Digital reconstruction of the left inner ear of <i>Pawpawsaurus campbelli</i> (FWMSH93B.00026).

<p>In dorsal (A), lateral (B), posterior (C), and anterior (D) views. Abbreviations: asc, anterior semicircular canal; cc, crus communis; fo, fenestra ovalis; lag, lagena; lsc, lateral semicircular canal; psc, posterior semicircular canal. Scale bar equals 10 mm.</p

Detail of the skulls of <i>Pawpawsaurus campbelli</i> (FWMSH93B.00026) (left) and the extant crocodile <i>Caiman</i> (right) in right lateral view.

<p>In the images at the top the bone is rendered solid (A,D), whereas in the images below, the bone is rendered semitransparent to show the nasal cavity and the neurovascular passages (B,E). In <i>Pawpawsaurus</i>, the lateral section of the orbital margins was sectioned parasagittaly to allow the observation of the anterior wall of the orbit. Nasal cavity and neurovascular passages rendered isolate (C,F). Abbreviations: dalv, dorsal alveolar canal (for maxillary branch of trigeminal nerve, and maxillary vein and artery); dalv.f, dorsal alveolar canal foramen in the anterior wall of the orbit; lac, lacrimal; mx, maxilla; nar, external nostrils; nas, nasal cavity; nlc, nasolacrimal canal; nlc.f, nasolacrimal canal/duct foramen; orb.r, orbital rim; pt, pterygoid. Not to scale.</p

Simplified line drawing of the right lateral side of the braincase of <i>Pawpawsaurus</i> (FWMSH93B.00026) showing the re-interpretation of the cranial nerves.

<p>Abbreviations: bo, basioccipital; bt, basal tuber; eo, exoccipital; fm, foramen magnum; fo, fenestra ovalis; ic, internal carotid artery; jv, jugular vein; ls, laterosphenoid; met, metotic foramen (for CN IX–XI); oc, occipital condyle; ocv, orbitocerebral vein; op, opisthotic; pop, paroccipital process; pro, prootic; q, quadrate; rmcv, rostral middle cerebral vein; so, supraoccipital; sph, sphenoid artery; II–XII, cranial nerves.</p

Volume-rendered CT-based reconstruction of the skull of the nodosaur dinosaur <i>Pawpawsaurus campbelli</i> (FWMSH93B.00026).

<p>In the images of the left side the bone is rendered semitransparent to show the endocranial cavity (in blue) and the nasal cavities (in light blue). Skull right lateral (A,B), right anterolateral (C,D) and ventral (E,F) views. Abbreviations: ch, choana; endo, cranial endocast; if, lateral temporal fenestra; nar, external nostrils; oc, occipital condyle; olf, olfactory region of the nasal cavity; orb, orbit; q, quadrate; th, teeth row; ves, vestibular region of the nasal cavity; 1, dorsal alveolar canal (for maxillary branch of trigeminal nerve, and maxillary vein and artery); 2, nasolacrimal canal (for nasolacrimal duct). Scale bar equals 5 cm.</p

Surface-rendered CT-based reconstruction of the cranial endocast and nasal cavities of <i>Pawpawsaurus campbelli</i> (FWMSH93B.00026).

<p>The posterior olfactory region of the nasal cavity is indicated in color magenta. The airflow pathway interpretation is indicated as black arrows in (C). In left lateral (A), dorsal (B) and lateroventral (C) views. Abbreviations: aw, airway; ca.lo, caudal loop?; dalv, dorsal alveolar canal (for maxillary branch of trigeminal nerve, and maxillary vein and artery); endo, endocranial cavity; nar, external nostril; nlc, nasolacrimal canal (for nasolacrimal duct); ob, olfactory bulbs; olf, olfactory region; ro.lo, rostral loop?; ves, vestibulum of the nasal cavity. Scale bar equals 10 mm.</p

A comparative study of eggshells of Gekkota with morphological, chemical compositional and crystallographic approaches and its evolutionary implications

<div><p>The Gekkota is an important clade in the evolution of calcified eggshells in that some of its families lay rigid eggshells like archosaurs. However, the fundamental differences and similarities between the mechanism of rigid eggshell formation of the Gekkota and Archosauria have not been investigated thoroughly due to the lack of knowledge of gekkotan eggshells. Here, we report for the first time a comprehensive analysis of morphological, chemical compositional, and crystallographic features of rigid and soft gekkotan eggshells. Exhaustive morphological description provided common characters for gekkotan eggshells, as well as unique features of each species. We found that elemental distribution of rigid gekkotan eggshells is different from that of avian eggshells, especially in the case of Mg and P. In addition, the crystallographic features (size, shape, and alignment of calcite grains) of gekkotan eggshells are completely different from those of archosaur eggshells. The result of this study suggests that soft gekkotan eggshells are morphologically more similar to tuatara eggshells rather than soft eggshells of derived squamates. The chemical compositional analysis suggests that the eggshell may act as a mineral reservoir for P and F as well as Ca. More importantly, all chemical compositions and crystallographic features imply that the gekkotan eggshell formation may begin at the outer surface and growing down to the inner surface, which is opposite to the direction of the archosaur eggshell formation. This character would be crucial for identifying fossil gekkotan eggs, which are poorly known in paleontology. All these lines of evidence support that soft gekkotan and tuatara eggshells share the primitive characters of all lepidosaurid eggshells. Finally, gekkotan and archosaur rigid eggshells represent a typical example of convergent evolution in the lineage of the Sauropsida.</p></div

Phylogenetic relationship of the Gekkota and related major clades in the Sauropsida modified from [3,9,10].

<p>The blue branches represent soft-shelled egg-layers while red branches rigid-shelled ones. The gekkotan genera used in this study are in parentheses.</p

Inverse pole figure (IPF) maps and lower hemisphere pole figures of gekkotan eggshells.

<p>Each row of lower hemisphere pole figures in right columns is corresponding to the area bounded by the white bars on the IPF map. The hexagonal columns in the IPF map show the direction of c-axis orientation. The big columns represent the main direction and small columns represent the subordinate direction (i.e., correspond to a strong signal and weak signal marked by white arrows in the pole figures, respectively). Note that a- and b-axes were not considered in the construction of hexagonal columns. The numbers above the color scale represent the number of data points used in pole figure construction. The numbers on the side of the color scale are the intensity of the signal. Outside of eggshell is up. Dashed lines indicate the boundary layer (E–G). (A) <i>Gekko gecko</i>. Note that lower hemisphere pole figures were constructed only for the area to the left of a dashed line in order to avoid any disturbance caused by ornamentation and pore-like structure in the right area. (B) <i>Paroedura pictus</i>. (C) <i>Paroedura stumpfii</i>. (D) <i>Phelsuma grandis</i>. (E) <i>Correlophus ciliatus</i>. (F) <i>Rhacodactylus leachianus</i>. (G) <i>Eublepharis macularius</i>. (H) An arrow in hexagonal column points to the direction of c-axis (upper left). An IPF legend shows the relationship between the color and c-axis orientation (lower left). A cylinder on the right shows c-axis orientation schematically. Red-colored parts of the IPF map show the region where c-axis of calcite crystal is aligned perpendicular to the eggshell surface. In contrast, blue- and green-colored parts are equivalent to the calcite crystals that have horizontally aligned c-axis (i.e., parallel to the eggshell surface).</p

Secondary electron images of gekkotan eggshells.

<p>Each column is outer, radial, and inner views, respectively. White and black bars on the side of a central column represent the boundary between the layers mentioned in the text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s001" target="_blank">S1 Text</a>. Outside of eggshell is up. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s004" target="_blank">S2</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s010" target="_blank">S8</a> Figs for details. (A) <i>Gekko gecko</i>. Ribbon-like structures in A3 are remnants of the shell membrane. (B) <i>Paroedura pictus</i>. White arrows in B1 point pore-like structures. Note columnar structure (white arrows) and ridge-like ornamentations (black arrows) in B2. The inner surface is characterized by a lot of pits. (C) <i>Paroedura stumpfii</i>. White arrows in C1 mark the fragments of sawdust so that they should be neglected. Note the absence of columnar structure in the plain layer and the presence of ornamentation (a white arrow) in C2. Protruding calcite concretions are distributed in C3 (white arrows). (D) <i>Phelsuma grandis</i>. Note that the boundary between the blocky and columnar layers in D2 is very similar to the inner surface of other rigid gekkotan eggshells where needle-like structure exists (a white arrow). (E) <i>Correlophus ciliatus</i>. The calcareous layer is weakly columnar in shape and morphologically different from the very thin calcareous layer of derived squamate eggshells. A white arrow in E3 marks the margin of the boundary layer. (F) <i>Rhacodactylus leachianus</i>. The gradual boundary between the capsule-like and flattened granules is marked in F1 (a white arrow) in the outer surface. Note the convex mounds in the boundary layer (white arrows) in F3. (G) <i>Eublepharis macularius</i>. Note that protein fibers near the calcareous layer have wave-like undulation in G2 (white arrows). The outline of eggshell is similar to those of scincid lizard eggshells [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.ref039" target="_blank">39</a>].</p

Backscattered electron (BSE) images of gekkotan eggshells.

<p>White bars on the side represent the certain boundary mentioned in the text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s001" target="_blank">S1 Text</a>. Outside of eggshell is up. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s011" target="_blank">S9</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.s017" target="_blank">S15</a> Figs for details. (A) <i>Gekko gecko</i>. White arrows point to the circular structures with a central hole, whereas black arrows mark the vesicles. Note the enigmatic bulbous structure in ornamentation (a white arrowhead) covered with a very thin layer consisting of polygonal structure in the outermost part of the eggshell (a black arrowhead). (B) <i>Paroedura pictus</i>. Note the circular structures with a central hole (white arrows) and abundant vesicles (black arrows). The ridge-like ornamentation is marked by a black arrowhead. (C) <i>Paroedura stumpfii</i>. Circular structures with a central hole (white arrows) are distributed in the eggshell except the inner portion of the plain layer. Vesicles are marked by black arrows. Note the highly irregular pores in the porous layer and a pore-like orifice (a black arrowhead). (D) <i>Phelsuma grandis</i>. Abundant circular structures (white arrows) and a few vesicles are present (black arrows). Note needle-like structures between the blocky and columnar layers (two lower white arrowheads). Spherical granular ornamentations are connected to the main eggshell (two upper white arrowheads) covered with a very thin covering layer (a black arrowhead). (E) <i>Correlophus ciliatus</i>. The boundary layer is marked by a dashed line. Note that calcareous layer occupies one-half of the eggshell although they coexist with protein fibers (fibers are represented by black dots and lines; white arrows). Pore-like and small chamber-like structures are pointed by black and white arrowheads, respectively. (F) <i>Rhacodactylus leachianus</i>. The boundary layer of the eggshell is marked by a dashed line. It has deeper mixed layer with a more compact outer portion than <i>Correlophus ciliatus</i> eggshell. The protein fibers are marked by white arrows. Note pore-like structure (a black arrowhead). (G) <i>Eublepharis macularius</i>. Columnar structure is clearly observable with pore-like structures between columns (black arrowheads). The stem-like structure of each columns consists of calcite and protein fibers (white arrows).</p