Mesozoic life - Origin of Mammals (final exam) Flashcards
What is the connection between fossils and the western interior seaway?
Where was the seaway in relation to Manitoba?
Deep into the seaway there are shales (indicates low oxygen) which means in that environment there were lots of animals dying and lots of fossils being preserved
Cut across the bottom left corner of Manitoba
What are the two branches of the reptile evolution from mid-late permian to the Triassic
the common ancestor: Protorothyrids (mississippian-permian) - considered one of the earliest true reptiles
> true reptile branch > Thecodontians (permian-triassic)
> true mammal branch > Pelycosaurs (pennsylvanian-permian) > Therapsids (permian-triassic) - ancestors of all mammals
List the 3 main families in order that are in the mammalian evolution branch leading up to mammals
Pelycosaurs > Therapsids > Cynodonts > Mammals
What are the modern mammal characteristics?
- warm-blooded
- hair or fur
- mammary glands
- generally give birth to live young
What are amniotes?
They are tetrapod vertebrate animals - it is a large group that comprises the vast majority of living terrestrial and semiaquatic vertebrates > mammals, birds, or reptiles
Explain the 3 different amniote skull types
Revolves around how many temporal fenestra’s they have (side skull holes) > these holes connect muscles (purpose ex. = feeding)
- Anapsid:
- don’t have any temporal fenestra
- ex. turtles - Synapsid:
- have one temporal fenestra on each side
- all mammals are synapsids (but not all synapsids are mammals) - Diapsid:
- two temporal fenestra on each side
- ex. reptiles
What groups are a part of the non-mammalian synapsids? When were there lots of synapsids?
Synapsids include stem-mammals (animals that lead into the evolution of a common ancestor) - which for mammals is the Pelycosaur family
Lots of synapsids during the early permian
- most famous = Dimetrodon (carnivore) and Edaphosaurus (one of the first vertebrate herbivores)
- famous because they had sails
What are some possible functions of the sail of Dimetrodons and Edaphosaurus’
- thermoregulation (ecotherms?)
- sexual display
- camouflage/intimidation
What is a big difference between synapsids and dinosaurs?
Synapsids have different specialized teeth throughout their mouths
Significance of Bathygnathus borealis?
Means, deep jaw from the north
First thought to be a dinosaur when it was found in 1845
What is the Therapsid group and their main features?
Therapsids are the more “mammal-like reptile”
- more derived / evolved from synapsids
- dominant in the late permian
Mammal-like features:
- fused bones in skull (more fused bones = simplifying over time)
- enlarged lower jawbone
- differentiation of teeth
- vertically placed legs
- endothermic (likely)
What is the Cynodonts group?
*late permian
- diversified after permian extinction (great dying)
- more derived from Therapsids > have even more mammalian characteristics (partly developed secondary palate, differentiated teeth, some occlusion - teeth grinding, probably endothermic, possibly mammal-like skin)
- continued developing through the Triassic
When did mammals evolve and what were they like? What were the 3 main groups they evolved into?
Evolved in late Triassic > most Mesozoic mammals were small
They diverged by the middle Jurassic into 3 main groups:
- Monotremes: egg-laying - most primitive of the true mammals we have today (ex. platypus, echidna)
- Marsupials: pouched (ex. opossums, wombats, kangaroos) - originated in Pangaea, migrated to Australia via Antarctica - limited species in the Americas (more prominent in southern hemisphere)
- Placental: Have uterine placentas (prolonged gestation - further development in the womb) > the amnion of amniote egg fuses to the uterus wall *90% of mammals are placental
Which groups of mammals produce milk
the Placentals and Marsupials have true mammary glands that produce milk
Explain how the break-up of Pangaea impacted mammal evolution
- south America was an island until about 3 million years ago
- then Marsupials reached Australia from South America and Antarctica
- only a few placentals reached Australia
How does the lower jaw differ between a typical reptile, cynodont, and mammal
reptile: dentary and several other bones
dynodont: dentary enlarged, other bones reduced
mammal: dentary bone only, except in earliest mammals
*basically just simplifying
How do ears differ in mammals compared to reptiles and cynodonts
Mammals have 3 ear bones - stapes, incus, and malleus, whereas reptiles only have stapes
What is the significance of the secondary palate in mammals?
Mammals have a secondary ‘hard’ palate to separate the nasal cavity from the mouth - allows them to breathe while chewing (reptiles don’t have this)
What are the main differences in teeth from reptiles to cynodonts to mammals?
Reptiles:
- lifelong tooth replacement
- undifferentiated teeth that are fused to the jaw
- no occlusion (chewing grinding)
Cynodonts:
- have some of each of these characteristics (in the middle)
Mammals:
- limited tooth replacement
- differentiated teeth that are double rooted
- tooth occlusion (grinding)
- periodontal ligament - teeth can move around and chew
What is the significance of the occipital condyle in mammals? (compared to reptiles and cynodonts)
Occipital condyle allow for head movement (fish can’t move their heads independently)
- reptiles and birds have a single pivot occipital condyle, acting as a pivot point
- cynodonts have a partly divided occipital condyle
- mammals have double occipital condyles - it is split in two
Are mammals, cynodonts, and mammals endothermic or ectothermic?
reptiles = ectothermic
cynodonts = probably endothermic
mammals = endothermic
How did the body coverings evolve from reptiles to cynodonts to mammals?
reptiles > scales
cynodonts > skin similar to mammals? (one fossil shows this)
mammal > skin with hair or fur
