6. The fish-amphibian transition was not a passage from water to land, but rather a transition from fins t feet that took place in water. Based on aspects of functional morphology, the earliest amphibian limt probably were used to scud around on the bottom in the water, as do some modern fish (such as the mu skippers, species of Boleophthalmus and Periopthaimus, of the Indo-Pacific), rather than to facilitate wall ing on land. It has been suggested recently that the origin of tetrapods and the invasion of land by ve: tebrates be decoupled. Several anatomical characters of the limbs separate tetrapods from their fish ancestors. These include th presence of digits, carpals (in the forelimb, the bones that make up the wrist) and tarsals (in the hindlim the bones that help make up the ankle), and bones in the limb of approximately equal length (e.g.. the u nus/radia of the forelimb) that both participate in the development of the joint. A. The following diagram illustrates the bone structure of (1) an early rhupidistian lobe-tinned fi: (Eusthenopteron), (2) a coelocanth fish (Latimeria), (3) an early tetrapod (Ichtityostega) and (4) an exta aquatic mammal (family Otaridae, the seals). Draw a vertical line separating the limbs of tetrapod tro fish. Upon which anatomical character(s) did you base this division? B. The carliest tetrapods retained a limb structure similar to that of the fins of ancestral figh. Rather than having limbs based upona fivetoed foot, as do modern tetrapods, these animals had more than five "toes, "This gave the feet the Jook of a short, stout fipper with many "toe rays" similar to fin ravs. Identify the early tetrapod by writing ICTHY on the diagram. How does the toe structure of this hind limb differ from that of the mammal? C. The fins of most lobe-finned fishes have a simple bifurcate design. That is, bones develop in a pattem of twos during embryogenesis. The mid-late Devonian thupidistian possessed this limb arthitecture. Its Eins were very similar to early amphibian feet in the overall layout of the major bones, except that there were no perceptible "toes," fust a set of identical fin rays. Identify the limb structure of Eusthenopteron by writing EU on the diagram. How does the bone structure of this fish compare with that of the early tetrapod? D. Land-dwelling arimals must bear weight on their limbs in order to move efficiently on terra firma. One feature that helped early vertebrates move on land, and allowed for weight to be borne, was the development of limb joints (elbows and knees). All but one of the early tetrapods are from continentai depoetits, and all possess simular arrangements of bones in the limbs as depicted in the drawing. Compare the skeletal arrangemens of the semi-aquatic mammal and the early tetrapod. What can you inier about the ability of each to move about on land..

1. 6. The fish-amphibian transition was not a passage from water to land, but rather a transition
from fins t feet that took place in water. Based on aspects of functional morphology, the earliest
amphibian limt probably were used to scud around on the bottom in the water, as do some
modern fish (such as the mu skippers, species of Boleophthalmus and Periopthaimus, of the
Indo-Pacific), rather than to facilitate wall ing on land. It has been suggested recently that the
origin of tetrapods and the invasion of land by ve: tebrates be decoupled. Several anatomical
characters of the limbs separate tetrapods from their fish ancestors. These include th presence of
digits, carpals (in the forelimb, the bones that make up the wrist) and tarsals (in the hindlim the
bones that help make up the ankle), and bones in the limb of approximately equal length (e.g..
the u nus/radia of the forelimb) that both participate in the development of the joint. A. The
following diagram illustrates the bone structure of (1) an early rhupidistian lobe-tinned fi:
(Eusthenopteron), (2) a coelocanth fish (Latimeria), (3) an early tetrapod (Ichtityostega) and (4)
an exta aquatic mammal (family Otaridae, the seals). Draw a vertical line separating the limbs of
tetrapod tro fish. Upon which anatomical character(s) did you base this division?
B. The carliest tetrapods retained a limb structure similar to that of the fins of ancestral figh.
Rather than having limbs based upona fivetoed foot, as do modern tetrapods, these animals had
more than five "toes, "This gave the feet the Jook of a short, stout fipper with many "toe rays"
similar to fin ravs. Identify the early tetrapod by writing ICTHY on the diagram. How does the
toe structure of this hind limb differ from that of the mammal? C. The fins of most lobe-finned
fishes have a simple bifurcate design. That is, bones develop in a pattem of twos during
embryogenesis. The mid-late Devonian thupidistian possessed this limb arthitecture. Its Eins
were very similar to early amphibian feet in the overall layout of the major bones, except that
there were no perceptible "toes," fust a set of identical fin rays. Identify the limb structure of
Eusthenopteron by writing EU on the diagram. How does the bone structure of this fish compare
with that of the early tetrapod? D. Land-dwelling arimals must bear weight on their limbs in
order to move efficiently on terra firma. One feature that helped early vertebrates move on land,
and allowed for weight to be borne, was the development of limb joints (elbows and knees). All
but one of the early tetrapods are from continentai depoetits, and all possess simular
arrangements of bones in the limbs as depicted in the drawing. Compare the skeletal
arrangemens of the semi-aquatic mammal and the early tetrapod. What can you inier about the
ability of each to move about on land.