Dreadnoughtus
| Dreadnoughtus Temporal range: Late Cretaceous,
| |
|---|---|
| File:Artist Rendering 2 - Hall - Dreadnoughtus reconstruction.jpg | |
| Life restoration of Dreadnoughtus schrani, by Jennifer Hall | |
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauria |
| Clade: | †Lithostrotia |
| Genus: | †Dreadnoughtus Lacovara et al., 2014 |
| Type species | |
| †Dreadnoughtus schrani Lacovara et al., 2014 (type)
| |
Dreadnoughtus (meaning "fearing nothing") is a genus of giant titanosaurian sauropod dinosaur discovered in the Upper Cretaceous (Campanian-Maastrichtian; 84–66 Ma) Cerro Fortaleza Formation of Santa Cruz province, Argentina. It is one of the largest of all known terrestrial vertebrates, possessing the greatest mass of any land animal that can be calculated with reasonable certainty,[1] using limb bone measurements.[2][3] In terms of skeletal completeness and ability to encode its anatomy into cladistic analyses, Dreadnoughtus schrani is the most complete gigantic titanosaurian sauropod dinosaur.[1]
Etymology
Dreadnought is a English term meaning "fears nothing". The genus name Dreadnoughtus alludes to the gigantic body size of the taxon (which presumably rendered healthy adult individuals nearly impervious to attack) and the predominant battleships of the early 20th century, two of which (the ARA Rivadavia and ARA Moreno) were part of the Argentine navy, honoring the country in which Dreadnoughtus schrani was discovered. The name of the type species, schrani, honors the American entrepreneur Adam Schran for his support of the project.[1]
Description
The discovery of Dreadnoughtus schrani provides insight into the size and anatomy of giant titanosaurian dinosaurs, especially of the limbs and shoulder and hip girdles. The majority of Dreadnoughtus 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.
Holotype and paratype specimens
The holotype specimen, MPM-PV 1156, consists of a partial skeleton, somewhat preserved in its original layout, that comprises: a maxilla (jaw) fragment; a tooth; a posterior cervical vertebra; cervical ribs; multiple dorsal vertebrae and dorsal ribs; the sacrum; 32 caudal vertebrae and 18 haemal arches (bones from the tail) 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.[1]
Size
| Dimension | metric | imperial |
|---|---|---|
| Mass | 59,300 kilograms (59.3 t) | 65.4 short tons (130,800 lb) |
| Total length | 26 m | 85 ft |
| Head and neck length | 12.2 m | 40 ft |
| Neck-only length | 11.3 m | 37 ft |
| Torso and hip length | 5.1 m | 16.7 ft |
| Tail length | 8.7 m | 30 ft |
| Shoulder height | ~ 2 stories (6 m) | ~ 2 stories (20 ft) |
At 1.74 m, the scapula of the holotype is longer than any other known Titanosaur scapula.[1] Its ilium, the top bone of the pelvis, is also larger than any previously reported, measuring 1.31 m in anterior to posterior length.[1] The forearm of the holotype is longer than any previously reported for a titanosaur, measuring shorter than only the elongate forearms of brachiosaurid sauropods that exhibited more inclined body posture.[1] Only Paralititan[4] preserves a longer humerus (upper arm bone). Although each species likely had slightly different body proportions, these measurements clearly demonstrate the massive nature of Dreadnoughtus schrani.[1]
Mass
Using Equation 1 of Campione and Evans (2012),[3] which allows inference of body mass of a quadrupedal animal solely from the minimum circumference of the shaft of its humerus and femur, the Dreadnoughtus type specimen weighed approximately 59.3 metric tons (65 short tons), or 59,291 kilograms.[1] Linear bone measurements indicate the holotype individual was approximately 26 metres (85 ft)* long and stood about 2 stories tall.[1] Its neck is estimated to have been 11.3 m long, its torso 4 m long, and its tail 8.7 m long.
| Sauropod | Taxonomic Group | Mass (kg) | Mass (short tons) |
|---|---|---|---|
| Dreadnoughtus schrani | Titanosauria | 59,291 | 65.4 |
| Brachiosaurus altithorax | Brachiosauridae | 56,255 | 62 |
| Turiasaurus riodevensis | Turiasauria | 50,923 | 56.1 |
| Elaltitan lilloi | Titanosauria | 42,798 | 47.2 |
| Futalognkosaurus dukei | Titanosauria | 38,139 | 42 |
| Giraffatitan brancai | Brachiosauridae | 34,003 | 37.5 |
| Diplodocus longus | Diplodocidae | 14,813 | 16.3 |
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 numbers of bones versus types of bones. The most important metric for understanding the anatomy of a fossil animal is 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 Dreadnoughtus schrani compared with other extremely massive (over 40 metric tonnes) sauropods is as follows:[2]
| Sauropod | Skeletal Completeness Total | Mirrored Postcranial Completeness (i.e. types of bones) |
|---|---|---|
| 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 Dreadnoughtus schrani is substantially more complete than those of all other extremely massive (>40 tonnes) dinosaurs.[1]
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,[5][6] 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.[1] This and the fact that the head of the femur was not turned in towards the body as in saltasaurids[5] 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.
Although the forelimbs of Dreadnoughtus schrani are longer than in any other previously known taxon they are not significantly longer than the hind limbs.[1] 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.[1]
Just like modern archosaurs with tails (for example crocodilians,[7] Dreadnoughtus 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.[1]
The shoulder girdle and forelimb of Dreadnoughtus 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 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.[1]
Discovery and study
Dr. Kenneth Lacovara, of Drexel University, 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 remote location where they were found, it took his team four austral summers to fully excavate the remains. Mules, ropes, hills, 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 will be returned to their permanent repository at the Museo Padre Molina in Rio Gallegos, Argentina.
3D imagery
The bones of both Dreadnoughtus specimens were scanned with a NextEngine 3D laser scanner.[1] 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. (2014) to study the heavy fossils of Dreadnoughtus schrani in a way that was safe for the fossils and enhanced virtual and long distance collaboration.
Phylogeny
Based on a cladistic analysis, Dreadnoughtus schrani appears to be a “derived” basal titanosaur that is not quite a lithostrotian.[1] Lacovara et al. (2014) note that because of the wide array of relatively “advanced” and “primitive” features in the skeleton of Dreadnoughtus schrani and the current instability of titanosaurian interrelationships, future analyses may find widely differing positions for it within Titanosauria.
Taphonomy
Based on the sedimentary deposits at the site, the two Dreadnoughtus schrani specimens appear to have been buried quickly during a fluvial avulsion event, or break in a levee resulting in a flood. This event generated a liquifacted[neologism?] crevasse splay deposit which entombed the two dinosaurs. Thus, rapid and relatively deep burial of the Dreadnoughtus type specimen accounts for its extraordinary completeness. Numerous small theropod teeth found amongst the bones are likely evidence of scavenging, most likely by megaraptorans,[1] perhaps Orkoraptor.
Ontogeny
The holotype specimen was likely not fully grown at the time of its death. The histology of the holotype humerus, which shows a lack of an external fundamental system (an outer layer of bone found only in fully-grown vertebrates) and abundance of fast-deposited or still-growing woven tissue in the primary fibrolamellar bone of the outer outer bone cortex, lead Lacovara et al. (2014) to determine that the specimen was still growing at the time of its death.[8][1] It remains unknown how large this individual would have grown had it not met an untimely demise.
References
- ^ a b c d e f g h i j k l m n o p q r s t u Lacovara, Kenneth J.; Ibiricu, L.M.; Lamanna, M.C.; Poole, J.C.; Schroeter, E.R.; Ullmann, P.V.; Voegele, K.K.; Boles, Z.M.; Egerton, V.M.; Harris, J.D.; Martínez, R.D.; Novas, F.E. (September 4, 2014). "A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina". Scientific Reports. doi:10.1038/srep06196.
- ^ a b Benson, Roger B. J.; Campione, Nicolás E.; Carrano, Matthew T.; Mannion, Phillip D.; Sullivan, Corwin; Upchurch, Paul; Evans, David C. (May 06, 2014). "Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage". PLOS Biology. doi:10.1371/journal.pbio.1001853.
{{cite journal}}: Check date values in:|date=(help)CS1 maint: unflagged free DOI (link) - ^ a b Campione, Nicolás E.; Evans, David C. (July 10, 2012). "A universal scaling relationship between body mass and proximal limb bone dimensions in quadrupedal terrestrial tetrapods". BMC Biology: 15. doi:10.1186/1741-7007-10-60.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ^ Smith, Joshua B.; Lamanna, Matthew C.; Lacovara, Kenneth J.; Dodson, Peter; Smith, Jennifer R.; Poole, Jason C.; Giegengack, Robert; Attia, Yousry (2001). "A Giant sauropod dinosaur from an Upper Cretaceous mangrove deposit in Egypt". Science. 292 (5522): 1704–1706. doi:10.1126/science.1060561. PMID 11387472. Retrieved 2014-08-31.
- ^ a b Wilson, Jeffrey A.; Carrano, Matthew T. (June, 1999). "Titanosaurs and the origin of "wide-gauge" trackways: a biomechanical and systematic perspective on sauropod locomotion". Paleobiology. 25 (2): 252–267. Retrieved 31 August 2014.
{{cite journal}}: Check date values in:|date=(help) - ^ Wilson, J. A. (February 2006). "An Overview of Titanosaur Evolution and Phylogeny". III Jornadas Internacionales sobre Paleontología de Dinosaurios y su Entorno: 169–190.
- ^ Wilhite, Ray (2003). "Biomechanical Reconstruction of the Appendicular Skeleton in Three North American Jurassic Sauropods". Louisiana State University Electronic Thesis & Dissertation Collection. Retrieved 31 August 2014.
- ^ Schroeter, Elena; Boles, Zachary; Lacovara, Kenneth (November 2011). "The Histology of a Massive Titanosaur from Argentina and Implications for Maximum Size" (PDF). Journal of Vertebrate Paleontology (Program and Abstracts Supplement): 189.
External links
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- 3D PDF files of the entire skeleton and selected bones are published in the supplementary section of Lacovara et al. (2014). In Acrobat, the viewer can zoom in and out on the skeleton, rotate the view, and turn individual bones on and off.
- Dreadnoughtus: A New Dinosaur Discovery on YouTube