Titanosaur

Titanosaurs Temporal range: Cretaceous 140–66 mya
Epachthosaurus skeleton, National Museum, Czech Republic, originally from South America
Scientific classification
Kingdom:	Animalia
Class:	Reptilia
Superorder:	Dinosauria
Order:	Saurischia
Suborder:	Sauropodomorpha
Infraorder:	Sauropoda
Superfamily:	†Titanosauroidea Lydekker, 1895
(unranked):	†Titanosauria Bonaparte & Coria, 1993

Argentinosaurus from Argentina

Qiaowanlong from China, 100 mya

Xinghesaurus from China, not yet described

A single vertebra: Argentinosaurus dorsal and sauropod paleontologist Matt Wedel

Titanosaurs were a group of large sauropod dinosaurs. Together with the brachiosaurs and relatives they make up the larger clade Titanosauriformes.

They were the largest and heaviest creatures ever to walk the Earth. Titanosaurs included Saltasaurus, Isisaurus, and Paralititan. The group includes the largest land animals known to have existed. Patagotitan – (37 m (121 ft) long) – is now installed in the Natural History Museum in London. Its weight in life is estimated at 69 tonnes (76 tons).

The comparably sized Argentinosaurus and Puertasaurus are from the same region, as is Abdarainurus and Aegyptosaurus. The group's name is from the mythological Titans of Ancient Greece.

The titanosaurs were the last great group of sauropods before the Cretaceous–Paleogene extinction event. They were the dominant herbivores of their time. The fossil evidence suggests they replaced the other sauropods: the diplodocids and the brachiosaurids died out between the Upper Jurassic and the mid-Cretaceous.

Original discovery

Titanosaurus indicus was first one found, by British paleontologist Richard Lydekker in 1877. He only had two caudals (tail bones) and a femur collected on different occasions at the same place in India.

Skeleton

Broadly, their skeleton was similar to earlier sauropods, but with a few key differences. The pelvis (hip area) was slimmer than some sauropods, but the pectoral (chest area) was much wider. This gave them a uniquely 'wide-gauged' stance: their front legs were wider apart, and usually longer than their hind legs. This can be seen very clearly in the Argentinosaurus. As a result, the fossilised trackways of titanosaurs are broader than other sauropods. Their vertebrae (back bones) were solid (not hollowed-out). Their spinal column was more flexible, so they were probably more agile than their cousins and better at rearing up.

Variety

The group was quite varied. Some of the smaller types did not have longer forelimbs (Epachthosaurus), and one Chinese find (Xinghesaurus) had an extremely long neck. These differences must reflect adaptations to differences in their habitats and life-style, but at present there is little known about this. Many of these discoveries are quite recent.

Global distribution

Titanosaurs were widespread. Their fossils have been found in all continents, even Antarctica. Four well preserved skeletons of a titanosaur species were found in Italy.

They were especially numerous in the southern continents (then part of the supercontinent of Gondwana). Australia had titanosaurs around 96 million years ago: fossils have been discovered in Queensland of a creature around 25 meters long (82 feet). Remains have also been discovered in New Zealand.

World record size

Titanosaurs hold the world record for the size of a land animal. One place in the Argentine had 150 bones from seven titanosaurs. The largest were from an animal 40 metres (~130 feet) long and 20 metres (35 feet) tall. It would have weighed about 77 tonnes. A local farm worker stumbled on the remains in the desert near La Flecha, about 250km (135 miles) west of Trelew, Patagonia. The BBC flew a team out to record the event. David Attenborough follows the story of how experts found the world's largest dinosaur measuring 121ft – and its heart weighed more than three people.

Estimated size & weight:

• Patagotitan 70,000 kg
• Argentinosaurus 70,000 kg
• Dreadnaughtus 55,000 kg

Paleobiology

As a group, titanosaurs were high browsers, eating leaves and branches from tall trees. This is in contrast to other herbivores like the Ceratopsia and Ankylosauria, which were low browsers, eating lower vegetation like ferns and cycads . As a general rule, high browsers can eat lower-growing plants, but low browsers cannot eat from tall trees. Like the earlier sauropods (e.g. Diplodocus) titanosaurs had peg-like teeth and no grinders. This means they used gastroliths to grind their food, and had a huge vat-like stomach.

Diet

Fossilized dung found with late Cretaceous titanosaurids suggests a broad, unselective plant diet. Besides the plant remains that might have been expected, such as cycads and conifers, there were an unexpectedly wide range of monocotyledons, including palms and grasses (Poaceae), including ancestors of rice and bamboo. This has given rise to speculation that herbivorous dinosaurs and grasses co-evolved.

Nesting

Diagram showing titanosaur nest excavation and egg laying

A large titanosaurid nesting ground was discovered in Auca Mahuevo, in Patagonia, Argentina. Another colony is reported in Spain. Several hundred female saltasaurs dug holes with their back feet, laid eggs in clutches averaging around 25 eggs each, and buried the nests under dirt and vegetation. The small eggs, about 11–12 cm (4–5 in) in diameter, contained fossilised embryos, complete with skin impressions. The impressions showed that titanosaurs were covered in a mosaic armour of small bead-like scales. The huge number of individuals suggests herd behavior which would have given protection against large predators such as Abelisaurus. Their primary protection was, of course, their size. It is difficult to imagine a predator tackling a fully-grown titanosaur, and probably none did. Young titanosaurs would need guarding, of course.