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More and more evidence of fossilized dinosaurs with feathers are appearing. Did many dinosaurs have feathers and did this change during the Mesozoic?

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    $\begingroup$ So all palaeontology (apart from biostratigraphy maybe?) questions should be asked at biology stack? I can live with that. $\endgroup$ – tobias47n9e Apr 17 '14 at 17:38
  • $\begingroup$ Is that policy? I was thinking of posting a question about the Ediacara - more of an evolutionary question than biostrat. $\endgroup$ – winwaed Apr 17 '14 at 18:01
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    $\begingroup$ If I may, Palaeontology is a field where you can come at it from both ends, biologists studying the anatomy and speciation, geologists studying the formation of fossils, special preservation conditions and stratigraphy, not to mention the blurred line that is palaeo-climate studies using forams/diatoms etc. I would argue a case-by-case basis is fair, but apart from a trained palaeontologist, who will make a fair judgement call on that? That said I'm new to SE. $\endgroup$ – Ben Brooks Apr 17 '14 at 18:32
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    $\begingroup$ I think the "what percentage" part of this question makes it unanswerable. It's the same as "what percentage of modern land vertebrates have feathers" - percentage of individuals? Percentage of species? If the later, how do you define species? Even if it's the number of species, this question still seems to lack anything more than random idle curiosity as a driving force... $\endgroup$ – naught101 Apr 18 '14 at 1:05
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    $\begingroup$ The question is off topic on ES and should be migrated to biology.stackexchange.com. $\endgroup$ – BHF Apr 21 '14 at 10:56
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Keep in mind that although I am a paleontologist, I am not a vertebrate paleontologist so I might not be aware of every single find ever made of feathered dinosaur.

As far as I can tell, all dinosaurs fossils exhibiting feathers belong to the Theropoda. Here is a (probably dated) phylogeny of dinosaurs from Sereno 1999:

Phylogeny of Dinosaurs by Paul Sereno, 1999, published in Science. Credit: Paul C. Sereno

Theropoda is the group from Eoraptor to Euornithes.

While Eoraptor is Triassic, the group diversifies mostly during the Jurassic (still Sereno 1999) and it is also during that time that we start having "common" feathered dinosaur fossil evidence (e.g. Zhang et al. 2008, Sullivan et al. 2014).
Birds (Aves) seem to have appeared in the late Jurassic / early Cretaceous as well, but modern birds (Neornithes), i. e. birds with living representative, appeared only in the late Cretaceous.

I don't know of any proper (sample-standardized, with coherent bias detection and removal) paleodiversity study for the theropods, although there is one for Aves (Brocklehurst et al. 2012), so it's hard to discuss about it at a species level.

In theory, feathers are more likely to fossilize than other soft tissue (Davis & Briggs 1995) but in practice they are mostly found in finely grained sediments such as limestones, thus limiting the amount of outcrops in which they can be found.

Sources:
Brocklehurst, N., Upchurch, P., Mannion, P. D., O'Connor, J., 2012. The Completeness of the Fossil Record of Mesozoic Birds: Implications for Early Avian Evolution. PLoS ONE 7(6): e39056.
Davis, P. G., Briggs, D. E. G., 1995. Fossilization of feathers. Geology, 23(9): 783-786.
Sereno, P., 1999. The evolution of Dinosaurs. Science, 284: 2137-2147.
Sullivan, C. et al. 2014. The vertebrates of the Jurassic Daohugou Biota of northeastern China. Journal of Vertebrate Paleontology, 34: 243-280.
Zhang, F. et al. 2008. A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature, 455: 1105-1108.

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    $\begingroup$ Additionally i d like to point out that i intentionally didn't give an answer on the "evolutionary process that led to the apparition of feathers" but i focussed only on what was the fossil record of feathered dinosaurs. $\endgroup$ – plannapus Apr 21 '14 at 11:12
  • $\begingroup$ It would be cool if someone had the time to edit the image to highlight which groups were feathered (it's just the four at the bottom left, right?). Also, some of those area species, and some are larger groups (genera?), and it would be interesting to add some info on how many known species were in each of the latter, if that information exists. $\endgroup$ – naught101 Apr 21 '14 at 12:57
  • $\begingroup$ As a matter of fact Sinosauropteryx is a feathered dinosaur and is a Compsognathidae, so this is possible that the whole group from node 49 on was/is feathered. As for the number of species: there are too many of them for a single non-specialist to make up a complete list of them. And given the very gappy fossil record of dinosaurs, that wouldn't be very informative anyhow. $\endgroup$ – plannapus Apr 21 '14 at 13:04
  • $\begingroup$ I wouldn't dare making an exhaustive list of families including feathered specimens either but i think apart from the Compsognathidae, they are Troodontidae, Dromaeosauridae, Oviraptorosaurid (i think?), Tyrannosauroidae,... specimens bearing feathers (or "feather-like" teguments). $\endgroup$ – plannapus Apr 21 '14 at 13:19

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