Here you will find some quick facts about some common types of fossils. You can click on a picture to enlarge it, or click the “Learn More” link for more information about that type of fossil.
Microfossils Foraminifera (fossils < 4mm)
Microfossils are normally not more than 4 mm in size, and often less than 1 mm, so that they can only be seen with a microscope. Macrofossils are larger, and can usually be seen with the naked eye, or with the assistance hand-held magnification.
However, there is no strict dividing line between the two types. Some organisms exist in large colonies, and could be classified on the basis of the whole colony or the individual members. An example of this is Bryozoa, which are studied by both paleontologists and micropaleontologists. Another instance where the distinction is blurred is with many types of Foraminifera, where tiny organisms lived in large shells.
Microfossils occur throughout geological history. They appear most often in the marine environment, but can also be found in fresh and stagnant water and in sedimentary deposits. Although they are not restricted to any part of the animal or plant kingdoms, microfossils are most likely to be from particular animal classes, such as acritarchs and chitinozoans, or from spores or pollen from vascular plants. Learn more about Microfossils >>
Trilobites Ancestor to the Horseshoe Crab
One of the earliest known fossils is Trilobita, an extinct group of marine arthropods whose appearance in the fossil record marks the Atdabanian stage in the Early Cambrian era. The word trilobite means “three lobes”. These were very successful early animals, surviving for 270 million years. They lived in the oceans through the whole of the lower Paleozoic Period, before becoming almost extinct in the Devonian (the one order that survived the Devonian era died out in the Permian).
Trilobites had already evolved a number of forms and become geographically diverse by the time they appear in the fossil record. This, together with the fact that their exoskeleton was easily fossilized, means that they left numerous fossils behind, covering around 17,000 species. Studying these fossils has allowed important discoveries to be made in the fields of evolution, paleontology, and plate tectonics. Taxonomists usually put trilobites within Schizoramia, a subphylum of Arachnomorpha, but alternative classifications are also used. Learn more about Trilobites >>
Eurypterids Sea scorpions
Eurypterida (also known as eurypterids or sea scorpions) are another extinct group, that includes some of the largest arthropods ever known to have lived. Some of them, such as the Jaekelopterus, could be as much as 2.5 m long. However, most were less than 20 cm. Although known as sea scorpions, they were not true members of the scorpion family.
They were a very diverse group of predators, and, although they lived long before fishes appeared, the first eurypterids discovered had wing-like appendages for swimming. In the earliest period (between 460 and 248 million years ago) they lived in the ocean, but later species moved to brackish or fresh water. The relocation to fresh water was probably completed by the time of the Pennsylvanian era.
Eurypterids became extinct around 250 million years ago and their fossils are widespread. However, it is thought that they shed their outer skeletons, meaning that fossilized carcasses cannot easily be distinguished from discarded molts. This makes it hard to assess their contribution to the ecosystem. Learn more about Eurypterids >>
Ammonites Nautilus type fossils
Ammonoidea (ammonites) are a group of extinct mollusks that lived in the sea. Their closest living relatives are squid, octopuses, and cuttlefish. They are used as a kind of index to geological periods, as their appearance in a particular rock layer often makes it possible to link that layer to a specific period.
Ammonite fossil shells are normally of a planispiral form, although helix spirals and even non-spiraled shapes have been found. The common spiral shape is supposed to resemble rams’ horns. This inspired the Roman naturalist Pliny the Elder to coin the name ammonis cornua, meaning “horns of Amun”, after the Egyptian god Amun, who was often shown with rams’ horns. Many ammonite names end with the suffix –ceras, meaning “horn” in Greek. Learn more about Ammonites >>
Brachiopods Bi-valves – clams and mollusks
Brachiopoda (or brachiopods) were ocean dwelling creatures with hard upper and lower shells, differing from bivalve mollusks which have their shells arranged on the right and left hand side. Their shells were hinged at the back, and opened at the front for feeding purposes, closing again when protection was necessary. Brachiopods came in two forms: articulate, with toothed hinges, and basic muscles for opening and closing; and inarticulate, with untoothed hinges, but more complex muscles to keep the upper and lower shell aligned. Most brachiopods had a stalk-like projection, called a pedicle valve, which allowed the animal to attach itself to the seabed, but kept it free of silt that would clog up the opening. As it has an upper and lower half, the name brachiopod derives from the Greek words for “arm” and “foot”. They are commonly called “lamp shells”: a reference to the curved shells of the Terebratulids which are supposed to resemble oil lamps.
Brachiopods live for anything from 3 to 30 years. The ova and sperm travel from the gonads to the coelom and from there to the mantle cavity, until they emerge as larvae. Inarticulate brachiopods have larvae that resemble the adult form, but are equipped with lophophores that allow them to feed and swim freely for several months, until they are heavy enough to sink to the seabed and remain there. In contrast, the larvae of articulate brachiopods have a distinctive form, living in plankton and feeding on yolk, metamorphosing only a few days later. Learn more about Brachipods >>
Crinoids Sea Lilies
Crinoidea (crinoids, or sea lilies) are also marine creatures. They are echinoderms, and their name derives from the Greek words for “lily” and “form”, a reference to those crinoids that attach themselves by a stalk to the ocean bed. Unstalked forms are known as comatulids, or “feather stars”. Crinoids can live in shallow water, but also in water as deep as 6,000 m.
The distinguishing feature of crinoids is a large mouth surrounded by arms for feeding. The gut is U-shaped, so that the anus is right next to the mouth. As is characteristic for echinoderms, they have fivefold symmetry, but they normally have more than five arms. Although many species attach themselves to the seabed or other surface, others are attached only when young, and swim freely as adults. Today only a few hundred crinoid species survive, but many more existed in the past. Some limestone layers of the Paleozoic Period consist almost completely of crinoid remains. Learn more about Crinoids >>
Fish Fossils Past and Present
Prehistoric fish are those fish that we only know about from their fossils. These include fish from the Cambrian and Tertiary Periods, and are the first known vertebrates. The study of these fish is known as paleoichthyology. Some species alive today, such as the coelacanth, are referred to as living fossils, or prehistoric fish, partly due to their rarity, but also because they resemble extinct species. However, the term “prehistoric fish” is not used for fish that have become extinct comparatively recently.
The first fish were the ostracoderms. They first appeared around 510 million years ago, in the Cambrian era, and became extinct over 100 million years later, in the Devonian Period. Most ostracoderms lived in fresh water. They were jawless and covered in bony scales, and were usually less than 30 cm long. Ostracoderms belong to the class Agnatha, which also includes some surviving jawless fishes such as lampreys and hagfishes, which are thought to be descendants of the ostracoderms. Paired fins, which later became limbs, first evolved within the Agnatha.
Placoderms were jawed fishes which first appeared around 416 million years ago, at the start of the Devonian period, and became extinct about 50 million years later, at the commencement of the Carboniferous. Current research indicates that this group are the closest ancestors of all jawed vertebrates alive today. Some placoderms, including antiarchs, were small and lived on the seabed. However others, such as the large and famous Dunkleosteus, lived in the middle of the ocean and were active predators. The upper jaw was fixed to the skull, but it was hinged to the rest of the body, allowing the mouth to be opened wide so that the animal could take large bites from its prey.
The first evidence of acanthodians (spiny sharks) appears in the late Silurian period, around 420 million years ago, and they became extinct 170 million years later. However, teeth and scales thought to belong to the acanthodians have also been found in the earlier Ordovician period, as have related gnathostome species such as Chondrichthyes and Osteichthyes. The acanthodians were small fishes of varying forms, with or without teeth, depending on whether they were filter-feeders or predators. At one time acanthodians were placed with other primitive fish in the class Placodermi, but they are now considered to be closer to the present day gnathostomes.
The Chondrichthyes, or cartilaginous fishes, a category which includes rays and sharks, arrived in the middle Devonian, about 400 million years ago. The Osteichthyes (bony fishes) appeared slightly earlier, in the late Silurian Period. These two classes could have evolved from either the Placodermi or the acanthodians.
Since Paleozoic times the main group of fishes has been the Actinopterygii (ray-finned fishes). These are a sub-class of Osteichthyes and include around 30,000 species living today. However, in the Devonian Period the most diverse group was the Sarcopterygii (another sub-class of Osteichthyes), which included coelacanths and lungfish. The distinguishing features of sarcopterygians are internal nostrils, a strong inner skeleton, and hard cosmoid scales. Learn more about Fish Fossils >>
Sea Monsters Plesiosaurs, Mesosaurs, Tylosaurs and Ichthyosaurs
The plesiosaurs (Plesiosauria) were sea dwelling reptiles. They appeared in the Early Jurassic Period, and quickly proliferated, but were extinct by the end of the Cretaceous era. Although plesiosaurs are often thought of as long-necked creatures, Plesiosauria also include other forms.
Mesosaurs (or middle lizards) arrived around 270 million years ago, in the Permian Period. They were the earliest aquatic reptiles. It is thought that their ancestors were land dwellers, but this cannot be established with any certainty. Because mesosaur skeletons do not seem to be fully adapted to living in the water, it is possible that they were amphibious. Certainly they inhabited coastal areas and probably restricted themselves to shallow water. There is also some doubt as to where they fit in relation to other classes, whether they are more closely affiliated to the sauropsids or to the parareptiles.
The Tylosaurus was a large, predatory mesosaur. In form it was lizard like, and had similarities with modern snakes and monitor lizards. One of the largest mesosaurs was Tylosaurus Proriger, which could grow up to 15 m. The mesosaurs were among the most important predators of the Late Cretaceous Period, along with sharks, fish, and plesiosaurs.
Although their ancestors have not yet been identified, the ocean living ichthyosaurs evolved from land based creatures. Appearing in the Middle Triassic Period, ichthyosaurs were giant reptiles resembling dolphins. They were the dominant predators during the Jurassic Period, but they lost their primacy with the arrival of the plesiosaurs in the later Cretaceous Period. Ichthyosaurs became extinct around 90 million years ago. Learn more about Sea Monsters >>
Dinosaur Fossils Land, Air and Sea Monsters
The word “dinosaur” was coined by Sir Richard Owen in 1842, from the Greek Words for “terrible” and “lizard”. The term was applied to a group of land living reptiles that became extinct during the Mesozoic period. In the mid nineteenth century only a few dinosaur skeletons had been found, but hundreds more have been discovered since that time.
The dinosaurs were the most successful terrestrial animals in history, and dominated the planet for more than 100 million years. This was due to their ability to adapt to a variety of environments. They eventually became extinct around 65 million years ago, although the avian species remained. The evidence for dinosaurs includes fossils and non-fossil remains including feathers, feces, and impressions of internal organs, skin, and soft tissues. Learn more about Dinosaurs >>
Plant fossils Plants, Flowers and Tree Fossils
An important branch of paleontology is paleobotany, or paleophytology. This is the study of plant remains, and the use of those remains to study past environments and the evolution of plants. Paleobotanists study land based fossils of plants, as well as marine remains, including prehistoric kelp, seaweeds, and algae. Palynology is an associated area of research, concentrating on fossilized pollen and spores.
The reconstructing of ancient environments is known as paleogeography. Paleobotanists also study prehistoric ecological systems (paleoecology) and climate (paleoclimatology). These disciplines are important for the understanding of how plants evolved. Paleobotany is also useful to archaeologists, particularly because phytoliths (fossilized plant particles) can be used for dating purposes. Learn More>>
Amber Fossils Trapped insects, small lizards and other small creatures
Amber is a particular type of plant fossil. It originates from a tree resin, and, because the resin is soft and sticky, it sometimes also includes animal material. Amber comes in five classes, according to its exact chemical make-up. Resinite is amber that occurs in coal seams, and ambrite comes from coal seams in New Zealand. Amber has been prized for its beauty and color since the Neolithic era, and today it is used for jewelry, in perfumes, and for its supposed healing properties. Learn more about Amber Fossils >>
Mammals The Wooly Mammoths, Giant Sloths, Saber Tooth Tigers and Ancient Man!
Mammals arrived on the scene in the Late Triassic, over 200 million years ago. However, they did not achieve diversity and dominance until the Miocene era (15 million years ago). It was the Pleistocene Ice Age, 2 million years ago, that finally allowed the giant land mammals to emerge. These included the mastodon, the wooly mammoth, and the Megatherium, a land sloth that weighed up to 5 tons. The Castorides was a gigantic beaver that grew as big as a bear. All of these animals died out around 12,000 years ago.
The Carnivora (carnivores, or meat-eaters) were large mammals with teeth specifically developed for biting meat, although some of them included plants in their diet as well. Carnivores included Ursus Spelaeus, a giant cave dwelling bear, Canis Diris (literally “dire wolf”), and saber cats like the smilodon with its massive jaws. Most toothed whales are excluded from the Carnivora order.
The first known mammals of the Triassic period were of the subclass Prototheria, and resembled small rodents. These small creatures were the only mammals that existed during the reign of the dinosaurs. Modern survivors of Prototheria are the duckbilled platypus and the spiny anteater.
After the disappearance of dinosaurs 65 million years ago mammals were finally able to become the dominant life form. At this time they shared the Earth with birds, insects, and flowering plants. Around 50 million years ago animals evolved that were recognizable ancestors of the mammals of today. Learn more about Mammal Fossils >>
Hominids Our ancestors
Paleoanthropology is the study of human fossils, a mixture of paleontology (the study of fossils and prehistoric life forms) and anthropology (the study of human beings). There is still much to be learned about human fossils, as the evidence is fragmented. However, new information is found all the time, and the picture is becoming more complete. This allows scientists to build up the history of human evolution.
As more types of fossils are discovered and more information is gathered, there is increased evidence in support of the evolutionary process, and the validity of this theory is more widely accepted. At one time it was thought that the final separation was some time between 15 and 40 million years ago. However, the current opinion is that it may have been as recently as 5 or 10 million years ago.
Learn more about the fossils of Hominids >>