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