The discovery in Spain of a 125-million-year-old fossil of a previously unknown extinct mammal with exceptionally well-preserved skin and fur is reported in a paper published in this week’s Nature. The creature was similar in size to some smaller species of opossum and was a member of a group of early mammals called triconodonts. The find pushes back the earliest record of mammalian soft-tissue preservation by over 60 million years.
The small mammal from Las Hoyas, Spain, is described by Thomas Martin and colleagues, who name it Spinolestes xenarthrosus, from the Latin word spinosus (spiny) and the Latin lestes (translated from the Greek word meaning robber). The fossil comprises a complete skeleton, with typical mammal-like features such as long hairs, underfur, an external ear, and a variety of skin structures including tiny spines, about a tenth of a millimetre in diameter, on its back that are similar to those of hedgehogs and other present-day mammals. In addition, fossilized soft tissues in the thorax and abdomen make up what the authors believe to be a muscular diaphragm. Such delicate skin structures, fur and soft tissues of mammals have tended to be poorly preserved in the fossil record prior to about 60 million years ago.
This fossil find shows that mammalian underfur, long hairs, and spines had already developed around 125 million years ago, early in the evolutionary history of mammals.
Universität Bonn, Bonn, Germany
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