Mammals:
* Taiga (a type of squirrel)
* Tamaraw (a small, wild buffalo)
* Tamandua (a type of anteater)
* Tamarin (a type of monkey)
* Tapir (a large mammal with a short trunk)
* Tarsier (a small, nocturnal primate)
* Tasmanian Devil (a carnivorous marsupial)
* Tayra (a weasel-like mammal)
* Tenrec (a small, spiny mammal)
* Tiger (a large, carnivorous cat)
* Tortoise (a type of turtle)
Birds:
* Tahr (a type of goat)
* Tailless Whipbird (a bird with a distinctive call)
* Tanager (a brightly colored bird)
* Teal (a type of duck)
* Tegu (a lizard)
Fish:
* Tarpon (a large, silvery fish)
* Tautog (a type of fish found in the Atlantic Ocean)
Insects:
* Tarantula (a type of spider)
* Tsetse Fly (a biting fly that can transmit sleeping sickness)
Other:
* Tapeworm (a parasitic worm)
* Taxidermy (the art of preserving animals)
This list is not exhaustive, but it gives you a good starting point. Keep in mind that many animal names have regional variations or are specific to certain species.