What happened to South America's missing mega-mammals? | Hacker News Reader

What happened to South America's missing mega-mammals?

nytimes.com

49 pointsbookofjoe23 comments

Geologist here! A fun fact that has received some previous discussion [1] here:

Some of these same missing megafauna (likely giant ground sloths) dug an impressive network of several-meter-diameter tunnels through the unusually stable, iron-rich soils of southern Brazil, which survive to this day [2].

You can actually go and walk through these burrows, despite the fact that the species who dug them are long-extinct.

[1] https://news.ycombinator.com/item?id=14014049

[2] https://www.discovermagazine.com/planet-earth/get-lost-in-me...

Totally amazing and wonderful. Though I've only been awake about 30 minutes, I'm willing to go out on a limb and say this will prove to be the best thing I learn today.

Saw the original HN link and was blown away, however there's a question that you as a geologist may be able to answer - how can nails (basically sloth fingernails) possibly compete with anything but soil? This (link 2) looks like sandstone and that's strong (relatively) and damn abrasive. I can't see it.

BTW that can't be soil, it would have collapsed (surely?)

They're soils, but they're special soils [1] that can harden to a brick-like consistency (called a "duricrust") upon being dried out and exposed to the air [2,3].

The unusual durability of such soils has made them a target for study in their own right, using cosmogenic isotopes to estimate erosion rates over Myr timescales (which turn out to be incredibly slow; 0.16–0.54 m/Myr) [4]

[1] https://www.cambridge.org/core/journals/clay-minerals/articl...

[2] https://en.wikipedia.org/wiki/Duricrust

[3] https://www.sciencedirect.com/science/article/pii/S016913681...

[4] https://www.sciencedirect.com/science/article/abs/pii/S00128...

A Most Excellent answer, thanks!

Well, if it's limestone, maybe they used urine.

Too slow. Assuming that was a serious suggestion anyway.

I still think that there are alternative, evident and simpler explanations for this tunnels.

Apparently the avocado is an evolutionary anachronism from the time when North America was populated by megafauna who were big enough to eat the fruit and move the pit around.

https://www.smithsonianmag.com/arts-culture/why-the-avocado-...

Interesting. Do people who research and speculate on such things feel the same about peaches and other large stone fruit?

Peaches, nectarines, apricots, cherries, almonds, and others I missed are all closely related species, and derive from fruit quite a bit smaller than the modern commercial cherry -- and unmarketably sour.

So, no. The only animal that peaches have ever catered to is Homo sap.

As far as I'm aware, only peaches and nectarines are the same species there. They're all in the Prunus genus, but split across several subgenera.

Though it’s definitely true that they’re close relatives.

A prof of Syracuse University has created trees which yield 40 different stone fruits each from almonds through apricots to peaches.

Thank you, corrected.

"The numerous forms grade into each other so imperceptibly and inextricably that the genus cannot readily be broken up into species." -- Liberty Hyde Bailey, 1898

Correct, the peach tree is called Prunus Persicus and was brought by the Romans to Europe from Persia. And the wilder ones are not sour but bitter and have a very distinctive aroma.

Here is a fruit that is common in parts of the United States but was only ever eaten and spread by megafauna. They litter the street around my house, apparently all spread by Mammoths long ago (or by settlers building hedges, I just learned): https://en.wikipedia.org/wiki/Maclura_pomifera

Another one, you've probably walked on its seed pods, that we've distributed even further than the megafuana that presumably ate it: https://en.m.wikipedia.org/wiki/Honey_locust

Quite a number of genera vanished at the end of the Pleistocene, precisely at the start of the Younger Dryas cold spell whose end 1300 years later marks the beginning of the Holocene epoch.

Evidence is accumulating for a multiple-bolide strike that triggered the YD and wiped out those genera, and many others in North America and even Southern Africa, along with the Clovis culture that dominated North America.

References at http://deadlyvoyager.net/References/ . The book, Deadly Voyager, is available free with on Kindle with a Prime subscription, and is a riveting read.

"While the American Interchange took millions of years, Dr. Carrillo said, the advent of industrial humanity has seen exotic species race around the globe, no land bridge required"

On that particular topic, I highly recommend "Super Species: The Creatures That Will Dominate the Planet" by Garry Hamilton. It's as interesting as it's terrifying.

I have had enough 'terrifying' for 2020 and am trying to limit my reading to things that either entertain me or where I can have a positive effect.

A wonderful entertainment: https://www.amazon.com/Once-Future-King-T-White/dp/044162740...

Without consulting it, I guess it is raccoons that will take over the world?

They were eaten. By us.

Reply on news.ycombinator.com