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, 106 (3), 832-4

A New Feather Type in a Nonavian Theropod and the Early Evolution of Feathers


A New Feather Type in a Nonavian Theropod and the Early Evolution of Feathers

Xing Xu et al. Proc Natl Acad Sci U S A.


All described feathers in nonavian theropods are composite structures formed by multiple filaments. They closely resemble relatively advanced stages predicted by developmental models of the origin of feathers, but not the earliest stage. Here, we report a feather type in two specimens of the basal therizinosaur Beipiaosaurus, in which each individual feather is represented by a single broad filament. This morphotype is congruent with the stage I morphology predicted by developmental models, and all major predicted morphotypes have now been documented in the fossil record. This congruence between the full range of paleontological and developmental data strongly supports the hypothesis that feathers evolved and initially diversified in nonavian theropods before the origin of birds and the evolution of flight.

Conflict of interest statement

The authors declare no conflict of interest.


Fig. 1.
Fig. 1.
EBFFs in Beipiaosaurus. (A) Beipiaosaurus sp. STM31-1. Arrows point to EBFFs. (B) Close-up of EBFFs in STM31-1. Arrow points to the basal end of a single EBFF. (C) Tail of the B. inexpectus holotype. Arrows point to separately preserved EBFFs, whereas most tail feathers overlap extensively. It should be noted that nearly all tail feathers are incompletely preserved in IVPP V11559 because of damage during preparation by an amateur collector. [Scale bar: 50 mm (A), 15 mm (B), and 10.5 mm (C).]
Fig. 2.
Fig. 2.
Comparative line drawings of filamentous feathers in several nonavian theropods. (A) EBFFs dorsal to the posterior portion of the skull and the anterior portion of the neck in STM31-1. (B) EBFFs near the end of the tail in IVPP V11559. (C) Filamentous feathers along the tail of S. prima (IVPP V12415). (D) Filamentous feathers along the tail of Dilong sp. (IVPP V11579). (E and F) Isolated filamentous feathers in the Sinornithosaurus millenii holotype (IVPP V12811). (C) E and F are modified from Fig. 3 in ref. and Figs. 3 and 4 in ref. . [Scale bar: 40 mm (A, B, and D), 30 mm (C and F), and 15 mm for (E).]

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