Dreadnoughtus

Credit: Mark Witton.

*Dreadnoughtus* is an extinct genus of titosaurian sauropod dinosaur that lived in Argentina during the Late Cretaceous.

## History

Kenneth Lacovara found the first *Dreadnoughtus* in the Cerro Fortaleza Formation in 2005, taking 4 austral summers to excavate because of how large the remains were and their remote locality; mules, ropes and many personnel were used to jacket the bones and fasten them to a truck. In 2009, they were moved to Philadelphia for preparation and study at Drexel University, the Academy of Natural Sciences of Drexel University and the Carnegie Museum of Natural History; the fossils were then moved back to the Museo Padre Molino in Rio Gallegos. They were scanned with a NextEngine 3D laser scanner, where each bone was positioned in 3D with Autodesk Maya to create a model skeleton, which was converted into 3D PDFs using GeoMagic. These allowed Lacovara et al. (2014) to study the bones without breaking them and allowed for long-distance collaboration. The holotype is MPM-PV 1156, comprised of a maxillary fragment, a tooth, a posterior cervical with ribs, several dorsals and ribs, the sacrum, 32 caudals and 18 haemal arches with 17 anterior and middle caudals and haemal arches, the left pectoral girdle, the forelimb minus the foot, both sternal plates, complete pelvic elements, the left hind limb minus a foot and right tibia, metatarsals I and II, and the claw of digit I.

MPM-PV 3546, the paratype found in the same location as the holotype, consists of a partial anterior cervical, some dorsals and ribs, the sacrum, 7 caudals and 5 haemal arches, a near-complete pelvic and a left femur. The chosen name "alludes to the gigantic body size of the taxon" and the 2 Argentine dreadnoughts that served in the first half of the 20th century, Rivadavia and Moreno. The specific epithet is after Adam Schran, who provided funding. Multiple size and weight estimates have been put in place, which are debated among scientists.

## Description

*Dreadnoughtus* displays size and anatomy insights in large Titanosaurs, especially the shoulders and hips. Most of the specimens are well preserved, lacking deformation, especially in the limbs Muscle anchors are clearly defined. *Dreadnoughtus* has a proportionally long neck, making about half of its total length. Its scapula, 1.74 meters long, is longer than any other Titanosaurs. The same is shared with the ilium, which is 1.31 meters long, and the forearms, which are only beaten by Brachiosaurids. Only *Paralititan* has a longer humerus. Only 116 bones were recovered, making it 45.3% complete, Excluding the skull, it is 58.7% complete. Of all, there are 100 types of bone, making it 70.4% complete.

The tail has a keel on the first vertebra, cavities caused by the air sacs at the neural spine bases, anterior and posterior boundaries of the neural spines have pre and postspinal laminae that connect them to the pre and postzygapophyses and triangular processes over the centrum in the middle of the tail, that precede each vertebrae; these distinguish *Dreadnoughtus* as a species. The chevrons form a Y-shape when seen in the anterior, with the bottom stem broadly expanded. The shoulder also possesses unique features; an oblique ridge over the interior face of the scapular bade that extends from the top far end to the bottom side nearer to the base. Each end of the radius has a concave embayment on the posterior with the bottom distal being nearly square in shape.

## Classification

*Dreadnoughtus* is a derived basal titanosaur that is not a lithostrotian. Lacovara et al. (2014) note a mosaic of advanced and primitive traits and the instability of titanosaurian taxonomy may lead to widely varied positions. They find:

A subsequent analysis of limb bones by Ullman and Lacovara finds it possessed many characters of Lithostrotians, specifically *Aeolosaurus* and *Gondwanatitan*, which may indicate a position close to Aeolosauridae. They did not conduct an analysis, but suggested a future study do so.

## Paleobiology

### Ontogeny

The holotype was immature, with histology of the holotype humerus showing a lack of an external fundamental system and abundant quickly deposited or growing woven tissue in the primary fibromellar bone of the outer bone cortex. This led Lacovara et al. (2014) to determine is was still growing, and it is unknown how large it may have grown if it had lived instead.

### Taphonomy

Sedimentary deposits show both were quickly buried during a fluvial avulsion event or a break in a levee that caused a flood. This generated a liquefacted crevasse splay deposit, which entombed both of them. This rapid burial accounts for the completeness. Some small theropod teeth found near shows evidence of scavenging, probably by Megaraptorans like *Orkoraptor.*

## References

https://en.wikipedia.org/wiki/Dreadnoughtus