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Lecture 8

BIOC50H3 Lecture 8: Lecture Eight


Department
Biological Sciences
Course Code
BIOC50H3
Professor
Jason Weir
Lecture
8

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Lecture Eight
- There were a lot of marine predators that evolved from land tetrapods that had gone back
into the ocean
- These reptilian marines monsters are the topics…they created a good food web
Different groups of reptilian monsters:
Mosasaurs
o Related to the monitor lizard found today and thus represent a clade of squamates
that adapted to marine environments
o They grew to large size in the marine environment
o The monitor lizards went into the ocean and essentially became mosasaurs
o Fossils of mesosaurs are known from a short time window towards the end of
Cretaceous
o During the 20-million-year window, they’re the dominant predator in the marine
environment
Largest mosasaurs would eat the smallest mosasaurs; also ate fish,
molluscs and other prey
o Ranged from 3 meters to 17.5 meters
o Propulsion came from moving body and tail like a crocodile
o Their tetrapod limbs have now become adapted back to flipper like structures
(Evolutionary reversal)
- Skeleton of three types of mosasaur
o Tail offers more propulsion
- They lived in the end of the Cretaceous
- Mosasaurs fit into the squamates as they are close relatives to the reptile and dragon
Ichthyosaurs
- Their tail is vertical compared to the dolphin tail that is horizontal
- Limbs modified back to fins similar to those in dolphins
- Main propulsion is side to side body motion like a fish, whereas a dolphin has an up
down body motion
- The tail fin is generally very deep…characteristic of swimmers that use fast acceleration
- Powerful jaw
- Good eyesight
- Some early ichthyosaurs had blunt, shell-crushing teeth for hunting ammonites and other
shelled cephalopods
o Most ichthyosaurs ate fish
- Specialized ichthyosaurs in morphology, Eurhinosaurus, similar to a sword fish
o Upper jaw used to slash its way through a school fish, the spinning around the
catch its crippled victims
- How did these species evolve:
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