Jelly comb According to a surprising discovery, Earth's first life was the ocean-drifting comb jelly, not the basic sponge. Scientists were surprised that the oldest organism could be so complicated. The mystery of the planet's original animal residents can only be deduced from fossils and the study of comparable creatures today. It is possible that other ancient forms existed that are now extinct.
Comb jellies are made up of cells called mesoglea, which are similar to those found in sponges. However, unlike sponges, which are filter feeders that collect water and small organisms for consumption by larger animals, comb jellies are carnivorous: they eat other smaller jellies and microorganisms.
They are also unique in that they have eight protruding stalks, each of which contains a single cell layer. These layers differentiate into hooks or teeth depending on the species. As the jellyfish ages, these become more rigid and turn white before disintegrating. A new set of stalks grows in its place. Comb jellies are found in all oceans except for deep hot vents where sulfurous chemicals would quickly destroy them. Although they are fragile, some species can reach sizes of over 100 feet (30 meters).
Their longevity is one reason why scientists think comb jellies may have been early life forms on Earth. They seem to appear quite suddenly, usually after a large amount of marine debris has accumulated in shallow waters.
According to New Scientist, sea sponges were among the earliest animal groups to form on Earth, but the finding of new chemical evidence now places the species' emergence 120 million years earlier than previously assumed. Sponges are primitive animals that lack nerve cells and an internal body cavity, instead receiving their nutrients through porous bodies called mesogloea. They are classified into three main groups: demosponges, hexactinellids, and bryozoans.
The oldest known sponge is named Gantoisia superba and it was found in France. The specimen is about 105 million years old. It shows that sponges were already highly evolved at that time. Today, almost all sponges are dependent on other organisms for feeding. However, there are some marine plants that are similar to sponges in appearance. They use water as a conductive medium to receive oxygen from the air through their roots and then spread it around with their stems. These plants include corallines, sea roses, and sea lilies. Corallines are related to corals; they live near reefs where the heat and light from the sun will cause algae to grow on the surface of the coral. If these algae are damaged or removed, then another type of organism will take its place which produces chemicals that are toxic to bacteria that would otherwise destroy the coral.
These groups of specialized, cooperative cells developed into the earliest animals, which DNA evidence says arose some 800 million years ago. Sponges were among the first creatures to evolve. They lack a defined brain and nervous system, but they do have tissues that react to stimuli and move under the control of special cells called neurons. Sponges are ancient organisms that date back to before there was air on Earth. They are found in marine environments all over the world.
As sponges evolved more complex behaviors, such as moving around and capturing food, other types of organisms began to develop brains and nerves systems. These evolving beings were not single-celled organisms like bacteria or algae. They were multicellular, including worms, jellyfish, arthropods (including insects and spiders), and vertebrates (animals with spinal cords and bones).
The evolutionary transition from unicellular to multi-cellular organisms is one of the most important events in history of life on Earth. It allowed species to grow larger and more complex, which is necessary for evolution toward higher levels of organization. Multi-cellularity is a prerequisite for evolution of intelligence because it requires cooperation between individuals of a group. Animals with brains and nerves systems have better chances of survival than those who don't. This is why these two features are usually found together.
The conventional idea that sponges were the first phylum to split from the common ancestor of metazoans is reaffirmed by Davide Pisani (Bristol University, UK). According to several recent research, comb jellies were the trend setters in animal development. They are the only known animals whose descendants include all subsequent animal phyla.
Sponges are multicellular organisms composed of an internal network of fibers and membranes. They lack a skeletal structure and contain no organs except for microscopic ova called "spicules" which they use to swim through the water searching for food. The earliest fossil evidence of a sponge comes from around 525 million years old, but it's likely they existed much earlier than this. Sponges are believed to be the most ancient phylum on earth.
Comb jellies are large gelatinous animals with a jelly-like body and eight whip-like tentacles attached to a central disk. There are three types of comb jellies: those that have radial symmetry, those that have bilateral symmetry, and those that are a mixture of both. Combin jellies are unique in that they are the only known animals that can reproduce asexually by cloning themselves. Each adult cell divides without limit many times to produce identical offspring that will eventually die and be replaced by new cells. This ability to reproduce by cloning has led some scientists to believe that comb jellies are immortal.
Fossil specialists in the United States have discovered the remnants of what they believe to be the first animal to step foot on land—an ancient scorpion. The first creatures were aquatic, but they soon adapted to land. Using their powerful tails, they could steer themselves toward water or away from danger.
Scientists have found that the first terrestrial animals looked much like modern-day arachnids: eight legs, two big eyes, and a tail with a stinger at the end. They were probably blind, but used other senses such as smell and touch to find food and avoid danger.
These new findings are based on studies of fossilized remains of the animal called Thalassoleon macouni. It was a relative of modern sea spiders and scorpions that lived about 500 million years ago. The species has been given the name "Macoun's centipede" in honor of its discoverer, Charles H. Macoun. He was an American geologist who spent his career studying fossils in North America.
Thalassoleon macouni was discovered in 1866 in the vicinity of present-day Washington, D.C. At the time, there were no facilities for preserving fossils, so researchers just packed the bones back into the rock where they were found to study them later.
To recap, the first known terrestrial creatures were arthropods (Little 1983)—members of the Myriapoda (millipedes, centipedes, and relatives), Arachnida (spiders, scorpions, and relatives), and Hexapoda (spiders, scorpions, and relatives). These early terrestrial creatures were not alive at a time when seas covered most of North America. Instead, they lived during the Late Cambrian period about 545 million years ago.
The first fish were also arthropods: members of the phylum Chordata (de Robertis et al. 1995). They appeared around 500 million years ago in the fossil record and quickly diversified into many different types of animals, including amphibians, reptiles, birds, and mammals. Although fish are usually considered to be vertebrates, with backbones, they are actually a type of deuterostome animal (similar to humans). Thus, both fish and people share several common ancestors. Modern fish descend from a last common ancestor that was already fully capable of breathing air like other land animals. This ability is seen in the fossil record as soon as 300 million years ago in some species that lived in shallow waters or on coral reefs.
It took another major evolutionary leap forward when the first tetrapods (four-legged animals) appeared about 450 million years ago in the fossil record.