Class Aves

• Birds and dinosaurs share several similarities:

  • Digits on foot similar to modern birds
  • Carpal bone structure (wrist) similar in theropods & early birds
  • Shoulder sockets of some theropods & modern birds are similar
  • Eggs incubated in nests
  • Molecular evidence linking birds and dinosaurs: T. rex sequence similarities to chickens
  • Fossilized melanosomes found in Cretaceous dinosaurs and birds
• Birds evolved from therapods, a group of dinosaurs
• Archaeopteryx, an early bird, had both avian and reptilian features:

  • Contour feathers in wing
  • Opposable hallux (big toe)
  • Furcula (wishbone)
  • Reptilian features like premixilla and maxilla bones with teeth, wing claws, long bony tail, and neck attachment to skull
• Diversity among extant birds:

  • Approximately 8,600 species in 23 living orders
  • Includes flightless birds like ostrich, kiwi, emu, and penguins
  • Passeriformes (perching birds) make up nearly 60% of living bird species
• Bird diversification:

  • Variations in beak shapes, feet, size, colors, habitats, locomotion, flight patterns, microhabitats, behavior, and life history traits
  • Driven by challenges like competition for resources, predation threats, and competition for mates
• Advantages of flight for birds:

  • Enhances hunting and scavenging skills
  • Provides escape from predators
  • Facilitates exploration of new niches and migration
• Anatomical adaptations for flight in birds:

  • Streamlined body with feathers
  • Reduction in weight with hollow bones and no teeth
  • Fusion of bones for strength during landing and takeoff
  • Lengthened forearms for wings
  • Well-developed keel on sternum for flight muscle attachment
• Feathers in birds:

  • Strong and light
  • Shed periodically through molting
  • Types include contour feathers, semiplumes, down feathers, filoplumes, and bristles
  • Feathers play roles in mate attraction, predator deterrence, and camouflage
• Wing shape and flight in birds:

  • Wing shape determines flight type
  • Different wing shapes correspond to trade-offs between speed, energy use, and maneuverability
  • Aspect ratio and wing loading affect flight performance
• Birds' diverse roles in the ecosystem:

  • Seed dispersal by frugivores
  • Pollination by nectarivores
  • Nutrient addition through droppings
  • Grazing, predation, and scavenging
  • Ecosystem engineering by modifying the environment
• Archaeopteryx lithographica is an early bird considered a transitional form between birds and reptiles, sharing characters with reptiles like a toothed jaw and long bony tail, and with birds having feathers, a pygostyle, and being bipedal
• In bird skeletons, adaptations for flight include a reduction in bones to reduce weight, a horny plate instead of teeth, a pygostyle (reduced tail bones), and hollow bones with struts to increase strength
• Feathers are made up of keratin and consist of structures like the calamus (hollow shaft attaching the feather to the bird's skin), rachis (central shaft where vanes are attached), vane (flattened part attached to the rachis), barbs (branches off the rachis forming vanes), and barbules (tiny extensions from barbs held together by barbicels)
• There are seven broad categories of feathers based on structure and location on the bird's body, each with different functions like flight, steering, insulation, and tactile purposes
• Birds have a variety of beaks specialized for their diet:

  • Carnivorous birds have strong, hooked beaks for tearing flesh (e.g., Eagles, Falcons)
  • Granivorous birds have short, robust beaks for breaking seeds (e.g., sparrows, finches)
  • Frugivorous birds have curved beaks for fruits and can move the upper beak independently (e.g., Parrots, Cockatoos)
  • Insectivorous birds have various beak shapes for hunting insects in different ways (e.g., Swallows, Woodpeckers, Hoopoes, Robins)
  • Piscivorous birds have beaks adapted for catching fish, some with a flexible pouch to store fish (e.g., Seagulls, Kingfishers, Pelicans)
  • Nectivorous birds have thin, long beaks adapted for feeding on nectar from flowers (e.g., Hummingbirds, Sunbirds, Honeycreepers)
  • Wading birds have long beaks for searching for invertebrates in shallow water habitats (e.g., Storks, Spoonbills)
• Anisodactyly is the typical foot configuration in birds with four toes, including a hallux that faces backward, allowing perching, while Zygodactyly has two toes forward and two back, useful for climbing (e.g., Woodpeckers, Parrots)
• Bird nests come in various types like cup nests (simple cup-shaped), platform nests (large, bulky structures), pendent nests (elaborately woven sacks), and scrapes on the ground (shallow depressions without much nesting material)