Writing Update: Cats, Toba, and the Deccan Traps


Most male tigers on Sumatra have a ruff like this.

Residence on that island may also be why Sumatran tigers are only about half the size of their Siberian and Bengal relatives.

” ‘sup?” — A 3-foot-high adult Maltese mastodon. (Image: Giovanni Dall’Orto via Wikimedia, see license details at link)

It’s called “insular dwarfing” and happened to mammoths, too, believe it or not!

But if you know I’m working on a book about cats and how they evolved, perhaps you’re wondering about recent posts on Toba’s supereruption 74,000 years ago in northern Sumatra and the Deccan Traps flood basalt eruption 66 million years ago that probably contributed to the end-Cretaceous extinction.

There are feline connections to those catastrophes.

Too, evolution is an intricate business. It seldom works in obvious ways, despite all that “descent with modification” and “natural selection” stuff in the basic definition.

When you actually start to look at it in a family of animals, evolution is very complex. I can’t begin to describe it in detail, but I do need to understand a little of it to see where family Felidae comes from.

Ryan Somma, CC BY-SA 2.0

Cats are especially challenging, say paleontologists, because they’re rare in the fossil record and they evolved relatively recently, so not many distinctive physical differences have developed yet to help experts sort through ancient feline species.

Yes, apart from size, house cats and tigers look very much alike under the skin!

In these posts, I’m just exploring a few of the more eye-catching recent events during the roughly 10-million-year-long evolution of modern cats, trying to get a feel for how these beautiful apex predators came to be, while also keeping an eye on major geological events as well as the green world (since, per Martin in the source list below, cats probably evolved in the edge zone where forests meet open land).

Sundaland

Another reason why Toba, in particular, is relevant is that it’s part of one of the world’s two great biodiversity “hot spots” — Sundaland. (The other is South America, also relatively untouched by the modern world and with its own collection of fascinating cats that we’ll meet later this year.)



We’ll also see how conservationists in Indonesia and around the world are working to protect Sumatra’s rainforests and wildlife.


In addition to orangutans and colorful birds, here be multiple lineages of wild cats, big and small. They’re all beautiful and some are downright weird.

Looking at you, flat-headed cat! (Image: Jim Sanderson via Wikimedia, CC BY-SA 3.0)

Besides Sumatran tigers (big cat lineage), there are clouded leopards (also big cats), flat-headed cats and fishing cats (both in the leopard cat lineage), marbled cats (bay cat lineage), and others.

You won’t find Sundaland on today’s political maps, though geographers know it well. It’s the Sundaic portion of Asia’s continental shelf, the part that occasionally emerges above the waves as dry land.

This has happened several times over the last two million years, as an ice age began and the formation of great continental ice sheets lowered global sea level by hundreds of feet.

Geoscientists don’t call it Atlantis, though that would be poetic. The name “Sundaland” comes from the underlying Sunda tectonic plate segment carrying this piece of Earth’s crust (and from the original namesake, the Sunda Islands).

Right now, most of Sundaland is submerged. Its highest peaks look like islands — the Indonesian archipelago (including Sumatra) and Borneo — as well as the Malay Peninsula, which is famous among felinologists for its black leopards, though there are quite a few traditionally spotted ones, too.


Sundaland a little over 20,000 years ago, when continental ice sheets were at their maximum extent. Toba is located in northern Sumatra. (Image: ש.מירון via Wikimedia, CC BY-SA 4.0)

Cats, volcanoes, and forests

So, what do Sundaland, Toba, the Deccan Traps, and family Felidae have in common?

  • At times when the Sunda Shelf was dry land, cats from Asia prowled its mountains, hills, marshy lowlands, and plains. Then, when the ice sheets melted, raising global sea level and flooding the land, they were isolated on islands and evolved in unique ways.

    This is why the Sumatran tiger looks different from Bengal and Amur tigers (there are pictures and video of these and other tiger subspecies in this post), and it’s also the basic idea behind the controversial proposal, described in that post, to have only two subspecies: mainland Asian and Sundaic tigers. (Kitchener et al.)

  • All tigers had a genetic bottleneck around the time of the Toba eruption, and some experts think that isn’t a coincidence.
  • Returning to India for a moment, many epochs after its eruption, the Deccan Traps large igneous province now hosts the largest and smallest members of the cat family.

    Bengal tigers live there in a variety of wooded habitats, but the little cat we’re going to meet tomorrow has only been sighted in the dry deciduous forest setting, as far as I can tell.


    Spoiler: It’s this cutie, only half as big as a house cat. (Image: Jiri Vaclavek, Shutterstock)

  • India and Sumatra have a geological connection. No, really. They do, through plate tectonics.

    It’s a killer connection. And apparently Earth is trying to break it up.


Yes, Australia is involved, too, but I am totally ignoring it here because none of these cats made it that far. (Why not? Like much else in this part of the world, it’s complicated and there is still much to be learned about it.)

One of the effects of that geological connection is Toba, just one of an entire range of volcanoes running along the western Sumatran coast parallel with the subduction trench just off shore.

Don’t worry — they’re not all supervolcanoes like Toba.

Koulakov et al. in the source list suspect that Toba’s massive cataclysms may have been caused by some unique topography of the subduction zone directly below (a seafloor fracture zone descends into the planet underneath Toba).

Still, many of these “non-super” volcanoes, known as the Barisan mountains, are active, and we’ll take a look at a few of them over the next couple of Sundays.

The Barisan Mountains also host what you and I would call jungle, but biologists have another name for it, as we’ll see this coming Tuesday.



That’s the view from above.

But it’s a whole different world on the ground.



So, after one last stop in India to see the world’s smallest cat, we’re going to start our Sundaland adventure and, in a few weeks, get acquainted with this mystery cat!


Featured image: Sumatran tiger, by Tambako The Jaguar, CC BY-ND 2.0.


Sources:

Kitchener, A. C.; Breitenmoser-Würsten, C.; Eizirik, E.; Gentry, A.; and others. 2017. A revised taxonomy of the Felidae: The final report of the Cat Classification Task Force of the IUCN Cat Specialist Group. https://repository.si.edu/bitstream/handle/10088/32616/A_revised_Felidae_Taxonomy_CatNews.pdf

Koulakov, I.; Kasatkina, E.; Shapiro, N. M.; Jaupart, C.; and others. 2016. The feeder system of the Toba supervolcano from the slab to the shallow reservoir. Nature Communications, 7: 12228.

Martin, L. D. 1989. Fossil History of the Terrestrial Carnivora, in Carnivore Behavior, Ecology, and Evolution, ed. Gittleman, J. L., 536-568. Ithaca, NY: Cornell University Press.

Turner, A., and M. Antón. 1997. The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.

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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