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Spinolestes, new Cretaceous eutriconodont mammal from Spain

Ben Creisler

A new paper in Nature:

Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad,
Zhe-Xi Luo & Angela D. Buscalioni (2015)
A Cretaceous eutriconodont and integument evolution in early mammals.
Nature 526, 380–384

The Mesozoic era (252–66 million years ago), known as the domain of
dinosaurs, witnessed a remarkable ecomorphological diversity of early
mammals. The key mammalian characteristics originated during this
period and were prerequisite for their evolutionary success after
extinction of the non-avian dinosaurs 66 million years ago. Many
ecomorphotypes familiar to modern mammal fauna evolved independently
early in mammalian evolutionary history. Here we report a
125-million-year-old eutriconodontan mammal from Spain with
extraordinary preservation of skin and pelage that extends the record
of key mammalian integumentary features into the Mesozoic era. The new
mammalian specimen exhibits such typical mammalian features as pelage,
mane, pinna, and a variety of skin structures: keratinous dermal
scutes, protospines composed of hair-like tubules, and compound
follicles with primary and secondary hairs. The skin structures of
this new Mesozoic mammal encompass the same combination of
integumentary features as those evolved independently in other crown
Mammalia, with similarly broad structural variations as in extant
mammals. Soft tissues in the thorax and abdomen (alveolar lungs and
liver) suggest the presence of a muscular diaphragm. The eutriconodont
has molariform tooth replacement, ossified Meckel’s cartilage of the
middle ear, and specialized xenarthrous articulations of posterior
dorsal vertebrae, convergent with extant xenarthran mammals, which
strengthened the vertebral column for locomotion.