Dreadnoughtus

Dreadnoughtus, name meaning "fears nothing", is a genus of sauropod dinosaur from the late Cretaceous period which was discovered in 2005 and described in 2014. Being 70% complete, it is one of the more complete dinosaur finds of South America. It was once thought to have been the heaviest dinosaur, and even heavier even than a Boeing airplane, however, it is now believed to have weighed 38,000 kilograms, and was 26 meters long. The holotype fossil is considered a juvenile, however, so it's likely Dreadnoughtus could grow much larger. Dreadnought was also the alternative name of all battle ships with a uniform main battery of guns.

## Description

The discovery of *Dreadnoughtus schrani*provides insight into the size and anatomy of giant titanosaurian dinosaurs, especially of the limbs and the shoulder and hip girdles. The majority of *D. schrani* bones are very well preserved. There is minimal deformation, especially in the limb bones. Fine features, such as locations of muscle attachment, are frequently clearly visible. It is also possible that *Dreadnoughtus* had large, back spines sticking out to the sides since it belongs to the lithostrotians, a class of titanosaurs that had large spines. *Dreadnoughtus* also has an unusually long neck for its body size, making up almost half of the animal's length.

### Size

 File:220px-Dreadnoughtus scale.png
Estimates based on measurements of the known parts of the skeleton suggest that the only known individual of *Dreadnoughtus schrani* was approximately 26 meters (85 feet) long and stood about 2 stories tall. At 1.74 m, its scapula is longer than any other known titanosaur shoulder blade. Its ilium, the top bone of the pelvis, is also larger than any other, measuring 1.31 m in length. The forearm of is longer than any previously known from a titanosaur, and it is only shorter than the long forearms of brachiosaurids, which had a more inclined body posture. Only *Paralititan* preserves a longer humerus (upper arm bone). Although each species likely had slightly different body proportions, these measurements demonstrate the massive nature of *Dreadnoughtus schrani*. The current estimate for the mass of the type specimen, created using a 3D skeleton and volume estimation of mass method, derives a range of 22.1–38.2 tonnes (21.8–37.6 long tons; 24.4–42.1 short tons).

### Completeness

Completeness may be assessed in different ways. Sauropod dinosaur skeletons are often recovered with little to no skull material, so completeness is often looked at in terms of postcranial completeness (i.e., the completeness of the skeleton excluding the skull). Completeness may also be assessed in terms of the numbers of bones versus the types of bones. The most important metric for understanding the anatomy of a fossil animal is the types of bones. The completeness statistics for *Dreadnoughtus schrani* are as follows:

* 116 bones out of ~256 in the entire skeleton (including the skull) = 45.3% complete
* 115 bones out of ~196 in the skeleton (excluding the skull) = 58.7% complete
* 100 types of bones out of ~142 types in the skeleton (excluding the skull) = 70.4% complete

The completeness of *D. schrani* compared with other extremely massive (over 40 metric tons) sauropods is as follows:[5]

Thus, the skeleton of *D. schrani* is substantially more complete than those of all other extremely massive (>40 metric tons) dinosaurs.

### Posture

All titanosaurs had what is called wide-gauge posture, a relative term to describe a stance in which the feet fell apart from the body midline. More derived titanosaurs had a greater degree of wide-gauge posture, with their limbs held more widely than their ancestors and contemporaneous counterparts. The stance of *Dreadnoughtus schrani* was clearly wide-gauge, but not to the degree of saltasaurids because the femoral condyles are perpendicular to its shaft rather than beveled. This and the fact that the head of the femur was not turned in towards the body as in saltasaurids support the phylogenetic conclusion that *Dreadnoughtus* was not a saltasaurid. The animal’s broad sternal bones also demonstrate a wide pectoral girdle, giving it a broad-shouldered, broad-chested appearance. Paleontologist Kenneth Lacovara compared the animal's gait to an Imperial Walker's.

Although the forelimbs of *D. schrani* are longer than in any other previously known titanosaur, they are not significantly longer than the hind limbs. Therefore, Lacovara et al. (2014) reconstructed its neck to have been held more horizontally, rather than anteriorly inclined in the manner of *Brachiosaurus*.

### Distinctive features

The tail of *Dreadnoughtus schrani* has several characteristic features included in the diagnosis of the species. The first vertebra of the tail has a ridge on its ventral surface called a keel. In the first third of the tail, the bases of the neural spines are extensively subdivided into cavities caused by contact with air sacs (part of the dinosaur’s respiratory system). In addition, the anterior and posterior boundaries of these neural spines have distinct ridges (pre- and postspinal laminae) connecting them to the pre- and postzygapophyses (the articulation points of the neural arches). In the middle of its tail, the vertebrae have a triangular process that extends over the centrum towards each preceding vertebra.

Just like modern archosaurs with tails (for example crocodilians, *D. schrani* had bones below the vertebrae called chevrons or haemel arches. These bones connect with the ventral surface of the vertebrae and are “Y” shaped when viewed anteriorly. In *Dreadnoughtus schrani* the bottom stem of the “Y” is broadly expanded, likely for the attachment of muscles.

The shoulder girdle and forelimb of *D. schrani* also exhibit unique features. An oblique ridge crosses the interior face of the scapular blade, extending from the top side near the far end of the blade to the bottom side near the base of the scapular blade. Finally, each end of the radius exhibits a unique form: the top, or proximal end, has a distinct concave embayment on its posterior face while the bottom, or distal end, is nearly square in shape instead of broadly expanded.