What is the difference between a crocodile and an alligator?

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1. 1

   Crocodylia (Wikipedia)

   WikipediaPublished Oct 16, 2026Checked Oct 17, 2026

   “Crocodylia or Crocodilia () is an order of semiaquatic, predatory reptiles that are known as crocodilians. They appeared 83.5 million years ago in the Late Cretaceous period (Campanian stage) and are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Members of the crocodilian total group, the clade Pseudosuchia, appeared about 250 million years ago in the Early Triassic period, and diversified during the Mesozoic era. The order includes the true crocodiles (family Crocodylidae), the alligators and caimans (family Alligatoridae), and the gharial and false gharial (family Gavialidae). Although the term "crocodiles" is sometimes used to refer to all of these families, the term "crocodilians" is less ambiguous. Extant crocodilians have flat heads with long snouts and tails that are compressed on the sides, with their eyes, ears, and nostrils at the top of the head. Alligators and caimans tend to have broader U-shaped jaws that, when closed, show only the upper teeth, whereas crocodiles usually have narrower V-shaped jaws with both rows of teeth visible when closed. Gharials have extremely slender, elongated jaws.”

2. 2

   Expanded phylogeny elucidates Deinosuchus relationships, crocodylian osmoregulation and body-size evolution.

   Communications biology (Walter et al.)Published Apr 23, 2025Checked Oct 17, 2026

   “We present an expanded phylogeny with increased spatiotemporally coherence that reinterprets species of Deinosuchus as stem-group crocodylians together with further putative alligatoroids, Leidyosuchus canadensis and the European Diplocynodon spp. (closely related to North American Borealosuchus). The novel topology elucidates the evolution of osmoregulation in Crocodylia and its close relatives by inferring plesiomorphic saltwater tolerance for Deinosuchus and the crown-group as well as secondary loss already in stem-group alligatorids. Divergence of Alligatoroidea coincided with extreme mid-Cretaceous sea level highs and the distribution of Deinosuchus across the Western Interior Seaway can be best explained by marine dispersal. Phylogenetic body-length analysis using a head-width proxy reveals phyletic dwarfism early in alligatoroid evolution and a reasonable total length estimate for the most complete specimen of Deinosuchus riograndensis. We find that gigantism in crocodyliforms is correlated with high-productive extensive aquatic ecosystems in the present and the past.”

3. 3

   Ontogenetic variability of the intertympanic sinus distinguishes lineages within Crocodylia.

   Journal of anatomy (Perrichon et al.)Published Jan 29, 2023Checked Oct 17, 2026

   “The phylogenetic relationships within crown Crocodylia remain contentious due to conflicts between molecular and morphological hypotheses. However, morphology-based datasets are mostly constructed on external characters, overlooking internal structures. Here, we use 3D geometric morphometrics to study the shape of the intertympanic sinus system in crown crocodylians during ontogeny, in order to assess its significance in a taxonomic context. Intertympanic sinus shape was found to be highly correlated with size and modulated by cranial shape during development. Still, adult sinus morphology distinguishes specimens at the family, genus and species level. We observe a clear distinction between Alligatoridae and Longirostres, a separation of different Crocodylus species and the subfossil Malagasy genus Voay, and a distinction between the Tomistoma and Gavialis lineages. Our approach is independent of molecular methods but concurs with the molecular topologies. Therefore, sinus characters could add significantly to morphological datasets, offering an alternative viewpoint to resolve problems in crocodylian relationships.”

4. 4

   Structure and evolution of the embryonic cartilaginous skull of crocodilians.

   Royal Society open science (Fernandez & Werneburg)Published Nov 5, 2025Checked Oct 17, 2026

   “We identified both qualitative and quantitative differences between major crocodilian clades, which may reflect diverse ecological demands. Within Crocodylidae, orbitotemporal proportions strongly influence chondrocranial morphology, likely reflecting adaptations related to bite force and visual acuity, linked to prey type and diverse aquatic habits. Within Alligatoridae, by contrast, the emphasis on nasal capsule proportions suggests a reliance on olfactory and respiratory functions, consistent with their occupation of densely vegetated environments and more restricted geographic ranges. Additionally, we identified a set of embryonic diagnostic features located in the splanchnocranium of Caiman and in the neurocranium of Alligatoridae. These findings shed new light on the developmental basis of cranial diversity in Crocodylia and emphasize the evolutionary significance of chondrocranial traits in shaping macroevolutionary patterns.”