# Cockroaches and mammals

**URL:** <https://boards.straightdope.com/t/cockroaches-and-mammals/225768>\
**Category:** Cecil's Columns/Staff Reports\
**Created:** [January 23, 2004, 3:08pm UTC](https://boards.straightdope.com/t/cockroaches-and-mammals/225768 "2004-01-23T15:08:06Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![JohnStracke](https://avatars.discourse-cdn.com/v4/letter/j/58956e/32.png) [@JohnStracke](https://boards.straightdope.com/u/JohnStracke)\
**Post date:** [January 23, 2004, 3:08pm UTC](https://boards.straightdope.com/t/cockroaches-and-mammals/225768/1 "2004-01-23T15:08:06Z")

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SDSTAFF Doug [wrote:](http://www.straightdope.com/mailbag/mcockroach.html)  
In fact, if you exclude birds and mammals, most of the world’s present-day life forms […] date back at least 100 million years.  
Why exclude mammals? Mammals predate the dinosaurs. Granted, we were pretty shrewish until they died off, but still.

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**Author:** ![Kat](https://avatars.discourse-cdn.com/v4/letter/k/b19c9b/32.png) [@Kat](https://boards.straightdope.com/u/Kat)\
**Post date:** [January 24, 2004, 1:46am UTC](https://boards.straightdope.com/t/cockroaches-and-mammals/225768/2 "2004-01-24T01:46:29Z")

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He’s not talking about the existance of mammals as a group, he’s talking about individual species. Sure mammals may have existed back then, but the mammals that exist today don’t resemble the mammals that existed then. Whereas a cockroach today is pretty comparable to a cockroach 250 million years ago.

Ants, flies, beetles, what have you, are pretty similar to ants, flies, beetles or whatever 100 million, or 150 million, or whatever million years ago…while today’s mammals don’t match up the same way to their ancestors.

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**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\
**Post date:** [January 24, 2004, 11:20pm UTC](https://boards.straightdope.com/t/cockroaches-and-mammals/225768/3 "2004-01-24T23:20:43Z")

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> [@Kat](#):
>
> He’s not talking about the existance of mammals as a group, he’s talking about individual species.

Not really (from the article):

> [@](#):
>
> In fact, if you exclude birds and mammals, most of the world’s present-day life forms ( **in general terms, not individual species** ) date back at least 100 million years.

Bolding mine. However, many “present-day” mammalian forms do vary quite a bit from the earliest ratty-looking mammals. The earliest placental mammals are around 125 million years old, so Doug may have been referring specifically to placentals.

And, for the record, mammals don’t really predate dinosaurs, either. Earliest mammal fossils: 220 million years old. Earliest dinosaur fossils: 225-230 million years old. Which also underscores the point about the cockroaches’ 250 million years not being terribly special.