Paleozoic Vertebrate Evolution (midterm 2) Flashcards
What group are vertebrates a part of?
Vertebrates are a subset of chordates - vertebrates possess a backbone (vertebral column) which some chordates lack
(all vertebrates are chordates but not all chordates are vertebrates)
What are the 3 characteristics that every chordate has?
- dorsal hollow nerve chord
- notochord
- pharyngeal (gill) slits
What are the other examples of Chordate characteristics (not the necessary ones)
- post-anal tail
- head region
- all soft tissue
What groups do the modern chordates include?
- vertebrates
- tunicates
- hagfish
- lancelets
What are two examples of the earliest chordates and main characteristic of them?
*first chordates were soft bodied
Yunnanozoon - from China
- 5cm long
- 525 million years old (early cambrian period) - before burgess shale
Pikaia - found in burgess shale
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 (during Devonian huge jump of diversity in Placodermi)
What are the two proposed first vertebrates?
ANATOLEPIS:
- generally agreed upon early jawless fish (vertebrate) represented by phosphatic plates > from the Cambrian
ARANDASPIDS:
- confirmed oldest vertebrates
- Ostracoderm is the oldest example
> from the Middle Ordovician
What did Ostracoderms exist and what are their important characteristics?
- from Middle 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 posterior gill arch develops into pectoral fin
- based on genetic data
Lateral fin fold theory:
- one lateral fin fold divides into the pectoral and pelvic fins
- supported by embryological and paleontological data
What is the main significance of Placoderms?
- start seeing jaws and teeth
- double hinged jaws
- consequently see a variety of diets and feeding strategies
> some people question if they can be considered true teeth because they lacked enamel
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 - allows a bigger opening allowing animal to bring in more oxygen for better 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 (this is usually all that is preserved)
- 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?
- aka ‘cartilage fishes’
- include sharks, rays, chimaeras and acanthodians
- 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
- specifically basal chondrichthyan = early relatives of modern sharks
Cartilaginous fish diversified during the Devonian
When did bony fish evolve and what are the two groups?
Evolved in the Devonian
Ray-finned fish (Actinopterygii)
- 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 (Sarcopterygii)
- musculature and thick bones extending into the fins
- include lungfish, coelacanths, and tetrapods (us)!
Significance of Coelacanth’s?
Thought of as a “living fossil”
- previously thought to be extinct until a fisherman found one off the coast of Madagascar in 1938
- Thought they went extinct with the dinosaurs but realized they just went deep down into places where we didn’t look
What are the 3 applications from researching Paleontology fossils
- phylogeny (how we’re all related)
- anatomy and behaviours
- ecology
