Horned armadillos and rafting monkeys

A giant caiman (Purussaurus neivensis) and small
litopterns (Megadolodus molariformis)
Illustration Velizar Simeonovski (C) 2016 by Darin A. Croft

I thoroughly recommend this new book on South American fossil mammals of the Caenozoic Era. Intended for a broad readership, it is a times fanciful. The full caption to the above figure reads, "A giant caiman (Purussaurus neivensis) finally strikes in a fury of mud and water after quietly approaching a group of small litopterns (Megadolodus molariformis) drinking at the river."

Indiana University Press ISBN 978-0-253-02084-0

The book is dedicated "to anyone who has ever wondered what a notoungulate looked like," which makes me the target audience. I read extensively about the fossil fauna when writing about the placentation of the extant species (here). The extinct families that lived side by side with marsupials and earlier xenarthrans were so unfamiliar as to seem wraith-like.

The xenungulate Carodnia vieirai from Itaboraí
Illustration Velizar Simeonovski (C) 2016 by Darin A. Croft

Darin A. Croft has worked closely with Velizar Simeonovski to bring extinct taxa to life. "The xenungulate Carodnia vieirai passes under the shadows of the dense vegetation of Itaboraí at high noon" is another example. This is the same artist who illustrated Extinct Madagascar (previous post).

After some introductory chapters the subject matter is arranged according to 15 fossiliferous localities. Conspicuously absent is Lagoa Santa in Brazil where the Danish palaeontologist P. W. Lund worked in the Nineteenth Century (here). His extensive Collection is housed at the Natural History Museum of Copenhagen University.

South American fossil ungulates are related to modern horses

Macrauchenia - an extinct South American native ungulate
Drawn by Kobrina Olga (Wikimedia Commons CC BY 3.0)

South American mammals either arrived recently during the Great American Interchange, came to South America by rafting (previous post), or have a shallow fossil record (xenarthrans). In contrast, South American native ungulates (SANU) have a deep fossil record. Though the lineage is now extinct, genera such as Macrauchenia (above) and Toxodon survived into the Late Quaternary. The conditions under which these fossils were conserved did not favour survival of their DNA. However, a paper just out in Nature (here) shows how proteomics can be used to probe their phylogenetic affinities.

The authors used MALDI-TOF mass spectrometry to determine the amino acid sequences of the alpha chains of type I collagen extracted from fossil bones. They then performed a phylogenetic analysis. This showed that Macrauchenia and Toxodon form a monophyletic group. Interestingly, this resolved as the sister group to modern Perissodactyla, i.e. horses, tapirs and rhinoceroses. Together they form a taxon named Panperissodactyla.

The modern species have an epitheliochorial placenta so perhaps this type was present in the sister species Macrauchenia  and Toxodon.