Volume-rendered CT-based reconstruction of the skull of the extinct turtle <i>Plesiochelysetalloni</i> (MH 435).

<p>In the images of the left side the bone is rendered opaque, whereas in the right side the bone is rendered semitransparent to show the endocranial cavity. The bone is shown in green, the cranial endocast and inner ear in light blue, the internal carotid arteries in pink, and the columella in fuchsia. Skull in left lateral (A) dorsal (B) and ventral (C) views. Abbreviations: col, columella auris; endo, cranial endocast; fpcci, foramen posterius canalis caroticus internus; fst, foramen staedio-temporale. Scale bar equals 10 mm.</p

Brain endocasts and left endosseous inner ears of turtles available in the literature displayed in a simplified cladogram (based on Joyce [25]).

<p>The black circle indicates a synapomorphy based clade definition while the white circle indicates a crown-group definition following Joyce et al. [54]. A, Brain endocasts comparison based on line drawings of extinct and extant turtles in right lateral view represented by (left to right) (1) <i>Bothremys cooki</i> (redrawn from [17]), (2) <i>Podocnemis unifilis</i> (after [33]), Chelidae <i>Emydura macquarii</i> (after [33]), Baenidae <i>Plesiobaena antiqua</i> (redrawn from [19]), <i>Plesiochelys etalloni</i> (this study), (3) <i>Corsochelys haliniches</i> (redrawn from [16]), (4) <i>Chelonia mydas</i>, (5) <i>Eretmochelys imbricata</i>, (6) <i>Caretta caretta</i>, (7) <i>Lepidochelys kempi</i>, (8) <i>Dermochelys coriacea</i> (after [23]), Chelydridae <i>Macrochelys temminckii</i> (after [33]), Emydidae <i>Pseudemys concinna</i> (after [33]), Testudinidae <i>Chelonoidis chilensis</i> (this study), Kinosternidae <i>Sternotherus odoratus</i> (after [33]), and Trionychia <i>Apalone ferox</i> (after [33]). Dashed line indicates the shape of the nasal cavity. Dotted line in <i>Plesiochelys etalloni</i> indicates reconstructed area of the endocast. Dark gray, extinct species. Light gray, extant species. Not to scale. B, Inner ear endocasts were redrawn from the following sources: <i>Plesiochelys etalloni</i> from this study and Chelydridae, Emydidae, Testudinidae, and Trionychia from Thewissen and Nummela [20] (Fig. 15.11 K-N). Chelydridae is represented by <i>Macrochelys temminckii</i>; Emydidae is represented by <i>Trachemys scripta</i>; Testudinidae is represented by <i>Chelonoidis nigra</i>; Trionychia is represented by <i>Carettochelys insculpta</i>. <i>Proganochelys quenstedti</i>, Meiolaniformes, and <i>Plesiochelys etalloni</i> are extinct taxa. Not to scale.</p

Detail of posterior region of the CT-based reconstructions of the cranial endocast and inner ear of <i>Plesiochelysetalloni</i> (MH 435) showing cranial nerves VII and VIII.

<p>The image shows the cranial endocast in light blue and the inner ear in light violet. Abbreviations: ccv, canalis cavernosus; lab, endosseous labyrinth; med, medulla oblongata; V–VIII, cranial nerves. Scale bar equals 10 mm.</p

Digital reconstruction of the skull of <i>Plesiochelysetalloni</i> (MH 435) in lateroposteroventral view.

<p>Detail of the posterior part of the middle ear showing the foramen for cranial nerve IX. The image shows the bone in green and the columella in fuchsia. Abbreviations: cavum acustico-jugulare; col. f, columellar foot; ct, cavum tympani; endo, endocranial cavity; fpcci, foramen posterius canalis caroticus internus; op, opisthotic; pal, palatine; pbs, parabasisphenoid complex; pt, pterygoid; sq, squamosal; IX, cranial nerve. Scale bar equals 10 mm.</p

Detail of posterior region of the CT-based reconstructions of the cranial endocast of <i>Plesiochelysetalloni</i> (MH 435) in left anteroventral view.

<p>The figure shows the cranial endocast in light blue, the columella in fuchsia, the internal carotid arteries in pink, the CN VI in yellow, and the cavum acustico-jugulare and the canalis stapedio-temporalis (rendered semitransparent to show the <i>Columella</i>) in purple. Abbreviations: ca, cerebral artery; ccv, canalis cavernosus; col, columella auris; ic, internal carotid; pa, palatine artery; pit, pituitary fossa; sa, stapedial artery; V–VIII, cranial nerves. Scale bar equals 10 mm.</p