ABSTRACT Nonnative species are drivers of global change, affecting biodiversity and burdening society with economic costs. Effective management of an invasion relies on the ability to make accurate predictions about the target species' spread and impact. This requires knowledge of the target species' biology, making taxonomic validation critical. Even so, external morphology is still widely used to determine the species identity of novel invaders. Here, we show that a nonnative pipid frog population in Riverview, Florida, USA, initially identified as African Clawed Frog ( Xenopus laevis ), is a cryptic invasion of Tropical Clawed Frog ( Xenopus tropicalis ) and the only known nonnative population of this species. We used DNA sequence data and osteology from high-resolution microcomputed tomography to confirm this identification. Furthermore, we conducted field surveys to delineate the population's invaded range in Florida. We detected the presence of adult X. tropicalis at 22 sites and larvae at a subset of 12 sites, representing an occupied area of approximately 1,630 ha. Differing body size and physiology of these two species of Xenopus suggest considerable differences in their impact, spread, and potential geographic range.

The anuran family Rhinophrynidae today comprises a single species restricted to southernmost Texas and Central America. Three extinct genera allied to this family are known from the Jurassic ( Rhadinosteus ) and Eocene ( Chelomophrynus , Eorhinophrynus ), whereas the sole extant genus Rhinophrynus is known from the latest Eocene (Chadronian) of Saskatchewan and the Pleistocene of Mexico. We provide the first records of the Rhinophrynidae from the Oligocene of eastern North America. From two of the oldest terrestrial vertebrate sites on the Florida peninsula (I-75, early Oligocene; Brooksville 2, late Oligocene), we have identified one nearly complete and several partial humeri, two radioulnae, two partial presacral vertebrae, three partial ilia, and one femur that are all referable to the Rhinophrynidae. These specimens are similar in size to the Eocene Rhinophrynus canadensis , smaller than the extant R. dorsalis , and might be distinguishable from both by features of the ilium and humerus. The presence of rhinophrynids during the Oligocene provides the first indication of change in the anuran fauna on the Florida peninsula during the Cenozoic.

Although the fossil record of pipoid frogs is more extensive than for other anuran clades, crown-group genera are poorly documented throughout the Cenozoic. We report an isolated neurocranium from the Nsungwe Formation (∼25 million years ago; Oligocene) in southwestern Tanzania, providing the earliest evidence for the genus Xenopus in sub-Saharan Africa. The specimen is well preserved, allowing us to use three-dimensional geometric morphometrics to compare the shape of this neurocranium to those of all extant species of Xenopus based on microcomputed tomography scans. Analyses revealed that this small fossil resembles diminutive extant species of Xenopus such as X. longipes . The fossil neurocranium preserves well-ossified tectum nasi and septum nasi, the latter separating large ovoid olfactory foramina, contributing to a more-ossified region surrounding the prootic foramen than observed in extant species of similar size. The Nsungwe Formation pipoid fossil contributes new information to the early biogeography and body-size diversification within the genus Xenopus .