Laquintasaura is a genus of Venezuelan ornithischian dinosaur containing a single species, Laquintasaura venezuelae. It is known for being one of the most primitive ornithischians in the fossil record, as well as the first dinosaur to have been identified from Venezuela. The name is derived from the La Quinta Formation, where it was discovered, and the feminine Greek suffix for lizard, with the specific name referring to the country of Venezuela. It is known from hundreds of fossil elements, all derived from a single extensive bonebed locality. Initially discovered by French palaeontologists, numerous expeditions have been conducted to excavate from the bonebed, largely led by Marcelo R Sánchez-Villagra. Once thought to represent remains of Lesothosaurus, it was formally named in a 2014 study; much of the abundant material was not yet prepared at the time and research remains ongoing.
A small animal, it is thought to have been a lightly built and would not have grown much larger than in length. One of the first species known to possess the distinctive bird-like hip bone of ornithischians, it would have been a capable bipedal runner. Showcasing rather primitive anatomy overall, its most noted characteristics are found in its teeth. Unlike the leaf shaped teeth of related ornithschians, those of Laquintasaura had a distinctive triangular shape, with distinct striations and sharp running down the edges. These may have contributed to an omnivorous diet unlike those of later relatives. They would have lived in groups, living on a seasonal alluvial plain and being preyed upon by the contemporary Tachiraptor.
Taxonomic uncertainty has led to conflicting hypotheses that it is either an early diverging ornithischian or part of the subgroup Thyreophora. Aspects of its femoral anatomy, possessing only some traits of later relatives, may be demonstrative of an important transitional step in the evolution from earlier types of dinosaur. Regardless of its precise classification, its dating to around 200 million years ago at the start of the Jurassic and primitive nature make it a key insight into early ornithischian evolution. Likewise, its discovery was considered significant to the understanding of the geographical distribution of early dinosaurs on the supercontinent of Pangaea. Previous research had cast doubt on whether dinosaurs lived around the equator during their early evolution, and on when ornithischians first spread to the northern Hemisphere; the discovery of Laquintasaura demonstrated both at a very early point in time.
Discovery and naming
Laquintasaura is known from a single locality, a bonebed in rocks of the La Quinta Formation, which is Early Jurassic in age. This bonebed was first discovered in the 1980s by a team of French palaeontologists on a reconnaissance mission to Venezuela, near a road between the towns of La Grita and Seboruco, in the state of Táchira. Initially, the French team discovered two teeth and the fragment of a (a bone at the back of the skull, articulating with the jaw). These fossils were brought to Paris, with intent to return the material to Venezuela after study, and described by D.E. Russel and colleagues in a 1992 publication. Based on similar cranial anatomy, they were tentatively referred to the genus Lesothosaurus but not to any specific species; this genus, also from the Early Jurassic, is found in South Africa and Lesotho. Unaware of the French team's discoveries, Marcelo R. Sánchez-Villagra and colleagues conducted their own expeditions into the La Quinta Formation in 1992 and 1993 following an initial survey in 1989. While they did not find vertebrate fossils during the 1989 trip, they rediscovered the bonebed during the later expeditions; dinosaur expert James Clark is credited with noticing the locality. A few plaster jackets worth of fossils were recovered and transported to Buenos Aires in Argentina, where Sánchez-Villagra and the team of Guillermo Rougier spent three months partially preparing the fossils. The fossils were then returned to Venezuela, being brought to Universidad Simón Bolívar. Several years later in the late 1990s, Sánchez-Villagra would become aware of the French specimens, which had remained in Paris, and co-ordinate their return to Venezuela as well. They were deposited in the collections of the Museu de Biología de la Universidad de Zulia (MBLUZ).
Soon after the transfer of material to the Universidad Simón Bolívar, Sánchez-Villagra became aware he was no longer permitted to study it there. He resolved to conduct expeditions to find additional material. The Universidad Simón Bolívar material has gone unstudied since. A successful trip was organized in December 1993 with a new team from Caracas, which produced abundant new material. This was deposited in the MBLUZ, like the original French material. Early preparation of these blocks was reported on at the 1994 conference of the Society of Vertebrate Paleontology. Sánchez-Villagra and Fernando Novas, who had met during the preparation in Buenos Aires, obtained a grant from the Jurassic Foundation to study this material. The project would eventually become based in the Natural History Museum in London, England, and would bring in Paul Barrett. He, Novas, Sánchez-Villagra, and colleagues described the material in a 2008 paper, identifying a likely new genus of ornithischian among many other indeterminate animals but not naming it until additional material was known.
This additional material was described in a 2014 paper by a team including Barrett and Sánchez-Villagra. Through comparisons using newly prepared material as well as new data on the usefulness of identifying features relied on by the 2008 study, it was found that almost all material in the bonebed in fact belonged to the previously identified ornithischian taxon. With the entire wealth of material now recognized as belonging to the taxon, they formally named it as Laquintasaura venezuelae. The generic name derives from the name of the geologic formation and the feminine Greek suffix for lizard; the specific name refers to the country and people of Venezuela. Among the material, the isolated tooth MBLUZ P.1396 was designated as the holotype, forming the type series with paratypes MBLUZ P.5017, a partial ; MBLUZ P.5018, a partial left ; and MBLUZ P.5005, a left astragalocalcaneum. Though the choice of a tooth as the type specimen is uncommon for a dinosaur, it was chosen due to being the most distinctive aspect of the anatomy, being a very abundant element of the sample, and the unlikelihood that teeth would be different across sections of the mouth due to the uniformity of the known teeth in related taxa. A later 2021 study by Carlos-Manuel Herrera-Castillo, Sánchez-Villagra, and colleagues described a that has been prepared and studied since the 2014 paper; at the time of this publication, study and preparation of much material remains ongoing. As it is the oldest reliably dated ornithischian, hailing from the very start of the Jurassic, its discovery is considered to very significant.
Hundreds of individual fossil elements are known for Laquintasaura, representing a minimum of four individuals and potentially many more. Material that had already been prepared upon publication of the 2014 paper included isolated cranial remains, an abundance of teeth, , , , and vertebrae, a , pelvic and hindlimb material, and other isolated l elements. Forelimb material was completely absent, and material from the feet was very limited. Much of the material was still unprepared at this time, and it is possible that much more material remains ungathered from the bonebed. Isolated theropod remains were also reported from the bonebed, some of which was later described as Tachiraptor; sauropod material was also later identified. Dental morphotypes similar to that of Laquintasaura have been described from the Kota Formation in India as well as from the White Limestone Formation in England. They date to the Bathonian age of the Middle Jurassic, more than 30 million years after Laquintasaura lived.
Description
Like other early members of Ornithischia, it is assumed that Laquintasaura was a lithe bipedal animal. The largest femur among the bonebed is in length; assuming similar proportions to similar animals like Hypsilophodon, Heterodontosaurus, and Hexinlusaurus, it was estimated the Laquintasaura individual could grow to around in length. However, this individual was a subadult, and more fragmentary remains appear to belong to slightly larger animals. The small size and conservative skeletal anatomy of Laquintasaura indicates it had not yet diversified extensively from their ancestral anatomical state. Only later would ornithischians diverge into larger, more specialized animals with traits like armor and quadrupedality.
The most distinctive anatomy of Laquintasaura is found in its dentition. The teeth are unusually tall and have their widest point immediately above the tooth root; the result of this is an isoceles triangle shape. Coarse denticles run along the entire crown margin (the edge of the exposed tooth). By comparison, the teeth of other primitive ornithischians have a stouter, sub-triangular shape that continues to widen farther up the tooth and only possesses denticles along the top of the crown. Additionally, the teeth of Laquintasaura possess uniquely prominent striations on both the inside and outside sides of the tooth. As opposed to the heterodont condition of later ornithischians, this dental anatomy is thought to have been uniform throughout the entirety of the mouth, both in the and the . Some teeth are, however, somewhat more recurved than others. Convergently similar anatomy, with a tall tooth construction and striations, does occur convergently in the neornithischian dinosaur Hexinlusaurus, which nonetheless has a differing tooth shape and denticulation. The of L. venezuelae has seven teeth in each position and does not present a diastema close to the premaxillo-maxillary suture. Such a high number of premaxillary teeth is uncommon in ornithischians, outside of some members of Ankylosauria. The high count in Laquintasaura elucidates the basal evolution state of Ornithischia, and indicates the species' dental anatomy is very primitive even compared to other Early Jurassic taxa.