Tuesday, 9 September 2014

The nearly complete skeleton of two gigantic Titanosaurs from Southern Patagonia, Argentina.

Titanosaurs were a group of Sauropod Dinosaurs that became the predominant large herbivores during the last 30 million years of the Cretaceous. They were a diverse group, and included several truly gigantic species, which are thought to have been the largest terrestrial animals ever to have lived. Unfortunately most of these gigantic species are known only from fragmentary remains, and we know relatively little about their biology or evolution (we know they were bigger than everything else, but not how big they actually got, nor do we know if gigantic Titanosaurs were a distinct evolutionary lineage, or if gigantism arose separately several times within the group).

In a paper published in the journal Nature Scientific Reports on 4 September 2014, a team of scientists led by Kenneth Lacovara of the Department of Biodiversity, Earth and Environmental Science at Drexel University describe the almost complete skeleton of two gigantic Titanosaurs from south-western Patagonia, Argentina.

The new specimens are determined to be distinct from any previously described Titanosaur, and placed in a new species, named Dreadnoughtus schrani, where ‘Dreadnoughtus’ derives from the Old English ‘dreadnought’ meaning ‘fearless’ and also alludes to the class of large battleships used in the early twentieth century, and ‘schrani’ honours the American entrepreneur Adam Schran, for his support of the research. 

Axial skeletal anatomy of the gigantic Titanosaur Dreadnoughtus schrani. Posterior (~9th) cervical vertebra in (A) left lateral, (B) right lateral, (C) posterior, and (D) ventral views. (E) Anterior (~4th) dorsal vertebra in right lateral view. Middle (~6th) dorsal vertebra in (F) left lateral and (G) anterior views. (H) Posterior (~7th) dorsal vertebra in right lateral view. Posterior (~8th) dorsal vertebra in (I) left lateral and (J) posterior views. (K) Partial sacrum in ventral view. (L) Biconvex first caudal vertebra in posterior view. (M) First 32 caudal vertebrae and 18 haemal arches in left lateral view (positions of first 21 caudal vertebrae and haemal arches 4 to 18 known with certainty).  Abbreviations: acpl, anterior centroparapophyseal lamina; apcdl, accessory posterior centrodiapophyseal lamina; a-spdl, anterior ramus of spinodiapophyseal lamina; cdf, centrodiapophyseal fossa; cpol, centropostzygapophyseal lamina; dp, diapophysis; nc, neural canal; ns, neural spine; pacdf, parapophyseal centrodiapophyseal fossa; pcdl, posterior centrodiapophyseal lamina; pcdl-f posterior centrodiapophyseal fossa, pcpl, posterior centroparapophyseal lamina; pe, paddle-shaped distal expansion; pocdf, postzygapophyseal centrodiapophyseal fossa; podl, postzygodiapophyseal lamina; posdf, postzygapophyseal spinodiapophyseal fossa; poz, postzygapophysis; pp, parapophysis; ppdl, paradiapophyseal lamina; prdl, prezygodiapophyseal lamina; prsdf, prezygapophyseal spinodiapophyseal fossa; prsl, prespinal lamina; prz, prezygapophysis; p-spdl, posterior ramus of spinodiapophyseal lamina; s6, sixth sacral vertebra; sdf, spinodiapophyseal fossa; spdl, spinodiapophyseal lamina; spof, spinopostzygapophyseal fossa; spol, spinopostzygapophyseal lamina; sprl, spinoprezygapophyseal lamina; sr, sacral rib; sy, sacricostal yoke; tp, transverse process; tpol, intrapostzygapophyseal lamina; tprl, intraprezygapophyseal lamina. Scale bars equal 50 cm. Lacovara et al. (2014).

Dreadnoughtus schrani is thought to have been one of the largest Titanosaurs (though it is not claimed that it was the largest species), and is sufficiently complete that it is possible to estimate its size when alive. The larger specimen is thought to have been about 26 m in length, and to have weighed about 59.3 tons; this compares to an estimated 35 tons for the largest known Brachiosaurid Sauropod, Giraffatitan, and 14.8 tons for the largest Diplodocid Sauropod, Diplodocus, although considerable smaller than the 170 tons reached by living Blue Whales. It was also possible to study the histology (cell structure) of several bones, which strongly suggests that this specimen was still growing at the time when it died.

Reconstruction, appendicular skeletal anatomy, and bone histology of Dreadnoughtus schrani. (A) Reconstructed skeleton and body silhouette in left lateral view with preserved elements in white. (B) Left scapula and coracoid in lateral view. (C) Sternal plates in ventral view. (D) Left forelimb (metacarpus reconstructed) in anterior view. (E) Left pelvis (ilium partially reconstructed) in lateral view. (F) Left hind limb in anterior view (metatarsus and pes partially reconstructed and reversed from right). (G) Transverse ground thin section of humeral shaft, showing heavy secondary remodelling (arrow indicates extent of dense osteon formation), a thick layer of well-vascularized fibrolamellar bone, and a lack of lines of arrested growth or an external fundamental system. Abbreviations: acet, acetabulum; acf, acromial fossa; acp, acromial process; acr, acromial ridge; ast, astragalus; cc, cnemial crest; cof, coracoid foramen; cor, coracoid; dpc, deltopectoral crest; fem, femur; fhd, femoral head; fib, fibula; flb, fibrolamellar bone; gl, glenoid; hum, humerus; il, ilium; ilp, iliac peduncle; isc, ischium; isp, ischial peduncle; lt, lateral trochanter; mtI, metatarsal I; mtII, metatarsal II; of, obturator foramen; pop, postacetabular process; prp, preacetabular process; pu, pedal ungual; pub, pubis; pup, pubic peduncle; rac, radial condyle; rad, radius; sc, scapula; scb, scapular blade; sr, secondary remodelling; tib, tibia; tpp, tuberosity on preacetabular process; ul, ulna; ulc, ulnar condyle. Scale bars equal 1 m in (A) to (F) and 1 mm in (G). Lacovara et al. (2014).

See also…

Titanosaurs were the dominant group of Sauropod Dinosaurs in many Late Cretaceous faunas. The group included the very largest Sauropods, and therefore also the very largest known land animals of any type. Titanosaur remains were first found in Madagascar in the 1890s, though the first species from Madagascar...

Sauropod dinosaurs were massive, long-necked, long-tailed creatures that have long been regarded as the largest land animals ever to have lived. They reached...

During the later part of the Cretaceous global sea levels were...

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