An international team of paleontologists has identified two new species of ancient mammals that lived about 13 million years ago (middle Miocene epoch) in what is now Bolivia.
The two newly-discovered Miocene species, named Theosodon arozquetai and Llullataruca shockeyi, belong to the Macraucheniidae family, a group of hoofed mammals (ungulates) in the extinct South American ungulate order Litopterna.
Well-preserved fossil material — including a partial skull, a nearly complete jaw, and a variety of bones — of the animals was recovered from several areas of outcrops of the Honda Group in western Tarija Department, southern Bolivia, that are collectively referred to as Quebrada Honda.
Both Theosodon arozquetai and Llullataruca shockeyi looked similar to small moose or deer.
The body mass of Theosodon arozquetai is estimated at 80-116 kg. Llullataruca shockeyi is among the smallest known macraucheniids and is estimated at 35–55 kg.
The discoveries, described in a paper published online May 30 in the Journal of Vertebrate Paleontology, are important because they come from the tropical latitudes of South America.
“These new species hint at what might be hiding in the northern parts of South America,” said Andrew McGrath, a Ph.D. student at the University of California-Santa Barbara.
“For example, close relatives of Llullataruca shockeyi disappeared from southern South America around 20 million years ago, but based on our research, we now know they were able to persist 7 million years longer in Bolivia and northern South America than in Patagonia.”
“Studying fossils from regions such as Bolivia, where few others have looked, has allowed us discover and describe a variety of new species that are changing our views about the history of South America’s mammals,” said Case Western Reserve University’s Professor Darin Croft.
Since South America was geographically isolated for most of the past 66 million years, its rich fossil record makes it a perfect location to investigate topics such as mammal adaptation, diversification, and community ecology.
“South America was untouched by mammals from other continents for millions of years, so the solutions its native mammals came up with were often different from those developed by mammals elsewhere,” Professor Croft said.
“By comparing how mammals on different continents have evolved to deal with similar ecological situations, we are able to gauge which characteristics developed due to universal ecological principles and which were peculiar to a certain place and time.”
Andrew J. McGrath et al. Two new macraucheniids (Mammalia: Litopterna) from the late middle Miocene (Laventan South American Land Mammal Age) of Quebrada Honda, Bolivia. Journal of Vertebrate Paleontology, published online May 30, 2018; doi: 10.1080/02724634.2018.1461632