Atacamatitan

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Atacamatitan
Temporal range:
Ma
Holotype SGO-PV-961
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Clade: †Sauropoda
Clade: †Macronaria
Clade: †Titanosauria
Clade: †Lithostrotia
Genus: †Atacamatitan
Kellner et al., 2011
Type species
†Atacamatitan chilensis
Kellner et al., 2011

Atacamatitan (meaning "

dinosaurs from the Late Cretaceous Tolar Formation of Chile
.

Discovery and naming

In February 2000, with the purpose of looking for Mesozoic fossils in Chile, Chilean and Brazilian researchers mounted a preliminary expedition that was organized by the Chilean National Museum of Natural History and the National Museum of Brazil heading to Antofagasta Region. During the expedition, they discovered the deposits of the Tolar Formation, located about 150 km north of Calama town and 50 km east from El Abra copper mine.[1]

The deposits of this formation consists of well-stratified, red succession of breccias,

titan. The specific name, chilensis, refers to Chile. The holotype is currently housed at the Chilean National Museum of Natural History.[3]

Description

Skeletal diagram of the holotype

The holotype, SGO-PV-961, consists of a right

Thomas Holtz estimated its possible weight between 8 and 16 t (8,000.0 and 16,000.0 kg).[4]

According to Kellner et al. 2011, Atacamatitan can be recognised in having dorsal centra with pleurocoels that are curved and do not point posteriorly, dorsal vertebrae with concave ventral surface, posterior caudal vertebrae with laterally compressed neural spine having a blade-like anterior margin, femur with the proximal end getting gradually reduced until two thirds of its total length.[3]

Vertebrae

Life restoration

The two preserved dorsal vertebrae are fragmented, with partial neural arches. Both vertebrae are opisthocoelic. Dorsal vertebra SGO-PV-961a features an elongated centrum, with pleurocoels in the lateral sides that are rounded and less elongated compared to other titanosaurs. The neural arch is missing, and due to the preserverd dimensions, it is likely that it was wider than high. The second dorsal vertebra SGO-PV-961b is antero-posteriorly compressed with the neural arch partially preserved. These dorsal vertebrae differ from other titanosaurs such as Gondwanatitan, Saltasaurus, Trigonosaurus and Uberabatitan, due to the strongly concave ventral margin of the centrum. By taking into account all the characteristics of the dorsal vertebrae, Atacamatitan differs from other titanosaurs by having pleurocoels rounded and less elongated not pointing posteriorly.[3]

Although some caudal vertebrae were discovered, only two are well preserved. Both vertebrae came from the middle and posterior end of the

prezygapophysis. The centrum is similar to SGO-PV-961c, only being smaller and posteriorly oriented. The prezygapophyses are elongated and reach nearly 30% of the anterior centrum. Postzygapophyses are reduced and positioned at the ventral margin of the neural spine. The neural arch is preserved in the anterior half of the centrum.[3]

Forelimb and hindlimb

Ribs were unearthed too, the most complete is SGO-PV-961d, though it is unknown if the ribs of Atacamatitan had

muscular attachment.[3]

The preserved right femur is more gracile compared to other elements, indicating that the animal had stronger forelimbs. This is seen as a possible and potential autapomorphy for this species. It measures 1.10 m (110 cm), the femoral head is missing and posteriorly, it preserves a well developed fourth trochanter, extending to the proximal quarter.[3]

Classification

In the original description, Atacamatitan was placed in the

Titanosauridae.[3] However given the fragmentary nature of the holotype, most cladistic analysis exclude Atacamatitan. Nevertheless, in 2012, Rubilar-Rogers and Gutstein conducted a preliminary cladistic analysis which ended in a polytomy within Nemegtosaurus, Rapetosaurus, Titanosaurus and the Saltasauridae. Atacamatitan was placed within the Lithostrotia.[5]

See also
Wikispecies has information related to Atacamatitan.

References

  1. ^ a b Vargas, A.; Kellner, A. W. A.; Diaz, G. C.; Rubilar, D.; Soares, M (2000). "New sauropod dinosaur from the Atacama desert, northern Chile". Journal of Vertebrate Paleontology. 20: 75A.
  2. ^ Maksaev, V. (1978). "Cuadrángulo Chitigua y sector occidental del cuadrángulo Cerro Palpana, Región de Antofagasta". Carta Geológica de Chile (31): 55.
  3. ^
    PMID 21437382
    .
  4. ^ Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Genus List for Holtz 2012 Weight Information
  5. doi:10.54830/bmnhn.v61.2012.162
    .
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