Origin of Vertebrates P2

What are Lissamphibia, and what are their defining characteristics?

1. Lissamphibia are modern amphibians. Their defining characteristics are as follows: 

• Adapted for land and jumping

• External fertilization (reproduces in water)

• Metamorphose

• 1st tympanic membrane (eardrum)

• Only 1 ear ossicle (stapes)

• Examples of Lissamphibia:

  • Caudata = salamanders (tailed amphibians) - external fertilization

  • Apoda (caecilians) - went through reverse evolution, limbless, burrowers, internal fertilization

What are the amniotes, and what characteristics define them now and in the past? What are the two main lineages?

1. The first amniotes were reptiles. Amniotes have amnion (amniotic fluid) and extraembryonic membranes. Some characteristics that define them now and in the past are their amniotic egg due to their calcareousness and their extraembryonic membranes due to the nutrients it stores and allows for eggs to be laid on land w/o drying out. The two main lineages: 

• Sauropsida: modern reptiles; ex. birds and dinos  

• Synapsida: mammal-like reptiles and it has a single ventral fenestra 

• Ancient reptiles → anapsids, diapsids, synapsids, euryapsids

What are some Sauropsids and what are their defining characteristics?

Some Sauropsids examples are modern lizards, snakes, birds, dinosaurs, pterosaurs, turtles and crocodiles. Their defining characteristics are as follows: 

• Amniotic eggs w/ protective shells for terrestrial reproduction

• Scales or feathers for water retention and thermoregulation 

• Specific skull and brain structure (dorsal ventricular ridge) for sensory processing

What are some synapsids and how did mammals evolve?

Some synapsids are all mammals and mammal-like reptiles. The synapsid reptiles evolved into mammals by first forming hair (modified reptile scales), stronger jaw, new jaw joint, three different type of teeth (canine, pre-molars, and molars), reorganized chewing muscles, and specialized ears for improved hearing→ 3 ossicles (stapes, malleus and incus). 

 

What are the defining characteristics of mammals? 

• Limbs under body

• Muscular diaphragm helps with breathing 

• Mammary glands → milk 

• Endothermic 

• Exothermic 

• Anucleated RBC’s → more oxygen = more brain activity 

• Taller skull → bigger brain

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