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ARTICLE
VELAFRONS COAHUILENSIS, A NEW LAMBEOSAURINE HADROSAURID (DINOSAURIA:
ORNITHOPODA) FROM THE LATE CAMPANIAN CERRO DEL PUEBLO FORMATION,
COAHUILA, MEXICO
TERRY A. GATES,
*,1
SCOTT D. SAMPSON,
1
CARLOS R. DELGADO DE JESÚS,
2
LINDSAY E. ZANNO,
1
DAVID EBERTH,
3
RENÉ HERNANDEZ-RIVERA,
4
MARTHA C. AGUILLÓN MARTÍNEZ,
2
and JAMES I. KIRKLAND
5
1
University of Utah, Dept of Geology and Geophysics/ Utah Museum of Natural History, 1390 E Presidents Circle, Salt Lake
City, UT, 84112, USA, tgates@umnh.utah.edu, ssampson@umnh.utah.edu, lzanno@umnh.utah.edu;
2
Secretaría de Educación y Cultura-Museo del Desierto, Dept. of Paleontology. Prol. Pérez Treviño 3745, Parque las Maravillas.
Saltillo, Coahuila, México. 25015, crenedel@hotmail.com, aguillonmc57@hotmail.com;
3
Royal Tyrrell Museum of Paleontology, PO Box 7500, Drumheller, T0J 0Y0, Alberta, Canada, David.Eberth@gov.ab.ca;
4
Instituto de Geología, Dept. of Paleontology, UNAM, Mexico City, M-04510, DF, Mexico, renedinosaurios@yahoo.com;
5
Utah Geological Survey, 1594 W North Temple Ste 3110, PO Box 146100, Salt Lake City, 84114-6100, USA,
jameskirkland@utah.gov
ABSTRACT—A new lambeosaurine hadrosaurid, Velafrons coahuilensis, is described as the first lambeosaurine from the
Cerro del Pueblo Formation of Coahuila, Mexico, and the first lambeosaurine genus to be named from North America
in more than 70 years. Although the holotype specimen is a juvenile individual—as evidenced by its incomplete crest
development and relative size compared to other North American lambeosaurines—ontogeny independent autapomor-
phies have been identified including quadrate with narrow quadratojugal notch and a postorbital with well developed,
dorsally positioned squamosal process. Additionally, this taxon is unique in that the prefrontal is not dorsally deflected
and anteroposteriorly expanded as in other lambeosaurine taxa of its size, but rather retains the frontal-prefrontal
“clamp” present in smaller individuals of other taxa. Phylogenetic analysis places Velafrons in a polytomy with numerous
other fan-crested lambeosaurines. The crest structure of Velafrons more closely resembles that of Corythosaurus and
Hypacrosaurus because it possesses an anteriorly projecting nasal process over the dorsal premaxilla process. Biogeo-
graphically, Velafrons is one of three distinct hadrosaurids known from approximately 73.5 Ma—two lambeosaurines and
one hadrosaurine—all restricted to the southern region of the Western Interior Basin of North America.
INTRODUCTION
The Cerro del Pueblo Formation (CdP Fm) in the state of
Coahuila, Mexico (Fig. 1) has been acclaimed as a productive
fossiliferous unit for decades (Wolleben, 1977; Vega and Feld-
mann, 1991; Kirkland et al., 2001), yet thus far it has been subject
to limited paleontological work. The majority of research in the
region to date has focused on the stratigraphy and sedimentology
of the Difunta Group (Fig. 1), a suite of formations bounded by
the Parras Shale below and the Rancho Nuevo Formation above,
of which the CdP Fm forms the base (Murray et al., 1962; Mc-
Bride et al., 1974; Kirkland et al., 2001; Eberth et al., 2004).
Eberth and colleagues (2004) estimated the age of the CdP Fm to
be approximately 73.5 Ma based on detailed magnetostratigra-
phy (32n.3r–32n.2n chron). Overall, the CdP Fm represents a
regressive sequence—from the underlying marine Parras Shale
to the terrestrial overlying Cerro Huerto Formation—of coastal
plain settings punctuated by small marine incursions (Eberth et
al., 2004).
Throughout the formation, including the small marine beds,
both vertebrate and invertebrate fossils are common. Fossils in-
clude ammonites, pelecypods, gastropods, mosasaurs, turtles,
crocodiles, mammals, and dinosaurs (Wolleben, 1977; Vega and
Feldmann, 1991; Hernandez, 1992; Hernandez and Kirkland,
1993; Hernandez et al., 1995; Hernandez Rivera, 1996; Aguillon-
Martinez et al., 1998; Aguillon et al., 1998; Rodriguez de la Rosa
and Cevallos Ferriz, 1998; Kirkland et al., 2001; Brinkman et al.,
2002; Garcia and Reynoso, 2002; Kirkland and Aguillon-
Martinez, 2002; Eberth et al., 2003; Perrilliat et al., 2003; Rod-
riguez de la Rosa, 2003; Rodriguez de La Rosa et al., 2003).
Although the dinosaurian fauna of the CdP Fm has not been
explored extensively, its diversity already surpasses that of any
other Cretaceous deposits in Mexico. Dinosaurian constituents
include troodontid, ornithomimid, and tyrannosaurid theropods
(Rodriguez de la Rosa and Cevallos Ferriz, 1998), an unde-
scribed ceratopsid, a putative protoceratopsid-grade ceratopsian,
a hadrosaurine (non-crested) hadrosaurid, and a new lambeo-
saurine (crested) hadrosaurid.
In 1986, the Royal Ontario Museum undertook the first large
paleontological expedition to the CdP Fm. Their efforts were
concentrated on hadrosaurid bonebeds around the town of Presa
de San Antonio, with sporadic collecting from Rincon Colorado
(Fig. 1). Subsequently, “Dinamation International Society” re-
turned to Rincon Colorado and established several quarries in
the area, including quarry 7A, which produced the skeleton of
this new lambeosaurine taxon. The quarry was worked season-
ally from 1992 to 2001, yielding a mostly complete postcranial
skeleton but no skull material. In 2002, a joint expedition involv-
ing the Utah Museum of Natural History, the Royal Tyrrell Mu-
seum of Paleontology, and the Museo del Desierto in Saltillo,
Coahuila, reinitiated excavations at the 7A quarry, recovering
*
Corresponding author.
Journal of Vertebrate Paleontology 27(4):917–930, December 2007
© 2007 by the Society of Vertebrate Paleontology
917
the disarticulated skull and several cervical vertebrae. The skull
and postcranium of the holotype specimen were disarticulated
but closely associated in a highly cemented calcareous grey mud-
stone. The quarry is associated with a brackish water molluscan
assemblage that includes Aphrodina tippana, Cerithium pueb-
loensis, and Nerita, with some of the bones encrusted by Flem-
ingostrea subspatula (Kirkland et al., 2001, fig 13g; Kirkland et
al., 2006).
Here we describe the first lambeosaurine hadrosaurid from
the Cerro del Pueblo Formation and the first new North Ameri-
can lambeosaurine genus named in over 70 years. Further, we
address the issue of crest development in this lambeosaurine
taxon compared to that of other lambeosaurine hadrosaurids
along with the biogeography of late Campanian hadrosaurids in
the Western Interior Basin (WIB).
Institutional Abbreviations—CMN, Canadian Museum of
Nature, Ottawa, Ontario, Canada; MOR, Museum of the Rock-
ies, Bozeman, Montana, USA; ROM, Royal Ontario Museum,
Toronto, Ontario, Canada; CPC, Colección Paleontológica de
Coahuila (Paleontological Collection of Coahuila) Saltillo, Coa-
huila, Mexico; TMP, Royal Tyrrell Museum of Paleontology,
Drumheller, Alberta, Canada; UMNH, Utah Museum of Natu-
ral History, Salt Lake City, Utah, USA.
SYSTEMATIC PALEONTOLOGY
DINOSAURIA Owen, 1842
ORNITHISCHIA Seeley, 1888
ORNITHOPODA Marsh, 1882
HADROSAURIDAE Cope, 1869
LAMBEOSAURINAE Parks, 1923
VELAFRONS, gen. nov.
Etymology—Vela (⳱sail, Spanish) + frons (⳱forehead,
Latin); meaning “sailed forehead,”in reference to the sail-like
crest that is found on the forehead of this taxon.
Diagnosis—as for type and only species.
VELAFRONS COAHUILENSIS, sp. nov.
Etymology—coahuil (⳱Coahuila, the Mexican state in which
the fossil was discovered) + ensis; meaning “from Coahuila.”
Holotype—CPC-59, partial subadult skull including left and
right premaxillae and maxillae, right jugal, nasal, quadrate,
mostly complete skull roof, dentary, and partial postcrania.
Type Locality—7A quarry, about 1 km northeast of the town
Rincon Colorado, Coahuila, Mexico (Fig. 1). The site occurs
approximately 335 m from the base of the Cerro del Pueblo
Formation (Eberth et al., 2004).
Diagnosis—Lambeosaurine hadrosaurid characterized by the
following autapomorphies: quadrate with narrow quadratojugal
notch; postorbital with a dorsally positioned, high arching squa-
mosal process; ceratobranchial with rounded anterior end; as
well as the unique suite of characters: a flat fan-like crest created
by the nasals and premaxillae, a jugal with poorly developed
posteroventral flange positioned more posteriorly than other
lambeosaurine taxa, and an anteriorly recurved posterior pro-
cess, and a well-developed raised squamosal shelf.
DESCRIPTION
The skull of CPC-59 consists of a complete dentary (lacking
teeth), ceratobranchial, mostly complete left and right premax-
illae, left and right maxillae, right jugal, quadrate, and nasal, and
a virtually complete skull roof with fragmentary braincase (Fig.
2). The entire skull was disarticulated, except for the skull roof,
and covered in a thick iron crust obscuring some sutures and
subtle surface morphology, such as foraminae. In particular, the
braincase suffers from preservational issues that prevent a de-
tailed reconstruction and description.
Based on a number of features (relative size, vertebral suture
closure, conformation of skull elements; see Discussion), it is
very likely that CPC-59 represents a juvenile individual. The
skulls, and particularly the crests, of lambeosaurines change dra-
matically during ontogeny (Dodson, 1975; Evans et al., 2005).
FIGURE 1. Map showing Cretaceous-aged fossiliferous basins in Coahuila, Mexico, and the stratigraphy of the Parras Basin. Modified from Eberth
et al. (2004:fig. 2, 3). Quarry 7A is located approximately 1 km northeast of Rincon Colorado. Abbreviations:P de S.A., Presa de San Antonio.
JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 4, 2007918
Thus, it is almost certain that the crest of Velafrons does not
represent the final adult form. Nonetheless, work by Evans
(2005) demonstrates that juveniles possess a number of genus-
level diagnostic characters. The morphological changes associ-
ated with crest growth in this taxon will be discussed more thor-
oughly below.
The postcranium of this specimen is not described here due to
space constraints, but is currently under study for publication at
a later date.
Cranium
The skull roof is mostly complete except for portions of the
frontal and the ventral processes of the postorbital and squamo-
sal. An iron crust obscures several of the sutures and there is
crushing through the right temporal bar. Nonetheless, the skull
roof provides critical information about the morphology and
phylogenetic relationships of Velafrons.
Premaxilla—The premaxilla (Fig. 3A–D) broadly contacts the
maxilla posteriorly, and the lacrimal, prefrontal, and nasal pos-
terodorsally. The oral margin of the premaxilla (Fig. 3C) is lined
with a series of six large denticles that likely served as attach-
ment points for a keratinous rhamphotheca (Morris, 1970). Pos-
teroventral to these denticles the premaxilla demonstrates the
double layered morphology (Fig 3D) as observed on all hadro-
saurids and illustrated on juvenile specimens of Hypacrosaurus
stebingeri by Horner and Currie (1994).
In anterior view, the oral margin is distinctly sigmoidal and
oriented subhorizontally, whereas in Hypacrosaurus and Cor-
ythosaurus, the lateral portion of the premaxilla is angled ven-
trally (Fig 3D). The premaxilla narrows abruptly posterior to the
oral margin, forming a pronounced, rounded flange (Fig 3C) and
then exhibits a more gentle lateral expansion as the element
ascends the face. This abrupt medial deflection of the premaxilla
posterior to the oral margin is present but less developed in
Lambeosaurus lambei (AMNH 5373) and H.stebingeri (MOR
549). The posterior extent of the bony external nares in Vela-
frons is unknown because the delicate bones that make up the
narial tunnel are not preserved.
In most lambeosaurines (e.g., Corythosaurus,Hypacrosaurus,
Lambeosaurus), the lateral process of the premaxilla remains
relatively narrow throughout the length of the snout, and ex-
pands abruptly immediately anterodorsal to the orbit. In con-
trast, the lateral process of Velafrons appears to widen progres-
sively throughout its length, forming a large, oblong-shaped ex-
tension in the posterior half (Fig 2). H.altispinus (TMP 82.10.01)
is perhaps the closest to this condition among other lambeosau-
rines. The rounded posterodorsal edge of the lateral premaxil-
lary process in Velafrons appears to fit into the correspondingly
rounded anterolateral edge of the nasal, mostly closing the pre-
maxilla-nasal fontanelle as in Corythosaurus (Evans et al., 2005).
However, Corythosaurus (Ostrom, 1961) and L.lambei (e.g.
AMNH 5373) have a dorsal lobe bifurcating the lateral process,
whereas this bifurcation is absent in Velafrons (Fig. 4). Although
there is clearly an ontogenetic component to this feature, speci-
FIGURE 2. Skull reconstruction of Velafrons coahuilensis based on
holotype specimen (CPC-59). Scale bar equals 10 cm. Note that the nasal
anterior process of Velafrons is illustrated with a single projection be-
cause there is only osteological evidence for one projection. However,
given the close phylogenetic affinity to Corythosaurus and Hypacrosau-
rus,Velafrons may similarly possess a bifurcated anterior nasal process.
FIGURE 3. Left premaxilla of Velafrons coahuilensis.A, posterodorsal portion in lateral view; and B, medial view; C, anterior portion in dorsal
view; and D, anterior view. Right nasal of Velafrons coahuilensis in E, lateral view. Abbreviations:ms, medial septa; nb, nasal base; npg, nasal process
groove; om, oral margin; pmd, dorsal premaxilla process; pml, lateral premaxilla process; pnf, crest fontanelle. Scale bar equals 5 cm.
GATES ET AL.—NEW LAMBEOSAURINE FROM MEXICO 919
mens of other genera of equivalent size to Velafrons (e.g., C.
casuarius, ROM 1947) already possess the small dorsal exten-
sion, indicating that its absence in Velafrons may be unrelated to
developmental stage.
The dorsal process of the premaxilla in Velafrons remains deli-
cate and slender throughout its length, contacting its opposite
medially and flanked laterally by the anterior process of the
nasal. The small size of the Velafrons dorsal process contrasts
with that seen in equivalent sized (and presumably aged) indi-
viduals of other genera (Fig. 4; see below). As reconstructed at
this developmental stage, the crestal portion of the dorsal pro-
cess terminates at the front of the crest, well anterior to the orbit.
Overall, given the presumed subadult age of CPC-59, the condi-
tion in Velafrons most closely resembles that of H.altispinus
(TMP 82.10.01), which retains a relatively narrow dorsal process
forming the anterior portion of the crest and contributing only a
thin process to the dorsum of this structure.
A large median septum extends posterodorsally on the medial
side of the premaxilla (Fig 3B). When articulated, the premax-
illae meet along this median septum, forming an “s-loop”like
that observed in Corythosaurus and L.lambei, but absent in H.
altispinus and all species of Parasaurolophus (Weishampel,
1981).
Nasal—As in Corythosaurus,Hypacrosaurus, and Olorotitan
(Godefroit et al., 2003) the nasal (Fig. 3E) of Velafrons is a
relatively large, flattened element that forms the bulk of the
dorsal portion of the crest. It is bounded anteriorly by the pre-
maxilla, ventrolaterally by the prefrontal, and posteroventrally
by the frontal. For the purposes of description, the nasal can be
subdivided into a thickened, transversely expanded ventral por-
tion and a relatively flattened dorsal portion that comprises the
majority of the element.
The ventral portion is transversely narrow posteriorly and ex-
pands anteriorly in association with the internal chamber of the
nasal vestibule (Fig. 2). The nasal-frontal contact is formed by
the posterolateral corner of the nasal base slotting into a right-
angled notch present on the frontal such that the frontal platform
underlaps the nasal. The frontal supports the base of the nasal in
all other North American lambeosaurines, except that in these
taxa—including juveniles—the posterolateral contact is not
squared as in Velafrons (Fig. 3E), but instead is rounded to sup-
port a nasal with differing morphology. In Velafrons, the nasal-
prefrontal contact is more complex, with the nasal slotting into a
well-developed clamp formed by the prefrontal above and the
frontal below. The premaxillary contact is less certain, since the
premaxillary portion of this union is disarticulated.
As preserved, the flattened dorsal portion of the nasal is
rounded and roughly fan-shaped. Medially, the nasal forms a flat
contact surface for its counterpart that extends throughout the
posterior half and most of the height of this element. The only
exception is a well-developed, ventrally located depression that
may be incipient development of the narial system into the nasal.
The top of the nasal in CPC-59 is not preserved from the mid-
point to its anterior edge (Fig 3E). However, a distinctive contact
surface preserved on the dorsal process of the premaxilla indi-
←
FIGURE 4. Comparison of skull and crest development between three
taxa of juvenile lambeosaurines. A,Velafrons coahuilensis;B,Corytho-
saurus casuarius;C,Lambeosaurus sp. Dark grey regions represent the
area of the crest occupied by the nasal whereas the light grey shows the
extent of the premaxilla for each specimen. Abbreviations:na, nasal; pf,
prefrontal; pmd, dorsal premaxilla process; pml, lateral premaxilla pro-
cess; pnf, crest fontanelle. Skulls not to scale. Note that the nasal anterior
process of Velafrons is illustrated with single projection because there is
only osteological evidence for one projection. However, given the close
phylogenetic affinity to Corythosaurus and Hypacrosaurus,Velafrons
may similarly possess a bifurcated anterior nasal process.
JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 4, 2007920
cates that an elongate process of the nasal extended forward to
clasp the dorsal premaxillae laterally (Fig. 4). As reconstructed
in Figure 2, the nasal possesses a single anteriorly projecting
process that overlaps the dorsal premaxillary process because
that is the only process of which there is osteological evidence.
However, both Corythosaurus and Hypacrosaurus have a bifur-
cated anterior process that may well have been present but not
preserved on CPC-59, especially given the overall similarity in
nasal morphology with the latter two taxa. The anteroventral
portion of the nasal is composed of a nearly vertical, thickened
margin that makes up the lateral edge of an anteroventrally fac-
ing premaxilla-nasal fontanelle visible on the lateral side of the
skull (Fig. 2) as on Corythosaurus,Lambeosaurus, and Hypac-
rosaurus (Fig. 4). This latter taxon differs from other taxa in that
the fontanelle closes quite early in development (Evans et al.,
2005). Posteriorly, the crest rises vertically a short distance from
the base of the nasal and then curves posterodorsally to form the
curved rear margin of the crest (Fig 3E). An equivalent mor-
phology is present in juveniles of both C.casuarius and H.alti-
spinus (Evans et al., 2005).
Maxilla—The maxilla (Fig. 5A, B) is typical of lambeosaurine
hadrosaurids, being relatively gracile with a pronounced dorsal
process near its midsection and a long ramp-like premaxillary
shelf anteriorly (Fig. 5A). A maxillary foramen occurs at the
base of the dorsal process (Fig. 2). The dorsal process is shaped
like a right-angled triangle in lateral view, with a steeply angled
anterior margin and a vertical posterior margin. It rises to a
height nearly equal to the depth of the main maxilla body some-
what posterior to the midpoint of the maxilla. The majority of
the posterior side of this process articulates with the palatine,
and a small portion of this element is preserved on the right
maxilla. A large opening, the maxillopalatine foramen, occurs at
the junction of these elements near the base of the dorsal pro-
cess. A third foramen occurs on the lateral side of the maxillary
body, immediately below the jugal process. Hypacrosaurus ste-
bingeri (MOR 549) has two foramina at this location.
The jugal articulation is represented by a ventral ridge and
large facet on the lateral side of the dorsal process. It appears
that the jugal covered most of the lateral side of the dorsal pro-
cess, not unlike that in other lambeosaurines.
The ectopterygoid ridge forms the prominent overhang seen
on the posterior half of the maxilla in lateral view. The ectoptery-
goid shelf is wider than the premaxillary shelf throughout its
length then rounds off abruptly at the posterior margin of the
maxilla. However, the shelf appears to be shorter anteroposte-
riorly than in Corythosaurus (Ostrom, 1961) or H.stebingeri
(MOR 549), possibly caused by posterior positioning of the dor-
sal process. The maxilla of Parasaurolophus cf. cyrtocristatus
(UMNH VP 16666.1) is more similarly shaped, including an ap-
parent posterior shift of the dorsal process. The palatine process
is located on the medial side of the ectopterygoid shelf, anterior
to the pterygoid process (Fig. 5A, B).
The virtually complete left maxilla contains approximately 33
tooth positions, each corresponding to a medially positioned
dental foramen. The tooth row (∼248 mm in length) is distinctly
sinusoidal in ventral view, with the most medial portion in the
anterior region and the most lateral portion located posteriorly,
a condition seen in other lambeosaurines.
Jugal—Overall, the jugal (Fig. 5C) most closely resembles that
of the Russian lambeosaurine Amurosaurus riabinini (Godefroit
et al., 2004). The element contacts the maxilla anteriorly, the
lacrimal and postorbital dorsally, and the quadratojugal and
quadrate posteriorly. The outer margin of the anterior process is
not preserved so the morphology of this region cannot be fully
reconstructed. However, the preserved portion of the anterior
process suggests that this structure was dorsoventrally symmetri-
cal, as in Corythosaurus (Fig. 4; Ostrom, 1961). Parasaurolophus
cf. cyrtocristatus (UMNH VP 16666.1) is dissimilar to Velafrons
because its anterior process is tall, anteroposteriorly compressed,
and possesses a virtually straight anterior margin. A prominent
lacrimal facet is present on the dorsal margin of the anterior
process, closely resembling that of Corythosaurus, but differing
drastically from the large lacrimal suture interfingering of P.
walkeri (ROM 768). The postorbital process is triangular at its
base and simultaneously flattens and twists dorsally such that it
transitions from facing anteriorly to facing laterally. The postor-
bital process is broken and offset 1 cm above the base, but the
approximate angle of ascent is 75º(Fig. 5C).
The jugal of Velafrons is distinctive in the position of the pos-
teroventral flange and the size and shape of the posterior pro-
cess. The posteroventral flange is poorly developed and more
posteriorly positioned compared to other North American lam-
beosaurines, particularly Lambeosaurus lambei (e.g., AMNH
5373) and both species of Hypacrosaurus (e.g. MOR 549, TMP
82.10.01). Velafrons, like L.lambei and juvenile H.altispinus
(CMN 2246) possesses a curved outer margin of the posterior
process, but unlike L.lambei the curvature extends dorsally until
FIGURE 5. Left maxilla of Velafrons coahuilensis in A, lateral view;
and B, medial view. Right jugal of Velafrons coahuilensis in C, lateral
view. Abbreviations:dp, dorsal process; ectp, ectopterygoid process; ja,
jugal articulation; lf, lachrymal facet; nf, nutrient foramina; palp, palatine
process; pms, premaxillary shelf; pop, postorbital process; pp, posterior
process; ptp, pterygoid process. Scale bar equals 5 cm.
GATES ET AL.—NEW LAMBEOSAURINE FROM MEXICO 921
the apex is directly above the posteroventral flange. This pro-
nounced curvature of the posterior process results in a narrow
lateral temporal fenestra (Fig. 4).
Prefrontal—The prefrontal (Figs. 6; 7A, B) is located on the
anterolateral region of the skull roof. Laterally, the prefrontal
makes up the rugose anterodorsal portion of the orbital rim in
association with the co-ossified supraorbital (Maryanska and Os-
mólska, 1979). As in other lambeosaurine taxa, the prefrontal
interdigitates with the postorbital posterolaterally, forming a
raised bony mound. Medially, the prefrontal articulates with the
frontal, nasal, and possibly the premaxilla, although the connec-
tion with the latter element is uncertain. Of these elements, the
contact with the frontal is by far the most extensive, dominating
the posterior and ventromedial sides of the prefrontal. Contrary
to the morphology seen on Amurosaurus and Jaxartosaurus
aralensis (Godefroit et al., 2004), the prefrontal does not form
any portion of the frontal platform, but instead overlaps the
frontal medially for a short distance before it deflects slightly
dorsally, forming the roof of a low angled bony clamp for the
base of the nasal (Fig. 6). In contrast, the prefrontal in other
lambeosaurines of comparable size is already expanded and de-
flected dorsally to almost a 90ºangle, and developed anteropos-
teriorly over the frontal to form a shallow dish shape. The com-
parative ontogeny of this structure is discussed more fully below.
Frontal—The frontals (∼75 mm mediolaterally, 75 mm antero-
posteriorly sensu Godefroit et al. [2004]) form the anteromedial
region of the skull roof, articulating with the prefrontals, the
orbitosphenoids and laterosphenoids, the postorbitals, and pari-
etals. Most of the anterior portions of the frontals are missing
from CPC-59. A small section preserved on the right frontal (Fig.
7A, D) indicates that the frontal-nasal contact is virtually square
(92ºangle between the lateral and posterior margins). H.stebin-
geri (MOR 553S) has a slightly square frontal-nasal contact,
whereas Corythosaurus (TMP 82.19.72) is well rounded posteri-
orly, and the Asian lambeosaurines Amurosaurus and Jaxarto-
saurus possess two posterior arches (Godefroit et al., 2004). The
prefrontals articulate with the anterolateral side of the frontals.
As described previously, a slight overlap between the two ele-
ments forms a clamp that grips the ventrolateral extension of
the nasal base. As in other lambeosaurines (Horner et al., 2004),
the postorbital also articulates with the lateral side of the frontal,
thereby excluding the latter from contributing to the orbital
rim (Fig. 7A, B, D, E). The frontals are depressed medially at
the triradiate contact of these three elements. Medial to this
depression is the frontal doming characteristic of juvenile lam-
beosaurines (Gilmore, 1937; Godefroit et al., 2004; Fig. 7D). The
parietals contact the frontals posteriorly via a long, V-shaped
suture. It is unclear if the frontals bifurcate posteriorly to accept
an interfrontal process from the parietal as in other hadrosau-
rids.
Postorbital—As is typical of hadrosaurids, the postorbital is a
triradiate structure (Fig. 7D) contacting the prefrontals, frontals,
laterosphenoids, parietals, and squamosals. Anteriorly, it articu-
lates with the prefrontal via a robust contact that forms an ob-
servable mound (Fig. 7D). The lateral side of the postorbital is
rugose, marking the posterior half of the dorsal orbital rim and
co-ossification with the supraorbital (Maryanska and Osmolska,
1979). The frontals articulate medially in a straight, interdigitat-
ing suture (Fig. 7D). A large concave depression is present on
the posteroventral surface of the postorbital, located almost di-
rectly ventral to the squamosal process and anteromedial to the
base of the jugal process. Just posterior to the jugal process and
ventral to the squamosal process, an additional small process
projects posterolaterally on the right postorbital (the same area
is not preserved on the left). This process is dorsoventrally com-
pressed, but the entire morphology of this structure is unclear as
it is broken near the base. This unusual projection has not been
described from any other lambeosaurine taxon and may repre-
sent an autapomorphy of Velafrons; however, due to the frag-
mentary nature of preservation, this potential character is cur-
rently unverifiable.
The laterosphenoid articulates with the postorbital in a pocket
at the junction of the three branches, and the parietal immedi-
ately dorsal to the laterosphenoid. The shape and position of the
squamosal process is autapomorphic for Velafrons (Fig. 2; 7E).
The base of the process is positioned toward the dorsal surface of
the postorbital. The process ascends at a steep angle and termi-
nates near the level of the raised squamosal shelf. This confor-
mation differs from other hadrosaurids, such as Corythosaurus
(Ostrom, 1961) and Parasaurolophus (Sullivan and Williamson,
1999) where the squamosal process ascends posterodorsally at a
shallow angle to contact a small squamosal shelf (Fig. 4). Con-
sequently, the dorsal rim of the infratemporal fenestra in Vela-
frons is raised above the dorsal margin of the orbit by approxi-
mately 2.5 cm (Fig. 2; 7E). The condition resembles, yet is also
distinct from, that of Amurosaurus (Godefroit et al., 2004),
where it is also considered an autapomorphy, and H.stebingeri
(MOR 553S). The squamosal process bifurcates posteriorly, mid-
way through its length (Fig. 7E).
Parietal—In dorsal view, the parietal (Fig. 7D) is a slightly
hourglass shaped element that extends anterolaterally to form an
elongate, angled contact with the frontals medially and the post-
orbitals laterally. As is typical, there is an extensive ventral con-
tact with the laterosphenoid. In all other hadrosaurids, an inter-
frontal process typifies the medial junction of these arms. This
structure is not seen in the type of Velafrons, although it is most
likely due to postmortem crushing and diagenesis. The body of
the parietal constricts posteriorly in conjunction with the supra-
temporal fenestrae, and widens at the articulation with the su-
praoccipital and the squamosals. The posterodorsal region of the
parietal bears a large vertical process that bisects the paired,
raised squamosals (Fig. 7D). Similar to Hypacrosaurus, the pro-
cess extends anteriorly over the supratempoal fenestrae to reside
dorsal to the rear margin of the frontals.
Squamosal—The paired squamosals (Fig. 7) form the majority
of the posterodorsal region of the skull. However, in dorsal view,
the squamosals are separated by a thin, median extension of the
parietal, and only seen to coalesce when one views the skull roof
in posterior view (Fig. 7F). This condition differs from Amuro-
saurus (Godefroit et al., 2004) and Hypacrosaurus stebingeri
(MOR 553S) that fully separate the squamosals by the parietal,
and is most similar to Corythosaurus (Ostrom, 1961). In dorsal
view, the squamosals form a raised shelf by a forward expansion
of the median rami over the parietal and supratemporal fenes-
trae (Fig. 7D). This anterior projection of the squamosal is more
strongly developed in Velafrons than in Corythosaurus, although
FIGURE 6. Anterior view of articulated braincase showing detail of
prefrontal “clamp”.Abbreviations:fns, frontal-nasal suture; pfc, pre-
frontal “clamp”. Scale bar equals 5 cm.
JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 4, 2007922
a large squamosal shelf is also present in H.stebingeri (MOR
553S). Parasaurolophus tubicen bears a large posterodorsally di-
rected process on the squamosal instead of the squamosal shelf
(Sullivan and Williamson, 1999). The transversely broad postor-
bital process extends anteriorly almost to the body of the post-
orbital, participating in the formation of the large canopy-like
structure over the supratemporal fenestrae. The quadrate coty-
lus lies at an angle of about 45ºto the horizontal, and is posi-
tioned on the ventrolateral border of the squamosal. Both the
precotyloid and postcotyloid processes are broken at their junc-
tion with the quadrate cotylus. In posterior view, a small tongue-
like supraoccipital facet overlaps the supraoccipital 1 cm (sensu
Godefroit et al., 2004).
Palatoquadrate
Quadrate—The quadrate is a relatively robust element that
notably recurves posteriorly (Fig. 8A). The degree of curvature
exceeds that seen in North American lambeosaurines but ap-
proximates that present in Amurosaurus (Godefroit et al., 2004).
Ventrally, the quadrate condyles differ greatly in size, with the
medial condyle only about one quarter the size of the lateral. As
in other lambeosaurines, the curved lateral wing is interrupted
by a well-developed quadratojugal notch (Fig. 8A). This notch is
much shorter in Velafrons than in other members of the group,
possessing a dorsoventral height/anteroposterior length ratio of
1, compared to 1.67 and 2.39 (TMP 81.16.175 and TMP
FIGURE 7. Articulated partial skull roof of Velafrons coahuilensis in A, dorsal, B, left lateral and C, posterior views. Schematic line drawing of
skull roof in D, dorsal; E, left lateral; F, posterior views. Note that the fronto-parietal suture is not illustrated due to preservational biases.
Abbreviations:exo, exoccipital; f, frontal; ltf, lateral temporal fenestra; or, orbital rim; p, parietal; pf, prefrontal; po, postorbital; soc, supraoccipital;
socf, supraoccipital facet; sq, squamosal. Scale bar equals 5 cm.
GATES ET AL.—NEW LAMBEOSAURINE FROM MEXICO 923
2002.12.74, respectively) for other lambeosaurine quadrates.
Hypacrosurus stebingeri possesses a quadratojugal notch that dif-
fers from that of Velafrons in that the ventral border of the
former taxon arches dorsally at the anterior opening of the
notch, whereas Velafrons is narrower and the ventral border
remains flat. A weak depression outlines the entire quadratoju-
gal notch, presumably indicating that the quadratojugal com-
pletely covered the paraquadratic foramen (Weishampel et al.,
1993).
The well-developed pterygoid wing is roughly quadrangular in
shape (Fig. 8B). It consists of a steeply angled (∼70º) concave
dorsal margin, a straight and steeply angled medial edge (60º),
and finally a slightly convex ventral border. Specimens of H.
stebingeri (e.g. MOR 553) have a quadrate morphology similar to
that of Velafrons, whereas other lambeosaurines such as Cor-
ythosaurus,Lambeosaurus, and Amurosaurus, possess a ptery-
goid wing that regularly slopes at approximately 45º, and a
rounded medial margin (Parks, 1923; Ostrom, 1961; Godefroit et
al., 2004). A vertically elongate fossa is present posteromedially
at the junction of the pterygoid wing and the shaft. On the pos-
terior side of the shaft, a small spur projects medially, level with
the ventral border of the pterygoid wing (Fig. 8B), appearing
otherwise only in H.stebingeri (MOR 553). In all other observed
lambeosaurine taxa, the spur is represented by only a minute
bump in the same area of the quadrate.
Braincase
The braincase of CPC-59 is poorly preserved. Fragments of
the supraoccipital, exoccipital, and basisphenoid are complete
enough to describe portions of their morphology. In contrast, the
orbitosphenoid and laterosphenoid, do not provide sufficient
morphology to warrant description. None of the cranial nerve
foramina or braincase sutures can be observed.
Supraoccipital—The supraoccipital (Fig. 7C, F) is a stout el-
ement, triangular in posterior view. It is flanked laterally and
ventrally by the exoccipitals, and the parietal and squamosal
dorsally. Overall, the morphology and relationships of this ele-
ment do not differ from that of other lambeosaurine taxa (Os-
trom, 1961; Gilmore, 1937). Poor preservation of the ventral side
of the supraoccipital prevents further description.
Exoccipital—Only the dorsomedial portions of this element
are preserved (Fig. 7C, F) and observed to articulate with the
squamosals, supraoccipital, and each other. The ventral-most
articulation of the exoccipitals along the midline marks the
dorsal margin of the foramen magnum. They form a deeper
shelf in Parasaurolophus cf. cyrtocristatus (UCMP 143270), than
in Velafrons, pushing the foramen magnum further into the
skull. However, the depth of the foramen magnum may vary
through ontogeny, since Horner and Currie (1994:fig. 21.7f) il-
lustrate a juvenile Hypacrosaurus with a relatively shallow fora-
men magnum.
Basisphenoid—Although the anterior half of the basisphe-
noid is severed, much of the posterior portion is preserved. Two
large semi-ovoid sutures that articulate with the basioccipital
accentuate the posterior aspect of the basisphenoid. The basi-
pterygoid processes descend ventrolaterally, separated at an
angle of 65º. The distal ends of the processes are rounded, lack-
ing the lateral projections present on Hypacrosaurus stebingeri
(MOR 553S) and Corythosaurus (Ostrom, 1961). A wing-like
process present on the right lateral side may represent the alar
process of the basisphenoid.
Lower Jaw and Hyoid Apparatus
Dentary—The only mandibular element of Velafrons pre-
served is the dentary (Fig. 9A, B). As in other lambeosaurines,
this element is long and slender with a slight downturning in the
anterior one-third, resembling the condition in Corythosaurus
(Fig. 4). The dorsoventral depth of the element at its center is
somewhat greater than that of Corythosaurus specimens of simi-
lar size (Table 1). The well-developed, largely horizontal pre-
dentary shelf projects medially about 20 mm and the symphysis
about 70 mm (Fig. 9B). The outer rim of the predentary contact
FIGURE 8. Right quadrate of Velafrons coahuilensis in A, lateral and
B, posterior views. Abbreviations:ptw, pterygoid wing; qjn, quadrato-
jugal notch; qs, quadrate spur. Scale bar equals 5 cm.
FIGURE 9. Mandibular complex of Velafrons coahuilensis. Right den-
tary in A, lateral view; and B, medial view. Ceratobranchial in C, lateral
view. Abbreviations:cp, coronoid process; pds, predentary shelf. Scale
bar equals 5 cm.
JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 4, 2007924
surface curves sharply posteriorly to become confluent with den-
tary body. In lateral view, the margin of this structure upturns
toward the dorsal edge of the body at almost a 90ºangle, a
steeper angle than observed in most other taxa.
The tooth row extends well posterior to the coronoid process
and includes 34 tooth positions. No teeth are preserved in the
dentary so the number of teeth per alveolus cannot be ascer-
tained. The coronoid process (Fig. 9A) angles weakly anteriorly
and made up mostly of the dentary. The dorsal portion of this
process possesses an anterior flange while the posterior region is
flush with the shaft. This condition is similar to that present in
Hypacrosaurus stebingeri (MOR 549), although the dorsal mar-
gin in that specimen curves less than in Velafrons. Medially, a
large facet indicates that the splenial extended about half the
length of the dentary (Fig. 9B). Below this groove, a portion of
the angular is present, demonstrating that it wrapped around the
medial side of the dentary, as in other hadrosaurids (Weishampel
et al., 1993).
Hyoid—The morphology of the ceratobranchial (Fig. 9C) is
similar to that of other hadrosaurids (Ostrom, 1961). The ante-
rior portion is dorsoventrally expanded, but unlike other taxa,
the head of the hyoid is rounded rather than square. The element
tapers posteriorly and bends dorsally to terminate in a blunt,
rounded end, approximately 80 mm long.
PHYLOGENETIC ANALYSIS
A phylogenetic analysis was performed using the Evans and
Reisz (2007) character matrix and a combination of MacClade
version 4.06 (Maddison and Maddison, 2000) and PAUP version
4.0b10 (Swofford, 2002). In the Majority Rules consensus tree of
27 most parsimonious trees produced from the branch and
bound search algorithm (Fig. 10; 18 taxa [Nipponosaurus was
removed from this analysis, see Evans and Reisz (2007)] with
Probactrosaurus gobiensis,Telmatosaurus transsylvanicus, and
Gryposaurus incurvimanus as outgroups, 94 characters, tree
length 113, CI: 0.89, RI: 0.92, RC: 0.82), Velafrons is posited
inside a polytomy with Corythosaurus,Olorotitan, a clade con-
taining the two species of Hypacrosaurus and a clade containing
the two species of Lambeosaurus. Within this polytomy, all of
the taxa share fan-shaped crests, but as has been noted through-
out this manuscript the development of the crest within Vela-
frons is more similar to Corythosaurus and Hypacrosaurus than
it is Lambeosaurus or Olorotitan. Both Corythosaurus and Hyp-
acrosaurus have long forking anterior nasal processes that sur-
round the dorsal process of the premaxilla. The dorsal process, in
turn, onlaps the nasal between these nasal processes (Fig. 4).
This relationship between the anterior nasal process and the
dorsal premaxilla process is unique to these two taxa (Evans et
al., 2005). Velafrons shares the long anterior nasal process with
Corythosaurus and Hypacrosaurus, but the type specimen of
Velafrons does not preserve this region of the crest therefore, the
exact morphology cannot be determined. Interestingly, even
though Velafrons and Amurosaurus possess many similar char-
acteristics including jugal morphology and a raised postorbital
posterior process, the latter taxon is posited as more primitive
than Velafrons.
DISCUSSION
The holotype specimen of Velafrons appears to represent a
subadult individual. This assessment is based on relative size and
degree of crest development, as well as comparison with overall
skull size with those of other juvenile lambeosaurine specimens.
Yet, despite incomplete crest development, the specimen pos-
sesses a number of taxonomically significant characters that can
be differentiated from ontogenetic variation. Horner (1992; and
this study) observed that, other than size, the morphology of
jugals and quadrates do not change significantly during growth,
and further that these elements are morphologically virtually
indistinguishable from adult elements at subadult growth stages.
Therefore, diagnostic characters present in these elements of
Velafrons are here regarded to be valid and not the result of
ontogenetic variation. Conversely, the postorbital does undergo
significant changes through ontogeny. In young individuals lack-
ing full crest development, the squamosal process of the postor-
bital lies nearly horizontal, but during growth the squamosal
process angles dorsally because the caudal-most margin of this
process articulates with a raised squamosal shelf. The degree of
angling depends on the height of the squamosal shelf in a par-
ticular genus of lambeosaurine. Velafrons, however, is outside
the known range of variation in this feature, relocating the base
of the squamosal process to the dorsal surface of the postorbital.
The squamosal process then rises near vertically and levels out to
contact the squamosal shelf.
Comparison With ?Lambeosaurus laticaudus
Morris (1981) described ?Lambeosaurus laticaudus from a
partial lambeosaurine skull found in the El Gallo Formation of
Baja California. Skull elements includes a partial left premaxilla,
as well as a maxilla, dentary, and jugal. He assigned this speci-
men to the genus Lambeosaurus based on a single character:
long open external nares of the premaxilla, which he posited to
be a generic autapomorphy of Lambeosaurus. However, numer-
ous other lambeosaurines have elongate open external nares,
including North American forms such as Corythosaurus and
Hypacrosaurus. Further, the oral margin of the premaxilla is
TABLE 1. Comparative measurements of select cranial elements from five lambeosaurine taxa.
Cranial element
Velafrons
coahuilensis
CPC-59
Corythosaurus
casuarius
ROM 1947
Corythosaurus
casuarius
CMN 34825
Hypacrosaurus
altispinus
CMN 2246
Lambeosaurus
lambei
ROM 869
Parasaurolophus cf.
cyrtocristatus
UMNHVP 16666.1
Skull (w) across orbits 179 145 134 132* 165 —
Nasal (h) 120 60 110 48* 90 —
Skull (w):nasal (h) 1.49 2.42 1.22 2.75 1.83 —
Quadrate (l) 225 210 220 189* 230 306
Jugal (l) 165 180 200 169* 230 209
Maxilla (l) 278 248 239 212* 250 350
Dentary (l) 370 330 340 —400 —
Dentary (h) near middle 65 57 63 —70 —
Dentary (h):(l) 0.18 0.17 0.19 —0.18 —
Dentary (l):quadrate (l) 1.64 1.57 1.55 —1.74 —
All measurements are in millimeters (mm). (w) equals width, (h) equals height, and (l) equals length of element. *represents measurements received
from D. Evans, 2005.
GATES ET AL.—NEW LAMBEOSAURINE FROM MEXICO 925
unlike other species of Lambeosaurus and more closely re-
sembles that of Hypacrosaurus, exhibiting a highly denticulated
oral margin and rounded, down-turned lateral edge.
A deep tail not observed in other species of Lambeosaurus
defines the species name, laticaudus. However, a similarly deep
tail is also present in Hypacrosaurus altispinus (Brown, 1913). In
fact, Morris (1981:457) states that, “Were it not for the open
narial crest ?L.laticaudus might easily have been called Hypac-
rosaurus sp. because this latter genus is the only hadrosaurid
thought to have a tall, flattened tail.”We consider the taxon
?Lambeosaurus laticaudus to be a nomen dubium because the
type specimen does not have any synapomorphies that unam-
biguously unite it with any lambeosaurine genus. Nor does it
possess autapomorphies that would permit erection of a new
genus. Based on the similarities of the premaxilla and the deep
tail, this taxon may represent the southernmost extent of the
genus Hypacrosaurus (see also Evans and Reisz, in press), but
any such referral must await discovery of additional material.
From this point forward, we refer to ?L.laticaudus as the “Baja
lambeosaur.”
Even though the Baja lambeosaurine specimen is fragmentary,
comparison with Velafrons reveals that the two Mexican taxa are
likely not equivalent. The premaxilla of Velafrons does not share
the rounded down-turned morphology of the Baja specimen,
instead possessing a uniformly arcuate oral margin with a sharp
constriction on the lateral edge. Both taxa share a highly den-
ticulated oral margin, but the amount of denticulation is variable
between individuals and is not a diagnostic character at the genus
level. It is not clear if Velafrons shares the elongate, open nares
of the Baja lambeosaurine because they are poorly preserved.
The remainder of the Baja lambeosaurine skull is too fragmen-
tary for further comparison.
Comparative Ontogeny
Since Velafrons is currently known from a single specimen,
there is little than can be said about the ontogenetic trajectory of
this taxon. Nevertheless, a number of skull features are consis-
tent with a juvenile stage of development that closely resembles
that of other lambeosaurines (Table 1). A number of authors
have studied ontogenetic changes in crest growth and develop-
ment within various lambeosaurine taxa (Parks, 1923; Sternberg,
1935; Dodson, 1975; Evans et al., 2005). Thus, a lengthy discus-
sion is not given here. However, it is important to establish key
FIGURE 10. Majority rules consensus cladogram showing phylogenetic position of Velafrons coahuilensis. The tree was produced using the Evans
and Reisz (in press) character matrix, tree generation in PAUP ver. 4.0b10 (Swofford, 2002), and tree manipulation in MacClade ver. 4.06 (Maddison
and Maddison, 2000). Tree statistics: 18 taxa, 94 characters, Length: 113, CI: 0.89, RI: 0.92, RC: 0.82. Numbers on stems are boot strap values of 1000
replicates.
JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 27, NO. 4, 2007926
similarities shared by Velafrons and juveniles of other lambeo-
saurine taxa so as to highlight potentially unique developmental
characteristics.
Based on the absolute size of the quadrate and nasal and to a
lesser extent the dentary (Velafrons is larger by 30 mm), Vela-
frons appears to be close to the developmental stage illustrated
by the Corythosaurus specimen CMN 34825 (Fig. 4), although,
there are greater differences between the size of other skull el-
ements in these specimens as well as in other lambeosaurine
individuals listed in Table 1. The transverse width of the skull
roof does not appear to be consistent across lambeosaurines. The
skull roof of Velafrons is wider than all other individuals of simi-
lar size and developmental stage. However, it is possible that
minor crushing of the measured skulls could account for at least
some of these deviations.
There appears to be no correlation to the height of the nasal
and the width of the skull at the orbits. In general, the crest
development in Velafrons parallels other lambeosaurines, in that
the nasal is positioned dorsal to the frontals, and the premaxilla
possesses lateral and dorsal processes that extend rearward to
contact the nasal. More specificly is the presence of a long an-
terior process of the nasal (Evans et al., 2005) shared exclusively
with Corythosaurus and Hypacrosaurus. The premaxilla-nasal
fontanelle, located on the lateral side of the crest between the
nasal and the lateral premaxillary process, is open at this stage of
development in Velafrons and Corythosaurus.Hypacrosaurus,
on the other hand, closes the fontanelle early in its development.
Consequently, this is one of only two characters that can be used
to distinguish immature individuals of Hypacrosaurus from Co-
rythosaurus (Evans et al., 2005).
Velafrons possesses the frontal-prefrontal “clamp”support
structure present in immature individuals of Corythosaurus,
Lambeosaurus, and Hypacrosaurus (e.g., TMP 86.26.31), but ap-
pears to have retained this feature longer through ontogeny. As
the crest develops in these taxa, the prefrontal elongates antero-
posteriorly, extending its medial wall dorsally to support the base
of the growing nasal bone. Simultaneously, the nasal loses the
ventrolateral extension and forms a bowl-like base, residing in
the foundation formed from the modified prefrontal. Yet, as
mentioned above, the nasal of Velafrons maintains the ventro-
lateral expansion and the frontal-prefrontal clamp, in spite of the
incongruence in prefrontal development between it and other
fan-crested lambeosaurines of equivalent crest size.
Sternberg (1935) described Tetragonasaurus cranibrevis—a
misidentified juvenile Lambeosaurus (Dodson, 1975; Evans et
al., 2005)—that possesses a much smaller nasal, yet more ad-
vanced modification of the prefrontal than Velafrons. In addi-
tion, a juvenile skull roof (ROM 694) only 145 mm wide at the
orbits, already possesses an upturned prefrontal. Without a
growth series of Velafrons, it is unclear when (or even if) the
prefrontal would have transformed into the upturned condition.
Several possible growth trajectories may be hypothesized for
future growth of the crest, given the current state of develop-
ment. One alternative is that the crest remained small and did
not develop the advanced supporting structure of other corytho-
saurs. Another possibility is that the crest may undergo a period
of rapid modification late in ontogeny. A third possibility is that
Velafrons was larger at adult size than other lambeosaurines and
the apparent delay in development is an artifact of more rapid
growth rates producing a larger skull when compared to other
North American lambeosaurines of equivalent age. In other
words, if Velafrons reached larger adult body size by increasing
growth rate rather than prolonging growth as has been demon-
strated in other dinosaurs (Erickson et al., 2001), then other
equivalently sized juvenile lambeosaurine taxa would be ex-
pected to be to be older, more developed individuals. Ultimately,
this may explain why the holotype of Velafrons appears ontoge-
netically less developed than other lambeosaurines of equivalent
size. This last alternative may be the most likely of the three
since, within the North American Western Interior Basin, south-
ern hadrosaurids in general appear to be larger than their north-
ern counterparts (personal observation), although no specific
study has quantitatively verified a size difference.
All of the changes associated with crest development men-
tioned above drastically alter the skull morphology between ju-
venile and adult growth stages. Therefore, specific apomorphies
based on crest characteristics in juvenile lambeosaurines are not
reliable because those features alter through growth. The apo-
morphies distinguishing Velafrons from all other lambeosaurine
taxa are based on skull elements that alter little with crest de-
velopment of this group (see Dodson, 1975; Evans et al., 2005).
As a result, we hypothesize that the diagnostic features of Vela-
frons will be present on both juvenile and adult skulls, because
these same bones undergo minimal shape change through on-
togeny in other closely related taxa. Although, once adult fossil
material of Velafrons is discovered, more apomorphies based on
adult crest morphology may further differentiate this taxon.
Biogeography
Velafrons lived near the southernmost point of the North
American continent around 73.5 Ma (Eberth et al., 2004). The
Baja lambeosaurine may have occupied a similar latitude be-
cause the terrestrial deposits of the “El Gallo”Formation have
drifted northward, upwards of 2000 km, along the San Andreas
Fault since the Late Cretaceous (Page and Engebretson, 1984;
Bartow, 1991). Within the Parras Basin, only one other hadro-
saurid has been described, a hadrosaurine from the contempo-
raneous Sabinas Basin referred to Kritosaurus (Kirkland et al.,
2006).
The only hadrosaurid fauna known from this time period in
North America is found in the southern region of the continent
due to the Bearpaw Transgression inundating portions of Mon-
tana and Alberta, (Tsujita and Westermann, 1998), while an un-
conformity developed in southern Utah (Bowers, 1990; Eaton et
al., 1999). Parasaurolophus tubicen (Wiman, 1931; Sullivan and
Williamson, 1999) and Kritosaurus (Horner, 1992; considered
Naashoibitosaurus in Horner et al., 2004) are found in sediments
of the Kirtland Formation of northern New Mexico, equivalent
in age to the Parras Basin (Fig. 11; although Horner [1992] ten-
tatively attributes a skull from the Bear Paw Shale to Kritosau-
rus). The distribution of these hadrosaurids at 73.5 Ma appears
to follow the same pattern developed by hadrosaurids earlier in
the Campanian, with the single hadrosaurine genus (but not nec-
essarily species), Kritosaurus, spanning large geographic regions
and the three lambeosaurine genera (i.e., Parasaurolophus, the
Baja lambeosaurine, and Velafrons) having smaller, more iso-
lated distributions (Gates and Evans, 2005). Interestingly, Para-
saurolophus, the tube-crested genus, stratigraphically co-occurs
with members of the Corythosaurini (sensu Evans and Reisz, in
press) clade at two different intervals of the late Campanian. P.
walkeri is found coincident—stratigraphically and geographi-
cally—with Corythosaurus at the base of the Dinosaur Park For-
mation, Alberta, Canada, around 76 Ma. Similarly, at 73.5 Ma, P.
tubicen is found in sediments in New Mexico, USA, stratigraphi-
cally equivalent to Velafrons in Coahuila, Mexico.
TABLE 2. Character coding of Velafrons coahuilensis based on the
character matrix presented in Evans and Reisz (in press).
111?? 11?01 ???11 ???11 11111 11111 01?11 00?1? ???1? ?1111 ?11?1
111?1 ????1 ????? ????? ????? ????? ????? ????
Characters 11, 12, 13, 16, 18, 33, 37, 38, and 41 were coded as question
marks because characters rely on adult conditions not present in CPC-59,
or uncertain morphology of the crest.
GATES ET AL.—NEW LAMBEOSAURINE FROM MEXICO 927
CONCLUSIONS
Velafrons is the first genus of North American lambeosaurine
to be named in over 70 years, and is the first dinosaur to be
identified to the species level from the Cerro del Pueblo Forma-
tion, of Coahuila, Mexico. This taxon is characterized by a fan-
shaped Corythosaurus-type crest, with unique features of the
jugal, postorbital, quadrate, and ceratobranchial. The crest mor-
phology is more similar to Corythosaurus and Hypacrosaurus
than to Lambeosaurus because it possesses a long anterior pro-
cess of the nasal that extensively overlaps the lateral surface of
the premaxilla dorsal process. Phylogenetic analysis places Vela-
frons within a polytomy with other fan-crested lambeosaurines
including Corythosaurus,Hypacrosaurus,Lambeosaurus, and
Olorotitan.
The type specimen of Velafrons is a juvenile individual, but
comparison of skull morphology and growth of other similarly-
sized taxa verifies that the apomorphies seen in Velafrons are
distinct and likely not ontogenetically variable. The size propor-
tions of most skull elements correspond with those seen in other
North American juvenile lambeosaurines. The most obvious dif-
ference is the relatively large size of the nasal and relatively
underdeveloped prefrontal. Velafrons appears to have exhibited
more rapid growth of the nasal than in other, similarly-sized taxa.
Yet at the same time, it retains the morphology of the prefrontal
seen in the youngest individuals of other lambeosaurines, that of
a nasal “clamp”instead of a “bowl”.
Biogeographically, Velafrons is significant because there are
only three other hadrosaurid taxa currently known from the lat-
est Campanian (approximately 73.5 Ma): the hadrosaurine Kri-
tosaurus, the lambeosaurine Parasaurolophus tubicen, and an
unidentifiable lambeosaurine from Baja California. The dino-
saur fauna of the Cerro del Pueblo Formation, has only recently
been targeted for detailed study. Results to date suggest that it
has potential to become one of the most interesting and impor-
tant Late Cretaceous faunas from North America. It offers a
unique opportunity to increase our understanding of dinosaur
diversity from an interval when terrestrial sediments are other-
wise limited. Moreover, it provides opportunities to explore pa-
leoecological patterns and processes in a terrestrial ecosystem at
the southernmost extreme of the North American continent, an
area that appears to have been strongly influenced by resurgent
coastal flooding.
ACKNOWLEDGMENTS
We sincerely thank Mike Getty and the 2002 field crew for
their assistance in excavating the holotype specimen; Rosario
Gomez for her invaluable assistance with logistics; “Pato”(José
López Espinosa), “Nacho”(JoséIgnacio Vallejo González), Ru-
ben A. Rodriguez-de la Rosa, and Don DeBlieux for preparation
and field work; Jerry Golden for his outstanding efforts prepar-
ing the skull. Thanks also to David Evans for many excellent
conversations about lambeosaurine ontogeny and for access to
unpublished data, and to Jim Gardner, Kevin Seymour, Carl
Mehling, and Jack Horner for access to collections and speci-
mens. Funding was provided by National Geographic Society
and the University of Utah.
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