Some Organisms do not Evolve into more Complex Forms
From the simple to the complex, some species have stabilized.
Some species stabilized long ago and have evolved little since then.
The general consensus has been is that life evolves from the simple to the more complex. This however, is not universally true. Although many contemporary forms have evolved out of earlier ones, some forms stabilize and remain virtually unchanged for hundreds of millions, even billions of years. Among these are cyanobacteria, diatoms, some snakes, sharks, jellyfish, sponges, dragonflies, scorpions and crocodilians. Stable species indicate stable environments and though some regions have been stable, most have not and life evolved in unstable regions. Instability can come from many sources, such as ice ages, volcanic eruptions, tectonic movements, impacts, global freezing or warming. These changes drive what is behind many extinctions. Of all the species that ever lived on Earth, 99 percent are extinct and just one percent survive. Among the one percent are all the species that stabilized eons ago. They did not evolve further simply because they did not have to for their ecological niche.
It is thought that all primates including all of the human sub-species and homo-sapiens evolved from one ancestor, the lemur. The lemur has been around for tens of millions of years and is still around today. Not so are human forms such as Neanderthal, which went extinct some 12,000 years ago. Other human sub-species disappeared even earlier, leaving just one survivor, homo-sapiens. Wild cat and dog species exist today in diversity and have not been reduced to one survivor and demonstrate that evolutionary branching does indeed exist. Homo-sapiens was just one twig on the branch of human species, which is on the larger branch of all primates. Among these branches are the sharks, sponges and crocodilians.
Cyanobacteria have been around for 2.8 billion years and are still with us in a world that evolved into the huge number of species we see today. Cyanobacteria are ultimately responsible for the oxygen content in the Earth's atmosphere. Cyanobacteria are considered to be among the first life forms on Earth. The first ones lived on sulfates and methane that was abundant in Earth's early atmosphere and seas. At first, they did not photosynthesize. This evolved later when more sunlight filtered though the density of the primordial atmosphere. Today's cyanobacteria exist in both states and are virtually identical to the oldest forms. On the west coast of Australia, cyanobacteria are busy building stromatolites in shallow seas just as they did billions of years ago. They have survived every major extinction event including the Permian extinction that killed 90 percent of the species at that time.
Sponges are among the first multicellular forms ever to have evolved and they are still with us. Geologic chemicals associated with sponges date back as far as 1.2 billion years ago. The oldest fossilized sponge dates back to 530 million years ago. They have no nervous system, no digestive system and no circulatory system. Everything happens at the cellular level and they consist of large colonies of cells, which group into colonies that filter feed by passing water through a jelly like porous skeleton. Modern sponges are close in structure to the oldest known sponges. They are found all over the world in fresh water and the oceans and at all depths. The modern sponge differs little from the ancestors of the remote past and has stabilized into the modern forms we see today. Though there are many more variations of the sponge today, in function they are identical throughout the extent of their existence. Clearly, they have not evolved into more complex species, although they were on an evolutionary branch that split and gave rise to more complex species on other branches of life. One of the species that evolved on a side branch was the jelly-fish.
Jellyfish are first seen in the fossil record of the Cambrian period 542 to 488 million years ago. Being soft bodied and 97 percent water, it is a wonder that some were even preserved at all. Jellyfish have a simple nervous system but are not divided into left and right. They have no skeleton but have a crude muscular system that allows them to pulsate and swim thereby. They are passive and opportunistic feeders, capturing prey in dangling strings of stinger cells. These cells retract and the jellyfish feeds from anything captured therein. They have survived hundreds of millions of years to the current era and proliferate in all oceans around the planet. In form and function, they are virtually unchanged.
Scorpions first evolved in the ocean and only later moved onto land. Sea scorpions first evolved during the late Silurian epoch of the Paleozoic era some 444 million years ago. By 400 million years, seas scorpions grew to a size larger than a man today. They were scavengers and active hunters. Sea scorpions were among the first creatures to leave the sea and move onto land. At first they lived in the sea and went out to hunt by stealth. Some species went to completely live on land. The modern scorpions that inhabit the world today are the direct descendants of the Silurian scorpions that had adapted fully to a life on land. They have not changed much during the full extent of time. The scorpion has been a successful species that survived through most of the great extinction events of the past to the present. They are among the oldest species that have remained constant. The physiology of the modern scorpion, though reduced in size due to lower atmospheric oxygen content is the same as long ago. They have similar lungs, exoskeletons, stinging mechanisms and pincher claws. Though some think scorpions are insects, they are actually arachnids, belonging to the same group as crayfish, lobsters, crabs and spiders.
Sharks evolved from their predecessors in the late Devonian period between 416 to 359 million years ago. Fossils of the original shark dating at 400 million years were found in Ohio, which was once under water, they were born hunters. Though sharks have many forms today, they all evolved from common ancestors, the Cladoselache. Though very similar to the dreaded great white shark of today with its torpedo like body, large eyes, large pectoral fins and large tail, the difference is that they had a blunt snout and teeth at the front of the face instead of below the snout like the modern shark. Otherwise, they were identical, both being formidable hunters of fish, squid and crustaceans. Sharks are among the most successful life forms, not having evolved much from their original form over hundreds of millions of years. Like crocodiles and scorpions, they lived through many major extinction events. They have several forms today and all are successful hunters. Today, for the first time, these remarkable survivors face extinction st the hand of man because of an obsession over their fins.
Dragonflies were in existence 320 million years ago during the Carboniferous period and were the first creatures to take flight. In the early days, they could grow to a wing-span size of nearly three feet/one meter. They were successful hunters over the early forests that evolved on land during the Carboniferous period. Over the eons, as the atmosphere became less dense, they shrank in size to the forms we see today. Otherwise, the modern form is virtually identical to the ancient one. All of them from then to now feed on flying insects that are captured and eaten in flight.
The oldest crocodile fossil found was called Protosuchus, which means "first crocodile". It was 240 million years old and thrived during the Jurassic period. Most early Archosaurs in general resembled modern day crocodiles, with narrow skulls, pointed snouts, teeth set in sockets and a modified ankle joint. Along with the dinosaurs and some of the first birds, many crocodilian species went extinct. Included among these distant ancestors of modern crocodiles are:
an ancient crocodilian also known as the "terrible crocodile".
This was also the largest crocodilian, growing up to 15 metres/50
feet, the size of a bus! Deinosuchus lived during the late Cretaceous
Geosaurus: an early crocodilian, which lived during the late Jurassic to early Cretaceous period. This aquatic reptile grew to a length of 3 metres/10 feet.
Leidysuchus: Fossils of this ancient crocodile also known as Leidy's crocodile have been found in North America. Leidysuchus was long snouted and lived during the late cretaceous period.
Today, crocodiles and birds are the only remaining Archosaurs. The crocodiles that live today are much like those that evolved 250 million years ago. There are 23 crocodilian species still roaming the Earth. Of those, 14 belong directly to the crocodile family with a variety of other species located in the wilds of Africa, Australia the southern U.S. and several other hot and steamy locations.
There are many other forms that live today that are similar to those of ancient time such as diatoms and snakes that have gone through many changes and proliferation of sub-species, but in form they are very similar to the ancient ones. These forms did not evolve into more complex ones, but they lived as part of a main branch that divided and the split off species went on to evolve into the host of complex species we see today. Man, shark, crocodile and scorpion co-exist in the world today. Man considered one of the most complex forms of the evolution on life tells us that some ancient organisms evolved to be more complex, but alongside man exists life like cyanobacteria, jellyfish, snakes, sharks and crocodiles that stabilized as less complex forms and stayed that way to the present era. It is quite possible that when humanity becomes extinct, sharks, crocodiles, snakes, jellyfish, dragonflies and scorpions will still be around.