Thursday, October 15, 2015

[PaleoMammalogy • 2015] Spinolestes xenarthrosus • A Cretaceous Eutriconodont and Integument Evolution in Early Mammals

Spinolestes xenarthrosus 
Martin, Marugán-Lobón, Vullo, Martín-Abad, Luo & Buscalioni, 2015
doi: 10.1038/nature14905   
life reconstruction in its natural environment of the Las Hoyas wetland. 
Illustration: Oscar Sanisidro

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.

Class Mammalia 
Order Eutriconodonta 

Family Gobiconodontidae 

Spinolestes xenarthrosus gen. et sp. nov.

Etymology. Spinosus (Latin), in reference to the spiny integument; λέστης (Greek) or lestes (Latin spelling), meaning robber and a common term in taxonomic names of mammals. The specific name xenarthrosus refers to the special additional (ξένος, (Greek) strange) articulation facets (ἄρϑρον, (Greek) articulation) of the dorsal vertebrae.

Locality and horizon. Las Hoyas Quarry, Calizas de la Huérgina Formation, southwestern Iberian Basin (Cuenca, Spain). Las Hoyas is latest Barremian (125–127 Ma) in age, on the basis of charophytes and ostracodes17. The Las Hoyas Konservat-Lagerstätte occurs in finely laminated limestones deriving from a freshwater wetland. Fossils are usually preserved fully articulated, including soft tissues such as mineralized muscle and skin. Potential mechanisms for exquisite preservation are microbial mats, anoxia, and rapid burial by sediments18.

Thomas Martin, Jesús Marugán-Lobón, Romain Vullo, Hugo Martín-Abad, Zhe-Xi Luo and Angela D. Buscalioni. 2015. A Cretaceous Eutriconodont and Integument Evolution in Early Mammals.  
Nature. 526, 380–384. doi: 10.1038/nature14905 

125-million-year-old mammal fossil preserved with hair, spines and even a fungal infection via @ScienceLife