; sa, surangular; saf, surangular foramen, so,
supraoccipital; sq, squamosal; sym, symphyseal surface; vc, vascular canal.
lower jaw; subcircular mandibular symphysis;
crowns with prominent mesial (medial) and
distal (lateral) ridges; scapula with prominent
rugosity on the medial aspect of the proximal
end of the blade.
The skull and neck of the holotypic specimen
of Nigersaurus taqueti were found in close asso-
ciation. Most of the dorsal skull roof is pre-
served (fig. 5.1A). The braincase is intact, with
the proximal end of the stapes in place in the
fenestra ovalis. The quadrate is the only palatal
bone preserved. All of these bones, with the
exception of the frontal and braincase, are
composed of thin laminae or narrow struts
and are extremely delicate. Five unique acces-
sory fenestrae are present, two in the jugal and
three in the surangular and angular (figs.
5.1–5.5). These accessory openings are bor-
dered by bone that tapers gradually in width to
a paper-thin edge that has a smooth margin. It
is highly unlikely, therefore, that they repre-
sent lesions or some other kind of bone
pathology, like the healed openings reported in
aged individuals of other dinosaurian species
(e.g., Brochu 2003).
The snout is proportionately much shorter
and the dental arcade is less prognathous than
in diplodocids or dicraeosaurids (figs. 5.1, 5.2).
As mentioned above, the external naris is not
retracted above the orbit in Nigersaurus. A
statement to the contrary—that the external
naris is positioned as in diplodocids—was
made on the basis of the maxilla before the pre-
maxilla was exposed (Sereno et al. 1999:1344).
Although the nasal and thus the posterior mar-
gin of the external naris are not known, the
anterior portion of the border is far anterior to
that in any known diplodocid. The external
naris is large, laterally facing, separated in the
midline from its opposite by a vertical premax-
illa–nasal septum, and surrounded by a more
pronounced narial fossa. As in other diplo-
docoids, the jaw articulation and laterotemporal
fenestra are shifted anteriorly under the orbit
(figs. 5.1, 5.2). The supratemporal fenestra is
very reduced or absent altogether, in contrast to
those in other diplodocoids (Holland 1924) or
other sauropods.
The transversely expanded form of the alveo-
lar ramus of the dentary is unique among
dinosaurs (fig. 5.1B). No other dinosaur has a
tooth row that extends lateral to the longitudinal
plane of the lower jaw. The maximal width
across the anterior end of the paired dentaries
slightly exceeds the length of the entire lower
jaw. Despite the gaping alveolar trough that
housed hundreds of slender teeth packed
together as a tooth battery, the dentary and other
bones of the lower jaw in Nigersaurus are as
lightly built as those in Diplodocus and much
more slender than those in Camarasaurus (figs.
5.1, 5.2). The description below is limited to the
tooth-bearing bones and the teeth.
The premaxilla is a slender bone, the ventral
third of which houses a battery of teeth aligned
in four columns (fig. 5.3, table 5.1). The dorsal
two-thirds of the premaxilla extends as a thin
lamina appressed to its opposite in the mid-
line. In lateral view, these two parts of the pre-
maxilla meet at an angle of approximately 30º,
greater than that in Diplodocus (figs. 5.1A,
5.2B). Four replacement foramina and a con-
necting groove for the dental lamina are visi-
ble on the posterior aspect of the bone. Unlike
those in other diplodocoids, the alveolar mar-
gin and space within the premaxilla housing
replacement teeth are not divided by bony
septa into discrete alveoli. Rather, they are
developed as an open trough, the arched ante-
rior wall of which is thin and extends more
than 1 cm farther ventrally than the posterior
wall (figs. 5.3, 5.4).
Although the active, or functioning, teeth
have fallen from the trough, a battery of replace-
ment teeth is visible in computed tomography
FIGURE 5.2. Skull reconstructions in lateral view of (A) the basal neosauropod Camarasaurus lentus and
(B) the diplodocid Diplodocus longus (from Wilson and Sereno 1998). a, angular; amf, anterior maxillary fora-
men; aofe, antorbital fenestra; ar, articular; asf, anterior surangular foramen; bo, basioccipital; d, dentary; f,
frontal; j, jugal; l, lacrimal; lf, lacrimal foramen; m, maxilla; n, nasal; nf, narial fossa; p, parietal; paofe, prean-
torbital fenestra; pl, palatine; pm, premaxilla; po, postorbital; popr, paraoccipital processes; pra, prearticular;
prf, prefrontal; ps, parasphenoid; psf, posterior surangular foramen; pt, pterygoid; q, quadrate; qj, quadratoju-
gal; sa, surangular; sf, surangular foramen; sq, squamosal; so, supraoccipital; v, vomer.
FIGURE 5.3. (A) Stereopair and (B) matching drawing of the right premaxilla of Nigersaurus taqueti (MNN GDF512) in
lateral view. am, articular surface for the maxilla; altr, alveolar trough; en, external naris; fo, foramen; nf, narial fossa;
plpr, palatal processes. Scale bars equal 5 cm.
Measurements of the Tooth-Bearing Bones and Teeth of Nigersaurus taqueti
Maximum length 209
Maximum width of maxillary articular surface, midheight 18
Alveolar trough, anteroposterior width 10
Posterodorsal ramus, length 77
Alveolar ramus
Preserved width 94
Depth (to ventral rim of antorbital fenestra) 73
Replacement foramen, height 11
Replacement foramen, width 3
Alveolar ramus, width 115
Alveolar trough, anteroposterior width of medial end 12
Dorsoventral height 21
Anteroposterior depth 23
Maxillary tooth
Crown height (25)
Basal crown width 4
Dentary tooth
Crown height (20)
Basal crown width 3
NOTE: Measurements are for the holotypic skull of Nigersaurus taqueti (MNN GDF512). Paren-
theses indicate estimated measurement. Measurements are in millimeters.
FIGURE 5.4. High-resolution
computed tomographic sec-
tions through the right premax-
illa of Nigersaurus taqueti
(MNN GDF512) in (A) longitu-
dinal and (B) cross-sectional
views. The packing pattern of
the tooth battery and the asym-
metrical distribution of enamel
on individual crowns are visi-
ble. altr, alveolar trough; mt,
mature tooth; nt, new tooth; rf,
replacement foramen.
(CT) scans in the upper half of the alveolar ramus
(fig. 5.4B). The premaxillary teeth are self-sup-
porting and in mutual contact along the lengths
of their crowns, which presumably erupted and
wore as a unit. The teeth originate just anterior to
the replacement foramina. As the teeth increase
in length, their roots extend into the upper half of
the alveolar ramus before migrating ventrally
toward the alveolar trough (fig. 5.4A).
The ventral one-fifth of the maxilla houses a
battery of teeth arranged in columns internal to
each oval replacement foramen (Sereno et al.
1999:fig.2D; fig. 5.5, table 5.1). The dorsal four-
fifths of the bone is developed proximally as a
thin plate and distally as a narrow and delicate
strut that divides the external naris and antor-
bital fenestra (fig. 5.1). As in the premaxilla, the
alveolar margin is developed as an undivided
trough, as seen in posterior view, with the labial
(anterior) wall extending approximately 1 cm
farther ventrally than the lingual (posterior)
wall. Unlike the premaxilla and dentary, bony
septa are present within the body of the alveolar
ramus. These septa join the posterior and ante-
rior walls, enclosing crypts for each replacement
series that are approximately twice as deep labi-
olingually (anteroposteriorly) as mesiodistally
Although all worn maxillary teeth have
fallen from the alveolar trough, columns of
replacement teeth are visible in the two most
mesial (medial) tooth positions (Fig. 5.5). As in
the premaxilla and dentary, the teeth originate
just labially (anteriorly) to each replacement fora-
men, extend with growth dorsally and ventrally
within the alveolar ramus, and then migrate in
series toward the alveolar trough.
The dentary has a very unusual structure in
Nigersaurus taqueti (figs. 5.1, 5.6, table 5.1). Other
rebbachisaurids may eventually be shown to
share some or all of these apomorphies. Several
aspects of the dentary, however, currently have
no parallel among reptiles.
In dorsal view, the T-shaped bone is divided
into a mandibular ramus, oriented anteroposte-
riorly, and an alveolar ramus, oriented trans-
versely (figs. 5.1B, 5.6). The posterior end of the
mandibular ramus, as in other dinosaurs, is ori-
ented in a parasagittal plane. It is divided into a
slender dorsal process, which contacts the suran-
gular, and a broader, tongue-shaped ventral
process. The anterior end of the mandibular
ramus, unlike that in any other sauropod, is
dorsoventrally compressed and flares in trans-
verse width before joining the alveolar ramus
(fig. 5.1B). As a consequence, this portion of the
mandibular ramus appears unusually slender in
lateral view (fig. 5.1A). In dorsal view, this portion
of the mandibular ramus is subtriangular with a
concave dorsal surface. Laterally it is bounded by
a sharp, upturned edge that joins the lateral
extremity of the alveolar ramus. A large oval fora-
men opens in the center of this portion of the
mandibular ramus. This foramen lies dorsal to a
sizable vascular canal that passes anteriorly
within the dentary toward the alveolar trough.
Shallow grooves also exit the foramen and pass
anteriorly toward the row of replacement foram-
ina (Sereno et al. 1999:fig. 2C; fig. 5.6).
The breadth of the alveolar ramus exceeds
the length of the mandibular ramus, a
remarkable proportion that results in lower
jaws that are as broad as they are long (figs.
5.1B, 5.6, table 5.1). The extraordinary width of
the anterior end of the lower jaws is the result
of the lateral extension of the alveolar ramus,
approximately 30% of which is positioned lat-
eral to the sagittal plane of the mandibular
ramus. The medial portion of the alveolar
ramus is subcylindrical. The mandibular sym-
physis, as a result, is subcircular (table 5.1).
The symphysial surface is smooth and gently
concave, suggesting that a small amount of
flexion about the sagittal plane may have been
The alveolar trough is nearly straight in
dorsal view (fig. 5.1B). It narrows in width
toward its lateral end. Other changes toward
the lateral side of the trough include a decrease
in the size of the replacement foramina and a
FIGURE 5.5. (A) Stereopair and (B) matching drawing of the left maxilla of Nigersaurus taqueti (MNN GDF512) in poste-
rior view with two replacement tooth columns exposed by erosion. al, alveolus; antfe, antorbital fenestra; apm, articular
surface for the premaxilla; apl, articular surface for the palatine; m1– m20, maxillary tooth positions 1–20; mfr, missing
fragment; rf, replacement foramen; sf, subnarial foramen. Scale bars equal 5 cm.
FIGURE 5.6. (A) Stereopair and (B) matching drawing of the left dentary of Nigersaurus taqueti (MNN GDF512) in dorsal
view. altr, alveolar trough; br, buccal ridge; d1–d34, replacement foramina for dentary tooth positions 1–34; mc, Meckel’s
canal; mfr, missing fragment; pdpr, posterodorsal process; pvpr, posteroventral process; sym, symphysis; t, tooth; vc, vascu-
lar canal. Scale bars equal 5 cm.
decrease in the distance between the replace-
ment foramina and the edge of the alveolar
trough. This gradual decrease in the width of
the trough and the size and position of the
replacement foramina suggests that the
replacement rate and/or tooth size decreased
toward the lateral end of the tooth row. Several
loose teeth are preserved in the bottom of the
alveolar trough and confirm the gradual
decrease in tooth size laterally along the bat-
tery. There are 34 replacement foramina and,
thus, 34 columns of teeth, which is 20 more
than are typically present in the dentary of the
diplodocid Diplodocus (Holland 1924; fig.
5.2B). As there are no septa at any depth within
the alveolar trough, dentary teeth would have
erupted and migrated toward the functioning
wear surface as a self-supporting dental battery.
No other sauropod has a dentary with an alveo-
lar ramus of similar form lacking septa.
The upper and lower teeth are virtually identi-
cal in form (Sereno et al. 1999: fig. 2C; fig.
5.7). These similarities are based on the pre-
maxillary, maxillary, and dentary teeth in situ
in MNN GDF513. Upper and lower teeth differ
only in size; dentary teeth are smaller, perhaps
by as much as 20%–30%. This is difficult to
estimate more accurately because the avail-
able dentary teeth, a few of which remain
within the alveolar trough, are of unknown
maturity. A similar size differential, with
upper teeth larger and longer than the lowers,
has been observed in Diplodocus (Holland
1924:389) and the titanosaur Nemegtosaurus
(Wilson 2005: 305).
The numbers of premaxillary, maxillary, and
dentary tooth positions are 4, at least 24, and
34, respectively. Maxillary and dentary tooth
counts are approximately double those in other
diplodocoids such as Diplodocus (Holland,
1924; fig. 5.2B). Although the maxillary tooth
row is incomplete laterally, there are probably
only a few missing tooth positions, because the
length of the combined premaxillary and maxil-
lary tooth rows in MNN GDF513 is only slightly
less than that for the dentary. The higher num-
ber of tooth positions in the dentary (34 versus
approximately 30 for the premaxilla plus
FIGURE 5.7. Isolated tooth of Nigersaurus taqueti (MNN GDF513) in (A) lingual (internal), (B) mesial or distal (medial or
lateral), and (C) labial (external) views. de, dentine; e, enamel; ee, enamel edge; ewf, external wear facet; iwf, internal wear
facet. Scale bar equals 1 cm.
maxilla) is consistent with the smaller size of
the dentary teeth.
Crown shape and structure are uniform
among upper and lower teeth. Unworn crowns
are gently curved along their length and taper
gradually to a narrow, rounded tip, which
shows subtle wrinkles on its thickly enameled
labial (external) surface. Teeth in place in the
premaxilla and maxilla and near their natural
position in the dentary confirm that the crowns
are convex labially (anteriorly) in both the upper
and the lower jaws.
At midlength, the crown has a trapezoidal
cross section, with smooth enamel and a longi-
tudinal groove on each side that accommodates
the edges of adjacent crowns (Sereno et al.
1999:fig. 2D; fig. 5.7). Toward its tip, the crown
has an oval cross section. The enamel is approx-
imately eight times thicker on the labial (exter-
nal), as opposed to the lingual (internal), side of
the crown in both upper and lower teeth.
Whereas other diplodocids and some titanosauri-
ans have similar-shaped, narrow, cylindrical
crowns, markedly asymmetrical enamel has not
been reported previously among sauropods and
is absent in other diplodocoids (Dicraeosaurus
[Janensch 1935–1936:pl. 12, fig. 16], Diplodocus
[Holland 1924:fig. 6].
Although wear facets are not present in teeth
preserved in the holotypic jaw bones of
Nigersaurus taqueti, worn teeth referable to this
species have been recovered from many sites in
the Gadoufaoua beds and show a distinctive
pattern of wear. There is little reason to doubt
the reference of these teeth to Nigersaurus
taqueti, despite the presence of an unnamed
titanosaurian in the same horizons; the crowns
have narrow cylindrical proportions and highly
asymmetrical enamel.
Unlike the teeth in nearly all other
sauropods, those in Nigersaurus taqueti have a
pair of wear facets located on opposite sides of
the crown. The first—a labial (external) facet—
is typical of dicraeosaurids and diplodocids; it
cuts the crown at a high angle and appears to be
the product of nonocclusal abrasion (Holland
1924; Upchurch and Barrett 2000; fig. 5.7B, C).
The elevated, rounded rim of thick enamel sug-
gests that the wear facet was produced by
ingested plant matter rather than the harder
enameled edge of an opposing crown. The
second—a lingual (internal) facet—resembles
the internal facet on some narrow-crowned
titanosaurians; it cuts the crown at a low angle
and appears to be the product of occlusal abra-
sion (fig. 5.7B, C).
Archosaur teeth, primitively, are anchored by
alveoli that are separated from adjacent teeth by
bony septa. They erupt en echelon along the jaw
rather than in unison as a single unit. In most
dinosaurian herbivores, wear facets develop
from tooth-to-tooth occlusion at several points
along the tooth row rather than developing as a
continuous wear surface.
A tooth battery, by contrast, is here defined as
a tooth composite composed of self-supporting
teeth that erupt and wear in unison. The teeth
are supported by adjacent teeth and erupt as a
unit with wear surfaces that are continuous
from one tooth to the next. In Nigersaurus part
of the dentition fulfills these criteria—the pre-
maxilla and dentary tooth rows. These bones do
not have alveoli, intervening septa, or even well-
developed grooves to guide erupting tooth
columns. Rather, the teeth are packed into an
open alveolar trough.
Although all functioning (worn) teeth have
fallen away from the jaws of the holotypic spec-
imen, the tooth battery is intact within the body
of the premaxilla (fig. 5.3), as visualized in cross
and longitudinal sections with high-resolution
CT (fig. 5.4). Embryonic teeth migrate into the
alveolar trough via replacement foramina. As
they grow in length and diameter, they migrate
deeper into the body of the premaxilla before
passing ventrally out of the alveolar trough (fig.
5.4A). There appear to be as many as 10 teeth at
a single tooth position, from embryonic tooth to
wearing crown. The four tooth columns in the
premaxilla are arranged en echelon so that
the widest portion of a given crown contacts the
more tapered portion of adjacent crowns, with
the prominent edge of enamel lodged in a
groove on the side of adjacent crowns (fig. 5.4B).
Less is known about the structure of the
tooth battery of the dentary, although it was
probably very similar. The crowns have the
same shape, structure, and orientation. The
position of the replacement foramina near the
margin of the alveolar trough indicates that
embryonic teeth began their trajectory closer to
the open end of the trough and grew deep into
the alveolar trough before emerging at the
functional end of the tooth battery. The most
distal (lateral) tooth columns in the dental bat-
tery of the dentary must have angled anterolat-
erally as shown by the extension of the trough
lateral to the lateral most replacement foramen
(fig. 5.1B).
The body of the maxilla has septa separating
columns of teeth (fig. 5.5). Closer to the ventral
end of the maxilla, the septa give way to an open
trough with a groove for each tooth column on
anterior and posterior walls. As in the premax-
illa, there appear to have been at least 10 teeth
to a column medially and fewer laterally; an
incomplete sequence of 8 teeth is visible in the
first column (fig. 5.5). The maxillary teeth, pre-
sumably, emerged from the alveolar trough as a
self-supported tooth battery.
Exactly how the tooth batteries of Nigersaurus
functioned to produce the wear facets evident on
isolated teeth remains unsolved, despite knowl-
edge of the general structure of the tooth batter-
ies. What we can outline at this point are several
observations that provide some insight into the
We know that teeth in lower and upper tooth
rows do not match one-to-one given their dif-
fering sizes and numbers. We also know that
both upper and lower tooth batteries were con-
structed in a similar manner, with the convex,
thickly enameled crown surface facing labially
(anteriorly). Many mammals, such as rodents,
have analogous anteriorly positioned, self-
sharpening lower and upper incisors with lin-
gual (internal) wear facets (Taylor and Butcher
1951). As in Nigersaurus, both lower and upper
incisors are externally convex, with thickened
enamel on their labial (external) sides and wear
facets facing lingually (internally). This is the
closest analogy to the structure and orientation
of the individual teeth in Nigersaurus. Mam-
malian incisors like these, however, are much
more robust and are sharpened in a manner
very different from that in any dinosaur. The
chisel-shaped edge is maintained by breakage
(preferential chipping of the softer dentine) and
by tooth-to-tooth abrasion. Unlike Nigersaurus,
the facets on lower and upper incisors are not
symmetrical (the uppers typically have higher-
angle, stepped facets), and the shearing break-
age that keeps the leading edge sharp rarely pro-
duces facets that are uniformly planar.
We strongly suspect that the low-angle, lin-
gual (internal) wear facet was produced by tooth-
to-tooth abrasion, because the facet is extremely
flat and cuts smoothly across the external mar-
gin of enamel. The high-angle labial (external)
wear facet, in contrast, appears to have been pro-
duced by tooth-to-plant abrasion, because the
facet is concave, with a rounded, polished rim of
enamel along its trailing labial (external) edge
(fig. 5.7).
Because all of the isolated teeth from Niger,
England (Naish and Martill 2001), and Brazil
(Kellner 1996) show a similar pattern of wear—
with the low-angle facet first to appear—it is
likely that both lower and upper teeth are rep-
resented and wear in a similar manner. Yet it is
not clear how this is functionally possible.
Hadrosaurid and ceratopsian tooth batteries
have opposing, mirrored patterns of tooth wear:
the enamel is thickest on opposing sides of the
crown (medially in maxillary teeth, laterally in
dentary teeth); the crowns curve in opposite
directions (laterally in maxillary teeth, medially
in dentary teeth); and the wear facets occur in
opposing orientations (medially or ventromedi-
ally in maxillary teeth, laterally or dorsolaterally
in dentary teeth). Although an isolated ornithis-
chian tooth from a tooth battery may be difficult
to assign to either the upper or the lower tooth
row (when upper and lower crowns have a sim-
ilar shape and ornamentation), these teeth have
mirrored positions when they are found in
place. One possible explanation for the uniform
pattern of wear in Nigersaurus is that the lingual
(internal), low-angle facet is produced by the
lower crowns passing lingually (internally) to
the upper crowns (the usual tetrapod condition)
but that the lower crowns are worn away and
eventually obliterated in the process. If this
were true, the entire sample of isolated teeth of
Nigersaurus and related taxa found now on sev-
eral continents would include only premaxillary
and maxillary teeth from the upper tooth bat-
teries. If not, and if we are correct that the low-
angle facet is produced by tooth-to-tooth oc-
clusion, there must have existed an occlusal
mechanism unlike any described to date among
tetrapods—a mechanism capable of producing
low-angle, lingual (internal) wear facets on both
lower and upper crowns.
Another conundrum involves the cutting
edge of the crown. In ornithischians with tooth
batteries and in mammalian herbivores, thick-
ened enamel is always positioned along the cut-
ting edge. This is not the case in Nigersaurus.
Not only are the lower and upper teeth oriented
with their curvature and thickened enamel on
the same (external) side, but the leading wedge-
shaped edge of the crown is formed entirely of
dentine. It is difficult to understand how this
edge, which is perfectly straight, is maintained
in the course of wear without the protection of
enamel (fig. 5.7). Even if one envisages adjacent
crowns, it is hard to understand how the soft
leading edge of dentine would not be concave
from wear rather than straight.
A final observation suggests that the tooth
battery of Nigersaurus is quite different from
that in ornithischians. To produce an elongate,
low-angle wear facet on the lingual (internal)
side of the crown (fig. 5.7A), most of this side of
the crown must have been exposed. The suc-
ceeding replacement crown, in other words,
must have been positioned at a good distance
from the cutting edge of the functional crown.
Only one crown in each tooth column could
have been functional. In ornithischian denti-
tions, higher-angle wear facets allow more than
a single crown in the same tooth column to par-
ticipate in the active, cutting surface of the den-
tal battery.
In the future, we plan to digitally define and
prototype the intact portion of the tooth battery
within the premaxilla in the hope that it will
shed further light on how the battery func-
tioned during mastication.
In general proportions, the skull of Nigersaurus
taqueti bears little resemblance to that of
diplodocids (figs. 5.1, 5.2B). It has a more abbre-
viate, less prognathous snout; the depth of the
cranium is approximately 90% of its length (as
measured from the snout to the quadrate
condyle). This cranial proportion is even more
abbreviate than that of Camarasaurus (fig. 5.2A)
and Jobaria (Sereno et al. 1999), which have a
cranial depth between 50% and 60% of its
length. The external naris in Nigersaurus is large
and parasagittal in position as in Camarasaurus
and Jobaria. In diplodocids, in contrast, the exter-
nal naris is smaller, dorsally facing, and retracted
to a position anterodorsal to the orbit (the condi-
tion in dicraeosaurids is as yet unknown). The lat-
erotemporal fenestra in Nigersaurus is propor-
tionately elongate and extends anteriorly as far as
the antorbital fenestra and external nares, farther
than in any sauropod described to date. There is
no development of a preantorbital fenestra as
occurs in other neosauropods (fig. 5.2B). The der-
mal bones of the skull roof in Nigersaurus are
remarkably slender and delicate compared to
those of other sauropods including diplodocids.
The posterodorsal ramus of the maxilla, which
separates the external naris and antorbital fossa,
is reduced to an extremely delicate, strap-shaped
lamina 1 mm thick and a few millimeters wide
(fig. 5.1).
The lower jaw is easy to distinguish from that
in diplodocids (figs. 5.1, 5.2B). The coronoid
process on the surangular is prominent and
deep in lateral view, more closely resembling
that in the titanosaurian Rapetosaurus (Curry
Rogers and Forster 2004) than the low profile
jaws of diplodocids (fig. 5.2B). In Nigersaurus the
teeth are restricted to the transverse portion of
the anterior end of the skull, and at least the
lower tooth row extends lateral to the parasagittal
plane of the lower jaw. In both of these attrib-
utes, Nigersaurus is unique among dinosaurs.
Diplodocids show an incipient condition in these
regards; all but the lateral extremities of the tooth
rows are positioned along the anterior, trans-
verse margin of the skull, and the dentary tooth
row flares just beyond the parasagittal plane of
the posterior portion of the lower jaw.
A dentary from Upper Cretaceous rocks in
South America referred to Antarctosaurus wich-
mannianus (Huene 1929:69, pl. 29, fig. 5) is sim-
ilar to that in Nigersaurus taqueti in the extreme
breadth of the transverse portion of the ramus
and the concomitant increase in tooth count.
There are at least 24 teeth in the dentary, with the
majority (approximately 18) located in the broad,
transverse portion of the ramus. The dentary of
this South American form, however, is not as
derived as that in Nigersaurus. The teeth are set in
sockets rather than an undivided alveolar trough,
the tooth row is L-shaped rather than straight and
restricted to the transverse portion of the ramus,
and the symphysial surface is narrow rather than
circular. Despite these similarities, the phyloge-
netic affinity of Antarctosaurus is not yet resolved.
There is a possibility that this taxon, which was
found together with titanosaur cranial and post-
cranial remains, may have acquired these fea-
tures convergently with Nigersaurus.
Teeth that closely match those of Nigersaurus
taqueti in form, structure, and wear have
been described recently from slightly older
Barremian-age beds on the Isle of Wight (Naish
and Martill 2001:pl. 36) and from the Upper
Cretaceous Bauru Group in Brazil (Kellner
1996:fig. 7). The crowns are narrow and sub-
cylindrical and, at midlength, have a trapezoidal
cross section. The size, form, and angle of the
pair of wear facets are exactly like those
described above for Nigersaurus taqueti. As
noted by Kellner (1996:619), the low-angle lin-
gual (internal) facet is the first to appear and is
always more elongate than the labial (external)
facet, as preserved in progressively worn
crowns. The enamel may have an asymmetri-
cal distribution on the crown, but this needs
firsthand verification. Kellner provisionally
regarded these teeth as titanosaurian, because
of the predominance of titanosaurian postcra-
nial bones from the same beds. It is very prob-
able, however, that these Brazilian teeth belong
to a rebbachisaurid diplodocoid that lived on
South America in the Late Cretaceous. (e.g.,
Limaysaurus; Salgado et al. 2004).
In other diplodocoids, the teeth are larger
relative to the jaw bones and anchored in indi-
vidual alveoli (fig. 2B; Dicraeosaurus [Janensch
1935–1936:figs. 107, 111]; fig. 2B). The crowns
have a circular cross section, symmetrical
enamel, and a single low-angle, labial (external)
wear facet (Holland 1924). Despite some varia-
tion, isolated teeth of Dicraeosaurus show the
same external facet (Janensch 1935–1936:pl. 12,
figs. 23, 25). This facet is characterized by a
rounded lip of enamel along its trailing (external)
edge (fig. 5.7; ewf) and scratches that course
across the dentine from the internal to the exter-
nal sides (Fiorillo 1991; Calvo 1994b; Upchurch
and Barrett 2000). How this wear facet formed
has remained a mystery ever since Holland
(1924) summarized early speculation, which
included scraping cycad trunks (Holland),
procuring fish hiding in stream beds (Tornier),
and munching on freshwater bivalves (Sternfeld).
Because Holland (1924:fig. 4) depicted “Diplod-
ocus seizing a mussel,” that hypothesis gained
the upper hand, although Holland maintained
no personal preference. More recent proposals
include stripping leaves from branches (Dodson
1990; Barrett and Upchurch 1994) and raking
bark (Bakker 1986). Nigersaurus adds a new wrin-
kle. Here we see the same kind of external facet
in teeth set into a tooth battery. These batteries, in
turn, are housed in a skull with a very different
shape and even more delicate construction than
in diplodocids (fig. 5.2).
Some titanosaurians have narrow-crowned
teeth that bear a general resemblance to those of
Nigersaurus taqueti, but these teeth have more
robust proportions (e.g., Kellner and Mader
1997:fig.2; Rapetosaurus [Curry Rogers and
Forster 2004:fig. 32]). The internal (lingual)
facet—the only one present—cuts the crown at
a low angle. An external (labial) facet has
never been described outside Diplodocoidea.
Nemegtosaurus, which has internal V-shaped and
apical wear facets (Nowinski 1971; Wilson
2005), has continued to confuse discussions of
tooth form and masticatory style among
diplodocoids (e.g., Upchurch and Barrett 2000).
Nemegtosaurus and the conspecific, or closely
allied, Quaesitosaurus from the Late Cretaceous
of Asia are better understood as titanosaurians
rather than diplodocoids (Calvo 1994a; Wilson
and Sereno 1998; Wilson 2002, 2005).
Nigersaurus taqueti must be placed within the
context of diplodocoid phylogeny to better under-
stand how its novel tooth battery evolved
(fig. 5.9). Diplodocoids include diplodocids,
dicraeosaurids, and rebbachisaurids. Diplodocids
are best known from the Late Jurassic of North
America and include Diplodocus, Apatosaurus,
FIGURE 5.8. Fi fth cervical vertebra and co-ossified rib of Nigersaurus taqueti (MNN GDF512) in lateral view. asp, anterior
spine; ns, neural spine; pl, pleurocoel; poz, postzygapophysis; prz, prezygapophysis; rs, rib shaft. Scale bar equals 5 cm.
Barosaurus, and others (Hatcher 1901; Holland
1924; Berman and McIntosh 1978; Ostrom
and McIntosh 1999). Dicraeosaurids include
Dicraeosaurus (Janensch 1935–1936) from the
Late Jurassic of Africa and the long-spined
Amargasaurus from the Early Cretaceous of South
America. Rebbachisaurids include Limaysaurus
(Calvo and Salgado 1995; Salgado et al. 2004)
from the Early Cretaceous of South America
and Nigersaurus (Sereno et al. 1999) and
Rebbachisaurus (Lavocat 1954) from the mid- and
Late Cretaceous of Africa. Rebbachisaurid teeth
and other fragmentary remains indicate that the
group was also present in Europe and persisted
to the end of the Cretaceous at least in South
America. As a sister taxon to dicraeosaurids and
diplodocids, rebbachisaurids must have diverged
from other diplodocoids before the end of the
Late Jurassic, although no trace of the group has
yet been found from this period (fig. 5.9).
Although the teeth of Nigersaurus are partic-
ularly slender, all diplodocoids are characterized
by proportionately narrow, subcylindrical
crowns that are only weakly expanded and
flattened (fig. 5.9, node 1). The rate of tooth
replacement, in addition, appears to have been
accelerated across the group, although this is
most apparent in Nigersaurus. In this regard, we
srm ewf
34 db 1
FIGURE 5.9. Phylogram showing the relationships and recorded durations of the three principal diplodocoid clades (Reb-
bachisauridae, Dicraeosauridae, Diplodocidae) and some of their feeding specializations. Node 1 (Diplodocoidea): slender
cylindrical crowns, low-angle external (labial) wear facet, teeth restricted anteriorly in subrectangular muzzle. Node 2 (Di-
craeosauidae + Diplodocidae): bifid cervical neural spines. Node 3 (Diplodocidae): nares retracted, 15 cervical vertebrae. Node 4
(Rebbachisauridae): low-angle, internal wear facet, increase in tooth number, asymmetrical enamel, dental batteries in some
taxa. 1–34, dentary teeth 1 through 34; 2–15, cervical vertebrae 2–15; db, dental battery; en, external naris; ewf, external wear
facet; iwf, internal wear facet; ns, neural spine; srm, subrectangular muzzle.
assume that the number of teeth in a single col-
umn is related to the replacement rate.
Diplodocus, for example, has as many as six
teeth in a single column in the maxilla (Marsh
1884:pl. 4, fig. 3). Worn diplodocoid teeth have
a characteristic external, low-angle, wear facet
on both upper and lower teeth (fig. 5.7 ewf)
that must have formed from tooth-to-plant
abrasion (contra Calvo 1994b; Barrett and
Upchurch 1994; Upchurch and Barrett 2000).
Most diplodocoid teeth are positioned in a
transverse row along the squared anterior mar-
gin of the snout (fig. 5.9, node 1).
Nigersaurus has further developed a number
of these features (fig. 5.9, node 2). Tooth size
decreases relative to the size of the jaw bones,
and tooth number increases to 30 or more in
lower and upper tooth rows. In Nigersaurus the
teeth are restricted to the anterior margin of the
snout and extend lateral to the sagittal plane of
the lower jaw, features unknown elsewhere
among dinosaurs. More teeth are present in a
single column, and the rate of replacement, pre-
sumably, has increased as well. Most of the teeth
in the jaws are pressed so close to one another
that there are no intervening septa and, for the
first time among sauropods, batteries of self-
supporting teeth erupt as a single unit. Although
still a functional conundrum, an additional low-
angle wear facet appears on the lingual (internal)
side of the active crowns in both lower and upper
tooth batteries.
Dicraeosaurids and diplodocids evolved
other features that likely impacted food procure-
ment but are not present in Nigersaurus or other
rebbachisaurids. These include a reduction in
the number of teeth, a projecting “chin” on the
dentary, a relative lengthening of the snout,
retraction of the external nares, and an increase
in the length and number of cervical vertebrae
(fig. 5.9, nodes 3, 4). In dicraeosaurids and
diplodocids, in addition, the resting curvature of
the neck arches anteroventrally (Janensch 1929;
Stevens and Parrish 1999). This is not the case
in Nigersaurus, as exemplified by the fifth cervi-
cal vertebra (fig. 5.8).
Tooth batteries evolved twice among ornithis-
chian dinosaurs from a hypothetical common
ancestor with a simple dentition characterized
by a suite of ornithischian features related to
herbivory—a predentary, cheek embayments on
the dentary and maxilla, asymmetrical enamel
in dentary and maxillary crowns, and wear
facets from tooth-to-tooth occlusion on the buc-
cal (lateral) and lingual (medial) sides of dentary
and maxillary teeth, respectively. Evolution of
tooth-supported batteries occurred first among
ornithopods, with initial changes toward a den-
tition occurring before the close of the Jurassic,
and later among ceratopsian dinosaurs, where
all structural changes occurred during the Late
Cretaceous (Sereno 1997, 2000).
The fully developed tooth batteries in
hadrosaurids and ceratopsids are structurally
very similar, evolved in comparable stages, and
involved an increase in body size of approxi-
mately an order of magnitude (Sereno 1997: fig.
7; 2000: fig. 25.9). Independent but similar
structural changes include a relative decrease in
tooth size and increase in tooth columns and
replacement rate, the loss of alveolar septa,
restriction of the enamel to opposing sides of the
crown in maxillary versus dentary teeth, an
increase in the prominence of a ridge on the
enameled side of the crown, adjustment of the
crown shape for efficient packing, an increase in
the volume of supporting bone in the maxilla
and dentary, a reduction of postdentary elements
in the lower jaw, and the development of a coro-
noid process with an expanded process for mus-
cular attachment.
The circumstances surrounding the evolu-
tion of tooth batteries in rebbachisaurid
sauropods bear a few similarities to and many
striking differences from those in ornithischi-
ans. Similarities include the reduction of tooth
size, increase in number of tooth columns,
increase in replacement rate (or at least the
number of teeth per column), loss of alveolar
septa between tooth columns, thickened
enamel on one side of the crown and near-loss
of enamel on the other, and adjustment of crown
shape for efficient packing. These similarities,
thus, are confined to the size, shape, number,
and rate of replacement of the teeth and the
asymmetrical distribution of enamel.
Fundamental differences begin with timing.
Available rebbachisaurid fossils suggest that a
tooth battery among sauropods had evolved some-
time during the Early Cretaceous; the teeth from
the Isle of Wight (Naish and Martill 2001) look
very similar to those of Nigersaurus and are
Barremian (ca. 125 Ma; middle Early Cretaceous)
in age. This postdates the establishment of tooth-
supported dentitions in ornithopods (Late
Jurassic) but predates the appearance of ceratop-
sian tooth batteries (Late Cretaceous). Another
basic difference involves body size. There was no
increase in body size among sauropods concomi-
tant with the development of tooth batteries.
Although Rebbachisaurus ranks among the largest
of sauropods, Nigersaurus ranks among the small-
est, with a body length of approximately 15 m.
The orientations of the tooth batteries are
diametrically opposed. The tooth batteries have
an anteroposterior, rather than a transverse, ori-
entation in ornithischians and rebbachisaurids,
respectively. The ornithischian tooth battery is
located posteriorly within the jaws and used for
food processing; cropping is a function of an
expanded, toothless bill. The sauropod dental
battery, in contrast, is located anteriorly and may
have been used primarily in cropping.
The presence or absence of gastroliths as an
accessory means to break down plant matter may
be correlated with the aforementioned funda-
mental functional differences. The absence of
gastroliths among ornithischians with advanced
dentitions (euornithopods, neoceratopsians)
including dental batteries suggests that more effi-
cient oral processing of plant matter has replaced
gut-processing by gastroliths (Sereno 1997:473).
In sauropods, in contrast, the group in which
dental batteries evolved (diplodocoids) has the
greatest proven incidence of gastroliths, suggest-
ing that their derived dental features did not func-
tion primarily in the breakdown of plant matter.
Gastroliths are present in rebbachisaurids (Calvo
1994b), dicraeosaurids (Janensch 1929), and
diplodocids (Cannon 1906; Brown 1941; Gillette
1990). The absence of gastroliths among
nondiplodocoid sauropods is based on many
articulated skeletons of Shunosaurus,
Camarasaurus, Jobaria, and Opisthocoelicaudia.
Cedarosaurus, a macronarian sauropod of uncer-
tain affinity, is thus far the only nondiplodocoid
sauropod with gastroliths (Sanders et al. 2001).
The pattern of wear in the rebbachisaurid
tooth battery is completely different from that
in ornithischians, which uses thickened enamel
and tooth-to-tooth occlusion to form a self-
sharpening cutting margin. In rebbachisaurids,
only one of a pair of wear facets is formed by
tooth-to-tooth occlusion, the sharp leading edge
of worn crowns is formed in dentine rather
than enamel, the thickened enamel is located
on the same (labial) side of lower and upper
crowns, and lower and upper crowns appar-
ently have identical wear patterns.
The locus of the most rapid replacement and
wear is different in ornithischian and reb-
bachisaurid tooth batteries. In ornithischians,
the crown size, the number of teeth in a col-
umn, and the distance of the replacement fora-
men from the alveolar margin are all greatest in
the middle of the tooth battery. In Nigersaurus,
in contrast, the crown size, the number of teeth
in a column, and, to a lesser degree, the distance
of the replacement foramen from the alveolar
margin are all greatest toward the midline.
Finally, the tooth-bearing bones are con-
structed differently in ornithischians and
sauropods with dental batteries. In ornithischi-
ans with tooth batteries, the dentary, in particu-
lar, is robustly constructed, with a thick and
prominent coronoid process for attachment of
substantial adductor musculature. Postdentary
elements are greatly reduced in size. This pat-
tern of change in the lower jaw closely mirrors
changes that occurred earlier in the evolution
of the mammalian masticatory apparatus
(Allin 1975). In Nigersaurus, in contrast, the
tooth-bearing elements are constructed of thin
laminae, the dentary does not gain in relative
length in the lower jaw, the coronoid process is
developed as a thin plate of bone, and the
supratemporal fenestra (the usual origin of
adductor musculature) is closed by approxima-
tion of surrounding bones.
Early in their evolution, sauropods adopted
tooth-to-tooth occlusion and, in consequence,
evolved lower and upper tooth rows of equivalent
length, characteristic patterns of wear facets, a
more substantial coronoid process, and a robust
mandibular symphysis (McIntosh 1990; Calvo
1994a; Wilson and Sereno 1998; Upchurch and
Barrett 2000). Among sauropods, it is now
apparent that diplodocoids evolved complex den-
titions during the Cretaceous, as exemplified by
the dental batteries of a recently named African
rebbachisaurid, Nigersaurus taqueti (Taquet 1976;
Sereno et al. 1999).
The dental battery on each side of the
upper and lower jaws is composed of more
than 30 columns of teeth that are packed into
a tight self-supporting unit in the premaxilla
and dentary. Individual teeth have slender rod-
shaped crowns characterized by highly asym-
metrical enamel. Dentary teeth are somewhat
smaller than but otherwise similar to premax-
illary and maxillary teeth. The crowns in both
lower and upper jaws have thickened enamel
on their convex labial (external) side. Wear
produces two stereotypical facets, the first
appearing as a low-angle, lingual (internal)
facet produced by tooth-to-tooth occlusion and
the second as a high-angle, labial (external)
facet produced by tooth-to-plant abrasion.
Both facets are well developed on crowns with
significant wear, resulting in a straight, sharp
apical wedge of dentine where the facets inter-
sect. How either of these facets was produced
remains a significant, and largely unanswered,
Unlike the parasagittal dental batteries of
ornithischians, the dental battery in Nigersaurus
is oriented transversely and may have been used
for cropping rather than prolonged oral process-
ing. Although the rebbachisaurid dental battery
is preserved only in Nigersaurus, isolated teeth
from Lower Cretaceous horizons on the Isle of
Wight and rocks of Late Cretaceous age in Brazil
suggest that related forms with potentially a sim-
ilar degree of dental complexity were present on
other continents. It is highly unlikely, however,
that rebbachisaurids with dental batteries ever
achieved the taxonomic diversity of ornithischi-
ans with dental batteries (hadrosaurids, ceratop-
sids) in Late Cretaceous faunas of North America
and Asia.
Dental batteries evolved three times inde-
pendently within Dinosauria—in euornithopod
and neoceratopsian ornithischians and in reb-
bachisaurid sauropods. Fundamental functional
differences coupled with their diachronous
appearance suggest that dinosaurian dental bat-
teries did not evolve in response to a single envi-
ronmental cue, such as the rise of angiosperms
during the mid-Cretaceous (Sereno 1997: Sereno
1999; Barrett and Willis 2001).
We thank members of the 1997 and 2000
expeditions for discovering the material, C.
Abraczinskas for drawing from specimens and
executing final drafts of reconstructions, E.
Dong, T. Keillor, and R. Masek for preparing
fossils, and B. Gado (Institut de Recherche en
Science Humaine), and I. Kouada (Ministère de
L’Enseignement Supérieur de la Recherche et
de la Technologie) for granting permission to
conduct fieldwork. This research was funded by
The David and Lucile Packard Foundation, the
National Geographic Society, the Comer
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... Moreover, rapid rates of growth (e.g., Curry, 1999;Lehman and Woodward, 2008;Sander et al., 2011) and unique morphologies often linked to specific niches and novel modes of food procurement (e.g., Christian et al., 2013;Hummel et al., 2008;Stevens and Parrish, 2005;Whitlock, 2011) may have driven their success as ecological titans. Dental complexes of sauropod dinosaurs have been studied in Diplodocidae, Rebbachisauridae, and Camarasauridae (D'Emic et al., 2013;Schwarz et al., 2015;Sereno et al., 2005;Stevens and Parrish, 2005) demonstrating that dental morphology and physiology (i.e., tooth and alveolar arrangement and tooth replacement strategies) directly impact feeding, digestion, and even food procurement. As such, these dental systems can provide considerable insight into sauropod paleobiology and paleoecology (e.g., Barrett and Upchurch, 1995;Fiorillo, 1998;Gee, 2011;McHugh, 2018;Tütken, 2011). ...
... Dietary habits and adaptations in sauropods have dominantly been studied through the lenses of rates of tooth replacement, neck biomechanics, tooth microwear, snout shapes, species richness, and estimates of population densities (e.g., Barrett and Upchurch, 1995;D'Emic et al., 2013;Fiorillo, 1998;Gee, 2011;McHugh, 2018;Schwarz et al., 2015;Sereno et al., 2005;Stevens and Parrish, 2005;Tütken, 2011;Whitlock, 2011;Whitlock et al., 2018). These studies reveal a wide range of diet-linked morphologies among different taxa; however, variance in the number of replacement teeth observed in the premaxilla, maxilla, and dentary among apatosaurine sauropods has yet to be fully investigated. ...
... Among neosauropods, tooth replacement in the premaxillae, maxillae, and/or dentaries have been described in a variety of taxa, including the flagellicaudatan genera Dicraeosaurus, Diplodocus, and Apatosaurus, the macronarian genera Brachiosaurus and Camarasaurus, and the rebbachisaurid genus Nigersaurus (Table 1) (D'Emic et al., 2013(D'Emic et al., , 2019McHugh, 2018;Schwarz et al., 2015;Sereno and Wilson, 2005). Of these taxa, macronarians are measurably disparate from those of the clades Flagellicaudata (including TATE-099) and Rebbachisauridae in tooth volume, shape, replacement rate, as well as fewer numbers of replacement teeth (D'Emic et al., 2013(D'Emic et al., , 2019. ...
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Dental complexes of sauropod dinosaurs have been studied in members of Diplodocoidea and Macronaria. However, the disparity among the number of replacement teeth between the premaxilla, maxilla, and dentary of apatosaurine sauropods has yet to be fully investigated. TATE-099, a nearly complete and associated apatosaurine skull and dental complexes from the upper Morrison Formation (Upper Jurassic) at Como Bluff, Wyoming, contains cranial characters consistent with Apatosaurus sp. Unerupted dental complexes of the right premaxilla, maxilla, and dentary were imaged and digitally reconstructed using computed tomography (CT). Results indicate four premaxillary alveolar positions each with 5-7 unerupted replacement teeth, 10 maxillary alveolar positions each with 3-5 unerupted replacement teeth, and 10 dentary alveolar positions each with only 1-2 unerupted replacement teeth. The capacity of replacement teeth in TATE-099 is higher than reported in the genus Diplodocus and consistent with data from previous studies on niche partitioning among coeval Morrison Formation sauropods. Disparity among the capacity of dental complexes of TATE-099 further suggests novel feeding mechanics in apatosaurines. CT data also support a new hypothesis of tooth replacement in diplodocids, where entire rows of teeth are replaced as a single unit, rather than individually. The high-capacity of replacement teeth in the premaxilla is only known to be succeeded by one taxon (Nigersaurus) and suggests frequent wear of the premaxillary teeth. However, considerably fewer replacement teeth in the dentary of TATE-099 suggests less-frequent. These results offer insight into the feeding mechanisms and disparity of sauropods within Flagellicaudata.
... Both the Amazonsaurus maranhensis (de et al. 2003) from the Itapecuru Formation and Itapeuasaurus cajapioensis (Lindoso et al. 2019) from the Alcântara Formation do not have any type of preserved or associated dental material. This, in addition to a dentition that is either very autapomorphic, as seen in the African taxon Nigersaurus taqueti (Sereno and Wilson 2005), or is very convergent with that seen in derived lithostrotians (Fernández-Baldor et al. 2011;Zaher et al. 2011;Wilson et al. 2016), can make it difficult to identify these isolated teeth. ...
Dinosaur fossils are commonly found in Brazilian Mesozoic strata, with teeth being frequently found in Cretaceous outcrops. Many studies have been made with the aim of reviewing the known diversity of Brazilian dinosaurs, mostly focusing solely on their palaeobiogeography. However, few tried to typify these body fossils in order to see which kinds were most prevalent in the fossil record. This study aims to count and identify all occurrences of non-avian dinosaur teeth (isolated or in situ) unearthed from Brazilian Cretaceous strata in order to objectively measure their representativity in the national fossil record. Our literature search showed that almost half of the dinosaur fossil record from the Cretaceous of Brazil is composed by teeth, those being particularly abundant in the Alcântara, Adamantina and Marília formations. Theropod teeth are more abundant in comparison to sauropod teeth, with spinosaurids, deinonychosaurs, and abelisaurids being amply found. Despite representing a large share of the Brazilian fossil record, dinosaur teeth have only recently been studied in depth, with many specimens being reassessed through the current identification methods. Other aspects besides primary taxonomic identification can also be further explored using the latest technologies on dinosaur teeth, allowing a deeper understanding of the palaeobiology of these reptiles.
... Among 'derived' titanosaurs, there is evidence for two main jaw shapes: jaws with rounded ends, like those of Ampelosaurus, Karongasaurus, Malawisaurus, Mansourasaurus, Nemegtosaurus, Quaesitosaurus, Rapetosaurus and Tapuiasaurus [17][18][19][20][21][22]115,160,168]; and squared-off jaws, like those of Antarctosaurus, Baalsaurus, Bonitasaura and Brasilotitan [141,145,[162][163][164][165]. This disparity parallels that seen in diplodocoids [105]: some have rounded jaws, such as the dicraeosaurids Suuwassea emilieae and Dicraeosaurus hansemanni [25,166]; some have squared-off jaws, such as the diplodocids Apatosaurus louisae, Diplodocus longus and Tornieria africana, and the rebbachisaurid Lavocatisaurus agrioensis [25,213,303,307]; and others have squared-off and transversely expanded jaws, namely the rebbachisaurid Nigersaurus [110,308,309]. ...
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Titanosaurian sauropod dinosaurs were diverse and abundant throughout the Cretaceous, with a global distribution. However, few titanosaurian taxa are represented by multiple skeletons, let alone skulls. Diamantinasaurus matildae, from the lower Upper Cretaceous Winton Formation of Queensland, Australia, was heretofore represented by three specimens, including one that preserves a braincase and several other cranial elements. Herein, we describe a fourth specimen of Diamantinasaurus matildae that preserves a more complete skull—including numerous cranial elements not previously known for this taxon—as well as a partial postcranial skeleton. The skull of Diamantinasaurus matildae shows many similarities to that of the coeval Sarmientosaurus musacchioi from Argentina (e.g. quadratojugal with posterior tongue-like process; braincase with more than one ossified exit for cranial nerve V; compressed-cone–chisel-like teeth), providing further support for the inclusion of both taxa within the clade Diamantinasauria. The replacement teeth within the premaxilla of the new specimen are morphologically congruent with teeth previously attributed to Diamantinasaurus matildae, and Diamantinasauria more broadly, corroborating those referrals. Plesiomorphic characters of the new specimen include a sacrum comprising five vertebrae (also newly demonstrated in the holotype of Diamantinasaurus matildae), rather than the six or more that typify other titanosaurs. However, we demonstrate that there have been a number of independent acquisitions of a six-vertebrae sacrum among Somphospondyli and/or that there have been numerous reversals to a five-vertebrae sacrum, suggesting that sacral count is relatively plastic. Other newly identified plesiomorphic features include: the overall skull shape, which is more similar to brachiosaurids than ‘derived' titanosaurs; anterior caudal centra that are amphicoelous, rather than procoelous; and a pedal phalangeal formula estimated as 2-2-3-2-0. These features are consistent with either an early-branching position within Titanosauria, or a position just outside the titanosaurian radiation, for Diamantinasauria, as indicated by alternative character weighting approaches applied in our phylogenetic analyses, and help to shed light on the early assembly of titanosaurian anatomy that has until now been obscured by a poor fossil record.
... An increase in relative crown height has been observed to some extent in sauropods 75 , while an increase in the number of teeth, in terms of accelerated tooth replacement, increased numbers of replacement teeth, and increased tooth counts are known in many dinosaur groups (e.g. sauropods 59,76 ; hadrosaurids 3,63 ; ceratopsids 14,77 ). However, it appears that marked asymmetrical thickening of the dentine component of the tooth crown only occurs in some basal iguanodontians, where tooth replacement has not yet accelerated to the same high rates seen in later-branching taxa, but where continual tooth-tooth occlusion and/or less frequently replaced teeth with longer functional lives require more resistant teeth. ...
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Dentitions of the sympatric herbivorous dinosaurs Hungarosaurus (Ankylosauria, Nodosauridae) and Mochlodon (Ornithopoda, Rhabdodontidae) (Santonian, Hungary) were analysed to investigate their dietary ecology, using several complementary methods—orientation patch count, tooth replacement rate, macrowear, tooth wear rate, traditional microwear, and dental microwear texture analysis (DMTA). Tooth formation time is similar in Hungarosaurus and Mochlodon, and traditional and DMTA microwear features suggest low-browsing habits for both taxa, consistent with their inferred stances and body sizes. However, Mochlodon possesses a novel adaptation for increasing dental durability: the dentine on the working side of the crown is double the thickness of that on the balancing side. Moreover, crown morphology, enamel thickness, macrowear orientation, and wear rate differ greatly between the two taxa. Consequently, these sympatric herbivores probably exploited plants of different toughness, implying dietary selectivity and niche partitioning. Hungarosaurus is inferred to have eaten softer vegetation, whereas Mochlodon likely fed on tougher material. Compared to the much heavier, quadrupedal Hungarosaurus, the bipedal Mochlodon wore down more than twice as much of its crown volume during the functional life of the tooth. This heavy tooth wear might correlate with more intensive food processing and, in turn, could reflect differences in the metabolic requirements of these animals.
... Paradoxically, the dinosaurs with the most significant masticatory forces applied to their cheek teeth, the ornithischians, lose mantle dentin altogether, although this has been linked to the development of a tooth battery (Wang et al., 2015). Corroborating evidence of this in sauropods comes from the rebbachisaurid Nigersaurus taqueti, previously hypothesized to have a dental array approximating a battery (Sereno and Wilson, 2005;Sereno et al., 2007). In that taxon, although mantle dentin is present, it is very thin (<5 µm; see Sereno et al., 2007: fig. ...
... In Malawi, lithostrotian titanosaurs were established as early as the Aptian [217][218][219][220][221][222], with evidence that Karongasaurus, which has narrow, chisel-like teeth, lived alongside Malawisaurus, which has broader, compressed-cone-chisel-like teeth [222]. Aptian-Albian deposits in Niger are dominated by rebbachisaurids [223][224][225][226], although titanosauriforms ( probably somphospondylans) were also present [227]. Aptian-Albian deposits in Cameroon preserve narrow-crowned sauropod teeth [228], possibly attributable to Somphospondyli [227]. ...
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The Upper Cretaceous Winton Formation of Queensland, Australia, has produced several partial sauropod skeletons, but cranial remains—including teeth—remain rare. Herein, we present the first description of sauropod teeth from this formation, based on specimens from three separate sites. An isolated tooth and a dentary fragment from the Diamantinasaurus matildae type locality are considered to be referable to that titanosaurian taxon. A single tooth from the D. matildae referred specimen site is similarly regarded as being part of that individual. Seventeen teeth from a new site that are morphologically uniform, and similar to the teeth from the two Diamantinasaurus sites, are assigned to Diamantinasauria. All sauropod teeth recovered from the Winton Formation to date are compressed-cone-chisel-shaped, have low slenderness index values (2.00–2.88), are lingually curved at their apices, mesiodistally convex on their lingual surfaces, and lack prominent carinae and denticles. They are markedly different from the chisel-like teeth of derived titanosaurs, more closely resembling the teeth of early branching members of the titanosauriform radiation. This provides further support for a ‘basal’ titanosaurian position for Diamantinasauria. Scanning electron microscope microwear analysis of the wear facets of several teeth reveals more scratches than pits, implying that diamantinasaurians were mid-height (1–10 m) feeders. With a view to assessing the spatio-temporal distribution of sauropod tooth morphotypes before and after deposition of the Winton Formation, we provide a comprehensive continent-by-continent review of the early titanosauriform global record (Early to early Late Cretaceous). This indicates that throughout the Early–early Late Cretaceous, sauropod faunas transitioned from being quite diverse at higher phylogenetic levels and encompassing a range of tooth morphologies at the start of the Berriasian, to faunas comprising solely titanosaurs with limited dental variability by the end-Turonian. Furthermore, this review highlights the different ways in which this transition unfolded on each continent, including the earliest records of titanosaurs with narrow-crowned teeth on each continent.
The sauropod genus Mamenchisaurus, from the Late Jurassic–Early Cretaceous of East Asia, has a convoluted taxonomic history. Although included in the first cladistic analysis of sauropods, only recently has the monophyly of Mamenchisaurus, and the anatomical diversity of the many penecontemporaneous East Asian eusauropods, been evaluated critically. Here, we re-describe the holotype and only specimen of M. sinocanadorum. Although the original diagnosis is no longer adequate, we identify several autapomorphies that support the validity of this species, including an elongate external mandibular fenestra and distinctive pneumatic structures on the cervical centra. We incorporate new data into a phylogenetic character matrix that also includes Bellusaurus and Daanosaurus, both of which are known only from juvenile material and are often hypothesized to be neosauropods (or close relatives thereof). We recover all species of Mamenchisaurus as part of a radiation of predominantly Middle–Late Jurassic East Asian eusauropods, but the genus is non-monophyletic, underscoring the need for further systematic revision of mamenchisaurid taxonomy. Analyses that score ontogenetically variable characters ambiguously recover Bellusaurus and Daanosaurus as juvenile mamenchisaurids, a hypothesis supported by several features that are unique to mamenchisaurids or exhibit little homoplasy, including anteriorly bifurcate cervical ribs. Finally, computed-tomography reveals extensive vertebral pneumaticity in M. sinocanadorum that is comparable to that of the largest sauropods, and updated scaling analyses imply a neck over 14 m long, rivalling estimates for other exceptionally long-necked sauropods. Previous work has suggested that the elongated cervical ribs of particularly long-necked sauropods such as M. sinocanadorum stabilized the neck by limiting its mobility. Given that extent of pneumaticity responds dynamically to a bone’s habitual loading, we propose that long cervical ribs – and other structural modifications that limited flexibility – promoted the evolution of increasingly long necks by producing a more predictable biomechanical milieu amenable to increased pneumatization.
With 17 species formally identified throughout the world, Rebbachisauridae is, at present, the best-represented group of South American diplodocoids, and it has a temporal record ranging from the Barremian up to the Turonian. Defined as all diplodocoids more closely related to Rebbachisaurus garasbae than to Diplodocus carnegii, these sauropods are characterized by postcranial synapomorphies (e.g., absence of the hyposphenal ridge on anterior caudal vertebrae; presence of spinodiapophyseal lamina in caudal vertebrae). Although relatively complete skulls are known in only a few genera (Limaysaurus, Lavocatisaurus, and Nigersaurus), the whole cranial evidence indicates that they were highly specialized with respect to other diplodocoids (for instance Diplodocidae). South America counts ten genera of Rebbachisauridae, most of them from the Argentine Patagonia. They embrace a rather diverse group of basally branching forms (Amazonsaurus, Zapalasaurus, Comahuesaurus, and Lavocatisaurus), derived forms (as the limaysaurines Limaysaurus and Cathartesaura and the rebbachisaurines Katepensaurus and Itapeuasaurus), together with forms of uncertain phylogenetic filiation (Rayososaurus). Rebbachisaurids were important in South America toward the end of the Early Cretaceous, integrating, at that time, the sauropod faunas together with macronarians (Titanosauriformes) and other diplodocoids (Dicraeosauridae). They persisted up to at least the Turonian, being the last diplodocoids in becoming extinct globally.
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Rapetosaurus krausei (Sauropoda: Titanosauria) from the Upper Cretaceous Maevarano Formation of Madagascar is the best-preserved and most complete titanosaur yet described. The skull of Rapetosaurus is particularly significant because most titanosaurs are diagnosed solely on the basis of fragmentary postcranial material, and knowledge of the titanosaur skull has remained incomplete. Material referred to Rapetosaurus includes the type skull from an adult that preserves the basicranium, rostrum, mandible, and palate. A second, juvenile skull preserves most of the braincase and cranial vault, as well as some of the palate and lower jaw. Here we provide a detailed description of Ropetosaurus cranial anatomy and highlight comparative relationships among known titanosaur and other neosauropod skulls. The Rapetosaurus skull is similar to those of diplodocoids in its overall shape, with retracted external nares and an elongated snout. However, extensive tooth distribution and bone articulations surrounding the external narial region and orbit are more similar to those of macronarians like Camarasaurus and Brachiosaurus. The maxilla, basicranium, paroccipital process, and pterygoid are among the most diagnostic elements of the Rapetosaurus skull, along with the enlarged antorbital fenestra, anteroventrally oriented braincase, and mandible. Titanosaur crania exhibit a greater diversity than previously recognized and, in light of Rapetosaurus, it is apparent that there is not a narrowly constrained bauplan for the skull of titanosaurs. Broad generalizations about evolution based on previously known, fragmentary fossils require re-evaluation. Ultimately, Rapetosaurus will be key in resolving titanosaur higher-level and ingroup phylogeny.
The newly organized Long Island Natural History Museum (LINHM) has assembled a small collection of fossil vertebrates from the Cretaceous of Morocco. Among the remains in this collection are two spinosaurid (Theropoda) teeth and one sauropod tooth that we refer to either the Diplodocidae or Titanosauridae. Because of the scarcity of spinosaurid and Cretaceous sauropod teeth, a short description of the material is presented here. In addition to the dinosaurian remains, the collection includes an unidentified crocodilian tooth and a tooth identified tentatively as that of a pterosaur, which we also describe briefly. Furthermore, there are other fossil reptile teeth from the Ksar es Souk Province in the collections of the LINHM. Some of these may represent groups of reptiles other than those discussed here, but the taxonomic identity of these teeth is still being determined.