Download Mammal-like reptiles and the origin of mammals

Mammal-like reptiles and the origin of mammals - Tom Kemp
SYNOPSIS OF THE LECTURES: 2015
Lecture 1. The evolutionary history of the synapsids (‘mammal-like reptiles’).
The differences between modern mammals and reptiles. The origin of the synapsid
lineage at the base of the amniote tree. The Upper Carboniferous-Lower Permian
pelycosaur radiation and the establishment of the first terrestrially-based tetrapod
fauna. The mid-Permian therapsid revolution heralding the escape from dependence
on tropical, permanently humid conditions to cooler, seasonal ones. Survivors of the
great end-Permian mass extinction. The Triassic cynodont radiation showing everincreasingly mammalian features. The emergence of the ancestral mammals as
miniaturised, nocturnal, insectivores in the Upper Triassic.
Lecture 2. The evolution of mammalian biology: jaws, teeth and ears.
Enlargement and reorganisation of the jaw-closing musculature leading to a
combination of very large yet at the same time very precisely applied jaw-closing
forces that is unique amongst vertebrates. This is associated with the evolution of
precisely engineered tooth occlusion which extended the range of diets and rate of
food assimilation. At the same time, the remarkable enlargement of the dentary bone
and reduction of the postdentary bones of the jaw led to increasing sensitivity to air
borne sound and eventually to the transformation of the cynodont jaw hinge bones
and angular into the mammalian-type ear ossicles and ectotympanic bone supporting
an ear-drum.
Lecture 3. The evolution of mammalian biology: locomotion.
The vertebral column lost the primitive property of lateral undulation and evolved the
characteristically mammalian regional differentiation, including a highly mobile atlasaxis complex supporting the head. The forelimb evolved greater flexibility and
amplitude of movement. The hind limb evolved a new stance and gait by getting the
feet under the body, and radically reorganising the musculature. The functional
significance of the anatomical changes relate to increased ventilation and to increased
agility of movement.
Lecture 4. The evolution of mammalian biology: the endothermic revolution.
Evidence for the evolution of enhanced ventilation, increased olfaction, enlarged
brain, and parental provision. The question of why, how, and when the metabolically
extremely expensive strategy of endothermy evolved has led to several theories.
Enlightenment lies in viewing the interactions between all the functions and processes
involved in endothermy as an integrated system. All the individual functions evolved
gradually and in a co-ordinated fashion with one another. The essence of mammalian
biology is centred on a higher metabolic rate, permitting fine physiological regulation
of the internal environment, and a complex brain and behaviour. Together these
permit a far higher level of independence of external environmental fluctuations and
therefore a greater range of habitats, niches, and lifesyles.
SYNOPSIS OF THE DEMONSTRATIONS: 2015
Demonstration 1. The synapsid radiation (Wednesday 12.00)
Pelycosaurs: the basalmost radiation of carnivorous and herbivorous taxa.
Therapsids: the Upper Permian therapsid community of several ecotypes, especially
the dominant herbivorous dicynodonts, and the specialised carnivorous gorgonopsians
and therocephalians.
The grades of cynodonts: the Permian Procynosuchus; the Lower Triassic
Thrinaxodon; the Triassic radiation of eucynodonts; the ‘near-mammalian’
tritylodonts and tritheledonts.
Demonstration 2. The evolution of mammalian biology (Friday 12.00)
Specimens showing stages in the evolution of synapsid jaws and teeth,
including the definitive mammalian condition as seen in Didelphis.
Specimens showing the pelycosaur, therapsid and cynodont grades of limb evolution,
compared to a modern reptile and a modern primitive mammal Didelphis.
Specimens showing various other features relating indirectly to physiology, such as
the secondary palate and internal surfaces of the snout.