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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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ReneTransitional fossils are important because they are visual evidence of one type of animal evolving into another type of animal. A transitional fossil always contains features of one type and features of another.
For example, Archaeopteryx is a transitional fossil that is a cross between a dinosaur and a bird. It has a bony tail, teeth, and claws like a dinosaur, but it has feathers and is able to fly like a bird. It is an important link in the evolution from dinosaurs to birds.
Transitional fossils are important because they are visual evidence of one type of animal evolving into another type of animal. A transitional fossil always contains features of one type and features of another.
For example, Archaeopteryx is a transitional fossil that is a cross between a dinosaur and a bird. It has a bony tail, teeth, and claws like a dinosaur, but it has feathers and is able to fly like a bird. It is an important link in the evolution from dinosaurs to birds.
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What is the importance of index fossils?
Index fossils are the fossils of short-lived species which, because of their short lives, can be used by scientists to identify the age of the rock strata in which they're found. (For example, if you know a certain species only lived in the Cambrian period, and you find some fossils of this species in some rock, then you know the other fossils you find in that rock must also have come from the Cambrian period.) Some examples of species that left behind index fossils, and their related historical periods, are:Billingsella corrugagta - Cambrian period, Palaeozoic eraCactocrinus multibrachiatus - Mississippian period, Palaeozoic eraScaphites hippocrepia - Cretaceous period, Mesozoic eraNeptunea tabulata - Quarternary period, Cenozoic eraSee the links below for more examples and info.
Are fossils examples of organic matter and why?
Yes, fossils are examples of organic matter because they are the preserved remains or traces of once-living organisms. Fossils can include bones, shells, teeth, and other organic materials that have undergone a process of mineralization or replacement with inorganic materials to become stone-like structures.
True or false the earliest known bird fossils are those of archaeopteryx?
True. Archaeopteryx is considered one of the earliest known bird fossils, dating back to the Late Jurassic period around 150 million years ago. It is a transitional species with both bird and dinosaur-like features.
What do fossilized tracks tell you about the reptiles that once lived in the canyon?
Well, the tracks are examples of trace fossils. Trace fossils are not fossils in the traditional sense. Instead, they are fossils of something other than the animal or plant's form, like a animal track or burrow, that tells us an animal has been there.
What do fossils feel like?
Fossils have layer upon layer of hardened tissue. Therefore they are quite rough in texture where the insides are more malleable. Depending on what the fossil is of some fossils give off a sour aroma. Most of the time animal fossils deteriate at a faster rate than fossils of humans or shells. Fossils are a unique study and I you study them further.
