Question

Ciliary pumps were replaced by pharyngeal pumps in early chordates because:

allowed for better dentition

pharyngeal pumps were more efficient, thus removing size limits of prey

mouth was undergoing modification at this time

collagen was being replaced by cartilage in the pharyngeal region

Answer 1

Ans:- pharyngeal pumps were more efficient, thus removing size limits of prey.

Prevertebrates, with their ciliary pump, and probably early agnathan vertebrates with their muscular pump, fed on sus- pended particles. Food-bearing currents carried enough organic material past mucus, where some collided with it and was gathered up. The transition from agnathan to gnathostome involved a switch in feeding method. Transi- tional species became raptorial feeders that plucked individ- ual food particles selectively from suspension or off surfaces. Some chosen food items would have been wary zooplankton ready to dash off when approached. Other items would have been particles with significant inertia, such as small worms, that required forceful effort to be ingested. Raptorial feeding favored a sudden and forceful expansion of the pharyngeal pump followed by certain mouth closure to prevent escape of captured food. Elastic recoil of the springy cartilaginous bars allowed early jawless vertebrates to produce a suction, drawing food into the mouth; however, this system was too weak to allow forceful capture and ingestion. With the advent of jaws powered by quick muscle action, pharyngeal expansion and suction became strong and active. The mouth could shut quickly with a strong bite, securing the "inhaled" prey. Limits to prey size were also removed. Active predation became a common lifestyle in subsequent verte- brate radiation.