Interdigital webbing

In oryzomyines, a mainly South American rodent group, the marsh rice rat, Pseudoryzomys simplex, and Sigmodontomys alfari all have small webs, which do not extend to the end of the proximal phalanges, whereas Amphinectomys savamis, Lundomys molitor and the members of the genera Holochilus and Nectomys have more expansive webbing, which extends beyond the proximal phalanges.

[7] Webbing is also present in the Australasian semiaquatic hydromyines (subfamily Murinae) of the genera Baiyankamys, Hydromys,[8] and Crossomys; in the latter, it is most well-developed.

[9] The African semiaquatic rodents Colomys goslingi and Nilopegamys plumbeus, also members of the Murinae, lack interdigital webbing.

[10] Webbing is present in the hind feet of the coypu (Myocastor coypus) of South America,[11] which is currently classified in its own family.

[15] Pits present on the sides of fossil proximal phalanges of pakicetids, ancestral whales, suggest that these animals had interdigital webbing,[16] a development hypothesized to lead to the fluke,[17] spurred by FGF8, a fibroblast growth factor.