How did dinosaurs get so big? Scientists now have an answer

SAO PAULO, Brazil — How did dinosaurs turn from small creatures into colossal giants? Researchers at the State University of Campinas (UNICAMP) in São Paulo state, Brazil, believe they finally have an answer. In a new study, they explain that the air sac formed the ancient dinosaur Macrocollum itaquii is the key to understanding the evolution of dinosaurs, which still captivates our imagination.

Macrocollum itaquii, which roamed southern Brazil about 225 million years ago, is the oldest dinosaur ever studied with air sac structures. These bone cavities, also found in modern birds, played a vital role in helping dinosaurs take in more oxygen, regulate their body temperature and survive the harsh conditions of their time. It is these adaptations that allowed some dinosaurs, such as the mighty Tyrannosaurus rex and Brachiosaurusto grow into massive creatures.

“The air sacs made their bones less dense, allowing them to grow to more than 30 meters,” Tito Aureliano, lead author of the study, said in a press release.

The research, which was carried out as part of Aureliano’s PhD, reveals how the largest dinosaurs of their time evolved from just one meter long to astonishing lengths. The research was part of a wider project “Taphnomic Landscapes” funded by the São Paulo Research Foundation (FAPESP), studying the preservation and fossilization of organisms.

Skeletal reconstruction of the unaysaurid sauropodomorph Macrocollum (CAPPA/UFSM 0001b) showing vertebral elements along the vertebral column and a possible reconstruction of the air sac systems involved.  (a) Pneumatic posterior cervical vertebra and cross-sectional CT slice b.  (c) Pneumatic anterior dorsal vertebra with cross-sectional CT slice d and details of the pneumatic opening e.  (f) detail of the pneumatic opening in a reconstructed 3D model of the element.  g) anterior cervical element (pneumatic).  (h) No traces of PSP in the posterior dorsal vertebra.  The sacral series (i) as well as the anterior (k) and middle caudal (j) series are pneumatic.  a, g, h, j, and k are in left side view.  c, e, and f are in right lateral view.  i'm in the back view.  ABD, abdominal diverticula;  CER, cervical diverticulum;  LUN, lung;  pf, pneumatic openings.  The reconstruction was done by Rodrigo T. Miller.  Scale bar for skeletal reconstruction = 500 mm;  a–j = 20 mm.
Skeletal reconstruction of the unaysaurid sauropodomorph Macrocollum (CAPPA/UFSM 0001b) showing vertebral elements along the vertebral column and a possible reconstruction of the air sac systems involved. (a) Pneumatic posterior cervical vertebra and cross-sectional CT slice b. (c) Pneumatic anterior dorsal vertebra with cross-sectional CT slice d and details of the pneumatic opening e. (f) detail of the pneumatic opening in the reconstructed 3D model of the element. g) anterior cervical element (pneumatic). (h) No traces of PSP in the posterior dorsal vertebra. The sacral series (i) as well as the anterior (k) and middle caudal (j) series are pneumatic. a, g, h, j, and k are in left side view. c, e, and f are in right lateral view. i’m in the back view. ABD, abdominal diverticula; CER, cervical diverticulum; LUN, lung; pf, pneumatic openings. The reconstruction was done by Rodrigo T. Miller. Scale bar for skeletal reconstruction = 500 mm; a–j = 20 mm. (Courtesy of FAPESP)

Fresia Ricardi-Branco, professor at UNICAMP and principal investigator of the project, emphasized the importance of the project. M. itaquii in the context of dinosaur evolution.

“This dinosaur walked the Earth during the Triassic period and paved the way for the remarkable diversity we see in the Jurassic and Cretaceous periods. The presence of air sacs gave dinosaurs an evolutionary advantage over other groups, allowing them to diversify rapidly,” explains Riccardi-Branco.

The recent discovery challenges previous assumptions about the evolution of air sacs. The team found internal pneumatic chambers M. itaquii, a new type of tissue with an intermediate texture that they propose to call a “protocamera.” This finding contradicts the widely accepted hypothesis that air sacs evolved from chambered to camellia structures. The researchers also found that air sacs existed in the cervical and dorsal regions of the dinosaur’s spine, contrary to previous theories that suggested they appeared only in the abdominal region.

“Evolution seems to have experimented with different shapes until it arrived at the final system where the air sacs extended from the cervical region to the tail. It was not a linear process,” explains Aureliano.

By revealing the role of air sacs in the evolution of dinosaurs, this research provides an invaluable insight into the extraordinary world of these prehistoric creatures. Discovery about M. itaquii’s the unique anatomical features are changing our understanding of the evolution of dinosaurs, paving the way for further fascinating revelations about their ancient existence.

The findings are published in the journal Anatomical record.

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