Life appeared on earth around 3.8 billion years ago. The first living organisms were simple bacteria, which developed in water. Over the course of time, these organisms multiplied and diversified. Some left the oceans for the terra firma. Some even managed to become airborne. Today, millions of species and billions of individuals populate our planet.
These species have undergone numerous changes over the course of their evolution. Some have occurred slowly over several generations. Other more rapid changes are related to mass extinctions such as that which resulted in the end of the dinosaurs (with the exception of birds).
Let’s have a closer look at some key moments of evolution.
With five eyes, 24 feet, rows of spines, or an armour of small plates, these strange fossil creatures discovered in the Burgess Shale certainly capture the imagination. Our model-maker worked for five months to meticulously recreate of five of these fantastic animals. Here: Aysheaia pedunculata (1-6cm long)
The most common species to be found in the Burgess shale is Marrella splendens, with 15,000 recorded fossils. It was a small marine arthropod that barely reached 20mm in length. It is recognized by its head shield topped by four backwards-pointing spikes.
Hallucigenia sparsa is probably one of the strangest and most difficult to determine of the Burgess specimens. This animal’s body is long and soft. It has seven pairs of spines and several tentacles (large ones at what is believed to be the back and small ones at the front). They can measure up to 3 cm in length.
The trilobites are the most diversified category of fossilized marine arthropods. There are more than 18,000 identified species. These different species occupied vast areas and succeeded one another in quick succession. This is what makes them good fossil date indicators. If two geographically distant geological strata contain the same species of trilobite, we can conclude that these strata date from the same period.
This trilobite, probably a Gerospina schachti, is small (38mm long), but some species measure up to 70cm.
Dunkleosteus was one of the largest placoderms ever (actual size of the skull: about 110cm long, 60cm high, 60cm high)
The placoderms were the first jawed fish. Powerful, they did not have teeth but instead sharp, bony plates.
As you can see with this Bothriolepis canadensis, the front of their body is covered with an armour of bony plates. The last of this species disappeared at the end of the Devonian period without descendants.
Actual size: 16.5cm high
Dating from the end of the Devonian period, Acanthostega gunnari is a primitive tetrapod living in an aquatic environment. Its limbs look more like legs than fins, but its joints, too stiff to bend, will not yet support the body outside of the water.
Actual size: 11.5 cm in length
Giant lycopods, horsetail, tree fern and conifers are the plants to which the Carboniferous period owes its name. Instead of being decomposed by bacteria, funguses and insects, as would happen today, all of these plants accumulated and formed coal over the course of time. The imprint of the stem of the lycopod Sigillaria ovata.
Actual size: 60 cm in length
The temnospondyls were amongst the first tetrapods to escape the aquatic environment. But these giant amphibians were probably still heavily dependent on it as they could only lay their eggs there. Most have a large, wide and flat head. But that of the Archegosaurus decheni is just 28cm and ends in a long, thin snout which suggests it fed on small fish.
The oceans of the Carboniferous period were teeming with sharks, starfish, gastropods, sea urchins, and cephalopods with external coiled shells (such as goniatites and nautiloids). Placoderms and most of the sarcopterygians (those “lobe-finned” fish gave rise to the tetrapods: amphibians, reptiles, mammals, dinosaurs, birds etc.) had disappeared, leaving actinopterygians (the “ray-finned” fish) like this 30 cm Benedenius deneensis to take their place.
The crinoidea, or sea lilies, were echinoderms like starfish and sea urchins. They were made up of a calcareous stalk at the end of which were flexible arms, which caught algae, unicellular organisms, small crustaceans and the larvae of invertebrates floating in the water. In abundance, fossilized species, such as the Seirocrinus subangularis, formed “meadows” on the seabeds. Having appeared in the Cambrian period, they were badly affected by the most significant mass extinction that earth has ever seen. Almost 95% of marine species and 70% of terrestrial species disappeared at the end of the Permian period, 250 million years ago.
Actual size: around 3 x 2m
With their slender, dolphin-like body, their four legs shaped like paddles and their fin-like tails, the ichthyosaurus, like this Stenopterygius longifrons, were amongst the reptiles best adapted to the marine environment. Along with the plesiosaurus, they were the biggest predators in the Jurassic seas.
Actual size of the skull: 40 cm in length
There is an exceptional fossiliferous deposit at the site of Messel, near Frankfurt in Germany. Dating to 47 million years ago, it owes its reputation to the quality, richness and diversity of its fossilized fauna - crocodiles, snakes, lizards, frogs, turtles, birds and insects as well as numerous mammals. This site provides an excellent illustration of the transition between primitive and modern fauna. For example, the snakes and lizards are rather primitive while some mammals (in particular bats) possess modern characteristics.
The bats from Messel strongly resembled their modern-day cousins, even though they probably did not yet possess echolocation. Here: Palaeochiropteryx sp. (actual size: 7cm tall)
This Kopidodon macrognathus was a small arboreal (tree-living) herbivore, now extinct.
Like today’s squirrels, it had a long, bushy tail serving as a pole for its balance as it leapt from branch to branch.
Larger specimens reached 115cm; this one is a little over 70cm long.
47 million years ago, the Messel site was a tropical lake. It is no surprise that fish, fresh water turtles, salamanders, frogs (such as this Eopelobates wagneri, 8cm high) and even crocodiles were discovered there.
Amongst the mammals found at Messel is this magnificent Eurohippus messelensis. Related to modern horses, it was just over 50 cm long, had four digits on each foreleg and three on each hind leg (as opposed to the single hoof of the modern horse), and lived in forests.
The Primitive Horse from Messel
English version (French and Dutch versions below)
Le petit cheval de Messel
Het Paardje van Messel
The thylacine, also known as the Tasmanian wolf or Tasmanian tiger, is an Australian marsupial. Or at least it was: Benjamin - the last one in captivity - died in Tasmania’s Hobart Zoo on 7th September 1936.
This animal was a victim of prejudice and ignorance about its way of life. The carnivore hunted at dusk and could open its mouth very wide, making people suspect that it was a threat to sheep and so they eliminated it systematically, encouraged by bounties. Things could have been different: thylacines were easy to tame.
New varieties of roses, orchids and tulips. Botanists are expert in the mechanisms of artificial selection. They systematically choose the specimens with the required characteristics (colour, odour and resistance to frost), and cross them again and again until the new variety exhibits these characteristics from generation to generation.
In the animal kingdom, breeders can attempt to foster creatures that run the fastest, carry the heaviest loads or produce the most milk. With the “Belgian Blue Beef” breed of cows (photo), the key consideration is muscular development and therefore the quantity of meat. This breed of cow today makes up almost 45% of the national herd, but without man they would not survive. Owing to their morphology – which has been fostered by breeders – most of the cows do not successfully calve naturally, and require a Caesarean to be carried out.
Propellonectes russeli, the imagined descendent of the Northern Giant Petrel (Macronectes halli), an existing seabird, has atrophied wings unfit for flight, but disproportionately large feet and an even more hydrodynamic body shape than its ancestor: it is an excellent swimmer. Length: 1 m
With a more massive head and shoulder girdle and hypertrophied, prominent incisors, this Corticochaeris gouldi could be a descendent of the capybara (Hydrochoerus hydrochaeris), the largest living rodent today. Length: up to 2 m
A potential descendent of the common brushtail possum (Trichosurus vulpecula), an arboreal marsupial, this Trichopteryx dixoni has a longer and more flexible prehensile tail, larger skin folds between its feet, and a ventral pouch that opens downwards, towards the tail. Length: 1.5 m, including the tail