Quiz 5

1. Which phylogenetically derived part of the skull (splanchnocranium etc.) comprises MOST of the mammalian skull?

Dermatocranium

2. The palatoquadrate bone and Meckel's cartilage are important bones for what reason?

They comprise the upper and lower jaws of early vertebrates. These two bones are believed to have arisen from the first visceral (branchial) arches of the splanchnocranium

3. Which class of vertebrates has an akinetic skull and why?

Mammals-

Adaptive reasons for akinesis: firmer substrate for chewing (only mammals extensively chew their food). The skull CAN'T move much because of the formation of the hard palate which is an adaptation for suckling and chewing. The hard palate allows both of these behaviors to occur while breathing.

4. What structure allows turtles to engage in suction feeding?

Greatly enlarged pharynx which allows the water to be half swallowed and not allow the prey to escape.

1. surrounds the otic (auditory) and olfactory capsules

chondrocranium

2. tracheal cartilage and hyoid bone

splanchnocranium

3. Meckel's cartilage and palatoquadrate

splanchnocranium

4. Bones that make up the lateral and

anterior portion of the cranium (e.g.

parietal, frontal bones etc.)

dermatocranium

Appendicular skeleton-Chapter nine

The appendicular skeleton includes the limbs, and their associated pelvic and pectoral girdles.

As such the appendicular skeleton serves primarily, if not exclusively, a locomotor function.

There are large and obvious differences in the form of limbs used in aquatic versus terrestrial systems, but within each system, there are specialization of movement

Consider sea horses, flying fishes, moray eels, and walking catfish with respect to fin use as example.

Or how a horse, mole, gibbon, bat, and bird use their appendages.

Clearly the broadest distinction lies between fins and tetrapod limbs

We already discussed the functional significance of fins so we won't be dwell on that topic now. What we didn't discuss was what they are and where they came from-especially paired fins.

Paired fins are of particular evolutionary significance because it is these from which tetrapod limbs are derived.

Since fins are designed mostly to push water, they often have projecting spines and broad surfaces

Ostheichthyes

Chondricthyes

These two fin types have influenced our understanding of where we think fins came from-

Where did fins come from? How did they evolve?

Question: There is dermal bone in the pectoral girdle but not the pelvic.

Why is this?

1. Dermal bone was necessary to reinforce the pectoral fins to a greater extent than pelvic fins and stabilize the fin

Dermal bones could attach to the pectoral girdle and allow for a more anterior orientation and leverage point of the pectoral fins.

Tetrapod limbs

Although the origin of paired fins lies buried in a murky and incomplete fossil record, the same does not hold true for the origin of tetrapod limbs.

Tetrapod limbs are derived from a Sarcoptergian ancestor, specifically, a Crossopterigian fish (like the Coelocanth) similar in limb form to the Coelocanth.

Fleshy lobed fins of these fishes have various bone elements that are easy to see the homology with early labrinthodonts

Show overhead page 168 Hildebrand

Show overhead page 280 Walker and Liem -pelvic girdle

Unfortunately, to avoid confusion-need to introduce new terminology associated with limbs-why? Because a hand isn't always a hand, and a foot isn't always a foot.

Modern lungfish and gill arch shape of sharks suggest origin

Fins arose from continuous paired folds along vetrolateral portion of the animal

Folds served as stabilizers of caudal, dorsal, and ventral fins (e.g like metapleural folds on Amphioxus).

Pterygiophores stabilized the fins-proximate basals, Distal radials

Basals extended inward and fused with other bones producing girdle

Dermal fin rays are modified scales

Fossil fish show evidence of remnants of fin folds

Acanthodii have double rows of spines along ventrolateral border

Shark fins develop from continuous thickening along ventrolateral wall that later separate

Other vertebrate limbs form from a longitudinal zone of limb-forming opaque cells.

Embryologically, dermal fin rays do appear to arise from scale-generating tissue in modern fishes

Fins originated as dermally-derived spines on ventrolateral portion of body

Anterior and Posterior pair became larger than others

Epidermis spread into sheets of webbing between spine and body

Fin rays developed to further stabilize and support membranes

Radial elements would support the large spine as a stabilizer at the base

More advance acanthodii have larger pectoral and pelvic spines with webbing

Latest acanthodii show weakly developed fin rays.

Antiarchs, another extinct group of primitive gnathostomes, had jointed spony armored pectoral appendages (but no pelvic).

Acanthodii bear many unique structures that do not suggest they were ancestors of modern fishes

Does not explain differences in dermal elements of pectoral versus pelvic girdle.

Fusion of all three bones in most mammals and birds to form innominate (or os coxa)