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08-11-2020, 00:34   #106
Adam Khor
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Floated across Bering Strait to North America. Then migrated south? Or island hopped east across south Pacific? Kon-Tiki hadrosaurs?


Unsure about continental drift 65 million plus years ago.

Asia and North America were connected by land (the so called Beringian land bridge) for most of the Cretaceous; dinosaurs would've walked from one continent to the other.

On the other hand, there's no evidence thus far of a land bridge between North and South America at the time. Hadrosaur remains are very common in Mexico, however, including those of Kritosaurus (the South American hadrosaurs are very much like Kritosaurus, with the better known being Kritosaurus australis (=Secernosaurus?), so they probably did island-hop, swim or float to South America from what is today Mexico.
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11-11-2020, 21:16   #107
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On the other hand, there's no evidence thus far of a land bridge between North and South America at the time. Hadrosaur remains are very common in Mexico, however, including those of Kritosaurus (the South American hadrosaurs are very much like Kritosaurus, with the better known being Kritosaurus australis (=Secernosaurus?), so they probably did island-hop, swim or float to South America from what is today Mexico.

Higher ocean levels? Smaller polar caps? Wonders if the same will occur with continued global warming?
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12-11-2020, 20:01   #108
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Higher ocean levels? Smaller polar caps? Wonders if the same will occur with continued global warming?
Yes, around 250 m higher than today's sea levels, on average, IIRC.

Here's National Geographic's take on what the world is heading to if the current global warming trend continues. You can see Central America becomes practically a chain of islands- eventually, both Americas could indeed become isolated again.

Interesting to see that the Amazon would again be connected to the Atlantic, as it was originally back in the days of the giant caiman Purussaurus.

https://www.nationalgeographic.com/m...horeline-maps/
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12-11-2020, 20:56   #109
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Yes, around 250 m higher than today's sea levels, on average, IIRC.

Here's National Geographic's take on what the world is heading to if the current global warming trend continues. You can see Central America becomes practically a chain of islands- eventually, both Americas could indeed become isolated again.
Read about various climate change models. One or more suggested that global warming would not be a simple straight line event. Rather, there may be a tipping point. Beyond which change may go up geometrically. From gradual to more sudden and consequential. Cannot remember the source. Perhaps from materials promulgated by Al Gore.



Would hadrosaurs float without the aid of swimming? Then move their legs and tail to navigate?
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12-11-2020, 23:20   #110
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Would hadrosaurs float without the aid of swimming? Then move their legs and tail to navigate?
I would imagine they'd use their legs when swimming, but they really weren´t made for it so to speak- the idea of aquatic hadrosaurs has long been out of favor.

The hadrosaur tail was very rigid, held stiff by special ossified tendons. This made the tail useful for counterbalance and maybe for defense, but it was not flexible enough to aid in swimming like that of a lizard or a crocodile.

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12-12-2020, 06:22   #111
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Famous hadrosaur Parasaurolophus reexamined. The paper includes an analysis not only of the Parasaurolophus holotype but also of the animal's portrayals in paleoart throughout the years. The most interesting find is that the "saddle" or kink on the anterior spine of the holotype is actually a pathological feature, likely caused by a heavy object, possibly a tree, that fell on top of the animal at some point.

https://onlinelibrary.wiley.com/doi/...OqaeOY.twitter

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14-01-2021, 22:09   #112
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Wonder why Hadrosaurs were so prolific?
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15-01-2021, 02:17   #113
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You mean prolific as a group, as in speciose, or prolific regarding the number of eggs they lay?

The key to their success as a group has often been suggested to be their masticatory apparatus, which was pretty sophisticated for a reptile. They had "dental batteries" consisting of many rows of teeth (hundreds of them) which were constantly being worn down and replaced, a little bit like shark teeth (except instead of falling out they'd be reabsorbed when worn out and new ones would erupt to occupy their place). This ensured that hadrosaurs were never left toothless (unlike say, elephants, which have only six sets of molars during their lives and often die of starvation once they have worn the last one).



The dental batteries functioned as a grinding surface, like a mammal's molars, allowing them to process hard, fibrous plant material that other dinosaurs could not eat (most plant-eating dinosaurs either had very simple masticatory capabilities, or none at all, using their beak or front teeth to crop vegetation and basically swallowing it whole).

This would have allowed hadrosaurs to feed on a wide array of foods and fill ecological niches with very little competition. Another advantage they had was their large size and the ability to stand on their hind legs to reach food located at 4 m above ground or more, again minimizing competition with other dinosaurs (the golden age of hadrosaurs was the late Cretaceous, when sauropods had become rare in the Northern Hemisphere. Perhaps it is no coincidence that hadrosaurs, although certainly present in South America, for example, never became as abundant and speciose as they did in the north; sauropods were very much still in business in the southern hemisphere all the way to the KT extinction).

As for why they lay so many eggs, I'd imagine for the same reasons ostriches, crocodiles and turtles do- to increase chances of survival of at least some of the clutch. Baby hadrosaurs also grew very rapidly to minimize their chances of being eaten by smaller predators.

Last edited by Adam Khor; 15-01-2021 at 20:31.
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15-01-2021, 18:46   #114
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Thanks Adam for indepth answer. Something I could sink my teeth into.
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29-01-2021, 01:08   #115
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Well preserved skull of a Parasaurolophus found. The skull is interesting because it belonged to a juvenile and shows exactly how the iconic animal's crest was formed. It also confirms the short-crested Parasaurolophus cyrtocristatus as a valid species (the long-crested Parasaurolophus walkeri is the one most often depicted in popular media).


http://www.sci-news.com/paleontology...tus-09292.html

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