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Tianyulong provides the following information â
Because the fibers are both dorsal and ventral to the body, and scales are
absent, a situation similar to Yixian birds, it is probable that most of the
body was covered. This is in contrast to the Yixian Psittcosaurus in which the
fibers are only dorsal to the tail, and scales are well preserved over most of
the rest of the body. Eventually additional small heterdontosaur fossils from
Yixian will address this item.
It is not possible for the fibers to represent internal collagen. They are
too long, extend much too far from the body even on the tail, and are oriented
in exactly the manner of external fur and feathers (sweeping outwards and a
little posterior rather than the more irregular, criss-cross pattern expected
collagen). This pattern is repeated on numerous Yixian theropod specimens as
well as birds. Nor has it been explained why small dinosaur skin was packed
with so much collagen -- they were not spring bodied ichthyosaurs after all.
collagen hypothesis is scientifically deceased unless heterodontosaurs or
small theropods with extensive scale coverings show up.
The absence of preserved protofeathers on Triassic and early Jurassic
theropods is meaningless because this is entirely negative evidence, and scales
not been found on them either. This is the same misleading nonargument for
naked dinosaurs that I dealt with in the 70s, 80s and 90s until the Yixian
fossils showed up.
That such a basal ornithischian and dinosaur had fibers is neither surprising
nor novel, it is eminently logical and goes aways back. I mentioned the
possibility that insulation was widespread in archosaurs and may be basal to
dinosaurs in the Dinosaurs Past and Present volume in 87, and Predatory
the World in 88. Not sure whether I or others published the hypothesis
earlier. The widespread distribution of insulation is logical in that it is
probable that dinosaurs were tachyenergetic endotherms. I have been
illustrating small ornithopods with archofur since the 80s to keep their little
warm. Some degree of tachyenergy may have been evolving fairly early in
archosaurs, including basal crocodilians, so insulation may extend well back
into the clade. That the idea of general dinosaur fiber coverings goes back
decades is not being properly covered in the literature or press.
The widespread distribution of dense fiber coverings in a variety of small
dinosaurs is strong evidence of their having elevated metabolic rates. Very
probably was critical to the ability of small dinosaurs to dwell in cold polar
winters that excluded reptiles in the Mesozoic.
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