Abstract
A new genus and species, Pseudorestias lirimensis, is described from the southern part of the Chilean Altiplano. While sharing several characters that clearly align the new species with Orestias, this new fish is characterized by numerous autapomorphies: the Meckel cartilage is a continuous cartilage that broadly expands posteriorly (in large specimens, it keeps its anterior part and is resorbed posteriorly), the basibranchials are fused into one long element, the second pharyngobranchial is not displaced dorsally over pharyngobranchial tooth plate 3+4, but they are aligned, the anterior and posterior ceratohyals are closely articulated keeping a scarce amount of cartilage between both bones and ventral to them, ossified middle and distal dorsal radials are present in females as well as ossified middle and distal anal radials. Pseudorestias lirimensis presents strong sexual dimorphism associated to size. Females are almost twice as large and long than males, neuromast lines are absent in males, a mesethmoid is present in males, squamation on head is reduced in males, and ossified middle and distal radial of dorsal fin are cartilaginous in males. Pseudorestias and Orestias are suggested as the sole members of the tribe Orestiini. A list of characters diagnosing the tribe is provided. The presence of the new genus is interpreted as a possible result of the ecosystem isolation where the fish is living from surrounding basins—as early as possibly from the Miocene-Pliocene times—and its physical and chemical characteristics. Small populations, living conditions, small habitat, and reduced distribution make this species a strong candidate to be considered critically endangered, a situation already established for all other Chilean species living in the Altiplano. There is high probability it will become extinct due to water demands and climate change in the region.
Highlights
Cyprinodontiformes, or killifishes, are known by an approximate number of 1,260 species, which are included in ten families [1] of primarily living in freshwater ecosystems
Members of the subfamily Cyprinodontinae are classified in two tribes: the Cyprinodontiini and the Orestiini [1,2,3,4], but their contents and phylogenetic relationships are in dispute
The Tribe Orestiini is diagnosed by the presence of the following characters: Reduced or absent cephalic sensory canals; cephalic sensory system represented by small neuromasts set close together into neuromast lines; pterotic moderately or strongly reduced dorsally leaving a space at the posterodorsal corner of skull roof; robust premaxillary blade with its distal portion broadly expanded; dentary with an expanded ventromedial region and bearing a notch at its medial margin; cartilaginous interhyal; third and fourth pharyngobranchial tooth plates fused to each other; second most anterior branchiostegal ray placed posterior to a deep constriction present in the anterior ceratohyal; thirty to 38 vertebrae; almost horizontally oriented narrow, elongate cleithrum with its largest expansion dorsally; and caudal hypural plate, epural and parhypural symmetrically arranged, several loses characterize Orestiini
Summary
Cyprinodontiformes, or killifishes, are known by an approximate number of 1,260 species, which are included in ten families [1] of primarily living in freshwater ecosystems. Orestiini sensu Parenti [2,3] would include two extant genera, Aphanius and Orestias, which have different geographic distributions. Orestias inhabits the Altiplano of Bolivia, Peru, and Chile (e.g., [3,9]) along the Continental Divide of South America in the Southern Hemisphere. In addressing the geographical distribution of the fishes, the Eurasian and American disjoint occurrence of the freshwater members of the tribe Orestiini is considered a major biogeographic challenge to Parenti’s [2] hypothesis of relationships based solely on morphological characters (for different biogeographic interpretations on the distribution of Orestias versus Aphanius see [4,13]). A recently published molecular study [15], which did not include Orestias, reached different results—with Cyprinodontidae not monophyletic and Aphanius and Valencia as sister taxa
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