Tuesday, 28 April 2015

Chilesaurus diegosuarezi, T-rex’s Vegetarian Cousin

Artistic interpretation of Chilesaurus diegosuareziis
Chilesaurus diegosuarezi
Artistic interpretation
Credit: Gabriel Lío
Researchers announced yesterday the discovery of a new dinosaur that although closely related to the carnivorous T-Rex it preferred to feed on plant material. The new lineage of dinosaur was discovered in Chile and has proven to be an evolutionary jigsaw puzzle.

Paleontologists are referring to the newly described species (Chilesaurus diegosuarezi) as the platypus-version of dinosaurs, due to the bizarre combination of traits from many different dinosaur groups. For instance, C. diegosuarezi boasted a proportionally small skull, hands with two fingers like T-rex and feet more akin to primitive long-neck dinosaurs.

The species is placed within the theropod group of dinosaurs, a group of popupar meat eaters like the Velociraptor, Carnotaurus and Tyrannosaurus, the same group from which today's birds evolved. The presence of herbivorous theropods was up until now only known in close relatives of birds, but Chilesaurus apparently managed to become a meat-free theropod much earlier than thought.

The species was named after the country where it was collected (Chilesaurus) and in honor of Diego Suárez (diegosuarezi), the seven year old boy who discovered the first bones. The boy found the fossil remains at the Toqui Formation in Aysén, south of Chilean Patagonia, in rocks deposited at the end of the Jurassic Period, approximately 145 million years ago.

The Discovery
In 2004, Diego was in the area with his parents, Chilean geologists Manuel Suarez and Rita de la Cruz, who were studying rocks in the Chilean Patagonia, with the aim to better understand the formation of the Andes mountain range. Diego came across the fossils while him and his sister, Macarena, were looking for decorative stones.

Due to bizarre combination of characters, it was initially believed that Diego had discovered several species. However, since Diego's find, researchers have excavated more than a dozen Chilesaurus specimens, including four complete skeletons, a first for the Jurassic Period in Chile. These specimens demonstrate that the dinosaur combined a variety of unique anatomical traits.

"The site yielded abundant and exquisitely preserved three-dimensional skeletons of small archosaurs. Several articulated individuals of Chilesaurus at different ontogenetic stages have been collected, as well as less abundant basal crocodyliforms, and fragmentary remains of sauropod dinosaurs (diplodocids and titanosaurians)" an xtract from the paper on the discovery.

Most of the specimens belonged to individuals the size of a turkey, but some isolated bones indicated that the maximum size of Chilesaurus was around three meters long. 

As aforementioned, the Chilesaurus is the only theropod known to be vegetarian.. Like other Jurassic theropods such as Allosaurus, Chilesaurus had robust forelimbs. However, its hands were provided with two blunt fingers, unlike the sharp claws of fellow theropod Velociraptor. Chilesaurus' pelvic girdle resembles that of the ornithischian dinosaurs, whereas it is actually classified in the other basic dinosaur division -- Saurischia.

The different parts of the body of Chilesaurus were adapted to a particular diet and way of life, which was similar to other groups of dinosaurs. As a result of these similar habits, different regions of the dinosaurs body evolved in a unique way, resembling those present in other, unrelated groups of dinosaurs, a phenomenon called evolutionary convergence.

Chilesaurus represents one of the most extreme cases of mosaic convergent evolution recorded in the history of life. For example, the teeth of Chilesaurusare very similar to those of primitive long-neck dinosaurs because they were selected over millions of years as a result of a similar diet between these two lineages of dinosaurs.

"Chilesaurus can be considered a 'platypus' dinosaur because different parts of its body resemble those of other dinosaur groups due to mosaic convergent evolution. In this process, a region or regions of an organism resemble others of unrelated species because of a similar mode of life and evolutionary pressures. Chilesaurusprovides a good example of how evolution works in deep time and it is one of the most interesting cases of convergent evolution documented in the history of life. Chilesaurus shows how much data is still completely unknown about the early diversification of major dinosaur groups. This study will force palaeontologists to take more care in the future in the identification of fragmentary or isolated dinosaur bones. It comes as false relationship evidence may arise because of cases of convergent evolution, such as that present in Chilesaurus." said Martín Ezcurra, researcher at School of Geography, Earth and Environmental Sciences, University of Birmingham.

Dr. Fernando Novas, Bernardino Rivadavia from the Natural Sciences Museum, Buenos Aires, Argentina, who led the research on Chilesaurus said:

"Chilesaurus is the first complete dinosaur from the Jurassic Period found in Chile and represents one of the most complete and anatomically correct documented theropod dinosaurs from the southern hemisphere. Although plant-eating theropods have been recorded in North America and Asia, this is the first time a theropod with this characteristic has been found in a southern landmass. Chilesaurus was an odd plant-eating dinosaur only to be found in Chile. However, the recurrent discovery in beds of the Toqui Formation of its bones and skeletons clearly demonstrates that Chilesaurus was, by far, the most abundant dinosaur in southwest Patagonia 145 million years ago."

- Novas, F., Salgado, L., Suárez, M., Agnolín, F., Ezcurra, M., Chimento, N., de la Cruz, R., Isasi, M., Vargas, A., & Rubilar-Rogers, D. (2015). An enigmatic plant-eating theropod from the Late Jurassic period of Chile Nature DOI: 10.1038/nature14307

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