[Paleontology • 2014] Melanosome Evolution indicates a Key physiological shift within Feathered Dinosaurs
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| The "rules"
allowing color reconstruction from the shape of melanin-containing
organelles originate with feathered dinosaurs, and are associated with
an increase in melanosome diversity. However, fuzzy dinosaurs like T. rex and Sinosauropteryx show
a pattern found in other amniotes like lizards and crocodilians in
which a limited diversity of shapes doesn't allow color reconstruction.
An explosion in the distribution of the shapes of melanin-containing
organelles preserved in living taxa and the fossil record may point to a
key physiological shift within feathered dinosaurs. DOI: dx.doi.org/10.1038/nature12973 |
Inference of colour patterning in extinct dinosaurs has been based on
the relationship between the morphology of melanin-containing organelles
(melanosomes) and colour in extant bird feathers. When this
relationship evolved relative to the origin of feathers and other novel
integumentary structures, such as hair and filamentous body covering in
extinct archosaurs, has not been evaluated. Here we sample melanosomes
from the integument of 181 extant amniote taxa and 13 lizard, turtle,
dinosaur and pterosaur fossils from the Upper-Jurassic and
Lower-Cretaceous of China. We find that in the lineage leading to birds,
the observed increase in the diversity of melanosome morphologies
appears abruptly, near the origin of pinnate feathers in maniraptoran
dinosaurs. Similarly, mammals show an increased diversity of melanosome
form compared to all ectothermic amniotes. In these two clades, mammals
and maniraptoran dinosaurs including birds, melanosome form and colour
are linked and colour reconstruction may be possible. By contrast,
melanosomes in lizard, turtle and crocodilian skin, as well as the
archosaurian filamentous body coverings (dinosaur ‘protofeathers’ and
pterosaur ‘pycnofibres’), show a limited diversity of form that is
uncorrelated with colour in extant taxa. These patterns may be explained
by convergent changes in the key melanocortin system of mammals and
birds, which is known to affect pleiotropically both melanin-based
colouration and energetic processes such as metabolic rate in
vertebrates, and may therefore support a significant physiological shift
in maniraptoran dinosaurs.
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| These are two of the fossil specimens sampled from the Cretaceous and Jurassic of China. Fuzz-covered dinosaur Beipiaosaurus shows
the rounder melanosomes seen in living lizards and crocodilians while
the bird shows the unique skinny melanosomes seen in living mammals,
birds and many of the studied feathered dinosaurs to date. Changes in
the diversity of these melanin-containing organelles may show a
physiological shift occurred in feathered dinosaurs closer to the origin
of flight. |
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| some of the 13 Jurassic and Cretacous pterosaur, dinosaur, turtle , bird and llizard fossils sampled for evidence of preserved melanosomes. |
Quanguo Li, Julia A. Clarke, Ke-Qin Gao, Chang-Fu Zhou, Qingjin Meng,
Daliang Li, Liliana D’Alba, Matthew D. Shawkey. 2014. Melanosome
Evolution indicates a Key physiological shift within Feathered
Dinosaurs. Nature. DOI: dx.doi.org/10.1038/nature12973
Revision to rules for color in dinosaurs suggests connection between color and physiology
New research revising rules on deciphering color in dinosaurs may
provide a tool for understanding the evolutionary emergence of flight
and changes in dinosaur physiology. While surveying melanosome shape in
fossil and extant specimens, a research team unexpectedly discovered
that ancient maniraptoran dinosaurs, paravians, and living mammals and
birds uniquely shared the evolutionary development of diverse melanosome
shapes related to color. The similarity could relate to a key shift in
dinosaurian physiology.
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