Tails of two tips: first reports of tail furcations in a dozen Australian skink species, with the description of a highly unusual tail duplication morphology in Carlia longipes (Macleay, 1877)

Abstract

Caudal autotomy and subsequent tail regeneration are well-known in lizards, but occasional abnormalities produce furcated (branched) tails. Here, we report 11 new records of tail furcations in Australian skinks, discovered through targeted searches of iNaturalist and Facebook supplemented by opportunistic observations. Among these, we document the first furcation records for the genera Bellatorias, Concinnia, Hemiergis, and Saiphos. To interpret the developmental origin of these anomalies, we propose a novel three‑category framework distinguishing furcations arising from regeneration following autotomy (Category I), injury‑induced blastema formation without complete autotomy (Category II), and those with no external signs of injury or regeneration, suggesting possible developmental duplication (Category III). Applying this scheme revealed multiple mechanisms operating across taxa. Most records conformed to Category II, but the symmetrical, externally normal tail duplication in Carlia longipes represents a compelling candidate for a true developmental anomaly (Category III). Our findings substantially expand the known taxonomic distribution of tail furcations in Australian skinks (to at least 33 species) and highlight the growing contribution of citizen science to documenting rare morphological anomalies. The lack of observed locomotor deficits or increased mortality in repeatedly sighted individuals suggests that furcated tails impose minor fitness costs, consistent with previous population‑level studies. We encourage continued reporting of such observations together with radiographic examination of Category III cases to clarify the developmental mechanisms underlying supernumerary tail formation.