3D premaxillary bone of the ornithischian Laquintasaura venezuelae
53
ANARTIA
Publicación del Museo de Biología de la Universidad del Zulia
ISSN 1315-642X (impresa) / ISSN 2665-0347 (digital)
Anartia, 32 (junio 2021): 53-60
Non-invasive imaging reveals new cranial element of the basal
ornithischian dinosaur Laquintasaura venezuelae,
Early Jurassic of Venezuela
Imágenes no invasivas revelan nuevo elemento craneal del dinosaurio ornitisquio
basal Laquintasaura venezuelae, Jurásico Temprano de Venezuela
Carlos Manuel Herrera-Castillo, Jorge D. Carrillo-Briceño & Marcelo R. Sánchez-Villagra
Universität Zürich, Paläontologisches Institut und Museum, Karl-Schmid-Straße 4, 8006 Zürich, Switzerland.
Correspondence: cmhc1995@gmail.com; jorge.carrillo@pim.uzh.ch; m.sanchez@pim.uzh.ch
(Received: 17-03-2021 / Accepted: 25-05-2021 / Online: 15-10-2021)
ABSTRACT
We report and describe the new le premaxillary bone of the basal ornithischian Laquintasaura venezuelae coming from
a bonebed of the La Quinta Formation in the Andes of Venezuela. Previous dating of the bonebed based on U-Pb zircon
analysis suggested an earliest Jurassic (Hettangian) maximum age. To our knowledge, for the rst-time high-resolution
computer tomography scanning was applied to rocks of this site to search for fossils, leading to the discovery reported here
and the promise of this method to cope with unprepared blocks from the same site. We created a three-dimensional model
of the fossil and show that the le premaxilla of L. venezuelae presents the unusual characteristic of a seven dental grooves
count. is number is known only in other two basal thyreophorans such as Huayangosaurus taibaii and Gargoyleosaurus
parkpini. is is consistent to the general trend reported for ornithischian evolution to lose premaxillary teeth, which
suggests that Laquintasaura represents the plesiomorphic state of the character, with a high tooth count. Only with new
anatomical data on Laquintasaura can we generate robust hypothesis of its evolutionary relationships, which address some
of the earliest history of dinosaurs and their occurrence in the otherwise poorly documented equatorial areas of the globe.
Keywords: Andes, premaxilla, computer tomography, anatomy.
RESUMEN
Se registra y describe un nuevo hueso premaxilar izquierdo del ornitisquio basal Laquintasaura venezuelae proveniente de
un lecho fosilífero de la Formación La Quinta en los Andes de Venezuela. La datación previa de este lecho fosilífero, basada
en el análisis de circón U–Pb, sugirió una edad máxima del Jurásico temprano (Hettangiana). Por primera vez se aplicó una
tomografía computarizada de alta resolución a las rocas de este sitio, lo que llevó al descubrimiento que se informa aquí,
raticando las potencialidades de este método para hacer frente a bloques no preparados y a la identicación de fósiles.
Hemos creado un modelo tridimensional del fósil y mostramos que el premaxilar izquierdo de L. venezuelae presenta la
característica inusual de un recuento de siete surcos dentales. Este número se conoce sólo en otros dos tireóforos basales,
tales como Huayangosaurus taibaii y Gargoyleosaurus parkpini. Este descubrimiento es consistente con la tendencia general
observada en la evolución de los ornitisquios a perder los dientes premaxilares, lo que sugiere que Laquintasaura representa
el estado plesiomórco del carácter, con un alto recuento de dientes. Sólo con nuevos datos anatómicos sobre Laquinta-
saura podemos generar hipótesis sólidas de sus relaciones evolutivas, que aborden parte de la historia más temprana de los
dinosaurios y su aparición en las áreas ecuatoriales del mundo, mismas que de otro modo estarían mal documentadas.
Palabras clave: Andes, premaxila, tomografía computarizada, anatomía.
DOI: https://doi.org/10.5281/zenodo.5571307
Herrera-Castillo, Carrillo-Briceño & Sánchez-Villagra
54
INTRODUCTION
Understanding the early diversication of dinosaurs
benets from new discoveries of fossils and investigations
of their palaeobiology (Sereno 1999, 2010, Irmis 2011,
Baron et al. 2017, Langer et al. 2010, 2017, Padian 2017,
and references therein). eir fossil record suggests that
this clade dates back to the Triassic (Sereno 1999, Sereno
et al. 1993, Nesbitt & Sues 2020, Tanner et al. 2004), with
a geographical origin in Laurasia (Baron et al. 2017) and/
or in Gondwana (Lee et al. 2018). e oldest known di-
nosaur Nyasasaurus parringtoni, of an African provenance
(Tanzania), supports a southern Pangaean origin (Nesbitt
et al. 2013). e appearance of dinosaurs in the Triassic
was an important event in the history of life, marking the
onset of a faunal diversication that dominated world-
wide terrestrial ecosystems for almost 230 Myr. (Langer et
al. 2010, Nesbitt et al. 2013). e phylogenetic relations
within members of the three major Dinosauria clades
eropoda, Sauropodomorpha, and Ornithischia, have
been a subject of debate (Baron et al. 2016, 2017, Padian
2017, Langer et al. 2017). e early evolution of the Or-
nithischian clade is critical in this regard. e exclusion of
Pisanosaurus mertii from Ornithischia (Agnolín & Roza-
dilla 2017, Baron et al. 2019) implies the absence of mem-
bers of this group during the Triassic, which raises ques-
tions regarding the origin of the clade (Baron 2019). For
example, Baron (2019) proposed that the solution to the
gap in the fossil record of ornithischians might be solved
through a reinterpretation of their phylogenetic position
as being nested within eropoda or Sauropodomorpha.
Laquintasaura venezuelae, as the earliest securely dated
representative of the ornithischians (Barrett et al. 2014),
nds itself in the middle of the debate. Previous studies
suggested that at the Triassic-Jurassic boundary ecosys-
tems near the palaeoequatorial region were inhospitable
for early dinosaurs (Tanner et al. 2004, Irmis 2011, Ez-
curra 2010). Nevertheless, the geographic location where
L. venezuelae was found challenged this idea (Barrett et
al. 2014), being congruent with the hypothesis that the
earliest diverging ornithischian lineages (e.g., heterodon-
tosaurids, Laquintasaura and Lesothosaurus) occurred in
Gondwanan (Lee et al. 2018). e phylogenetic position
of L. venezuelae falls in a polytomy at the base of the or-
nithischian tree according to Barrett et al. (2014), more
recently resolved to a higher denition at the base of the
yreophora group, as a sister taxon to Scutellosaurus
(Baron et al. 2016, Raven & Maidment 2017). Presence
of premaxillary teeth, convergently reduced in many de-
rived forms of the inner clades, is consistent with a basal
position of Laquintasaura on the ornithischian tree of life
(Nabavizadeh & Weishampel 2016). Details of premaxil-
lary anatomy would further provide relevant anatomical
information.
Here we describe a new premaxillary bone attributable
to L. venezuelae, which comes from a sandy siltstone block
collected in 1993, housed in the collection of the Univer-
sity of Zulia (Maracaibo, Venezuela). For the rst time
CT scan and a 3D model was carried out in remains of the
L. venezuelae. e presence of recognizable apomorphies
sheds new light on the anatomy of L. venezuelae, and its
potential signicance in understanding its phylogenetic
position.
MATERIALS AND METHODS
Referred material
e new premaxillary bone MBLUZ P-4882 described
herein, and other hundreds of new postcranial elements
(currently under study), including all the specimens re-
ferred in Barrett et al. (2008, 2014), come from a sandy
siltstone block collected by MRSV and collaborators in
December 1993 from a single bonebed (see below section)
of the La Quinta Fm. (Fig. 1). e specimens reported
here are housed at the Museo de Biología de la Universi-
dad del Zulia (MBLUZ P-). anks to the permissions is-
sued by the authorities of the MBLUZ, and the Instituto
del Patrimonio Cultural de Venezuela (IPC, certicates
N° 002/15, and 071/15), rock blocks were brought on
loan to the University of Zurich (Switzerland) for prep-
aration and study. e fossil preparation ended in 2017,
and it resulted in abundant disarticulated skeletal remains,
most of them still embedded in the block matrix. is is
the case of the premaxillary bone MBLUZ P-4882, which
we have scanned using a Nikon XT H 225 ST at the Uni-
versity of Zurich. A 3D model of the maxillary bone was
performed using the image segmentation soware Mimics
(Materialise NV, Leuven, Belgium, 1992-2015). Due to
the lack of contrast between the bones and the surround-
ing sediment, the segmentation was performed layer by
layer, dierentiating the bone from the matrix by hand.
Geological settings and the “bonebed findings”
e La Quinta Formation consists mainly of conti-
nental red beds and volcanic rocks that where deposited
in a series of restricted tectonic basins associated with the
breakup of Pangaea during the early Mesozoic and in the
Andes of Venezuela (Schubert et al. 1979, Maze 1984,
Schubert 1986). e dinosaur bonebed is located on the
right bank of the Río La Grita, near the Sector Llano de
Cura, close to a road cut between the towns of La Grita and
3D premaxillary bone of the ornithischian Laquintasaura venezuelae
55
Seboruco, Táchira state (Fig. 1). is bonebed is character-
ized by a medium to poorly sorted sandy siltstone with an-
gular to sub-angular clast and pebbles (Moody 1997). e
bonebed section is located directly opposite the type sec-
tion of the La Quinta Fm. (Schubert et al. 1979, Schubert
1986), possibly separated by one or more faults (Russell
et al. 1992, Moody 1997, Barrett et al. 2008). Because of
this faulting, precise stratigraphic placement of the bone-
bed has been dicult, with interpretations ranging likely
from the middle to upper portion of the La Quinta Fm.
(Barrett et al. 2008). Dating based on U-Pb zircon analy-
sis suggests an earliest Jurassic (Hettangian) maximum age
for the bonebed (Barrett et al. 2014, Langer et al. 2014).
A couple of French paleontologists discovered the
bonebed and rst dinosaur remains from Venezuela in
the 1980s. ese specimens were originally attributed to
Lesothosaurus sp. based on the similarities of few cranial
elements (Russell et al. 1992). ese rst remains where
represented by a premaxillary and a maxillary tooth, and a
le quadrate bone fragment (Russell et al. 1992, g.4). For
many years these remains described by Russell et al. (1992)
were housed in Paris, and in the late 1990s under the co-
Figure 1. e La Quinta Fm. bonebed and its geographical location. a) Location map. b-c). Outcrop of the bonebed. In the picture (c),
Marco Badaracco, Cathy Villalba and Sylvia Lim in the bonebed in 1993 (photo by MRSV).
Herrera-Castillo, Carrillo-Briceño & Sánchez-Villagra
56
ordination MRSV, all the specimens returned to Venezu-
ela and were deposited the at the Museo de Biología de la
Universidad del Zulia (MBLUZ) (see acknowledgments
section in Barrett et al., 2008). Oblivious to the previous
work by the French team, and due to the potentialities of
the La Quinta Fm., MRSV carried out a reconnaissance
trip in 1989 to locate vertebrate material visiting the type
section of this unit together with the Venezuelan geologist
Oscar Odreman, whom he had met at the Latinamerican
herpetological congress that took place in Mérida that
year. Vertebrate fossils could not be found. Posteriorly
in 1992 and 1993, MSRV organized three expeditions
(Sánchez-Villagra & Clark 1994). e rst in early 1992
resulted in the relocation of the bonebed rst discovered
by the French team, thanks to the good eye and expertise
of James Clark, a dinosaur expert who visited Venezuela
and recognized fossils where Marcelo Sánchez would have
not. ey collected some plaster jackets, one of which
was transported by Marcelo Sánchez to Buenos Aires to
learn and conduct preparation of it there, under the kind
supervision of Dr. Guillermo Rougier and his team; there
rst contacts with Fernando Novas were made. Work
during three months resulted in dierent blocks with ex-
posed fossils that were transported back to Venezuela, to
the Laboratorio de Paleobiología of Omar Linares at the
Universidad Simón Bolívar (USB-PB), where Sánchez-
Villagra had conducted his Licenciatura thesis. ese
fossils housed have remained since then without being
studied to our knowledge. Another trip was coordinated
by MRSV in the company of Omar Linares from the Uni-
versidad Simón Bolívar, which ended up a failed attempt
to reach La Quinta outcrops, as in the middle of the way
to Táchira from Caracas the car loaned by MRSV’ father
broke down (total loss, see acknowledgments section in
Barrett et al. 2008). Before starting doctoral studies in the
USA, MRSV learned that he could not have access to the
materials he had collected and prepared in Buenos Aires
before (housed in the Universidad Simón Bolívar), and
given the commitment to SVP and the need to report to
them, he had to coordinate a whole new expedition. In the
December 1993, MRSV invited Marco Tulio Badaracco,
Cathy Villalba and her US-American friend Sylvia Lim to
travel from Caracas to Táchira. is team collected abun-
dant rock blocks from the fossiliferous bonebed (Fig. 1b-
c), which were deposited in the MBLUZ, in coordination
with John Moody. Preparation anew of fossils from one of
the blocks resulted in the report at SVP by Sánchez-Vil-
lagra and Clark (1994). e premaxillary bone MBLUZ
P-4882 described herein, all the specimens described in
Sánchez-Villagra and Clark (1994), Barrett et al. (2008,
2014), and Barrett and Sánchez-Villagra (2012), as well as
hundreds of new specimens under study, come from this
1993 expedition, which includes to-date still unprepared
blocks in the MBLUZ collections. In 2000, Fernando No-
vas and MRSV obtained a grant from the Jurassic Foun-
dation to study the materials in Maracaibo, which was
started with a visit by Fernando Novas to the collection in
LUZ. Eventually, this project could be brought to comple-
tion in 2008 with the publication led by Paul Barrett from
the Natural History Museum in London, where MRSV
was based when the project was reactivated in 2005 (Bar-
rett et al. 2008). Further studies led to the description of
Laquintasaura in 2014 by Barrett et al.
In 1994, John Moody from MBLUZ led an expedi-
tion to La Quinta Fm. that resulted in the collection of
abundant rock blocks from the bonebed section, which
led to the rst report of an indeterminate theropod dino-
saur in the unit (Moody 1996, 1997). Additional thero-
pod materials (a partial femur and two partial teeth) from
the La Quinta type locality, were also collected in 1996
by geologists of the Instituto Universitario de Tecnología
de Maracaibo(IUTM). ese specimens were loaned and
prepared by John Moody in MBLUZ, and posteriorly
returned to the collections of the IUTM (Moody, per-
sonal communication). Posteriorly, Langer et al. (2014)
described the theropod Tachiraptor admirabilis based on
specimens coming also from the bonebed.
e only remain of dinosaurs in Venezuela that has not
been collected in the bonebed or in the type locality of the
La Quinta Fm. is a leg bone fragment been attributed to a
dinosaur of big size (see Sachs 1991); although the remain
was considered not diagnostic enough to explain in more
detail its phylogenetic position. is specimen was col-
lected by the geologist Oscar Odreman in the surrounding
of the La Fundación town (Táchira state), in an outcrop of
the La Quinta Fm. (Sachs 1991); however, no other pre-
cise stratigraphic a location information exist about. e
fossil was donated by Odreman to MSRV, who deposited
it in 1992 in the Universidad Simón Bolívar, Laboratorio
de Paleobiología (USB-PB).
TAXONOMIC DESCRIPTION
DINOSAURIA Owen, 1842
ORNITHISCHIA Seeley, 1887
Laquintasaura venezuelae Barrett et al., 2014
Description and remarks
e specimen MBLUZ P-4882 (Fig. 2b-g) corre-
sponds to a le premaxilla of approximately 38 mm in
length (from the anterior most part of the bone until the
posterolateral process), attached to the vomer, which is
3D premaxillary bone of the ornithischian Laquintasaura venezuelae
57
dorsoventrally attened and anteroposteriorly elongated,
attached to the premaxilla by a diagonal suture. MBLUZ
P-4882 is still embedded in the block matrix, and it is only
observable in ventral view (Fig. 2c). e rostral premaxil-
lary border is rugose in the midline, a characteristic that
is diagnostic of Ornithischia (Weishampel et al. 2007). A
premaxillary foramen is present, perforating the premax-
illa from the ventral surface, anterior to the rst premax-
illary tooth alveoli, to the dorsal surface, anterior most
part of the bone (Fig. 2d-e). e external naris size is small
and entirely overlying the premaxilla, as opposed to nares
extending over the maxilla. e posterolateral process of
the premaxilla contacts only with the nasal and maxilla.
e premaxillary palate is horizontal and connected to
the vomer by a diagonal suture. As in other ornithischians,
it is at and extends caudally passed the last premaxillary
tooth. No signs of a fossa-like depression positioned on
the premaxilla-maxilla boundary is found.
Seven dental grooves are well preserved in MBLUZ
P-4882 (Fig. 2c-d). is gure contrasts with that of oth-
er basal ornithischians, which are characterized by fewer
teeth, for example ve in Scelidosaurus (Norman 2020)
and Emausaurus (Weishampel et al. 2007), six in Lesotho-
saurus (Sereno 2010, Porro et al. 2015) and Scutellosau-
rus (Weishampel et al. 2007). Only the basal stegosaurid
Huayangosaurus taibaii from the Middle Jurassic, and the
ankylosaurid Gargoyleosaurus parkpini from the Upper
Jurassic are found to have a premaxillary tooth count of
seven (Sereno & Zhimin 1992, Carpenter et al. 1998). e
prosauropod Plateosaurus is reported to have four or ve
premaxillary teeth (Prieto-Márquez & Norell 2011), and
none of the silesaurids are observed to have more than four
premaxillary teeth (Müller & García 2020). In MBLUZ
P-4882, the rst premaxillary tooth is positioned adjacent
to the symphysis (Fig. 2d).
DISCUSSION AND CONCLUSIONS
Premaxillary dentition is a trait commonly observed in
basal thyreophorans (Nabavizadeh & Weishampel 2016).
e common number of teeth observed in this group is
ve or six, as seen in basal ornithischians Scelidosaurus
harrisonii (Norman 2020), Emausaurus (Weishampel
et al. 2007), Lesothosaurus diagnosticus (Sereno 2010,
Porro et al. 2015), and Scutellosaurus (Weishampel et al.
2007). Given the phylogenetic position of Laquintasaura
at the base of the thyreophoran tree, it is of interest to
understand how the premaxillary tooth count evolved in
the group. e premaxillary dentition is also present in
the basal stegosaur Huayangosaurus taibaii (tooth count
seven) (Sereno & Zhimin 1992), and nodosaurids such
as Silvisaurus (tooth count eight or nine) (Eaton 1960),
Pawpawsaurus (tooth count six) (Lee 2010), Gargoyleo-
saurus parkpini (tooth count seven) (Carpenter et al.
1998, Kilbourne et al. 2005), Tatankacephalus cooneyo-
rum (Parsons & Parsons 2009) and Sauropelta (Lee
2010). In contrast, other derived nodosaurids such as
Edmontonia, Panoplosaurus, and ankylosaurids lack pre-
maxillary teeth (Lee 2010, Nabavizadeh & Weishampel
2016). e same is true for Stegosaurus and other derived
stegosaurids (Sereno & Zhimin 2010, Nabavizadeh &
Weishampel 2016).
Figure 2. a-g) Original (c) and 3D model (b, d-g) of the le premaxilla MBLUZ P-4882 of Laquintasaura venezuelae. Drawing of skull
(a) based on Lesothosaurus, and modied aer Crompton & Attride (1986). Abbreviations: antr (anterior), asm (articular surface of
the maxilla), asn (articular surface of the nasal), na (nares), ppa (premaxillary palate), pmf (premaxillary foramen), pmt (premaxillary
teeth grooves), post (posterior), vo (vomer). Views: anterior (f), dorsal (e), le lateral (b), posterior (g), ventral (c-d).
Herrera-Castillo, Carrillo-Briceño & Sánchez-Villagra
58
In ornithischians the premaxillary dentition has been
convergently lost in the derived taxa in each subclade.
is has been attributed either to the development of an
elongate diastema in some groups, or to the development
of a much broader oral margin of the premaxilla with a
denticulate edge of its own (Nabavizadeh & Weishampel
2016). e information provided by the study of MBLUZ
P-4882 suggests that L. venezuelae presents the plesio-
morphic characteristic of a high premaxillary tooth count
(7), coherent with the narrow oral margin and lack of pre-
maxillary-maxillary diastema. is makes Laquintasaura
the oldest genus to have this characteristic, which, given
its position at the base of the yreophora clade, implies
that this is the plesiomorphic state from which the lesser
premaxillary tooth count of evolved. is morphological
trend may relate to the evolution of new feeding mecha-
nisms (Nabavizadeh & Weishampel 2016).
e bonebed of the La Quinta Fm. oers to date the
only known dinosaur remains from the earliest Jurassic of
the region. Despite the disarticulated nature of the remains
and the granularity of the sandy sediments where those
are embedded, some bones have been preserved, includ-
ing some fragile structures, such as the vomer found in the
premaxilla of MBLUZ P-4882. ese remains are of inter-
est to understand the evolution of early dinosaurs. As de-
scribed, the presence of the seven-tooth count on the pre-
maxilla is congruent with other discoveries that indicate
that the presence of premaxillary teeth is common among
basal ornithischians (Nabavizadeh & Weishampel 2016).
Knowledge of the general morphology of a dinosaur as L.
venezuelae helps understanding the early evolution and di-
versication of ornithischian and oers another data point
with which to analyse the history of the group.
From the La Quinta Fm. bonebed, two dinosaur species
have been named, Laquintasaura venezuelae (Barrett et al.
2014), and the small theropod Tachirraptor admirabilis
(Langer et al. 2014). e remains attributable to L. vene-
zuelae are abundant in the bonebed, especially postcranial
elements. Barrett et al. (2008, 2014) referred few cranial
bones of la L. venezuelae. Among these a right premaxilla
(MBLUZ P-5014) missing all teeth was mentioned but
not described or illustrated (Barrett et al. 2014, electronic
supplementary material). e le premaxilla MBLUZ
P-4882 (Fig. 2b-g) described herein sheds new light on
the anatomy of the Venezuelan basal ornithischian.
ACKNOWLEDGEMENTS
e authors thank Tito Barros and Gilson Rivas and
the Universidad del Zulia for their valuable support and
for the invitation to submit a paper to ANARTIA. We
thank Dinorah Cruz at Isabel De Jesús at the Instituto
del Patrimonio Cultural de Venezuela for kindly provid-
ing permits. Upon insistence of JDCB, MRSV included
in this manuscript a telegraphic account of the long saga
of trips to Táchira, missed opportunities and failures that
involved the early collection of study of what later be-
came Laquintasaura. MRSV thanks the Society of Verte-
brate Palaeontology (SVP) for the support via the Patter-
son Award and Jim Clark, whose keen eye and expertise
made the beginning of this project possible, and who
helped MRSV justify to the SVP the delays in reporting
to the SVP. Later, Paul Barrett brought this project to
salvation with his dedicated study of the many isolated
bones. Many thanks to John Moody for the revision of
the manuscript and all his constructive suggestions and
corrections.
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