Zygonectes, Agassiz, 1854

Figure 2. Reconstruction of ancestral habitats for the North American killifish families Cubanichthyidae, Cyprinodontidae, Fundulidae, Goodeidae, and Profundulidae.A, distribution of North American killifish families with respect to the boundary (red line) between the coastal plain and continental interior (uplands). B, pie charts at each node represent the probability of each character state: coast including coastal plain, upland, or both.

Figure 3. Phylogenetic relationships and divergence times among taxa within North American killifish families Cubanichthyidae, Cyprinodontidae, Fundulidae, Goodeidae, and Profundulidae recovered by Bayesian inference with five concatenated loci (three mitochondrial and two nuclear) and 130 species.Red dots depict nodes with posterior probabilities <95%. Green arrows show fossil calibration points and brown arrows show secondary calibration points (Table 1). Numbered nodes are associated with environmental and geologic events in our biogeographical synthesis (Table 2).

Figure 8. Early–Middle Miocene diversification of North American killifishes in the Gulf of México region.Phylogenetic nodes (Fig.3) are indicated as N5–N7, N9–N11, and N14–N17, showing hypothetical separations between lineages (for details, see main text, Table 2, and Figs 6, 7). The Early Miocene Red River followed the Sabine route to an independent delta, potentially the estuary of origin for subgenus Fundulus, with subgenus Zygonectes arising in the Mississippi River estuary to the east (N15). The Red River joined the Mississippi River in the Middle Miocene.A Guadalupe River drainage emerged to the west in the Early–Middle Miocene, potentially the estuary of origin for the Fundulus similis species group, which diverged from subgenus Fundulus (N16). Widespread, sustained tectonism across southwestern North America isolated western tributaries from the Gulf of México, becoming endorheic drainages, some of which evidently harboured killifishes. Owing to a long history of tectonic activity, the details of these ancient endorheic drainages are unknown.Break-up of the Oligocene Río Grande drainage (Fig. 7) isolated Wileyichthys inland from Lucania (N14). Break-up of the Oligocene Madrean River drainage (Fig. 7) isolated Empetrichthyinae from Goodeinae (N6). Further break-up of the Madrean River separated Goodeinae from Characodontini-Illyodontini (N7). In the southern Gulf, capture of the upper Río Grijalva from an ancestral Río Coatzacoalcos isolated Profundulus from Tlaloc (N5). In the western Gulf, inland immigration of cyprinodontids resulted in peripheral isolates Cualac in the Río Pánuco (N9) and Megupsilon in the Late Miocene Río San Fernando (N11). The base map is a reconstruction for 20 Mya (Early Miocene, used with permission ©2023 Colorado Plateau Geosystems Inc.). The narrowed Gulf Trough follows Popenoe (1990) for Early Miocene.Later sea-level rise flooded the trough and isolated the Ocala High as an island. Two putative dispersal events are illustrated: N10, cyprinodontid eastward coastal immigration, founding Jordanella floridae on the Ocala High; and N17, Fundulus inland immigration up the Mississippi River, founding Fundulus sciadicus–Plancterus on the Northern High Plains.