[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: did Jurassic dinosaurs have feathers?

I wonder if the Type I/II/III inference system may be a little wobbly when it 
comes to dinosaur integument, given that the concept of phylogenetic bracketing 
might be strained for two reasons: (1) the frequency of reversals; (2) the 
sheer rarity of taxa that have any integument preserved at all.  

For example, if protofeathers served a thermoregulatory function, then large 
dinosaurs may be pre-disposed to losing feathery integument and reverting to a 
more scaly integument.  For example, the basal tyrannosaur _Dilong_ has a downy 
body covering, but later and larger tyrannosaurs appear to have more 
scaly/tubercular skin.  As the _Dilong_ paper puts it: 

          "Given the diverse morphologies of integumentary structures in living 
birds, it is possible that non-avian theropods had different integumentary 
           morphologies on different regions of the body, and derived, large 
tyrannosauroids might bear both scale-like and filamentous integumental 
           appendages. Alternatively, the lack of filamentous integumentary 
structures in derived tyrannosauroids is correlated with the large size, a 
           physiological strategy also adopted by some mammals such as 
elephants, which lose most of their body hairs as they mature.  This therefore 
           supports the hypothesis that the original function of protofeathers 
is correlated with thermoregulation."

One possibility (definitely Type III = no bloody evidence at all!) is that a 
fuzzy body covering is primitive for Ornithodira, and was retained by certain 
pterosaurs (like _Sordes_ etc) and dinosaurs (especially small theropods), but 
lost (or scaled back) independently in many lineages.  Under this hypothesis, 
sauropodomorphs would be secondarily 'naked'.  Most (and maybe all) 
ornithischians might be naked too - either due to large body size, or to a 
burrowing ecology in the smaller and/or more basal ornithischians.  The tail 
'quills' of _Psittacosaurus_ could even be highly modified versions of these 
filamentous structures.  This hypothesis would mean that a fuzzy integument 
would go back to lagosuchian-grade archosaurs.  Highly speculative, I know, and 
as I write this I find myself less and less convinced that it's even plausible.



> Date: Mon, 7 Jan 2008 13:04:11 -0500
> From: tholtz@umd.edu
> Subject: RE: did Jurassic dinosaurs have feathers?
> To: mike@indexdata.com
> CC: keenir@hotmail.com; dinosaur@usc.edu
>> From: Mike Taylor [mailto:mike@indexdata.com]
>> Thomas R. Holtz, Jr. writes:
>>>> ....and while all the "birds" had feathers, in both the
>> Jurassic>> and Cretaceous (the book was arranged by era
>> *then* by>> clade)...the maniraptors and other predatory
>> dinosaurs only were>> illustrated with feathers in the Cretaceous.
>>>> is there reason to think that Jurassic predatory
>> dinosaurs>> would/wouldn't be feathered?
>>> Jurassic maniraptorans would have almost certainly have
>> been> feathered. Compsognathids and tyrannosauroids would
>> be fuzzy. More> basal theropods (including Allosaurus,
>> Ceratosaurus, etc.) would be> scaled.
>> WHat's our reason for being confident that Allosaurus didn't
>> have feathers? My understanding is that we have some
>> preserved tyrannosaur skin impressions that show scales and
>> no feathers, but that this is not taken as evidence that
>> tyrannosaurs were not feathered -- only that they had scales
>> but that these could have been as well as, rather than
>> instead of, feathers. What's to stop the same being true of
>> Allosaurus or Ceratosaurus, or for that matter Brachiosaurus
>> or Triceratops?
> Okay, to be fair it is ambiguous (a Type II inference) for Allosaurus: we
> have no indication of scales over the whole body within Carnosauria, so the
> presence of Allosaurus scales on the limited skin impressions could be a
> tyrannosaurid-type situation or a lepidosaur-type situation.
> Nearly the entire surface of Carnotaurus is (alledgedly) known from skin
> impressions, and these are scales-only. So at least in the adult stage of
> one ceratosaur there are only scales, and no evidence within Ceratosauria or
> basal-ward [with respect to Coelurosauria] to it of protofeathers. Inference
> of protofeathers is at present a Type III inference with no supporting
> evidence. Could easily change with a single discovery, but that's the
> situation now. Hence putting protofeathers on Ceratosaurus or abelisaurs (or
> more basal theropods) is AT PRESENT unsupported by confirmatory evidence,
> and contradicted by both observational evidence and phylogenetic inference.
> Same goes for all dinosaurs basalward [again, with respect to
> Coelurosauria]. And no, there are NOT protofeather impressions of
> coelophysoids/dilophosaurids in the Newark Supergroup: those are algal mat
> drag marks, as Tony Martin has shown. (This does not demonstrate lack of
> protofeathers in these guys, but is simply not evidence FOR protofeathers.)
> Thomas R. Holtz, Jr.
> Email: tholtz@umd.edu Phone: 301-405-4084
> Office: Centreville 1216
> Senior Lecturer, Vertebrate Paleontology
> Dept. of Geology, University of Maryland
> http://www.geol.umd.edu/~tholtz/
> Fax: 301-314-9661
> Faculty Director, Earth, Life & Time Program, College Park Scholars
> http://www.geol.umd.edu/~jmerck/eltsite/
> Fax: 301-405-0796
> Mailing Address: Thomas R. Holtz, Jr.
> Department of Geology
> Building 237, Room 1117
> University of Maryland
> College Park, MD 20742 USA

Make distant family not so distant with Windows Vista® + Windows Live™.