Comparative Anatomy Concepts & Premises Kardong Chapters 1 & 2 Part 2

Phylogeny Historical relationship between organisms or lineages Ancestry shown by phylogenetic tree Phylogenetic Systematics- shows relationships from past to present Shows evolutionary relationships Figure 2.1. Phylogenetic tree of vertebrates.

Major Vertebrate Groups Figure 2.2.

Cladistics Method for studying phylogeny Shows ancestry of derived features Figure 2.3. Advanced structures are derived, synapomorphic Primitive structures are not derived (ancestral, symplesiomorphic )

Convergence- organism response to similar environment Similar structures yet distantly related organisms Ex: limbs of fishes and marine mammals Parallelism- structure similarities in closely related organisms Similar morphology due to parallel evolution Ex: Dog and gray wolf skull Figure 2.4.

Paedomorphosis 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- Ontogenetic changes occur as larval features of an ancestor become morphological features of descendant Juvenile character stage of ancestor is retained

Paedomorphosis (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).

Paedomorphosis (cont.) Neoteny- delayed rate of somatic development Progenesis- precocious sexual maturation in morphological juvenile Behavioral Paedomorphology- juvenile behavioral stage retained Ex: wolf pup and domestic dog Heterochrony- change in rates of character development during phylogeny

Generalized- structure with broad function Ex: human hand Specialized- structure with restricted function Ex: single digit hand Modification- change from previous state, may be preadaptive Preadaptation- current trait that will be useful in future Ex: biconcave vision and thumb

Higher vs. Lower Vertebrates Amniotes- higher vertebrates with amniotic sac Ex: reptiles, birds, mammals Anamniotes- lower vertebrates without amniotic sac Ex: fish, amphibians Amnion- membrane sac that surrounds embryo Cleidoic- amniotic egg with shell

Serial homology- serial repetition of body parts in single organism Ex: Somites Figure 2.7. Somite formation in 4 week old embryo.

Vestigial Vestigial- phylogenetic remnant that was better developed in ancestor. (e.g., human appendix; python leg spurs) Figure 2.8. Ball python spurs.

Rudimentary Phylogenetic sense- structure is fully exploited by a descendant Ex: rudimentary lagena in fish (sac of semicircular canals) develops into Organ of Corti in mammals Ontogenetic sense- structure is underdeveloped or not fully developed from embryo to adult Ex: Muellerian tract in females develops into reproductive tract, yet in males, duct is rudimentary Ex: Wolffian duct in males develops into sperm duct, yet in females, duct is rudimentary

Adaptive Radiation- diversification of species into different lines through adaptation to new ecological niches. Figure 2.9. Branching evolution; increased diversity.

Sea Squirt Free Swimming Larva Figure 2.10. Larval form of sea squirt. Figure 2.11. Lamprey larval structures. Larval stage of sea squirt resembles vertebrate tadpole Developed notochord and dorsal nerve cord Rudimentary brain and sense organs

Sea Squirt Sessile Adult Figure 2.12. Adult sea squirt. Figure 2.13. Adult sea squirt structures (see book figure 2.25). Once larva attaches, notochord and nervous system disappear Resembles invertebrate Both urochordates and vertebrates probably arose from a common ancestor

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