Anura, Gardner & Redman & Cifelli, 2016

Gardner, James D., Redman, Cory M. & Cifelli, Richard L., 2016, The Hopping Dead: Late Cretaceous Frogs From The Middle - Late Campanian (Judithian) Of Western North America, Fossil Imprint 72 (1 - 2), pp. 78-107 : 92-93

Anura indeterminate morph 2

( Text-fig. 9 )

M a t e r i a l a n d o c c u r r e n c e s: Two maxillae from

Dinosaur Park Formation, Alberta, Canada (Appendix 2).

D e s c r i p t i o n: The two specimens are both from the Irvine locality and preserve about the posterior two-thirds of a left maxilla. UALVP 40191 ( Text-fig. 9a, b ) lacks the posteriormost end of the processus posterior and most of the processus pterygoideus, but anteriorly preserves the base of the processus palatinus. UALVP 40192 ( Text-fig. 9c–g ) is broken farther behind the processus palatinus, but preserves an intact processus posterior and more of the processus pterygoideus. The two specimens are similar in size ( UALVP 40191 is 6.0 mm long and UALVP 40192 is 6.7 mm long); the latter is from a slightly larger individual. They also resemble one another in the following features: bone elongate and low in labial or lingual outline; margo orbitalis shallowly concave and moderately elongate; processus zygomaticomaxillaris low and broadly convex dorsally, bearing grooves dorsolingually for contact with squamosal (these features are more prominently developed in the larger UALVP 40192 ); processus posterior only moderately elongate, with its posterodorsal edge moderately ( UALVP 40191 ) or more steeply ( UALVP 40192 ) declined; and lamina horizontalis moderately deep and lingually wide, with convex lingual surface. Although neither specimen retains any intact teeth, as indicated by their preserved tooth shafts the teeth are small and closely spaced. Judging by the profile along the anteriormost portion of the preserved dorsal edge in UALVP 40191 , the processus frontalis would have been taller than the processus zygomatico-maxillaris. UALVP 40192 is informative for showing that the processus posterior tapers to a blunt point, that near its posterior end that same process lingually bears a small, shallow facet for contact with the jugal, and that the processus pterygoideus was a welldeveloped, lingually projecting flange with a shallowly concave dorsal surface. The specimens exhibit three differences. First, the posterior end of the tooth row lies approximately in line with ( UALVP 40191 ) or slightly behind ( UALVP 40192 ) the level of the processus pterygoideus. Second, a deep groove descends from the margo orbitalis anteroventrally along the lingual face of the pars facialis in UALVP 40192 ( Text-fig. 9f : arrow), whereas no such groove is present in UALVP 40191 . Finally, the labial surface of the pars facialis in UALVP 40191 is ornamented with low ridges that are arranged in a loosely reticulate pattern and enclose shallow pits, whereas in UALVP 40192 the labial surface is less obviously ornamented. Instead, the labial surface of the latter specimen has a roughened texture and, when viewed under low angle lighting, extremely low ridges enclosing shallow pits can be seen along the dorsal half of its labial surface. This less pronounced labial ornament does not seem to be an artefact of wear or abrasion .

R e m a r k s: The two small, low, and elongate maxillae from Irvine are similar to one another in many respects, but exhibit some differences (i.e., relative positions of posterior end of tooth row; variable presence of groove lingually below margo orbitalis; expression of labial ornament). The presence of more prominently expressed labial ornament in the smaller specimen is at odds with the general trend of cranial ornament (where present) becoming more pronounced with growth in anuran species. Determining whether these maxillae belong to separate species or simply are variants within a single species will require additional specimens. Even with this uncertainty, UALVP 40191 and 40192 are sufficiently distinct that they cannot be assigned to any of the species or other morphs recognized here. Nor are they closely comparable with other maxillary specimens known to us from Upper Cretaceous deposits elsewhere in the Western Interior.

Figures

Text-fig. 9. Maxillae ofAnura indeterminate morph 2 from the middle – late Campanian (Judithian) ofAlberta, Canada. Both specimens are from the Irvine locality in the Dinosaur Park Formation. Except where noted otherwise, images are photographs and depict specimens lightly dusted with ammonium chloride to enhance details and texture. Images at same magnification; see scale bar. a, b – incomplete left maxilla, UALVP 40191, in labial (a) and lingual (b) views. c–g – incomplete left maxilla, UALVP 40192, in labial (c, d) and lingual (e, f) views and, with anterior to right, in dorsal (g) view (images in d and f are scanning electron micrographs). Arrow (f) points at groove extending diagonally along lingual surface of pars facialis below margo orbitalis.