Wildlife

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Sharks –

Every time we head into the mountains on a hike do we think about getting eaten by a bear? Some of us do and these same wildlife questions gets brought up when we do anything outdoors including ocean sports. Though instead of bears some people worry about sharks.

Shark attacks are rare and fatal attacks are even less frequent. In fact, more people die annually from falling coconuts (150) and being struck by lightning (47) than from being attacked by a shark. In the Northeast cold waters it is even more rare. In the Carolinas it is the small aggressive sharks that bite like dogs. As you head north on the east coast theses sharks are not found. In the Northeast we have Great Whites and they have patterns they follow from south to north. Great Whites like colder deep waters, unless they are following a food source. “Seals” Cape Cod Massachusetts has had some Shark sightings mostly because of all the seals that are found in that area. Anytime you are involved in any outdoors activity you must take wildlife into consideration.

History: The planet earth is at least 4500 million years old. The earliest signs of life date back 3000 million years, and by 600 million years ago quite complex animals and plants existed. The story of the backboned (vertebrate) animals -the fishes and other forms that eventually led to humans -began about 600 to 500 million years ago. The first definite fossil of a creature with a stiffening notochord along its back was a Cambrian animal called Pikaea, which was discovered in 560- million-year-old rocks in Canada .

The oldest complete fish fossil so far found came from central Australia , and was a jawless, armoured fish called Arandaspis, which dates from the early Ordovician period. This small filter-feeding or mud- grubbing fish lived in shallow coastal waters over 480 million years ago.

In the next 100 million years all the major fish groups that are found on earth today evolved, although their origins and relationships to one another are still uncertain. In the Silurian period -some 400 million years ago -the jawless fishes were the most numerous, although primitive bony and cartilaginous jawed fishes had begun to appear at about that time. Fossils of the so-called ‘spiny sharks’ -which had large fin spines -and of the earliest true sharks have also been found in Silurian rocks. By the Devonian period -about 30 million years later -fishes had diversified and spread into all parts of the world.

By the end of the Devonian, some 25 million years further on, certain fishes had moved onto land. From these first amphibians evolved the four-legged animals, including reptiles such as dinosaurs, and eventually mammals.

The early evolutionary history of sharks and shark-like fishes is still poorly understood. Until recently scientists thought that there were no shark fossils to speak of in rocks older than those from the Middle Devonian. Now, however, it is certain that sharks did not appear suddenly at that time -it was just that researchers were looking for the wrong kind of evidence. Microscopic examination of ancient sediments has revealed fossilized remains of sharks which may push their origins back at least 50 million years further.

The evolution of sharks remains unclear partly because it has been difficult to analyse- particular characters -such as the shapes ofbraincases or finstructures -of modern sharks,which are an extremely diverse group, adapted to many habits and habitats. Any analysis of fossil sharks has had to rely almost solely on hard parts, such as teeth. Other features such as fins are only rarely preserved. Much more needs to be known about ancient sharks before any assessment can be made as to which characters were ‘primitive’ and which were ‘advanced.

Sharks are rarely found as complete fossils because their skeletons are made of cartilage. Normally only the hard parts, such as teeth, scales and fin spines, are found. However, under certain special conditions, complete fossil sharks are preserved, and these provide scientists with vital information. One such deposit, found last century in Upper Devonian Cleveland shales from the USA , yielded entire shark carcasses which had been preserved in a bacteria-free environment so that even muscle and kidney tissue could be examined in the rock.

The very earliest signs of sharks are minute fossil scales and teeth which are found in rocks from the late Silurian to early Devonian period {around 400 million years ago). It becomes more and more difficult, however, to identify shark scales in older rocks because they closely resemble those from jawless fishes called the lodonts, which lived at the same time. Only microscopic differences separate shark and the lodont scales, and the two kinds seem to become more and more alike the further one goes back.

A similar problem exists with ancient shark teeth, which did not seem to be present in rocks older than those from the mid-Devonian. It now seems that the reason for this was that scientists were not looking in the right places, and that early shark teeth were often very small. In 1986 teeth were found in Lower Devonian rocks from Spain which belonged to a group of sharks called Xenacanthids. Although there is evidence of earlier sharks, the first complete fossils of shark-like fishes have been discovered in mid-Devonian rocks. Most frequently found are members of the genus Cladoselache, streamlined fish that grew to a length of about two meters.

Fortunately, complete specimens of Cladoselache have been preserved in the remarkable Cleveland shales, so quite a lot is known about them. They had five pairs of gill slits, a fin spine and all the same fins as modern sharks, except for an anal fin. These spines, which become more common and elaborate in later sharks, and which still persist in some species today; were positioned in front of the dorsal fins and acted as cutwaters. Cladoselache had distinctive teeth with a large central cusp flanked by sever-al smaller points, and apparently they lived on small fish -the remains of which have been found in the stomachs of fossilized specimens. These sharks are not now considered to be the main line leading to the modern species.

Although sharks and shark-like fishes have a long history, the modern sharks (Cneoselachians) did not rise to dominance until after the Jurassic period, when, for some reason that is not yet clear, many of the more ancient forms had become extinct. Some Jurassic sharks are closely related to modern sharks, and this gives many present-day shark families histories which stretch back for 135 million years or more. The skates and rays, another group of cartilaginous fishes, also appeared in the mid-Jurassic, but they did not really come into their own until the Tertiary period, between 65 and 2 million years ago, when they were able to exploit a dramatic rise in the numbers of bivalve shellfish in the oceans.

The fossil record of modern sharks is fairly good, but again it normally consists only of hard parts such as teeth and scales. The appearance and relationships of present-day groups are well understood compared with the situation in the Paleozoic and Mesozoic eras. Oceans in the Cretaceous period (140 to 65 million years ago) were dominated by goblin, sand, probable, nurse, cow and angel sharks. Early sawfishes appeared and later evolved into the modern sawsharks. At the beginning of the Tertiary period, the gray nurse sharks were found in large numbers. All modern forms of sharks were present in seas of the Miocene epoch ( 25 to 5 million years ago), including the giant Carcharodon megalodon, perhaps the most awesome of all sharks, now extinct.

There has been an upsurge of interest in fossil sharks in recent years as more information has become available from new fossil discoveries, especially in the southern continents, and from a microscopic examination of existing fossil remains. In many cases these discoveries have helped scientists to understand some of the finds made last century~ There are still few definite answers about the origins and relationships of all the known fossil, and some modern, sharks but progress is being made. These stories and words are borrowed from other surf, and non-surf companies, and added to for informational purposes only. They are not copyrights of NES Surf Company.