
I think this might be it?
https://www.mangago.zone/read-manga/tensei_shitara_ken_deshita/
Not an animal tho. But it's good and it even has anime (=・ω・=)

Check out these(not all animal):
Please Call Me Red Panda
S-Rank Monster no Behemoth Dakedo, Neko to Machigawarete Erufu Musume no Kishi (Pet) Toshite Kurashitemasu
Evolution Begins With A Big Tree
Mushroom Brave
Shirokuma Tensei
Reborn to the Phoenix It's Not Normal Bird That Can Beat Dragon Right ?
Nyankees
At the Northern Fort
Tensei Shitara Dragon no Tamago Datta - Saikyou Igai Mezasa Nee
(๑•ㅂ•)و✧
Does anyone know any manhwas where the mc gets isekaied and they STAY an animal?