Why have so few paleo-Indian skeletons been found?

Question

I recently read Charles C. Mann's 1491: New Revelations of the Americas Before Columbus, Second Edition, and was intrigued by the footnote on page 174:

[Aleš] Hrdlička's complaint about the lack of skeletal evidence [at Clovis] was unfair for another reason: paleo-Indian skeletons are extremely rare. In Europe, archaeologists have discovered scores of skeletons ten thousand years old or more. By contrast, fewer than a dozen reasonably complete skeletons of similar age have been found in North America (a few more exist in South America, although, as with the Lagoa Santa skeletons, their provenance is often unclear). "It's a big mystery why we don't find the burials," the University of Vermont archaeologist James Petersen told me. "Some Indians will tell you that their dead all moved to a spiritual plane, and that's about as good as any answer that we've got."

I've Googled for more information about this (searches like rarity of paleo-Indian skeletons), but what I've found has just left me with more questions. For example:

"Paleoamerican skeletons are rare for several reasons," [James] Chatters said. "The people themselves were few; they were highly nomadic and seem to have buried or cremated the dead where they fell, making the locations of graves unpredictable; also, geologic processes have destroyed or deeply buried their graves." [link]

These statements seem possible, but seem to be at odds with Mann's footnote (and with his thesis more generally).

I obviously don't expect that anyone here can authoritatively answer this, since there seems to be at least some disagreement and doubt; but I wonder what the status of the question is: what the major theories are, what the evidence for them is, how big the different "camps" are?

Answer 1

20th C. Answer: No People to Leave Remains

The Clovis first hypothesis states that the Clovis people were the first Native Americans, and that the arrived in North American around 12,000 BC via an ice free corridor in Alaska / Canada. We would not expect many Native American remains older than 10,000 years because Native American populations would have been small at such an early point in their history.

This theory has been seriously challenged by various finds that point to a human presence around 15,000 BC in the Americas - identifying potential ice free travel corridors in the time period is challenging, since the Ice Age is still in full swing.

21 C. Answer: Taken by the Sea

The Coastal Migration hypothesis proposes that the Americas were populated around 15,000 BC by a kind of early maritime culture - the people fished and traveled by boat. They did not require an ice free travel corridor because they "island hopped" and used the ice shelf and open coastline.

These first Native Americans would have lived in coastal areas which have since been flooded - there was a rapid sea level rise around 14,000 BC as ice sheets collapsed and even as recently as 12,000 BC sea levels around Alaska were 60m below the current height.

Thus many of these early sites might be miles off shore, and very much inaccessible to modern archeologists.

The rare inland finds we have from these time periods likely represent pioneers moving inland via rivers, and thus Clovis might be an offshoot of one or more of these inland groups.