Animals: Vertebrates Flashcards
Chordates
animals with a notochord; form a clade within the Deuterostomes
Notochord
flexible, rod-shaped structure that arises from mesodermal tissue during embryonic development
- found in the embryonic stage of all chordates and the adult stage of some chordate species
- located between the digestive tract + nerve cord
- provides support throughout the length of the body
Dorsal Hollow Nerve Cord
nerve cord that arises from ectodermal tissue that rolls into a hollow tube during development; located dorsal (along the back) from the notochord
- other animal phyla have SOLID nerve cords located ventrally or laterally
- this chord found in most chordate embryos develops into the brain + spinal cord, which compose the CNS
Pharyngeal Slits
openings in the pharynx (region just being the mouth) that extends to the external environment
- for aquatic residing organisms, they allow for the exit of water that enters the mouth during feedings
- some invertebrate chordates use these to filter food out of water that enters the mouth
- in vertebrate fishes, these are modified into gill supports and/or jaw supports
- in tetrapods (amphibians, reptiles, birds, mammals) the slits are modified into components of the ear + tonsils
Muscular Post-Anal Tail
a posterior elongation of the body, extending beyond the anus; contains skeletal elements + muscles that provide a source of locomotion in aquatic species
- in some terrestrial vertebrates, the tail helps with balance, courting, and signaling danger
- in apes + humans, the tail is vestigial (reduced in size + nonfunctional)
Chordate Review
- 3% of all animals species
- invertebrates or vertebrates
- 3 types of invertebrate chordates: lancelets, tunicates, and hagfish
- all possess a notochord, dorsal hollow nerve chord, pharyngeal slits, and muscular post-anal tail
- triploblastic deuterostomes that evolved from an ancestor with cephalization
New Chordate Vertebrate Adaptations
- Cranium
- Vertebral Column
- Jaw
- Cartilaginous Skeletons
- Mineralized (bony) Skeletons
- Lungs
- Lobed Fishes
- Four Limbs
- Amniotic Egg
Cranium (Skull)
evolved in a group of chordates called CRANIATES
- fossils of the earliest craniates date to the Cambrian Explosion
- Modern day hagfish (Myxini) are non-vertebrate chordates that are the only living species with a skull but no vertebral column. They have some vertebrate-like structures from a MRCA like a skull, notochord, and no jaw
Vertebral Cloumn
evolved in an early craniate, resulting in the first VERTEBRATE
- presence of a column replaces the notochord, which is only seen in the embryonic stage
- fish were the earliest vertebrates with jawless species early and jawed species later
- jawless fish are called Agnathostoems
Jaw
hinged structure attached to the cranium that allows an animal to grasp/tear food; evolved in a group of vertebrates called Gnathostomes / “jaw-mouths”
- ONE OF THE MOST SIGNIFICANT DEVELOPMENTS IN EARLY VERTEBRATE EVOLUTION
- facilitated evolutionary arms race between predators, competitors, and prey
- earliest Gnathostomes also possessed two sets of paired fins, allowing for a more mobile life and better predators. this allowed them to exploit food resources unavailable to jawless fish
- most modern fish have jaws
Cartilaginous Skeletons
appear in cartilaginous fish (Chondrichthyes) - gnathostomes that possess paired fins + a skeleton made of cartilage
- EX: sharks, rays, sawfishes, chimaeras)
- first appear in FR ~395 MYA and may have evolved from one group of early placoderms
- some evidence suggests that possibly-placoderm ancestors of these fish once had bony endoskeletons that was in time replaced with cartilage
Mineralized (Bony) Skeletons
evolved in bony fishes (Osteichthyes), appearing in the FR ~420 MYA
- may have evolved from another group of placoderms, distinct from the ancestors of cartilaginous fish
- largest class of vertebrates in existence today
- bony fishes include ray-finned and lobe-finned fish
Lungs
first appeared in early Osteichthyes; these lungs later evolved into swim bladders which are present in modern-day fish
- early lungs allowed fish to “gulp” air in oxygen poor conditions; this air could then supplement O2 obtained from gills + circulated in the circulatory system
Lobed Fins
adaptation that appeared in lobe-finned fishes (Sarcopterygii) ~425 MYA; these fish allowed for later evolution of tetrapods
- differ from ray-finned fishes in that the fin extends from a fleshy lobe-like structure that resembles a limb bud and is connected to the body by a single bone
- most of these fish are now extinct, but living species include coelacanths + lungfishes
Four Limbs
first appeared in an early group of TETRAPODS ~400 MYA in a now-extinct amphibian species. Evolution of tetrapods from lobe-finned freshwater fishes REPRESENTED A SIGIFICANT CHANGE IN BODY PLAN THAT SUITED TO ORGANISMS THAT RESPIRED + SWAM IN WATER TO BREATHING + MOVING ON LAND
