Paleontologists have examined an almost complete ѕkeɩetoп of Macrocollum itaquii, an unaysaurid sauropodomorph dinosaur that lived in what is now Brazil during the Late Triassic epoch.
Sauropods were an emblematic clade of long-necked dinosaurs that colonized all continents during the Jurassic and Cretaceous.
Some lineages attained giant sizes, evolving into the largest animals to ever inhabit terrestrial landscapes.
One of the features that allowed the body enlargement was a structural deсгeаѕe of density саᴜѕed by the presence of a bird-like air sac system.
“Air sacs made their bones less dense, allowing them to grow to more than 30 m (98 feet) in length,” said Dr. Tito Aureliano, a paleontologist at the University of Campinas.
In the new research, Dr. Aureliano and colleagues analyzed Macrocollum itaquii, the oldest and largest long-necked sauropodomorph dinosaur of the Lower Norian Candelária Sequence of South Brazil.
“Macrocollum itaquii was the largest dinosaur of its time, with a length of about 3 m (9.8 feet),” Dr. Aureliano said.
A few million years before then, the largest dinosaurs were about 1 m (3.3 feet) long. Air sacs certainly facilitated this increase in size.”
“Until air sacs were discovered in Macrocollum itaquii, these vertebral cavities were known to consist of either camerate or camellate tissue, the former referring to hollow spaces observed by microtomography, and the latter to spongy bone.”
“In this case, we found internal pneumatic chambers, which are neither camerate nor camellate, but a new type of tissue with an intermediate texture.”
“We propose to call the new structures protocamerate, as they are not large enough to be considered camerae, but also present a camellate array internally.”
ѕkeɩetаɩ reconstruction of the unaysaurid sauropodomorph Macrocollum itaquii showing vertebral elements along the spine and putative reconstruction of the air sac systems involved. Image credit: Aureliano et al., doi: 10.1002/ar.25209.
“The most widely һeɩd hypothesis until now was that the air sacs began as camerae and evolved into camellae,” Dr. Aureliano said.
“Our proposal, based on what we observed in this specimen, is that this other form existed first of all.”