Lect 18 Flashcards
Synapsida
• Synapsids were abundant and diverse from the late Paleozoic and into the Mesozoic
• Suffered significant extinction at the end of the Permian and the end of the Triassic
One of the three main types of amniotes —> single temporal Fensetrae
We’re not true mammals, but cold mammal, like reptiles
Superficially looked at them from the outside. It looked like reptiles, but internal structures didn’t match reptiles. During that time they were more mammal, like such as one temple Fenestra
Synapsid skull evolution
Basal synapsid
• Jaw joint: articular-quadrate
• Temporal fenestra small, separate from orbit
• Cheek continuous with skull
(Similar to reptiles that live during that time)
Derived mammal
• Jaw joint: dentary-squamosal
• Temporal fenestra large, often joined
with orbit (in many cases, the bar between the temple fenestrate an orbit has been lost so they are continuous with one another)
• Cheekbone distinct: zygomatic arch (separate from the skull in that there’s a space between it and the rest of the skull)
The change in jar helped pinpoint what makes mammals mammals
Heterodonty
Different kinds of teeth
• Incisors
• Canines
• Premolars
• Molars
Premolars and molars develop cusps
• Upper and lower teeth occlude
(They meet up with each other nicely allows for a good chewing)
Mammals are diphyodont
• Only two sets of teeth throughout life
Unknown if diphyodont or occlude occurred 1st
Synapsid skeleton evolution
Relatively reptile-like:
• Sprawling limbs
• Ribs on all trunk vertebrae
• Phalangeal formula = 2:3:4:5:3
(Strong pectoral girdle. Humerus and femer extend outwards)
Some mammal-like traits:
• Posture more upright
• Seven cervical vertebrae
• Pectoral girdle reduced
• Phalangeal formula = 2:3:3:3:3
(Humerus and femur extend downward)
More mammal-like:
• More complex limb joints (due to a difference in development and growth. Allows ends of bones to become more complex)
• Reduction of lumbar ribs (increase the flexibility (up and down) help run better)
• Secondary palate (separate nasal cavity from mouth cavity)
• Bowed zygomatic arch
Mammalian:
• No lumbar ribs
• Mammalian joint structures
Evolution of the mammalian jaw joint
Basal synapsids retain multiple bones in the lower jaw
Dentary grows
• Contacts squamosal to contribute
to jaw joint
• Excludes other bones from jaw joint
In some of the transitional species of this evolution lineage, there was two joints on each side, articular—quadrate was retained, but also there was a denture—squamosal joint
Chewing muscles may have helped this evolution process —> more support, and took pressure off of bones
Evolution of the mammalian jaw joint and ear
Those small bones were still connected to the lower jaw through cartilage
• Separation from dentary allowed the former posterior jaw bones to develop with the skull
• Eventually became middle ear ossicles
HS: Hyomandibula to stapes (most internal)
QI: Quadrate to incus
AM: Articular to malleus (most external)
Chewing
• Masseter and temporalis help jaw close with teeth in occlusion
• Molars become more complex
• Muscular tongue and secondary palate allow for food manipulation
• Secondary palate allows for simultaneous breathing and chewing
Integument
Hair
• Provides insulation, camouflage,
communication
• Vibrissae: hairs that provide mechanoreception
• Moved by arrector pili muscles
Glands
• Sebaceous: oil glands; entire body
• Apocrine: scent glands; regionalized
• Eccrine: vary by species
• Just hands and feet for grip
• Entire body for sweat
Lactation
Mammary glands
• Modified, branching apocrine glands
Facial muscles
• Derived from neck constrictor
muscles of more primitive synapsids
• Orbicularis oris: allow young to suckle
Separates nourishment of young from seasonal food supplies
Monotremes lack nipples (have beaks)
Brain and senses
• Mammals have large brains, particularly the neocortex
• Chemoreception is strong in most mammals
• Sight: most mammals have good low-light vision, apes are unusual in range of colour vision
• Hearing: external pinnae are unique to derived mammals
• Expanded cochlea allows for detection of high frequency sounds
Connective tissue characters
Blood
• Red blood cells lose nuclei
• Platelets for blood clotting
Fat deposits
• Around some organs for
metabolism and support
• Subcutaneous fat as insulation
Extant mammals
Marsupials and eutherians (placentals) more closely related than either is to monotremes
Allotheria: an extinct lineage
• More closely related to marsupials and eutherians
Monotremata
• mono “one” + trema “hole”
• Retain ancestral cloaca for
excretion and reproduction
• Live in Australia and surrounding islands
• Oviparous
• Lower metabolic rates than
other mammals
• Extant species lack teeth as adults
Platypus
• Semiaquatic
• Hands and feet are webbed
• Males have venomous spurs on hind legs
• Beaks house electroreceptors and mechanoreceptors
• Eat invertebrates
• Have five pairs of sex chromosomes
Echidna
• Spiny anteaters, four species
• Terrestrial
• Front limbs have large claws
• Males have scent glands on hind
legs
• Beaks house electroreceptors and mechanoreceptors
• Eat worms, ants, and termites
