Evolutionary history '', an
Eocene gar from the
Messel of
Germany '', an Eocene gar from
Fossil Butte,
Wyoming Gars are considered to be the only surviving members of the
Ginglymodi, a group of
bony fish that flourished in the
Mesozoic. They exhibit the slowest known rate of molecular evolution among all jawed vertebrates, with DNA evolving up to a thousand times more slowly than in other groups, which has consequently reduced their rate of speciation. The closest living relatives of gars are the
bowfin, with the gars and bowfin together forming the clade
Holostei; both lineages diverged during the
Late Permian. The closest extinct relatives of gar are the
Obaichthyidae, an extinct group of gar-like fishes from the
Early Cretaceous of Africa and South America, which likely diverged from the ancestors of true gars during the
Late Jurassic. The oldest anatomically modern gar is
Nhanulepisosteus from the Upper Jurassic (
Kimmeridgian) of
Mexico, around 157 million years old.
Nhanulepisosteus inhabited a marine environment unlike modern gars, indicating that gars may have originally been marine fish prior to invading freshwater habitats before the Early Cretaceous. Although most succeeding gar fossils are known from freshwater environments, at least some marine gars are known to have persisted into the
Late Cretaceous, with the likely marine
Herreraichthys known from Mexico and the definitely marine
Grandemarinus known from
Morocco. Gars diversified in
western North America throughout the Early Cretaceous.
Atractosteus and
Lepisosteus had already diverged by the end of the Early Cretaceous, about 105 million years ago. From western North America, gars dispersed to regions as disparate as Africa, India, South America and Europe, and fossil remains of gars were widespread worldwide by the end of the Cretaceous. Several different gar genera survived the
Cretaceous–Paleogene extinction event, although they remained restricted to North America and Europe after this point. One species (
Atractosteus grandei, a relative of the modern
alligator gar) is the oldest known articulated vertebrate specimen of the
Cenozoic, with one fossil specimen dated to just a few thousand years after the
Chicxulub impact, indicating a rapid recovery of freshwater ecosystems. Two short-snouted gar genera,
Masillosteus and
Cuneatus, are known from the
Eocene in western North America and Europe, but disappear shortly afterwards.
Lepisosteus and
Atractosteus show a similar initial distribution and eventual contraction, but both genera dispersed to
eastern North America prior to their disappearance from western North America and Europe, with
Atractosteus also dispersing further south to the
Neotropics. Eastern North America has since served as a vital
refugium for gars, with
Lepisosteus undergoing a diversification throughout it.
Phylogeny The following phylogeny of extant and fossil gar genera was found by Brownstein
et al. (2022): A slightly different phylogeny was found by Cooper
et al (2023): ==Distribution==