It seems that quite a few stories from Nature caught my attention this week. This is another story about dinosaurs, specifically feathered dinosaurs. Not about a new species, their ecology, or their behavior, but rather about the development of feathers.
Two 125-million year old Similicaudipteryx specimens have been recovered from the Lower Cretaceous Yixian Formation of western Liaoning in China. Similicaudipteryx belongs to the group of dinosaurs known as oviraptorosaurs (egg-stealing dinosaurs). The specimens show the dinosaur species in two stages of development - early adulthood and juvenile. The adult has pennaceous or contour wing and tail feathers which resemble a quill pen and are mostly similar in size. The juvenile has longer tail than wing feathers which both have a flat, ribbon-like stem at one end and are pennaceous at the tip. This is the first time that juvenile dinosaurs have been found to have different types of feathers than adults, a transition that we do not observe in modern birds. Other scientists have suggested that the juvenile feathers may be from a moulting phase. The paper's authors explain that if this is the case you would expect the ribbon-like part of the feather to be shorter. They continue on to suggest that the juvenile's partially-pennaceous feathers may be the result of delayed gene expression, expression that is activated early in the life of modern birds.
The Nature article:
Xu Xing, Xiaoting Zheng and Hailu You (2010) Exceptional dinosaur fossils show ontogenetic development of early feathers. Nature: 464, 1338–1341. (DOI: 10.1038/nature08965)
(Full Text -- if you have access, it includes some really great photos and diagrams)