The only official sources I've found that explicitly describe Yoda's species don't offer any definite answer to what type of organism he is. That said, here's the relevant information that is offered:
- The New Essential Guide to Alien Species (2006, Legends) characterizes the species based on the examples of Yoda, Yaddle, and Vandar (from Knights of the Old Republic). It describes the species as "bipedal" and "humanoid" and characterizes it as having hair and "gnarled fingers". The only "new" information is a a mention of the species's "strange tastes in food, often consuming meals that others could not even bear to smell", although this could just be in- or out-of-universe extrapolation from Yoda's rootleaf stew.
- Note that its classification as "humanoid" doesn't answer this either way, since explicitly reptilian species such as Duros are also described as humanoid within the same guide.
- The Complete Star Wars Encyclopedia (2008, Legends) doesn't have an entry for it.
- Alien Archive (2019, Canon) doesn't describe the species at all, just listing it under the name "Unknown" and describing its "ancient and secretive nature", then including a biography of Yoda.
Speculatively, it's unlikely that this will ever be answered definitively, for the same reasons that Yoda's species hasn't been explored—George Lucas felt that any definition of Yoda's background would be detrimental to the character, and Lucasfilm under Disney seems to feel the same way.
- Every member of Yoda's species seen so far (Yoda, Yaddle, Grogu, and Legends examples Vandar and Minch) has had hair. On Earth this would imply that they were mammalian.
- Yoda's species also has forward-facing eyes, which in real life (according to Wikipedia) is typically only seen in vertebrates among primates, carnivorous mammals, and birds of prey.
- Note, however, that this isn't necessarily the case in Star Wars—reptilian aliens such as Trandoshans also have forward-facing eyes.
- Yoda's species also has visible ear pinnae, which in real life only exist in mammals.
- Likewise for cheeks.
- We see Grogu eat small animals and eggs in The Mandalorian, and Yoda eats rootleaf stew in The Empire Strikes Back and hunts for meat in the canon comic The Trial of Dagobah. This indicates that the species is omnivorous. This, however, doesn't shed much light on what type of animal the species is, since mammals, reptiles, and birds can all be omnivores.
- In works such as Clone Wars (2003, Legends) and the arc of The Clone Wars on Ilum, where Yoda has been seen in cold environments, he hasn't shown obvious signs of discomfort:
He also sometimes wears a hooded cloak in the cold, which would be of limited use for a cold-blooded creature:
He also uses a blanket on Dagobah, which would be actively unhelpful for a cold-blooded creature near a fire:
From this, it seems likely that Yoda's species is warm-blooded.
Given the evidence that we have, Yoda's species appears to be closer to primates than to any other real-world type of animal. That said, it's unclear whether these similarities were deliberate, or if the creators of these works just gave the species human-like attributes out of familiarity (see TVTropes: Humanoid Aliens).