Macrochelys temminckii (Troost, 1835)

Paulina-Carabajal, Ariana, Sterli, Juliana, Georgi, Justin, Poropat, Stephen F & Kear, Benjamin P, 2017, Comparative neuroanatomy of extinct horned turtles (Meiolaniidae) and extant terrestrial turtles (Testudinidae), with comments on the palaeobiological implications of selected endocranial features, Zoological Journal of the Linnean Society 180 (4), pp. 930-950 : 930-931

drid Macrochelys temminckii (Troost, 1835) ( Edinger,

1934) and the pelomedusoid Erymnochelys madagascariensis (Grandidier, 1867) ( Gaffney & Zangerl, 1968; see Paulina-Carabajal et al., 2013: fig. 7A for comparisons). Furthermore, although turtles are a group whose fossil record extends from the Late Triassic to the Holocene, few descriptions of endocranial morphology (including both the empty space occupied by the brain or the cast) have been published for extinct taxa (e.g. Zangerl, 1960; Gaffney & Zangerl, 1968; Gaffney, 1977, 1982; Paulina-Carabajal et al., 2013; Deantoni, 2015). Examples incorporate the chelonioid Corsochelys haliniches Zangerl, 1960 , from the Late Cretaceous of Alabama, the bothremydids Bothremys cooki Leidy, 1865 and B. barberi ( Schmidt, 1940) from the Late Cretaceous of North America ( Gaffney & Zangerl, 1968; Gaffney, 1977), the Late Cretaceous baenid Plesiobaena antiqua Lambe, 1902 from Canada ( Gaffney, 1982) and the pancryptodiran Plesiochelys etalloni ( Pictet & Humbert, 1857) from the Upper Jurassic lithographic limestones of Western Europe ( Joyce, 2007; Paulina-Carabajal et al., 2013). Inner ear osteology has also been reconstructed three-dimensionally in the extant pleurodiran chelid Chelus fimbriatus ( Schneider, 1783) , the chelydrids Macrochelys temminckii and Chelydra serpentina (Linnaeus, 1758) and carettochelyid Carettochelys insculpta Ramsay, 1886 ( Georgi, 2008; Thewissen & Nummela, 2008; Walsh et al., 2009). Among testudinoids, the inner ear morphology of Chelonoidis chilensis ( Gray, 1870) , C. nigra (Quoy & Gaimard, 1824) , Terrapene carolina (Linnaeus, 1758) and Trachemys scripta (Schoepff, 1792) has been studied or illustrated (e.g. Georgi, 2008; Thewissen & Nummela, 2008; Walsh et al., 2009). Finally, for extinct turtles only the inner ear of the Jurassic P. etalloni has been documented ( Paulina-Carabajal et al., 2013).

Because so few studies have been conducted, our understanding of turtle palaeoneurology remains poor. In this work, we present the first CT generated digital 3D reconstructions and accompanying detailed descriptions of the nasal cavity, cranial endocast, inner ear and internal carotid passage of three meiolaniids and six extant testudinoid species assessed as comparative analogues for these extinct terrestrial turtles; these contrasting model lineages encapsulate a substantial degree of temporal and phylogenetic variation.

The clade Meiolaniidae was a peculiar group of large, fully terrestrial turtles with cranial horns, frills and armoured tails terminating in a club that lived in South America and Australasia between the Middle Eocene and Holocene ( Gaffney, 1996; Sterli, de la Fuente & Krause, 2015; Poropat et al., 2016). Those taxa with the bestpreserved cranial remains were selected for our analysis: the Australian Meiolania platyceps Owen, 1886 and Patagonian Niolamia argentina Ameghino, 1899 and Gaffneylania auricularis Sterli et al., 2015 . Meiolania platyceps is the most skeletally complete meiolaniid taxon, with hundreds of specimens recovered from the Pleistocene of Lord Howe Island, Australia. Anderson (1925) and Gaffney (1983, 1985, 1996) described its osteology in detail, but only a few aspects of its endocranial morphology were mentioned or illustrated ( Gaffney, 1983, 1996). The meiolaniid record from South America is restricted to the Palaeogene of Patagonia, Argentina, with two species: N. argentina documented by Smith Woodward (1901) and recently re-described by Sterli & de la Fuente (2011), and G. auricularis , which represents the most complete meiolaniid reported from South America thus far ( Sterli et al., 2015).

As northern hemisphere ecological analogues, testudinids were chosen for comparison with the aforementioned meiolaniid taxa because they are also terrestrial turtles. Testudinidae today have a near-global distribution (excluding Antarctica and Australia), and a fossil record extending back to the Paleocene ( Hay, 1908; Auffenberg, 1964; Crumly, 1984 and references therein; Tong et al., 2016). In this work, we include five living species for examination: Gopherus berlandieri , Testudo hermanni , Testudo graeca , Kinixys belliana and C. chilensis (see Table 1).

Institutional Abbreviations: AM F, Australia Museum, Fossil collection, Sydney, Australia; AMNH, American Museum of Natural History , New York, USA ; MPEF, Museo Egidio Feruglio, Trelew, Argentina ; MLP, Museo de La Plata , La Plata, Argentina ; MMF, Geological Survey of New South Wales (specimen formerly registered as a Mining Museum Fossil), Sydney, Australia ; RAM, Raymond M. Alf Museum of Palaeontology , Claremont, USA ; YPM, Yale Peabody Museum of Natural History , New Haven, USA .