Mammals Flashcards
Evolution of mammals within synapsids
- Pelycosaur (first tetrapods in terrestrial habitats that were widely spread)
- Derived pelycosaur
- Therapsids
- Cynodont (derived therapsids)
- Mammal
When did mammals appear
During the very end of the Triassic and probably descended from cynodonts
Early mammals appeared around 205 mega around the same time as dinosaurs
Synapsid trends
-gradual and coordinated modification of trains that reflect increased energy intake and expenditure (increased metabolic rate)
-axial and appendicular skeletons
-skull, jaw and teeth
Pelycosaurs
-resemble reptiles
-sprawling limb posture
-lumbar ribs
-long, heavy tails m-fine shaped teeth
Therapsids include what
Include basal forms and derived forms called cynodonts
Changes in the skeleton when we compare the therapsids with pelycosaurs
- Limbs becoming longer, more slender and increasing held under the body
-more erectile stance
-loss of lumbar ribs (cynodont)
-increased Dorso-ventral flexion
-reduced tail (cynodont)
Why is losing the lumbar ribs so important
Mammals developed a diaphragm which suggests an increased metabolism and respiratory rate
Absence of ribs would give the animal the ability to flex in the dorsal-ventral direction
Changes in the skull, jaw and teeth from pelycosaur to therapsids
-larger dentary, other jaw bones reduced
-increased heterodonty
-multi-cussed teeth (cynodonts)
-secondary palate (cynodonts)
-nasal turbinate bones (cynodonts) that increase surface area inside the nose.
Further Modifications from cynodonts to early mammals
-Two bones of mandible (articular and Quadrate) shrank and separated to become part of the middle ear-malleus and incus)
-dentary-squamosal jaw joint now used
-molars with cusps (chewing surface)
-diphyodont teeth (two sets): indicates suckling -two sets of teeth over lifetime
Traits of early mammals
-higher metabolic rates
-oviparous
-probably endothermic with film coat of hair
-mammary glands
Were mammals small during dinosaur times
Not just small; shrew-like animals that creeped in shadows of dinosaurs.
-were diverse forms from terrestrial carnivores to aquatic mammals to squirrels like gliders.
Monotremes
Mammals that still lay eggs
Mesozoic mammals
- Earliest mammal is called Morganucodon-small, nocturnal, insect/eating mammal
- Monotremes
- Multituberculates
- Therians
Multituberculates
Characteristics
-flourished in Cretaceous
-survived and recovered after KPg
-extinct 34 mya
-rodent like
-filled similar niches: burrowing, grazing and arboreal
-first grass eating mainly
Therian animals
When did they expand
Includes marsupials mammals (metatherians) and placental mammals (eutherians)
-expanded after KPg extinction
Are monotremes and marsupials related?
Not closely
The therian mammals includes _____ and _____
Placental
Marsupial
Monotremes
-oldest fossil
-where do current species live
Jurassic from Australia
Australia, new guinea, Tasmania
Includes platypus and 2 echidna
Monotremes reproduction
-Traits shared with reptiles
-traits shared with other males
-true cloaca
-long, filiform sperm
-oviparous: 10-11 day inculcation, artificial young
-lactation (4-7 months): mammary glands
-hair (fur)
Weird trait of monotremes
-Electroreception to find prey (on beak)
Marsupials make up what percent of worlds mammals?
Where do they live?
6%
Australia/ Tasmanian/ N and S America
Evolutionary history and dispersal of marsupials
- NH origin: diverged from placentals 175mya
- N. America to South America (60-80mya)
- South American-> Antarctica-> Australia (55mya)
- Modern lineages appeared in Australia 20-40 mya
Marsupial traits compared to placentals
-lower Basal metabolic rate at 35.5° vs 36-38°
-50% have marsupium (pouch)
-limited range in body size (2g to 66kg)
-difference in placenta, gestation and length of lactation
Placenta
Temporary organ formed by the interaction of embryonic and maternal structures
Difference in placental and marsupial mammals extra-embryonic membranes
Parts of extra-embryonic membranes interact with maternal structures to form a temporary organ called a placenta.
Placenta of marsupials:
-Choriovitelline placenta: enlarged yolks sac fused with chorion. Weak attachment to uterine wall. Blastocyst does not sink deep into endometrium, no villi
Placenta of placental mammals:
-Chorioallantoic placenta: all placentals and few marsupials have it. Blastocyst sinks deeply into endometrium, placenta developed from chorion and Allantois membranes, chorionic villi project into endometrium to increase surface are for gas exchange.
Chorioallantoic placenta function
- Nutrient and gas exchange
-maternal and fetal circulation are in close contact but not fused: substances move between them larger by diffusion
-maternal blood provided O2 and nutrients and removed CO2 and waste from infants blood - Produces substances to suppress maternal rejection
- Produced hormones to support pregnancy
- Fetus spends longer in uterus and is more developed at birth
Incubation, gestation and lactation of marsupials and placentals
Marsupials:
-brief gestation (weeks)
-highly altricial young
-long lactation
Placentals:
-long gestation (varies based on body mass)
-short lactation
-developed today young at birth: altricial in rodents and carnivores, precocial in ungulates
Of marsupials and placentals, who spends more overall time (gestation and lactation) with dependent offspring
Marsupials
Invest little into gestation, but more into lactation
Reproductive timing usual order of events
Estrous
Ovulation
Mating
Fertilization
Implantation of blastocyst
Development of embryo
Parturition (birth)
induced ovulation
The act of mating induced ovulation
Common in rabbits, Felids, camels and rodents
Bat reproductive timing strategies
Sperm storage before ovulation
Delayed development after implantation
Delayed implantation
Development of blastocyst stops after fertilization and waits to be implanted.
In bears, weasels, seals, insect eaters, rodents and kangaroos
Delayed implantation reasons
Obligate: synchronize birth with seasonal cycle
Facultative: food availability
Integument and derivatives function
Protective layer between animals and environment: repels heat, water, physical attack, microorganisms, conserves heat and moisture
Unique mammalian derivatives of epidermis serve different functions: insulation, communication, locomotion, nourishment (mammary glands)
Types of glands
Sebaceous glands
-most associated with hair follicles
-secrete sebum (oil) that helps to keep skin and hair moist and waterproof
Sweat glands
-secrete water for cooling
-secrete moisture on palms of feet for traction
Scent glands
-modified sebaceous or sweat glands
Scent gland purpose
Used to mark territory
Males use it to attract females
Males use it to destroy competing males
Deter enemies
Mammary glands
Specialized epidermal glands
-functional only in females
-number and location of glands vary
-protein and fat content varies by species and with age of infant
Hair-epidermal derivative keratin
Types
Palage: overall coat
-guard hair
-underfur: soft and heat trapping
-molt: juvenile or annual
Modified guard hairs
-vibrissae
-quills
-spines
Horns and antlers
Only found in ungulates (hooves animals)
-True horns in sheep and goats have an inner core of dermal bone and a keratin sheath. They grow continually and produce a single horn
-Antlers found in cervidae (deer family) shed annually, thin layer of epidermal velvet covers growing dermal bone, branched
Claws, nails and hooves are derived from what
Epidermis
Keratin
Claws
Cover dorsal and part of ventral side of digit. Shared with reptiles and birds
Nails
Only on dorsal surface, accompanied by increase in nerve endings at tip of digits. Mostly in primates
Hooves
In ungulates
Point of contact with ground
Modifications for running lifestyle
-Increased limb length to increase stride length
-elongation of distal limb segments
-change in foot posture
Plantigrade
Digitigrade
Ungulates
Plant heel and palms on the ground as they walk
Plant their phalanges on the ground and raise the heel and metatarsals off the ground
Stand on their toes or hood
Jumping lifestyle body modifications
-centre of gravity shifts posterior
-long hind limbs, feet
-larger tail for balance
-kangaroos, rabbits, jumping rodent
Arboreal lifestyle body modifications
Tree climbing mammals grip the tree with claws or with sensitive digits
Often have long tails for balance
Wide range of movement in their limbs and feet
Gliding life style modifications
Skin membrane called patagium
Not powered flight. They glide down from higher up
Among mammals, only ____ have powered flight
Bats
Elongated fore arm and phalanges
Thin sheet of skin (patagium)
Fossorial or burrowing life style body modifications
Subterranean mammals
-short, strong limbs
-long claws
-tubular body form
-some use teeth to dig (large incisors)
-poor sight
-well developed hearing
-vibrissae (tactile receptors)
Star nose mole adaptations
- 22 fleshy appendages with 25000 Eimers organs: sensory receptors used to explore environment and find prey.
-bubble bowling behaviour to sleep when under water
Swimming lifestyle types
Amphibious: use terrestrial and aquatic
Semi-amphibious: most of the time in the water but use land to mate
Fully aquatic: never move to land
Whale evolution
Animal that resembles deer!!!
Hind limbs lost
Forelimbs became flippers
Tail fluke
Nostrils posterior and dorsal
Ear modified to localize sound
Loss of hair
Echolocation
Baleen
Modern whales
- Toothed whales (Odontoceti)
-pursuit predators
-echolocation
-dolphins, beluga, narwhal, spermatids whale - Baleen whales (Mysticeti)
-filter-feeders
-blue, grey, humpback
Homodont teeth
Heterodont
Most fishes and reptiles
All the teeth are the same
Mammals and whales (secondarily heterodont)
Teeth are varied
Carnassial teeth
Last premolar of upper jaw and first molar on bottom jaw
Used to shear meat
Herbivores dentition, muscle and gut
-incisors to clip vegetation
-cusps modified into grinding ridges (cheek teeth)
-diastema between incisors and cheek teeth
Large masseter muscles for side to side chewing
Complex digestive system and long intestinal tract
Fermentation chamber with microbes to digest cellulose (in stomach, colon or cecum)
Gnawing herbivores
Rodents, rabbits and some marsupials
Same adaptation as other herbivores but with ever-growing incisors
Carnivores dentition, muscles and gut
-Large canines (seize prey)
-shearing teeth (carnassial)
Large temporalis rise to seize prey and hold jaws closed
Short intestine with a small or no cecum (food digests rapidly)
Convergence of carnassial teeth
The Tasmanian devil, a marsupial predator also had molars modified to shear prey
Insect eaters dentition, and gut
Numerous sharp teeth to pierce and crush insects
Short intestine, no cecum
Digestive tracts of two types of herbivores
Non/ruminant- use their Colons and cecums as fermentation chambers
Ruminant-special stomach chambers for fermentation
Mammal brains: Expansion of _______
Neocortex (cerebral cortex) = six layers of gray matter that cover the cerebrum
Specific regions correspond to function
Bird vs mammals brains
Different but equivalent parts of brain integrate information
Mammals: cerebral cortex
Birds: pallium
Olfaction in mammals
-Chemoreception occurs as air passes over olfactory receptors in epithelium in nasal passages
-complex nasal turbinates in many mammals increase surface area for olfactory epithelium
-increased number of olfactory genes compared with other vertebrates
Flehmen testing and vomeronasal organ
Flehmen or lip curl testing is done in breeding season by male ungulates to pick up a females urine and expose it to the vomeronasal organ. This is done to assess whether a female is in estrous or not.
Hearing in mammals
Pinna: external ear
-focuses sound on tympanic membrane (ear drum)
-assists in locating sound
-pinnae lost in some groups (whales)
Vision in mammals
-colour vision well-developed in other vertebrates (birds, fishes, reptiles)
-capacity to perceive colour probably reduced in early mammals due to more nocturnal lifestyle
Nocturnal vision
- Rod cells - sensitive to wide range of wavelengths of light. Results in large number of rod cells that are sensitive to low light levels but do not provide much visual acuity.
- Tapetum lucidum-mirror reflects back image onto retina
- Large curved lens
Colour vision in mammals
Monochromatic
Dichromatic: most mammals, 2 cone cells types
Trichromatic: 3 cones, primates, some marsupials, humans
Tactile mammals
Sensitive digits (primates, raccoons)
Vibrissae (whiskers)
Eimers organs (star-nosed mole)
What is a primate?
- Arboreal: grasping extremities, sensitive digits, nails, improved vision
- Large brain
- Monkeys and apes have acute daylight Vision: trichromatic
- Eat fruit, seeds and foliage
- Slow reproduction: increased parental care, delayed sexual maturity, one infant/cycle, long life span
Habitat of most primates
Mostly tropics
Exception: snow monkey and humans
Two lineages of primates
Haplorrhine
Strepsirrhine
Haplorrhine characteristics
Simple or dry nosed
-tarsiers, monkeys and apes
-almost all diurnal except tarsier and night monkey
-most are highly social
Strepsirrhine characteristics
Wet nosed
-lemurs, lorises, galagos
-longer rostrum with wet “doggy” nose
-smaller brain
-most nocturnal
-some solitary
New world monkeys
Platyrrhini
Monkeys living in central and South America
Prehensile tails
Monkeys that can hang from their tail
Only south and Central American monkeys
Old world monkeys
Asian and African monkeys (Catarrhini)
Terrestrial and arboreal forms
Apes, orangutan, gorilla, chimps and humans
Single young, long lactation (2-4 years), delayed maturity
All endangered except humans
Humans (Hominins): Genus Homo
-Bipedal
-Larger brains
-Reduced Sexual Dimorphism
-Multi-male, Multi-female communities
-Extent of culture differs form apes (use of tools, language)
Significant events in Human Evolution
6.6 mya-last shared common ancestor with chimpanzees
3.7-3.0 mya- Australopithecus
2.4-2Mya-Genus Homo appeared in Africa with larger brains than other early humans
3mya - 25,000 ya- different honk in species lived at the same time, including members of Genus homo and Australopithecus
Homo sapien time frame
Modern humans
200,000-100,000 ya: living in Africa
Reached max brain size 100,000 years ago, increased cultural artifacts (50,000ya)
Other homo spp. went extinct by 25,000 ya
Pleistocene extinctions
13,000-8000ya
Mostly affected large mammals (>10kg)
Wooly mammoth, saver-toothed cats, camels, wooly rhinos, giant ground sloths
Caused by human migration leading to over killing and or climate change
