Leonerasaurus

Leonerasaurus is a basal genus of sauropodomorph dinosaur. Currently, there is only one species known, named L. taquetrensis by Diego Pol, Alberto Garrido and Ignacio A. Cerda in 2011. The fossil, an incomplete subadult individual, was found in the Las Leoneras Formation in Argentina. This formation is probably Early Jurassic in age. Leonerasaurus was a small non-sauropod sauropodomorph, showing an unusual combination of basal and derived characters. This indicates that the evolution of early sauropodomorphs witnessed a great degree of convergent evolution.[1]

Leonerasaurus
Temporal range: Early Jurassic
~199 Ma
Leonerasaurus
Restored skeleton, photographed at the special exhibition "DINOSAURIER – Giganten Argentiniens" when stationed at the ForschungsMuseum Alexander König in Bonn in 2009.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Clade: Sauropodiformes
Clade: Anchisauria
Genus: Leonerasaurus
Pol, Garrido & Cerda, 2011
Species:
L. taquetrensis
Binomial name
Leonerasaurus taquetrensis
Pol, Garrido & Cerda, 2011

Description

Leonerasaurus NT
Restoration

Leonerasaurus taquetrensis is known from one incomplete individual. Parts of a dentary and some teeth, neck and trunk vertebrae, a sacrum, parts of the pectoral (shoulder) and pelvis (hip) girdle as well as several limb bones were found. Much of the remains were found in articulation.[1]

Dentary and teeth

Of the skull only the anterior part of the right dentary was found. Near the area where it touches the contralateral element at the tip of the lower jaw (the symphysis) the bone is straight and only gently arched medially, as is seen in basal sauropods. More derived sauropods (eusauropods) have medially broadly arching symphyseal regione and anterior portions of the tooth row. The ventral (lower) edge of the dentary is damaged, but does not appear to be ventrally deflected at the symphysis as in some basal sauropodomorphs such as Plateosaurus. Also, a longitudinal ridge that is seen in some basal sauropodomorphs (e.g., Massospondylus, Coloradisaurus and Plateosaurus) is not preserved in Leonerasaurus. However, this may be related to the damaged state of the specimen.[1]

Leonerasaurus dentary
Lateral and medial view of the dentary

On the dentary, 13 teeth or tooth fragments were found. There are two empty alveoli, so that the total tooth count on one side was at least 15. Three teeth were found isolated near the dentary. The teeth and alveoli are angled forward (procumbent) by ~60°, similar to eusauropods, but also to juveniles of Mussaurus. Tooth height and width decreases from the front to the back, and neighboring teeth overlapping each other. The edges of the teeth in the front of the jaw likely were not serrated, or at least only at the crown tips. This is usually the case in eusauropods. Teeth further back in the dentary are nearly all damaged, but a not erupted tooth has large denticles similar to basal sauropodomorphs.[1] This pattern of teeth without denticles in front, and teeth with denticles in the back of the lower jaw is also seen in juveniles of Mussaurus and Melanorosaurus. Also, in contrast to eusauropod teeth, there are no high-angle wear facets on the teeth of Leonorasaurus.[1]

The anterior teeth are spoon-shaped, with the outer surface convex (bulging out), the inner one concave (hollowed out), again resembling basal sauropods. The surface texture, however, is more similar to basal sauropodomorphs, and not to sauropods.[1]

Vertebrae

The neck of Leonorasaurus is known almost completely, only the atlas is lost. The nine remaining cervicals were found articulated with the first five complete dorsal (trunk) vertebrae. Additionally, a probable sixth dorsal and an articulated group of three mid-dorsals were found. Fragments of more posterior dorsals and of ribs were also recovered. The sacrum (fused vertebrae that form the core of the hip), consisting of four vertebrae, is nearly complete, but no bones of the tail was recovered.[1]

Leonerasaurus cervical vertebrae
Cervical vertebrae
Leonerasaurus sacrum
Sacrum in dorsal, ventral, and lateral view

The overall shape of the neck vertebrae is typical for basal sauropodomorphs, but Pol et al. interpret the remains of the neural arches to indicate a more sauropod-like shape. Some characters, however, show an intermediate development.[1] In the trunk, the vertebrae show typical non-sauropod characters, such as relatively long and low neural arches with a narrow anterior ridge (the anteriormost dorsal vertebrae have slightly high neural arches), an anteriorly placed parapophysis (one of the articulation points for the ribs), and lack of or less strong development of certain laminae (thin ridges). The diapophysis (the second articulation for the rib) is also in the same position as in basal sauropodomorphs. A lamina connecting the diapophysis to the prezygapophysis on all dorsals, but not in no-sauropod sauropodomorphs, is present in the posterior dorsals.[1]

Phylogenetic position

Leonerasaurus appears to be belong into the Anchisauria, as the closest sister taxon to the group sauropods (following Yates)[2] + Melanorosaurus (M. is seen as a sauropod by some researchers).

A cladogram after Pol, Garrido & Cerda, 2011,[1] illustrates a possible placing of Leonerasaurus in Sauropodomorpha:

Sauropodomorpha

Saturnalia

Pantydraco

Thecodontosaurus

Efraasia

Ruehleia

Plateosaurus

Massopoda

Riojasaurus

Massospondylus

Coloradisaurus

Lufengosaurus

Gyposaurus

Yunnanosaurus

Anchisauria

Anchisaurus

Aardonyx

Leonerasaurus

Melanorosaurus

Sauropoda

Antetonitrus

Lessemsaurus

Kotasaurus

Vulcanodon

Eusauropoda

Discovery

Leonerasaurus humerus
Right humerus in anterior, posterior, and lateral view

The fossils assigned to Leonerasaurus were found near Cañadón Las Leoneras (an affluent of the left margin of the Chubut river), southeast of Sierra de Taquetrén, Chubut Province, Central Patagonia, Argentina. This formation is probably early Jurassic in age,[3] interpreted as Pliensbachian to Toarcian[4] or late Sinemurian to Toarcian.[5] The volcanic facies of the overlying Lonco Trapial Formation is certainly from the Middle Jurassic, so that the younger boundary of the Las Leoneras Formation is well constrained. However, a Late Triassic affinity cannot be rules out, because the lower constraint of the formation is not well-defined.[1]

Etymology

The generic name is derived from Leoneras, in reference to the lithostratigraphic unit where this taxon was found, and saurus, "lizard" (Latinized Greek). The specific name taquetrensis refers to the Sierras de Taquetrén, where Las Leoneras Formation crops out in Central Patagonia.[1]

References

  1. ^ a b c d e f g h i j k l Diego Pol, Alberto Garrido, Ignacio A. Cerda (2011). "A New Sauropodomorph Dinosaur from the Early Jurassic of Patagonia and the Origin and Evolution of the Sauropod-type Sacrum". PLoS ONE. 6 (1): e14572. doi:10.1371/journal.pone.0014572. PMC 3027623. PMID 21298087.CS1 maint: Uses authors parameter (link)
  2. ^ Yates, A.M. (2010). "A revision of the problematic sauropodomorph dinosaurs from Manchester, Connecticut and the status of Anchisaurus Marsh". Palaeontology. 53 (4): 739–752. doi:10.1111/j.1475-4983.2010.00952.x.
  3. ^ C. Nakayama (1973). "Sedimentitas pre-bayocianas en el extremo austral de la Sierra de Taquetrén". 5° Congreso Geológico Argentino, Actas. 3: 269–277.CS1 maint: Uses authors parameter (link)
  4. ^ E. Figari, S.F. Courtade (1993). "Evolución tectosedimentaria de la Cuenca de Cañadón Asfalto, Chubut, Argentina". 13° Congreso Geológico Argentino y 2° Congreso de Exploración de Hidrocarburos, Actas. 1: 66–77.CS1 maint: Uses authors parameter (link)
  5. ^ Page, R., Ardolino, A., de Barrio, R.E., Franchi, M., Lizuain, A., et al. 2000. "Estratigrafía del Jurásico y Cretácico del Macizo de Somún Curá, provincias de Río Negro y Chubut." In: Caminos, R., (ed.) Geología Argentina. Buenos Aires: Subsecretaría de Minería de la Nación. pp. 460–488.
Anchisauria

The Anchisauria were a clade of sauropodomorph dinosaurs that lived during the Late Triassic and Early Jurassic. The name Anchisauria was first used by Galton and Upchurch in the second edition of The Dinosauria. Galton and Upchurch assigned two families of dinosaurs to the Anchisauria: the Anchisauridae and the Melanorosauridae. The more common prosauropods Plateosaurus and Massospondylus were placed in the sister clade Plateosauria.

However, recent research indicates that Anchisaurus is closer to sauropods than traditional prosauropods; thus, Anchisauria would also include Sauropoda.The following cladogram simplified after an analysis presented by Blair McPhee and colleagues in 2014.

Averostra

Averostra, or "bird snouts", is a clade that includes most theropod dinosaurs that have a promaxillary fenestra (fenestra promaxillaris), an extra opening in the front outer side of the maxilla, the bone that makes up the upper jaw. Two groups of averostrans, the Ceratosauria and the Orionides, survived into the Cretaceous period. When the Cretaceous–Paleogene extinction event occurred, ceratosaurians and two groups of orionideans within the clade Coelurosauria, the Tyrannosauroidea and Maniraptoriformes, were still extant. Only one subgroup of maniraptoriformes, Aves, survived the extinction event and persisted to the present day.

Avetheropoda

Avetheropoda, or "bird theropods", is a clade that includes carnosaurians and coelurosaurs to the exclusion of other dinosaurs.

Cerapoda

Cerapoda ("ceratopsians and ornithopods") is a clade of the dinosaur order Ornithischia.

Dinosauriformes

Dinosauriformes is a clade of archosaurian reptiles that include the dinosaurs and their most immediate relatives. All dinosauriformes are distinguished by several features, such as shortened forelimbs and a partially to fully perforated acetabulum, the hole in the hip socket traditionally used to define dinosaurs. The oldest known member is Asilisaurus, dating to about 245 million years ago in the Anisian age of the middle Triassic period.

Haya griva

Haya is an extinct genus of basal neornithischian dinosaur known from Mongolia.

Jeholosauridae

Jeholosaurids were herbivorous neornithischian dinosaurs from the Cretaceous Period (Aptian - Santonian, with a possible Campanian record) of Asia. The family was first proposed by Han et al. in 2012. The jeholosaurids were defined as those ornithischians more closely related to Jeholosaurus shangyuanensis than to Hypsilophodon foxii, Iguanodon bernissartensis, Protoceratops andrewsi, Pachycephalosaurus wyomingensis, or Thescelosaurus neglectus. The Jeholosauridae includes the type genus Jeholosaurus and Yueosaurus.

Jingshanosaurus

Jingshanosaurus (meaning "Jingshan lizard") is a genus of sauropodomorph dinosaurs from the early Jurassic period.

Melanorosauridae

The Melanorosauridae were a family of sauropodomorph dinosaurs which lived during the Late Triassic and Early Jurassic. The name Melanorosauridae was first coined by Friedrich von Huene in 1929. Huene assigned several families of dinosaurs to the infraorder "Prosauropoda": the Anchisauridae, the Plateosauridae, the Thecodontosauridae, and the Melanorosauridae. Since then, these families have undergone numerous revisions. Galton and Upchurch (2004) considered Camelotia, Lessemsaurus, and Melanorosaurus members of the family Melanorosauridae. A more recent study by Yates (2007) indicates that the melanorosaurids were instead early sauropods.

Mussaurus

Mussaurus (meaning "mouse lizard") is a genus of herbivorous sauropodomorph dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since Mussaurus is now known from adult specimens, the name is something of a misnomer; adults possibly reached 6 metres (20 ft) in length and weighed more than 1,000 kilograms (2,200 lb). Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.

Neotheropoda

Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and the only group of theropods who survived the Triassic–Jurassic extinction event. Yet all of the neotheropods became extinct during the early Jurassic period except for Averostra.

Orionides

Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.

Orodrominae

Orodrominae is a subfamily of parksosaurid dinosaurs from the Cretaceous of North America and Asia.

Pulanesaura

Pulanesaura is an extinct genus of basal sauropod known from the Early Jurassic (late Hettangian to Sinemurian) Upper Elliot Formation of the Free State, South Africa. It contains a single species, Pulanesaura eocollum, known from partial remains of at least two subadult to adult individuals.

Raeticodactylidae

Raeticodactylidae is a family of eudimorphodontoid eopterosaurian pterosaurs that lived in Switzerland during the Late Triassic. The family includes Caviramus, and the type genus Raeticodactylus, which are both known from the Kössen Formation, around 205 mya. Raeticodactylidae was first used in 2014 by Andres et al., as a group of all pterosaurs closer to Raeticodactylus than Eudimorphodon. The following phylogenetic analysis follows the topology of Andres et al. (2014).

Riojasauridae

Riojasauridae is a family of sauropod-like dinosaurs from the Upper Triassic. It is known primarily from the genera Riojasaurus and Eucnemesaurus. Sites containing Riojasauridae include the Lower Elliot Formation of Orange Free State, South Africa (where fossils of Eucnemesaurus have been found), and Ischigualasto, in La Rioja Province, Argentina ( where fossils of Riojasaurus have been recovered).

Xingxiulong

Xingxiulong (meaning "Xingxiu Bridge dragon") is a genus of bipedal sauropodiform from the Early Jurassic of China. It contains a single species, X. chengi, described by Wang et al. in 2017 from three specimens, two adults and an immature individual, that collectively constitute a mostly complete skeleton. Adults of the genus measured 4–5 metres (13–16 ft) long and 1–1.5 metres (3 ft 3 in–4 ft 11 in) tall. Phylogenetic analysis suggests that Xingxiulong is most closely related to its contemporary Jingshanosaurus, although an alternative position outside of both the Sauropodiformes and Massospondylidae is also plausible.

Despite their close relationship, Xingxiulong prominently differs from Jingshanosaurus - and from most basal sauropodomorphs - in having a number of sauropod-like traits. These include a sacrum containing four vertebrae; a pubis with an exceptionally long top portion; and the femur, the first and fifth metatarsals on the foot, and the scapula being wide and robust. These probably represent adaptations to supporting high body weight, in particular a large gut. Unlike sauropods, however, Xingxiulong would still have been bipedal.

Xixiposaurus

Xixiposaurus is a genus of prosauropod dinosaur which existed in what is now Lower Lufeng Formation, China during the lower Jurassic period. It was first named by Sekiya Toru in 2010 and the type species is Xixiposaurus suni.

Yueosaurus

Yueosaurus is an extinct genus of basal ornithopod dinosaur known from Zhejiang Province, China.

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.