List of transitional fossils

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Possibly the best known of all transitional fossils, the Berlin specimen of Archaeopteryx lithographica

This is a tentative list of transitional fossils (fossil remains of a creature that exhibits primitive traits in comparison with more derived organisms to which it is related). The fossils are listed in series, showing the transition from one group to another, representing significant steps in the evolution of major features in various lines. These changes often represent major changes in anatomy, related to mode of life, like the acquisition of feathered wings for an aerial lifestyle in birds, or legs in the fish/tetrapod transition. As noted already by Darwin, the fossil record is incomplete.[1]

Ideally, this list would only recursively include 'true' transitionals, fossils representing ancestral species from which later groups evolved, but most if not all, of the fossils shown here represent extinct side branches, more or less closely related to the true ancestor.[2] They will all include details unique to their own line as well. Fossils having relatively few such traits are termed "transitional", while those with a host of traits found neither in the ancestral or derived group are called "intermediate". Since all species will always be subject to natural selection, the very term "transitional fossil" is essentially a misconception. It is however a commonly used term and a useful concept in evolutionary biology. The fossils listed represent significant steps in the evolution of major features in various lines and therefore fit the common usage of the phrase.

Nautiloids to ammonoids[edit]

The NautiloidsAmmonoids Evolutionary Series
Appearance Taxa Relationships Status Description Image
>500 Ma

Subclass:

OrhtocerasNautiloid092313.jpg
390 Ma

Order:

  • Member of the Nautiloids.
  • Direct ancestor of the ammonoids.
370 Ma

Subclass:

  • Direct descendants of Bactirida.
Ammonite Asteroceras.jpg

Cephalopods[edit]

The Cephalopod Evolutionary Series
Appearance Taxa Relationships Status Description Image
296 Ma

Genus

The earliest described octopod.
164 Ma

Genus:

A primitive octopod. Proteroctopus ribeti.jpg
165–164 Ma

Genus:

An early Vampyromorphida. Vampylarge.JPG
89 - 71 Ma

Genus:

A primitive octopod. Palaeoctopus newboldi.jpg

Evolution of insects[edit]

The Insect Evolutionary Series
Appearance Taxa Relationships Status Description Image
400 Ma

Genus:

The world’s oldest known insect.

400 Ma

Genus:

Early springtail.

300 Ma

Genus:

Ancestral to cockroaches, mantids and termites.

316.5 Ma

Genus:

A primitive cockroach.

140 Ma

Genus:

The earliest known Lepidopteran.

92 Ma

Genus:

The oldest known species of bee.

80 Ma

Genus:

The earliest known species of ant.

56 - 34 Ma

Genus:

First leaf insect from the fossil record.

Evolution of spiders[edit]

The Spider Evolutionary Series
Appearance Taxa Relationships Status Description Image
390 Ma

Genus:

Previously thought to be the world's oldest spider.
165 Ma

Genus

The oldest known haplogyne spider.

Invertebrates to fish[edit]

The InvertebratesFish Evolutionary Series
Appearance Taxa Relationships Status Description Image
523 Ma

Genus:

Lancelet-like in appearance. Oldest known ancestor of modern vertebrates

Vertebrate characters

Pikaia Smithsonian.JPG

504 Ma

Class:

Had fin rays, chevron-shaped muscles and a notochord. Conodonts.jpg
530 Ma

Genus:

Appears to have a cranium, thus being a craniat.[3] Haikouichthys NT.jpg
480 to 470 Ma

Genus:

Jawless fish A well armoured jawless fish, resembling a large tadpole in life Arandaspis prionotolepis fossil.jpg
422-412 Ma

Genus:

An anapsid, ancestral to the jawed vertebrates,[4] An unarmored, scaly jawless fish Birkenia elegans.jpg
419 Ma

Genus:

Oldest known bony fish[5] Guiyu BW.jpg

Chondrichthyes[edit]

The Chondrichthyes Evolutionary Series
Appearance Taxa Relationships Status Description Image
370 Ma

Genus:

An early primitive shark. Early Shark.jpg
70 - 65 Ma

Genus:

An early sawfish
99 – 65 Ma

Genus:

An early stingray-like skate Cyclobatis major 1.JPG

Bony fish[edit]

The Bony Fish Evolutionary Series
Appearance Taxa Relationships Status Description Image
420 Ma

Genus:

The earliest-known Actinopterygiian.

 ??? Ma

Genus:

An early relative of the flatfishes, one eye had already migrated towards the body midline. Amphistium.JPG
48 – 37 Ma

Genus:

The earliest known true flatfish
183.7–125.0 Ma

Genus:

One of the first teleosts. Leptolepis dubia cm4694.jpg
99 – 93 Ma

Genus:

The oldest known eel.
13 Ma

Genus:

One of the oldest known seahorses. Tunjice Hills Hippocampus.jpg
13 Ma

Genus:

One of the oldest known seahorses. Hippocampus slovenicus.jpg
83 - 70 Ma

Genus:

The oldest known lamprid fish Nardovelifer altipinnis.jpg
56 - 34 Ma

Genus:

A primitive sunfish
58 - 55 Ma

Genus:

The oldest known member of the catfish family Callichthyidae. Corydoras revelatus.JPG
56 - 34 Ma

Genus:

A primitive rabbitfish.
48 - 37 Ma

Genus:

A primitive perch Palaeoperca proxima.jpg
58 - 55 Ma

Genus:

A primitive pomfret Trachicaranx tersus.jpg
48 - 40 Ma

Genus:

An early handfish
48 - 40 Ma

Genus:

The oldest known ostraciid boxfish Eolactoria sorbinii.jpg
48 - 40 Ma

Genus:

The oldest known aracanid boxfish Proaracana dubia.jpg
48 - 40 Ma

Genus:

A basal surgeonfish
48 - 40 Ma

Genus:

A primitive monodactylid moonyfish Psettopsis subarcuatus.jpg
48 - 40 Ma

Genus:

A primitive monodactylid moonyfish Pasaichthys pleuronectiformis.jpg
48 - 40 Ma

Genus:

A short-snouted ancestor of the modern Moorish Idol.
83 - 65 Ma

Genus:

A primitive member of the Tetraodontidae
83 - 65 Ma

Genus:

A primitive Perciforme
58 - 55 Ma

Genus:

A primitive member of the Zeidae
58 - 55 Ma

Genus:

A primitive member of the Zeidae
 ??? Ma

Genus:

A primitive member of the Ichthyodectidae Cooyoo australis.jpg
65 Ma

Genus:

A primitive tetraodontid

Fish to tetrapods[edit]

The FishTetrapods Evolutionary Series
Appearance Taxa Relationships Status Description Image
416-359 Ma

Genus:

An early member of the Tetrapodomorpha, the piscine line leading to tetrapods, Osteolepis is generalised enough to give a fair approximation of the common ancestor of tetrapods and lungfish.[6] Fish A small to medium sized sarcopterygian fish with internal nostrils and pectoral fins stiffened by bony components broadly homologous to the humerus and radius/ulna found in tetrapods.[6] Osteolepis macrolepidotus.jpg
385 Ma

Genus:

Belonging to the family Tristichopteridae, a family that form a sister group to Panderichthys and the tetrapods.[6] Though not on the evolutionary path to tetrapods, Eusthenopteron is of fairly general build and is very well known, serving as an iconic model organism in tetrapod evolution.[7] A medium sized, mainly pelagic fish, Eusthenopteron mainly use the pectoral and pelvic fins for navigation, and the tail for propulsion.[7] The fin was of diphycercal, foreshadowing the straightening of the spine and the evolution of a contiguous fin in fish like Panderichthys Eusthenopteron foordi 1.JPG
380 Ma

Genus:

Very close to the origin of tetrapods, a "fishapod" elpistostegalian.[6] Fish A large, predatory shallow water fish. As common in shallow water fish, the pectoral and pelvic fins were flexible and paddle-like for propulsion.[8] The dorsal and anal fins are lost, the tail fin contiguous.[9] The spiracles were short and wide, indication large amount of oxygen were taken up by the lungs rather than through the gills.[10] Panderichthys BW.jpg
375 Ma

Genus:

A "fishapod" more tetrapod-like than Panderichthys.[6] A fish, transitional between fish and the early, fish-like labyrinthodonts.[11][12] "Fish" with stout, fleshy pectoral fins with a joint between the innermost and the two next bony elements, corresponding to the elbow in higher tetrapods. The cleithrum bone was free of the skull, functioning as anchoring for the pectoral fins, and at the same time allowing for movement of the neck.[12][13] Tiktaalik belgium.JPG
368 Ma

Genus:

Analysis of the cranial material shows it was more advanced than Tiktaalik, and together with Obruchevichthys form a sister group to the higher tetrapods.[14] A fairly fragmentary find, Elginerpeton straddles the fish/tetrapod divide with a mosaic of features resembling Panderichthys, Ichthyostega and Hynerpeton.[14] Probably one of the "fishapods".[15] Though fragmentary, the find includes a shoulder blade (Cleitrum bone) as well as elements of the limbs, which shows it had comparable limbs Ichthyostega and Hynerpeton, indicating feet rather than fins. Elginerpeton BW.jpg
365 Ma

Genus:

Known only from fragmentary remains, mostly a lower jaw, Ventastega is morphologically midway between Tiktaalik and Acanthostega/Ichthyostega.[16] Possibly oldest animal to have feet rather than fins.[16] A large, dorso-ventrally flattened predatory fish with a well armoured labyrinthodont-like skull. While the fins themselves has not been found, the shoulder girdle is essentially similar to that of Acanthostega, indicating it too had feet rather than fins.[16] Ventastega BW.jpg
365 Ma

Genus:

Together with Ichthyostega the sole early labyrinthodont known from fairly complete skeletons. It is the oldest animal known to have feet rather than fins, thus making it a true tetrapod and the oldest known unquestionable ichthyostegalian.[17] First known animal with toes rather than fins. The feet were broad and paddle-like, adapted for movement in water.[18] It retained functional gills in adulthood, behind a fleshy operculum. Acanthostega.JPG
365 Ma

Genus:

Fairly closely related to Acanthostega. It possibly represent an early (and ultimately unsuccessful) line adapted to moving on land by inchworm-like movements. Together with Acanthostega the sole early labyrinthodont known from fairly complete skeletons. Early labyrinthodont with polydactylous, paddle-like feet and reinforced vertebrae and neural spines. It probably spent time on land, yet retained gills and a tail with fin rayes. Ichthyostega skull.jpg
360 Ma

Genus:

While known only from fragmentary remains, it is more advanced than Ichthyostega. Early labyrinthodont amphibian A large, basically salamander-like creature. The shoulder girdle was powerful, indicating it was a competent walker.[19] Hynerpeton BW.jpg
 ??? Ma

Genus:

An advanced ichthyostegalian, it straddle the divide between the fish-like Devonian forms and the more advanced Carboniferous amphibians. It has been suggested it is an early reptil-like amphibian.[20] A large animal with paddle-like six-toed feet. It did however not have gills in adulthood, and is thus the oldest labyrinthodont known to depend entirely on breathing with its lungs.[21] Tulerpeton12DB.jpg
359 - 345 Ma

Genus:

Hailing from the fossil-poor Romer's Gap, Pederpes may be ancestral to the higher labyrinthodonts. Intermediate between the earlier Ichthyostegalian and the later, more advanced labyrinthodonts. Despite an extra toe on the forelimbs, Pederpes had limbs that terminated in feet adapted primarely for walking rather than paddles for combined swimming and walking like the earlier groups.[22] Pederpes22small.jpg
295 Ma

Genus:

The Temnospondyli are derived paleozoic amphibians, possibly ancestral to modern amphibians A "classical" temnospondyl, an advanced labyrinthodont group. One of the best known labyrinthodonts, Eryops combines the large, flat skull and short limbs typical of the group. Eryops skeleton.png
The LabyrinthodontiaLissamphibia Evolutionary Series
Appearance Taxa Relationships Status Description Image
290 Ma

Genus:

Colloquially referred to as a "frogamander" due to this taxon being both chronologically and morphologically basal to both anurans and salamanders One of the first transitional fossils towards modern amphibians (Lissamphibia).[23] Primitive traits
  • Backbone with intermediate characteristics
  • Retains a fully developed tail

Derived traits

  • Bears a large space for a tympanic ear
  • Ankle bones are fused together like in salamanders
  • Lightly built wide skull as in frogs[23]

Gerobatrachus NT.jpg

250 Ma

Genus:

Intermediate between generalized amphibians and derived frogs Early "almost frog" transitional amphibian Primitive traits
  • Possessed short limbs and therefore was unable to hop, unlike all extant anurans
  • Retains fourteen vertebra unlike modern frogs who have four to nine vertebra
  • Tibia and fibula are not fused into a tibiofibula

Derived traits

  • Skull resembles that of modern anuran skull with a latticework of thin bones in skull

Triadobatrachus BW.jpg

190 Ma

Genus:

Another transitional form which could be properly classified as a frog An intermediate form which may replace Triadobatrachus as the "ultimate" ancestor of anurans Primitive traits
  • Still possess relatively short limbs

Derived traits

  • Tail is greatly reduced
  • Does not have greatly enlarged legs, but shows some adaptations for hopping, such as a three-pronged pelvis
Prosalirus BW.jpg
213-188 Ma

Genus:

A derived fossil frog completing the series of transitional fossils between early amphibians and modern anurans The oldest "true" frog[24] Primitive traits
  • Retains ten presacral vertebra

Derived traits

  • Hind legs are adapted for hopping

Vieraella NT.jpg

210 Ma

Genus:

Intermediate between basal amphibians and caecilians An early caecilian Primitive traits
  • Bears three-toed vestigial limbs
  • The size of the orbits indicates well developed eyes and suggest a non-subterranean lifestyle

Derived traits

  • The body has been adapted to a sort of serpentine shape

Eocaecilia BW.jpg

Amphibians to amniotes (early reptiles)[edit]

The AmphibiansReptiles Evolutionary Series
Appearance Taxa Relationships Status Description Image
326 - 318 Ma

Genus:

One of the early reptile-like amphibians Amphibian A large, somewhat lizard-like labyrinthodont with a deep skull, laterally placed eyes and five digits to each foot. Proterogyrinus NT.jpg
 ??? Ma

Genus:

The order Diadectomorpha is the sister group of the amniotes. The Limnoscelis was originally described as a "cotylosaur" (early reptiles) together with the other diadectomorphans. Today the large-bodied diadectomorphs are thought to have had a larval stage, falling close to, but just outside the amphibian/reptile divide. A large, predatory reptile-like amphibian. The limbs are extremely heavily built, indicating it fed on slow moving prey. Limnoscelis(Cast)-RedpathMuseumMontreal-June6-08.png
 ??? Ma

Genus:

Uncertain phylogeny, possibly a Seymouriamorph or Diadectomorph[25][26] Amphibian A medium sized, probably herbivorious animal Tseajaia BW.jpg
350 Ma

Genus:

Uncertain phylogenetic position. Westlothiana may be a small-bodied diadectopmorph, falling just outside the amphibian/reptile divide Originally described as the first reptile, it is now considered an advanced reptile-like amphibian. Small, probably insectovorious animal. The body and tail was long, the limbs small, somewhat like a modern skink. Westlothiana BW.jpg
320-305 Ma

Genus:

Possibly allied to the Diadectomorpha, or belonging to a sister group to Diadectomorpha and Amniota[27] Likely an amphibian[27] Smallish, likely carnivorious.[28] Solenodonsaurus1DB.jpg
340 Ma

Genus:

The fragmentary nature of the fossil (it lacks a cranium) makes an exact phylogenetic position hard to establish. Possibly the first animal with an amniote egg, and thus the first reptile. Small lizard-like animal, the first known tetrapod to possess claws, indicating it has reptilian type skin with scutes.[29] Casineria kiddi tilted.jpg
315 Ma

Genus:

One of several small, basal reptile genera Reptile An early anapsid reptile, considered to be ancestral to both the synapsid and sauropsid lines, and thus the oldest representative of the crown group amniotes. Hylonomus BW.jpg
312 - 304 Ma

Genus:

One of several small, basal reptile genera Reptile (most likely a sauropsid) An early anapsid reptile. In phylogenetic analysis it falls on the sauropsid side, it is thus likely a progenitor of the diapsids Paleothyris BACKGROUND.JPG

Turtles[edit]

The Turtle Evolutionary Series
Appearance Taxa Relationships Status Description Image
220 Ma

Genus:

The oldest known turtle.

Odontochelys BW.jpg

210 Ma

Genus:

Proganochelys Quenstedti.jpg
164 Ma

Genus:

An evolutionary bridge between early land turtles and sea turtles.

From lizards to snakes[edit]

The LizardSnake Evolutionary Series
Appearance Taxa Relationships Status Description Image
92 Ma

Genus:

A transitional form between Cretaceous lizards and limbless snakes retaining distinct, if non-functional, legs.[30] Eupodophis descouensi Holotype.jpg
90 Ma

Genus:

A basal snake with two hind-limbs.

Lizards[edit]

The Lizard Evolutionary Series
Appearance Taxa Relationships Status Description Image
61 - 58 Ma

Genus:

The earliest known chameleon.
92 Ma

Genus:

A basal mosasauroid from the Upper Cretaceous of North America.
71 - 82 Ma

Genus:

One of the earliest Varanoidea.
146–100 Ma

Genus:

An primitive iguanid
97–100 Ma

Genus:

The oldest known gecko

Pterosaurs[edit]

RhamphorhynchoideaPterodactyloidea Evolutionary Series
Appearance Taxa Relationships Status Description Image
160 Ma

Genus:

Basal to both rhamphorhynchoids and pterodactyloids Darwinopterus.jpg
160 Ma

Genus

Archosaurs to dinosaurs[edit]

The ArchosauriaDinosauria Series
Appearance Taxa Relationships Status Description Image
 ??? Ma

Genus:

The oldest known archosaur, Proterosuchus was one of the largest land reptiles during the Early Triassic, about the size of to today's Komodo dragons. It looked somewhat crocodile-like, with sprawling legs, long jaws, powerful neck muscles and a long tail. A distinct proterosuchid trait is the peculiar hook-shaped mouth.

Archosaurus ross1DB.jpg

 ??? Ma

Genus:

Marasuchus.JPG
 ??? Ma

Genus:

The oldest known animal on the dinosaur/pterosaur side of the archosaurian tree (the Ornithodira), dating to about 245 million years ago.[33] A small, lightly built animal. It had a fairly long neck (contrary to the short necked relatives of crocodiles), but ran on all four legs. Asilisaurus.jpg
 ??? Ma

Genus:

Known from a somewhat fragmentary find, Spondylosoma was possibly an early dinosaur, or near dinosaur.[34] It has however also been classified as a rauisuchian.[35]
228 Ma

Genus:

A very early representative of the sauropod stem line or perhaps even the Saurischia as a whole.[36][37][38] A small (1 meter, ~ 10 kg) bipedal carnivore with numerous sharp teeth. It was a swift digigrade runner. The forelimbs were half the length of the hindlimbs and the hands had five fingers EoraptorBrussels.jpg

Dinosauria[edit]

The Dinosauria Evolutionary Series
Appearance Taxa Relationships Status Description Image
228 to 216.5 Ma

Genus:

The oldest known ornithischian.

Pisanosaurus.jpg
216–200 Ma

Genus:

The most primitive well-known representative of the sauropodomorph dinosaurs. Thecodontosaurus.jpg
 ??? Ma

Genus:

The oldest and most primitive known stegosaur. Huayangosaurus taibaii 20050707 07.jpg
 ??? Ma

Genus:

A basal pachycephalosaur from the Barremian Stage of the Cretaceous.
160 Ma

Genus:

A genus of basal ceratopsian dinosaur from the Late Jurassic Period of central Asia. Yinlong skull.jpg
160 Ma

Genus:

A genus of proceratosaurid tyrannosauroid dinosaur, one of the earliest known examples of the lineage. Guanlong fossil.jpg
126 Ma

Genus:

An early genus of therizinosaur Falcarius.jpg
208–194 Ma

Genus:

One of the most primitive thyreophorans. Scelidosaurus skeleton.png
130–125 Ma

Genus:

A possible ancestor of the duck-billed dinosaurs. ProbactrosaurusGobiensis-PaleozoologicalMuseumOfChina-May23-08.jpg
 ??? Ma

Genus:

A primitive (basal) ornithomimosaur.

Dinosaurs to birds[edit]

Further information: Origin of birds
Further information: Evolution of birds
The Dinosaursbirds Evolutionary Series
Appearance Taxa Relationships Status Description Image
152-151 Ma

Genus:

Primitive traits
  • Undifferentiated hind digits displaying no specialties for climbing
  • Spine attaches to the back end of the skull rather than the base
  • Moderately long, bony tail

Derived traits

  • Basic proto-feathers cover parts of the body for insulation
Juravenator starkae.JPG
168-152 Ma

Genus:

The find is represented only by a hind leg, but one that is very bird-like. It belonged to a small maniraptoran dinosaur with long, pennaceous feathers on its hind legs and (in all likelihood) arms.
161-151 Ma

Genus:

Basal troodontid Although once classified as a bird, Anchiornis is now considered a basal troodontid which bears pennaceous, symmetrical feathers on all four limbs. Primitive traits
  • Wings symmetrical and rounded, probably not used for flight but instead insulation, mating displays, and gliding
  • Long legs overall morphology similar to that of other troodontids
  • Spine attaches to the back end of the skull rather than the base
  • Moderately long, bony tail

Derived traits

  • Flexible wrists which are more similar to aves than other theropods
  • Like birds and unlike troodontids, Anchiornis had arms nearly the same length as the hind legs
  • Bore primary and secondary pennaceous symmetrical wings on both arms, legs, toes, and wrist
Anchiornis BW.jpg
150–145 Ma

Genus:

Known for its mosaic of avian and theropod characteristics Archaeopteryx is both the first primitive bird in the fossil record and one of the first transitional fossils discovered. Traditionally seen as the first proper bird, though it is not directly ancestral to modern birds.[39] An excellent intermediate form between dinosaurs and birds. Capable of gliding, but lacking alula and keel, it could likely not sustain powered flight. Primitive traits
  • Slower dinosaur-like growth rate
  • No keel
  • Spine attaches to the back end of the skull rather than the base
  • Forelimbs have three unfused, clawed fingers, no alula
  • Maxilla and premaxilla bore unserrated teeth
  • Moderately long, bony tail

Derived traits

  • Fully developed asymmetrical flight feathers
  • Fused furcula from two joined clavicles
  • Backward and elongated pubis similar to maniraptors, but not found in more primitive theropods
Archaeopteryx lithographica (Berlin specimen).jpg
120 Ma

Genus:

Found in the famous Liaoning province Confuciusornis is the first primitive bird with a pygostyle. With its short tail and toothless beak, Confuciusornis is very modern looking compared to Archaeopteryx. The toothless beak is however a case of convergent evolution, as more advanced birds retained teeth, illustration the sometimes confusing mosaic evolution of the dinosaur-bird transition. Primitive traits
  • Retained unfused clawed digits, no alula
  • Sideways-facing glenoid joint

Derived traits

  • Short tail with fused vertebrae at the end (pygostyle)
  • Larger sternum with a low primitive keel
  • Unlike other early birds Confuciusornis had a toothless beak
Confuciusornis sanctus (2).jpg
115 Ma

Genus:

Primitive bird and possibly a descendant of "urvogels" like Archaeopteryx. First bird to possess an alula. Plesiomophic traits
  • Two unfused, functional digits remain on second and third digit

Derived traits

  • First digit bearing an alula rather than claw
93.5-75 Ma

Genus:

Considered a close relative to the ancestor to modern birds A flying bird found in several epochs in the late Cretaceous which still bore teeth, but in most respects very similar to Neornithes. Primitive traits
  • Numerous sharp teeth in much of the beak

Derived traits

  • Fused bones (metacarpals) II & III of the hand
  • Rigid ribcage with a well-developed carina
  • No functional claws on the hand
  • Short childhood with distinct adult stage.[40]
Ichthyornis yale.JPG

Bird evolution[edit]

The Bird Evolutionary Series
Appearance Taxa Relationships Status Description Image
60-58 Ma

Genus:

The earliest-known Penguin.

Waimanu BW.jpg
 ??? Ma

Genus:

An early flamingo.
 ??? Ma

Genus:

An early gaviiform.
55-48 Ma

Genus:

An early psittacine.
 ??? Ma

Genus:

A basal falconiform.
50 Ma

Genus:

An early apodiform.

Synapsid ("mammal-like reptiles") to mammals[edit]

The SynapsidsMammals Evolutionary Series
Appearance Taxa Relationships Status Description Image
 ??? Ma

Genus:

Known from very fragmentary finds, Protoclepsydrops may be the earliest synapsid (mammal-like reptile) A low-slung, lizard-like animal of moderate size.
306 Ma

Genus:

The oldest undisputed synapsid (mammal-like reptile) Primitive traits
  • A relatively flat, reptile-like skull
  • Typically reptilian sprawling gait
  • Generally lizard-like proportions with a dorso-ventrally flattened body

Derived traits

Archaeothyris BW.jpg
297 Ma Genus: A primitive member of the Sphenacodontidae, or possibly just outside the group.[41][42] A pelycosaur-grade synapsid Derived traits
  • Two or three moderately large canine-like teeth about a third down the maxilla.[43]
  • Dentary bone the largest element of the lower jaw[42]
  • The skull deeper than in Archaeothyris
Haptodus BW.jpg
265 Ma

Genus:

An advanced member of the family Sphenacodontidae, from which the therapsids (advanced synapsids) evolved A pelycosaur-grade synapsid. At up to 4 meters, Dimetrodon was one of the largest animals of its time. The distinct sail of the back makes it the most recognized synapsid known

Primitive traits

  • Cold blooded metabolism dependent of external heat source (hence the "sail")[44]
  • Sprawling gait
  • No secondary palate
  • No enlarged side teeth in the lower jaw

Derived traits

  • Distinctly elongated 2nd and 3rd tooth on the maxilla, corresponding to the canine in mammals. The first canine generally longer than the second.[45]
  • Skull deep and narrow
  • Body overall deeper than in earlier forms
Dimetrodon skeleton.jpg
267 Ma

Genus:

A primitive therapsid. About the size of a large dog, Biarmosuchus was a lightly built and likely fairly agile animal for its size.[46]

Primitive traits

Derived traits

  • A single canine as the first tooth on the maxilla, all other maxillary teeth small
  • Tendency for an enlarged caninelike tooth on the dentary
  • Internal nostrils covered by a partial fleshy palate[48]
  • Enlarged temporal opening giving more powerful bite
Biarmosuchus.jpg
248-245 Ma

Genus:

A small bodied relative of the larger Cynognathus. Am advanced cynodont, just on the reptilian side of the reptile/mammal divide Primitive traits

Derived traits

  • Well developed respiratory turbinates and palate, indicating homeothermy
  • Generally mammal-like dentition.
  • Mammal-like ecology: Burrowing and small size
  • Animals of different sizes found together, indicating post-hatching parental care.
Thrinaxodon Lionhinus.jpg
205 Ma

Genus:

An early mammal, but outside the crown group (a mammaliform) Morganucodon.jpg
125 Ma

Genus:

An early crown group mammal. Yanoconodon BW.jpg

Evolution of mammals[edit]

The Mammal Evolutionary Series
Appearance Taxa Relationships Status Description Image
100–104 Ma

Genus:

The earliest known monotreme.

125 Ma

Genus:

The oldest metatherian known.

Sinodelphys szalayi.JPG
 ?? Ma

Genus:

The earliest-known marsupial.

Djarthia murgonensis.jpg
164-165 Ma

Genus:

The oldest known eutherian[50]

Juramaia NT.jpg
63-50 Ma

Genus:

The earliest known proboscidean.

60-55 Ma

Genus:

The possible ancestor of the modern order Carnivora.

Miacis.jpg
15.97–11.61 Ma

Genus:

The earliest known cervid.

Heteroprox eggeri.JPG
20-18 Ma

Genus:

The earliest known bovid.

Eotragus sansaniensis.JPG
45-40 Ma

Genus:

The oldest camel known, it was also the smallest.

 ??? Ma

Genus:

Suspected to be the ancestor of modern tapirs and rhinoceroses.

Hyrachyus.png
55.4—48.6 Ma

Genus:

Suspected to be the ancestor of modern tapirs.

Heptodon posticus.jpg
38—33.9 Ma

Genus:

The earliest known canid.

Hesperocyon Gregarius.jpg
 ??? Ma

Genus:

The earliest known lagomorph.

52.5 Ma

Genus:

One of the two oldest known monospecific genera of bat.

2 Ma

Species:

The earliest known member of the giant panda clade.

63 - 61.7Ma

Genus:

Believed to be the earliest example of a primate or a proto-primate, a primatomorph precursor to the Plesiadapiformes. Purgatorius BW.jpg
12.5-8.5 Ma

Genus:

This genus may have been the ancestor to the modern orangutans.

Sivapithecus.jpg
16 - 8 Ma

Genus:

An possible ancestor of living hippopotamids.
 ?? Ma

Genus:

The earliest known true (and scaled) pangolin. Eomanis waldi 1.JPG

Early artiodactylans to whales (evolution of whales)[edit]

The whale Evolutionary Series
Appearance Taxa Relationships Status Description Image
55.8 ± 0.2 - 33.9 ± 0.1 Ma

Genus:

Skull Pakicetus inachus.jpg
50 Ma

Genus:

Ambulocetus et pakicetus.jpg
46 Ma

Genus:

Kutchicetus BW.jpg
47 Ma

Genus:

41-33 Ma

Genus:

Dorudon atrox Senckenberg.jpg
25 Ma

Genus:

Aetiocetus BW.jpg
40-34 Ma

Genus:

Basilosaurus skeleton.jpg
8-15 Ma

Genus:

Eurhinodelphis longirostris.jpg
26 Ma

Genus:

Evolution of sirenians[edit]

The Sirenia Evolutionary Series
Appearance Taxa Relationships Status Description Image
50 Ma

Genus:

A primitive sirenian.

Dans l'ombre des dinosaures - Pezosiren - 016.jpg
40 Ma

Genus:

Prorastomus BW.jpg

 ??? Ma

Genus:

48.6–33.9 Ma

Genus:

An evolutionary bridge between primitive land-dwelling sirenians to aquatic sirenians

Eotheroides sp.JPG
??? Ma

Genus:

Halitherium.jpg

Evolution of the pinnipeds[edit]

The Pinniped Evolutionary Series
Appearance Taxa Relationships Status Description Image
21 to 24 Ma

Genus:

The oldest known pinniped.

Puijila darwini.jpg

 ??? Ma

Genus:

A very basal pinniped. Potamotherium.jpg
24-22 Ma

Genus:

An early seal, but with more primitive skull and feet.

Enaliarctos mealsi.JPG

Evolution of the horse[edit]

The HyracotheriumEquus Evolutionary Series
Appearance Taxa Relationships Status Description Image
60-45 Ma

Genus:

HyracotheriumVasacciensisLikeHorse.JPG
40-30 Ma

Genus:

Mesohippus Bairdii.jpg
20 Ma

Genus:

Parahippus Cognatus.jpg
17-11 Ma

Genus:

Anchitherium.jpg
12 Ma

Genus:

Pliohippus Pernix.jpg
1.8-0 Ma

Genus:

Img 3372 Me trot.jpg

Human evolution[edit]

Further information: Timeline of human evolution
The Human Evolutionary Series
Appearance Taxa Relationships Status Description Image
36-32 Ma

Genus

The oldest primitive monkey known in the fossil record, dating back before the split between Old and New world monkeys. Basal to both Old and New world monkeys. Primitive traits
  • Smaller canines than later monkeys such as Parapithecus
  • Retains some post-cranial characters seen in prosimians

Derived traits

  • Fused mandibular symphysis
  • Scapula similar to modern squirrel monkeys
  • Low rounded molar cusps rather than high cusps as is seen in tarsiers and strepsirrhine
33 Ma

Genus

A Miocene monkey which bridges the gap between the Eocene ancestors of Old world monkeys and Miocene ancestor of Hominoidea. Tentatively positioned transitional form prior to the Old world monkey/ape split. Primitive traits
  • Retained auditory features similar to Old world monkeys
  • Incapable of true brachiation unlike extant apes
  • Reduced capitular tail, but was proportionally smaller than Apidium

Derived traits

  • Ape-like teeth including broad, flat incisors and sexually dimorphic canines
  • A low sagittal keel and strong temporalis muscles
  • Increased size in the visual cortex
Aegyptopithecus NT.jpg
27-14 Ma

Genus

This primate exhibits very ape-like features like its teeth, but much of its post-cranial remains are more similar to monkeys. Universally accepted to be intermediate between 'ape-like monkeys' such as Aegyptopithecus and later apes including hominids. Primitive traits
  • Monkey-like wrist
  • Narrow, monkey-like illium

Derived traits

  • Completely lacked a fully formed tail
  • 5-Y pattern on lower molar cusps as also seen in hominoids
Proconsul africanus.JPG
13 Ma

Genus:

A European ape which is considered to be the predecessor of the great apes. Some objections have been raised to this fossils status due to its location in Spain, but Pierolapithecus is likely a transitional taxon between generalized apes and the lineage which led to great apes. Pleisomorphic traits
  • Relatively short fingers and walked in a similar quadrupedal fashion like baboons
  • Lacks adaptations for both gibbon-style brachaition as well as derived knuckle-walking like in chimpanzee's and gorilla's

Derived traits

  • Flat, wider rib cage like great apes for tree-climbing
  • The clavicle is large and similar to modern chimps suggesting a dorsally positioned scapula
4.4 Ma

Genus:

A woodland hominid adapted to quadruped arboreal locomotion, but also for bipedalism. Intermediate between the last common ancestor of chimps and humans, and the australopithecines. Primitive traits
  • Brains smaller than later hominids ranging from about 300-350 cc
  • Foot thumb is not retracted into the foot as a 'big toe'
  • Phalanges are more heavily curved than in Australopithecus

Derived traits

  • Reduced size in canines, however still retained dimorphic characters
  • Hind leg dominant, bipedal locomotion while walking, however were quadrupedal while climbing trees
Ardi.jpg
4.4-2.0 Ma

Genus:

First known genus of fully bipedal apes which are probably ancestral to robust australopiths and the genus Homo. Intermediate between extinct quadrupedal and bipedal apes. While the relationship between some species are being revised, Australopithecus afarensis is considered to be, by most experts, the ancestor to all later hominids. Primitive traits
  • Some species retain a sagittal crest
  • Curved phalanges, indicating semi-arboreal lifestyle
  • Semisectorial premolar is present
  • Prognathic face to varying degrees

Derived traits

  • Fully bipedal as indicated by many features including the knee joint, hips, lumbar curve in the spine, position of the foramen magnum, and feet
  • Increase in brain size ranging from about 375-500 cc
  • Development of a parabolic jaw
Australopithecus africanus - Cast of taung child Face.jpg
2.3-1.4 Ma

Species:

An early human which is the morphological link between australopithecines and later human species. Perfect intermediate between early hominids and later humans, possibly ancestral to modern humans. Primitive traits
  • Pronounced brow ridge
  • Foramen magnum is not positioned as anteriorly like in modern humans, giving a slightly semi-erect appearance
  • Although reduced in size the teeth are still fairly large

Derived traits

  • Increase brain size ranging from 510-800 cc
  • Face is slightly prognathic, but at a much steeper angle
  • Bulge in the Broca area, possibly the first hominid to use rudimentary speech
  • Associated with the first use of stone tools
Homo habilis.jpg
2.0-1.0 Ma

Species:

Very successful hominid, which was probably ancestral to both modern humans and neanderthals. Probably the first hominid to leave and successfully colonize territories outside of Africa. Ancestral to modern humans and neanderthals. Primitive traits
  • Still retains a heavy brow ridge and nuchal torus
  • Lacked the complexity of modern human language, but does show increase in the Broca area
  • Thicker bones and larger teeth than modern humans

Derived traits

  • Rounder and larger brain (about 900-1100 cc) than H. habilis
  • Face is orthognathic compared to H. habilis
  • Probably lived in bands and was an active group hunter
  • Associated with advanced stone tools and possibly the first hominid to use and produce fire
Homo erectus tautavelensis.jpg
500 Ka-recent

Species

Homo rhodesiensis was the immediate ancestor of modern humans which evidently displaced the neanderthals in Europe and the island 'hobbits' of southeast Asia. H. rhodesiensis evolved from Homo erectus about half a million years ago but still retains some primitive characteristics such as relatively thick bones and molars larger than modern humans. Ancestral to modern humans. Primitive traits
  • Large teeth
  • Heavy brow ridge
  • Extremely robust build in most groups

Derived traits

  • Rounder, less broad based cranium
  • Larger brain size, approaching (and sometimes exceeding) modern values
Skhul.JPG

See also[edit]

References[edit]

  1. ^ Darwin, C (1859) On the Origin of Species. Chapter 10: On the Imperfection of the Geological Record.
  2. ^ Weishampel D.B. (1996). "Fossils, Phylogeny, and Discovery: A Cladistic Study of the History of Tree Topologies and Ghost Lineage Durations". Journal of Vertebrate Paleontology 16 (2): 191–197. doi:10.1080/02724634.1996.10011307. JSTOR 4523710. 
  3. ^ Shu, D. G.; Morris, S. C.; Han, J.; Zhang, Z. F.; Yasui, K.; Janvier, P.; Chen, L.; Zhang, X. L.; Liu, J. N.; Li, Y.; Liu, H. -Q. (Jan 2003), "Head and backbone of the Early Cambrian vertebrate Haikouichthys", Nature 421 (6922): 526–529, Bibcode:2003Natur.421..526S, doi:10.1038/nature01264, ISSN 0028-0836, PMID 12556891  edit
  4. ^ Ahlberg, Per Erik (2001). Major events in early vertebrate evolution: palaeontology, phylogeny, genetics, and development. Washington, DC: Taylor & Francis. p. 188. ISBN 978-0-415-23370-5. 
  5. ^ Zhu, M.; Zhao, W.; Jia, L.; Lu, J.; Qiao, T.; Qu, Q. (2009). "The oldest articulated osteichthyan reveals mosaic gnathostome characters". Nature 458: 469–474. Bibcode:2009Natur.458..469Z. doi:10.1038/nature07855. PMID 19325627. 
  6. ^ a b c d e Ahlberg, P. E.; Johanson, Z. (1998). "Osteolepiforms and the ancestry of tetrapods". Nature 395 (6704): 792–794. Bibcode:1998Natur.395..792A. doi:10.1038/27421. 
  7. ^ a b R. Cloutier (1996). "Taxonomic review of Eusthenopteron foordi.". Devonian Fishes and Plants of Miguasha, Quebec, Canada. Dr. Friedrich Pfeil, München. pp. 487–502. 
  8. ^ Nature: The pelvic fin and girdle of Panderichthys and the origin of tetrapod locomotion
  9. ^ Carroll, R. (1995). "Between fish and amphibians". Nature 373 (6513): 389–390. Bibcode:1995Natur.373..389C. doi:10.1038/373389a0. 
  10. ^ Brazeau, M.D.; Ahlberg, P.E. (2006). "Tetrapod-like middle ear architecture in a Devonian fish". Nature 439 (7074): 318–321. Bibcode:2006Natur.439..318B. doi:10.1038/nature04196. PMID 16421569. 
  11. ^ John Noble Wilford, The New York Times, Scientists Call Fish Fossil the Missing Link, 5 April 2006.
  12. ^ a b Shubin, Neil (2008). Your Inner Fish. Pantheon. ISBN 978-0-375-42447-2. 
  13. ^ "Meet Your ancestor, the Fish that crawled". New Scientist Magazine. Retrieved 2007-02-07. 
  14. ^ a b Ahlberg, Per E. (1995). "Elginerpeton pancheni and the earliest tetrapod clade". Nature 373 (6513): 420–425. Bibcode:1995Natur.373..420A. doi:10.1038/373420a0. 
  15. ^ Elginerpeton pacheni at Devonian Times Archived 18 January 2010 at WebCite
  16. ^ a b c Ahlberg, Per. E.; Jennifer A. Clack, Ervins Luksevics, Henning Blom and Ivars Zupins (26 June 2008). "Ventastega curonica and the origin of tetrapod morphology". Nature 453 (7199): 1199–1204. Bibcode:2008Natur.453.1199A. doi:10.1038/nature06991. PMID 18580942.  article
  17. ^ Clack, J. (2005-11-21). Getting a leg up on land. Scientific American. Archived from the original on 2006-11-04. 
  18. ^ "Acanthostega gunneri," Devonian Times. Archived 17 January 2010 at WebCite
  19. ^ Shubin, Neil (2009). Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body. New York: Vintage. p. 13. ISBN 978-0-307-27745-9. 
  20. ^ Lebedev, O.A. (1984). "The first find of a Devonian tetrapod vertebrate in the USSR". Doklady Akademii Nauk SSSR. Palaeontology (in Russian) 278: 1470–1473. 
  21. ^ Gordon, M.S.; Long, J.A. (2004). "The Greatest Step In Vertebrate History: A Paleobiological Review of the Fish-Tetrapod Transition" (PDF). Physiological and Biochemical Zoology 77 (5): 700–719. doi:10.1086/425183. PMID 15547790. 
  22. ^ Clack, J. A. (2002). "An early tetrapod from 'Romer's Gap'". Nature 418 (6893): 72–76. doi:10.1038/nature00824. PMID 12097908. 
  23. ^ a b Anderson, J. S., Reisz, R. R., Scott, D., Fröbisch, N. B., Sumida, S. S. (2008). "A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders". Nature 453: 515–518. Bibcode:2008Natur.453..515A. doi:10.1038/nature06865. PMID 18497824. 
  24. ^ Estes, R., and O. A. Reig. (1973): The early fossil record of frogs: a review of the evidence. Pp. 11-63 In J. L. Vial (Ed.), Evolutionary Biology of the Anurans: Contemporary Research on Major Problems. University of Missouri Press, Columbia.
  25. ^ Moss J.L. (1972). "The Morphology and phylogenetic relationship of the Lower Permian tetrapod Tseajaia campi Vaughn (Amphibia: Seymouriamorpha)". University of California Publications in Geological Sciences 98: 1–72. 
  26. ^ Berman, D.S.; Sumida, S.S.; Lombard, R.E. (1992). "Reinterpretation of the temporal and occipital regions in Diadectes and the relationship of diadectomorphs". Journal of Paleontology 66: 481–499. 
  27. ^ a b Gauthier J., Kluge, A.G., & Rowe, T. (1988) The early evolution of the Amniota. In: M. J. Benton (ed.) The phylogeny and classification of the tetrapods, Volume 1: amphibians, reptiles, birds (1): pp 103-155. Oxford: Clarendon Press.
  28. ^ Solenodonsaurus on the TOL-web
  29. ^ R. L. Paton, T. R. Smithson and J. A. Clack, "An amniote-like skeleton from the Early Carboniferous of Scotland", (abstract), Nature 398, 508-513 (8 April 1999)
  30. ^ "Fossilized Snake With Two Legs Found - Science - redOrbit". Retrieved 2008-04-16. 
  31. ^ Blogspot.com
  32. ^ Wordpress.com
  33. ^ Nesbitt, S.J.; Sidor, C.A.; Irmis, R.B.; Angielczyk, K.D.; Smith, R.M.H.; Tsuji, L.M.A. (2010). "Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira". Nature 464 (7285): 95–98. Bibcode:2010Natur.464...95N. doi:10.1038/nature08718. PMID 20203608. 
  34. ^ Langer, M.C. (2004). Basal Saurischia. In: Weishampel, D.B., Dodson, P., and Osmólska, H. (eds.). The Dinosauria (second edition). University of California Press:Berkeley, 25-46. ISBN 0-520-24209-2
  35. ^ Galton, P.M. (2000). "Are Spondylosoma and Staurikosaurus (Santa Maria Formation, Middle-Upper Triassic, Brasil) the oldest saurischian dinosaurs?". Palaontologische Zeitschrift 74 (3): 393–423. doi:10.1007/bf02988109. 
  36. ^ R.N. Martinez et al. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science, Vol. 331, 14 January 2011, p. 206.
  37. ^ Kaplan M, "Move over Eoraptor", http://www.nature.com/news, 13-1-2011.
  38. ^ Apaldetti, C; Martinez, RN; Alcober, OA; Pol, D (2011). "A New Basal Sauropodomorph (Dinosauria: Saurischia) from Quebrada del Barro Formation (Marayes-El Carrizal Basin), Northwestern Argentina". PLoS ONE 6 (11): e26964. doi:10.1371/journal.pone. 
  39. ^ Padian, K. & Chiappe, L.M. (1997): Bird Origins. In: Encyclopedia of Dinosaurs (red. Currie, P.J & Padian, K., Academic Press, San Diego, pp 41–96, ISBN 978-0-12-226810-6
  40. ^ Chinsamy A., Martin L.D., Dobson P. (1998). "Bone microstructure of the diving Hesperornis and the volant Ichthyornis from the Niobrara Chalk of western Kansas". Cretaceous Research 19 (2): 225–235. doi:10.1006/cres.1997.0102. 
  41. ^ Jörg Fröbisch, Rainer R. Schoch, Johannes Müller, Thomas Schindler and Dieter Schweiss (2011). "A new basal sphenacodontid synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany". Acta Palaeontologica Polonica 56 (1): 113–120. doi:10.4202/app.2010.0039. 
  42. ^ a b Michel Laurin (1994). "Re-evaluation of Cutleria wilmarthi, an Early Permian synapsid from Colorado". Journal of Vertebrate Paleontology 14 (1): 134–138. doi:10.1080/02724634.1994.10011544. 
  43. ^ Romer, A.S.; Price, L.L. (1940). "Review of the Pelycosauria". Special Papers of the Geological Siciety of America 28: 1–538. doi:10.1130/spe28-p1. 
  44. ^ GA Floridesa, Kalogiroua SA, SA, Wrobelb, L Tassoub (2001). "Natural environment and thermal behavior of Dimetrodon limbatus".". Journal of Thermal Biology 26 (1): 15–20. doi:10.1016/S0306-4565(00)00019-X. 
  45. ^ Kenneth D. Angielczyk, Dimetrodon Is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution Evolution: Education and Outreach, Volume 2, Number 2, 257-271, doi:10.1007/s12052-009-0117-4
  46. ^ a b White, T. & Kazlev, M. A. (2009): Therapsida: Biarmosuchia: Biarmosuchidae / Eotitanosuchidae, from Palaeos website.
  47. ^ Ruben, J.A.; Hillenius, W.J., Kemp, T.S. and Quick, D.E. (2011). "The Evolution of Mammalian Endothermy". In Chinsamy-Turan, A. (ed.). Forerunners of Mammals. Bloomington: Indiana University Press. pp. 272–286. ISBN 0-253-35697-0. 
  48. ^ Maier, W.; Heever, J.; Durand, F. (27 April 2009). "New therapsid specimens and the origin of the secondary hard and soft palate of mammals". Journal of Zoological Systematics and Evolutionary Research 34 (1): 9–19. doi:10.1111/j.1439-0469.1996.tb00805.x. 
  49. ^ Czaplewski, Terry A. Vaughan, James M. Ryan, Nicholas J. (2000). Mammalogy (4th ed. ed.). Fort Worth: Brooks/Cole Thomson Learning. p. 51. ISBN 003025034X. 
  50. ^ Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng and Qiang Ji (25 August 2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals". Nature 476 (7361): 442–445. Bibcode:2011Natur.476..442L. doi:10.1038/nature10291. PMID 21866158.  Electronic supplementary material

External links[edit]