H8 Sheldon- Birds I + II: Evolutionary origins and diversification of birds + Adaptation and Ecology of Birds

describe birds

• birds are a group of the amniota in the tetrapoda clade (sarcopterygians class of osteichthyes, vertebrate subphylum, chordate phylum, deuterostomia clade of bilaterian animals)

• derived from theropod dinosaurs, most diversified after the cretaceous period (post-mass extinction), so hard to determine phylogenies

• endothermic

• high metabolic rate

• feathers (evolved before flight, initially unrelated)

• 98% capable of powered flight

• hard-shelled eggs are normally cared for by both parents (obligate oviparous)

• light, pneumatized (air-filled) bones

• keratinaceous beak, no teeth

• female heterogamy (ZW), small genomes (adaptation to fit in smaller cells- greater sa:v ratio, accommodates faster metabolism for flight)

less variation in body size and reproduction because:

• flight requires light bones, constraining mass

• high metabolic rate sets a minimum mass to cope with heat loss

• flight imposes obligate oviparity

describe the paleognathae

• the paleognathae is the oldest lineage of birds (a group of the amniota in the tetrapoda clade, sarcopterygians class of osteichthyes, vertebrate subphylum, chordate phylum, deuterostomia clade of bilaterian animals)

• this includes the ratites (eg. ostriches, emus, kiwis)

• few species

• either flightless or poorly flying, except for the tinamous- flight lost independently 3 times to fill niches left by dinosaurs

• sex chromosomes are only semi-differentiated

what key adaptations enabled bird diversity? include examples

keratins allowing adaptive flexibility:

• feathers- plumaceous insulating section + pennaceous mechanical section, with interlocking barbules, branching off a central rachis (ends at the calamus)

• these can have biochrome pigments (melanins, carotenoids and porphyrins) and structural colours by light scattering

• feathers allowed worldwide dispersal + diversity of form encourages fast speciation

  • sandgrouse transport water in arid habitats by soaking their belly feathers- helical barbules uncoil for water retention

  • filamentous barbs reduce air turbulence to allow silent flight in owls

  • woodpeckers use thickened rachis in tail feathers for tripod support

  • filamentous penguin feathers have anti-icing properties

  • ornamental feathers are used for sexual display + selection

• beaks- diversity allowed for feeding specialisation

  • adaptive radiation of honeycreeper beaks from one colonising ancestor + darwin’s finches

long-distance movement through flight:

• migration allows the tracking of seasonal solar energy fluxes (exploiting variation in productivity), to adapt to many niches

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