Evolution of Sharks

Insert Name: Instructor’s Name: Course: Date: 08/July/2010 Sharks have been in existence for more than 300 million years. Their evolution occurred over 150 million years earlier than that of the dinosaurs. Most of the existing fossil data of early sharks was collected from fossilized teeth together with several skin impressions. primitive sharks (Cladodonts) , had teeth which were double-pointed, up to 2metres in length, ate fish as well as crustaceans, and existed approximately 360 million years ago.

The earliest shark-like beings shown in the fossil records seem to have existed towards the start of the Silurian age, close to 450 million years ago, however the earliest fossil teeth known of actual sharks was not discovered until the Devonian age, about 400,000,000 years ago. Their teeth were not more than 4 millimeters or 0. 16 inches across. A candidate for close comparison is Antarctilamna, whose bones have been discovered in the Antarctic continent rocks.

This fish was forty centimeters long, and conspicuously shark-like. Its spine was located at the front of a long dorsal fin, additionally its teeth that had 2 huge splayed cusps, and smaller cusps positioned between them. The era of fishes During the Devonian period the first key radiation of sharks began. This is referred to as the ‘age of fishes’—during this period all fishes, including sharks, began to diversify greatly. Cladoselache was one of the most primitive true shark skeletons discovered intact.

Fossils of ray-finned fish were found intact in some of their stomachs, their direction shows that they were captured tail-first, and therefore Cladoselache must have been skilled in swimming faster than its prey. Close to twenty five per cent of species so far discovered had been feeding on Convaricaris crustacean which obscured itself in sediments on the sea floor and fed on the lifeless flesh of squid and fish. Sharks and Cladoselache existing in the Devonian seas had to struggle with the dreadful placoderm fishes which were armor-plated.

Sharks had gained a tactical lead by having body shapes that was both streamlined, hydro dynamically and efficient. With a flexible skeleton of cartilage that provided them with strength, they were better suited than their rivals and destined to go on to even superior things. The era of sharks When the Carboniferous period began, approximately 360 million years ago, sharks evolved and proliferated at a fast rate to the extent that scientists named it the ‘golden age of sharks’. Furthermore, to the apparent shark-like species, some can only be termed as bizarre. Stethacanthus almost certainly grew up to 3. meters long and was different from any other shark, dead or living. it had a helmet of miniature teeth on its head and a probing structure which looked like a square shaving brush clearly visible out of its back, approximately where its frontal dorsal fin ought to be. Both male and female sharks had dozens of teeth, larger teeth at the back and small ones at the front. Such a noticeable and awkward formation must have had a significant purpose. It might have had a function in courtship, or defense, or perhaps it enabled Stethacanthus to secure itself, as in case of a modern remora, to the base of a bigger fish.

Early sharks Sharks and chimaeras fit in to Class Chondrichthyes, since they lack true bones. in its place, their skeletons (counting their jaws and vertebrae) are composed of cartilage. The cartilage is regularly calcified, causing it to be hard, similar to bone, but not really ossified. Chondrichthyes only bony part are their teeth and scales also known as dermal denticles. The 1st shark fossils are composed of small dermal denticles. They are structurally alike to teeth. These first recognized sharks are contemplated to have been vigorous swimmers with harmonizing fins and a torpedo-shaped structure.

Many sharks in the Paleozoic age resembled current dynamically swimming sharks but had more archaic skeletons. The body and fin support structures varied extensively. They all had huge triangular matching pectoral fins and a lot of also had matching pelvic fins, the majority had tails in which the higher and subordinate lobes were of identical size, unlike a number of modern sharks, similar to great whites, where the top lobe is considerably larger than the underside lobe. 1 odd fossil type from this instance, Xenacanthus, had a tail with no connected lobes, similar to a modern sea snake.

Early sharks did not have calcified vertebrae, even if they had unfossilized cartilage parts. Their notochord, was rigid but bendable rod where the present spinalcord would be probably located. (In most current vertebrates, the backbone is present only at the embryo stage, but its initial function was to help the primary fish with swimming. ) 300 million years ago, in the late Carboniferous age, the era of rapid diversification ended, and sharks existed through millions of years with minimal evolutionary transformation.

Then, a global catastrophe took place at the end of the Permian age, 245 million years ago, widespread volcanic eruptions, jointly with the ensuing climate change and fluctuations in sea level, led to the disappearance of about ninety per cent of aquatic life Most species of sharks, many of which had turn into victims of their own evolution, joined the casualty record, but a small number survived and a subsequent evolutionary jolt brought about two main shark species to fill the empty ecological niches.

One species incorporated the xenacanth sharks. They seem to have avoided extermination by relocating into freshwater. One group, Xenacanthus, was a seventy five centimeters in length, eel-like shark that looked like a modern conger eel. Its dorsal fin extended along its back and around the tail and connected to an odd double anal fin. The main striking feature was a single self-protective spine growing from the top of its head. Other survivors were the hybodonts, they were unspecialized sharks that looked like modern sharks but weren’t immediate ancestors.

Their triumph confirmed that the fundamental shark structure and manner of life had evolved effectively millions of years before present sharks appeared. At the beginning of the Jurassic era, two hundred and thirteen million years ago, the initial ‘modern’ sharks were testing the hybodonts. The new sharks had extra flexible jaws that were capable of thrusting frontwards, providing them with a distinct advantage in the struggle for food. The hybodont ancestry started to end, and sharks amazingly similar to current species began to take over.

Hybodonts Throughout the early Paleozoic and Mesozoic ages, the major sharks belonged to a set called Hybodontoidea. They had fins and bony structure which was more superior than that of previous sharks. Male species had 1 or 2 pairs of spines on their heads, this were used throughout mating season to grasp the male and female jointly. Hybodontoidea was a similar ancestry of current shark species. Its 1st representatives were discovered around the Mississippian era 360 million years ago and existed until the finish of the Cretaceous age 80 million years ago, at his point in time they became extinct alongside the dinosaurs.

Hybodontoidea, then, existed for a longer duration than the dinosaurs did, though they are now wiped out, they were a very triumphant species. Early naturalists considered them to be the associates of current sharks, but they have a several exceptional characteristics therefore, even before the topic of cladistics was formalized, scientists discovered that the hybodonts had no existing offspring. Arrival of Modern sharks The Cretaceous and Jurassic periods were the era of reptiles’.

In the ocean, shark-like ichthyosaurs which were relatives of the dinosaurs became fast-swimming, streamlined, and developed remarkable set of senses which made them strong competitors The cretoxyrhinid sharks, became vigorous hunters with lengths over 6 meters and had weight in excess of one tone. The ptychodonts, a species of sharks identified simply from their teeth. This crushing teeth configuration, appropriate for handling hard-bodied creatures e. g. bivalves, ammonites and gastropods.

Cretaceous deposits also had shark teeth which look remarkably similar to those tiger sharks and also there were the identifiable teeth of huge lamnid sharks, relatives of modern mackerel sharks, and this species have got to have been over 6 meters in length. Fossils from prehistoric porbeagles Lamna, have been discovered in rocks. The fact that sharks arose at all is impressive and a miracle, for they started to change during a series of destructive episodes in history that had a lot of effect on sharks and their food.

Near the end of the Triassic age, an additional 20 per cent of aquatic families were struck badly by another mass destruction, and at the last part of the Jurassic era there was additional minor occurrence. Then, at the close of the Cretaceous age, approximately sixty million years ago, close to 70 per cent of all existence, as well as the dinosaurs, were wiped out. However, it was an opening, for others to thrive, and several of the new shark species survived the calamity. A distinct failure of diversity in the species emerged, but the survivors were a strong, well-honed group.

These integrated vast filter feeders, for example Cetorhinus the basking sharks, straining the ocean water for krill in the mode of current baleen whales; in addition, small fossil teeth, strongly resembling those from filter-feeding super mouth Megachasma, are still being found in Tertiary rocks. They evolved to be fast-swimming predators, too, together with a new species of sharks that rule the oceans to the present day this includes –the requiem sharks (carcharonids). With the downfall of the gigantic reptiles, the mammals started to fill up some of the empty niches, and several went back to the sea.

The, seals dolphins, whales and sea cows became the chief supply of food for 1 species of sharks in particular–the prehistoric family of the great white shark. The most primitive fossil teeth similar to those of present great whites were discovered in rocks about sixty million years aged. Even at this pre historic age, the great white’s relatives were perched in evolutionary conditions to exploit the imminent superabundance of fat and meat, and some varieties of sharks took full advantage, including the main dominant predators known to have existed in the ocean.

Currently, the only remaining species are the great white shark and its relatives the porbeagles and makos. Also approximately 60- 55 million years ago, Carcharodon megalodon, the toughest of all sharks populated the Earth,. Megalodon was the largest predator recognized in the seas and oceans of earth. These huge creatures could reach sixty feet in length and had more than 30 tons, equivalent to an average sperm whale. Its teeth of strongly resembled that of its lesser cousin the white shark, only four times the size, in excess of six inches long.

Owing to similarities in jagged edges and of the teeth, an accepted theory explained that the white shark megalodon and the white shark were directly related, if not in fact family of the identical species (Ferrari, 1999). This hypothesis recommended that due to a decrease in prey volume, the megalodon became lesser in size ultimately adapting into the great white shark. At present a new well-liked hypothesis suggests that the 2 enormous hunters diverged from a similar line and 1. Megalodon became wiped out and the other continuous to exist to this day.

Many still believe that it is likely that megalodon may still live in the mainly the isolated parts of the seas and oceans. Researchers have also discovered moderately fossilized massive teeth of C. megalodon at enormous depths of the seas leading some to think that megalodon was living 2 million years ago. It was usually acknowledged that sharks are merely primitive, mindless hunters. We nowadays know that this cannot be true. Human beings have lately come to be grateful for these sea creatures for their amazing past and deep origin. Sharks have definitely evolved from humble ways millions of years ago, to modern day predators of the ocean.

Since many present day shark species evolved more than a few million years ago and have stayed unaffected troughout all that time is purely remarkable. Science and research in these wonderful animals has enabled us to increase our understanding of their place on planet Earth.

Work Cited James Seth. Voracious Evolution. New York: Scribner’s, 2008: 62-87. Ezekiel, G. Robinson. Silent Hunters of the Deep. NewYork: Burdett, & co, 2008: 35-47. Steve and Jane Parker. The Encyclopedia Of Sharks. London: Elsevier, 2006 : 96-123 .

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