Laquintasaura is a genus of Venezuelanornithischiandinosaur containing only the type speciesLaquintasaura venezuelae. The species was the first dinosaur to have been identified from Venezuela. It is known from extensive remains, all from a singular bonebed locality which has been sampled for specimen blocks over the course of several expeditions, largely led by Marcelo R Sánchez-Villagra. A small, very primitive animal, it is known for its distinct dental anatomy and for being one of the earliest and most primitive ornithischians in the fossil record. Taxonomic uncertainty has led to conflicting theories that it is either as the base of Ornithischia or at the base of the subgroup Thyreophora. In either model, its dating to around 200 million years ago, at the start of the Jurassic, existence in equatorial latitudes, and primitive nature make it a key view into early ornithischian evolution. It's thought that Laquintasaura would've lived in groups and had a possible omnivorous diet, living on a seasonal alluvial plain and being preyed about by the contemporary Tachiraptor.
Locality of the bonebed where all known material of Laquintasaura has been found
The bonebed would produce material eventually named as Laquintasaura was originally discovered in the 1980s, by a team of French palaeontologists. The bonebed is found near a road between the towns of La Grita and Seboruco, in the Táchira state of Venezuela, in rocks pertaining to the Early JurassicLa Quinta Formation; it is directly opposite to the type section of the formation, separated by possible geologic faults. These initial French discoveries - two teeth and a quadrate would be brought to Paris and described by D.E. Russel and colleagues in a 1992 study; based on similar cranial anatomy, they were referred to the genus Lesothosaurus, an early ornithischian from the Early Jurassic of Lesotho and South Africa. Unaware of the French team's discoveries, Marcelo R. Sánchez-Villagra and colleagues would make their own expeditions into the La Quinta Formation; initially finding no vertebrate fossils in 1989, they'd later rediscover the bonebed in the first of three expeditions in 1992 and 1993; dinosaur expert James Clark was the one to first notice the easy to miss locality. A few plaster jackets worth of fossils were recovered and transported by Sánchez-Villagra to Buenos Aires in Argentina, where he and the team of Dr. Guillermo Rougier spent three months partially preparing the fossils. After this they were returned to Venezuela, being brought to Universidad Simón Bolívar where Sánchez-Villagra had written his thesis. Several years later in the late 1990s, Sánchez-Villagra would become aware of the French specimens and co-ordinate their return to Venezuela as well, deposited in the collections of the Museu de Biología de la Universidad de Zulia (MBLUZ).[1]
Sánchez-Villagra become aware he was no longer permitted to study the fossils that had been deposited at the Universidad Simón Bolívar soon after they have been transferred, and resolved to conduct new expeditions to gather additional material from the bonebed; the Universidad Simón Bolívar material has gone unstudied since. Shortly before hearing this news an attempted expedition had failed due to a truck failure. 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 the 1993 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 would finally publish on the material in a 2008 paper in the scientific journalPalZ, identifying a likely new genus of ornithischian among many other indeterminate animals but not naming it until further material was known.[1]
Tibia and ischium of Tachiraptor, whose remains are found in the same bonebed as Laquintasaura
That further material would become recognized and published on in a 2014 paper in the journal Proceedings of the Royal Society B by a team including Barrett and Sánchez-Villagra. This paper would re-evaluate the 2008 paper's conclusions, finding through comparisons with newly prepared material as well as new data on the usefulness of identifying features relied on by the 2008 study that almost all material in the bonebed (excepting two theropod teeth, later described with a newly recognized tibia as Tachiraptor[1][2]) 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. Material prepared as of the publication of the paper included isolated cranial remains, an abundance of teeth, all four major types of vertebrae, a scapula , pelvic and hindlimb material, and other isolated postcranial elements. Forelimb material was completely absent, and material from the hindfeet was very limited. Much of the material was still unprepared at this time, and it's possible much more material remains ungathered from the bonebed.[3] A later 2021 study by Carlos-Manuel Herrera-Castillo, Sánchez-Villagra, and colleagues described a premaxilla prepared and studied since the 2014 paper; at the time of this publication, study and preparation of much material remains ongoing.[1] As it is the oldest reliably dated ornithischian, hailing from the very start of the Jurassic, its discovery is considered to very significant.[1][3]
Hundreds of individual fossil elements are known for Laquintasaura, representing a minimum of four individuals and potentially many more. The majority of known remains are thought to represent subadult individuals, but one small tibia is thought to belong to a juvenile (organism) and a scapular fragment is thought to be long to an adult. 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 femur; MBLUZ P.5018, partial left ischium ; 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 different in different parts of the mouth due to the uniformity of the known teeth and anatomy of relatives.[3]
Description
Size diagram of Laquintasaura, based on known remains; adults may have grown slightly larger
Like other early members of Ornithischia, it is assumed that Laquintasaura was a lithe bipedal animal. The largest femur among the bonebed is 90 millimetres (3.5in) in length, which was used to estimate the body size of the animal based on comparisons to other taxa. Assuming similar proportions to similar primitive ornithischians Hypsilophodon, Heterodontosaurus, and Hexinlusaurus, it was estimated the Laquintasaura individual was around 1 metre (3.3ft) in length. The individual in question was, however, a subadult, indicating that the species may have gotten slightly larger as an adult, as indicated by other more fragmentary elements less useful for size estimation. Its small size and conservative skeletal anatomy indicates it, and other ornithischians at the very beginning of the Jurassic, had not yet diversified extensively from their ancestral anatomical state. Only later would the group diverge into larger, more specialized animals with traits with armor and quadrupeality.[3]
The most distinctive part of the anatomy is Laquintasaura is found in its dentition, with numerous autapomorphies found therein. The teeth are unusually long, tapering from the central apex of the tooth crown and forming an isosceles triangular shape overall. Coarse denticles run along the entire crown margin (the edge of the exposed tooth). The teeth are laterally widest near this apex, and they possess uniquely prominent striations on both the inside and outside sides of the tooth. This anatomy is seen among all teeth in the bonebed sample, indicating it was likely uniform throughout the entirety of the mouth, both in the premaxilla and the maxilla .[3] The premaxilla 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; later members of Ornithischia would reduce their premaxillary tooth count until many didn't possess any whatsoever. The high count in Laquintasaura elucidates the basal state of having many teeth, and indicates its dental anatomy is very primitive even compared to other Early Jurassictaxa.[1]
The postcranial anatomy of Laquintasaura is less remarkable than that of its dentition, but still possesses a few autapormophies. The upper surface of the ischium further up than the obturator process is highly inflected; in closely related taxa both sides of the ischium form a more continuous, smooth surface. The epicondyle at the connection of the femur and the fibula is inset in the middle from a ventral or posterior view, a trait of derived ornithischians completely absent in any other basal taxa, which have a smooth transition without any notch forming a "step". Finally, the astragalus has a broad and deep U-shaped notch on its top surface; a similar V-shaped notch is seen in Scutellosaurus, but is noticeably less developed in that genus, being less than half as deep. In contrast to these unique traits, ornithischian synapomorphies can be seen in the pelvic anatomy. In addition to its diagnostic features, numerous differences from other individual basal ornithischian taxa were noted, described in detail in the supplementary material of the 2014 description paper.[3]
The histology of the bone microstructure of specimens referred to Laquintasaura indicate it had secondarily reduced growth rates compared to the presumed ancestral state of ornithischians, similar to other small thyreophorans like Scutellosaurus but unlike Lesothosaurus, ornithopods, and marginocephalians. However, the lack of data on primitive ornithischian histology as well as the limited sample size available for Laquintasaura, these conclusions remain uncertain.[3]
The specifics of the phylogenetic relationships of Laquintasaura remains somewhat uncertain.[4][5][6]Phylogenetic analyses as well general anatomy demonstrate robustly that it's a very basal member of the group Ornithischia. Its exact position within this clade was unresolved by the original 2014 description, which found it in a large polytomy with Eocursor, Lesothosaurus, Stormbergia, Scutellosaurus, the clade Thyreophora, and the clade Neornithischia.[3] Some later phylogenetic analyses have had to remove the taxon outright due to being too fragmentary and lowering the resolution of the results.[7][8] Some studies, such as that of Matthew G. Baron and colleagues or that of Thomas J. Raven and Susannah Maidment, both in 2017, have found it to be a very early member of the group Thyreophora, as the sister taxon of Scutellosaurus.[9][10] Bone histology, similar to Scutellosaurus but unlike Lesothosaurus, has been posited as circumstantial evidence of this placement.[11] On the other hand, the analysis of a study on ornithischian phylogeny by P. E. Dieudonné and colleagues in 2021 found Laquintasaura not as a thyreophoran but in a more primitive position outside of the clade Genasauria.[12] The cladogram from Baron et al. (2017) is shown below on the left, and that of Dieudonné et al. (2021) is shown on the below right. Clade names have been inserted based on definitions established by a paper by Daniel Madzia and colleagues in 2021 for clarity.[9][12][13]
Arrangement of the continents are the time Laquintasaura lived, 200 million years ago; as today, Venezuela was at the time in the northern hemisphere near the equator
Laquintasaura hails from the La Quinta Formation of northern South America, in what is now Colombia and Venezuela, and was found in the Venezuelan part of the formation.[3][14] The exact age of the La Quinta Formation was traditionally very unclear, with estimates variably placing anywhere from the Permian to the Cretaceous, but modern estimates tend to find that the section containing the Laquintasaura bonebed dates to very near the boundary of the Triassic and Jurassic periods, specifically at start of the Hettangian age around 200 million years ago and potentially as little at 150 thousand years from the end of the Triassic, though some uncertainty still exists.[2][3][15] This very old age makes Laquintasaura one of the earliest known members of Ornithischia, making it important to understanding their early evolution.[1][3] It provides concrete evidence that they had spread to the northern hemisphere by the start of the Jurassic,[5] and its geographic placement in an equatorial region demonstrates dinosaur presence in equatorial latitudes, as well as such region's role in early dinosaur evolution, something traditionally doubted.[1][3][16] Though the genus' presence so soon after the end-Triassic extinction indicates ornithischians achieved quick expansion in diversity and distribution, its conservative anatomy indicates that increases in body size and anatomical specialization did not occur until later in the Jurassic.[3]
Skull of Lesothosaurus, another early ornithischian; it may have shared omnivorous behaviour with Laquintasaura lost in later relatives
The ecosystem that Laquintasaura lived in is thought to represent an alluvial plain, with both arid and humid seasons.[2] The early theropod dinosaur Tachiraptor would have lived alongside Laquintasaura, and likely preyed upon it.[2][17] The sauropod dinosaur Perijasaurus also hails from the La Quinta Formation, but is thought to have lived at a later time near the end of the Early Jurassic, around 175 million years ago.[14]Laquintasaura is thought to have been primarily herbivorous, but the unusually tall structure of the teeth are reminiscent of carnivorous animals, indicating they may have also eaten things like small insects as part of their diet.[16][18] Similar omnivorous behaviour has been suggested in the fellow primitive ornithischian Lesothosaurus,[19] as well as more tentatively in taxa like Agilisaurus, Hypsilophodon, and Orodromeus before disappearing in more derived relatives like iguanodontians.[20]
The exact nature of the taphonomy of the Laquintasaura bonebed remains incompletely studied. The remains are thought to have undergone some degree of low-energy transport, but the lack of any damage to the bones, or signs of things like plant root damage or insect boring holes, indicating the remains were not exposed for a long time prior to being buried.[3] The bonebed is entirely devoid of microfossils, invertebrates, or plant remains, and is palynologically barren; the only other animal found at the site is the scant remains of Tachiraptor.[2][3] All of this indicates the four or more individuals at the site likely died together and maybe have lived together in life, indicative of social behaviour. Herding is known in ornithischians of the Late Jurassic and Cretaceous, but its presence in Laquintasaura would be the first recognized in such an early member of the group (though more recent research has also indicated presence in the genus Lesothosaurus[11]).[3]
Related Research Articles
Thyreophora is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous.
Lesothosaurus is a monospecific genus of ornithischian dinosaur that lived during the Early Jurassic in what is now South Africa and Lesotho. It was named by paleontologist Peter Galton in 1978, the name meaning "lizard from Lesotho". The genus has only one valid species, Lesothosaurus diagnosticus. Lesothosaurus is one of the most completely-known early ornithischians, based on numerous skull and postcranial fossils from the Upper Elliot Formation. It had a simpler tooth and jaw anatomy than later ornithischians, and may have been omnivorous in some parts of the year.
Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are known to have first appeared in the Middle Jurassic, and persisted until the end of the Cretaceous Period. The two main families of Ankylosaurs, Nodosauridae and Ankylosauridae are primarily known from the Northern Hemisphere, but the more basal Parankylosauria are known from southern Gondwana during the Cretaceous.
Kentrosaurus is a genus of stegosaurid dinosaur from the Late Jurassic in Lindi Region of Tanzania. The type species is K. aethiopicus, named and described by German palaeontologist Edwin Hennig in 1915. Often thought to be a "primitive" member of the Stegosauria, several recent cladistic analyses find it as more derived than many other stegosaurs, and a close relative of Stegosaurus from the North American Morrison Formation within the Stegosauridae.
Scelidosaurus is a genus of herbivorous armoured ornithischian dinosaur from the Jurassic of the British Isles.
Echinodon is a genus of heterodontosaurid dinosaur that lived during the earliest Cretaceous of southern England and possibly western France in the Berriasian epoch. The first specimens were jaw bones named Echinodon becklesii by Sir Richard Owen in 1861, and since their original description only additional teeth have been discovered. The specific name honours collector Samuel Beckles who discovered the material of Echinodon and many other taxa from across England, while the genus name translates as "prickly tooth" in reference to the dental anatomy of the taxon.
Heterodontosaurus is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic, 200–190 million years ago. Its only known member species, Heterodontosaurus tucki, was named in 1962 based on a skull discovered in South Africa. The genus name means "different toothed lizard", in reference to its unusual, heterodont dentition; the specific name honours G. C. Tuck, who supported the discoverers. Further specimens have since been found, including an almost complete skeleton in 1966.
Alocodon is a genus of ornithischian dinosaur known from multiple teeth from the Middle or Late Jurassic Cabaços Formation of Portugal, and also the Forest Marble and Chipping Norton Formations of England. A single species is known, A. kuehnei.
Trimucrodon is a genus of ornithischian dinosaur from the Late Jurassic Lourinhã Formation of Portugal. The type, and currently only, species is T. cuneatus.
Neornithischia is a clade of the dinosaur order Ornithischia. It is the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside of their lower teeth. The teeth wore unevenly with chewing and developed sharp ridges that allowed neornithischians to break down tougher plant food than other dinosaurs. Neornithischians include a variety of basal forms historically known as "hypsilophodonts", including the Parksosauridae; in addition, there are derived forms classified in the groups Marginocephalia and Ornithopoda. The former includes clades Pachycephalosauria and Ceratopsia, while the latter typically includes Hypsilophodon and the more derived Iguanodontia.
Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic. Its fossils have been found in Mecklenburg-Vorpommern, northern Germany. Emausaurus is the only known Toarcian thyreophoran, as well as the only dinosaur from the zone of the same age with a formal name.
Heterodontosauridae is a family of ornithischian dinosaurs that were likely among the most basal (primitive) members of the group. Their phylogenetic placement is uncertain but they are most commonly found to be primitive, outside of the group Genasauria. Although their fossils are relatively rare and their group small in numbers, they have been found on all continents except Australia and Antarctica, with a range spanning the Early Jurassic to the Early Cretaceous.
Eocursor is genus of basal ornithischian dinosaur that lived in what is now South Africa during the Early Jurassic. Remains of this animal have been found in the Upper Elliot Formation and it is among the most completely known early ornithischians, shedding new light on the origin of the group.
Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word gena meaning ‘cheek’ and the Greek word saúra (σαύρα) meaning ‘lizard.’ It is hypothesized that Genasauria had diverged from Lesothosaurus by the Early Jurassic. Cranial features that characterize Genasauria include a medial offset of the maxillary dentition, a sprout-shaped mandibular symphysis, moderately sized coronoid process, and an edentulous anterior portion of the premaxilla. A distinguishing postcranial feature of Genasauria is a pubic peduncle of the ilium that is less robust than the ischial peduncle. Genasauria is commonly divided into Neornithischia and Thyreophora. Neornithischia is characterized by asymmetrical distributions of enamel covering the crowns of the cheek teeth, an open acetabulum, and a laterally protruding ischial peduncle of the ilium. Neornithischia includes ornithopods, pachycephalosaurs, and ceratopsians. Thyreophora is characterized by body armor and includes stegosaurs, ankylosaurs, Scelidosaurus, and Scutellosaurus.
The La Quinta Formation is a Jurassic geologic formation which crops out in the Cordillera de Mérida and Serranía del Perijá of western Venezuela and northeastern Colombia. The formation is also present in the subsurface of the Cesar-Ranchería and Maracaibo Basins. At its type locality near La Grita, Táchira, it consists of a basal dacitic tuff followed by interlayered sandstones, tuffs, siltstones and rare limestones. Dinosaur remains including Laquintasaura, Tachiraptor, and Perijasaurus are among the fossils that have been recovered from the formation.
Pegomastax is a genus of heterodontosaurid dinosaur that lived during the Early Jurassic of South Africa. The only known specimen was discovered in a 1966-1967 expedition in Transkei District of Cape Province, but wasn't described until 2012 when Paul Sereno named it as the new taxon Pegomastax africana. The genus name is derived from the Greek for "strong jaw", and the species name describes the provenance of Africa; it was originally spelled africanus, was corrected to africana to align with the gender of the genus name.
Isaberrysaura is a genus of stegosaurian ornithischian dinosaur from the Middle Jurassic Los Molles Formation of Patagonia, Argentina. The genus contains a single species, I. mollensis, described by Salgado et al. in 2017 from a single specimen. Although initially classified as a basal neornithischian, subsequent analysis has allied it with the Stegosauria; the morphology of its skull resembles those of other members of the group.
Jakapil is a genus of basal thyreophoran dinosaur from the Candeleros Formation of Argentina. The type species is Jakapil kaniukura.
References
1 2 3 4 5 6 7 8 Herrera-Castillo, Carlos M.; Carrillo-Briceño, Jorge D.; Sánchez-Villagra, Marcelo R. (2021). "Non-invasive imaging reveals new cranial element of the basal ornithischian dinosaur Laquintasaura venezuelae, Early Jurassic of Venezuela". Anartia. 32: 53–60. doi:10.5281/zenodo.5571307.
↑ Han, Fenglu; Forster, Catherine A.; Xu, Xing; Clark, James M. (2017). "Postcranial anatomy of Yinlong downsi (Dinosauria: Ceratopsia) from the Upper Jurassic Shishugou Formation of China and the phylogeny of basal ornithischians". Journal of Systematic Palaeontology. 16 (14): 1159–1187. doi:10.1080/14772019.2017.1369185. S2CID90051025.
1 2 Rincón, Aldo F.; Raad Pájaro, Daniel A.; Jiménez Velandia, Harold F.; Ezcurra, Martín D.; Wilson Mantilla, Jeffrey A. (2022). "A sauropod from the Lower Jurassic La Quinta Formation (Dept. Cesar, Colombia) and the initial diversification of eusauropods at low latitudes". Journal of Vertebrate Paleontology. 42: e2077112. doi:10.1080/02724634.2021.2077112.
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