Comparative AnatomyComparative Anatomy

Concepts & PremisesConcepts & Premises

KardongKardongChapters 1 & 2Chapters 1 & 2

Part 2Part 2

PhylogenyPhylogeny

Historical relationship Historical relationship between organisms or between organisms or lineageslineages

Ancestry shown by Ancestry shown by phylogenetic treephylogenetic tree

Phylogenetic Phylogenetic SystematicsSystematics- shows - shows relationships from past relationships from past to presentto present Shows evolutionary Shows evolutionary

relationshipsrelationships Figure 2.1. Phylogenetic tree of vertebrates.

Major Vertebrate GroupsMajor Vertebrate Groups

Figure 2.2.

CladisticsCladistics Method for Method for

studying phylogenystudying phylogeny Shows ancestry of Shows ancestry of

derived featuresderived features

AdvancedAdvanced structures are derived, synapomorphic structures are derived, synapomorphic PrimitivePrimitive structures are not derived (ancestral, structures are not derived (ancestral,

symplesiomorphic )symplesiomorphic )

Figure 2.3.

ConvergenceConvergence- organism response to similar - organism response to similar environmentenvironment Similar structures yet distantly related organismsSimilar structures yet distantly related organisms

Ex: limbs of fishes and marine mammalsEx: limbs of fishes and marine mammals

ParallelismParallelism- structure similarities in closely related - structure similarities in closely related organismsorganisms Similar morphology due to parallel evolutionSimilar morphology due to parallel evolution

Ex: Dog and gray wolf skullEx: Dog and gray wolf skull

Figure 2.4.

PaedomorphosisPaedomorphosis

PaedomorphosisPaedomorphosis- Ontogenetic changes occur as - Ontogenetic changes occur as larval features of an ancestor become larval features of an ancestor become morphological features of descendantmorphological features of descendant

Juvenile character stage of ancestor is retainedJuvenile character stage of ancestor is retained

Figure 2.5. (Left) Larval state salamander with external, feathery gills; (Center) Adult salamander that lost gills; (Right) Adult axolotl salamander retains juvenile external gills.

Paedomorphosis Paedomorphosis (cont.)(cont.)

Figure 2.6. Natural selection pressures on the wolf may have lead to the formation of a new species, the domestic dog. The prehistoric adult dog skull (center) can be compared to the adult wolf skull (left) and particularly the juvenile wolf skull (right).

NeotenyNeoteny- delayed rate of somatic development- delayed rate of somatic development ProgenesisProgenesis- precocious sexual maturation in - precocious sexual maturation in

morphological juvenilemorphological juvenile Behavioral PaedomorphologyBehavioral Paedomorphology- juvenile - juvenile

behavioral stage retainedbehavioral stage retained Ex: wolf pup and domestic dogEx: wolf pup and domestic dog

HeterochronyHeterochrony- change in rates of character - change in rates of character development during phylogenydevelopment during phylogeny

PaedomorphosisPaedomorphosis (cont.)(cont.)

GeneralizedGeneralized- structure with broad function- structure with broad function Ex: human handEx: human hand

SpecializedSpecialized- structure with restricted function- structure with restricted function Ex: single digit handEx: single digit hand

ModificationModification- change from previous state, - change from previous state, may be preadaptivemay be preadaptive

PreadaptationPreadaptation- current trait that will be useful - current trait that will be useful in futurein future

Ex: biconcave vision and thumbEx: biconcave vision and thumb

Amniotes- higher vertebrates with amniotic sac Amniotes- higher vertebrates with amniotic sac Ex: reptiles, birds, mammalsEx: reptiles, birds, mammals

Anamniotes- lower vertebrates without amniotic Anamniotes- lower vertebrates without amniotic sacsac

Ex: fish, amphibiansEx: fish, amphibians

Amnion- membrane sac that surrounds embryo Amnion- membrane sac that surrounds embryo Cleidoic- amniotic egg with shellCleidoic- amniotic egg with shell

Higher vs. Lower VertebratesHigher vs. Lower Vertebrates

Serial homology- serial repetition of body parts Serial homology- serial repetition of body parts in single organismin single organism

Ex: SomitesEx: Somites

Figure 2.7. Somite formation in 4 week old embryo.

Vestigial- phylogenetic remnant that was better developed in ancestor.

(e.g., human appendix; python leg spurs)

Figure 2.8. Ball python spurs.

VestigialVestigial

RudimentaryRudimentary

Phylogenetic sensePhylogenetic sense- structure is fully exploited by a - structure is fully exploited by a descendantdescendant

Ex: rudimentary Ex: rudimentary lagenalagena in fish (sac of semicircular canals) in fish (sac of semicircular canals) develops into Organ of Corti in mammalsdevelops into Organ of Corti in mammals

Ontogenetic senseOntogenetic sense- structure is underdeveloped or - structure is underdeveloped or not fully developed from embryo to adultnot fully developed from embryo to adult

Ex: Ex: Muellerian tractMuellerian tract in females develops into reproductive tract, in females develops into reproductive tract, yet in males, duct is rudimentaryyet in males, duct is rudimentary

Ex: Ex: Wolffian ductWolffian duct in males develops into sperm duct, yet in in males develops into sperm duct, yet in females, duct is rudimentaryfemales, duct is rudimentary

Adaptive RadiationAdaptive Radiation- diversification of species - diversification of species into different lines through adaptation to new into different lines through adaptation to new ecological niches.ecological niches.

Figure 2.9. Branching evolution; increased diversity.

Sea Squirt Sea Squirt Free Swimming Larva Free Swimming Larva

Larval stage of sea squirt resembles Larval stage of sea squirt resembles vertebrate tadpolevertebrate tadpole Developed notochord and dorsal nerve cordDeveloped notochord and dorsal nerve cord Rudimentary brain and sense organsRudimentary brain and sense organs

Figure 2.10. Larval form of sea squirt. Figure 2.11. Lamprey larval structures.

Sea Squirt Sea Squirt Sessile AdultSessile Adult

Once larva attaches, notochord and nervous system disappearOnce larva attaches, notochord and nervous system disappear Resembles invertebrateResembles invertebrate Both urochordates and vertebrates probably arose from a Both urochordates and vertebrates probably arose from a

common ancestorcommon ancestor

Figure 2.13. Adult sea squirt structures (see book figure 2.25).

Figure 2.12. Adult sea squirt.

Figure 2.14. Overview of phylogenetic relationships within the deuterostomes (book figure 2.33).