| Ichthyosauria | |
|---|---|
| |
| Several species of ichthyosaurs | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sauropsida |
| clade: | †Eoichthyosauria |
| Order: | †Ichthyosauria Blainville, 1835 |
Ichthyosaurs were a type of large carnivorous marine reptile that closely resembled modern day dolphins and sharks which is called convergent evolution. Ichthyosaurs thrived from the middle Triassic Period to the late Cretaceous Period. Ichthyosaurs include the largest marine reptiles known to date. There have been Ichthyosaur fossils recorded at 21 to 23 meters. Although some Ichthyosaurs were huge, the average size for an Ichthyosaur was about two-four meters; some were even smaller than that.
Ichthyosaurs are often compared to modern-day cetaceans such as whales and dolphins. This is mainly because they were air-breathing and viviparous (able to give birth to live young). Although Ichthyosaurs were reptiles and had descended from egg-laying ancestors, the ability to give birth to live young is not as unexpected as it might seem. All air-breathing marine creatures must either come to the surface and on to the shore to lay eggs, like turtles, or else give birth to live young in surface waters, like whales and dolphins. Because their streamlined bodies were heavily adapted for fast swimming, it would have been difficult for ichthyosaurs to successfully make it onto land to lay eggs. Researchers concluded that Ichthyosaurs most likely gave birth in the water. They have been found as such.
Discovery[]
The first known illustrations of ichthyosaur bones, vertebrae and limb elements were drawn by Edward Lhuyd in his book of ichnofossils in 1699. Lhuyd thought they were fish. In 1708, Johann Jakob Scheuchzer talked about ichthyosaur bones thinking they belonged to a man drowned in the Universal Deluge. In 1779, ichthyosaur bones were illustrated in John Walcott's Descriptions and Figures of Petrifications. Near the end of the eighteenth century, British fossil collections and galleries quickly increased in size. Those of the naturalists Ashton Lever and John Hunter were taken by museums; later, it was found that they had dozens of ichthyosaur bones. The bones had typically been labelled as belonging to fish, dolphins or crocodiles; the teeth had been seen as those of sea-lions.
The demand by collectors led to more intense commercial digging. In the early nineteenth century, this resulted in the discovery of more complete fossils. In 1804, Edward Donovan at St. Donats uncovered a four metre long specimen containing a jaw, vertebrae, ribs and a shoulder. It was thought to be a giant lizard. In October 1805, a newspaper article reported the find of two additional skeletons, one discovered at Weston by Jacob Wilkinson, the other, at the same village, by Reverend Peter Hawker. In 1807, the last fossil was described by the latter's cousin Joseph Hawker. This specimen thus gained some fame among geologists as Hawker's Crocodile. In 1810, an ichthyosaur jaw was found that was combined with plesiosaur bones to obtain a more complete specimen, indicating that the distinctive nature of ichthyosaurs was not yet understood, awaiting the discovery of far better fossils.
In 1811, in what is the Jurassic Coast of Dorset, the first complete ichthyosaur skull was found by Joseph Anning, the brother of Mary Anning in 1812. Their mother, Molly Anning, sold the fossil. Henley lent the fossil to the London Museum of Natural History. When this museum got closed, the British Museum bought the fossil. It still belongs to the collection of the now independent Natural History Museum and has the inventory number BMNH R.1158. It Is a specimen of Temnodontosaurus platyodon. In 1814, the Annings' specimen was described by Professor Everard Home, in the first scientific publication dedicated to ichthyosaurs. Intrigued by the strange animal, Home tried to find additional fossils. In 1816, he wrote about ichthyosaur fossils owned by William Buckland. In 1818. In 1819, he wrote two articles about specimens found by Henry Thomas De la Beche and Thomas James Birch. A last publication of 1820 was dedicated to a discovery by Birch at Lyme Regis.[11] The series of papers covered the entire anatomy of ichthyosaurs.
Home felt uncertain how the animal should be looked at. Though most skeletal elements looked very reptilian, the anatomy as a whole looked like that of a fish, so he initially assigned the creature be a fish, as seemed to be confirmed by the flat shape of the vertebrae. At the same time, he considered it a transitional form between fish and crocodiles. In 1818. In 1819, he considered it a form in-between newts, like Proteus, and lizards; he now gave a formal generic name: Proteo-Saurus. However, in 1817, Karl Dietrich Eberhard Koenig had already referred to the animal as Ichthyosaurus, "fish saurian" from Greek ἰχθύς, ichthys, "fish". This name at the time was an invalid nomen nudum and was only published by Koenig in 1825,[14]but was adopted by De la Beche in 1819 in a lecture where he named three Ichthyosaurus species. The type species was Ichthyosaurus communis, based on a now lost skeleton. Conybeare considered that Ichthyosaurus had priority relative to Proteo-saurus. The latter name became a nomen oblitum or "forgotten name". In 1821, De la Beche and Conybeare provided the first description of ichthyosaurs, comparing them to another newly identified marine reptile group, the Plesiosaurs.
Biology[]
Ichthyosaurs are fish-like reptiles that lived from the mid triassic to the beginning of the late Cretaceous. They all shared traits that were that they all looked fish-like, they all had bodies that were highly evolved for swimming and living their entire lives in water and they were all carnivorous. Some had no dorsal fins or very small dorsal fins like Shastasaurus and Cymbospondyus. The reason for this is that they were slow swimmers or had a dorsally balancing part somewhere else like their tail or they had bigger and rounder fins.