Ceratophrys rusconii Agnolín 2005

Nicoli, Laura, 2019, The fossil record of Ceratophrys Wied-Neuwied (Anura: Ceratophryidae): a revision and update of fossil South American horned frogs, Zootaxa 4658 (1), pp. 37-68 : 49-50

Ceratophrys rusconii Agnolín 2005

Agnolín (2005) named Ceratophrys rusconii on the basis of a single, incomplete skull (MACN 19744; Fig. 3D, E, I ) from the vicinity of the city of Mar del Plata in the province of Buenos Aires, Argentina. This specimen was collected at Playa Dorada, a locality north of Mar del Plata ( Fig. 1 , locality 8), in the basal third of the cliff where the sediments are exposed. The recent geological analyses of this locality, also known as Playa Santa Elena, indicated that these sediments have been deposited since the Plio-Pleistocene ( Cione et al. 2007; Isla et al. 2015; Prevosti et al. 2004).

Osteological features. MACN 19744 is a well-ossified skull that is incompletely preserved ( Fig. 3D, E, I ), and resembling the general morphology of all Ceratophrys . The premaxillae and most of both maxillae are missing; thus, the overall cranial proportions cannot be evaluated. The skull is high, but its greatest height is less than a half of its greatest width. Tuberculate ornamentation is evident, but no crests are developed.

The squamosal otic ramus is expanded and lacks a lateral wall. The otic plate is subquadrangular, without concave surface; its posterior margin ends at the level of the occipital condyles and does not project dorsal to the skull roof ( Fig. 3E, I ). The vomers bear dentigerous processes, but the poor preservation of these bones prevents determining whether of true teeth are present. A delicate ventral process is present on the lateral margin of the anterior ramus of pterygoid.

Remarks. The holotype and single specimen of C. rusconii has several possible synapomorphies of Ceratophryidae (viz., skull exostosis, parieto-squamosal arch present, maxilla-squamosal contact, expanded squamosal otic ramus overlapping prootic, and absence of pars palatina on the anterior maxilla). In addition, it has several possible synapomorphies of Ceratophrys (viz., robust, bar-shaped maxillary processes of nasals, postorbital fenestra). These characters support its inclusion in Ceratophrys .

The specific status of Ceratophrys rusconii , however, is questionable. Agnolín (2005) thought that it differed from C. cranwelli and C. ornata in having: (1) the postemporal fossa laterally expanded and anteroposteriorly reduced; (2) the postemporal fossa close to the orbit; (3) frontoparietal posteriorly constricted; (4) in lateral view, a large temporal fenestra, and an elongated quadratojugal and squamosal ventral ramus; (5) in posterior view, epiotic eminences reduced and angular; and (6) anterior ramus of pterygoid lacking robust posterolateral process. Agnolín’s (2005) postemporal and temporal fenestrae presumably are the postorbital and subtemporal fenestrae, respectively. His Characters 1–5 reflect small differences in the cranial proportions that vary intraspecifically in C. cranwelli and C. ornata ( Fig. 3 ). Additionally, the ventral ramus of squamosal seems to be broken; thus, its shape or expansion cannot be evaluated (Character 4, Fig. 3I ). Agnolín (2005) also reported that in lacking a robust posterolateral process on the anterior ramus of pterygoid (Character 6) C. rusconii can be distinguished from C. cranwelli and C. ornata and he cited the unpublished thesis of Perí (1993c). As mentioned above, there are some inconsistencies in the naming and the scoring of the states of this character in this thesis. Nevertheless, the delicate ventral process observed on the anterior ramus of the pterygoid in MACN 19744 matches that observed in the species of Ceratophrys of the southeastern clade and in C. stolzmanni .

No distinctive characters (or combination there of) support the status of Ceratophrys rusconii as a valid species. In addition, the combination of characters of MACN 19744 could be plesiomorphic for Ceratophrys . Thus, MACN 19744 is assigned to Ceratophrys and C. rusconii considered species inquirenda.

Figures

FIGURE 1. Distributional map of extant and fossil Ceratophrys. The phylogeny of the extant species of Ceratophyrs were proposed by Faivovich et al.(2014). The numbers in circles represent the fossiliferous localities mentioned in the article: 1, Arroyo Chasicó; 2, Arroyo Tapalqué; 3, Conchillas; 4, Farola Monte Hermoso; 5, Fortín Necochea; 6, Lagoa Santa; 7, Laguna de Los Tres Reyes; 8, Mar del Plata and Miramar cities; 9, Ñuapua; 10, Olivos; 11, Puerta de Corral Quemado; 12, Quehué; 13, San Antonio and Paso Alsina; 14, Tarija. Black circles: localities where the presence of Ceratophrys was confirmed; white circles: the presence of Ceratophrys remains unconfirmed. The distributions of the extant species of Ceratophrys are represented by areas that approximately include all the reported records for each species; the distribution of most species, however, is not well known. Distributions are based on Lynch (1982) with corrections and additions from Barrio-Amorós 2004; Barrio 1980; Langone 1995; Maciel et al. 2013; Maneyro & Langone 2001; Ortiz et al. 2013; Peters 1967; Rivero 1961; Stuart et al. 2008.

FIGURE 3. Comparison of selected fossil and living Ceratophrys. A, B, G, H, Ceratophrys ensenadensis, type series; A, B, holotype (PVL 767); G, H, paratype (PVL 699). D, E, I, C. rusconii, holotype (MACN 19744). C, F, J, C. ornata (C, AMB 160; F, J, AMB 154). A, D, G, ventral views; B, C, E, F, H, dorsal views; I, J, lateral views Abbreviations: ds, dorsal shield; fp, frontoparietal; n, nasal; oc, occipital condyles; pl, palatine; ppa, discrete pars palatina absent; pof, postorbital fenestra; psa, parietosquamosal arch; pt, pterygoid; qj, quadratojugal; sop, squamosal otic plate; v, vomer; V, vertebra; vr, squamosal ventral ramus; zr, squamosal zygomatic ramus. Scale bar is 5mm.