How long do you think it took animals to colonize all of the earth? I imagine they may have been limited to small stretches of ocean at first. The poles and other frozen territories may have been avoided until endothermic evolved?
The earliest known members of Animalia, sponges, seem to have actually evolved during the Cryogenian period and the “Snowball Earth” glaciations – suggesting that cold conditions probably weren’t much of a problem for early animals, and might even have driven their evolution in the first place. I’d guess they probably spread pretty much everywhere in the oceans soon after they first appeared.
We even have some fossil evidence of ancient polar communities. There are mid-Ordovician (~465 mya) deposits from Portugal – which was near the south pole at the time – full of animals like giant trilobites, cephalopods, graptolites, hyoliths, gastropods, bivalves, brachiopods, and echinoderms.
Plus there were plenty of periods in Earth’s history when the polar regions weren’t nearly as frigidly cold as they are today, so even if we narrow things down to just terrestrial vertebrates there were still opportunities for animals to hang out at the poles without strictly having to be endothermic like modern polar tetrapods. The giant temnospondyl amphibian Koolasuchus is known from then-polar Australia during the Early Cretaceous, for example.
Every once in a while I remember that baby salmon are called smolts and I will think about it for like 5 hours. For once I’m not exaggerating like I’ll stop working every 20 minutes or so just to look at nothing and imagine an anonymous person saying ‘smolts’ with an echo chamber effect.
So I did a survey of my dormouse boxes yesterday. For those what don’t do Conservation for a living and so are unfamiliar, dormouse boxes are like bird boxes that have a hole in the back rather than the front and you put them on trees at chest height. Over the winter, mice will move in and hibernate, but they have a sort of revolving occupancy; the mice vacate in spring when their lease expires, and the birds move in instead, before leaving again in the middle of summer. But of course, many things actually live in the boxes. The most exciting thing I personally ever found was a pygmy shrew, UKvia’s smallest mammal and about the size of a thumb.
Anyway, ‘tis bird season, so I was looking for chicks. The first box I checked is always my same one when I do this, because it’s close to the path and almost always occupied, and when I opened the lid this time it was no exception; it was full of fresh moss. Except, that usually means mice? And for those what don’t do Conservation for a living and so are unfamiliar, the way you check for a mouse is to just shove your fingers inside and see if you feel fur, and if it’s a dormouse it’ll just wiggle a bit and if it’s a woodmouse it will probably remove your fingertip because they are bitey fucks.
So, in accordance with Standard Procedures, I shoved a finger inside, and to my surprise given the time of year, I felt fur.
Amazing, right?? In May! And it was really, really warm, so it wasn’t an old dead one, either. So I had to carefully pull the moss aside to see if I could find the mouse and thus record a species.
And thus it was that I pulled back the top layer of moss and came face to face with bees. Bumblebees. Furry little bumblebees, completely bewildered at the presence of a giant who was apparently coming to pet them all. I had just shoved my hand into a live bumblebee nest. I’d felt bees. Just poked a bee.
I put the moss back and closed the box and left, obviously.
The next box I opened literally contained four woodmice. I have no fucking idea what is going on with them boxes.
(But of course, I did find birbs too.)
Final tally: two boxes of bees (yes I did shove my hand in both), one box of mice, five boxes empty, and the rest full of birbs.