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Ichthyosaurs• “Ichthyosaur” means “fish lizard”• predatory marine reptiles that swam the world’s oceans while dinosaurs walked the land• Appeared slightly earlier than dinosaurs (250 million years ago)
Ichthyosaurs• These animals rapidly diversified from being lizards with fins to developing a much more streamlined, fish-like form built for speed
Ichthyosaurs• Triassic period to middle Jurassic Period• Streamlined shape• four, strong, crescent-shaped fins• Homocercal caudal fins• They breathed air with lungs through nostrils.
A specimen of the Jurassic icthyosaur Ichthyosaurus intermediusMore advanced ichthyosaurs — like the one shown above, ondisplay at the Senckenberg Museum in Frankfurt, Germany — hadcompact, very fishlike bodies with crescent-shaped tails.
There was ageneraltransitionfrom lizard-shaped bodyplan to fish-shaped bodyplan.
THREE STRANGE FEATURES1. Limb skeletons that look like corncobs2. Gigantic eye bones3. Vertebrae resembling ashtrays or hockey pucks
1. Limb skeletons that look like corncobs• The limb skeletons went through a drastic modification as Ichthyosaur a. The lower arm bones became shorter and shorter b. Finger bones also became shorter and shorter, and eventually became disk-shaped c. The number of finger bone increased early in the evolution d. Thumb disappeared at one point
2. Gigantic eye bones• Ichthyosaurs had exceptionally well- developed sclerotic rings• Sclerotic rings maintain eye shape during locomotion
3. Vertebrae resembling ashtrays or hockey pucks• The only thing that is unusual about the backbone of lizard-shaped ichthyosaurs is that there are too many vertebrae compared to average reptiles
Viviparity• most ichthyosaurs are believed to have given birth to live young, rather than laying eggs like contemporary land-bound reptiles thus, they did not have to come ashore to reproduce The proof of this lies in the remains of some ichthyosaurs, such as Temnodontosaurus, that contain fossilized fetuses
Ichthyosaurs• Despite their fish-like appearance, their anatomy shows they were once land-lubbers • two pairs of limbs, with digit-like bones rather than rays or spines in their flippers • a shoulder girdle connected to the skull. The roof of the skull had a pair of openings called fenestra: a hallmark of reptiles (diapsids). • lack of gills
Plesiosaurs• “near lizard”• Small head like a head of a lizard• broad body• short tail• Their limbs evolved into (four) limb flippers• 2m to 20m long• Long neck• Lacked streamlined, hydrodynamic body shape
Plesiosaurs• It is thought that they swam slowly below the surface of the water, and then used their long necks to position to snap up fish or cephalopods.• flippers gave them ultimate maneuverability which helped them rotate their body quickly to catch escaping prey.
Ichthyosaurs Plesiosaurs“fishlizard” "near lizard"crescent-shaped fins long necks Pointed tailsStreamlined body Limbs evolved toshape flippersFast swimmers Lacked streamlined body shape Slow swimmers