Category Zoology

                    It all started some 200 million years ago, when some smaller dinosaurs made their homes among rocks on high cliff sides. By doing this, they were protecting themselves from larger meat-eating dinosaurs that were too big and heavy to climb over loose rocks. It was here that the pterodactyls (meaning ‘wing finger’) were found. They were flying reptiles, and their ability to fly helped them to escape from the clutches of an enemy, and to swoop down to grab food.

                  During this period, many small reptiles were evolving characteristics, which separated them from the reptile group – their feathers. The Archaeopteryx was the most familiar of these early reptilian avian.

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                    About 9,000 different species of birds exist today in our world. They come in all sizes, forms, and colours. There are brightly coloured parrots and macaws in tropical America, and large cassowaries and emus that cannot fly in Australia. Tiny warblers and sparrows are found in temperate America, and ducks, bustards and cranes in India. Gulls and vultures soar through the skies the world over. Plump chickens and turkeys are found in farmyards everywhere.

                   There are two main bird groups- paleaeognathae and neognathae. The paleaeognathae, includes birds that first evolved during the Cenozoic Era, after the dinosaurs became extinct-mostly ratites such as ostriches, emus and kiwis. The neognathae can trace their roots much farther back into the Mesozoic Era, and includes all other types of birds.

               The number of fish species runs to more than 20, 000 in the entire world! They can be classified into three broad categories: bony, cartilaginous and jawless. These species are spread across various biospheres. Around 10,000 species are found in freshwater; whereas, around 20,000 live in saltwater. There are also fish species that can live both in fresh and salt Water.

               The most commonly found fishes fall in the category of bony fishes. Tiny bones make up the skeleton of these fishes. They also have scales all over their body. They breathe through gills that appear at both sides of their head.

                On the other hand, cartilaginous fish have skeletons made out of cartilage. Cartilage is a kind of flexible tissue, and it is less brittle than bone. Sharks and rays have cartilages instead of brittle bones. As you may have observed, sharks have several gill slits on either side of their heads. They do not have scales like fishes. However, they have little interlocking teeth that make up its tough skin.

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               If you carefully analyse the fish in your aquarium, you would see a skeleton inside its body. The parts of the skeleton are a skull, backbone and fin supports. The skull of a fish has a cranium, and visceral arches. The bony cover that surrounds, and protects the brain is called the cranium. The visceral arches in the body of a fish support of its gills. These arches are also called the gill arches.

               The backbone of a fish is series of disc like bones. The backbone protects the spinal cord of the animal. There are thin, needle-like ribs that extend from the backbone toward the belly. This structure supports the entire body of a fish.

               Many fins are found in the body of a fish. Each fin has a large support at its base. They have two sets of fins, which are paired. One pair is called the pectoral fins, which lie just behind the head, one on both sides; and the other pair is called the pelvic fins, which may be far back on the body or under the head. The pelvic fins are smaller than the pectoral fins and are always on the belly side of the fish. Other fins of the fish are generally un-paired. It means that there is only one of each. The dorsal fin is found at the centre of the back of the fish. Fishes have an anal fin on the belly side too, just in front of the tail. The tail of the fish is called the caudal fin.

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          Can you imagine rivers, lakes or great oceans without fishes? These animals make grand water bodies livelier. However, millions of years ago, there were no fishes in waters!

          Scientists who study fossils to place various prehistoric organisms say that the first fish probably came into existence about 500,000,000 years ago, in the Ordovician Period.

          The ancient fishes did not have the kind of mouth fishes have now. They were jawless. They just had a small opening as their mouths, with which they ate only tiny organisms found hidden in the mud. These fishes gradually evolved and spread in number to other bodies of water later. During the Devonian Period, fishes were the most common animals in the planet. Therefore, the period is also known as the age of fishes.

          Jawless fishes and fishes with jaws became abundant during this time. Ostracoderms were a group of jawless fishes. However, they soon became extinct.

          The jawless fishes died out because fishes with jaws were evolving. Early fishes with jaws are called Placoderms. Do you know that the sharks and bony fishes of the present day come from Devonian Placoderms?

                  Vertebrates represent the majority of life in the phylum Chordata. There are more than 65,000 species among vertebrates. Of these, the fishes constitute the majority. There are thousands of fish species across the globe. The fish diversity is spread across lakes, rivers, streams, seas, bays and oceans. They are found in the cold Arctic, in the hot tropics and in other temperate zones. When it comes to the number of species or individuals, fishes outnumber all other vertebrates.

                   Do you know that a scientist who studies fishes is called and an ichthyologist? The word comes from two Greek words: ‘ichthyos’, meaning fish, and ‘logos’, meaning study.