Therapsida

Therapsida 2018-05-29T10:59:05+00:00

Synapsid is a lineage that evolved separated form the remaining amniotes since the Carboniferous, around 300 millions years ago, and that have mammals as the only living representative. The fossil transition documenting the origin of mammals is richly illustrated by fossils recording important morphological changes occurring during 100 millions of years. The most representative place to study the forerunners of mammals is South Africa, where fossil lineages of synapsids are represented from 270 to 190 millions years ago.

Two major groups are traditionally recognized in synapsids: a) the paraphyletic pelycosaurs, which are especially documented in faunas from the northern hemisphere (e.g. the United States) and only known by less than ten specimens in the South African Karoo; b) the monophyletic therapsids a group that includes living mammals and in which several important skeletal changes show the path of evolution that led to the origin of mammals. Four to five main therapsid lineages are represented which are generally considered in two groups  basal therapsids, including biarmosuchians, dinocephalians and anomodonts and advanced therapsids including gorgonopsians, therocephalians (probably a paraphyletic group) and cynodont ( a group that is monophyletic only when includes living mammals).

Most of my activity in the study of therapsids has been concentrated in non mammaliaform cynodonts: these are Permo-Jurassic fossils that include the taxon which is the closest relative to mammals. I study(ied) carnivorous and herbivorous species from the Triassic of Argentina where they are known in the breathtaking landscapes of the Moon Valley (Ischigualasto) and Talampaya in the western (Andean) provinces of San Juan and La Rioja. They are also represented in the also Andean Mendoza province. I also study(ied) non mammaliaform cynodonts from the southernmost state of Brazil: Rio Grande do Sul, which is the only other place in South America where they are represented.

Ventral view of the skull of the traversodontid cynodont Andescynodon mendozensis from the Middle Triassic of Argentina.
Paleontología de Vertebrados Lillo collection, Universidad Nacional de Tucumán, Argentina.

Palate of the traversodontid cynodont Exaeretodon riograndensis from the Late Triassic of Brazil. Note the wide postcanine teeth.
Paleontological collection of the Museu de Ciências e Tecnologia, Pontificia Universidade Católica do Rio Grande do Sul, Brazil.

I also work on mamal like cynodonts from southern Africa. Most of my research was concentrated in the Permo-Triassic Karoo Basin of South Africa, where I studied basal carnivorous forms and herbivorous/omnivorous gomphodonts. I also studied cynodont fossils from the Middle Triassic of Namibia. Topics of these work are mostly taxonomic, evolutionary, biostratigraphic, and most recently also ontogeny, including dental replacement.

Dorsal view of the skull of a juvenile of the cynodont Thrinaxodon liorhinus from the Lower Triassic of South Africa.
Material from the Iziko South African Museum.

Dorsal view of the skull of a juvenile of the cynodont Thrinaxodon liorhinus from the Lower Triassic of South Africa.
Material from the Iziko South African Museum.

Specimen from the collection of the Bernard Price Institute, University of the Witwatersrand, South Africa.
Ct-scan images from European Synchrotron Radiation Facility (Grenoble, France).