Sunday, August 5, 2018

Ingentia: Prehistoric Beast of the Week

This week we'll be checking out a newly discovered dinosaur that was a giant long before we thought giants existed.  Make way for Ingentia prima!

Ingentia was a plant-eating dinosaur that lived in what is now Argentina during the Late Triassic Period, between 210 and 205 million years ago.  Sadly, only a partial skeleton is known so far from two individuals, including vertebrae, shoulder blades, and arm and hand bones.  However, this material is enough, with the help of referencing other kinds of dinosaurs that are similar and closely related, to estimate Ingentia was between twenty five and thirty three feet long from snout to tail.  This makes Ingentia the largest known animal in its environment.  The genus and species of this dinosaur translate to "First Huge One".

Ingentia prima knocking over a tree fern (and scaring the daylights out of a sphenodontid)  in watercolors by Christopher DiPiazza.

Ingentia belonged to a group of dinosaurs called the sauropodomorphs, which which are famous for having long necks and eating plants.  Brontosaurus, Apatosaurus, Diplodocus, and Brachiosaurus, are probably the most recognizable members of this group.  These famous dinosaurs are from the later major branch of the sauropodomorph tree, which flourished in the late Jurassic Period, growing to gigantic proportions and sporting column-like legs and feet.  Ingentia, however, appears to have been from the earlier branch of this major group of dinosaurs that flourished in the late Triassic and early Jurassic periods which were overall smaller in size.  They are sometimes referred to as the basal sauropodomorphs, or prosauropods.  The most famous member of this group of dinosaurs would be Plateosaurus. (Which is sadly still not nearly as famous as the late Jurassic giants mentioned earlier.)  Prosauropods had five fingers and three claws on each hand hands, and many species walked on their hind legs. 

Since Ingentia appears to be from the basal sauropodomorph group, it supports the notion that extremely large body size in dinosaurs not only started much earlier than we thought, but it also occurred twice in the sauropodomorph family tree.  Looking at cross sections of Ingentia's bones, paleontologists could tell that it was growing in spurts throughout the year, probably based on the seasons.  During the times when food was more abundant, Ingentia grew rapidly.  It's growth slowed down when resources were less available.  This is in contrast to the growth patterns we see in the later kinds of sauropodomorphs which grew constantly, but at a more steady pace. 

Figure from Apaldetti's paper describing Ingentia showing the known bones.

Ingentia's vertebrae show that they would have had air sacs in them in life, like modern birds have.  Ingentia wasn't using air sacs to fly, obviously, but they would be great adaptations for staying relatively light for the animal's size, which allowed it to grow much larger than an creature that had solid bones.  This is why the largest dinosaurs exceed the largest land animals, which have solid bones, by so much..  A mammal beyond a certain size would collapse under its own density, while a dinosaur, which is much lighter for its volume, could grow much more before hitting its threshold.  Air sacs also help keep the inside of the body from overheating, and help keep a more constant supply of fresh oxygen circulating throughout the body. 

Ingentia has been depicted walking on all fours in life a lot so far, but since most of its hind limbs have yet to be uncovered, we still don't know for sure if it could also walk on just two legs, as well.  There is even a chance it was an obligatory biped, only walking on its hing legs, like its later relative, Plateosaurus
 

References

Apaldetti, Cecilia; Martínez, Ricardo N.; Cerda, Ignatio A.; Pol, Diego; Alcober, Oscar (2018). "An early trend towards gigantism in Triassic sauropodomorph dinosaurs". Nature Ecology & Evolution.

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