Lecture 2 Flashcards
Mammals predate dinosuars
TRUE
Synapsids are ______ mammals
Stem
NOT true mammals, ANCESTRAL to mammals
Cretaceous mammals
Pangea: Single giant land mass; super continent
Continents are separating in Cretaceous, still tenuous connections between continents
Much biotic interchange between the continents in Jurassic - sets the stage for mammal diversification
Flowering plants become dominant flora over evergreens and gymnosperms
Insects radiate with flowering plants in Cretaceous = insects important food sources for mammals
Dinosaur fauna begins to decline
Mammalian faunas begin to radiate
Are mammals synapsids?
YES
Mammal taxonomy
Kingdom Animalia
Phylum Chordata
Subphylum Vertebrata
Clade Amniota
Superclass Tetrapoda
Clade Synapsida
Class MammaliaMammals are:
Animals Chordates Vertebrates Tetrapods Amniotes Synapsids
Sauropsida is _____ to synapsida; amniotes that are not mammals (turtles, reptiles, dinosaurs, birds)
Synapsida
Synapsid skulls
1 post-temporal opening
Compare to Diapsids: 2 post-temporal openings
Pelycosaurs are prime examples of
Synapsids
Function of temporal opening
Allows for enlargement of muscles associated with chewing
Synapsid Evolution
Single temporal fenestra
Retained ancestral tetrapod features of eye with poor color vision (probably nocturnal)
Splayed limb posture
-NO hair yet, no scales
Glandular skin without reptile-like scales
Probably oviparous (laid eggs) -NO evidence of vivipary in early mammals
Synapsid Evolution: Early Innovations
Narrowing of the snout
3 vertebrae fused to hip bones
-Prior, it was 1 vertebra fused to MASSIVE hip bones
Pelycosaurs are an offshoot of the synapsid lineage; one radiating branch of the synapsis led to the pelycosaurs
Dimetrodon is a pelycosaur
Pelycosauria
Pelycosaurs are NOT the direct ancestor of mammals
“Sailbacks” of the late Paleozoic, but very few actually possessed sails
Generalized amniotes
“Non-therapsid synapsids”
No evidence of increased metabolic rate
Diverse group
- Large specialized herbivores
- Large carnivores with enlarged canines
- -E.g. Dimetrodon
- -Ate fish, amphibians
- -Up to 3m long
One group of carnivorous synapsids led to the
Therapsida
Therapsida Evolutionary Innovations
Limbs positioned under the body
-No longer splayed posture
Deep acetabulum
-Acetabulum: Head of femur is ball, acetabulum is socket it fits into; very deep socket to accomodate this posture
Enlarged temporal opening = more muscles
Enlarged canines
Therapsida
Arose from common ancestor with pelycosaurs in mid-Permian (~275Mya)
Enlarged upper canines (other teeth roughly the same size)
Upright posture begins
New arrangement of muscles associated with chewing
Model of early synapsids
Expansion of post-temporal opening
Upright Posture
Axial musculature used for locomotion in ancestral vertebrates also used in rib ventilation
Mammals use limbs primarily for running, keep their trunk more rigid; bring limbs directly below the trunk
Dorso-ventral flexion of the vertebral column for a bounding gate -> quicker and more efficient locomotion
Appendicular Skeleton: Reptiles
Sprawling posture; limbs not in line with CoG (Center of Gravity), takes lots of energy
Many bones in pectoral and pelvic girdles, lots of cartilage
Appendicular Skeleton: Mammals
Improved posture; limbs in line with CoG; more energy efficient
Reduction in number of bones in girdles; ossified; stronger
Mammals are THERAPSIDS and SYNAPSIDS
MUST be to be a monophyletic group
“Therapsida” includes non-mammalian therapsids and mammals (it’s a monophyletic group, or clade)
Modifications indicating increased metabolic rate = probably had hair
Heavy, stumpy legs
Herbivores
- Some large, heavy, slow-moving, herding
- Some small and rodent-like
Carnivores
- Some large, ferocious, cat-like
- Some small, insectivorous, fox-like
Some HETERODONTY (tooth differentiation)
Tooth Morphology and Replacement: Ancestrally
Homodont: All teeth have the same shape (cone-shaped)
- Mostly for gripping food
- Don’t fit together well
- Tend to wear down quickly
- -Teeth did NOT fit together
Polyphyodont:
-Continuously replaced as needed
Used for gripping food; example of what ancestral condition looked like (alligators, crocs)
Tooth Morphology and Replacement: Derived…
Heterodont:
- Differentiation into 4 types of teeth
- Incisors (I) = cutting/nipping
- Canines (C) = piercing
- Premolars (P) = grinding/crushing/slicing
- Molars (M) = grinding/curshing/slicing
Therapsida: Theriodontia
Particular branch of the Therapsids that give way to the Cynodontia
Late Permian to Early Triassic (~250Mya)
Gave rise to Cynodontia (“Non-cynodont theriodonts”)
Primarily carnivores
- Built like wolves and coyotes
- Canine teeth long and blade-like
- Well-developed incisors
- Small post-canine teeth (cheek teeth)
- Incisors used to tear flesh
Some development of a secondary palate
Secondary palate
Purpose: Allows you to breathe with mouth closed; allows for SUCKLING
ONLY present in mammals
Therapsida: Cynodontia
Non-mammalian Cynodonts
late Permian to mid-Jurassic (~200Mya)
Reduction in body size
-Range from mouse-sized to dog-sized
Large temporal opening, large dentary bone
Heterodont, polyphyodont (teeth continuously replaced)
-Can differentiate canines from incisors, etc.
2 occipital condyles but no axis/atlas
- Occipital condyles articulare with spinal column
- Another character of mammals but NOT a synap
Vertebral differentiation, upright posture
Evolutionary transitions: Temporal Opening
Dimetrodon had a small temporal fenestra
Advanced therapsids had a larger inferior temporal fenestra
Mammals:
- Lose post-orbital bar
- Inferior temproal fenestra becomes temporal fossa
- Pronounced zygomatic arch
Evolutionary Transitions: Lower Jaw
Enlargement of the dentary bone in the lower jaw
Ancestrally 7 bones in lower jaw; Articular and Quadrate bones form the jaw joint and the lower jaw used in feeding and sound transmission
Progressive reduction and loss of most elements of lower jaw
Dentary becomes entire lower jaw, jaw joint now dentary and squamosal bones, jaw used only for feeding in mammals
Different jaw joint than what we see in modern mammals
Evolutionary Transitions: Jaw Muscles
Masseter muscles with the same attachments as mammals was a cynodont innovation
Originate on the zygomatic arch and insert on the dentary - powerful adductors
- Muscular sling enhancing control of the movements
- Increased bite force
- Focused force on point of the bite, not jaw joint
VERY powerful bite force; focused force on the point of the bite
Opening of fenestra for muscle attachment and migration of bones to form inner ear
Ear Evolution in Mammals
How do we know bones we hear with came from bones reptiles eat with? Transitions shown in fossil record; you start to see larger bones holding teeth
Evolutionary Transitions: Jaw joints and Ear Bones
Early Amniotes:
- Had 7 bones in the lower jaw, including the angular and articular
- Jaw joint = articular and quadrate (birds and reptilians still use this jaw joint)
- Stapes was already used in sound transmission from external ear, through middle ear, to inner ear
- -Stapes = columella of other tetrapods
Mammals use a dentary squamosal jaw joint
The jaw was remodeled during the evolution of mammals from non-mammalian synapsids
Mammals:
- Only dentary comprises the lower jaw
- Jaw joint = dentary and squamosal
- 2 bones that were formerly part of the jaw joint now incorporated into the middle ear- the articular and quadrate
Character of TRUE Mammals
Lower jaw joint made of single bone (Dentary)
Mammalian characters
3 middle ear bones
Dentary-squamosal jaw joint
Single jaw bone (dentary)
Evolution of ear bones
Stapes = columella Incus = Quadrate Malleus = Articular
Grade
A collection of organisms that are similar by way of physiology and anatomy; NOT a formal taxonomic or phylogenetic designation
Synapsid Grade of Evolution
They have a similar morphology
Therapsid Grade:
Increased size of temporal fossa
Cynodont grade:
Appearance of secondary palate, heterodont teeth
Early mammal grade
Dentary-squamosal jaw joing, single lower jaw bone, 3 middle ear bones
Increasing size of temporal fenestra
More jaw muscles = more food intake
Becomes temporal fossa
Lower temporal bar becomes ________-
Zygomatic arch
Indicates large masseter muscle = more food; bows outward to allow more muscle
Lower jaw and jaw joint
Dentary takes over and postdentary bones become co-opted for use in hearing
Teeth
Greater specialization of teeth from homodont pelycosaurs to heterodont mammals
Polyphyodonty to diphyodonty
Secondary Palate
Allows breathing and eating at the same time
None in pelycosaurs, present in mammals
Greater respiration rate
Loss of parietal foramen
Pineal eye in pelycosaurs used for controlling temp behaviorally
Lost in Cynodonts
Limb position from splayed to upright
More activity
Easier to breathe and run simultaneously
Reduction in girdles
Shape of limb girdles
From Large ventral components to support sprawling to reduced components
Weight passes through limbs now
Shape of feet
Long toes used as holdfasts for sprawling gait, reduced toes used more as levers in upright posture
Loss of lumbar ribs
Presence of diaphragm = greater respiration
Thoracic and lumbars specialized
Reduced/lost ribs on cervical vertebrae
Long tail in pelycosaur reflects movement by
Axial Flexion
Shorter tail in therapsids reflects upright posture and limb propulsion is used
Mammaliformes: Morganucodonts
We have no evidence that live birth was a character of these early mammals
Most were shrew-like; had complete mammalian teeth, skull, and jaw articulation
First mammals had hair and mammary glands, laid eggs
Larger brains than contemperary cynodonts
Diphyodont with precise occlusion of the molars
Upper cheek teeth fit precisely into lower cheek teeth
Tooth Morphology and Replacement
Diphyodont
- Compare with polyphyodont
- 2 sets of teeth
- -Deciduous (I, C, P)
- -Permanent (I, C, P, M)
- Often become more efficient as they wear down
Diphyodonty arose around the same time as precise occlusion
What is a mammal?
The essence of mammalian life is to be found in their endothermic (warm-blooded) temperature physiology, greatly enlarged brain, dentition capable of chewing food, highly agile, energetic locomotion, and so on. The organisms that achieved this grade of overall organization are deemed to be Mammalia, and consequently those characters that they possess are the defining characters of the group.
Mammals exhibit increased:
1) Intelligence
2) Information gathering ability
3) Endothermy
4) Reproductive efficiency
5) Ability to obtain and use food
What is a Mammal? Characteristics NOT preserved in fossils
External covering of hair (except in certain highly specialized groups)
Nourishment of young by milk produced by mother’s mammary glands
Four chambered heart (separation of blood flow to lungs – for reoxygenation – from circulation to rest of the body)*
-Birds CONVERGENTLY evolved 4-chambered heart
Muscular diaphragm (increased oxygen consumption)
Higher metabolic rates
Better vision, hearing, olfaction – cerebrum relatively larger
Enucleate erythrocytes: SYNAPOMORHPY (strictly mammalian)
Mammals have a larger brain
What is a mammal? Characteristics Preserved in Fossils
Single lower jaw bone
Dentary-squamosal jaw joint
3 middle ear bones
Diphyodonty (*exceptions)
Heterodont dentition (*exceptions)
- Precise occlusion
- Complex crowns
Secondary bony palate
-Allows breathing when the mouth is closed
Ribs usually limited to thoracic region
2 occipital condyles
Mammalian Characters
Single lower jaw bone (i.e. dentary)
Dentary-squamosal jaw joint
3 middle ear bones (incus, malleus, stapes)
Occipital Condyle
Mammals have 2 occipital condyles (synap)
Articulates with first vertebrae; having 2 condyles allows mammals to move head in almost any direction
All mammals have hair at some point in their lives
TRUE
Gray whales have whiskers as babies, armadilloes have hairs
Hair has several functions
Insulation Protection from environment Tactile snese (vibrissae/whiskers) Cryptic coloration/camouflage Warning coloration
Sea otter fur is the ______ of any mammal
Densest
Consists of around 100000 haris per cm^2
Camouflage: Seasonal Change
Arctic hare: Pelage/fur changes for season (bronw in summer, white in winter0
Pelage variation
Confusion patterns (Zebra stripes), warning colors (skunk), camouflage, communication
Why do Zebras Have stripes?
Hypotheses:
- Stripes cause little convex air circulations right next to skin which would act as a cooling mechanism
- Stripes are how zebras recognize one another
- Type of cryptic coloration by confusing predators
- Striped pattern protects against fly bites
Tested fly hypothesis: Put Zebra and horse skins in room; flies only landed on horse coat; supports hypothesis that stripes prevent bug bites
Protect against SMALL predators (flies), not large predators (lions, hyenas, etc.)
Skin Glands: Sweat Glands
Produce sweat to cool via evaporative heat loss
Helps keep body temp in a neutral range
Eccrine sweat glands:
- Thin sweat (watery)
- NOT near hair follicles
Apocrine sweat glands:
- Thick sweat (oily)
- Near hair follicles
Skin glands: Sebaceous Glands
Associated with hair follicles and secrete an oil (sebum) that keeps hair shaft moist and waterproof
Sebaceous glands that aren’t on hairs are found on the lips, penis, labia, minora, and nipples
Produce pheromones for signaling
Skin Glands: Scent Glands
Either modified sweat or sebaceous glands
Modified for a variety of functions, usually intraspecific communications (Pheromones)
- Predator deterrent (e.g. skunks)
- Scent marking (e.g. deer)
- Sexual communication (e.g. rodents)
Found in many locations on the body
Skin Glands: Mammary Glands
Unique to mammals (SYNAP)
Specialized epidermal glands derived from SWEAT GLANDS
Glands send ducts up an elevated nipple or teat, adipose fat forms beneath the glands
Number and location vary among species
Mammary glands are derived from sweat glands
Sweat glands and sebaceous glands are types of epidermal glands
Varies from 2 (primates) to 13 nipples/teats
Adipose forms beneath the glands
Composition o milk varies by nutritional demand
Seal milk has more fat than terrestrial carnivore milk because seals need to store fat for insulation in cold water
Axial Nipple
Nipple in armpit
Found in manatees
Cistern
Where milk would collect
Found in cattle, goats (animals that produce a lot of milk)
Lactation evolved ______ ability to give birth
BEFORE
Monotremes evolved _____ of other lineages
Independently
Composition of Milk
Water: 40-90%
Salts: 1-58%
Carbohydrates: 0-9%
Lipids: 1-52%
Protein: 4-12%
Do male mammals lactate?
Males of 2 species of bats have been discovered to lactate
VERY small amounts of milk
Not clear if they are feeding young
