About 180 million years ago, the ancient supercontinent of Gondwana began to slowly disintegrate, a process that would lead to the individual formations of modern continents and regions in the southern hemisphere. This fractionation would lead to a unique evolution of the ancestors of modern mammals.
Now an international team of researchers, led by David Krause, a senior paleontologist at the Denver Museum of Nature and Science and a professor at Stony Brook U., have discovered the “mad beast .” Adalatherium hui, named for the Malagasy meaning of “madman” and the Greek word for “beast”, represents the most complete skeleton of an ancient animal that lived in Gondwana.
It is the unique location of this specimen that probably led to its peculiar evolution. A. hui was only known from a set of jaws, teeth, and an individual skull, so its life history, biology, anatomy, and phylogenetic relationships were poorly understood.
“This skeleton reveals a series of unusual and even unique adaptations that, according to our hypothesis, are due to evolution in an insular environment ,” write the authors of the study in the journal Nature, adding that it also had a large number of vertebrae on the trunk, a small, broad tail, and it is so well preserved that the researchers were even able to detect cartilaginous tissue.
“Among mammals, the most obvious and quantifiable influences on island evolution are those related to body size. This observation has led to the articulation of the ‘island rule’, which establishes that, evolutionarily, small mammals on islands increase and large mammals decrease in size ”, the authors point out, adding that the island rule it is somewhat controversial and “clearly not ubiquitous.”
Referencia: “Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity” by David W. Krause, Simone Hoffmann, Yaoming Hu, John R. Wible, Guillermo W. Rougier, E. Christopher Kirk, Joseph R. Groenke, Raymond R. Rogers, James B. Rossie, Julia A. Schultz, Alistair R. Evans, Wighart von Koenigswald and Lydia J. Rahantarisoa, 29 April 2020, Nature. DOI: 10.1038/s41586-020-2234-8
