Alligatoridae
Channel: all the knowledge of the universe PRINCIPIA
Date: 2021-12-02

Alligatoridae, by Wikipedia https://en.wikipedia.org/wiki?curid=1380 / CC BY SA 3.0

#Crocodilians
#Alligatoridae
#Taxa_named_by_John_Edward_Gray
#Reptile_families
#Extant_Campanian_first_appearances
#Campanian_taxonomic_families
#Maastrichtian_taxonomic_families
#Danian_taxonomic_families
#Selandian_taxonomic_families
#Thanetian_taxonomic_families
The family Alligatoridae of crocodylians includes alligators and caimans.
A. olseni fore limb Alligator prenasalis fossil The superfamily Alligatoroidea includes all crocodilians （fossil and extant） that are more closely related to the American alligator than to either the Nile crocodile or the gharial.
This is a stem-based definition for alligators, and is more inclusive than the crown group Alligatoridae.
As a crown group, Alligatoridae only includes the last common ancestor of all extant （living） alligators, caimans, and their descendants （living or extinct）, whereas Alligatoroidea,
as a stem group, also includes more basal extinct alligator ancestors that are more closely related to living alligators than to crocodiles or gavialids.
When considering only living taxons （neontology）, this makes Alligatoroidea and Alligatoridae synonymous, and only Alligatoridae is used.
Thus, Alligatoroidea is only used in the context of paleontology.
The below cladogram shows Alligatoridae's relationships to other crocodilians, based on the results of a 2018 tip dating study by Lee & Yates that simultaneously used morphological, molecular （DNA sequencing）, and stratigraphic （fossil age） data.
The below cladogram shows the internal relationships within Alligatoridae: The superfamily Alligatoroidea is thought to have split from the crocodile-gharial lineage in the late Cretaceous, about 87 million years ago.
Leidyosuchus of Alberta is the earliest known genus.
Fossil alligatoroids have been found throughout Eurasia as land bridges across both the North Atlantic and the Bering Strait have connected North America to Eurasia during the Cret...