GEOS 26400/36400/BIOS 23255/EVOL 32300: Principles of Paleontology Diversity, Origination, and Extinction, I. I. Nature of taxonomic data -large compilations mostly from literature (primary or secondary) -taxonomic level -species: finer resolution, but spottier record -genera & families: heterogeneously defined, but better record -Genus is "operational taxonomic unit" for many paleontologists -Genus & family patterns often match those of species. -orders & higher: may be proxies for major morphological/ecological designs -tabulating diversity (richness=number of taxa) -number of taxa depends on interval length -(number)/(interval length) problematic (error in numerator & denominator) -best to stick with intervals of roughly equal length, if possible -alternative: count taxa that cross interval boundaries (standing diversity) *advantage: not sensitive to interval length *get estimate of diversity at a point in time *disadvantage: may underestimate average standing diversity if interval boundaries are extinction pulses II. Some further uses of taxonomic data A. Description of faunal composition of fossil record -e.g., Three Great Evolutionary Faunas (marine animals) *Faunas have successively higher diversity, successively lower rates of taxonomic evolution. *Agreement between global and local composition (Peters 2004 study) *An important result that had not been predicted by many critics of global-scale analyses. B. Analysis of ecological structure -e.g., comparison between Paleozoic and Mesozoic diversification -Paleozoic: many new families, also many new orders, classes, phyla -Mesozoic: many new families, fewer new orders, classes, phyla than Paleozoic -possible interpretation: Many adaptive zones already occupied in early Mesozoic, so major innovations more difficult -implicit assumption: higher taxa are proxy for major innovations C. Relationships between evolutionary patterns and ecological factors [Covered separately under Evolutionary Paleoecology] D. Origination and extinction patterns 1. methods **Review estimate of rates based on "four fundamental classes of taxa" **But most people use... -E & O metrics ("rates") based on counts of events within interval -normalization by diversity -normalization by interval length -problem: error in interval duration -problem: assumes events spread randomly through interval -more on this under Temporal Scaling of E & O Metrics *We often find that different metrics yield same temporal patterns! 2."Big Five" mass extinctions -but extinction intensities seem to form continuous distribution, with no clear evidence for distinct "population" of mass extinctions *Despite this, there is evidence for different selectivity patterns in background vs. mass extinction events. -e.g., Late Cretaceous background vs. K/T mass extinction (Jablonski): -background: Planktotrophs, genera with many species, and genera with widespread species were favored. -mass: only genera with broad ranges (irrespective of species' range) were favored *differences may reflect quantitative effects (in part): -E.g., with random extinction, species richness affects odds of survival less when species-level extinction rate is higher 3. Phanerozoic decline in background extinction and origination rates -decline weaker or absent in single classes; may imply culling of extinction-prone taxa 4. periodicity in extinction -Criticism: noise in data -Response: noise degrades pattern, does not create it. -Criticism: periodicity inherent in time scale -Response: time scale is based largely on extinction events 5. Temporal Scaling of E & O metrics -time-normalized E rates may vary inversely with interval length -analogous to morphological rates -Factors that contribute to this pattern 1.Expected ratio of total events to total progeny nonlinear -relevant for proportional extinction per m.y. -not relevant for per-capita rates 2.Extinction may be highly episodic, with big episodes serving to define interval boundaries. -similar results for origination metrics -best to stick with intervals of roughly equal length, if possible E. Diversity dynamics: Relationships between diversity and evolutionary rates 1. diversity-dependence of taxonomic rates 2. relationship between diversity change and taxonomic-rate change a. rationale: Diversity change itself tells us only whether origination exceeds extinction or vice versa; understanding dynamics requires closer look. b. observations (Phanerozoic marine animals): i. positive correlation between change in origination rate and change in diversity ii. negative correlation between change in extinction rate and change in diversity iii. Paleozoic: div.-ext. correlation stronger than div.-orig. correlation iv. post-Paleoz.: div.-orig. correlation stronger than div.-ext. correlation v. Reason(s) for Paleozoic/post-Paleozoic difference unclear --possible relation to geographic and environmental differences discussed earlier (see Nature of the Fossil Record) --Test of environmental hypothesis: Are diversity dynamics of genera that prefer carbonate environments more "Paleozoic-like" than those of genera that prefer terrigenous clastic environments? -Answer: Evidently, yes.