Dreadnoughtus
Dreadnoughtus is a genus of titanosaurian sauropod dinosaur containing a single species, Dreadnoughtus schrani. It is known from two partial skeletons discovered in Upper Cretaceous rocks of the Cerro Fortaleza Formation in Santa Cruz Province, Argentina. It is one of the largest terrestrial vertebrates known, with the immature type specimen measuring in total body length and weighing .
Dreadnoughtus is known from more complete skeletons than any other gigantic titanosaurian. Drexel University paleontologist Kenneth Lacovara, who discovered the genus, chose the name Dreadnoughtus, which means "fears nothing", stating "I think it's time the herbivores get their due for being the toughest creatures in an environment." Specifically, the name was inspired by the dreadnought, an extremely influential early 20th-century battleship type, known for revolutionarily outclassing the smaller, weaker battleships that came before.
Discovery and study
American palaeontologist Kenneth Lacovara discovered the remains in the Cerro Fortaleza Formation in Santa Cruz Province, Patagonia, Argentina in 2005. Due to the large size of the bones and the remote location where they were found, it took his team four austral summers to fully excavate the remains. Mules, ropes and many team members were needed to finally get the field-jacketed bones to a truck.In 2009, the fossils were transported to Philadelphia via an ocean freighter for preparation and study. Fossil preparation and analysis occurred at Drexel University, the Academy of Natural Sciences of Drexel University and the Carnegie Museum of Natural History. Dreadnoughtus schrani fossils were returned to their permanent repository at the Museo Padre Molina in Rio Gallegos, Argentina in March 2015.
The bones of both Dreadnoughtus specimens were scanned with a NextEngine 3D laser scanner. Using the software Autodesk Maya, the scans of each bone were positioned in 3D space to create a digital articulated skeleton, which was then converted into 3D PDF files using the software GeoMagic. The high fidelity of these scans allowed Lacovara et al. to study the heavy fossils of Dreadnoughtus schrani in a way that was safe for the fossils and enhanced virtual and long-distance collaboration.
File:Kenneth J. Lacovara and Dreadnoughtus.jpg|thumb|upright=1.2|Lacovara with fibula and humerus of Dreadnoughtus
The holotype specimen, MPM-PV 1156, consists of a partial skeleton, somewhat preserved in its original layout, that comprises: a maxilla fragment; a tooth; a posterior cervical vertebra; cervical ribs; multiple dorsal vertebrae and dorsal ribs; the sacrum; 32 caudal vertebrae and 18 haemal arches that include a sequence of 17 anterior and middle caudal vertebrae and their corresponding haemal arches found in their original layout; the left pectoral girdle and forelimb minus the front foot; both sternal plates; all pelvic elements; the left hind limb lacking a hind foot and right tibia; metatarsals I and II; and one claw from digit I.
The paratype, MPM-PV 3546, consists of a partially articulated postcranial skeleton of a slightly smaller individual whose remains were discovered in the same location as the holotype. It includes a partial anterior cervical vertebra, multiple dorsal vertebrae and ribs, the sacrum, seven caudal vertebrae and five haemal arches, a nearly complete pelvis, and the left femur.
According to the research team that discovered the taxon, including notably Jason Schein, the genus name Dreadnoughtus "alludes to the gigantic body size of the taxon " and to the two Argentine dreadnoughts that served in the first half of the twentieth century, Rivadavia and Moreno. Thus, the genus name also honors the country in which Dreadnoughtus schrani was discovered. The name of the type species, schrani, was given in recognition of the American entrepreneur Adam Schran for his financial support of the project.
Controversy over the mass/weight
The researchers who described Dreadnoughtus schrani estimated its weight using Equation 1 of Campione and Evans, which allows the body mass of a quadrupedal animal to be estimated based only on the circumference of the humerus and femur. Using this scaling equation, they concluded that the Dreadnoughtus type specimen weighed about. By comparison, this would mean D. schrani weighed more than eight and a half times as much as a male African elephant and even exceeded the Boeing 737-900 airliner by several tons. This very large mass estimate was quickly criticized. On SV-POW web blog, sauropod researcher Matt Wedel used volumetric models, based on the published figures, that yielded estimates between, or even as low as approximately, based on a 20% shorter torso. Researcher Gregory S Paul posted a response to Lacovara et al., pointing out that the error margins using equations based on limb bones are large; using the same equation the Dreadnoughtus type specimen could have been anywhere between. Using volumetric techniques based on a more accurate skeletal restoration, Paul estimated as low as. Benson et al. suggested a maximum body mass of, but these estimates were questioned due to a very large error range and lack of precision.A formal re-evaluation of the animal's weight was published in June 2015. In it, a research team led by Karl T. Bates compared the simple scaling equation results with results found using a volume-based digital model with various amounts of soft tissue and "empty space" for the respiratory system. They found that any model using the scale-based weight estimate would have meant the animal had an impossible amount of bulk layered onto its skeleton. They compared their D. schrani volumetric model to those of other sauropods with more complete skeletons and better understood mass estimates to conclude that the D. schrani type specimen must have weighed in the range of. Ullmann and Lacovara disputes the methods used by Bates et al., arguing that the new study treats Dreadnoughtus as an exception to well-established mass estimate methods proven on living animals, and that the limb bones would be unnecessarily large if the new mass estimates were correct. In 2019, considering the argument of Ullmann and Lacovara, Gregory S. Paul moderated his mass estimate of Dreadnoughtus type specimen at, slightly higher than his previous estimation; he even noted that the holotype may have been heavier a tonne or so. In 2020, two studies estimated the mass of Dreadnoughtus much higher at.
Description
The discovery of Dreadnoughtus schrani provides insight into the size and anatomy of giant titanosaurian sauropods, 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. Dreadnoughtus also has an unusually long neck for its body size, making up almost half of the animal's length.Size
Estimates based on measurements of the known parts of the skeleton suggest that the only known individual of Dreadnoughtus schrani was approximately 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 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. Although each species likely had slightly different body proportions, these measurements demonstrate the massive nature of Dreadnoughtus schrani. The estimated mass of the type specimen is about.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. 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 = 45.3% complete
- 115 bones out of ~196 in the skeleton = 58.7% complete
- 100 types of bones out of ~142 types in the skeleton = 70.4% complete
| Sauropod | Skeletal Completeness Total | Mirrored Postcranial Completeness |
| Dreadnoughtus schrani | 45.5% | 70.4% |
| Turiasaurus riodevensis | 44.1% | 45.8% |
| Futalognkosaurus dukei | 15.2% | 26.8% |
| Paralititan stromeri | 7.8% | 12.7% |
| Argentinosaurus huinculensis | 5.1% | 9.2% |
| Antarctosaurus giganteus | 2.3% | 3.5% |
| Puertasaurus reuili | 1.6% | 2.8% |
Thus, the skeleton of D. schrani is substantially more complete than those of all other extremely massive dinosaurs.
In 2022, Schroeter and her colleagues discovered soft tissues and collagens from the holotype specimen. They noted the possibility that the individual, to which the holotype specimen belongs, may have been trapped in a rapid burial event; this may explain why the holotype of D. schrani is more completely preserved than other titanosaurs.
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.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. reconstructed its neck to have been held more horizontally, rather than anteriorly inclined in the manner of Brachiosaurus.