BIOL2712 Study Guide - Final Guide: Dasyuromorphia, Dentition, Terrestrial Animal
25 Jun 2018
School
Department
Course
Professor
Origin and Evolution of Mammals
Overview
Mammal-like reptiles and reptile-like mammals
What makes a mammal
Monotremes, marsupials, placentals
oKey features
Australia mammal evolution
Skull Anatomy
Major groups of reptiles characterized by distinctive differences in holes for jaw
muscles
Mammal-like Reptiles (Synapsids) 300 mya
1. Trend toward limbs under body in Therapsida (leading to modern mammals)
oUses less energy standing and moving
2. Teeth differentiated into incisors, canines and post-canines
oHeterodont
3. Pelycosaurs most common land vertebrates of early Permian (280 mya)
oIncluded largest land animals to evolve up until that time
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find more resources at oneclass.com
Cynodonts
Gave rise to true mammals
oHad many “mammal” characteristics but most probably still laid eggs
Upright walking stance
Herbivores, omnivores and carnivores
Bony secondary palate separated nasal region from mouth
oYoung could breathe and suckle at same time
oTongue can better manipulate food – complex chewing/ faster metabolism
Some had complex social behaviour
oTriassic (230 mya) Trirachodon – some of the earliest multi-chambered
tetrapod burrows with up to 20 skeletons
Thermoregulatio
Protection
Reproduction
Rearing young
Evolution of the Jaw Joint
Form of jaw joint formerly a defining trait of
true mammals; since noted in some ancestral
forms
oLoss of smaller bones from back of lower
jaw
oGradual incorporation into middle ear
Improved sound amplification
oReflected in ontogeny and evolutionary
intermediates
Intermediate forms between mammal-like
reptile and mammals called mammaliaformes
oIncludes some animals with
“mammalian” jaw joints, some with
“reptilian” jaw joints, and some forms
with a double-jointed jaw
Defined as clade originating from most recent
common ancestor of moganucondonta and
brown group mammals
Separation of middle ear bones:
oHappens twice
Once in theriand
Once in monotremes (mammals that lay eggs)
find more resources at oneclass.com
find more resources at oneclass.com
Mammaliaform Evolution
Mammaliaform Diversity
Mesozoic mammalioformes were small, nocturnal insectivores
o550 dinosaur genera known
o310 Mesozoic mammal genera
Recent finds in China and Mongolia reveal they filled a diverse range of ecological
niches
oAlthough most were terrestrial
Haramiyavia
210Ma (late Triassic)
Hypothesised earliest mammal
New jaw joint morphology suggests not true mammal
Wareolestes rex
Morganucodontan
Middle Jurassic (165 mya)
Had deciduous (milk) teeth as well as adult teeth
Evidence that young were suckling
Castorocauda
Middle Jurassic (164 mya) cross between a beaver and an otter
Postcranial skeleton similar to modern Platypus
Earliest known species with hair
oIncludes guard hairs and underfur
Largest mammaliaform of the Jurrasic
Piscivorous
Volaticotherium
Middle Jurrasic (164 mya)
Glider
Fruitafosser
155 mya
Armadillo-like anteater
Body mass 6 grams
Repenomamus
Early Cretaceous (130 mya)
Badger-like species (1m long, 12-14 kg)
At small vertebrates including young dinosaurs
Largest known Mesozoic mammal
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Major groups of reptiles characterized by distinctive differences in holes for jaw muscles. Gave rise to true mammals: had many mammal characteristics but most probably still laid eggs. Bony secondary palate separated nasal region from mouth: young could breathe and suckle at same time, tongue can better manipulate food complex chewing/ faster metabolism. Some had complex social behaviour: triassic (230 mya) trirachodon some of the earliest multi-chambered tetrapod burrows with up to 20 skeletons. Form of jaw joint formerly a defining trait of true mammals; since noted in some ancestral forms: loss of smaller bones from back of lower jaw, gradual incorporation into middle ear. Improved sound amplification: reflected in ontogeny and evolutionary intermediates. Intermediate forms between mammal-like reptile and mammals called mammaliaformes: includes some animals with. Reptilian jaw joints, and some forms with a double-jointed jaw. Defined as clade originating from most recent common ancestor of moganucondonta and brown group mammals. Separation of middle ear bones: happens twice.
