Ch 5 Macroevolution

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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

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ReviewAncestral traits - similarities shared by many distantly-related groups that are inherited from a remote ancestor

Derived traits - reflect specific evolutionary lineages-modified traits from last common ancestor unique to a given group

Shared Derived traits - shared traits between two life-forms that are the most useful in constructing cladograms

CLADISTICS uses DERIVED TRAITS

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.

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Generalized and Specialized TraitsGeneralized - adapted for many functions-retaining ancestral traits-give flexible evolutionary springboard for rapid diversification which leads to:

Specialized - modification to narrow ecological niche-derivedE.g., Hominin feet evolution

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Fossils and fossilization processesMineralization - 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 stoneAnthr 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

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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

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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.

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Intraspecific - variation = individual, age, sex differences within species-If variation in fossils compares to related extant organisms, then designate single species

Interspecific - such variation represents differences between species

Splitters - speciation occurred more often

Lumpers - more likely intraspecific variability

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Types of variation continued

Macroevolution - the long conGeographical 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)

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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

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Cretaceous-Tertiary Mass Extinction~66 mya - Cretaceous-Tertiary or K-T boundary

-Large asteroid impacted the Earth caused dramatic changes in the global environmentEx: Plants and plankton could not photosynthesis

75% of plants and animals went extinct

-Dinosaurs died off SO empty ecological niches

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~75 mya emerged

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

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Mammalian Evolution

Distinctive mammalian featuresLarge brains - selected for information processing but required longer, more intense periods of growthEx. cerebrum enlarged - trend continued to increase in primates

Placental - give live birth another innovation widespread by the CenozoicLonger in utero development - central nervous system to develop more completelyInternal development in particular was a major innovation for land vertebrates

Heterodont - ancestral mammalian teeth patterns:3 incisors, 1 canine, 4 premolars, 3 molars = process a wide variety of foods

Endothermic - maintained constant internal temperature thru metabolic activities 14

Distinctive mammalian featuresLarge brains - complex information processingEx. cerebrum enlarged - trend continued to increase in primates

Placental - give live birth

Heterodont - ancestral mammalian teeth patterns -generalized

Endothermic - maintained constant internal temperature thru metabolic activities

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Primate features and evolution-features found in mammals but collected together can distinguish the primate order

1. Limbs and locomotion

2. Diet and teeth

3. Senses and brain

4. Maturation and behavior

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Primate characteristics - hypothesesArboreality - living in the trees

Adaptive niche in the trees

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