# What Is The Closest Non-Mammal Relative To Humans That Is Still Alive? **URL:** \ **Category:** Factual Questions\ **Created:** [July 3, 2022, 11:23pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362 "2022-07-03T23:23:42Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![SmartBulbInc](https://avatars.discourse-cdn.com/v4/letter/s/7cd45c/32.png) [@SmartBulbInc](https://boards.straightdope.com/u/SmartBulbInc)\ **Post date:** [July 3, 2022, 11:23pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/1 "2022-07-03T23:23:42Z")
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? ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [July 3, 2022, 11:34pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/2 "2022-07-03T23:34:36Z")
All birds and reptiles are equally close relatives to humans [Sauropsida](https://en.wikipedia.org/wiki/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. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [July 4, 2022, 6:56am UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/3 "2022-07-04T06:56:43Z")
@Andy_L got it in one. > [@SmartBulbInc](#): > > how do we know it is the closest living relative for sure? Nowadays? [Computational phylogenetic analysis](https://en.wikipedia.org/wiki/Computational_phylogenetics), mostly. It’s a _very_ deep field. ---
**Author:** ![iiandyiiii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/iiandyiiii/32/7924_2.png) [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)\ **Post date:** [July 4, 2022, 12:20pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/4 "2022-07-04T12:20:17Z")
Do we know what that most recent common ancestor of mammals, birds, and reptiles looked like? ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [July 4, 2022, 12:56pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/5 "2022-07-04T12:56:06Z")
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. > **[Casineria](https://en.wikipedia.org/wiki/Casineria)** > > Pages for logged out editors learn more > > > Casineria is an extinct genus of tetrapod which lived about 340-334 million years ago in the Mississippian epoch of the Carboniferous period. Its generic name, Casineria, is a latinization of Cheese Bay, the site near Edinburgh, Scotland where the holotype fossil was found. When originally described in 1999, it was identified as a transitional fossil noted for its mix of basal (amphibian-like) and advanced (reptile-like) characteristics, puttin... ---
**Author:** ![ASL\_v2.0](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asl_v2.0/32/3525_2.png) [@ASL\_v2.0](https://boards.straightdope.com/u/ASL_v2.0)\ **Post date:** [July 4, 2022, 1:17pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/6 "2022-07-04T13:17:26Z")
We’re all just fish out of water in the end. ---
**Author:** ![What\_Exit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/what_exit/32/10652_2.png) [@What\_Exit](https://boards.straightdope.com/u/What_Exit)\ **Post date:** [July 4, 2022, 1:31pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/7 "2022-07-04T13:31:08Z")
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. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [July 4, 2022, 1:58pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/8 "2022-07-04T13:58:05Z")
That’s like saying that the cousin who’s most closely related to me is the one who looks most like Gramma and Grandpap. ---
**Author:** ![MrDibble](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mrdibble/32/114_2.png) [@MrDibble](https://boards.straightdope.com/u/MrDibble)\ **Post date:** [July 4, 2022, 2:43pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/9 "2022-07-04T14:43:43Z")
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. ---
**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\ **Post date:** [July 4, 2022, 2:57pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/10 "2022-07-04T14:57:20Z")
> [@Chronos](#): > > That’s like saying that the cousin who’s most closely related to me is the one who looks most like Gramma and Grandpap. 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. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [July 4, 2022, 3:17pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/11 "2022-07-04T15:17:55Z")
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. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [July 4, 2022, 5:56pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/12 "2022-07-04T17:56:53Z")
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. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [July 4, 2022, 8:38pm UTC](https://boards.straightdope.com/t/what-is-the-closest-non-mammal-relative-to-humans-that-is-still-alive/967362/13 "2022-07-04T20:38:13Z")
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.