help with number 4!!!! ck dv Thl Fig. 1. Leg feathers in the basal avialan Sapeo

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help with number 4!!!!

ck dv Thl Fig. 1. Leg feathers in the basal avialan Sapeorvis. Photograph (A) and drawing (B). Abbreviations:cv cervical vertebrae; dv, dorsal vertebrae; If, leg feathers hl, left hindlimb; lil, left ilium; lis, left ischium; rhl, right hindlimb; sk, skllt tail feather Fig. 4. Evolution of leg feathers in cochurosaurian dinosaurs. Four major stages in the evolution of integumentary structures on the hindlimb are represented by the compsognathid Sinocalliopteryx (short filamentous feathers covering legs, including fect); the basal deinonychosaurian Anchiorvis and the basal avialan Sapeornis (large pennaccous feathers on legs, including feet, forming a winglike structure); the enantiornithine Cathayornis (large femoral and crural feathers forming a reduced winglike structure); and ornithuromorphs (small femoral and crural feathers and featherless feet).

Explanation / Answer

3. Arboreal hypothesis: supports the powered flight originated from unpowered gliding by tree climbing or arboreal animals. These small arboreal animals are nothing but the dinosaurs having feathers which then developed into longer, stiffer feathers for aerodynamics through wings.

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