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Re: Follow-up: the truth about killer dinosaurs


Michael Mortimer wrote:

Dilong doesn't not show it though. Remember, the soft tissue over the body often decayed in Yixian animals. That's why we get halos of integument for the most part in coelurosaurs. In Dilong, we have tail feathers dorsal and ventral to the vertebrae and chevrons, with absolutely nothing preserved where any skin or scales would be.

IMHO this is probably due to taphonomy. For some reason, the feather impressions were preserved in this sedimentary environment, but the scales/scutellae were not. The _Archaeopteryx_ specimens preserve evidence of feathers, but no scales, even though parts of the body (e.g., face, feet, maybe the hands) were undoubtedly scaly in life. Similarly, the internal organs decayed before they could leave any impression. Compare this to _Scipionyx_, where we have guts but no integument. Those microbes are fickle beasties.

T. Michael Keesey wrote:

It is true that the only known feathers in non-maniraptorans appear to
be for insulation. But a _T. rex_ would have benefitted from
insulation throughout much of its early life, and it would be simpler
to reduce the feathers (or even just not grow them any further--let
them stay the same size and, as the animal's surface area increases,
they spread apart) as it grew bigger than it would be to molt them and
replace them with scales. Maybe that's what they did, but it seems
like a more complicated scenario than is required to fit the known
evidence.

I would argue that the first feathered theropods had both scales and proto-feathers over the body. In the course of evolution, the former gradually disappeared from most of the body surface, but remained on the feet and part of the head.

Yes, but _Carnotaurus_ lies well outside the clade of feathered theropods (all of which are coelurosaurs). I think there is also a juvenile _Allosaurus_ specimen showing scales--what this suggests is that feathery integument evolved somewhere within non-tyrannoraptoran
_Coelurosauria_.

Yes, at the moment the phylogenetic bracket for feathers is hovering somewhere around the base of the Coelurosauria, with compsognathids and tyrannosauroids the most basal *known* theropods to display this kind of integument. This does not mean that carnosaurs, ceratosaurs, herrerasaurs were not feathered; but applying the principal of phylogenetic bracketing we cannot infer the existence of feathery integument in these non-coelurosaur groups with any confidence.

(Of course, there are also those weird quills in that _Psittacosaurus_ to consider....)

Yes, this could change things. There's a fellow named George Olshevsky who has a lot to say about this...

David Marjanovic wrote:

At least one _Microraptor_ specimen
shows a mane-like crest -

Does it? Or is that just yet another artifact of 2D preservation of a water-soaked carcass?

Here's what Xu et al. (2003) say about the feathery crest of _Microraptor gui_:

"The body is covered by plumulaceous feathers that are about 25−30 mm long. The feathers attached to the skull roof are up to 40 mm long in IVPP V13352 (Fig. 2a), and in TNP00996 they are proportionately even longer (Fig. 2b). Some feathers on the head display well-organized pennaceous vanes (Fig. 2c). These feathers are most probably functionally related to display, as in some modern birds such as _Pithecophaga jefferyi_. Large pennaceous feathers are attached to the distal tail, forelimb and hindlimb (Figs 1a, c and 2d−g)."

My hair points away in all directions when I dive and don't move too fast.

Well, if your hair makes you look like a dead _Microraptor_, I would consult your barber.

;-)

Cheers

Tim