PALEONEUROLOGY OF LITOPTERNA: DIGITAL AND NATURAL ENDOCRANIAL CASTS OF MACRAUCHENIIDAE

DOZO, MARÍA TERESA; MARTÍNEZ, GASTÓN; GELFO, JAVIER

Paleoneurology of Amniotes: New Directions in the Study of Fossil Endocasts

Springer

Año: 2023; p. 809 - 836

The Litopterna Ameghino 1889, is the second largest group of South American native ungulates in abundance and diversity after Notoungulata. The study of digital endocasts of Cramauchenia normalis, Theosodon cf. T. gracilis, and Macrauchenia patachonica provide an interesting perspective to understand litoptern brain evolution within the Macraucheniidae. The neuromorphology with the Sylvian region slightly developed, presents some differences when compared to Proterotheriidae. Also, the three-dimensional reconstructions show different morphologies of the frontal sinuses between Cramauchenia normalis, Theosodon cf. T. gracilis, and Macrauchenia patachonica. Differences are mainly attributed to the retraction of the nasal aperture and the relocation of the nasal bones, particularly in Macrauchenia and, to a lesser degree, in Theosodon. Regarding the relative brain size, the EQ obtained for the Oligocene Cramauchenia normalis are higher than those of the coeval notoungulates “notohippids” Rhynchippus equinus, Eurygenium latirostris, Mendozahippus fierensis, and the leontinid Gualta cuyana. When compared to similar-sized Holarctic ungulates from the late Oligocene, the EQ of Cramauchenia normalis is below that of the perissodactyl Mesohippus and around the values obtained for the artiodactyl Poebrotherium. Finally, a concretion recovered from the Deseadan SALMA (late Oligocene) was interpreted as the first natural braincast assigned to a litoptern (potentially referable to Macraucheniidae).