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This 3 page Class Notes was uploaded by Bri M on Friday October 7, 2016. The Class Notes belongs to 3030 at Clemson University taught by Blob in Fall 2016. Since its upload, it has received 8 views. For similar materials see Vertebrate Biology in Biology at Clemson University.
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Date Created: 10/07/16
TETRAPOD ORIGINS - LECTURE 11 SARCOPTERYGIANS are osteichthyans that have a robust, skinny skeleton in appendages (fins/limbs) Tetrapodomorpha are united together by sharing a CHOANAE (internal nostril) FOSSIL RELATIVES OF EARLY TETRAPODS (DEVONIAN) ❖ Eusthenopteron ➢ They have a choana but generally retain fish like traits/features ❖ Panderichthys ➢ Lose dorsal and anal fins ➢ Flat body ➢ Fore fin is closer to tetrapod limb than hindlimb ➢ Still looks like a fish ❖ Acanthostega (early tetrapod) ➢ Has dactylus limbs → limbs with digits ➢ Still contains a tail ❖ As evolution and time went on the animals began to look more like what we know as tetrapods ➢ Their limbs used to be all fused together with large bones ➢ As evolution continued the shapes of toes and fingers became more distinct and less connected TETRAPODS SYNAPOMORPHY → have four feet EARLY TETRAPODS ❖ Acanthostega (discovered in Greenland) ❖ They had limbs but… ➢ Retain tail fin rays ➢ Hand and foot polydactylous (7 hind and 8 fore digits) ➢ Gills (blood vessel grooves on arches) ■ Are able to be seen in fossil records that have been found ❖ The first tetrapods were aquatic - tetrapod features are not necessarily for living on land (possible for walking in shallow water or living sometimes on land/sometimes in water) EARLY TETRAPODS AND EVOLUTION OF DEVELOPMENT ❖ Polydactyly in fossil taxa - they conta digits NOT ancestral for tetrapods ❖ As the foot develops it starts from the ankle, down to one side of the toes to the other ➢ So as evolution went on...the three extra toes in development stopped EARLY TETRAPODS: CHANGES IN FEEDING AND HEARING ❖ Skull mobility is reduced ➢ Suction is not longer used for feeding (because suction doesn’t work on land) ➢ HYOMANDIBULA changes function, from skull flaring to head ■ It now connects skill to tympanic membrane = eardrum, passing sound waves to the brain ❖ ACANTHOSTEGA (early tetrapod skull) ➢ Flat head, nose, and eyes on top of skull ➢ Looks almost snake like ➢ Hunting in shallows, not surrounded by water so use biting/ram feeding in place of suction (need solid skull to do this) ➢ 1st STAPES big and chunky, vibrate slowly so bad for high pitch (frequency) sounds EARLY TETRAPODS AND THE INVASION OF LAND ❖ Old idea → escape drying conditions of the sea ➢ But tock record from Devonian shows no sign of droughts ❖ New idea → exploration of novel food sources ➢ Other animals (invertebrates) and plants had already invaded land so many vertebrates were just following them ❖ Newer idea → go on land to heat up their bodies more quickly and they are then able to carry heat with them back into the water ➢ Maybe the water temp was very cool EARLY TETRAPOD RELATIONSHIPS ❖ Basal tetrapod diversity ❖ Batrachomorphs vs. reptilamorphs (similar to amphib vs. amniote) ❖ Pre-batrachomorph diversity (lepospondyls) ❖ Representative temnospondyls and origin of modern amphibians (lissamphibians) Basal Taxa Pre-Batrachomorph (Lepospondyls) ❖ BATRACHOMORPHS include most taxa thought of as AMPHIBIANS, distinguished by: ➢ Have flat skill, no kinesis and four or fewer fingers on hand ➢ LEPOSPONDYLS include diverse small taxa ❖ Derived Batrachomorphs = TEMNOSPONDYLS ➢ Many of them were bigger in size ➢ The later survivors were mainly aquatic ➢ They are a GRADE of taxa from which modern amphibian groups evolved ➢ Survived permian, but, except for modern groups, died out in Cretaceous ❖ Basil reptilomorph diversity ➢ Deeper skills, more terrestrial ➢ More specialized for land than earlier animals In Paleozoic World - Contents converging to supercontinent PANGEA - No flowering plants, trees from ferns, horsetail etc, - There was a higher 02 level so bugs/insects grew larger