Download Major Vertebrate Groups

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

Figure 2.4.
Ex: Dog and gray wolf skull
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


Specialized- structure with restricted function



Ex: human hand
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


Anamniotes- lower vertebrates without
amniotic sac


Ex: reptiles, birds, mammals
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).