First Digital Cranial Endocasts of late Oligocene Notohippidae (Notoungulata): Implications for Endemic South American Ungulates Brain Evolution

Abstract

Notohippidae were middle-sized toxodonts recorded from the Eocene to the early Miocene. We provide the first description of the cranial endocasts of Rhynchippus equinus and Eurygenium latirostris based on three-dimensional reconstructions extracted from high-resolution X-ray computed tomography imagery. The endocasts of R. equinus and E. latirostris indicate that they were similar in size, proportions of the encephalic components, and neocortical design. The endocranial morphology of these notohippids is very close to that of toxodontids Adinotherium and Nesodon and differs markedly from both other Toxodontia and Typotheria. Notohippids, together with toxodontids, show the most complex neocortical surface among notoungulates. On the other hand, the neuromorphology of notohippids is in contrast to the neocortical morphological pattern described for Tertiary euungulates (Perissodactyla and Artiodactyla) from the Northern Hemisphere and litoptern Protetotheriidae, South American native euungulates. The relative brain size of R. equinus and E. latirostris compared with coeval holarctic euungulates from the late Oligocene are significantly below Perissodactyla and near the values obtained for Artiodactyla. Regarding the location of some functional neocortical areas, the expansion of the frontal lobe in Notohippidae may reflect the acquisition of heightened tactile sensitivity in the front of the snout, as recorded in the somatic sensory cortex of living euungulates. The bulging temporal lobe may reflect expansion of the auditory cortex, likely related to the marked enlargement of the middle ear chamber. Both neuromorphological and quantitative data suggest that during the late Paleogene, notohippids developed as complex and encephalized brains as those of the coeval Artiodactyla of northern continents.

Virtual endocast of the early Oligocene Cedromus wilsoni (Cedromurinae) and brain evolution in squirrels

“…; Ramdarshan & Orliac, ; Bertrand & Silcox, ; Bertrand et al. ; Dozo & Martínez, ). The equations produced by Jerison () and Eisenberg () will be used to compare the EQ of our specimens with those calculated for members of other mammalian orders.…”

“…This equation has a substantively lower slope but a slightly higher intercept compared with the equation of Eisenberg (1981). In spite of these issues, it remains standard practice to report EQs based on both Jerison's and Eisenberg's equations to allow for comparison to other publications (Macrini et al 2007;Silcox et al 2009Silcox et al , 2010Silcox et al , 2011Orliac et al 2014;Ramdarshan & Orliac, 2015;Dozo & Mart ınez, 2016). The equations produced by Jerison (1973) and Eisenberg (1981) will be used to compare the EQ of our specimens with those calculated for members of other mammalian orders.…”

Endocranial shape variation in the squirrel‐related clade and their fossil relatives using 3D geometric morphometrics: contributions of locomotion and phylogeny to brain shape

“…Endocasts are the imprint of the brain against the inner part of the cranium and are the best proxy for investigating brain shape and size in fossil mammals because brain tissues are not preserved in the fossil record (e.g., Edinger, ; Jerison, ). With increased access to Micro‐CT scanners, it is now possible to create endocasts virtually, expanding considerably the range of specimens from which endocasts can be acquired, and leading to new insights into how the brain of modern groups evolved (e.g., Silcox, Benham & Bloch, ; Orliac & Gilissen, ; Dozo & Martínez, ; Harrington et al ., ; Bertrand et al ., ).…”

Virtual brain endocast of Antifer (Mammalia: Cervidae), an extinct large cervid from South America

“…Geomagic Editor was used to delimit the areas and volumes of the endocast in order to make the percentage calculations. Additionally, we provided linear measurements and ratios (taken according Dozo & Martínez, 2015 and Bertrand & Silcox, 2016; supporting information 1, Table S4).…”

“…With the advance of technologies for visualizing and analyzing fossils using computed tomography (CT) and rendering software, it is now possible to noninvasively analyze the internal cavities of the skull of extinct species (Cunningham, Rahman, Lautenschlager, Rayfield, & Donoghue, 2014; Das, Murmann, Cohrn, & Raskar, 2017). The use of these approaches has increased the knowledge on the paleoneurology of extinct species significantly through anatomical reconstructions (Bertrand, Amador‐Mughal, & Silcox, 2016; Orliac & Gilissen, 2012; Pierce, Williams, & Benson, 2017) and morphometric studies (Ahrens, 2014; Bertrand, San Martin‐Flores, & Silcox, 2019; Iurino et al, 2015), as well as general interpretations of patterns and modes of neurological diversification through time (Rowe, 1996; Marino, Uhen, Pyenson, & Frohlich, 2003; Bloch & Silcox, 2006; Tseng & Wang, 2010; Rowe, Macrini, & Luo, 2011; Orliac & Gilissen, 2012; Koyabu et al, 2014, Dozo & Martínez, 2015; Fernández‐Monescillo et al, 2017; Bertrand, Amador‐Mughal, Lang, & Silcox, 2018; Rodrigues et al, 2018, among several others). However, data on the neuroanatomy and encephalization of extinct cervids are still quite scarce (Czyzewska, 1982; Palombo, Kohler, Moyà‐Solà, & Giovinazzo, 2008), which is especially true for the South American forms.…”