Old Earth Ministries Online Dinosaur Curriculum
Free online curriculum for homeschools and private schools
From Old Earth Ministries (We Believe in an Old Earth...and God!)
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Lesson 73 - Ichthyosaur
Ichthyosaurs (Greek for "fish lizard") were giant marine reptiles that resembled fish and dolphins. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 245 million years ago (mya) and disappeared about 90 million years ago, about 25 million years before the dinosaurs became extinct. During the middle Triassic Period, ichthyosaurs evolved from as-yet unidentified land reptiles that moved back into the water, in a development parallel to that of the ancestors of modern-day dolphins and whales. They were particularly abundant in the Jurassic Period, until they were replaced as the top aquatic predators by another reptilian order named plesiosaurs in the Cretaceous Period.
Length: 6 - 13+ feet
Date Range: 245 - 90 Ma, Triassic - Cretaceous Period
Above: CGI reconstruction of
Ichthyosaurus communis (Picture
Below: Mounted fossil of Temnodontosaurus trigonodon (Picture Source)
Ichthyosaurs averaged 2–4 meters (6.6–13 ft) in length (although a few were smaller, and some species grew much larger), with a porpoise-like head and a long, toothed snout. Built for speed, like modern tuna, some ichthyosaurs appear also to have been deep divers, like some modern whales. It has been estimated that ichthyosaurs could swim at speeds up to 40 kilometres per hour (25 mph). Similar to modern cetaceans such as whales and dolphins, they were air-breathing.
According to weight estimates by Ryosuke Motani a 2.4 meters (7.9 ft) Stenopterygius weighed around 163–168 kilograms (360–370 lb) whilst a 4 meters (13 ft) Ophthalmosaurus icenicus weighed 930–950 kilograms (1.03–1.05 short tons).
It has been determined by teeth records that several sea-dwelling reptiles, including Ichthyosaurus, had a warm-blooded metabolism similar to that of mammals. They had the ability to generate endothermic heat to survive in colder habitats.
Although ichthyosaurs looked like fish, they were not. Ichthyosaurs had fin-like limbs, which were possibly used for stabilization and directional control, rather than propulsion, which would have come from the large shark-like tail. The tail was bi-lobed, with the lower lobe being supported by the caudal vertebral column, which was "kinked" ventrally to follow the contours of the ventral lobe.
Apart from the obvious similarities to fish, the ichthyosaurs also shared parallel developmental features with dolphins, lamnid sharks, and tunas. This gave them a broadly similar appearance, possibly implied similar activity levels (including thermoregulation), and presumably placed them broadly in a similar ecological niche.
They were viviparous (bore live young). Some adult fossils have even been found
For their food, many of the fish-shaped ichthyosaurs relied heavily on ancient cephalopod kin of squids called belemnites. Some early ichthyosaurs had teeth adapted for crushing shellfish. They also most likely fed on fish, and a few of the larger species had heavy jaws and teeth that indicated they fed on smaller reptiles. Ichthyosaurs ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Typical ichthyosaurs have very large eyes, protected within a bony ring, suggesting that they may have hunted at night.
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