Organisms that have this ability possess a specialized leading digit known as an alula. Animals that have lost this ability tend to have symmetrical remiges (“re-MEE-jez”). Echelon (10[1])formations are adopted by groups of organisms with this ability. Structures that confer this ability are categorized as primary or secondary, and can include small serrations to reduce noise. Tree-down and ground-up are two theories for the evolution of this ability, (10[1])seen in the transition (-5[1])species Archaeopteryx (10[3])(“arch-ee-op-te-rix”). Organisms with this ability have hollow bones. (10[1])For 10 points, name this ability (10[1])to generate lift in the air possessed by animals like birds. ■END■ (10[1])