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

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

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

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

Line profile analyses of gekkotan eggshells.

<p>Vertical yellow bars represent the locations where analyses were conducted. Horizontal red bars on the graph are auxiliary lines that mark the same position in the eggshell. The boundaries of the eggshell are marked by black bars. The units are in weight percent. Outside of eggshell is up. (A1–A2) <i>Gekko gecko</i>. A1 shows the elemental profile of the main eggshell, while A2 represents the result of ornamentation area. Note the correlation between the level of Mg and S (white arrows). A black arrow points a small Ca peak caused by a very thin layer consisting of polygonal structure of the covering layer. (B) <i>Paroedura pictus</i>. Note the correlation between the level of Mg and S (white arrows). (C) <i>Paroedura stumpfii</i>. A drop of Ca level reflects the empty spaces in the porous layer rather than low concentration of Ca in the porous layer (a white arrow). (D) <i>Phelsuma grandis</i>. Note the correlation between the level of Mg and S in the main eggshell (white arrows). The level of P gradually decreases from the inner surface of the columnar layer, but it increases near the outer surface of the eggshell. (E) <i>Correlophus ciliatus</i>. The hatched rectangle marks the crack. The level of Mg, P, and Ca begins to change at the same position (i.e., the boundary between the shell membrane and calcareous layer). (F) <i>Rhacodactylus leachianus</i>. Note the level of Mg and P changes more abruptly at the boundary between the shell membrane and calcareous layer compared to <i>Correlophus ciliatus</i> eggshell. (G) <i>Eublepharis macularius</i>. Note that <i>Eublepharis macularius</i> eggshell has a relatively short calcareous layer.</p

Schematic views of the seven different gekkotan and representative derived squamate eggshells.

<p>Most of the terminology followed [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.ref002" target="_blank">2</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0199496#pone.0199496.ref015" target="_blank">15</a>] and otherwise new terms are proposed in this study. The light gray areas in <i>Gekko gecko</i> (A), <i>Paroedura stumpfii</i> (C), and <i>Phelsuma grandis</i> (D) eggshells show the location and shape of “dark bands”. The dark gray areas in rigid gecko eggshells (A–D) signify the shape of extinction pattern under polarized light. The jargon “calcareous layer” is used in soft gekkotan eggshell to refer to stem-like and cap-like structures, collectively. The figures are not drawn to scale. In <i>Gekko gecko</i> eggshell (A), a pore-like and bulbous structures are associated with the ornamentation. The eggshell of <i>Paroedura stumpfii</i> has a peculiar porous layer (C). The mixed layer of <i>Rhacodactylus leachianus</i> eggshell (F) can be further differentiated into two sub-layers. The protein fibers in <i>Eublepharis macularius</i> eggshell (G) are undulated unlike other soft eggshells (E, F). Note that soft eggshells of derived squamates do not have stem-like structure that extends to the shell membrane (H).</p