Paleozoic Vertebrate Evolution (midterm 2) Flashcards
(18 cards)
What group are vertebrates a part of?
Vertebrates are a subset of chordates - vertebrates possess a backbone (vertebral column) which some chordates lack
What are the 3 characteristics that every chordate has?
- dorsal hollow nerve chord
- notochord
- pharyngeal (gill) slits
What is the main characteristic of the earliest chordates?
*first chordates were soft bodied
Important characteristics of the first vertebrates? (aka what makes them vertebrates)
- have a differentiated head
- have vertebrae (endoskeleton)
Explain the debate around the first vertebrates
- Debate regarding what counts as the first vertebrate
- Lots of fossils not good enough to tell whether they were vertebrates for sure
- Debate about what time period they began too > first vertebrates in the Cambrian?
- also diversified very quickly so it’s hard to boil it all back down
What was the oldest confirmed vertebrates?
ARANDASPIDS:
- Ostracoderm is the oldest example
> from the Middle Ordovician
When did Ostracoderms exist and what characteristic emerged with them?
- from Ordovician to end of Devonian
- “bony skin” (very thin)
- armoured jawless fish
- emergence of paired fins > pectoral girdle and pelvic girdle
**Can learn about features that we have through them (ex. paired fins turned into our limbs)
Explain the two different theories for the evolution of paired fins
Gill arch theory:
- last gill arch develops into pectoral fin
Lateral fin fold theory:
- one lateral fin fold divides into the pectoral and pelvic fins
What is the main significance of Placoderms?
- start seeing jaws and teeth > double hinged jaws
- consequently see a variety of diets and feeding strategies
How and why did jaws evolve?
the first and second gill arches developed into the upper and lower jaw
- Originally, first evolved to help with respiration
- Also later more advantages for feeding
What are the main characteristics of Placoderms? (and when did they exist)
- “plate-skinned”
- heavily armoured head and shoulders
- soft body and particular skeleton composition
- key to understanding the origin of jaws and teeth
Existed from the Silurian to the end of Devonian
What is unique about the Alienacanthus (type of Placoderms)
Has a huge long jaw sticking out
- shows a more complex feeding strategy (replicating sword fish?)
- long jaw is supposed to confuse the prey and then there are also teeth near the back of the mouth that are angled towards the back so the prey can’t get out once they’re in there
What was most common and diverse Placoderm group?
The Arthrodires
What are Chondrichthyans?
when did they evolve?
- aka ‘cartilage fishes’
- include sharks
- cartilaginous skeleton
- evolved in the early Deconian (evolved from Acanthodians)
- Not much in the fossil record because bone preserves better than cartilage
What were Acanthodians? (when did they exist)
- ‘resembling spines’
- had large bony spines and scales covering much of the body
- existed from Silurian to Permian but most abundant in the Devonian
What did the sharks evolve from? and when?
Sharks evolved from Cartilaginous fish (Chondrichthyes) - bodies are made of cartilage
Cartilaginous fish diversified during the Devonian
When did bony fish evolve and what are the two groups?
Evolved in the Devonian
Ray-finned fish
- small thin bones that support the fin
- most diverse group of vertebrates today
- 99% of modern fish species (what you think of when you think of fish)
- variety of feeding styles
Lobe-finned fish
- musculature and thick bones extending into the fins
- includes tetrapods (us)!
Significance of Coelacanth’s?
Thought of as a “living fossil”
- previously thought to have gone extinct with the dinos until a fisherman found one off the coast of Madagascar deep in the water
