This is a very tentative list of transitional fossils. As new fossils are discovered and more is learned about the ones we have, this list is very likely to change, as the fossil record is far from complete, and far from producing a seamless lineage from one group to the next.

Remember that transitional fossils display features of two types of animals and are examples of the transition from one type of animal into another. They serve to "bridge the gap" in evolutionary history between two types of related animals. They can be identified by their retention of certain primitive traits in comparison with their more derived relatives.

Below is just a brief list containing a few examples of transitional fossils for each milestone in the development of life. Ideally, this list would only recursively include "true" transitionals, fossils representing ancestral specie from which later groups evolved. But due to the incomplete nature of the fossil record, most, if not all, of the fossils listed here represent extinct side branches, more or less closely related to the true ancestor. If you are interested in a certain group there is free information online where you can find the full list of transitional forms.

They are listed in transitional order. For example, Pikaia was the most invertebrate-like and Guiyu was the most fish-like.

Invertebrates to fish

These transitional forms had notochords and gills but were jawless:

Pikaia

Conodont

Haikouicthys

Arandaspis

Berkenia

Guiyu

Fish to tetrapods

These fossils display a mosaic of fish-like and amphibian-like features:

Osteolepis

Eusthenopteron

Pandericthys

Tiktaalik

Elginerpeton

Ventastega

Acanthostega

Icthyostega

Hynerpeton

Tulerpeton

Pederpes

Eryops

Labyrinthodonts to Modern Amphibians

They show archaic amphibian features and modern amphibian features:

Gerobatrachus

Triadobatrachus

Prosalirus

Viaraella

Eocaecilia

Amphibians to amniotes

These show features of early reptiles:

Proterogyrinus

Limnoscelis

Tseajaia

Westlothiana

Solenodonsaurus

Casineria

Hylonomus

Paleothyris

Synapsids to mammals

These show the transition from "mammal-like" reptiles to modern mammals:

Protoclepsydrops

Archaeothyris

Clepsydrops

Dimetrodon

Procynosuchus

Diictodon

Thrinaxodon

Cynognathus

Morganucodon

Yanoconodon

Archosaurs to dinosaurs

These reptiles had hips that were less sprawled and walked more upright:

Euparkeria

Proterosuchus

Postosuchus

Marasuchus

Asilisaurus

Spondylosoma

Eoraptor

Dinosaurs to birds

These had feathers but retained some reptile-like characteristics:

Pedopenna

Anchiornis

Scansoriopteryx

Sinornithosaurus

Microraptor

Archaeopteryx

Confuciusornis

Eoalulavis

Ichthyornis

Early artiodactyls to whales

These fossils show a progression from land mammals to modern whales:

Pakicetus

Ambulocetus

Kutchicetus

Artiocetus

Dorudon

Aetiocetus

Basilosaurus

Eurhinodelphis

Mammalodon

Early perissodactyls to modern horses

The ancestors of horses were small, with no hooves, but gradually grew larger:

Hyracotherium

Mesohippus

Parahippus

Merychippus

Pliohippus

Equus

Early primates to modern humans

They show the transition from early primates to great apes to early hominids:

Apidium

Aegyptopithecus

Pierolapithecus

Proconsul

Ardipithecus

Australopithecus

Homo habilis

Homo erectus

Homo sapiens (archaic subspecies)

Homo sapiens

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