The king of the abelisaurids is Brazilian
March 01, 2017
By Peter Moon | Agência FAPESP – Pycnonemosaurus. The name combines the Greek pycnos (“dense”) with the Latin nemus (“vegetation”) – it literally means “the lizard that lives in thick forest,” but it can be translated as “reptile from Mato Grosso” (the Brazilian state). And it is no ordinary dinosaur.
Pycnonemosaurus nevesi, the only known species in the genus Pycnonemosaurus, was a gigantic carnivorous dinosaur that lived 70 million years ago, during the Cretaceous, in what is now Central-Western Brazil. A new study concludes that it was the largest of its breed, the abelisaurids, whose trademark features are a pair of small horns and vestigial forelimbs.
P. nevesi was 8.9 m long from its snout to the tip of its tail. It was much larger than the most famous member of its family, Carnotaurus sastrei, also the only known species of the genus Carnotaurus. A 7.8 m specimen of C. sastrei was described in Argentina in 1985, and a life-sized replica occupies the place of honor in the entrance lobby to the University of São Paulo’s Zoology Museum (MZ-USP) in Ipiranga, a district of the city of São Paulo, Brazil.
The study published in the journal Cretaceous Research contains a complete description of P. nevesi, including a new estimate of its body length. The authors are paleontologists Orlando Grillo, affiliated with the National Museum in Rio de Janeiro (MN-UFRJ), and Rafael Delcourt, a researcher at MZ-USP.
Delcourt was awarded a doctoral scholarship by FAPESP, and his PhD research was supervised by Professor Hussam Zaher, one of MZ-USP’s curators. Delcourt’s thesis compared the anatomical evolution of tyrannosaurids and ceratosaurs.
“When I went to Argentina to study their abelisaurids, I was struck by the bones of Carnotaurus, at that time considered the largest species in the group,” said Delcourt, currently a post-doctoral fellow of Trinity College, Dublin, in Ireland. “Carnotaurus is very big, but I realized Pycnonemosaurus was even bigger.”
Delcourt recollected a picture of a gigantic 87 cm tibia from Pycnonemosaurus he had seen a few years before in Rio de Janeiro. As was to become clear in the course of the study, the abelisaurid with longest tibia after Pycnonemosaurus is Skorpiovenator, at 65 cm. The tibia is the longer of the two lower leg bones that connect the femur to the foot.
The Pycnonemosaurus fossils were found in 1952 by Llewellyn Ivor Price (1905-80), one of the pioneers of vertebrate paleontology in Brazil. Six vertebrae, the giant tibia and part of the pelvis were found at Fazenda Roncador in Querência, Mato Grosso.
The bones were housed at the National Department of Mineral Production (DNPM), where they remained until 2002, when paleontologists Diógenes de Almeida Campos at DNPM and Alexander Kellner at the National Museum described and named the creature, estimated to have been 7 m to 8 m in length.
The abelisaurids were a family of large carnivorous dinosaurs (or theropods) that evolved on the ancient southern supercontinent Gondwana. They spread around the world as India, Madagascar and Africa broke away from the supercontinent.
The new study investigated 37 specimens from eight countries, including India, Niger, Libya and Madagascar. In addition to Pycnonemosaurus and Carnotaurus, the other ten South American abelisaurids, all with new size estimates produced by Grillo and Delcourt, are from the following genera: Abelisaurus, Aucasaurus, Eoabelisaurus, Ekrixinatosaurus, Ilokelesia, Ligabueino, Quilmesaurus, Skorpiovenator, Viavenator, and Xenotarsosaurus.
Among the largest are Abelisaurus and Ekrixinatosaurus, both at 7.4 m; the others range between 5.2 m and 6.2 m. The smallest is Ligabueino, at only 80 cm, likely because it is a basal genus from the Lower Cretaceous and the ancestral lineage for all the others.
Specimens were also found in Madagascar, India, Pakistan, South Africa, Niger, Kenya, Morocco and France, though none exceed 7 m.
“Looking at the abelisaurid family as a whole, you can see there were species of all sizes, occupying all theropod food niches,” Delcourt said.
According to Grillo, “When we analyzed the diversity of the abelisauroids [the superfamily to which the abelisaurids belong] that occurred during the Cretaceous in Europe, North Africa, India, Madagascar, Brazil and Patagonia, we found a pattern in the composition of each location and age in terms of size.
“There are always predators of medium and large sizes, varying between 4 m and 8 m, and small species, ranging from 1 m to 2 m. This pattern is well observed in places with many fossils, such as Patagonia. In central Brazil, we have Pycnonemosaurus, which is large, and other medium-size individuals.”
Titanosaurs in South America
The abelisaurids were not the largest carnivorous dinosaurs – the tyrannosaurids, carcharodontosaurids and spinosaurids include larger species. The largest tyrannosaurid was the North American Tyrannosaurus rex, at 12.6 m.
Among carcharodontosaurids, the largest was the North African Carcharodontosaurus saharicus, with a length of 13.5 m and a weight of 7 tons, representing the heaviest known carnivorous dinosaur but not the longest. This distinction is reserved for two spinosaurids, the Egyptian Spinosaurus aegyptiacus, with a length of up to 18 m and a weight of up to 9 tons, and possibly Oxalaia quilombensis, from Maranhão State in Brazil. Although very few fossils of O. quilombensis have been found, it may have reached 14 m in length.
It is known that giant theropods lived in Brazil, as evidenced by the abundance of specimens from Argentina. However, it is unclear whether titanosaurs, a group of long-necked quadrupedal herbivores that included the largest animals ever to have walked on Earth, also inhabited Brazil.
Five of the 11 known dinosaurs with lengths exceeding 30 m have been found in Argentina: Futalognkosaurus, Puertasaurus and Notocolossus, all of which were more than 30 m long, and Argentinosaurus, at 35 m; the longest of all, at 37.5 m, has not yet been named.
“If gigantic titanosaurs are found in Argentina, it is highly likely that others will be found in Brazil,” Grillo said.
The largest Brazilian dinosaur, described in October 2016, is Austroposeidon magnificus, at 25 m. Similar to Pycnonemosaurus, it was found in the 1950s by Llewellyn Ivor Price and housed at DNPM.
The article “Allometry and body length of abelisauroid theropods: Pycnonemosaurus nevesi is the new king” (doi: http://dx.doi.org/10.1016/j.cretres.2016.09.001), by Orlando Nelson Grillo and Rafael Delcourt, can be retrieved from sciencedirect.com/science/article/pii/S0195667116301902.
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