Heritage Cases

The supercontinent Pangaea formed during the Carboniferous (359-299 mya) and broke up at the end of the Triassic (about 199 mya). Due to this and other factors, the climate of the Permian (299-252 mya) was significantly different from that of today (Schneider, 2018). At the start of the Permian, the carbon dioxide concentration, temperature range and polar ice caps were like present-day Earth (Schneider, 2018). However, the climate changed considerably during the 48-million-year course of the Permian. The Permian Period represents dramatic seasons and strong monsoonal circulation (Schnieder, 2018). As there was one large landmass the continental interior was extremely dry and hot and large deserts formed (Schnieder, 2018). This was contrasted by very cold conditions in the higher latitudes in the south (Schnieder, 2018). In this climate, the dominant life forms were therapsids, a clade of mammal-line synapsids that diversified during the Early Permian (Kemp, 2016). Therapsids first appeared in temperate palaeolatitudes of the middle Permian, suggesting that some degree of temperature and osmotic regulatory strategies had already evolved (Kemp, 2006a and b). Most of the ‘pelycosaurs’, a paraphyletic clade of basal stem-synapsids, went extinct around this time as well, leaving open niches for therapsids were able to capitalise on (Kemp, 2012). This caused a shift in the composition of the tetrapod communities. During the Late Carboniferous to the Early Permian the terrestrial communities were comprised of a relatively higher proportion of carnivores to herbivores. Kemp (2006b) and others (e.g. Olson, 1986) attributed this to the ecosystem still relying heavily on freshwater productivity. However, the therapsid communities that followed saw a shift to a higher proportion of herbivores in the ecosystems (Nicolas and Rubidge, 2009). The almost complete dependency on terrestrial plants as primary producers and herbivorous tetrapods as the primary consumers, which is what our modern community structure is based on, was seen for the first time (Kemp, 2012). The end-Guadalupian extinction event saw the disappearance of several therapsid lineages including dinocephalians, and lycosuchid and scylacosaurid therocephalians (Huttenlocker and Smith, 2017). How ever, dicynodonts had no supra-generic losses (Huttenlocker and Smith, 2017). The loss of large bodiedinocephalians is attributed to the appearance of large gorgonopsians and dicynodonts in the following Lopingian Epoch (Day et al., 2015). No study has investigated the bone microanatomy pattern of a large sample of Anomodontia. The present study seeks to elucidate the different bone microanatomies of 18 different taxa spanning the entire clade. The aim of the study is to assess, in terms of lifestyle, phylogeny, and body mass, the bone microanatomy of anomodont therapsids. The present study seeks to find an ecological signal within the bone microanatomy of the Anomodontia. The objectives of the study are to (1) quantitatively describe the patterns in the bone microanatomy of South African anomodonts, (2) investigate possible reasons for the differences and/or similarities in the microanatomy. Materials and Methods Study taxa The taxa chosen for the present study represent a vast array of both stratigraphic range and taxonomic range, from the non-dicynodont anomodont, Galeops, to highly derived dicynodonts. The study effectively spans 22 mya (from 259 to 237 mya) of the 60 million years the clade existed for (Angielczyk and Kammerer, 2018). Figure 2 shows the cladogram of the taxa used in the study. Table 1 is a list of the taxa and their elements that will be used in the study with the corresponding accession numbers. Methods In order to study the bone microanatomy of a specimen, a transverse section needs to be produced. Preferably the sections are taken at the midshaft as it undergoes the least secondary remodelling and therefore provides the most complete record of the animal’s growth (Chinsamy, 1990; Francillon-Vieillot et al., 1990). Many of the specimens for the present study are from the National Museum, Bloemfontein and Iziko South African Museum of Cape Town and thin sections have already been produced. It is preferable that new thin sections of Daptocephalus, Endothiodon and Kannemeyeria be made for this study. These specimens will be sourced from the Iziko South African Museum of Cape Town and the Evolutionary Studies Institute, University of the Witwatersrand in Johannesburg. The thin sectioning process will follow that of Chinsamy and Raath (1992) with modifications outlined here. After photographs and measurements have been taken the specimens will be placed under a vacuum and embedded in Struers EpoFix resin. Embedded samples are then transversely thin-sectioned in the Struers Accutom-100 cutting and grinding machine into 2 mm thick sections. Thin sections are glued to plastic slides using Struers EpoFix resin. The Struers Accutom100 then grinds the samples to a thickness of approximately 100 µm. Renders, where photographs of the entire bone cross section are stitched together, will be made using the software NIS Elements 4.5 (Nikon Corp.) connected to a DS-Fi3 camera mounted on a Nikon Eclipse Ci-POL microscope. The renders will be transformed into binary images in Photoshop CC 2019 (Adobe Systems). This is done using a Wacom Intuos Art graphics tablet, where bone is black and the cavities are white. The level of the compactness can then be determined using Bone Profiler for Windows. The Min, Max, S, and P values are used to estimate a lifestyle reading for the humerus (Canoville and Laurin, 2010), radius (Laurin et al. 2011), and tibia (Kriloff et al., 2008). The lifestyle reading of the ulna and fibula will not be produced as there is currently no formula available for it. The femur (Quemeneur et al., 2013) will not be possible in the current study as Rmin (value of the lower asymptote based on the average of 60 profiles) and Ti (snout length) are unobtainable.