Draft: Finishing Up the Precambrian, Part 1

This feline giant, apparently based in Antarctica, is pawing at the 3-billion-year-old cratons of Madagascar.

There are at least two more — the Kaapvaal and Zimbabwe cratons — directly across that narrow strait, on mainland Africa.

What’s a craton?

Basically, it’s a continental nucleus that formed 2 to 3-plus billion years ago and somehow has survived down through time. These ancient relics fascinate geologists.

Madagascar did undergo a major change when it was split up by plate tectonics towards the end of the last Dinosaur Age.

The island’s now-missing half, the Western Dharwar Craton (Rogers and Santosh), stuck to the Indian subcontinent — see that, in the right upper corner of that picture? — and zoomed northward, smashing into Asia.

What’s a cat?

Well, that’s what we’re here to find out.

Did the first animals evolve on cratons?

Probably not, although some paleontologists suggest that the ancestors of today’s carnivores, hoofed plant-eaters like horses and deer, and rodents might have evolved on the Indian “ark” and then stepped off it, dispersing throughout Asia and, eventually, across the rest of the world over land bridges. (Beard)

That’s just one hypothesis about evolutionary events that happened tens of millions of years ago — “late last week,” in geological terms, with today being “Monday.” As we’ll see later in the series, there are other views on where carnivores come from.

Most experts agree, though, that animals as a group (technically, metazoans) evolved in the sea.

Exactly when that happened isn’t clear, but some sources date it back at least 1 billion years. (Source)

We’ll look at that more closely next week.

Cratons do preserve evidence of early forms of life, and they certainly were around at the dawn of Eukarya: a biological domain that eventually developed animals, vegetables, and — fungi?! (Knoll, 2014; Rogers and Santosh)

But we’ll be here all day if we try to cover evolution AND more than 4 billion years of Earth changes (that’s how long the Precambrian lasted).

So let’s just focus on Madagascar today with this simple video showing that plate tectonics and life are intertwined, and how scientists have tried to figure it all out.

They present only one of many models for what Earth might have been up to during the Precambrian — supercontinents before Pangea are a hot research topic (no pun intended) — but it’s a common model.

It’s also good background for future posts.

For instance, a little later in the series, we’ll watch cats — however they arrived in Asia — spread, but only over the Northern Hemisphere. Why?

This video shows why: because they couldn’t swim.

Pangea was breaking apart then, and cats started out on the remains of Laurentia (Asia). Seas separated them for a long time from the Gondwanan continents of Africa and South America.

Yes, in geologic terms, lions are recent immigrants to Africa! (Werdelin et al.)

The visuals are gorgeous, but it doesn’t get into Precambrian biology at all; I’ll do that over the next few days in a cat-related way.

This video is almost an hour long, but it has about 1.5 million views at time of writing. Because of plate tectonics, the cratons mentioned above, like many others, have roamed the Earth’s surface for billions of years, either on their own or as a part of a continent or supercontinent. Around and eventually on them, the entire history of terrestrial life has played out.

To most of us, the Precambrian is like that white area on old maps, filled with sketchy monsters and bearing the legend “Here be dragons.”

This eon covering more than 80% of Earth’s history isn’t much better known to scientists.

They are trying their best to fill in the blanks, but it can be quite a tangle for the curious layperson, since there’s very little consensus about almost anything.

Fortunately, we’re just interested in where cats come from. That allows us to focus on just a few points.

Not those points! (Image: Lottie, public domain)

Next time: Cats and Eukarya.

Featured image: Mallika Home Studio/Shutterstock

Sources: Full list will come at end of “Finishing Up the Precambrian.” Specific references in this section:

Beard, K. C. 1998. East of Eden: Asia as an important center of taxonomic origination in mammalian evolution. Bulletin of the Carnegie Museum of Natural History, 34: 5-39.

Knoll, A. H. 2014. Paleobiological perspectives on early eukaryotic evolution. Cold Spring Harbor Perspectives in Biology, 6(1): a016121.

Rogers, J. J., and Santosh, M. 2004. Continents and Supercontinents. Oxford University Press. PDF

Werdelin, L.; Yamaguchi, N.; Johnson, W. E.; and O’Brien, S. J.. 2010. Phylogeny and evolution of cats (Felidae), in Biology and Conservation of Wild Felids, eds. Macdonald, D. W., and Loveridge, A. J., 59-82. Oxford: Oxford University Press.

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