A new genus and species of silesaur being named Amanasaurus nesbitti has been discovered by a duo of paleontologists at the Federal University of Santa Maria.
Life reconstruction of Amanasaurus nesbitti. Image credit: Matheus Fernandes.
Amanasaurus nesbitti lived in what is now Brazil during the Carnian age of the Late Triassic epoch, some 233 million years ago.
The ancient creature was a member of Silesauridae, an extinct family of Triassic dinosauriform reptiles.
Silesaurids had a fairly long neck and legs, and possibly quadrupedal habits.
They are most commonly considered to be a group of non-dinosaur dinosauriforms, and the sister group of dinosaurs.
They occupied a variety of ecological niches, with early silesaurids being meat-eating and later species having adaptations for specialized herbivory.
“Silesaurs are part of the wide Triassic radiation of archosaurs,” said Federal University of Santa Maria paleontologists Rodrigo Müller and Maurício Garcia.
“Most silesaurs are characterized by slender limbs and a beak-like projection from the anterior tip of the lower jaw.”
“Whereas these reptiles are present in the fossil record of Middle to Upper Triassic, no records have been reported from Jurassic or younger layers.”
“Silesaurs are particularly interesting because of their close phylogenetic relationships with dinosaurs, with several studies placing silesaurs as the closest evolutionary relatives of dinosaurs.”
Provenance of Amanasaurus nesbitti: (a) surface distribution of the geologic units in the area depicting the location of the Pivetta site, Brazil; (b) general view of the Pivetta site; (c) hypothetical reconstruction of the skeleton of Amanasaurus nesbitti depicting (in orange) the preserved portions (d and e). Image credit: R.T. Müller & M.S. Garcia, doi: 10.1038/s41598-023-32057-x.
In their study, the researchers examined two bone fragments — a portion of a right femur and a portion of a left femur — of Amanasaurus nesbitti.
The fossils were found at the site of Pivetta, between the municipalities of Restinga Sêca and São João do Polêsine, Rio Grande do Sul, Brazil.
“It is the first time that silesaurs rivaling in size with early dinosaurs are recovered from the oldest unequivocal dinosaur-bearing beds, challenging the idea that in faunas where silesaurs and unambiguous dinosaurs co-occurred, silesaurs were relatively smaller,” the scientists said.
“This discovery reinforces the complex scenario regarding the radiation of Pan-Aves during the Triassic.”
“Surely, the body plan of early diverging forms being surpassed by late diverging dinosaurs does not fit within the current models anymore.”
“Actually, silesaurs — independent of their phylogenetic position — persisted during most of the Triassic period, with its plesiomorphic body size advancing through the dawn of dinosaurs, instead of silesaur lineages decrease in body size through time.”
The team’s results were published in the journal Scientific Reports.
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R.T. Müller & M.S. Garcia. 2023. A new silesaurid from Carnian beds of Brazil fills a gap in the radiation of avian line archosaurs. Sci Rep 13, 4981; doi: 10.1038/s41598-023-32057-x
