Titanosaurs - The Last of the Sauropods

By the beginning of the Cretaceous period, about 140 million years ago, gigantic herbivores like Diplodocus and Brachiosaurus were on the decline. However, this didn't mean that sauropods as a whole were destined for early extinction; an offshoot of these huge, four-footed plant-eaters, known as titanosaurs, continued to prosper right up to the K/T Extinction 65 million years ago. (See a gallery of titanosaur pictures.)

The problem with titanosaurs--from a paleontologist's point of view--is that their fossils tend to be scattered and incomplete, much more so than for any other family of dinosaurs. Very few articulated skeletons of titanosaurs have been found, and virtually no intact skulls, so reconstructing what these beasts looked like has required a lot of guesswork. Fortunately, their close similarity to earlier sauropods, their wide geographic distribution (titanosaur bones have been found on every continent except Australia), and their extensive number of genera (possible as many as 100) has made it possible to hazard some reasonable theories.
Titanosaur Characteristics

As stated above, titanosaurs were very similar in build to earlier sauropods: they were quadrupedal, long-necked and long-tailed, and tended toward enormous sizes (one of the biggest titanosaurs, Argentinosaurus, may have reached lengths of 100 feet, though genera like Saltasaurus were considerably smaller). What set titanosaurs apart from the pack were subtle anatomical differences involving their skulls and bones, and, most famously, their rudimentary armor: it's believed that most, if not all, titanosaurs had tough, bony plates covering their bodies.

This last feature raises an interesting question: could it be that earlier sauropods perished at the end of the Jurassic period because their juveniles were preyed on by carnivorous dinosaurs? If so, the development of titanosaur armor (even though it wasn't nearly as ornate or dangerous as the armor found on ankylosaurs) might have been a key evolutionary adaptation that allowed these gentle herbivores to survive.
Titanosaur Habitats & Behavior

Despite their limited fossil remains, titanosaurs were clearly some of the most successful dinosaurs ever to walk the earth. In the Cretaceous period, most other types of dinosaurs were restricted to certain geographic areas--pachycephalosaurs in North America and Asia, for example--but titanosaurs attained worldwide distribution. There may, however, have been stretches of millions of years when titanosaurs were clustered on the southern supercontinent Gondwana (which is where Gondwanatitan gets its name); more titanosaurs have been discovered in South America than on any other continent.

Paleontologists know about as much about the everyday behavior of titanosaurs as they do about the everyday behavior of sauropods in general--which is to say, not a whole lot. There's evidence that some titanosaur genera may have roamed in herds of dozens or hundreds of adults and juveniles, and the discovery of nesting grounds (complete with fossilized eggs) hints that females may have laid their eggs in groups, to better protect their young.
Titanosaur Classification

Moreso than with other types of dinosaurs, the classification of titanosaurs is a matter of ongoing dispute: some paleontologists think "titanosaur" isn't a very useful designation, and prefer to refer to smaller, anatomically similar, and more manageable groups like "saltasauridae" or "nemegtosauridae."

The doubtful status of titanosaurs is best exemplified by its eponymous genus, Titanosaurus. Over the years, Titanosaurus has become a kind of wastebasket genus to which poorly understood fossil remains have been assigned (meaning that many of the species assigned to this genus may not actually belong there!).

Classification controversies aside, here's a list of the most notable titanosaur genera; just click on the links for more information.

Aegyptosaurus Guess what country this dinosaur was found in?

Alamosaurus No, it wasn't named after the Alamo, but it should have been.

Ampelosaurus One of the best-known of the armored titanosaurs.

Andesaurus This titanosaur rivaled Argentinosaurus in size.

Antarctosaurus Despite its name, this titanosaur may or may not have lived in Antarctica.

Bonitasaura This titanosaur wasn't as beautiful as its name implies.

Epachthosaurus This "heavy lizard" was relatively primitive for its time and place.

Futalognkosaurus It sounds like a hot dog, but it was one of the biggest dinosaurs that ever lived.

Gondwanatitan Yet another titanosaur from South America.

Hypselosaurus This titanosaur's eggs were a foot in diameter.

Isisaurus Otherwise known as the Indian Statistical Institute Lizard.

Nemegtosaurus This titanosaur has been recreated from a single, incomplete skull.

Paralititan This huge sauropod was discovered recently in Egypt.

Quaesitosaurus This titanosaur may have had unusually sharp hearing.

Rapetosaurus The only sauropod ever to be discovered on modern-day Madagascar.

Saltasaurus The first armored sauropod ever to be discovered.

Titanosaurus This sauropod may--or may not--have been a unique member of its genus.