Evolution of Feeding

What was the ancestral feeding condition?

no jaws, suspension/filter feeding using pharyngeal apparatus

What nonvertebrates or early vertebrates represent the ancestral vertebrate condition?

lancelets, pikaia first vertebrate fossil

Does jawlessness necessitate filter feeding?

no, adult hagfish & lamprey don’t filter feed

How does ancestral filter feeding work?

water enters mouth, passes through pharyngeal slits, food particles trapped

Where did jaws originate from?

pharyngeal arches, modification of existing structures

Describe how pharyngeal arches became jaws:

anterior arch becomes mandibular arch

dorsal part becomes palatoquadrate

ventral part becomes Meckel’s/mandibular cartilage

second arch becomes Hyoid arch for support/suspension

Describe the history of jaws briefly:

early jawless ostracoderms were heavily armored

placoderms earliest radiation of jawed

entelognathus (placoderm) jaws look similar to jaws of later gnathostoma

early cartilage fish & spiny sharks have both primitive & derived jaw characteristics

Does having jaws increase the amount of energy an animal can capture?

often but not necessarily, it expands the size & types of food an animal can exploit

Describe the pros & cons of suspension feeding:

food items tiny in large quantities, capture rate depends on water particle conc and filtration efficiency, only energetically favorable under certain conditions

Describe the pros & cons of predator feeding:

prey packages larger, jaws help capture restrain and process prey, but energy needed to spend on finding, pursuing, & capturing prey

What prey types do suspension feeders vs predators need?

suspension: tiny & numerous

predator: larger & more rare

If jaws are such a great innovation, why did some of the largest vertebrates evolve secondary suspension/filter feeding?

jaws are less efficient in larger animals because they would expend too much energy finding, hunting, and capturing larger prey as a predator

Is secondary suspension/filter feeding similar to the ancestral suspension feeding?

not really, evolved different & highly specialized mechanisms by convergent evolution

How do whale sharks feed?

ram feeding, move to prey with mouth open, water flows across filtering pads covered in mesh, don’t use a lot of energy, high surface area on mesh

How do baleen whales feed?

fill mouths by expanding throat, use baleen made of keratin to trap plankton, extreme skull modifications for more mouthspace

What are the trade offs of consuming large, individual prey?

lots of energy per capture, relatively rare, expensive to locate & capture

What are the tradeoffs of consuming tiny prey?

little energy per individual, occur at huge densities, harvest thousands to millions at once, if high enough density, bulk filtration more efficient

Ram Feeding

predator moves toward prey with mouth open

Suction Feeding

rapid expansion of buccal cavity lowers pressure, open mouth rapidly, draw water & prey in

Crushing/Durophagy

blunt or ridged teeth used to crush hard bodied prey

Benthic Feeding

suction, excavation, picking, detritivory to eat food from seafloor

Grazing/Scraping

remove attached food from a surface, seen in cichlids catfish & parrotfish