Gavialoidea is
cladistically defined as
Gavialis gangeticus (the
gharial) and all
crocodylians closer to it than to
Alligator mississippiensis (the
American alligator) or
Crocodylus niloticus (the
Nile crocodile). As a crown group, Gavialidae only includes the
last common ancestor of all
extant (living) gavialids and their descendants (living or
extinct), whereas Gavialoidea, as a
total group, also includes more
basal extinct gavialid ancestors that are more closely related to living gavialids than to
crocodiles or
alligators. When considering only living taxa (
neontology), this makes Gavialoidea and Gavialidae
synonymous, and only Gavialidae is used. Thus, Gavialoidea is only used in the context of
paleontology. Traditionally, crocodiles and alligators were considered more closely related and grouped together in the taxon
Brevirostres, to the exclusion of the
gharials. This classification was based on
morphological studies primarily focused on analyzing skeletal traits of living and extinct fossil species. However, recent molecular studies using
DNA sequencing have rejected Brevirostres upon finding the crocodiles and gavialids to be more closely related than the alligators. The new clade
Longirostres was named by Harshman
et al. in 2003. ==References==