Leonerasaurus
Encyclopedia
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.
, 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.
) 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.
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 an not erupted tooth has large denticles similar to basal sauropodomorphs. 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 factes on the teeth of Leonorasaurus.
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.
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.
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. 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.
, as the closest sister taxon
to the group sauropods (following Yates) + Melanorosaurus (M. is seen as a sauropod by some researchers).
A cladogram
after Pol, Garrido & Cerda, 2011, illustrates a possible placing of Leonerasaurus in Sauropodomorpha:
, Central Patagonia
, Argentina. This formation is probably early Jurassic in age, interpreted as Pliensbachian
to Toarcian
or late Sinemurian
to Toarcian. 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.
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of sauropodomorph
Sauropodomorpha
Sauropodomorpha is an extinct clade of long-necked, herbivorous, saurischian dinosaurs which includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had long necks and tails, were quadrupedal, and became the largest animals to ever walk the Earth. The...
dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
. Currently, there is only one species known, named L. taquetrensis by Diego Pol, Alberto Garrido and Ignacio A. Cerda in 2011
2011 in paleontology
-Lobopods:-Arachnids:-Insects:-Newly named jawless vertebrates:-Newly named acanthodian:-Newly named cartilaginous fishes:-Newly named bony fishes:-Newly named lepospondyls:-Newly named temnospondyls:-Newly named lissamphibians:...
. The fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
, an incomplete subadult
Juvenile (organism)
A juvenile is an individual organism that has not yet reached its adult form, sexual maturity or size. Juveniles sometimes look very different from the adult form, particularly in terms of their colour...
individual, was found in the Las Leoneras Formation in Argentina
Argentina
Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...
. This formation is probably Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
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.
Description
Leonerasaurus taquetrensis is know from one incomplete individual. Parts of a dentary and some teeth, neck and trunk vertebrae, a sacrumSacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
, parts of the pectoral
Pectoral
Pectoral may refer to:* Pectoral cross, a cross worn on the chest* a decorative, usually jeweled version of a gorget* Pectoral , often iconographic with hieroglyphs* Pectoralis major muscle, commonly referred to as "pectorals" or "pecs"...
(shoulder) and pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
(hip) girdle as well as several limb bones were found. Much of the remains were found in articulation.
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 symphysisSymphysis menti
The external surface of the mandible is marked in the median line by a faint ridge, indicating the symphysis menti, mandibular symphysis, or line of junction of the two pieces of which the bone is composed at an early period of life....
) 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
Plateosaurus
Plateosaurus is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 216 to 199 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal sauropodomorph dinosaur, a so-called "prosauropod"...
. Also, a longitudinal ridge that is seen in some basal sauropodomorphs (e.g., Massospondylus
Massospondylus
Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...
, Coloradisaurus
Coloradisaurus
Coloradisaurus is a genus of massospondylid sauropodomorph dinosaur. It lived during the Late Triassic period in what is now La Rioja Province, Argentina. It is known from the holotype PVL 5904, nearly complete skull...
and Plateosaurus
Plateosaurus
Plateosaurus is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 216 to 199 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal sauropodomorph dinosaur, a so-called "prosauropod"...
) is not preserved in Leonerasaurus. However, this may be related to the damaged state of the specimen.
On the dentary, 13 teeth or tooth fragments were found. There are two empty alveoli
Dental alveolus
Dental alveolus are sockets in the jaws in which the roots of teeth are held in the alveolar process of maxilla with the periodontal ligament. The lay term for dental alveoli is tooth sockets...
, 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
Mussaurus
Mussaurus was a genus of herbivorous prosauropod dinosaur that lived in southern Argentina during the Late Triassic Period, about 215 million years ago...
. 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 an not erupted tooth has large denticles similar to basal sauropodomorphs. 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
Melanorosaurus
Melanorosaurus , is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. A herbivore from South Africa, it had a large body and sturdy limbs, suggesting it moved about on all fours...
. Also, in contrast to eusauropod teeth, there are no high-angle wear factes on the teeth of Leonorasaurus.
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.
Vertebrae
The neck of Leonorasaurus is known almost completely, only the atlasAtlas (anatomy)
In anatomy, the atlas is the most superior cervical vertebra of the spine.It is named for the Atlas of Greek mythology, because it supports the globe of the head....
is lost. The nine remaining cervicals
Cervical vertebrae
In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...
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.
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. 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
Lamina of the vertebral arch
The laminæ are two broad plates, extending dorsally and medially from the pedicles, fusing to complete the roof of the vertebral arch.Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava....
(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
Articular processes
The articular processes or zygapophyses of a vertebra, two superior and two inferior, spring from the junctions of the pedicles and laminæ...
on all dorsals, but not in no-sauropod sauropodomorphs, is present in the posterior dorsals.
Phylogenetic position
Leonerasaurus appears to be belong into the AnchisauriaAnchisauria
The Anchisauria were a clade of sauropodomorph dinosaurs which 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...
, as the closest sister taxon
Taxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
to the group sauropods (following Yates) + Melanorosaurus (M. is seen as a sauropod by some researchers).
A cladogram
Cladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
after Pol, Garrido & Cerda, 2011, illustrates a possible placing of Leonerasaurus in Sauropodomorpha:
Discovery
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 ProvinceChubut Province
Chubut a province in the southern part of Argentina situated between the 42nd parallel south and the 46th parallel south , the Andes range separating Argentina from Chile, and the Atlantic ocean...
, Central Patagonia
Patagonia
Patagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
, Argentina. This formation is probably early Jurassic in age, interpreted as Pliensbachian
Pliensbachian
The Pliensbachian is an age of the geologic timescale or stage in the stratigraphic column. It is part of the Early or Lower Jurassic epoch or series and spans the time between 189.6 ± 1.5 Ma and 183 ± 1.5 Ma . The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.The...
to Toarcian
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...
or late Sinemurian
Sinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
to Toarcian. The volcanic facies of the overlying Lonco Trapial Formation is certainly from the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
, so that the younger boundary of the Las Leoneras Formation is well constrained. However, a Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
affinity cannot be rules out, because the lower constraint of the formation is not well-defined.