Evolution of Mammals Flashcards
Synapsida
One pair of temporal openings
First amniotes lineage to radiate extensively into variety of terrestrial habitats
“Pelycosauria”
Most basal synapsids
Adaptive radiation (carnivores/herbivores)
Heterodonty: Beginning of tooth type differentiation (i.e. caniniform teeth in derived carnivorous pelycosaurs)
Extinct by end of PALEOZOIC
Paraphyletic: Therapsids emerged from a carnivorous pelycosaur lineage
Therapsida
Persisted into Mesozoic
Gait with limbs under body (SYNAPOMORPHY)
Adaptive radiation (carnivores/herbivores)
Cynodonts emerged from a therapsid lineage
Cynodonta
Persisted deep into Mesozoic
Turbinate bones (SYNAPOMORPHY) -Suggests endothermy (putative synapomorphy)
Greater degree of heterodonty
Changes in jaw musculoskeletal structure (SYNAPOMORPHY)
- Enlargemet of dentary and reduction of posterior jaw bones
- Evolution of masseter muscles
Mammal lineage emerged from a cynodont lineage
Mammalia: SYNAPOMORPHIES
Mammary and other skin glands
hair (derived from reptile scales)
Diphyodont dentition: Teeth replaced only one time in life
New jaw joint between squamosal and dentary (quadrate and articular incorporated into middle ear)
“Early mammals”
Arose >200 mya (Triassic)
Had hair: Likely endothermic
Secondary palate (shared with cynodonts) -Separates feeding and breathing pathways to permit suckling young
Mammals and dinosaurs coexisted for _____-
~140 mya
- Mammals smaller than most dinosaurs
- Few lineages of mammals
Extinction of dinosaurs occurred _______
~65 mya (early Cenozoic)
Mammals diversified into many lineages and many achieved large body size
Jaw joint and ear evolution
Reduction, loss, specialization, and new roles for old parts
Quadrate -> Incus
Articular -> Malleus
Integument of mammals
Distinctive and tends to be thick compared to that of other vertebrates
Derivatives of Integument
Horns and antlers
Horns
Bovids (e.g. cattle, goats, antelope, etc.)
Bony core covered by keratinized sheath
Usually in both sexes
Unbranched
Not shed
Antlers
Cervids (deer)
Solid bone
Usually only in males
Branched
Shed annually
-Big energetic investment for sexually selected trait
Functions for horns and antlers
Intrasexual competition between males for access to females (original function) and protection against predators (secondary function)
Irish elk
Actually a deer
2.1m (6.9ft) tall at shoulders
Largest antlers of any known cervid: Up to 3.65m (12ft) across and 40kg (88lb)
-Antler size result of sexual selection and positive allometry (antlers relatively larger in larger species)
Hair
Unique mammalian structure
Dead cells impregnated with keratin
Epidermal structure (hair follicles producing hairs sunk into dermis)
Derivatives of Hair
Vibrissae
- “Whiskers” in many mammals
- Tactile sensory structures (mechanoreception)
- Analogy in some birds? yes, used for catching insects
Spiny armor
- Echidnas, procupines, and hedgehogs evolved spines derived from hair (convergence/analogy)
- Protection against predators
Mammal jaw function
Evolution of zygomatic arch and masseter muscle (cynodonts)
Masseter muscles insert on lateral aspect of dentary
Pterygoid muscles insert on medial aspect of dentary
Forms a muscle sling that allows side-to-side movements of lower jaw - more complex chewing and slicing motions
Glands
Mammals have greatest variety of glands among vertebrates (humans have all major glands)
Sweat glands
-Evaporative cooling
Scent glands
- Communication (attracting mates), territorial marking, defense
- Various locations among species: eyes, cheeks, between digits, genitals, anus, and more
- Used for defense in skunks
Sebaceous glands
-Expel sebum to keep hair and skin pliable and glossy
Mammary glands (i.e. Mammalia)
- Possessed by females (rudiments in males)
- Derived from sweat glands (homologous)
- Mile secreted from glandular tissue to feed young
- Humans: adipose tissue around glandular tissue forms breasts (unique and plays role as visual signal of sexual maturity/fertility)
Mammals: Prototheria
Monotremes
1 order
3 species in 1 order: echidna (2) and platypus (1)
Oviparous: lay and incubate eggs
Young fed with milk from mammary glands
Found in Australia:
- Platypus
- -Venomous spurs on hind limbs (males only): used in competition for females
- -Electroreception for detecting aquatic prey
- Echidnas
- -Protective spines derived from hair
- -4-headed penis: uses 2 heads on one side during mating and switched sides with each mating
Mammals: Metatheria
Marsupials
334 species 7 order: Australia (>200), South/Central America (>100), and North America (1)
-Kangaroos, wallabies, opossums, marsupial mice, Tasmanian devils, Tasmanian wolves, bandicoots, wombats, and others
Viviparous with ALTRICIAL young
Evolved most ecological types observed in eutherians except powered flight (some glide) and marine habit
Females: Vagina with 3 canals (2 lateral and 1 medial)
Males: Forked penis fits into lateral vaginal canals
Sperm travel up lateral vaginal canals and young pass through medial vaginal canal
young born (~1g), climb to teat in pouch using strong forelimbs, and have extended development while nursing
Mammals: Eutheria
Placentals
Viviparous with PRECOCIAL young
Tremendous variety of forms in almost every imaginable habitat
Huge range of body size: 2g (Etruscan shrew and bumblebee bat) to 190,000kg (blue whale)
Worldwide distribution
> 500 species in 22 orders
-Nearly 1/2 are rodents and nearly 1/4 are bats
Uterus/uteri join single vaginal canal
Connection between fertilized egg and maternal uterine tissue form placenta
-Site of gas and nutrient exchange
More energy towards in utero development and less towards lactation (compared to metatherians)
Whale evolution
Extinct forms
Closest living relative to whales is Hippopotamus (same order as deer, pigs, camels, giraffes, buffalo, cows)
