After Czerkas & Czerkas: De oerwereld van de Dinosauriërs (1993)

This is a simplified family tree of the quadrupeds and the birds. The first column gives the geological periods. The amphibians were the first vertebrate land animals: they descend from the lobe-finned fishes or the lungfishes. From the amphibians the reptiles came into existence at some moment in the Carboniferous. The main difference between these two groups is the fact that reptiles lay eggs with a shell which makes them independent of the water. Amphibians, on the contrary, always have to go back to the water to lay their eggs. Think e.g. of the frogs.  The tree above shows also that Hylonomus (a very early reptile) still lived at the time when the mammal-like reptiles branched off . From this latter group the mammals came forth. Further it can be seen that the birds descend from the reptiles. Know more? Reptiles in general

This is one of the many fine paintings in the above mentioned book. It is a landscape from the Carboniferous and in the background a big stump of the clubmoss tree Sigillaria can be seen. The animal is a Hylonomus snapping at an insect.  Its height is over 20 cm. The fossils of this very old reptile have been found in hollow tree stumps in which the animals were trapped. They couldn't escape and got covered with sand and mud. Their skeletons fossilized. Other quadrupeds underwent the same fate. The link below shows the process with many figures.   How do the scientists know that the fossil is a reptile and not an amphibian? Eggs have not been found but it can be concluded from the structure of the skull. In reptiles some of the bones are merged, which were separate in amphibians. Know more? How Hylonomus was found

Evolution 36

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