Ch 5 Macroevolution 1
Announcements and summary * April 19 = Midterm and Essay 1 due and MUST bring in hard copy of essay Midterm - 3x5 flash card Extra credit study-guide and outline on course website Today: fossils, vertebrates and mammals 2
Species Concepts Biological Species Concept - BSC - Species boundaries form due to reproductive isolation -New species form due to some type of isolation -The accumulated effects of drift and natural selection are emphasized Other concepts - Ecological, Morphological, Phylogenetic, etc. Speciation - Most basic process of macroevolution - process through which new species emerge from earlier species Various types of isolation - geographical, behavioral, reproductive 3
Unit 3: Macroevolution and primates Macroevolution - synonymous with speciation Focuses on large-scale evolutionary processes Synthesize our understanding of modes of evolutionary change, geologic time, and taxonomic classification 4
Taxonomy and Species Concepts Biological Species Concept (BSC) - isolated populations gradually change over time and become distinct taxonomic groups -Taxonomic grouping heavily influenced by genetic drift and natural selection Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Family: Hominidae Genus: Homo Species: sapiens We are Homo sapiens (also H. sapiens for short). 5
Classification schemes: Systematics and Cladistics Similar: use homologies to trace evolutionary relationships Differ: Systematics - uses homologies to trace common ancestry over time vs. Cladistics - uses homologies identify different evolutionary lineages 6
Cladistics more explicit and rigorous Ancestral traits - similarities shared by many distantly-related groups that are inherited from a remote ancestor E.g., Grasping hand in humans -Mice, bears, and lizards all have lungs -Remember the similar bone structures between whales, bats, and humans? Derived traits - reflect specific evolutionary lineages -modified traits from last common ancestor unique to a given group CLADISTICS uses DERIVED TRAITS 7
Cladistics more explicit and rigorous Shared Derived traits - shared traits between two life-forms that are the most useful in constructing cladograms E.g., feathers in the proposed relationship between some (theropod) dinosaurs and birds is an example. 8
Adaptive radiation and ecological niche Adaptive radiation - rapid expansion and diversification of new life forms into open ecological niches . Ecological niche - Micro-habitat in a shared environment to which populations adapt. -diet, terrain, vegetation, predation, interaction with other species, etc. 9
Generalized and Specialized Traits Generalized - adapted for many functions -retaining ancestral traits -give flexible evolutionary springboard for rapid diversification which leads to: Specialized - modification to narrow ecological niche -derived E.g., Hominin feet evolution 10
Fossils and fossilization processes Fossils - traces of ancient organisms manifested through various physical processes -Most fossil evidence = pieces of shells, bone, teeth - basically the hard parts of an organism 11
Fossils preservation Taphonomy - studies the processes preserving fossils are preserved Teeth - hardest, most durable portion of vertebrate skeleton and so they're most likely to mineralize Preservation depends on how and where the individual died -Need rapid sedimentation to cover up the individual or volcanic ash Land - the circle of life makes fossilization rare 12
Fossils and fossilization processes Mineralization - After an organism dies the hard tissues slowly replaced by other minerals, then solidify Insects are trapped in tree sap - hardens over time. The lack of oxygen results in very well preserved insects (we can extract DNA from them!). Impressions of leafs/things left in clay which hardens into stone Anthr E.g. 47 mya well preserved primate skeleton with soft-body imprint and fossilized remains associated with the digestive tract (Franzen et al 2009). Footprints from dinosaurs and early Hominins, too, are preserved 13
Identifying paleospecies -grouped by the clusters of derived traits -use living species as proxy Concerns -variation spatially (over space) and temporally (through time) -fossils separated by millions of years. -blurs taxonomic boundaries 14
Different types of variation in morphology Individual variation - the variation seen in an individual's phenotype due to recombination Age change variation - some fossil forms have deciduous teeth (20) while others are matured to having permanent teeth (32) Sexual dimorphism - physical characteristics differ between males and females Remember these variables to avoid errors. 15
Types of variation continued Intraspecific - variation = individual, age, sex differences within species -If variation in fossils compares to related extant organisms, then disignate single species Interspecific - such variation represents differences between species Splitters - speciation occurred more often Lumpers - more likely intraspecific variability 16
Macroevolution - the long con Geographical changes in Paleozoic and Mesozoic influenced vertebrate evolution Continental drift = continents move like sliding plates on the Earth's surface -Large landmasses shifted dramatically throughout geologic time -Induces volcanic activity (Pacific Rim); mountain building (Himalayas); earthquakes Pangea - late Paleozoic singular land mass but large chunks split to the north and south in the early Mesozoic ~65 mya -isolated by oceans => distributed mammals and other land vertebrates -Continental drift is still happening today - slow process (uniformitarianism) 17
Geological Time Scale
Vertebrate evolution - spans Paleozoic, Mesozoic, and the Cenozoic eras Fish ~500 mya in the Paleozoic (earliest out of reptiles, mammals, and birds) Mammal-like reptiles ~250 mya - diversify in Late Paleozoic Reptiles/dinosaurs ~252 mya = most dominant land vertebrates cf Mesozoic -expanded into a wide array of econiches 19
Cretaceous-Tertiary Mass Extinction ~66 mya = Cretaceous-Tertiary or K-T boundary -Large asteroid impacted the Earth caused dramatic changes in the global environment Ex: Plants and plankton could not photosynthesis 75% of plants and animals went extinct -Dinosaurs died off SO empty ecological niches 20
Mammalian Evolution ~75 mya diverged -became dominant land-living vertebrates -rapid growth starting the Cenozoic Era Major Mammal Groups *Monotremes - egg-laying = most ancestral *Marsupials - pouched = immature young complete development in external pouch *Placental - long development period in utero and placental tissue specialized to provide nourishment 21
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