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what are the closest living relatives of vertebrates?
marine animals such as the sea squirts and amphioxus
When did deuterostomes and chordates originate?
What are the key characters of chordates?
- a hollow nerve cord
- segmentation - myomeres arranged along body wall (muscles)
- Pharyngeal slits (gill slits)
- endostyle organ(equivalent to the tyroid gland)
- post anal tail
How do extraordinary new fossil discoveries from China help us understand the ancestry of vertebrates?
generally made from an outer sheath of collagen, a tough fibrous connective tissue that encloses turgid fluid-filled spaces.
v-shaped muscle blocks running along the length of the bodies of chordates.
includes the bilaterally symmetrical organisms, comprising three clades, Lophotrochozoa (brachiopods, phoronids, annelids, molluscs and many minor groups), Ecdysozoa (arthropods, nematodes, priapulids and some minor groups) and Deuterostomia (echinoderms, hemichordates and chordates).
Urochordata: sea squirts
The larval sea squirt has a notochord that runs along the tail, identifying it as a chordate. The larva has a dorsal nerve chord, running along the tail just above the notochord, and this expands at the front into a very simple brain which indludes a light sensor and a tilt detector.
- Looks like a young lamprey without a head.
- Has a pharynx, notochord, dorsal nerve cord, myotomes, and endostyle, makes it typically chordate.
- more closely related to echinoderms than to chordates.
- They do not have a notochord at any state, but they possess gill slits, as in chordates, and giant nerve cells in the nerve cord of the collar region that are probably equivalent to similar nerve cells in amphioxus and primitive vertebrates.
most invertebrates, the blastopore (first opening) becomes the mouth.
- a few invertebrates, and all chordates, the blastopore becomes the anus and the mouth is a secondary perforation.
- include the phyla chordata, hemichordata, and echinodermata.
possible early chordates
- 1. urochordates
- 2. cephalochordates
- 3. vetuliocolians
- 4. carpoids
the full development of the gonads and reproductive abilities in an essentially juvenile body.
living individuals may differ from parents how?
- changes in timing of appearance of characters
- animals with vertebral columns
- Arose form invertebrates
animals showing radial symmetry, i.e. echinoderms
Additional vertebrate characters
- specialized kidney tubules; marine origins
- Brain case and vertebral column
- Blood circulation patterns
- Gut outgrowths-liver and pancreas
- neural crest cells
- Neural photoreceptors
- Bilateral cleavage in embryos
- Secondarily formed mouth, not derived from blastopore
Early important new characters of vertebrates
- pharyngeal pumping mechanism for water circulation and improvement of feeding capabilities
shared derived characters: dorsal, hollow nerve cord, notochord
Transition to land
- Amphibians adapted to survive at land-water interface
- Reptiles can remain on land, including reproductive changes no water immersion requirements
heirarchical, may be based on grade level organization
all lower levels contained within higher one, relationships based on clades
- Agnatha: jawless fishes
- Chondrichthyes: Cartilagionous fishes
- Osteichthyes: bony fishes
- Amphibia: amphibians
- Reptilia: reptiles
- Aves: birds
- Mammalia: mammals
Vertebrate Paleontology Origins
- fossils not always recognized for what they are
- "Dragon bones" in many mythologies
- Rancho La Brea fossils used to pave early roads
- -believed to be remains of cows and other living species
- -nothing different from extant species
- extinction had to be discovered
Many different kinds of fossils
- Flattened organisms
- 3D organisms, preserved bone by bone
- Skin and other feature impressions
- Natural casts