Verts Exam 3

BIRBS (Class Aves)

Defining features:

• feathers, flight

• lightweight fused skeleton (furcula, wishbone)

• toothless beaks

• pygostyle (fused tail vertebrae)

• air sacs/air filled bones

• amniotic hard-shelled eggs

• four-chambered hearts, and endothermic

Where do birds fit in?

• modern birds have more traits common with reptiles than mammals

• good evidence for birds arising within the reptile clade after the split between sauropsids/diapsids and synapsids

Archaeopteryx

• first described from one fossilized feather in 1861 Germany

• Archaeopteryx represents a mix of non-avian reptile traits and bird traits

• Bird traits= feathers, skeletal structures for flight, backwards pointing first toe.

• Reptile traits = many small teeth, unfused bones, claws on forelimbs, and long bony tail

Velociraptor

• small (about turkey sized) but it, along with other dromaeosaurs all probably hunted solitarily, pinning prey with a large toe claw

Theropod Hypothesis

• concern and debate about theropods lacking a furcula ceased to be a concern as new fossils were found

• more evidence suggesting a gradual progression from ealry archosaurs to modern avian traits

Avian respiration

• Dinos took sauropsid respiratory systems one step further to evolved air sac, extending into hollow bones

• Living birds need 2 breaths to completely move air in and out of their bodies for energy efficiency

Theropods

• one of the 3 major clades of dinos characterized by hollow bones and three toes and claws on each limb

Bird eggs

• like all archosaurs, birds lay shelled eggs, and theropods laid shelled eggs as well

• preserved nests and eggs and parental skeletons nearby suggest parental care like brooding

Feathers

• preserved fossils of feathered theropods were found in China

• feathers’ original function might have been for thermoregulation (protecting from sun to cool off, retain heat to keep warm

• another possible function was display for territory or courtship

• flight feathers = exaptation, a change or addition to a traits function to become co-opted for another function

Flyin

2 distinct hypotheses to explain how flight arose:

• Arboreal = feathers went from being used for temperature control to gliding from tree to tree (matches the thecodont origin of birds

• Cursorial = feathers went from temp regulation to an insect net to flight (fits the theropod origin of birds)

• in 2003, wing-assisted incline running was proposed to explain flight, where flapping rapidly would assist in moving up inclines. this merged the 2 hypotheses and is now the most widely accepted

• some maniraptorian (but non0avian) theropods even took to the seas and skies as swimmers and gliders

4 winged dinos

• many species were found to have legs that acted as wings

• the lift-to-drag ratio was critical for gliding flight

• they jumped off trees with legs straight back forming a canopy over the tail, and brought legs down when approaching a tree to increase drag for landing

How do we know archaeopteryx and microraptors had black feathers?

• many fossil feathers show evidence of melanosomes (organelles containing pigments)

• shape of melanosomes correlated with pigment color

Becoming birds

• by early cretaceous, true burds (avialans) appeared, and selective pressures were refining their powered flight adaptations

• broad sternum with a keel to anchor flight muscles, a pygostyle (fused caudal vertebrae in the tail) and synsacrum (fused pelvis) gave strength to the spine and greater flight control

• short trunk and tail (shifted center of mass)

Opposite birds

• enantiornithines, most divers of all cretaceous birds

• dominant in their time, ranging from hawk to sparrow size, and being on all continents

Trends in Avian Evolution

• during jurassic, theropods began a marked reduction in size, where bird became much smaller than basal theropods like tyrannosaurs

• toothless beaks evolved repeatedly in birds (seed-eating and insect-eating beaks first evolved in the cretaceos and flourished in the new cenozoic era alongside flowering plants

caw CAW (bird vocalizations)

• avian syrinx (vocal cords) is made of hardened cartilage and not easily fossilized

• fossils of a basal anseriform bird include a well-preserved syrinx (may have made honks or quacks like modern geese and ducks, their closest living relatives)

Class Aves Phylogeny

• ~11,250 species worldwide

• Birds live EVERYWHERE, because of flight they can reach most land masses in the world

• some birds secondarily flightless

Feather structure

• defining integumentary structure shared by all living birds

• beta-keratins are a class of proteins unique to reptiles and birds (scales, claws, horny bill covering), feathers have a special type of beta-keratins

Types of feathers

• contour feathers - gives shape to the body, with a rigid pennaceous portion providing aerodynamic sleekness and a soft, fluffy plumulacous portion

• down feathers - beneath most feathers, to insulate

• Flight feathers - asymmetrical feathers used to fly and for streamlined rows, coverts overlay the wings, both outer primaries and inner secondaries

Bird Bones and muscles!

• tells the story of bone reduction, fusion, reinforcement and power adapted to flight

• strong fliers have more flight muscles, while birds of prey and land birds have more leg muscles to grab and run

Bird toe arrangement

• loons and grebes are plantigrade (flat-footed), but most birds are digitigrade, or walk on their toes

• anisodactyl feet are most common, especially in perching birds

• zygodactly feet (ospreys, owls, cuckoos, parrots, turacos, woodpeckers, PEEPINS)

• seimming birds have webbed toes, either palmate, totipalmate, or lobate

Flight mechanics

• must overcome gravity (weight) and drag (turbulence and friction)

• lift counteracts gravity, while thrust counteracts drag

• wings function as airfoils, their upper surfaces are curved more strongly than lower surfaces, increasing airflow on the upper surface to generate lift

• stalling occurs when lift i reduced as the angle of attack in birds increases too much (typically 15 degrees); raise their alula on each wing to allow air through

Bird wing shapes

• reveal different flight capabilities

• aspect ratio = measurement of the wings loading (mass over surface area)

• higher aspect ratio increases flight speed but decreases maneuverability, long wings are less maneuverable than short

• soaring uses air columns over slopes or water where no flapping is required to save energy

Bird beaks/bills!

• reflects diets

• some birds are very adaptable omnivores, but many species are specialized for certain diets

• forest birds tend to be insectivorous, seed eaters, or pollinators

• waterbirds eat fish, aquatic plants, and some steal prey from other birds (kleptoparasitism)

• large raptors are apex predators

da crop

• use the crop to store or digest food

• adult pigeons, penguins, and flamingos feed their chicks with liquified food in their crop using crop milk

• birds use their muscular gizzard (often containing sand or grit) to grind their food, as they lack teeth

• birds also have variable tongues; long and sticky to grab onto prey, or short and maneuverable to handle it

• in gizzards, the bird makes a pellet from undigested prey parts, that it then regurgitates to clear out the crop

old and new jaws (evolutionarily)

• the two major clades of living birds can be distinguished by their bill anatomy

• paleognaths (ratites and tinamous) have reduced mobility in their jaws

• neognaths (all other modern birds) have more flexible jaws that can move upward for a wider gape

paleognaths

• big birds don’t fly

• constrained by how heavy they are, all ratites are flightless

• they very in how they use their wings; most use for courtship, but can run to escape predators and deliver killer kicks

• living paleognaths are restricted to the southern hemisphere, recent DNA studies from fossils suggest that giant flightless ratites evolved from flying ancestors across oceans

galloanserae

• land and waterfowl

• galliforms and anseriformes are sister taxa

• regularly lay multiple eggs, chicks and ducklings are very precocious and can run,, swim and dive shortly after hatching

• many species polygynous (1 male many females) or polyandrous (1 female many males)

• modern fowl puny compared to their extinct flightless relatives

Mirandornithes

• odd waterbirds…

Bird eyes

• tetrachromatic (can see in the UV range) + oil droplets in eyes that interact with pigments

• 4 cone vsison

• owls and nightjars have excellent low-light vision, and some birds glow to each other under UV light

• predatory birds have forward-facing eyes, prey have sideways eyes.

• eyes are not very moveable, they rotate their necks instead

Bird scent

• keep sense of smell in many species

• vultures can use stench of decay to locate prey

• tube-noses can detect the dimethyl sulfide released by plankton in the ocean

• some birds have sensitive bill tip organs that allow them to sense prey vibrations in soil, can help with manipulation of food items with the bill as well

Bird vocals

• birds produce sound with a vocal organ called the syrinx at the base of the trachea

• through lateralization of the trachea, a bird can use the muscles on each side to make 2 sounds at once

• syrinx most complex in oscines (songbirds), and some birds have elongated tracheas for bugling calls

Bird calls and songs

• differ in length, complexity and context

• calls are simpler and shorter, for alarms or as contact calls

• songs are longer and more complex, to defend territories and attracting mates

• song learning (through listening and mimicking) occurs in parrots, hummingbirds, and oscine songbirds (dialects possible)

• some birds are excellent mimics, used for flock recognition (captive birds try to sound like their human “flock mates”), or could be used to mimic predators to deter other birds

Mobbing and alarm calls

• birds can attack, or mob predators that may pose a threat to their young (often attack in flocks, calling loudly and harassing predators to drive them away

• alarm calls warn predators when a flock will attack, some alarms are used for certain predators

Other bird sounds

• storks and vultures lack a syrinx and rattle their bills or hiss

• woodpeckers drum on percussive objects in a distinct drumming pattern specific to their species

• some birds can produce sounds by rapidly moving their feathers on their wings and tails

displays and courtship

• birds use vocalizations and/or visual displays to attract mates

• complex sensory systems generate amazing opportunities for sexual selection on bird traits

• grebes, cranes, boobies and albatrosses dance together to form a pair bond that can last a lifetime

• same-sex couples form occasionally as well

Bird eggs

• all birds lay eggs to reproduce, and avian sex determination is always genetic

• males = ZZ females = ZW

• viviparity may be impossible to evolve due to the high body temps that birds maintain

• baby birds have an egg tooth to help them hatch with a hatching muscle on their neck

• fledglings are fed by parents until they can fly out of the nest (sometimes fed after that as well)

• altricial young are born blind, helpless and dependent, while precocial young are feathered, sensing and more independent

Bird nests

• many birds build nests to lay eggs in, they incubate using a brood patch, a bare belly of skin

• nest vary highly between species, families and environments

Parental Care

• common for both parents to raise offspring to independence, but many birds are highly promiscuous

• monogamous species share parental care duties, while polygamous species usually the female or one parent raise the young

• some birds have cooperative breeding, aided by close relatives to raise chicks

• brood parasites lay their eggs in other bird nests for them to raise

Da flock

• flocks are gatherings of birds for food and travel, often in migration

• may consist of one or many species (core species attract other birds and provide alarm calls and protection in numbers) + predator satiation

Migration

• around 1,800 species regularly migrate long distances to breeding and feeding grounds each year using flyways

• typically fly to warmer climates in the winter and back to breed in the spring

• there are reverse migrants that go north instead of south

• some migrants have been recorded to fly millions of miles, and the bar-tailed godwit has the longest nonstop flight of 11,000 km from alaska to new zealand

• birds rely on cues to migrate, which is typically day length changes

• they also use cues during migration by remembering landmarks, sun and stars, magnetic fields, and even odors

Threats to birds

• human activities that most commonly kill migrants

• illegal hunting and the pet trade

• outdoor domestic cats

• fishery bycatches

• collisions of human structures and cars

• bioaccumulation (chemical pollutants and consuming plastic)

• oil spills

• climate change changing migration timing, breeding timing, etc

Mammals are the sole surviving…

• synapsids!

• modern mammals arose in the Triassic, including the egg-laying monotremes, while marsupials and placental mammals diverged around 160 MYA

• since 66 MYA, mammals have dominated the Earth

• became more mammal like and smaller in the Mesozoic

Mammalian traits:

• hair or fur on bodies

• glands producing milk and sweat

• mostly viviparous

• external ears in most species

• a mobile snout

• single lower jawbone

• 3 middle ear bones

• tooth replacement

• endothermic

• four-chambered heart

• neocortex in the brain

• two occipital condyles of skull

Synapsids to mammals

• early synapsids had scaleless skin and looked like reptiles

• descendants gained more flexible necks, differentiated teeth, middle ear bones, simplified jawbones, hair and milk

• the lower jaw evolved into one bone, and the other bones migrated to the inner ear to create the ossicles for great hearing in mammals

• synapsids evolved fewer ribs, longer legs, and more upright posture for faster locomotion

• synapsids = one temporal fenestra on each side of their skull

• sauropsids and synapsids both arose in Carboniferous, but synapsids quickly dominated the Permian on land

Therapsids

• more upright postures and were likely endothermic

• carnivorous and herbivorous, very large

• later therapsids evolved integumentary hairs and eventually sensory vibrissae (whiskers) on their faces controlled by their muscular snouts

• Conodonts had hair follicles and perhaps glandular skin that produced secretions to keep their eggs moist that may have been the precursor to mammalian milk

Mammal teeth

• therian mammals (marsupials and placentals) have tribosphenic molars, with multiple shearing crests that fit into teeth sockets and fit together for efficient chewing (speeds up digestion and enzyme activity)

• mammals have two sets of teeth (baby teeth and adult teeth)

• some whales and rodents don’t replace teeth, and some keep growing their teeth continuously

Mammalian hair and fur

• hair provides insulation and can dissipate heat and protect against UV

• fur is tightly backed hair that forms a pelt

• some aquatic or selected species are hairless

• quills of hedgehogs and porcupines are defensive

• all mammals but great apes have facial vibrissae, and eyelashes protect eyes from dirt

Mammalian skin

• highly variable epidermis thickness

• claws, nails and hooves are made of keratin and protect the ends of mammalian digits. horns have keratin sheaths over bone interiors

• arrector pili muscles allow hairs and keratin to stand on end

• glandular skin (like amphibians; a basal condition)

Lactation

• female mammals (and a few male bats) nourish their young through production of milk

• mammary glands are derived from modified apocrine glands and secrete milk through ducts in nipples and teats

• milk teeth shed as juveniles ween off their mother’s milk

• lactation allows females to raise young on their own, and small birth size of offspring relative to their mothers

• the secondary palate of mammals enables offspring to suckle while breathing through their nose, suckling also gave way to powerful facial muscles to allow for suckling

Mammal olfaction

• greatest olfactory of any amniotes

• mammals often utilize their vomeronasal organ, which detects non-volatile signals like pheromones (flehmen response allows males to detect females reproductive status, and for females to time births in a herd)

mini to mighty mammals

• mammals and descendants stayed small (<100mm avg) and were typically prey for dinosaurs

• mammals show greatest size range of vertebrates (from whales to shrews and bats)

Why did endothermy evolve?

• fossil evidence shows mammals first evolved endothermy sometime from late triassic to mid jurassic

• endothermy = maintaining internal body temps using metabolic heat

• one hypothesis is that endothermy was linked to being nocturnal to avoid diurnal dinos

• warmer body temps in birds and mammals increase metabolic rates and hasten embryonic and neonatal development

nocturnal mammals

• mammals rely more on hearing and smell than vision than other tetrapods, fitting a nocturnal bottleneck hypothesis explaining ancestral habits

• other traits signaling being nocturnal include whiskers, brown fat, fur, endothermy, limited color vision, and burrowing

• most mammals have dichromic vision and are essentially colorblind (exceptions include primates, whom became trichromatic for eating fruit and foliage)

• nocturnal mammals are monochromatic to see in low light

Multituberculates

• a now extinct subclass of therian mammals

• burrowers, hoppers, and tree climbers, they had haw and teeth anatomy very similar to later rodents

• long gestation periods and complex brains

• likely went extinct due to competition or predation