Triassic Dinosaurs Just Got a Lot Bigger! According to New Research

Ingentia prima – Giant Late Triassic Sauropodomorph from Argentina

Argentina might have been home to huge, plant-eating dinosaurs associated with Cretaceous-aged strata, after all, one of the biggest terrestrial vertebrates known to science is the titanosaur called Argentinosaurus (A. huinculensis), just one of a number of super-sized leviathans from this part of the world.  However, a team of scientists, writing in the academic journal “Nature Ecology & Evolution” have announced the discovery of yet another giant, South American dinosaur. However, this one is a Triassic dinosaur. One that roamed northern Argentina around 210 million years ago.

A Giant Triassic Dinosaur

The dinosaur, classified as a member of the Sauropodomorpha, has been named Ingentia prima and it was certainly very big for a Late Triassic animal, with an estimated body weight of around ten tonnes and a length of approximately ten metres.  To provide a comparison, the sauropodomorph Plateosaurus (P. engelhardti), from the Late Triassic of western Europe, that would have been a contemporary of Ingentia prima, is estimated to have reached a length of about eight metres with a body mass of around four tonnes.  The later sauropodomorph Lufengosaurus (L. huenei), from the Early Jurassic of China, might have been around six metres long and is estimated to have weighed more than 1.5 tonnes, Ingentia is much, much bigger.

Sauropodomorpha Size Comparison

Picture credit: Everything Dinosaur with I. prima illustration by Jorge A. González

First Giant

The discovery of Ingentia prima does rather upset the dinosaurian apple cart.  It had been thought that gigantism in the sauropodomorphs evolved in the Early Jurassic, however, here was a ten-tonne giant, comparable in size to those Early Jurassic sauropods that roamed some thirty-five million years later.  The evolution of giant, plant-eating, long-necked dinosaurs came about as a result of the development of numerous anatomical characteristics but I. prima displays many features of the body plan of basal, small sauropodomorphs and lacks most of the anatomical traits previously regarded as adaptations to gigantism.

The Fossilised Material in the Field (Partial Exposure)

Picture credit: Cecilia Apaldetti

Lead author of the scientific paper, Dr Cecilia Apaldetti (Universidad Nacional de San Juan, San Juan, Argentina), commented:

“It [Ingentia] was enormous.  It was at least twice as large as the other herbivores of the time and until now it was believed the first giants to inhabit the Earth originated in the Jurassic, about 180  million years ago.”

The dinosaur’s scientific name pays tribute to its size, the name translates from the Latin to “first giant”.  It had been thought, that if the first dinosaurs appeared around 230 million years ago, it took fifty million years for the first giants to evolve, the discovery of a partial skeleton in San Juan Province (north-western Argentina), has changed all that.

Quebrada del Barro Formation

The fossil material consisting of shoulder blades, cervical vertebrae (neck bones) and elements from the forelimbs, heralds from the Quebrada del Barro Formation.  The Ingentia fossil material was found adjacent to the fossilised remains of three individuals belonging to the already known and closely related species Lessemsaurus sauropoides, which had been named and scientifically described back in 1999.

The researchers, in addition to describing I. prima formally for the first time, were able to examine the three new specimens of Lessemsaurus sauropoides.  Ingentia has been placed in a newly erected family of long-necked dinosaurs, the Lessemsauridae, a branch of the Sauropoda that evolved gigantic forms like the later Eusauropods (true sauropods).  The Eusauropoda includes those famous Jurassic giants such as Diplodocus, Brontosaurus and Brachiosaurus, as well as the later titanosaurs such as the mighty Argentinosaurus, which roamed Argentina some 115 million years after Ingentia became extinct.

Circular Saws were used to Help Extract the Large Fossil Bones

Picture credit: Cecilia Apaldetti

Why was a Triassic Dinosaur so Big?

Early sauropodomorphs were small, agile bipeds, but the ancestors of Ingentia adopted a different evolutionary strategy.

A spokesperson from Everything Dinosaur commented:

“Developing a larger gut would allow more effective processing of tough vegetation, enabling these types of dinosaurs to extract more nutrients from the plants that they consumed.  Furthermore, by becoming big, these dinosaurs would have had less to fear from the predators that shared their environment, including theropod dinosaurs.  If you are very large, a meat-eating dinosaur might avoid you and look for an easier meal elsewhere.  Becoming a giant is an evolutionary strategy found in a number of herbivorous animals”.

The Remarkable Skeleton of Ingentia prima

The lessemsaurids (Ingentia, Lessemsaurus and a third Early Jurassic dinosaur from South Africa named Antetonitrus), may have lacked the extremely long necks found in later eusauropods, but their bones reveal some remarkable adaptations nonetheless.  Pneumatic structures have been identified in the vertebrae (air sacs), this indicates that these dinosaurs had a sophisticated and extremely efficient bird-like respiratory system.  These air sacs will have also helped to prevent these animals from overheating, a problem with large creatures, (surface area to volume ratio – hence one of the reasons why African elephants have large ears).  This kind of respiratory system implies the presence of cavities in their bones – a pneumatised skeleton that would have helped to lighten the animal and make locomotion more efficient.

Although Ingentia shows these adaptations to gigantism, it lacks many of the features associated with the later sauropods.  For example, its legs were more bent and not the huge, weight-bearing columns associated with the Diplodocidae and the Macronaria.

The Remarkable Bones and Respiratory System of Ingentia prima

Picture credit: Jorge A. González

A Triassic Dinosaur Ahead of its Time

The quality of bone preservation permitted the research team to examine the histology of the dinosaur’s bones.  The scientists compared the bone growth in the new fossils with those of an earlier, bipedal sauropodomorph as well as a later eusauropod.  The histology of the earlier sauropodomorph revealed a cyclical growth pattern, the animal growing in spurts, whereas, the eusauropod bones, when examined in cross-section, revealed another pattern of growth.  This dinosaur grew acyclically, growing throughout its long life.  Members of the newly erected Lessemsauridae family grew differently.  Their bones show evidence of growth spurts, a trait found in their ancestors but when they grew, they really put on a spurt.  The researchers identified a growth rate of around two to three times faster than the already impressive rate of the later eusauropods.

Ingentia demonstrates that the first wave of colossal giant dinosaurs evolved some thirty-five million years earlier than previously thought.  In addition, with an accelerated growth rate, unique limb adaptations and a bird-like respiratory system, the Lessemsauridae got big but they did it in a different way when compared to the later long-necked dinosaurs.

When it comes to the “LESSemsauridae” – Less may actually mean more…

The scientific paper: “An Early Trend Towards Gigantism in Triassic Sauropodomorph Dinosaurs” by Cecilia Apaldetti, Ricardo N. Martínez, Ignacio A. Cerda, Diego Pol & Oscar Alcober published in the journal Nature Ecology & Evolution.

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