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Ignotosaurus, new silesaurid from Triassic of Argentina



From: Ben Creisler
bcreisler@gmail.com


A paper in the new JVP Memoir:


Ricardo N. Martínez, Cecilia Apaldetti, Oscar A. Alcober, Carina E.
Colombi, Paul C. Sereno, Eliana Fernandez, Paula Santi Malnis, Gustavo
A. Correa & Diego Abelin (2013)
Vertebrate succession in the Ischigualasto Formation.
Basal sauropodomorphs and the vertebrate fossil record of the
Ischigualasto Formation (Late Triassic: Carnian-Norian) of Argentina.
Journal of Vertebrate Paleontology Memoir 12:  10-30
DOI:10.1080/02724634.2013.818546
http://www.tandfonline.com/doi/abs/10.1080/02724634.2013.818546#.UlTA_FB6YYE


The Upper Triassic (Carnian–Norian) Ischigualasto Formation has
yielded a diverse vertebrate fauna that records the initial phase of
dinosaur evolution. Radioisotopic dates from ash layers within the
formation provide a chrono- stratigraphic framework, and stratigraphic
and sedimetological studies have subdivided the formation into four
members and three abundance-based biozones. We describe two new basal
dinosauromorphs, an unnamed lagerpetid and a new silesaurid,
Ignotosaurus fragilis, gen. et sp. nov., which increase to 29 the
number of vertebrates in the Ischigualasto fauna. We provide a census
of 848 fossil specimens representing 26 vertebrate taxa logged to
stratigraphic intervals of 50 m. This temporally calibrated census
shows that abundance and taxonomic diversity within the Ischigualasto
Formation does not change suddenly but rather appears to gradually
decline in response to climatic deterioration. The only abrupt shift
in faunal composition occurs at the end of the second of three
biozones, when the abundant cynodont Exaeretodon is replaced by the
rare dicynodont Jachaleria.