Introduction to Sharks

Sharks are a large group of fish that have inhabited the oceans for over 400 million years, even before dinosaurs populated our planet. They belong to the superorder Selachimorpha, and modern sharks have specific characteristics like a cartilaginous skeleton, five or six pairs of gills and several rows of teeth.

Ancient Sharks lived before land vertebrates populated the Earth and even before many plant species developed on continents. While they were very different from those found today, sharks have been on this planet for a long time.

The shark species as we know them have been around for 100 million years; this means that they were dwelling the oceans when dinosaurs were roaming the land. This record-breaking survival cannot be anything but astonishing, developing an anatomy during this time which only has improved over those million years of evolution.

These unique animals cause all kind of human feelings: fear, awe, curiosity, respect and love. They have been widely represented in the popular culture as ruthless predators, which is the main reason why they cause all these different reactions. However, the truth is pretty different. Sharks are complex and fascinating creatures, which are distant from the general representation. Even more, many species are docile and harmless.

Learning about the world of sharks, knowing their features, discovering their secrets, and recognizing their importance in our world is the first step to their conservation. When most people think about sharks, they have a mental picture of a deadly predator. However, sharks are far more than this and play a vital role in the oceans and nature.

EVOLUTION OF SHARKS.

Some shark fossils discovered date back as far as 420-450 million years.

Their evolution has produced several species with different sizes, anatomies, habits and behaviors.

Their classification according to the features such as the fin types, spine, snout and body shape determine the genus and family of each species. For example, the great white shark has the mouth behind its eyes and a large dorsal fin by the middle of its body and a second dorsal fin behind. An angel shark, on the other hand, has a couple of fins in the dorsal area near the tail and a flat nose with the mouth underneath.

SHARK BEHAVIOR.

The evolutionary features of sharks, not only defined their look but also the adaptations they have to survive in the wild. There are three types of sharks according to the place they live which is closely related to the form and functions of their body. Some sharks dwell at the surface of the ocean and move slowly, other sharks inhabit the pelagic zone and have amazing swimming capabilities and some others stay at the seafloor, in the benthic zone, and move slowly searching for food on the sea floor.

According to those areas where sharks live, there are also specific ways of surviving. Therefore in each of these parts, the prey behave in different ways which led to the developing of the hunting skills that they acquired.

TAXONOMY OF SHARKS.

Sharks are 470 species belonging to the superorder Selachimorpha. The scientific classification of all sharks is as follows:

Kingdom: Animalia

Phylum: Chordata

Class: Chondrichthyes

Subclass: Elasmobranchii

Superorder: Selachimorpha

The classification continues with eight orders, organized in 37 families which include all the species. Let’s take a closer look at each of these eight orders and the families that belong to each of them:

1. Hexanchiformes.

This classification includes the most primitive sharks, those with six or seven gill slits, a dorsal fin, and lack of nictitating membranes in their eyes.

Two families. Six species.

Frilled sharks. (2 species)

Cow sharks. (4 species)

2. Squaliformes.

This order includes species characterized by having two dorsal fins and five gill slits.

Seven families. 126 species.

Gulper sharks. (18 species)

Kitefin sharks. (9 species)

Bramble sharks. (2 species)

Lantern sharks. (44 species)

Rough sharks. (5 species)

Sleeper sharks. (18 species)

Dogfish sharks. (30 species)

3. Squatiniformes.

This order includes sharks with a wide flat body and pectoral fins, characteristics that make them similar to rays.

One family. 21 Species.

Angel sharks. (21 species)

4. Pristiophoriformes.

The species belonging to this order have a long snout and serrated teeth.

One family. 8 Species.

Sawsharks. (8 species)

5. Heterodontiformes.

It is an order of small sized species with spikes on the front part of their dorsal fins.

One family. 9 Species.

Bullhead sharks. (9 species)

6. Orectolobiformes.

The species that belong to this order are also called carpet sharks and have two dorsal fins without spines, and some species feature patterns decorating their skin.

Seven families. 44 Species.

Blind sharks. (2 species)

Nurse sharks. (4 species)

Bamboo sharks. (16 species)

Wobbegong sharks. (12 species)

Collared carpet sharks. (8 species)

Whale sharks. (1 species)

Zebra sharks. (1 species)

7. Carcharhiniformes.

It is the largest order, and its members are also called ground sharks. They have nictitating membranes in their eyes, anal fin, and five gill slits.

Eight families. 280 Species.

Requiem sharks. (62 species)

Weasel sharks. (8 species)

Barbeled houndshark. (1 species)

Finback catsharks. (7 species)

False catsharks. (4 species)

Catsharks. (150 species)

Hammerhead sharks. (8 species)

Houndsharks. (40 species)

8. Lamniformes.

Members of this order have two dorsal fins, an anal fin, five gill slits and a large mouth that extends behind the eyes.

Seven families. 16 species.

Thresher sharks (4 species)

Basking sharks (1 species)

Mackerel sharks (5 species)

Megamouth sharks (1 species)

Goblin sharks (1 species)

Sand sharks (3 species)

Crocodile sharks (1 species)