Figure 1.
Sclerotic rings of five specimens of mosasaurs representing four genera.
All showing left ring in outer view, where vertical arrows point dorsally and horizontal ones anteriorly. A, Tylosaurus proriger (FFHM 1997–10); B, Platecarpus tympaniticus (LACM 128319); C, P. tympaniticus (KU 1001); D, Clidastes propython (CFDC M74.10.06); E. Mosasaurus sp., cf. M. missouriensis (TMP 2012.010.0001). Abbreviations: f, frontal; j, jugal; os, orbitosphenoid; pra, prearticular; pof, postorbital frontal; prf, prefrontal. Scale bars equal 1 cm.
Figure 2.
Structure of a generalized reptilian eye.
A, Cross section of a lizard eye; B, Corneal section of an eye. Abbreviations: Bm, Brücke’s muscle; c, cornea; Cm, Crampton’s muscle; cp, corneal process; i, iris; IED, distance between internal and external borders of sclerotic ring; l, lens; s, sclera; sr, sclerotic ring; sm, sphincter muscle; ss, sulcus.
Figure 3.
Observed arrangement of scleral ossicles in mosasaurs and a modern monitor lizard.
A, Tylosaurus proriger (FFHM 1997–10, outer view of left ring); B, Platecarpus tympaniticus (LACM 128319, ditto); C, Clidastes propython (CFDC M74.10.06, ditto); D, Mosasaurus sp., cf. M. missouriensis (TMP 2012.010.0001, ditto); E, Mosasaurus sp., cf. M. hoffmannii (NHMM 2013001, ditto); F, Varanus dumerilii (NSM PO 391, ditto). Dark gray, light gray, and white indicate the ossicles of the minus-, the plus- and the imbricating-types, respectively. Except for final ossicle, only the plus- and the minus-type are numbered. Cross-hatching indicates broken parts. See main text for further explanation. Figures are not to scale. Abbreviations: d, dorsal; n, nasal; t, temporal; v, ventral.
Figure 4.
Difference of surface conditions between inner and outer side of the sclerotic ring in Platecarpus tympaniticus.
A, interpretative drawing of inner side of the sclerotic ring based on KU 1001; B, cross sectional view of a single scleral ossicle along the line I-I’ in A; C, cross sectional view of a boundary of adjacent scleral ossicles along the line II-II’ in A. On the inner side, the raised middle area shaded in blue is roughened/asperate, resulting in obliterating ossicle boundaries.
Table 1.
The values of IED and width of each ossicle in FFHM 1997–10 (Tylosaurus proriger) and TMP 2012.010.0001 (Mosasaurus sp., cf. M. missouriensis).
Figure 5.
Sclerotic ring of a modern monitor lizard.
A, outer surface; B, inner surface; C, lateral view. White arrow indicates the sigmoid flexure that supports a circular depression/sulcus which surrounds the cornea of the lizard eyeball.