Vertebrates 8 - Appendicular skeleton Flashcards
Parts of appendicular skeleton
Pectoral and pelvic girdles, attached limb
Parts of fin
Basals, radials, and fin rays (majority of surface area). Most of these formed of cartilage in chondrichts. and bone in bony fish
Fins in extinct lobe finned fish
Fin rays, radials, basals still present. Radials branch on basals. A humerus is present which connects to pectoral girdle. Some have large basals and humerus
Evolution of tetrapods theories
Lobe-fin fish walk onto land, or amphibian with legs leaves water. Arose in devonian period about 400-375mya
Fish to tetrapod transitional fossils
tiktaalik (most like a fish with an amphibian head = fishapod) and acanthostega (more amphibian like = tetrapod). Both found in the arctic (Canada and Greenland). Both had moveable heads (opercular bones more like separate shoulder). Fossilized tetrapod tracks in Poland.
Gene expression in fish vs tetrapods
Hox genes. Fish express certain hox genes to form fin, only one time. Amphibians and mammals express these genes two times, contributing to extension of limb and digits.
Early tetrapod limb skeleton (Acanthostega)
Same bones for the most part. Humerus attaches to girdle, radius, ulna, carpals, metacarpals. Hindlimb is also similar. Acanthostega had 8 digits.
Phalangeal formula in most lizards.
1 is most medial. 2-3-4-5-3
Primate forelimb
Opposable thumb, rotation and flexibility, doesn’t bear any weight. 2-3-3-3-3.
Ungulate limbs
Bear weight on end of last digit (only one in horse, Phalangeal = 00300). Long limb, extra joints for flexibility speed
Therapod limbs
Hindlimb is robust, thick. To decrease this weight, they have more spongy bone in whole skeleton. Hindlimb 2-3-4-4-0, hallux (thumb) in rear), 3-4-0-0-0 forelimb, not sure what used for.
Reading: Difficulty with whale evolution
Lack of transitional fossils. Hard to determine the ancestors
Reading: possible ancestors of whales
Artiodactyl (ungulates) or mesonychian (hoofed wolf-like animal)
Reading: Ankle bones and cetaceans
Transitional forms had remnants of legs and ankles. Astralagus has two “pulleys” where it articulates. This is found in artiodactyls and whale transitional forms but not mesonychian
Video which had to do with reading: Evidence of whale evolution (not bones)
The way their spine undulates is just like otters or even dogs as they run
Reading: Whale evolutionary forms
Pakicetus, ambulocetus, rodhocetus, dorudan, basilosaurus, modern whale
Reading: Whale evolution progressive steps: Pakicetus and ambulocetus
Pakicetus inner ear was removed from skull, would help hear better in water; Ambulocetus more streamline, flat feet, smaller limbs;
Reading: Whale evolution progressive steps: Rodhocetus, dorudan
Rodhocetus totally aquatic, long digits as tho webbed, large spines for swimming, reduced sacrum, nares move back, more dorsal; Dorudon has no pelvic girdle but still small hindlimb, more lumbar vertebrae, muscular articulating tail, forelimb couldn’t support body but could steer, fused cervical vertebrae;
Reading: Whale evolution progressive steps: basilosaurus and modern whales
basilosaurus has minimized sternum, hindlimb almost nonexistent, nares further back; modern whales nares very far back, dolphins (toothed) and baleen whales which still have pelvis and hindlimb (most dolphins don’t), baleen don’t have teeth
Evolution of wings
First in Reptilia (pterosaurs), then birds, then mammals. Convergent evolution, totally unrelated.
What is a wing?
A modified forelimb. Generally long, a large surface area, with a specific shape.
Wings in reptilia
Pterosaur. In Cretaceous. Skin membrane stretched across the elongated arm and digit four down to the hindlimb. Had 3 free claws, climb to heights to take off possibly. 23440
Wings in birds
In Jurassic. Wing on arm and digit 3 is biggest. Surface area increased by feathers. No free digit, less friction. Feathers are an advantage because you don’t need blood etc, so it is much lighter
Wings in mammals
Bats. In Tertiary period. Arm and 4 digits used to support the skin membrane. One free grasping digit normally
Pterosaur
Is not a dinosaur!! Just a reptile (different skull)
Girdles
Pectoral and pelvic girdles. Pelvic is more often connected to the axial skeleton at the sacrum, bears more weight.
Pelvic girdle features
Ilium, ischium, pubis (clockwise). Acetabulum is ball and socket joint, bears weight and provides flexibility. Fused at pubic (pelvis) symphysis. Obturator foramen is the window in the pelvis.
Pelvic girdle in mammals vs reptiles
Rotated underneath more which is better for running. Reptile limbs are more splayed out.
Pelvic girdle groups in dinosaurs
Saurischian “lizard hip”, large pubis; and Ornithischian “bird hip”, ischium is long.
Confusion with dino groups
Ornithischian means bird hip, but birds evolved from therapods which were saurishcians. Their pelvic girdle today has evolved to look like ornitischian’s.
