When we think about “human relative” we almost always think of the great apes, monkeys, or small rodents. However, because all life on earth is biologically related (no matter how distant) it than stands to reason that humans would have a “closest” living relative that is not a mammal. What species is this, how long ago did they “split” from the human family tree, and how do we know it is the closest living relative for sure?
All birds and reptiles are equally close relatives to humans
Sauropsida (which include birds and reptiles are a sister group to mammals - and everything that’s non-mammalian but closer to us than the Sauropsida are extinct.
Looks like they separated from mammals (and thus humans) 300 million years ago.
@Andy_L got it in one.
Nowadays? Computational phylogenetic analysis, mostly. It’s a very deep field.
Do we know what that most recent common ancestor of mammals, birds, and reptiles looked like?
When you go back that far it’s hard to tell whether something is close to the trunk of the family tree of modern species or on a dead end side branch, but things looked pretty lizard like well after the split between the amniotes that are our ancestors and ancestors of the lizards and birds.
We’re all just fish out of water in the end.
Maybe I’m getting this wrong, but of the Sauropsida class I thought the crocodilians were the closest to the common ancestor of the mammals?
Basically, the crocodiles have remained the least changed.
They’re also the closest relatives of the birds.
That’s like saying that the cousin who’s most closely related to me is the one who looks most like Gramma and Grandpap.
Yes, that.
And in any case, lizards/snakes split off before turtles, crocs & dinos, so I don’t see how it can be argued crocs are closer to mammals than other Sauropsids are in any sense. I mean, all archosaurs are equally close, I don’t see the logic in singling out crocs.
Equivalently, suppose that there was a language which we will refer to as A which was spoken 2000 years ago, but no current person speaks. There are five languages today that are clearly derived from A, which we will refer to as B, C, D, E, and F. B is more like A than the others, although it’s different enough to clearly be a different language. It just happened to change less in the past 2000 years than C, D, E, and F did. That doesn’t necessarily make B the closest language to any one of C, D, E, and F.
Yeah, that’s the analogy I was going to go with. Lithuanian apparently retains a lot of proto-Indo-European features - but that is irrelevant to determining whether Lithuanian is more closely related to French or English.
Another way of putting it is that every living species on Earth is a modern species, even if some look more similar to their distant ancestors than others. Contemporary horshoe crabs are entirely as modern as apes.
The way I would say it is that the last common ancestor of the reptiles and mammals likely had as many reptilian descendants as mammalian descendants. Every mammal bears the same relation to every reptile; namely through that last common ancestor.