Variation in the ilium of central European water frogs Pelophylax (Amphibia, Ranidae) and its implications for species-level identification of fragmentary anuran fossils

Abstract

Background: In the opinion of all field herpetologists and archaeozoologists, green frogs (living and sub-fossil specimens) are among the most difficult European amphibians to identify. Here, we examine the intra-and interspecific variation in both continuous and discrete iliac characters for refining the criteria for species-level identification among European green frogs Pelophylax ridibundus, Pelophylax lessonae and their associated klepton Pelophylax kl. P. esculentus (Amphibia, Ranidae). Results: A total of 454 ilia of modern green frogs from the former German Democratic Republic have been studied: 168 for P. lessonae (86 of males and 82 of females), 118 for P. ridibundus (44 of males and 74 of females) and 168 for P. kl. P. esculentus (86 of males and 82 of females). The origin, sex, population structure and phenotype are known for each of the studied specimens. Eight variables have been taken (one angle and seven measurements), mainly on the distal part of the element in order to be able to apply them to fragmentary fossil ilia. Interspecific variations, sexual dimorphism and population structure have been investigated. Results suggest that the secure determination of a single fossil ilium at species level is quite impossible, but that at population level, it may be possible to distinguish between a 'pure' species or a 'pure' species plus its cohabiting hybrid form, as some minor differences have been evidenced in particular in the angle of the tuber superior in relation to iliac's main axis (character 2) and the width of the pars ascendens (character 8); two parameters significantly non size-dependent. No sexual dimorphism has been detected, except for P. lessonae. Conclusions: We propose here a new biometrical method in order to differentiate between the fossil ilia of central European water frogs (genus Pelophylax) at population level.

An extinct vertebrate preserved by its living hybridogenetic descendant

“…If it was ever present in Italy, why this taxon disappeared remains a mystery. Water frogs fossils from the middle Pleistocene to the Holocene are found throughout Italy 21 but distinguishing between potential Pelophylax residents is challenging with current biometric methods 22 . Yet, many of these records were attributed to marsh frogs “ P. ridibundus ” 23 and could thus belong to P .…”

Flesh and bone: An integrative approach towards sexual size dimorphism of a terrestrial salamander (genus Salamandrina)

“…As bones have lower water content, they are expected to be less affected by the shrinkage process or the physical constitution of the individual than soft tissue. Whereas many studies in anurans showed dimorphic humeri (e.g., Duellman, ; Duellman & Savitzky, ; Howard & Kluge, ; Lynch, ; Padhye, Jadhav, Sulakhe, & Dahanukar, ) or ilia (Blain, Lózano‐Fernández, & Böhme, ), the morphometric osteology of salamanders was rarely investigated (Herre, ; Ivanović et al, ; Ivanović & Kalezić, ).…”

Pleistocene amphibians and squamates from the Upper Jordan Rift Valley, Gesher Benot Ya’aqov and Nahal Mahanayeem Outlet (MIS 20–18 and MIS 4/3)

“…There are no clear-cut distinctive morphological traits differentiating between the various Pelophylax species (Blain et al, 2015, and references therein). Moreover, as far as we are aware, no morphological traits have been published for Pelophylax bedriagae .…”