Anura, Gardner & Redman & Cifelli, 2016
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publication ID |
https://doi.org/ 10.14446/FI.2016.78 |
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DOI |
https://doi.org/10.5281/zenodo.4773192 |
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persistent identifier |
https://treatment.plazi.org/id/947587F2-6679-FFC4-FF34-11FDFA78FA8A |
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treatment provided by |
Felipe |
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scientific name |
Anura |
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Anura View in CoL indeterminate morph 1
( Text-fig. 8 View Text-fig )
M a t e r i a l a n d o c c u r r e n c e s: Maxilla from Dinosaur Park Formation, Alberta, Canada; maxillae from Judith River Formation, Montana, USA; maxillae from Mesaverde Formation, Wyoming, USA; maxillae and squamosal from Kaiparowits Formation; maxilla from Wahweap Formation; and maxillae from Aguja Formation, Texas, USA (Appendix 2).
D e s c r i p t i o n: All figured examples (maxillae and a squamosal) are incomplete. Two maxillary specimens consist of the preorbital region. The more nearly complete specimen, (UALVP 40169: Text-fig. 8a, b View Text-fig ), preserves an intact, relatively prominent processus palatinus and a nearly complete lamina anterior that is moderately tall, with its anterior end bluntly tapered and bearing only a rudimentary rostellum. The other specimen (AMNH FARB 8461: Text-fig. 8c, d View Text-fig ), is broken in front of the processus palatinus and is missing both the anterior and dorsal portions of the lamina anterior. The remaining maxillae ( Text-fig. 8e–l View Text-fig ) preserve portions along the suborbital region and, in some, also the region bearing the processus pterygoideus. Collectively the figured maxillary specimens show that this bone could be relatively large and robust, the pars facialis is moderately high, the margo orbitalis is shallowly concave in labial or lingual outline, the processus palatinus is well developed, the processus zygomatico-maxillaris is moderately tall and dorsolingually bears a facet for articulation with the squamosal, the lamina horizontalis is a well-developed bony shelf, the processus pterygoideus is robust, wing-shaped, and projects posterolingually for a short distance, and the posterior end of the tooth row (not intact in any specimen) extends back at least to the level of the processus pterygoideus. None of the maxillae has intact teeth, however, OMNH 23837 preserves several bicuspid replacement crowns in situ along the lingual surface of the crista dentalis (not figured). Although the lamina horizontalis is consistently deep along the suborbital region in all specimens, variation is evident in other aspects of its structure. In some specimens the lamina horizontalis may be relatively narrow (i.e., labio-lingual width less than vertical depth) and its lingual face shallowly convex and lingually directed (OMNH 23837; Text-fig. 8e View Text-fig ). In others, the lamina horizontalis may be relatively wider (i.e., maximum labio-lingual width subequal to depth) and its lingual face either more deeply convex and directed lingually (OMNH 67094 and TMM 43057-256; Text-fig. 8h and j View Text-fig , respectively) or flatter and tilted ventrally (OMNH 25243; Text-fig. 8l View Text-fig ).
The figured squamosal (OMNH 23538: Text-fig. 8m, n View Text-fig ) is an incomplete bone from the left side. It preserves the dorsal and posterior portions of the lamella alaris. Its medial surface preserves the broken base of the processus posterolateralis. The processus posterodorsalis is intact; that process is acuminate in medial or lateral outline, appears to have projected posterodorsally, and its smooth dorsal margin indicates it did not contact the frontoparietal. The smooth posterior face of the posterior margin of the squamosal and its overall shallowly concave profile suggest it formed the anterior rim of the tympanum.
A size range of individuals is represented by the maxillary and squamosal specimens. For the former, judging by the depth of the lamina horizontalis, the largest specimen (AMNH FARB 8461) is over twice as large as the smallest (OMNH 25243; cf. Text-fig. 8c, d View Text-fig versus 8k, l). The squamosal probably is from a moderately large individual, perhaps comparable in size to the one represented by the maxilla OMNH 23837 (cf. Text-fig. 8m, n View Text-fig versus 8e, f) from the same formation. All maxillae and the squamosal are ornamented externally by narrow and moderately high ridges that are arranged in a reticulate pattern and enclose moderately broad, flat- or shallowly concave-bottomed pits. On the maxillae, this ornament is restricted to the pars facialis portion of the bone (i.e., about the upper two-thirds of the labial surface and, depending on the specimen, ridges may be in either an irregular polygonal pattern or more loosely arranged (cf. Text-fig. 8e, g, i, j View Text-fig versus 8a, c). As show by the maxilla UALVP 40169 ( Text-fig. 8a View Text-fig ), towards the anterior end of the bone the pit-and-ridge pattern is replaced by low, discontinuous ridges that roughly parallel one another and extend anteriorly and slightly dorsally.
R e m a r k s: Specimens described above and listed in Appendix 2 for our morph 1 are grouped together largely on the basis of their style of pit-and-ridge labial ornamentation. That pattern clearly differs from the pustulate ornament characteristic for Scotiophryne and Theatonius (cf. Text-figs 3 View Text-fig , 5g, h View Text-fig ) and the unornamented or weakly ornamented conditions seen in certain Judithian maxillae reported here (cf. Text-figs 5a–f View Text-fig , 7 View Text-fig , 9 View Text-fig , 10 View Text-fig ). Subtle, but consistent differences in details of their respective pit-and-ridge ornament also separate these morph 1 specimens from Hensonbatrachus , whose ornament is coarser and less regular in shape, consisting of deeper pits and short grooves enclosed by relatively thicker ridges (cf. Text-fig. 4a–n View Text-fig ), and from our unnamed genus and species I, whose ornament is finer and more net-like, consisting of more irregular and smaller pits enclosed by narrower ridges that may break up into isolated ridges or tiny pillars (cf. Text-fig. 6a–m View Text-fig ). Additional features related to size, form, and structures further differentiate morph 1 specimens from other Judithian maxillae and, where known, squamosals.
Historically, isolated fossil anuran skull bones having ornament similar to our morph 1 specimens have been compared to Eopelobates PARKER, 1929 , an extinct pelobatid genus containing four species from the Eocene – Pliocene of Europe and two species from the Eocene of the USA; see recent revision by Roček et al. (2014) and references therein. Based largely on similarities to the cranial ornament in those Tertiary species (all of which are known by skeletons) isolated skull bones bearing reticulate ornament from the North American Late Cretaceous (Santonian – Maastrichtian) and early Paleocene routinely have been identified as belonging to Eopelobates or to an Eopelobates -like taxon (e.g., Estes et al. 1969, Estes 1970, Fox 1976a, Estes and Sanchiz 1982, Sanchiz 1998, Holman 2003, Gardner 2008, Gardner and DeMar 2013). As pointed out by Roček et al. (2014), such identifications were based entirely on general resemblances, especially the Eopelebates -like pattern of cranial ornament (which is relatively widespread among anurans as a whole), rather than synapomorphies or unique sets of features shared with the unequivocal Tertiary species of Eopelobates . Although using the name “ Eopelobates ” for such material has been a useful convention for labelling North American Late Cretaceous and Paleocene anuran fossils characterized by a reticulate, Eopelobates -like cranial ornament, following from Roček et al.’s (2014) critique of that practice and its potential for taxonomic confusion, here we instead use the informal name “morph 1” for these kinds of specimens.
Based on previous reports of Eopelobates -like occurrences and our examination of specimens available to us, we record Anura morph 1 in six of the ten formations included in our review (Appendix 2): Dinosaur Park Formation, Alberta; Judith River Formation, Montana; Mesaverde Formation, Wyoming; Kaiparowits and Wahweap formations, Utah; and Aguja Formation, Texas. Eopelobates -like anurans previously have been listed (no vouchers indicated) for the first four of those formations (e.g., Fox 1976a: 8 as “ Eopelobates n. sp. ”, in what is now considered the Dinosaur Park Formation; Bryant 1989: 34 as “ Eopelobates ”, in the Judith River Formation; Breithaupt 1985: 165 as “cf. Eopelobates sp. ”, in the Mesaverde Formation; Eaton et al. 1999: table 5 as “ Eopelobates sp. ”, in the Kaiparowits Formation). “? Eopelobates sp. ” has long been recorded for the Fruitland Formation of New Mexico ( Armstrong-Ziegler 1978, 1980, Hunt and Lucas 1992, 1993), on the basis of a fragmentary maxilla described and figured by Armstrong-Ziegler (1980: pl. 1c–d). However, judging by those published drawings, that specimen differs from North American Cretaceous maxillae historically assigned to “ Eopelobates ” and here to our morph 1 in having labial ornament formed by narrow, short, and irregular grooves instead of polygonal pits. Based on that difference, we regard the maxilla from the Fruitland Formation as indeterminate (see Appendix 2: “Other occurrences of Judithian anurans”). One of our morph 1 specimens (maxilla AMNH FARB 8461) from the Judith River Formation previously was designated by Sahni (1972b: 347 and fig. 7P–Q) as the exemplar for his “Discoglossid A”, which he characterized as “large frog with sculpted maxilla”. In our opinion, assignment of such a fragmentary maxilla to the Discoglossidae GÜNTHER, 1858 , whether in the loose or strict sense of that name (cf. Sanchiz 1998 versus Frost et al. 2006) or to any other anuran family cannot be supported. Differences in size and lingual structure among the specimens assigned to our morph 1, plus the extensive latitudinal spread among their localities, suggest that our morph 1 grouping contains several species. Better preserved specimens will be needed to tease those species apart.
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