Vertebrate Evolution Flashcards
What are the 3 groups of chordates?
Vertebrata, Cephalochordata and Urochordata.
What 5 anatomical structures must be possessed at some point in the life cycle of a chordate?
1) Notochord.
2) Tubular dorsal nerve tube.
3) Pharyngeal slits.
4) Endostyle/Thyroid glands.
5) Postanal tail.
What is the notochord?
A rod-like flexible structure found dorsally along the longitudinal axis of the body.
What anatomical feature was the precursor to the backbone?
The notochord.
Describe the location of the notochord.
Between the digestive tract and the nerve cord.
Describe the structure of the notochord.
A core of fluid-filled cells encased in a stiff, fibrous connective tissue sheath.
What is the function of the notochord?
It provides support whilst remaining flexible and allows swimming motion through lateral pressure against surrounding substrate.
What feature of the backbone is a remnant of the notochord?
The gelatinous material of the disks between vertebrates.
What is the dorsal tubular nerve cord?
A hollow cord dorsal to the notochord.
What does the dorsal tubular nerve cord develop from?
Dorsal ectodermal cells that form an invagination and sink inward.
Describe the structure of the dorsal tubular nerve cord.
A fluid-filled tube of nerve tissue running the length of the animal.
Describe the location of the dorsal tubular nerve cord.
Dorsal to the notochord and running the length of the animal.
What does the dorsal tubular nerve cord develop into in chordates?
The CNS.
How does the nerve cord of non-chordates differ to the nerve cord of chordates?
Non-chordate nerve cords are solid and are usually ventrally located.
What are pharyngeal slits?
Filter-feeding organs that resemble a series of slits.
Describe the location of pharyngeal slits.
Caudal to the mouth.
How have pharyngeal slits evolved in fish?
They have become modified to contain filaments for gas exchange (gills) and are supported by gill arches.
When are pharyngeal slits present in terrestrial chordates?
Only in embryonic development.
What is an endostyle?
A groove in the pharyngeal floor of protochordates that secretes mucus.
What is the function of the endostyle?
To secrete mucus which traps small food.
What organ is derived from the endostyle? What additional activity links the 2 organs?
The thyroid gland is derived from the endostyle as both organs have iodine-concentrating activity.
What is a postanal tail?
An extension of the spinal cord that extends beyond the anus.
What are myotomes?
Blocks of muscle surrounding the notochord and nerve cord.
What is the function of the postanal tail in aquatic chordates?
To provide propulsion.
How are chordates classified?
Urochordata = tail chordates. Cephalochordata = head chordates. Vertebrata = backbone chordates.
What are urochordates commonly referred to as?
Tunicates, sea squirts, salps and larvaceans.
At what life stage(s) do urochordates show the 5 anatomical structures found in chordates?
As larvae.
How do urochordate larvae and adults differ?
Larvae are mobile whilst adults are sessile. Adults can be both solitary or colonial. Larvae are just solitary.
What occurs during urochordate metamorphosis?
Larvae settle head first on hard substrates. The tail, notochord, muscle segments and nerve cord disappear.
How do adult urochordates feed?
They are filter feeders that draw in water through an incurrent siphon. Plankton is trapped in a mucus sheet and cilia direct food-laden mucus to the stomach.
How many species are there in cephalochordata?
25
Where are cephalochordates found?
Exclusively in marine environments.
From which sub-phyla of the chordates did vertebrates evolve from?
Branchiostoma (lancelets) - a group within the sub-phyla cephalochordata.
How do cephalochordates feed?
They are filter feeders.
At what life stage(s) do cephalochordates show the 5 anatomical structures found in chordates?
Throughout their entire life.
What features do cephalochordates lack, meaning they are not vertebrates?
Very small + poorly developed brain.
Poorly developed sense organs.
Notochord is not replaced by vertebrae.
What features class a chordate as a vertebrate?
Neural crest.
Pronounced cephalisation.
Vertebral column.
Closed circulatory system.
What is the clade Craniata? What are some example craniates?
A clade of chordate animals with a bone or cartilage skull. Examples include hagfish (non-vertebrate craniate) and lampreys (vertebrate craniate).
How do craniates differ to vertebrates?
Both possess a neural crest and pronounced cephalisation but craniates lack a vertebral column and closed circulatory system.
What are vertebrates in relation to craniates?
Craniates with a backbone.
Describe the anatomical features of lampreys.
Ectoparasitic blood-suckers as adults (filter feeders as young).
Circular adhesive disk + rasping tongue.
No gill arches - gills contained in 7 muscular pouches.
From what organ are jaws derived in vertebrates?
Gill supporting structures. All modern vertebrates except lampreys have jaws.
How did the evolution of jaws and fins benefit fish?
Jaws + teeth allowed the exploitation of food supplies unavailable to jawless fish. Fins + tail enabled accurate maneuvering.
What group includes the jawless vertebrate fish?
Agnatha
What group includes the jawed vertebrates?
Gnathostomata
