Monday, 1 November 2010

Mysterious Living "Fossils" In The World

These mysterious creatures exist today more or less unevolved from the forms they had hundreds of millions of years ago

Platypus


The Platypus (Ornithorhynchus anatinus) is a semi-aquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young. It is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species have been found in the fossil record.

The bizarre appearance of this egg-laying, venomous, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, with some considering it an elaborate fraud. It is one of the few venomous mammals; the male Platypus has a spur on the hind foot that delivers a venom capable of causing severe pain to humans. The unique features of the Platypus make it an important subject in the study of evolutionary biology and a recognisable and iconic symbol of Australia; it has appeared as a mascot at national events and is featured on the reverse of the Australian 20 cent coin. The Platypus is the animal emblem of the state of New South Wales.

Southern Cassowary


The cassowary (genus Casuarius) is a very large flightless bird native to the tropical forests of New Guinea, nearby islands and northeastern Australia.
The Southern Cassowary is the third tallest and second heaviest living bird, smaller only than the ostrich and emu.
Cassowaries feed mainly on fruits, though all species are truly omnivorous and will take a range of other plant food including shoots, grass seeds, and fungi in addition to invertebrates and small vertebrates.

Opossum


Opossums (Didelphimorphia, pronounced are the largest order of marsupials in the Western Hemisphere. They are also commonly called possums, though that term is also applied to Australian fauna of the suborder Phalangeriformes. The Virginia Opossum was the first animal to be named an opossum; usage of the name was published in 1610. The word opossum comes from the Algonquian aposoum, meaning "white beast". Opossums probably diverged from the basic South American marsupials in the late Cretaceous or early Paleocene.

Their unspecialized biology, flexible diet and reproductive strategy make them successful colonizers and survivors in diverse locations and conditions. Didelphimorphs are small to medium-sized marsupials, with the largest just exceeding the size of a large house cat, and the smallest the size of a mouse. They tend to be semi-arboreal omnivores, although there are many exceptions. Most members of this taxon have long snouts, a narrow braincase, and a prominent sagittal crest.

Crocodilia


Crocodilia (or Crocodylia) is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period (Campanian stage). They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria. Members of the crocodilian total group, the clade Crurotarsi, appeared about 220 million years ago in the Triassic Period and exhibited a wide diversity of forms during the Mesozoic Era.

The correct vernacular term for this group is "crocodilians" and it includes the alligator, crocodile, gharial and caiman families. The term 'crocodiles' is sometimes incorrectly used to refer to alligators and caiman, or even their distant prehistoric relatives, "marine crocodiles". Today, there are 23 species of alligators and crocodiles, so they can hardly be held to a strict interpretation of the living fossil ideal. They are instead included because they are the only reptilian survivors of the Archosauria group, home to the dinosaurs.

Tuatara


The tuatara is a reptile endemic to New Zealand which, though it resembles most lizards, is actually part of a distinct lineage, order Sphenodontia. The two species of tuatara are the only surviving members of its order, which flourished around 200 million years ago. Their most recent common ancestor with any other extant group is with the squamates (lizards and snakes). For this reason, tuatara are of great interest in the study of the evolution of lizards and snakes, and for the reconstruction of the appearance and habits of the earliest diapsids (the group that also includes birds and crocodiles).

Tuatara are greenish brown, and measure up to 80 cm (31 in) from head to tail-tip and weigh up to 1.3 kilograms (2.9 lb) with a spiny crest along the back, especially pronounced in males. Their dentition, in which two rows of teeth in the upper jaw overlap one row on the lower jaw, is unique among living species. They are further unusual in having a pronounced parietal eye, dubbed the "third eye", whose current function is a subject of ongoing research but is thought to be involved in setting circadian and seasonal cycles. They are able to hear although no external ear is present, and have a number of unique features in their skeleton, some of them apparently evolutionarily retained from fish. Although tuatara are sometimes called "living fossils", recent taxonomic and molecular work has shown that they have changed significantly since the Mesozoic era.

Okapi


The okapi (Okapia johnstoni; pronounced /oʊˈkɑːpiː/) is a giraffid artiodactyl mammal native to the Ituri Rainforest, located in the northeast of the Democratic Republic of the Congo, in Central Africa. Although the okapi bears striped markings reminiscent of the zebra, it is most closely related to the giraffe.

The animal was brought to prominent European attention by speculation of its existence found in popular press reports covering Henry Morton Stanley journey's in 1887. Remains of a carcass were later sent to London by the English adventurer Harry Johnston and became a media event in 1901[2]. Today there are approximately 10,000–20,000 in the wild; 40 different worldwide institutions display them.

Lamprey


Lampreys (sometimes also called lamprey eels) are jawless fish, whose adults are characterized by a toothed, funnel-like sucking mouth. Translated from Latin, lamprey means stone lickers (lambere: to lick, and petra: stone). While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, most species of lamprey are non-parasitic and never feed on other fish. In zoology, lampreys are sometimes not considered to be true fish because of their distinctive morphology and physiology. It is one of only two vertebrates to remain jawless; it never evolved fins, scales, true teeth, or limbs. And while today's lampreys are slightly longer than those from hundreds of millions of years ago, they are very much alike in most every other respect.

Horseshoe Crab


Horseshoe crabs are arthropods that live primarily in shallow ocean waters on soft sandy or muddy bottoms. They will, however, occasionally come on shore, e.g. for mating. They are commonly used as bait and in fertilizer, and in recent years there has been a decline in number of individuals, as a consequence of coastal habitat destruction in Japan and overharvesting along the east coast of North America.
Horseshoe crabs look similar to crustaceans, but actually belong to Chelicerata, and are therefore more closely related to spiders and scorpions. The earliest horseshoe crab fossils are found in geologic layers from the late Ordovician period, roughly 450 million years ago.

Coelacanth


The coelacanths, which are related to lungfishes and tetrapods, were believed to have been extinct since the end of the Cretaceous period. More closely related to tetrapods than even the ray-finned fish, coelacanths were considered the "missing link" between the fish and the tetrapods until the first Latimeria specimen was found off the east coast of South Africa, off the Chalumna River (now Tyalomnqa) in 1938. This discovery 65 million years after they were believed to have gone extinct makes them arguably the most well-known example of a Lazarus taxon, a species that seems to have disappeared from the fossil record only to reappear much later. Since 1938, Latimeria chalumnae have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, and in iSimangaliso Wetland Park, Kwazulu-Natal in South Africa.

Ginkgo


The Ginkgo is a living fossil, with fossils recognisably related to modern Ginkgo from the Permian, dating back 270 million years. The most plausible ancestral group for the order Ginkgoales is the Pteridospermatophyta, also known as the "seed ferns," specifically the order Peltaspermales. The closest living relatives of the clade are the cycads, which share with the extant G. biloba the characteristic of motile sperm. Fossils attributable to the genus Ginkgo first appeared in the Early Jurassic, and the genus diversified and spread throughout Laurasia during the middle Jurassic and Early Cretaceous. It declined in diversity as the Cretaceous progressed, and by the Paleocene, Ginkgo adiantoides was the only Ginkgo species left in the Northern Hemisphere while a markedly different (and poorly documented) form persisted in the Southern Hemisphere. At the end of the Pliocene, Ginkgo fossils disappeared from the fossil record everywhere except in a small area of central China where the modern species survived.

Nautilus


Nautilus (from Greek ναυτίλος, 'sailor') is the common name of marine creatures of cephalopod family Nautilidae, the sole extant family of the superfamily Nautilaceae and of its smaller but near equal suborder, Nautilina. It comprises six living species in two genera, the type of which is the genus Nautilus. Though it more specifically refers to species Nautilus pompilius, the name chambered nautilus is also used for any species of the Nautilidae.

Nautilidae, both extant and extinct, are characterized by involute or slightly evolute shells that are generally smooth, with compressed or depressed whorl sections, straight to sinuous sutures, and a tubular, generally central siphuncle. Having survived relatively unchanged for millions of years, nautiluses represent the only living members of the subclass Nautiloidea, and are often considered "living fossils."

Vampire Squid


The vampire squid (Vampyroteuthis infernalis, lit. "vampire squid from 'Hell'") is a small, deep-sea cephalopod found throughout the temperate and tropical oceans of the world. Unique retractile sensory filaments justify the Vampire Squid's placement in its own order: Vampyromorphida (formerly Vampyromorpha), which shares similarities with both squid and octopuses. As a phylogenetic relict it is the only known surviving member of its order, first described and originally classified as an octopus in 1903 by German teuthologist Carl Chun, but later assigned to a new order together with several extinct taxa.

Paddlefish


Paddlefish (family Polyodontidae) are primitive Chondrostean ray-finned fishes. The paddlefish can be distinguished by its large mouth and its elongated snout called a rostrum (bill). These spatula-like snouts comprise half the length of their entire body. There are only two extant species of these fish: the Chinese and the American paddlefish. In some areas, paddlefish are referred to as "Spoonbill", "Spoonies" or "Spoonbill Catfish". The American species is Missouri's State Aquatic Animal.

These fish are not closely related to sharks, which are in a different class, but they do have some body parts that resemble those of sharks such as their skeletons, primarily composed of cartilage, and deeply forked heterocercal tail fins.

4 коментара:

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