DOI: 10.5061/dryad.gtht76hqp
title: Data from: Cranial endocast of Anagale gobiensis (Anagalidae) and its implications for early brain evolution in Euarchontoglires

description: Anagalids are an extinct group of primitive mammals from the Asian
 Palaeogene thought to be possible basal members of Glires. Anagalid
 material is rare, with only a handful of crania known. Here we describe
 the first virtual endocast of an anagalid, based on the holotype of
 Anagale gobiensis (AMNH 26079; late Eocene, China), which allows for
 comparison with published endocasts from fossil members of modern
 euarchontogliran lineages (i.e. primates, rodents, lagomorphs). The
 endocast displays traits often observed in fossorial mammals, such as
 relatively small petrosal lobules and a low neocortical ratio, which would
 be consistent with previous inferences about use of subterranean food
 sources based on heavy dental wear. In fact, Anagale gobiensis has the
 lowest neocortical ratio yet recorded for a euarchontogliran. This species
 was olfaction-driven, based on the relatively large olfactory bulbs and
 laterally expansive palaeocortex. The endocast supports previous
 inferences that relatively large olfactory bulbs, partial midbrain
 exposure and low encephalization quotient are ancestral for
 Euarchontoglires, although the likely fossorial adaptations of Anagale
 gobiensis may also partly explain these traits. While Anagale gobiensis is
 a primitive mammal in many aspects, some of its derived endocranial traits
 point towards a new, different trajectory of brain evolution within
 Euarchontoglires.
description: The endocast of <em>Anagale gobiensis</em> was
 generated from CT scan data of AMNH 26079. The endocast of <em>Anagale
 gobiensis</em> (Fig. 3) is compared to the sample of previously
 published endocasts pertaining to early members of Euarchontoglires. In
 particular, the comparative sample includes early Glires, that is,
 “ischyromyids” (<em>Paramys, Pseudotomus, Reithroparamys,
 Rapamys</em>, and <em>Ischyromys</em>; Bertrand
 & Silcox, 2016; Bertrand et al., 2016a, 2019), fossil sciuroids
 (Bertrand et al., 2017, 2018), <em>Rhombomylus</em> (Meng et
 al., 2003) and a stem lagomorph (López-Torres et al., 2020); Primates,
 including “plesiadapiforms” (Silcox et al., 2009, 2010a; Orliac et al.,
 2014) and early Tertiary fossil euprimates (Kirk et al., 2014; Harrington
 et al., 2016, 2020; Ramdarshan and Orliac, 2016); and the most primitive
 apatemyid known from endocranial data (<em>Labidolemur
 kayi</em>; Silcox et al., 2011). A sample of extant rodents
 (Bertrand & Silcox, 2016; Bertrand et al., 2017, 2018, 2019) and
 extant lagomorphs (López-Torres et al., 2020) were used to provide context
 to the fossil data in the quantitative analyses. 
 Surface area, length and
 volumetric measurements were taken on the endocasts to calculate several
 ratios using Avizo 9.0.1 (Table 1). The volume of the endocast of
 <em>Anagale gobiensis</em> was obtained by isolating the more
 complete half of the endocast using the ‘volume edit’ module and doubling
 its volume. The volume of the olfactory bulbs was obtained by isolating
 the two olfactory bulbs, also using volume edit. The petrosal lobules were
 re-segmented in the transverse plane (XZ dimension) using a distinct
 labelfield module and the volume measured from the resulting
 reconstruction.  To
 obtain the neocortical surface area, the area above the rhinal fissure was
 selected, whereas the circular fissure and the confluence of sinuses were
 excluded. We followed Jerison (2012) and Long et al. (2015), who measured
 only one side of the neocortex (the more complete hemisphere), excluding
 the superior sagittal sinus, and then doubled the area of the
 hemisphere.  For comparative purposes, we calculated the
 encephalization quotient (EQ) using equations from Jerison (1973) and
 Eisenberg (1981). For the calculation of EQs, it is important to have an
 accurate estimation of the body mass of the animal in question.
  We consider the best
 estimate for a range of body masses for AMNH 26079 to be 1122.77—1464.68
 g.  We
 generated a series of bivariate plots as well as boxplots based on the
 data in Table 1, combined with values collected from the literature
 (endocranial volume and surface area, olfactory bulb volume, petrosal
 lobule volume, neocortical surface areas; Gingerich & Gunnell,
 2005; Silcox et al., 2009, 2010a, 2011; Kirk et al., 2014; Orliac et al.,
 2014; Harrington et al., 2016, 2020; Ramdarshan & Orliac, 2016;
 Bertrand et al., 2019, 2021; López-Torres et al., 2020; see data in Table 1 and in López-Torres et
 al., 2022, tables S1-S4) using the software PAST (Hammer et al.,
 2001). 
description: All files are submitted in .xlsx format, and are readable by
 Excel.