| Leonerasaurus | |
|---|---|
 | |
| Restored skeleton, photographed at the special exhibition "DINOSAURIER – Giganten Argentiniens" when stationed at theForschungsMuseum Alexander König inBonn in 2009. | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropodiformes |
| Clade: | †Anchisauria |
| Genus: | †Leonerasaurus Pol, Garrido & Cerda, 2011 |
| Species: | †L. taquetrensis |
| Binomial name | |
| †Leonerasaurus taquetrensis Pol, Garrido & Cerda, 2011 | |
Leonerasaurus is abasalgenus ofsauropodomorphdinosaur. Currently, there is only onespecies known, namedL. taquetrensis by Diego Pol, Alberto Garrido and Ignacio A. Cerda in2011. Thefossil, an incompletesubadult individual, was found in theLas Leoneras Formation inArgentina. This formation is probablyEarly 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 ofconvergent evolution.[1]
The fossils assigned toLeonerasaurus were found near Cañadón Las Leoneras (an affluent of the left margin of the Chubut river), southeast of Sierra de Taquetrén,Chubut Province, CentralPatagonia, Argentina. This formation is probably early Jurassic in age,[2] interpreted asPliensbachian toToarcian[3] or lateSinemurian to Toarcian.[4] The volcanic facies of the overlying Lonco Trapial Formation is certainly from theMiddle Jurassic, so that the younger boundary of the Las Leoneras Formation is well constrained. However, aLate Triassic affinity cannot be rules out, because the lower constraint of the formation is not well-defined.[1]
Thegeneric name is derived fromLeoneras, in reference to the lithostratigraphic unit where this taxon was found, andsaurus, "lizard" (Latinized Greek). Thespecific nametaquetrensis refers to the Sierras de Taquetrén, where Las Leoneras Formation crops out in Central Patagonia.[1]
Leonerasaurus taquetrensis is known from one incomplete individual. Parts of adentary and some teeth, neck and trunkvertebrae, asacrum, parts of thepectoral (shoulder) andpelvis (hip) girdle as well as several limb bones were found. Much of the remains were found in articulation.[1] It was only 2.40 meters long, 1 m high and weighing about 70 kg.
Of the skull only the anterior part of the rightdentary was found. Near the area where it touches the contralateral element at the tip of the lower jaw (thesymphysis) 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 asPlateosaurus. Also, a longitudinal ridge that is seen in some basal sauropodomorphs (e.g.,Massospondylus,Coloradisaurus andPlateosaurus) is not preserved inLeonerasaurus. However, this may be related to the damaged state of the specimen.[1]
On the dentary, 13 teeth or tooth fragments were found. There are two emptyalveoli, 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 ofMussaurus. 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 ofMussaurus andMelanorosaurus. Also, in contrast to eusauropod teeth, there are no high-angle wear facets on the teeth ofLeonorasaurus.[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]
The neck ofLeonerasaurus is known almost completely, only theatlas is lost. The nine remainingcervicals were found articulated with the first five completedorsal (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]
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 certainlaminae (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 theprezygapophysis on all dorsals, but not in no-sauropod sauropodomorphs, is present in the posterior dorsals.[1]
Leonerasaurus appears to be belong into theAnchisauria, as the closest sistertaxon to the group sauropods (following Yates)[5] +Melanorosaurus (M. is seen as a sauropod by some researchers).
Acladogram after Pol, Garrido & Cerda, 2011,[1] illustrates a possible placing ofLeonerasaurus in Sauropodomorpha:
The following cladogram shows the position ofLeonerasaurus within Massopoda, according to Oliver W. M. Rauhut and colleagues, 2020:[6]
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