Re: Devonian origin of amniotes.

On 5/21/25 11:58 AM, x wrote:

On 5/14/25 17:01, erik simpson wrote:

The split between synapsids (us) and sauropsids (reptiles) has generally though to have happened in the Carboniferous ~350 Mya.  New trackways found in Australia suggests that the split occurred in the Devonian, about 35-40 My earlier.
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https://www.nature.com/articles/s41586-025-08884-5
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Earliest amniote tracks recalibrate the timeline of tetrapod evolution
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Abstract
The known fossil record of crown-group amniotes begins in the late Carboniferous with the sauropsid trackmaker Notalacerta1,2 and the sauropsid body fossil Hylonomus1,2,3,4. The earliest body fossils of crown-group tetrapods are mid-Carboniferous, and the oldest trackways are early Carboniferous5,6,7. This suggests that the tetrapod crown group originated in the earliest Carboniferous (early Tournaisian), with the amniote crown group appearing in the early part of the late Carboniferous. Here we present new trackway data from Australia that challenge this widely accepted timeline. A track-bearing slab from the Snowy Plains Formation of Victoria, Taungurung Country, securely dated to the early Tournaisian8,9, shows footprints from a crown-group amniote with clawed feet, most probably a primitive sauropsid. This pushes back the likely origin of crown-group amniotes by at least 35–40 million years. We also extend the range of Notalacerta into the early Carboniferous. The Australian tracks indicate that the amniote crown-group node cannot be much younger than the Devonian/Carboniferous boundary, and that the tetrapod crown-group node must be located deep within the Devonian; an estimate based on molecular-tree branch lengths suggests an approximate age of early Frasnian for the latter. The implications for the early evolution of tetrapods are profound; all stem-tetrapod and stem-amniote lineages must have originated during the Devonian. It seems that tetrapod evolution proceeded much faster, and the Devonian tetrapod record is much less complete, than has been thought.

 So
 Some fish have scales
 All living amphibians do not have sales
 Some reptiles have scales
 Some mammals have hair
 So
 What was the scale, hair, feather situation for these vertebrates?
 

Actually, as John Harshman has pointed out, some caecilians (living amphibians) do have scales.  The earliest body fossils are from the Carboniferous, and display keratinized (scaly) skin.  The Devonian trackways are just trackways, and the only thing we can say about them is they had claws (unlike amphibians).  The tracks appear to have been made by sauropsids, I don't know how you could tell synapsids and sauropsids apart without body fossils, and even then they were probably very similar.
The earliest unambiguous fossil hair is much later, but therapids ~290 MYa show evidence of whiskers.