Vertebrate Evolution Flashcards
The urochordates include the _______. These are mostly sessile, filter-feeding animals that look almost nothing like a chordate. However, their larval form possesses all of the basic characteristics of a chordate.
Tunicates
Briefly describe the subphyla, cephalochordata
- Cephalochordates, the lancelets retain a chordate body plan throughout life
- In addition to other defining chordate characteristics, lancelets, as well as tunicate larvae, have somites.
- Somites are blocks of musculature arranged in segments along the bodies of lancelets and fishes (as well as derivations of this segmentation found in tetrapods)
In lancelets, ______________ serve as filter-feeding devices in primitive chordates.
Water exits via the _______.
- Pharyngeal slits.
- atriopore
Briefly describe the class, myxini
- Class Myxini are represented in modern times by the hagfish, (slime eels)
- These are jawless invertebrate chordates
- Technically, hagfish are not fish; they are more like “sophisticated” lancelets
Hagfish have cartilaginous skulls but no jaws and no vertebrae
Briefly describe the class, Petromyzontidae
- Petromyzontidae is represented in extant lineages by lampreys
- Lampreys lack jaws, like their non-vertebrate, chordate ancestors and hence are known as jawless fish
- Jawless fish were the vertebrate forerunners of the jawed fish
- Lampreys, in addition, lack paired fins
- As vertebrates, lampreys are (just barely) members of subphylum vertebrata
- *Lamprey have vertebrae but no jaw
Briefly describe the superclass Gnathsomata
- Jawed fish are referred to as gnathostomes for their defining feature: jaws
- Jawed fish also have skulls, vertebrae and paired fins
Briefly describe the class, Chondricthyes
- Chondrichthyes includes the sharks and rays
- Members of this class are named for their cartilaginous skeletons, i.e. unmineralised (or less mineralised) skeletons
Briefly describe the class, Actinopterygii
- Members of class Actinopterygii are the ray-finned fish
- The lobe-finned fish are members of Sarcopterygii
What is special about coelacanths?
- Lobe fins are supported by musculature and a bony skeleton; they may be employed for “walking” upon the bottom and other substrate found within bodies of water
Briefly describe the class, Dipnoi
- Members of class dipnoi are the lung fish
- The lungfish are named for the lungs they retain and use for gulping air, especially when air is less readily available within the freshwater in which they reside
What are the three types of extant lungfish
- Australian lungfish
- South american lungfish
- African lungfish
What is special about australian lungfish?
- The larval stage of australian lungfish resembles tadpoles, and their eggs like those of amphibians
Briefly describe the class Amphibia
- Amphibians are the lineage descended from the earliest tetrapods: the terrestrial vertebrates
- The amphibians were the dominant terrestrial vertebrates during the carboniferous period, i.e. the same time the seed-less vascular plants dominated the land
- Most amphibians are dependent on the water: eggs are not desiccation resistant
- Amphibians employ their skin for gas exchange, thus requiring are not well-adapted to multi-generational excursion away from moist habitats
Briefly describe the class, Reptilia
- Note how the reptiles are indicated as a sister group to the mammals
- In fact, the reptile and mammals together form a clade known as the amniotes
- The defining features of the amniotes are keratinised (waterproof) skin and the amniotic (shelled) egg
What are the amniotes?
- The amniotes were the first fully terrestrial vertebrates achieving true freedom from water except of course, for the need to drink
