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[creature386]

Nov 9, 2023 3:08:31 GMT 5 Exalt said:

1.Why is it called the KPG event and not the CPG event?

The Cretaceous is named "Kreidezeit" in German which is where the "K" comes from. I suppose that "C" is avoided to avoid confusing it for the Carboniferous or the Cambrian.

[Exalt]

How might Glyptodonts have nursed? Given how close their bodies are to the ground, I would think that the young would not have clearance for their armor, and the adult would probably struggle if they tried to get on their side or back. I could be entirely wrong here

[Infinity Blade]

That's one of those paleontology questions we don't ask nearly as often as we should. So, this is going to sound weird, but it's possible glyptodonts (at least some taxa?) could have reared up on their hindlimbs and let their babies suckle (Elissamburu, 2015). Here's a piece by Rodrigo Vega illustrating this.




So my question we don't ask nearly as often as we should is, how did azhdarchids sleep? What pose did they adopt?

[Exalt]

That art was actually the only thing on the subject that I could find whatsoever. I guess it could work if the tail is heavy enough that they could maintain the position?

Your question feels like if my question was a boss fight, and then you get past it and suddenly there's a more menacing one. I'm so tempted to just ask Darren Naish about this one. There really is not a good modern comparison to something as derived as an azhdarchid. How strong are the forelimbs, for one?

[theropod]

Nov 22, 2023 8:32:30 GMT 5 Infinity Blade said:

That's one of those paleontology questions we don't ask nearly as often as we should. So, this is going to sound weird, but it's possible glyptodonts (at least some taxa?) could have reared up on their hindlimbs and let their babies suckle (Elissamburu, 2015). Here's a piece by Rodrigo Vega illustrating this.

That’s a cool concept I thought I could briefly try to test:

Here’s a simplistic model based on this skeleton: www.zoochat.com/community/media/glyptodon-skeleton.258832/full?d=1401839112

quadruped version/rearing version (not precisely to scale; if to scale, the dorsal views should have the same maximum width):


For simplicity’s sake and since I found no top view I am assuming the shell is circular in cross-section in the normal, horizontal pose.

From that we can estimate center of mass (see the vertical line):
quadruped version:


rearing version:


This is of course very simplified; I didn’t include the limbs, for instance, and in reality the shell is not perfectly circular but rather opens on the bottom (though I think this should not impact horizontal COM estimation much as it is true throughout the body and also might not have much of an effect on mass). However it does suggest that due to the shape of the shell (quite "globular" but tapering somewhat towards the front) it would be quite feasible for a glyptodont to rear up onto its hindlimbs, as it looks like getting the COM placed above the feet shouldn’t be much of an issue (it looks to be quite close to the posterior rim of the shell in the rearing model).

In case you’re wondering, I didn’t have a scale in the images, so I can’t give you a mass estimate here. But assuming pixels are equivalent to millimeters (which would put the quadrupedal model at around 2.5 m total length), it would be about 1.4 t for both the quadruped and rearing models, which I believe is at least reasonably within Glyptodon’s expected size range (there is a difference of about 40 kilos between the two models due to the change in the body axis and segment boundaries relative to the axis of slicing, which is not entirely avoidable with this technique, but also fairly minor. The quadrupedal model is likely the more accurate one and it’s about 1360 kg at 252 cm).

[Exalt]

I don't think I entirely understand the model, but a cursory search suggested that more people believe that they could stand on two legs, even the larger Doedicurus. (I actually learned during this process that Glyptodonts vary more in size than I would have thought...)

This would probably also be a factor in my previous question about how Glyptodonts would have mated.

My next question might seem odd, but is there any evidence of extant species being predated upon by extinct ones, back when they were around?

[mechafire]

Nov 23, 2023 19:21:25 GMT 5 Exalt said:

I don't think I entirely understand the model, but a cursory search suggested that more people believe that they could stand on two legs, even the larger Doedicurus. (I actually learned during this process that Glyptodonts vary more in size than I would have thought...)

This would probably also be a factor in my previous question about how Glyptodonts would have mated.

My next question might seem odd, but is there any evidence of extant species being predated upon by extinct ones, back when they were around?

Smilodon populator ate broad-snouted caimans


Dantas et al. 2018. Integrative isotopic Paleoecology (δ13C, δ18O) of a Late Pleistocene vertebrate community from Sergipe, NE Brazil

[Exalt]

Wait, they think that S.populator could have hunted Eremotherium?

[Infinity Blade]

Well, it also lists Notiomastodon, which weighed 6,300 kg according to their estimation. I don't think they'd actually argue that Smilodon populator went after adult proboscideans as heavy as modern bush elephants, nor do I think it could go after healthy adult ground sloths >3 tonnes.

Interestingly, one of the Eremotherium individuals they examined was from a juvenile, perhaps a suckling. Its carbon isotope signatures were not different from those of the adults. That makes sense, considering how it would feed on milk from its mother, resulting in their isotope signatures being about the same. So the megaherbivore signatures (like elephants and ground sloths) could easily be from young individuals (in fact I think that's more likely than predation on adults).

[Exalt]

I forgot about the obvious answer of it being juveniles at the time. I was a bit bewildered, because it seemed that somehow, we'd circled back to Smilodon hunting something that's possibly in an elephants weight class.

(And in a certain show that we're familiar with, a Smilodon tries to fight an Eremotherium's cousin, and, well...)

[mechafire]

Carbon isotope analysis also shows what an animal ate, not how it got its meals. So it's possible larger bodied animals were scavenged or killed via pack hunting. What I think is interesting is just how much caimans these Smilodons had in their diet: around 10 percent. It seemingly implies a rather jaguar-like animal.

[Exalt]

For those who believe in Smilodon's canines as being fragile, how would they believe that it would go after the caimans? Since it would not be able to bite them in the back of the head/neck the same way.

[Infinity Blade]

Smilodon canines can stab through bone if necessary (e.g. the cranium of another Smilodon), so they're definitely not as fragile as they're often made out to be (the truth of the matter is that they're more fragile *in certain directions*, particularly side-to-side stress). That said, it probably does make sense for it to not routinely stab into the osteoderms or bones of a caiman when hunting, lest its teeth become worn over time. Honestly, given how Smilodon populator was so much more powerful than a modern jaguar, it could probably overpower a broad-snouted caiman enough to flip it on its back and expose the throat for a bite.

[Exalt]

Nov 26, 2023 7:04:58 GMT 5 Infinity Blade said:

 Honestly, given how Smilodon populator was so much more powerful than a modern jaguar

TFW I really almost asked what the technical basis for this premise is, and then I compared the weights.

[Infinity Blade]

Nov 26, 2023 7:27:31 GMT 5 Exalt said:

Nov 26, 2023 7:04:58 GMT 5 Infinity Blade said:

 Honestly, given how Smilodon populator was so much more powerful than a modern jaguar

TFW I really almost asked what the technical basis for this premise is, and then I compared the weights.

Also have a look here. Left is a jaguar (yes, the modern big cat used for comparison just so happened to be it), right is Smilodon fatalis. Look how much thicker the cortical bone is in Smilodon's upper arm bone (Meachen-Samuels & Van Valkenburgh, 2010).