Lecture 4: A N I M A L E V O L U T I O N :F R O M T H E C A M B R I A N T O T H E C E N O Z O I C Flashcards
what Eon, era, period and epoch are we in?
We are in:
*Phanerozoic Eon
*Cenozoic Era
*Quaternary Period
*Holocene Epoch
how is life spread across geological time?
*Earth is ~4.5 Billion years old
*Not a lot happened for the vast majority of that
*Events within the last ‘3 hours’:
*540MYA -Cambrian Explosion
*360MYA –Vertebrates on land
*65MYA –Dinosaur extinction
*2MYA –Human evolution
what happened in P R E-C A M B R I A N L I F E?
*For the majority of 3bn yrs -Microbial films growing on sediment surface *These did build up on top of each other to form reef like structures
*Snowball earth event terminates the period of microbial dominance due to anoxia
*Mid Ediacaran 580Ma –Gaskier’sglaciation opening of ecological niches
*Ediacaran biota: A glimpse into early complex life which sit at the base of the animal evolutionary tree
*Generally soft-bodied and feed through absorption from water
what is biomineralization?
550Ma: Very early evidence for animals making shells (biomineralization
560Ma: Trace fossils from worm-like animals
what are the features of the Cambrian explosion?
*Cambrian explosion 541 Mya –diversification of most modern taxa but also lots of evolutionary dead ends with strange shapes and features that haven’t been seen since
*Land was still barren but oceans became diverse and complex ecosystems
*Lots of evidence from Burgess Shale in Canada
*beginning of “hard bodied” animals, generally all very small (<15cm)
*Development of first apex predators and active hunting –Anomalocaris(60cm)
*Common after mass extinctions to get many strange animals quickly adapting to fill nich
Weird “mistakes?”e.g. Opabiniaand Hallucigenia
Mouth parts that are not seen on any modern arthropod
D E F I N I N G C A M B R I A N E X P L O S I O N- Taxonomic
Taxonomic
*Animals represent highest level of bodily organisation
*Sudden explosion in number of different body plans that are present
*Not the origin of animals but the start of diversification and origin of body plans we still recognise today
*Stabilises in Ordicivica
D E F I N I N G C A M B R I A N E X P L O S I O N- ecological
Ecological
*Animals and their interspecies interactions become much more dynamic –food web development
*E.g. burrowing and ecosystem engineering –higher diversity of trace fossils
*New lifestyles e.g. pelagic, planktonic
D E F I N I N G C A M B R I A N E X P L O S I O N- anatomical
Anatomical
*Diversification of biomineralization
*Different groups used different minerals (calcium, silica, etc)
*Evolution of skeletons for protection from predatio
C A U S E S O F T H E C A M B R I A N E X P L O S I O N
Oxygenation Event
Lack of Oxygen was holding back animal evolution pre-CambrianOxygenation event happens and larger and more complex animals able to evolve.
*At the end of snowball earth -> nutrients into water -> more photosynthetic algae -> oxygen increases
*Also end of snowball earth -> glacial erosion -> minerals into water -> more bioavailable minerals for shells
Result of a Mass Extinction
*Niches created by a suspected end-Ediacaran Mass extinction event
*Rapid evolutionary arms race between predator/prey interactions
*e.g. vision occurs right at the start –is this the trigger?
*Huge selection on soft bodied animals to evolve hard defensive parts and faster locomotion
what are characteristics of vertebrates?
*Extremely simple to complex
*Increased germ layers
*Radial/bilateral symmetry
*Development of digestive system
*Open/closed circulatory systems
*Deuterostome development
*Notochord structure
what are the characteristics of jawless fish?
*508Ma first fish, no jaw, no fins or gills
*Stuck sucking prey and generally limited on how to feed
*Some later developed teeth but without the leverage that comes from a jaw
*Most likely had strong muscles to help close mouth
*Some extant species like hagfish and lamprey
how did fish evolve jaws
*Most fish have jaws, and are Gnathostomes, including tetrapods. The origins of gnathostomes date back to the Ordovician (450-500 mya) but it was not till the devonian that their diversity expanded
*Entelognathusfirst animal with modern jaw
*Primitive jaws allowed fish to develop into more niches including predatory ones which had previously only been arthropods
*Began with development of gills which acted as a precursor for jaws –theorised first pair of gill arches moved forwards to create a mouth structure
what are characteristics of the Devonian age of fishes?
*Explosion in Devonion408Ma into big, heavily armoured fish which dominated over inverts for first time -Placoderms
*First fish with pectoral and tail fins
*Give them stability in water and faster locomotion
*Developed as jaws allowed them to fill more niches e.g. apex predators that required faster swimming
*Dunkleosteus–most powerful bite ever?
*Ancestors of all modern fish and vertebrates
*Evidenced by jaws –shared by all other vertebrates
*Two bones on top jaws (maxilla and pre-maxilla) that we still have
Placoderms go extinct at end-Devonian mass extinction.Also see evolution of cartilaginous fish –sharks and rays
what are characteristics of LOBE-FINNED F I S H E S ( S A R C O P T E R Y G I A N S )?
L O B E-F I N N E D F I S H E S ( S A R C O P T E R Y G I A N S )
*Develops as a dominant group by the end of Devonian
*Only 4 extant lobe finned fish (lungfish, coelacanth)
*Primitive lungs -probably also used for buoyancy and later divergent into separate lungs and swim bladders
*The Lobe fin eventually develops to the tetrapodlimb and all land-based vertebrate groups descend from this
*375Ma Tiktaalik –primitive hips, wrist and shoulder joints which enabled to use fins to come out of water somewhat or at least be in very shallow water where it could follow small fish into shallow water without fear of getting stuck. Also feed on beached carcasses
what are the problems with water species invading land?
Lots of problems… so why do it?Support –no longer buoyed by water, need muscle strength
*Locomotion –need legs
*Respiration –new breathing system
*Reproduction –eggs need to be in water