Here we describe the “lost” holotype of Chamasaurus dolichognathus from the Permo-Carboniferous Cutler Group of El Cobre Canyon, New Mexico, USA. While C. dolichognathus has been suggested to be either an amniote or amphibian, we conclude that it is more likely a part of pan-Amniota. We also observe that there is little diagnostic material that would assign this specimen to a more specific clade, although the moderate degree of basal tooth infolding could prove to be of diagnostic utility if additional specimens are discovered. However, we declare the species as nomen dubium until such specimens are found.

Etheostoma xanthovum, the Clarks Darter, is described as a new species endemic to the Clarks River drainage in Kentucky and Tennessee, USA. Etheostoma xanthovum was previously recognized as Etheostoma oophylax based on morphological characters. Subsequent to the description of E. oophylax, molecular phylogenetic analyses consistently resolved specimens from the Clarks River drainage and E. chienense as sister species, which together formed a sister clade to all other sampled populations of E. oophylax. Our analyses of morphological trait data, mitochondrial DNA, and genomic sampling using double digest restriction-site associated DNA sequencing support the distinctiveness of E. xanthovum. Morphologically, E. xanthovum differs slightly from E. oophylax in the modal number of dorsal fin rays (12 versus 11) and in the average number of scale rows around the caudal peduncle (21.8 versus 20.4). Etheostoma xanthovum does not share mitochondrial DNA haplotypes with E. oophylax or E. chienense. Phylogenomic analysis of an average of 28,448 double digest restriction-site associated DNA loci per sampled specimen resolves E. xanthovum and E. chienense as sister species, and assessment of genomic divergence supports the hypothesis that each of these two species represents a distinct and independently evolving lineage. In addition, we report a range extension of E. oophylax in the Obion River drainage, a direct tributary of the Mississippi River.

The Kentucky Arrow Darter, Etheostoma spilotum, endemic to the upper Kentucky River basin of eastern Kentucky, is redescribed and recognized as a distinct species closely related to E. sagitta in the upper Cumberland River basin and E. nianguae in the Osage River drainage (Missouri River basin). Originally described as a subspecies of E. nianguae, it was later considered a full species and then a subspecies of E. sagitta, based on close geographic proximity to Cumberland basin populations and overlapping meristic variation interpreted as character intergradation. We present meristic, morphometric, and genetic data that support species-level recognition of E. spilotum. It differs from E. sagitta by lower counts of total and pored lateral scales, lower counts of caudal peduncle scales, fewer second dorsal-fin rays, and fewer pectoral-fin rays. Interspecific divergence of E. spilotum and E. sagitta is further demonstrated through analyses of variation in the mitochondrial nd2 gene and species delimitation using genome-wide double digest restriction-site associated DNA sequencing. Although allopatrically distributed, both species inhabit upland headwater streams on the Cumberland Plateau and have similar life history characteristics. Endemism, fragmented distributions, and low densities and genetic diversity within populations make these species extremely vulnerable to anthropogenic activities. Etheostoma spilotum was federally listed as threatened in 2016 due to degradation of stream habitat and water quality in the upper Kentucky basin that has eliminated the species from a significant portion of its range.