Sarmientosaurus

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Sarmientosaurus
Temporal range: Cenomanian-Turonian
Skull in side views
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Clade: †Macronaria
Clade: †
Titanosauriformes
Clade: †Somphospondyli
Clade: †Diamantinasauria
Genus: †Sarmientosaurus
Martínez et al., 2016
Type species
Sarmientosaurus musacchioi
Martínez et al., 2016

Sarmientosaurus is a

Period about 95 million years ago.[2] The type species
is Sarmientosaurus musacchioi.

Discovery

Right lower jaw

In 1997,

Chubut province, discovered a sauropod skull. This proved to be connected to the first few cervical vertebrae.[3]

In 2016, the type species Sarmientosaurus musacchioi was named and described by

Life Science Identifiers are 537DFE26-54EC-4978-AC86-E83A04FA74DE for the genus and C1090B8D-D051-44F3-B869-8B4A0C802176 for the species.[3]

The holotype, MDT-PV 2, was found in the upper Lower Member of the Bajo Barreal Formation, dating from the Cenomanian to Turonian ages. It consists of an almost complete skull with lower jaws, articulated with the first seven vertebrae of the front neck. Several neck parts, among them the entire atlas and fourth neck vertebra, were too eroded to be salvaged. The specimen represents an elderly individual. It is one of the few titanosaurs for which skull material has been found.[3] Uniquely, at the side of the neck an elongated structure was discovered that was identified as an ossified tendon.[3]

From the Bajo Barreal Formation another titanosaur sauropod is known,

cladistic analysis both genera occupied different positions in the evolutionary tree. Also, fragmentary fossils, of postcranial bones that differ from those of Epachthosaurus and skull bones that are dissimilar to the Sarmientosaurus cranium, show that in any case several titanosaur species were present in the habitat.[3]

Description

3D video of the skull

Size and distinguishing traits

Sarmientosaurus has an estimated length of twelve metres and a weight of ten tonnes.

The describing authors indicated nine unique distinguishing traits,

nervus trigeminus. An inner vein channel connecting the infundibulum with the brains stem, is lacking. The premaxillary teeth are positioned vertically, the maxillary teeth are inclining to the front and the dentary teeth are inclining to the rear. The middle neck vertebrae have strut-like, instead of plate-shaped, ridges between the front joint processes and the vertebral centrum. A long and thin ossified tendon is running along the low side of the series of neck vertebrae and neck ribs.[3]

Skeleton

Skull in front and hind views

The skull has a length of forty-three centimetres. In top view the skull is more or less tongue-shaped. The

cranial nerve, the nervus trigeminus, has extra exits for the branches towards the maxilla and the lower jaw, whereas other sauropods possess but single exit. The front of the lower jaw has an almost constant height.[3]

The praemaxilla bears four teeth, the maxilla eleven (right side) or twelve (left), and the dentary thirteen. The premaxillary teeth are positioned vertically, the maxillary teeth incline to the front while the teeth of the lower jaw incline to behind, a unique configuration. The build of the teeth is in-between the more spatulate form of basal sauropods and the pencil shape of derived species. The teeth are moderately elongated. They each have sharply-angled wear facets in a high and a low position which, together with their strange orientation, indicates some special, as yet not fully understood, way of cropping vegetation.[3]

The neck vertebrae are long and elongated. Their internal structure is camellated, i.e. with many small air spaces inside. The middle neck vertebrae have oval, narrow and deep pleurocoels in their sides, pneumatic excavations that nearly touch each other on the midline, separated by a narrow bone plate. The rear joint processes are uncommonly long, reaching beyond the edge of the vertebral body. The front joint processes are supported from below by struts with an oval cross-section, apparently formed by a perforation of the normally plate-shaped ridges in this position. The neck ribs are delicate, thin and rod-shaped.[3]

Ossified tendon

Ossified cervical tendon

Parallel to the ribs, on the outer side of the neck a cable-shaped structure was discovered with a constant diameter of three millimetres. It had an oval cross-section and a rough and striated surface. The structure originated directly behind the skull and continued over a length of several vertebrae, thus of some metres. It was interpreted by the describing authors as an ossified

Musculus longus colli ventralis or the Musculi intertransversarii. The internal structure of the tendon, with much reworked bone tissue, indicated a swift ossification at a young age.[3]

Classification

Axis and neck vertebra

Martínez and colleagues placed Sarmientosaurus in a basal position within the clade Lithostrotia, above Malawisaurus in the evolutionary tree.[3] However, in 2021, Stephen Poropat and colleagues instead identified it as part of the new clade Diamantinasauria, along with Savannasaurus and Diamantinasaurus.[4]

Palaeobiology

It had very large eye sockets, meaning that it may have had better vision than other titanosaurs. Based on the ear and neck tendon, Sarmientosaurus most likely hung its head and neck down "like an enormous Eeyore". This posture implies that Sarmientosaurus may have eaten much lower-lying plants than other sauropods.[5] The correlation between inner ear structure and head posture has been questioned in previous studies.[6][7]

See also

References

  1. ^ Joyce, Christopher (April 26, 2016). "Superhearing And Fast Growth ... Scientists Learn Why Sauropods Ruled". All Things Considered. npr.org. The team called this new species sarmientosaurus, a member of a subgroup of sauropods called titanosaurs.
  2. ISSN 0362-4331
    . Retrieved 2016-04-27.
  3. ^
    PMID 27115989.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
  4. doi:10.1093/zoolinnean/zlaa173
    .
  5. ^ "New Droopy Dinosaur Hung Its Head Like an Enormous Eeyore". National Geographic News. 2016-04-26. Archived from the original on April 26, 2016. Retrieved 2016-04-26.
  6. doi:10.4202/app.2009.0007
    .
  7. PMID 23940837
    .

External links

Videos accompanying research article:

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