Old Earth Ministries Online Dinosaur Curriculum

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Lesson 45 - Titanosaurs

Titanosaurs (members of the groups Titanosauria and/or Titanosauroidea) were a diverse group of sauropod dinosaurs, which included Saltasaurus and Isisaurus. It includes some of the heaviest creatures ever to walk the earth, such as Argentinosaurus and Paralititan — which might have weighed up to 100 tonnes (110 short tons) or, perhaps even larger. They were named after the mythological Titans, the early deities of Ancient Greece, who preceded the Twelve Olympians. Together with the brachiosaurids and relatives, they make up the larger clade Titanosauriformes.

Description

Titanosaurs had small heads, even when compared with other sauropods. The head was also wide, similar to the heads of Camarasaurus and Brachiosaurus but more elongated. Their nostrils were large ('macronarian') and they all had crests formed by these nasal bones. Their teeth were either somewhat spatulate (spoon-like) or like pegs or pencils, but were always very small.

From skin impressions found with the fossils, it has been determined that the skin of many titanosaur species was armored with a small mosaic of small, bead-like scales around a larger scale. One species, Saltasaurus, has even been discovered with bony plates, like the Ankylosaurus.

While they were all huge, many were fairly average in size compared with the other giant dinosaurs. There were even some island-dwelling dwarf species such as Magyarosaurus, probably the result of allopatric speciation and insular dwarfism.

Range

The titanosaurs were the last great group of sauropods before the Cretaceous-Tertiary extinction event, about 90–65 million years ago and were the dominant herbivores of their time. The fossil evidence suggests they replaced the other sauropods, like the diplodocids and the brachiosaurids, which died out between the late Jurassic and the mid-Cretaceous Periods.

Titanosaurs were widespread. Fossils have been found on all continents except Antarctica. Four well preserved skeletons of a titanosaur species were found in Italy, a discovery first reported on May 2, 2006. They are 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.

Paleobiology

Diet

Fossilized dung associated with late Cretaceous titanosaurids has revealed phytoliths, silicified plant fragments, that offer clues to a broad, unselective plant diet. Besides the plant remains that might have been expected, such as cycads and conifers, discoveries published in 2005  revealed an unexpectedly wide range of monocotyledons, including palms and grasses (Poaceae), including ancestors of rice and bamboo, which has given rise to speculation that herbivorous dinosaurs and grasses co-evolved.

Nesting

A large titanosaurid nesting ground was discovered in Auca Mahuevo, in Patagonia, Argentina and another colony has reportedly been discovered 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 gives evidence of herd behavior, which, along with their armour, could have helped provide protection against large contemporary predators such as Abelisaurus.

Systematics

The fossil record of titanosaurs, as plains-dwelling herbivores, has been disappointingly fragmentary for such a widespread and successful group (they represent roughly a third of the total sauropod diversity known to date). Only recently have skulls or relatively complete skeletons (see Rapetosaurus) of any of the roughly 50 species of titanosaur been discovered. Many species are poorly known. Much material may be reclassified and some genera renamed as understanding of the clade grows.

The family Titanosauridae was named after and anchored on the poorly known genus Titanosaurus, which was coined by Richard Lydekker in 1877, on the basis of a partial femur and two incomplete caudal vertebrae. Fourteen species have since been referred to Titanosaurus, which distribute the genus across Argentina, Europe, Madagascar, India and Laos and throughout 60 million years of the Cretaceous Period. Despite its centrality to titanosaur systematics and biogeography, a re-evaluation of all Titanosaurus species recognises only five as diagnostic. The type species T. indicus is invalid, because it is based on 'obsolescent' characters - once diagnostic features that have gained a broader taxonomic distribution over time. Consequently, use of the genus Titanosaurus has largely been abandoned. The most well known Titanosaurus specimens have since been re-assigned to other genera, including Isisaurus.

Some paleontologists (such as Sereno, 2005 ) have contended that Titanosaurus is too poorly known to use as a basis for classification, family names for which it is the type genus (e.g. Titanosaurinae, Titanosauridae, Titanosauroidea) should not have other genera referred to them. Weishampel et al., in the second edition of The Dinosauria, also did not use the family Titanosauridae, and instead used several smaller titanosaur families such as Saltosauridae and Nemegtosauridae.

Select Genus

Argentinosaurus

An early reconstruction by Gregory S Paul estimated Argentinosaurus at between 30–35 metres (98–115 ft) in length and with a weight of up to 80–100 tonnes (88–110 short tons). Other estimates have compared the fragmentary material to relatively complete titanosaurs to help estimate the size of Argentinosaurus. In 2006 Carpenter used the more complete Saltasaurus as a guide and estimated Argentinosaurus at 30 metres (98 ft) in length. An unpublished estimate used published reconstructions of Saltasaurus , Opisthocoelicaudia , and Rapetosaurus as guides and gave shorter length estimates of between 22–26 metres (72–85 ft). Weight estimates are less common, but one estimate provides a range of 60–88 tonnes (66–97 short tons), and consider 73 tonnes (80 short tons) to be the most likely, making it the heaviest sauropod known from good material.

Saltasaurus

Saltasaurus (which means "lizard from Salta") is a genus of titanosaurid sauropod dinosaur of the Late Cretaceous Period. Relatively small among sauropods, though still massive by the standards of modern creatures, Saltasaurus was characterized by a diplodocid-like head (with blunt teeth, only in the back of the mouth). It was the first genus of sauropod known to possess armour of bony plates embedded in its skin. The small bony plates (called osteoderms, a feature of modern crocodiles) have since been found on other titanosaurids. When the plates of a saltasaur were originally found, independently of skeletal remains, they were assumed to be from an ankylosaurian, whose plates they resemble. A crest of scutes has also been discovered running down the back of diplodocid sauropods.

Saltasaurus was first described by José Bonaparte and Jaime E. Powell, in 1980 and had an estimated length of 12 metres (39 feet) and a mass of 7 tonnes (8 tons). Like all sauropods, Saltasaurus was herbivorous, and its name is derived from the region of north-west Argentina, where the first fossils were recovered. Other fossils have since been found in Uruguay.

A large titanosaurid nesting ground was discovered in Auca Mahuevo, in Patagonia, Argentina (another titanosaur nesting site has reportedly been discovered 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 showing a mosaic armour of small bead-like scales. The huge number of individuals gives evidence of herd behavior which, along with the armour, could have helped provide protection against contemporary predators such as Abelisaurus.

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