Intro and evolution

Página 1

Introduction

Introduction to mammals

INTRODUCTION TO MAMMALS

* 98 % are terrestrial

* Features of mammals include (LACTATION, ENDOTHERMY, HAIR/FUR, UNIQUE DENTITION (HETERODONT), SENSES (LARGE GRAIN SIZE and HIGHLY DEVELOPED SENSE ORGAN e.g. EXTERNAL EAR)

* 3 groups (MONOTREMES i.e. egg laying, MARSUPIALS i.e. pouched and PLACENTAL MAMMALS)

Note: Success of a group measured by WIDE DISTRIBUTION IN DIFFERENT ENVIRONMENTS, No. OF SPECIES i.e. SPECIES RICHNESS and No. OF INDIVIDUALS OF A SPECIES

EVOLUTION OF MAMMALS

* AMNIONTA (common mammal and reptile ancestor 305 mya), laid terrestrial egg which wasn't reliant on water and had direct development

* Were of 3 types, mammals evolved from SYNAPSIDS (had temporal fenestra i.e. opening low in the skull under the eye resulting in a bony arch beneath each eye).

* PELYCOSAURS (early for of synapsids that were either semi aquatic fish eaters e.g. Ophiacodon, Terrestrial herbivores or terrestrial carnivores e.g. Dimetrodon)

* THERAPSIDS (came into existence 270 mya, descended fro ma single pelycosaur ancestor i.e. monophyletic. Dominant in late Permian period, had canine tooth, stronger skull and jaw and endothermy probably developed now)

* Drop in diversity around 250 mya due to natural disasters ?

* Early mammals appear in Triassic period (250-203 mya)

* Small mouse sized during Jurassic period (200-150 mya)

* Juramaia sinensis (Early relative of placental mammal 160 mya)

* Extinction of dinosaurs in Cretaceous period (65 mya) allowed adaptive opportunity and hence mammal radiation worldwide

* Mammal diversification (70 - 50 mya), break up of Pangaea isolated groups of mammals and helped specialisation.

MAMMAL FEATURES

* LACTATION (mammary glands , varying fat content between spp.) (Increased survival rate as young isn't on its own, transfer of immunity, parental care i.e. learning behaviour, strong social bonding) [Drawback is high energy investment by mother]

*ENDOTHERMY (internal regulation of body temp. using metabolic heat) (enables survival in wide range of habitats, can remain active in cold temp., energetic movement) [drawback uses 80-90% energy from food for thermoregulation and hence little chance for large biomass growth, need more food]

* HAIR/FUR (unique to mammals, conserve heat by insulation, colour can reflect heat)

* DENTITION (simplified lower jaw bone which is single, heterodont specialised dentition, molars with 3 triangular cusps for chewing, variation between spp.) (Mammals have milk teeth and permanent teeth, palate divides chewing and breathing apparatus to enable simultaneous breathing and eating)

* DENTAL FORMULA ICPM (half top jaw/half bottom jaw)

EVOLUTIONARY TIMELINE

CARBONIFEROUS PERIOD (350 - 290 MYA) [Appearance of Amniotes]

PERMIAN PERIOD (290 - 250 MYA) [Appearance of Therapsids]

TRIASSIC PERIOD (250 - 200 MYA) [Decline of Therapsids, Cynodonts appear and early mammals]

JURASSIC PERIOD (200 - 150 MYA) [Juramaia sinensis, early placental mammal ancestor]

CRETACEOUS PERIOD (150 - 65 MYA) [Dinosaur extinction, mammal radiation and diversification, Pangaea break up isolate and specialise mammals]

TERTIARY (65 - to date) [mammal diversification continues 70-50 mya]

New Page