Registro de la información en los papeles de trabajo

(FIGURE 4.4)

Several cranial fragments of Chrysemys wallacei are currently known. These include a nearly complete left maxilla (ETMNH-20544), left and right quadrates (ETMNH-3559), and a nearly complete set of lower jaws (ETMNH-12491). While only a few cranial fragments are preserved, their preservation shows distinctions with modern Chrysemys. The left maxilla (ETMNH-20544) is missing its anterior portion that would articulate with the premaxilla (Fig. 4B–D). However, it is still relatively short at 10.8 mm maximum length of the external (lateral) surface. A small portion of the caudolateral surface is also broken. This bone preserves a ventral portion of the fossa orbitalis, and the sutural surface for the jugal shows a distinct “v”-shaped or triangular attachment surface. This attachment is similar to that in modern Chrysemys, however, the sutural surface (and therefore the jugal) are more rostral and ventral in C. wallacei This leads to a smaller fossa orbitalis and orbit. Similar to C. picta, the foramen supramaxillare lies at approximately the same level as the anterior extent of the maxilla-jugal sutural contact dorsally; however, in C. wallacei it is enlarged and more conspicuous. The posteromedial

extension of the maxilla is robust and rounded inC.wallacei, although it would ap- pear to have a stronger apex if it was attached to the jugal. Ventrally (viscerally), there are several foramina along the triturating surface medial to the labial ridge. These foramina sit between a raised median ridge that runs through the middle of the triturating surface and the labial ridge. These foramina lie in a shallow depression, as in modernChrysemys. This depression becomes more pronounced posteriorly in C. wallacei, distinctly more so than in modernChrysemys. The trit- urating surface ofC. wallaceiis also relatively wider in C.wallacei than inC.picta, while the median ridge is more pronounced in the former as well.

The quadrates are isolated but well preserved in ETMNH-3559. Both the left and right quadrates are nearly complete and preserve the condylus mandibularis (or mandibular condyle) and a significant amount of the cavum tympani. The left quadrate has a maximum dorsoventral preserved height of 9.9 mm, while the right is 11.2 mm. The processus articularis caudoventrally has a similar trapezoidal morphology within both C. wallacei and C. picta. The condylus mandibularis is similar in morphology to that of modern C. picta, although its concavity, located anteroventrally on the processus articularis, is less conspicuous. The processus ar- ticularis has dimensions of 3.8 x 3.7 mm. A small portion of the canalis system is preserved with both quadrates, although part has been sheared off and is incom- plete, leading to difficulty determining which portions of the mainly pneumatic canalis systems are preserved. There is a deep, pronounced, concavity immedi- ately rostral (anterior) to the condylus mandibularis that is more pronounced inC.

wallacei than in adult specimens of modern C. picta (e.g., ETVP 9672). However,

this concavity appears to be more pronounced in ontogenetically youngerC.picta

specimens (e.g., ETVP 9691), implying the concavity is ontogentically variable. Re- gardless, this concavity is deeper inC.wallaceithan in even ontogenetically young

modernC. picta. A foramen is present dorsal to this concavity on the rostral sur- face of the quadrate. This foramen is also present in modernChrysemys, although it is situated more lateral in C. wallacei. The morphology of the cavum tympani can also be partially derived from the quadrates. While in modernChrysemysthe cavum tympani is well rounded, inC. wallacei it would have been rostrocaudally compressed, making it more oval. A slight curve toward the middle portion makes it appear as a crescent. A rostrodorsal compression of the cavum tympani is also seen in ontogenetically younger modernChrysemys specimens. The cavum tym- pani appears to anteroposteriorly inflate and become more rounded as individuals age. This curvature is also not present in modern Chrysemys. Even if ETMNH- 3559 is an ontogenetically younger individual and some of the morphology of the quadrates would change in older individuals, there are still distinctions regardless of the ontogenetic ages being compared.

A nearly complete set of lower jaws is preserved with ETMNH-12491 (Fig. 4F–G, I). The lower jaws consist of the right and left dentaries, although most of the caudal elements of the lower jaws were not recovered. The jaws have a maximum rostrocaudal length of 12.1 mm, a maximum overall length of 16.1 mm (measured from apex along right dentary to its distal point), and a maximum preserved width of 19.9 mm. The angle of the lower jaws (in dorsal and ventral views) is distinctly larger in Chrysemys wallaceicompared to modernChrysemys. Indeed, the angle of the lower jaws is 86◦ in the former, but only approximately 74◦–78◦ in modernC.

picta. These wider jaws suggest a wider skull inC.wallaceias well. Rostrally (ante-

riorly), the hook on the rostromedial portion of the labial ridge is not preserved. A tomial (or medial) ridge, more pronounced than in modernChrysemys, is present on the lower triturating surface, with a shallow depression between this ridge and

the labial ridge. The labial ridge is smooth as in otherChrysemys. The lower tritu- rating surface is relatively wider inC. wallaceithan in modern Chrysemys, but not significantly so. The sulcus cartilaginis meckelii is pronounced, particularly since the tomial ridge provides a distinct ledge for it dorsally. While it is more promi- nent than in modernChrysemys, it is significantly less than that inPseudemys. The foramen alveolare inferius is pronounced and is larger than in modernC.picta. Lat- erally, the foramen dentofaciale majus is more pronounced inC.wallaceicompared

toC.picta, although the lateral overhang from the caudal portion of the labial ridge

is less pronounced in the former.