Draft:Paleontology

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This is a photograph of the skeleton of Alligator prenasalis. Credit: Ghedoghedo.

Paleontology is a study of fossils, plant and animal remains found on the Earth.[1]

Paleontology is a large subject because it includes aspects of geology and biology. Depending on the particular branch of paleontology studied, it may also require knowledge of chemistry, climatology, physics, and astronomy among others. It may also involve creating new techniques both in application and in theory. Paleontologists may work in outdoors, in an office or laboratory, or in a library; they may use a huge range of tools from bull dozers to computers.

The study of paleontology covers the entire history of life on Earth, which is about 4 billion years.

Paleontology is the branch of science dealing with study of past life. Paleontologists are the scientists that carry out this study.

The study of past life is done through the study of fossils which are evidence of that past life. Fossils may be the remains of organisms (plants, animals, etc.) or the remains of their activities (footprints, burrows, etc.). The later are called trace fossils.

Paleontology covers the entire span of life on Earth, from the first organisms around 4 billion years ago, up to the present day. However, scientists which study recent human activity, the last 12,000 years or so, are generally called archaeologists, and their study is called archaeology. There is a blurry line where archaeology begins and paleontology leaves off.

Paleontology is generally considered a part of geology, though because it involves life, it can also be considered a part of biology. Paleontologists must know something of both geology and biology. In particular in geology they must understand sedimentary geology - the study of sediments. In biology paleontologists need to know something about comparative anatomy, and in particular the anatomy of the organisms they study.

There are many sub-groups within paleontology, depending on what specifically is being studied. Among these is Vertebrate Paleontology (the study of fossil animals with backbones), Invertebrate Paleontology (the study of animals without backbones), Paleobotany (the study of fossil plants), and Paleoecology (the study of ancient environments). Almost everything within paleontology has it's own specialist name.

Theoretical paleontology[edit]

Def. the "[s]tudy of the forms of life existing in prehistoric or geologic times"[2] is called paleontology.

Clades from the paleontological rock record sometimes display a clade asymmetry. "(Our two cases of Metazoa and mammals represent the first filling of life's ecological "barrel" for multicellular animals, and the radiation of mammals into roles formerly occupied by dinosaurs.)"[3]

Fossils[edit]

This may be an ammonite fossil. Credit: Halvard : from Norway.

Def. "[t]he mineralized remains of an animal or plant" or "[a]ny preserved evidence of ancient life, including shells, imprints, burrows, coprolites, and organically-produced chemicals"[4] is called a fossil.

Derived terms include ichnofossil, index fossil, living fossil, mesofossil, microfossil, and trace fossil.[4]

Micropaleontology[edit]

The image shows Nummulitid foraminiferans from the Eocene near Al Ain, United Arab Emirates. Credit: Mark A. Wilson.

Micropaleontology is a study of fossil micro-organisms, including foraminifera, which have applications in stratigraphic correlation and age dating along with paleoecology and paleoclimatology.

The image at the right shows microspheric and megalospheric Nummulitid specimens.

Paleobotany[edit]

This image is of Ginkgoites huttoni from Scalby Ness, Scarborough, England. Credit: Ghedoghedo.

Paleobotany is the study of plant or plant-like fossils.

The image at the right shows fronds impressed onto shale in a specimen on display at the Paläontologische Museum München. The fossil is from Scalby Ness, Scarborough, England.

Palynology[edit]

A spore tetrad (green) and trilete spores (blue, ~30-35μm diameter) from a late Silurian sporangium (Burgsvik beds, Sweden) are shown. Credit: Smith609.

Although regarded as a separate field of its own, in a real sense palynology is the micropaleontological equivalent of paleobotany that involves the study of fossil pollen and spores.

The image at right contains a spore tetrad (in green) of genus Scylaspora and trilete spores (blue, ~30-35μm diameter) from a late Silurian sporangium (Burgsvik beds, Sweden).

Invertebrate paleontology[edit]

These are bryozoan fossils in an Ordovician oil shale from Estonia. Credit: Mark A. Wilson.

Invertebrate paleontology is a study of fossil invertebrate animals, those which lack a backbone. Included are magafaunas whose study doesn't require a microscope, found in various phyla. Applications include stratigraphic dating and correlation, and paleo-ecology.

At the right is an example of invertebrate paleontology, specifically bryozoan fossils in an Ordovician oil shale from Estonia.

Vertebrate paleontology[edit]

This is a photo of a Mosasaurus hoffmannii skeleton. Credit: Ghedoghedo.

Vertebrate paleontology is any study of prehistoric animals with backbones, e.g. fish of various kinds, marine and terrestrial reptiles, dinosaurs, birds, and mammals.

As a representative of vertebrate paleontology, the image at the right shows a skeleton of Mosasaurus hoffmannii on display at the Natural History Museum of Masstricht.


Paleoecology[edit]

A group of Brancasaurus brancai is in their natural habitat together with some pycnodontiformes, Caturus and Hybodus in the far background. Credit: Joschua Knüppe.{{free media}}

In the image on the right, a group of Brancasaurus brancai are portrayed in an artists impression of their natural habitat together with some pycnodontiformes, Caturus and Hybodus in the far background.

Paleoclimatology[edit]

Paleoclimatology is the study of ancient climates. This helps paleontologists understand the environments that existed over the history of the Earth.

Paleoclimatology is also particularly important in understanding how climate might change in the future.

Geologic time[edit]

This clock representation shows some of the major units of geological time and definitive events of Earth history. Credit: Woudloper.

At right is a geologic clock representation. It shows some of the major units of geological time and definitive events of Earth history. The Hadean eon represents the time before fossil record of life on Earth; its upper boundary is now regarded as 4.0 Ga (billion years ago).[5] Other subdivisions reflect the evolution of life; the Archean and Proterozoic are both eons, the Palaeozoic, Mesozoic and Cenozoic are eras of the Phanerozoic eon. The two million year Quaternary period, the time of recognizable humans, is too small to be visible at this scale.

The following four timelines show the geologic time scale. The first shows the entire time from the formation of the Earth to the present, but this compresses the most recent eon. Therefore the second scale shows the most recent eon with an expanded scale. The second scale compresses the most recent era, so the most recent era is expanded in the third scale. Since the Quaternary is a very short period with short epochs, it is further expanded in the fourth scale. The second, third, and fourth timelines are therefore each subsections of their preceding timeline as indicated by asterisks. The Holocene (the latest epoch) is too small to be shown clearly on the third timeline on the right, another reason for expanding the fourth scale. The Pleistocene (P) epoch. Q stands for the Quaternary period.

SiderianRhyacianOrosirianStatherianCalymmianEctasianStenianTonianCryogenianEdiacaranEoarcheanPaleoarcheanMesoarcheanNeoarcheanPaleoproterozoicMesoproterozoicNeoproterozoicPaleozoicMesozoicCenozoicHadeanArcheanProterozoicPhanerozoicPrecambrian
CambrianOrdovicianSilurianDevonianCarboniferousPermianTriassicJurassicCretaceousPaleogeneNeogeneQuaternaryPaleozoicMesozoicCenozoicPhanerozoic
PaleoceneEoceneOligoceneMiocenePliocenePleistoceneHolocenePaleogeneNeogeneQuaternaryCenozoic
GelasianCalabrianPleistocenePleistocenePleistoceneHoloceneQuaternary
Millions of Years

Cenozoic Era[edit]

Laurus nobilis leaf is a fossil of the Cenozoic. Credit: Lubman04.{{free media}}

After the dinosaurs became extinct, the Cenozoic began.

The Cenozoic Era is comprised of the following:

  • Quaternary Period (2.588 mya to present)
    • Anthropocene Epoch (up to the present)
    • Holocene Epoch (11,700 yrs to the beginning of the Anthropocene)
    • Pleistocene Epoch (2.588 mya to 11,700 yrs)
  • Neogene Period (23.03 to 2.588 mya)
    • Pliocene Epoch (5.332 to 2.588 mya)
    • Miocene Epoch (23.03 to 5.332 mya)
  • Paleogene Period (65.5 to 23.03 mya)
    • Oligocene Epoch (33.9 to 23.03 mya)
    • Eocene Epoch (55.8 to 33.9 mya)
    • Paleocene (65.5 to 55.8 mya)


Anthropocene Epoch[edit]

The Anthropocene Epoch is a newly added geologic time period. It is the "age of humans", when human activity grew to be the dominant force in shaping the Earth. The time of the beginning of this Epoch has not been completely settled upon. Claims run from 12,000 years ago when widespread agriculture began, to 1945 C.E. when the first atomic bomb was exploded.

For purposes of paleontology, the Anthropocene is primarily ignored, and is relegated to the science of archaeology, or the study of history, depending on when it is considered to have begun.

Holocene Epoch[edit]

Helicodonta obvoluta is a European pulmonate land snail; fossil (Holocene) from The Netherlands. Credit: Tom Meijer.{{free media}}

The Holocene starts at ~11,700 b2k and extends to the beginning of the Anthropocene Epoch.

Pleistocene Epoch[edit]

This is the skull of the wolf (Canis lupus). Credit: Didier Descouens.{{free media}}

The Pleistocene dates from 2.588 x 106 to 11,700 b2k.

People appear.

GIS 3[edit]

The stronger GIS 3 interstadial occurred about 27.6 kyr B.P.[6]

"In the Karginian Age (MIS 3) alluvial deposits of the described locality [occur] the remains of Elasmotherium sibiricum, Mammuthus ex gr. trogontherii-chosaricus, Mammuthus primigenius, Bison sp. AMS Radiocarbon dating of the Elasmotherium skull gave a young age - 26038 ± 356 BP (UBA-30522)."[7]

Hasselo stadial[edit]

Fossil of Elasmotherium, an extinct mammal, is at Natural History Museum, London. Credit: Ghedoghedo.{{free media}}

The "Hasselo stadial [is] at approximately 40-38,500 14C years B.P. (Van Huissteden, 1990)."[8]

"The rhinoceros Elasmotherium sibiricum, known as the ‘Siberian unicorn’, was believed to have gone extinct around 200,000 years ago—well before the late Quaternary megafaunal extinction event. However, no absolute dating, genetic analysis or quantitative ecological assessment of this species has been undertaken. [By] accelerator mass spectrometry radiocarbon dating of 23 individuals, including cross-validation by compound-specific analysis, [...] E. sibiricum survived in Eastern Europe and Central Asia until at least 39,000 years ago, corroborating a wave of megafaunal turnover before the Last Glacial Maximum in Eurasia, in addition to the better-known late-glacial event. Stable isotope data indicate a dry steppe niche for E. sibiricum and, together with morphology, a highly specialized diet that probably contributed to its extinction. [With] DNA sequencing data, a very deep phylogenetic split between the subfamilies Elasmotheriinae and Rhinocerotinae [occurred] that includes all the living rhinoceroses, settling a debate based on fossil evidence and confirming that the two lineages had diverged by the Eocene. As the last surviving member of the Elasmotheriinae, the demise of the ‘Siberian unicorn’ marked the extinction of this subfamily."[9]

Pliocene Epoch[edit]

Hexaplex hertweckorum (Petuch, 1988) here is a fossil murex snail shell (7.7 cm across at its widest) from the Pliocene of Florida. Credit: James St. John.{{free media}}

The Pliocene ranges from 5.332 x 106 to 2.588 x 106 b2k.

Miocene Epoch[edit]

Epipliopithecus vindobonensis (Zapfe & Hürzeler, 1957) here is a fossil primate skull (cast) from the Miocene of Slovakia on public display, Field Museum of Natural History, Chicago, Illinois, USA. Credit: James St. John.{{free media}}

The Miocene dates from 23.03 x 106 to 5.332 x 106 b2k.

"A giant goose that lived on a Mediterranean island between six and nine million years ago had wings tailored for combat."[10]

"Weighing 22 kilograms and standing perhaps 1.5 metres tall, Garganornis ballmanni might be the biggest member of the duck, goose and swan family ever to have lived. Its fossilised bones have been found at Gargano and Scontrone in central Italy – a region that, during the Miocene, consisted of islands populated by unique species."[10]

"Its wing bones are short for its size, suggesting it couldn’t fly. [The] carpometacarpus bone – equivalent to the hand bones in humans – had a rounded lump called the carpal knob, a feature present in modern birds that fight each other over territory. These include some ducks, geese and the extinct Rodrigues solitaire, the closest relative of the dodo."[10]

“It’s covered over with hard skin, so it becomes a really effective weapon. In solitaires, they certainly broke each others’ bones.”[11]

"Battles over territory are the most likely reason for Garganornis‘s fighting adaptation."[11]

"Ducks and geese that live on islands, such as the extinct moanalo of Hawaii, often evolve to be terrestrial and territorial. That’s because fresh water is often in short supply, and so they live in forests as herbivores."[10]

“You’ve got this big bird, with its wings used for fighting, that would have been incredibly aggressive and would have been able to defend its young against most predators.”[11]

Oligocene Epoch[edit]

Oligocene-era gecko has been trapped in amber. Credit: PG Palmer.{{free media}}

The Oligocene dates from 33.9 ± 0.1 x 106 to 23.03 x 106 b2k.

The Oligocene Epoch covers 34 - 23 Mya.[12]

"As the Earth began to cool, the tropical plants that had previously been found relatively widespread began to recede towards the equator where it was still warm. The general tropical plants began a transition to more forest like areas. The first grasses also appeared in the late Oligocene. The appearance of these grasses led to to evolution of various herbivore animals. With bodies low to the ground, animals would take advantage of the new grasses that appeared."[12]

Eocene Epoch[edit]

Crassostrea gigantissima (Finch, 1824) is a giant oyster from the Eocene of Texas. Credit: Wilson44691.

The Eocene dates from 55.8 ± 0.2 x 106 to 33.9 ± 0.1 x 106 b2k.

Paleocene Epoch[edit]

Fossil foliage of Glyptostrobus europaeus is from the Paskapoo Formation. Credit: Georgialh.{{free media}}

The Paleocene dates from 65.5 ± 0.3 x 106 to 55.8 ± 0.2 x 106 b2k.

Mesozoic Era[edit]

With another mass extinction Mezozoic era started. Now dinosaurs rule.

The Mesozoic Era is divided into the Cretaceous, Jurassic, and Triassic Periods.

"A high diversity of terrestrial vertebrates with dinosaurs as the dominant group is strongly indicated but not much of it is yet recorded."[13]

For much of the dinosaur era, the smallest sauropods are larger than anything else in their habitat, and the largest are an order of magnitude more massive than anything else that has since walked the Earth.


Cretaceous Period[edit]

"The Cretaceous period is the third and final period in the Mesozoic Era. It began 145.5 million years ago after the Jurassic Period and ended 65.5 million years ago, before the Paleogene Period of the Cenozoic Era."[14]

Late Cretaceous[edit]

Rock strata from the Late Cretaceous epoch form the Upper Cretaceous series.

The Late Cretaceous (100.5–66 Ma) is the younger of two epochs, the other being the Early Cretaceous, into which the Cretaceous period is divided in the geologic timescale.

Maastrichtian[edit]

Fossil is a mummified Edmontosaurus annectens (AMNH#5060). Credit: Claire H. from New York City, USA.{{free media}}
Hemipneustes leymeriei is a Hemipneustidae. Credit: Jean Fontayne.{{free media}}
Photograph is of a fossil ammonite Jeletzkytes spedeni. Credit: Dlloyd.{{free media}}
Fossil of Hainosaurus, an extinct reptile, is in the Natural History Museum of Bruxelles. Credit: Ghedoghedo.{{fairuse}}

The Maastrichtian is the most recent stage of the upper Cretaceous from 66.0 - 72.1 Ma. The mummified Edmontosaurus annectens in the image on the right is from the Maastrichtian.

The Lameta Formation is a sedimentary rock formation found in Madhya Pradesh, Gujarat, and Maharashtra, India, of Maastrichtian age (Upper Cretaceous), notable for its dinosaur fossils, several genera of dinosaurs from these rocks, including the titanosaur sauropod Isisaurus, the abelisaurs Indosaurus, Indosuchus, Laevisuchus, and Rajasaurus and possible stegosaurs.[15][16]

Traditionally, pterosaur faunas of the Maastrichtian appeared to be dominated by Azhdarchidae, with other pterosaur groups having become extinct earlier on, but, more recent findings suggest a fairly composite pterosaur diversity: at least six (Nyctosaurus lamegoi, a Mexican humerus, a Jordan humerus and several taxa from Morocco) Nyctosauridae date to this period, as do a few Pteranodontidae, and Navajodactylus, tentatively assigned to Azhdarchidae, lacking any synapomorphies of the group.[17][18] This seems to underscore a higher diversity of terminal Cretaceous pterosaurs than previously thought.[19][20][21]

The specimen second down on the left is Jeletzkytes spedeni from the Maastrichtian (Upper-Cretaceous) Fox Hills Formation, locality - South Dakota, USA. Matrix free specimen is 7.5 cm (3") in diameter, displaying pearly aragonite preservation of the shell.

The type species of Hainosaurus is H. bernardi, named after the Belgian Léopold Bernard, owner of the phosphate chalk exploitation where the fossil was unearthed.[22] In a paper published in 2016, Hainosaurus was considered congeneric with Tylosaurus.[23]

Campanian[edit]

Pinacosaurus skeleton is displayed in Hong Kong Science Museum. Credit: Laikayiu.{{free media}}
A juvenile Chasmosaurus fossil is seen from the side. Credit: Philip Currie.
Scales of T. proriger (KUVP-1075) are shown. Credit: A. G. Da Lee, Lawrence, Kansas.

The Campanian was an age when a worldwide marine transgression or sea level rise drowned many coastal areas, preserved as an unconformity beneath a cover of marine sedimentary rocks.[24][25]

During the Campanian age, an evolutionary radiation among dinosaur species occurred, where in North America, for example, the number of known dinosaur genera rises from 4 at the base of the Campanian to 48 in the upper part, sometimes referred to as the "Campanian Explosion" the generally warm climates and large continental area covered in shallow sea during the Campanian probably favoured the dinosaurs, but in the following Maastrichtian stage, the number of North American dinosaur genera found is 30% less than in the upper Campanian.[26]

The image on the right shows a juvenile Chasmosaurus fossil seen from the side.

"The Ceratopsidae are one of the more immediately recognizable groups of dinosaurs. Characterized by sharp beaks and flamboyant horns and frills, these herbivores almost all lived in what is now Western North America right at the end of the Cretaceous period, 100 to 66 million years ago."[27]

"Chasmosaurus belonged to this group [...] The 75 million-year-old fossilized Chasmosaurus was spotted in 2010 within the Dinosaur Park Formation in Alberta, Canada. In 2013, paleontologists completely unearthed it, and this week, they have described what is undoubtedly a rare specimen."[27]

“For the first time ever, we have a complete skeleton of a baby ceratopsid.”[28]

"Only its forelimbs are completely missing."[27]

"The adult variants are certainly distinctive, with large openings in their head ornaments earning them their appropriate name, which literally means “opening lizard.” Fully grown, they reach a size of up to 4.8 meters (16 feet) and a weight of roughly 2 tonnes (2.2 tons)."[27]

"This juvenile Chasmosaurus is an adorable 1.5 meters (4.9 feet) in length, and would have weighed less than 100 kilograms (220 pounds). It’s so young that its vertebrae had not properly fused, its limbs were not fully articulated (joined up), and it had a particularly short snout. Due to its ornamental opening being fully enclosed by a single bone, scientists have deduced it is likely a species called Chasmosaurus belli."[27]

“We've only had a few isolated bones before to give us an idea of what these animals should look like as youngsters, but we've never had anything to connect all the pieces. All you need is one specimen that ties them all together. Now we have it!”[28]

Tylosaurus proriger is from the Santonian and lower to middle Campanian of North America (Kansas, Alabama, Nebraska, etc.).[29]

Santonian[edit]

This photograph of Claosaurus was taken at the Peabody Museum, Yale University, in June 2000. Credit: Greygirlbeast.{{free media}}
This is the right dentary. Credit: Zoltan Csiki-Sava, Eric Buffetaut, Attila Ősi, Xabier Pereda-Suberbiola, Stephen L. Brusatte.{{free media}}
The fossil pieces of a baby Tylosaurus were discovered more than 25 years ago in Kansas. Credit: Christina Byrd of Sternberg Museum of Natural History.{{fairuse}}

The specimen Hungarosaurus tormai designated as the holotype is MTM Gyn/404 (in the collections of the Magyar Természettudományi Múzeum, Budapest, Hungary) and consists of 450 bones, including portions of the skull (premaxilla, left prefrontal, left lacrimal, right postorbital, jugal and quadratojugal, left frontal, pterygoid, vomer, the right quadrate and a fragment of the left quadrate, basioccipital, one hyoid), an incomplete right mandible, three cervical vertebrae, six dorsal vertebrae, ten caudal vertebrae, ossified tendon fragments, three cerival and thirteen dorsal ribs, five chevrons, the left scapulocoracoid, right scapula, portions of the right manus, a partial pelvis, and more than one hundred osteoderms.[30]

The length of Hungarosaurus has been estimated at about 4 to 4.5 meters.[31]

The exposure of the Csehbánya Formation that produced Hungarosaurus tormai has also yielded remains of bony fishes, turtles, lizards, crocodiles, and pterosaurs, along with teeth from a diminutive dromaeosaurid-like theropod and a Rhabdodon-like ornithopod.[30]

The image in the center shows fossil pieces identified as a baby Tylosaurus.

Coniacian[edit]

Bactrosaurus skeleton is displayed in Hong Kong Science Museum. Credit: Laikayiu.{{free media}}
Mounted replica skeleton is in the Royal Ontario Museum. Credit: .{{free media}}

The holotype of the type species, Futalognkosaurus dukei, was originally estimated at 32–34 metres (105–112 ft) in length.[32] In 2008 this was down-sized to 26 metres (85 ft).[33] Holtz estimated it at 28 metres (92 ft).[34] An estimate by Gregory S. Paul was that Futalognkosaurus had a maximum length of 30 metres (98 ft).[35] Its weight has been estimated between 38.1–50 tonnes (42.0–55.1 short tons).[36][37][35] Its long neck contained 14 vertebrae, and was over a meter deep in places, due to its extremely tall neural spines which had a distinctive "shark-fin" shape. The hips were also extremely large and bulky, reaching a width of nearly 3 metres (9.8 ft).[38]

The genus name is derived from the local indigenous language Mapudungun and is pronounced foo-ta-logn-koh-sohr-us: "futa" means "giant" and "lognko" means "chief".[32]

Futalognkosaurus is a member of the Titanosauridae (or Lithostrotia, depending on the definitions being used), and most closely related to Mendozasaurus, defining a new clade for the group containing both Futalognkosaurus and Mendozasaurus, their common ancestor, and all descendants, which they named the Lognkosauria.[32] Malawisaurus is the sister group of this new clade. Another, much later member of Lognkosauria is the colossal Puertasaurus,[39]

Turonian[edit]

Talarurus plicatospineus is in the Dinosaurium exhibition, Prague, Czech Republic. Credit: Radim Holiš.{{free media}}

Cenomanian[edit]

Unenlagia paynemili fossil casts are in Copenhagen. Credit: FunkMonk (Michael B. H.).{{free media}}
A 100-million-year-old chunk of amber found in Myanmar contains the head, neck, wing, tail and feet of a hatchling. Credit: Lida Xing, Jingmai K. O'Connor, Ryan C. McKellar, Luis M. Chiappe, Kuowei Tseng, Gang Li, Ming Bai.{{fairuse}}

During the Cenomanian was the origin of the crown-group Crocodylia, the true-crocodiles[40]

An unnamed Enantiornithes bird is of northern Gondwana[41]

In 1996 in the Neuquén province of Argentina a skeleton of a theropod was discovered in the Sierra del Portezuelo and reported the same year.[42]

In 2002 near the Lago Barreales a second skeleton was uncovered and reported in 2003.[43]

In 2004 it was named and described as a second species: Unenlagia paynemili, where the holotype MUCPv-349, a partial skeleton consisting of a humerus and two pubes and several paratypes were also assigned: MUCPv-343, a claw; MUCPv-409, a partial ilium; MUCPv-415, a phalanx and MUCPv-416, a vertebra.[44]

Neuquenraptor may be a junior subjective synonym of Unenlagia.[45]

The body length of Unenlagia has been disputed, due to the fact that only the leg length is well known and it is uncertain whether this should be extrapolated using the proportions of the low-slung Dromaeosauridae or the long-legged basal birds with estimates varied between a length of 3.5 metres and a weight of 75 kilogrammes on the one hand,[46] and a length of just two metres on the other.[47]

The pelvic region of Unenlagia, especially the form of the ilium, was very similar to that of the early bird Archaeopteryx.[48]

The shoulder girdle of Unenlagia was originally interpreted as if it was adapted for flapping, with a flat scapula positioned on top of the ribcage, making the shoulder joint point more laterally, but this would imply that the shoulder-blade was dorsoventrally flattened instead of laterally as with other theropods and that it thus were more likely the scapula was located on the side of the ribcage.[49]

This conformed to a later hypothesis that non-avian theropods like Unenlagia were unable to lift their forelimbs above their back, as even would still have been the case for the basalmost bird Archaeopteryx.[50]

South-American workers have remained unconvinced though, countering that a laterally positioned scapula would make the coracoid of Unenlagia jut into its ribcage, which seems anatomically implausible.[47]

Unenlagia was a member of the Dromaeosauridae.[51][52] Unenlagia would have belonged to the extremely bird-like Gondwanan clade of dromaeosaurids called the Unenlagiinae, and be closely related to species such as Buitreraptor and Neuquenraptor (which might be the same species as Unenlagia), with the 'flying raptor' Rahonavis as a member of this group, which would mean that either Unenlagia is secondarily flightless, having evolved from flying, Rahonavis-like ancestors, or that bird-like flight evolved at least twice.[53] Rahonavis was found be the sister taxon of Unenlagia.[54]

But, Unenlagiidae was positioned within Avialae.[55]

The second image down on the right contains a 100-million-year-old chunk of amber found in Myanmar with the head, neck, wing, tail and feet of a hatchling.

"It’s the most complete and detailed view we’ve ever had."[56]

"While it looks as if the actual skin and flesh of the bird are preserved in the amber, it’s basically a very detailed impression of the animal. Studies of similar finds show the flesh has broken down into carbon – and there’s no usable DNA".[56]

"The unfortunate youngster belonged to a group of birds known as the 'opposite birds' that lived alongside the ancestors of modern birds and appear to have been more diverse and successful – until they died out with the dinosaurs 66 million years ago."[57]

"In appearance, opposite birds likely resembled modern birds, but they had a socket-and-ball joint in their shoulders where modern birds have a ball-and-socket joint – hence the name. They also had claws on their wings, and jaws and teeth rather than beaks – but at the time the hatchling lived, the ancestors of modern birds had not yet evolved beaks either."[57]

Early Cretaceous[edit]

Albian[edit]

Animantarx is a genus of nodosaurid ankylosaurian dinosaur from the Upper Cretaceous of western North America. Credit: Kabacchi.{{free media}}
This is a cranium of Pawpawsaurus campbelli. Credit: Ghedoghedo.{{free media}}
Thrissops formosus is from Eichstätt (Upper Jura). Credit: Haplochromis.{{free media}}

Aptian[edit]

Australiceras is exhibited in the Houston Museum of Natural Science, Houston, Texas, USA. Credit: Daderot.{{free media}}
Lurdusaurus forelimb is in the Royal Belgian Institute of Natural Sciences. Credit: Eduard Solà Vázquez.{{free media}}
Skull of Theiophytalia kerri was an advanced iguanodontid ornithopod. Credit: Anky-man.{{free media}}
Skeletal mount is of Acrocanthosaurus. Credit: Sergey Galyonkin.{{free media}}
Anterior portion of the skull of the theropod dinosaur Genyodectes saurus is shown. Credit: Patricia Curcio.{{free media}}

Barremian[edit]

Jinzhousaurus yangi fossil is displayed in Hong Kong Science Museum. Credit: Laikayiu.{{free media}}

Hauterivian[edit]

Valanginian[edit]

Femur is from Elrhazosaurus (formerly Valdosaurus) nigeriensis. Credit: Ghedo.{{free media}}
A 133-million-year-old fossilized dinosaur brain — the first found — was initially picked up in 2004. It’s shown next to a two-pence coin, which is slightly bigger than a penny. Credit: Jamie Hiscocks.{{fairuse}}

"The unusual aspect of this [fossilized dinosaur brain, second image down on the right] is the way the soft tissues, which are so fragile and 133 million years old, have actually been preserved. It’s not the entire brain — it’s just remarkable preservation of soft tissues you wouldn’t expect to have preserved."[58]

"The acid solution would have pickled the parts of the brain that were immersed."[58]

The "highly detailed mineralization of soft tissues associated with a naturally occurring brain endocast of an iguanodontian dinosaur [was] found in c. 133 Ma fluvial sediments of the Wealden at Bexhill, Sussex, UK."[59]

Berriasian[edit]

Holotype right humerus of Pelorosaurus Conybearii is one sixth natural size. Credit: Jos. Dinkel.{{free media}}

Jurassic Period[edit]

This is an example of Neophyllites antecedens showing suture marks. Credit: Günter Knittel.

"The Jurassic Period takes place after the Triassic Period and before the Cretaceous Period. This period is well known for the reign of the dinosaurs of its time and the global tropical landscape."[60]

"The Jurassic is a geologic period and system that extends from about 199.6±0.6 Ma (million years ago) to 145.5±4 Ma; that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period is marked by the major Triassic–Jurassic extinction event. However, the end of the period did not witness any major extinction event."[61]

The first modern mammals evolved during the Jurassic Period.

Aalenian Age[edit]

Leioceras opalinum, Graphoceratidae; has a diameter: 4.5 cm; Lower Aalenian, Middle Jurassic; between Ohmenhausen and Reutlingen, Germany. Credit: H. Zell.

Leioceras opalinum is an ammonite from the Aalenian.

The Aalenian Age was the earliest part of the Middle Jurassic Period, and lasted from about 174.1 to about 170.3 Ma.

Sinemurian[edit]

Eteoderoceras armatum is a Sinemurian ammonite. Credit: Ghedoghedo.
Selected Preserved Elements of Ledumahadi mafube and Geography and Stratigraphy of Type Locality are shown. Credit: Blair W. McPhee, Roger B.J. Benson, Jennifer Botha-Brink, Emese M. Bordy and Jonah N. Choiniere.{{fairuse}}

The Sinemurian is an age in the Early or Lower Jurassic that spans the time between 199.3 ± 2 Ma and 190.8 ± 1.5 Ma (million years ago).[62]

The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian.[63]

The upper Elliot Formation is a stratigraphic unit dating to roughly between 200 and 190 million years ago and covering the Hettangian to Sinemurian stages.[64]

The "upper Elliot Formation [is] one of the lowermost Jurassic continental successions (Hettangian-Sinemurian, ∼200–195 mya [...])."[65]

In the second image down on the right are selected preserved elements of Ledumahadi mafube and the geography and stratigraphy of the type locality.

"Preserved bones (A–K) are as follows: (A) middle/posterior cervical vertebra in left lateral view; (B) anterior dorsal vertebra in anterior and right lateral views; (C) middle dorsal vertebra in posterior and right lateral views; (D) first and second “primordial” sacral vertebrae in left lateral view; (E) anterior caudal vertebra in left lateral view; (F) right ulna in proximal and medial views; (G) first metacarpal in proximal and ?dorsal/ventral views; (H) left ?third metacarpal in proximal and ventral views; (I) pedal ungual in ?lateral and proximal views; (J) anterior chevron in posterior view; and (K) distal right femur in distal, lateral, and anterior views."[65]

"(L) Simplified geological map of the Elliot Formation in the Republic of South Africa and Lesotho indicating the location of farm Beginsel 346 and aerial extent of the Elliot Formation outcrop area (map modified after the 1:1,000,000 geological map of Republic of South Africa and Lesotho, 1984)."[65]

"(M) Landscape view of the local geology at the Ledumahadi site. Note that the contact of the lower and upper Elliot Formations (LEF and UEF, respectively) has been identified at 1,685 m above sea level; thus the UEF is ∼60 m thick. The poorly exposed LEF, which is ∼10 m thick here, only contains massive mudstones with very weakly developed pedogenic alteration features, green-gray mottles, and very rare desiccation cracks."[65]

"Abbreviations: ap, anterior process; ns, neural spine; op, olecranon process; poz, postzygapophysis; rf, radial fossa; sr, sacral rib; tfc, tibiofibular crest; vt, ventral tubercle. All scale bars represent 5 cm."[65]

An unnamed ornithischian genus has been reported from the Upper Elliot Formation.[66] Geographically it was located in the Mafeteng district, Lesotho.[66] Ornithischian tracks have been reported from the Upper Elliot Formation.[66] Geographically they were located in Leribe District,[67] Mafeteng district, and Mohales Hoek District, Lesotho.[66] Possible indeterminate ornithischian remains have been reported from the Lower and Upper Elliot Formation of Cape Province, South Africa[67] and the Mohales Hoek District, Lesotho.[66]

Hettangian Age[edit]

Psiloceras spelae tirolicum has its first occurrence at the Triassic-Jurassic boundary as geochron for the base of the Jurassic. Credit: Axel von Hillebrandt et al.
Fossil shell of Psiloceras planorbis from Germany, on display at Galerie de paléontologie et d'anatomie comparée in Paris. Credit: Hectonichus.
This is an example of Psiloceras psilonotum from the Hettangian. Credit: Günter Knittel.

Psiloceras psilonotum, Psiloceras spelae tirolicum and Psiloceras planorbis are from the Hettangian.

The Hettangian Age was the earliest part of the Early Jurassic Period, and lasted from about 199.3 to about 201.3 Ma.

Triassic Period[edit]

This is an example of Psiloceras tilmanni from the Jurassic. Credit: Günter Knittel.

Although the example of Psiloceras tilmanni is from the Jurassic. Its lowest occurrence is in the New York Canyon section of Nevada USA which may be Triassic.

It was during the Triassic Period that the first dinosaurs evolved.

Ladinian Age[edit]

This is the earliest Ladinian crinoid from the Atlasov Cape section. Credit: Alexander M. Popov.
Cast of Megachirella wachtleri is at the Sauriermuseum in Aathal, Switzerland. Credit: Ghedoghedo.{{free media}}

The Atlasov section of the Ladinian contains the crinoid on the right.

The Ladinian Age was the later stage of the Middle Triassic Period and lasted from about 237 to about 242 Ma.

A phylogenetics analysis in 2013 of the cast of Megachirella wachtleri in the image on the left confirmed that it was a lepidosauromorph closely related to the crown group Lepidosauria.[68]

Geckoes are the earliest crown group squamates, not Iguanomorpha (iguanians).[69][70]

The specimen was probably transported to a shallow coastal environment due to heavy storms after it died.[71]

Anisian Age[edit]

Ussuriphyllites amurensis (Kiparisova) is from the Lower-most Anisian, Atlasov Cape area. Credit: Alexander M. Popov.

An example of Ussuriphyllites amurensis (Kiparisova) is on the right. It is from the Lower-most Anisian, Atlasov Cape area.[72]

The Anisian Age was the early part of the Middle Triassic, and lasted from about 242 to about 247.2 Ma.

Olenekian Age[edit]

Olenekoceras meridianum (Zakharov) is found in the Upper Olenekian, Atlasov Cape area. Credit: Alexander M. Popov.

Olenekoceras meridianum is a "typical Late Olenekian [fossil which] differs in its lithology from the same zone of Russian Island, where the Zhitkov Suite has been rec- ognized (Zakharov, 1997; Zakharov et al., 2004)."[72]

The Olenekian Age was the later part of the Lower Triassic, and lasted from about 247.2 to about 251.2 Ma.

Induan Age[edit]

Hindeodus parvus is now recognized as the index fossil, occurring in the Zone above the P-T boundary. Credit: Yin Hongfu, Zhang Kexin, Tong Jinnan, Yang Zunyi and Wu Shunbao.

Hindeodus parvus, a conodont, on the right, is now recognized as the index fossil for the Triassic Induan.

The Induan Age was the earliest part of the Triassic Period, and lasted from about 251.2 to about 251.902 Ma.

Paleozoic Era[edit]

The Paleozoic era spanned 542.0 ± 1.0 to 251.0 ± 0.7 Mb2k.

The mollusks, arthropods, fish, reptiles, and amphibians appeared.

Next 550 mya, after the death of vendobionts, a new era began-the Paleozoic.

After extinction, new spieces named vendobionts appeared.

650 million years ago (mya) a mass extinction happened (mass extinction-is a period when many spieces of animals or plants die).

The Paleozoic Era is divided into eight Periods: the Permian, Carboniferous, Pennsylvanian, Mississippian, Devonian, Silurian, Ordovician, and Cambrian.

Permian Period[edit]

The Permian lasted from 299.0 ± 0.8 to 251.0 ± 0.4 Mb2k.

Pennsylvanian Period[edit]

The Pennsylvanian lasted from 318.1 ± 1.3 to 299.0 ± 0.8 Mb2k.

Mississippian Period[edit]

The Mississippian lasted from 359.2 ± 2.5 to 318.1 ± 1.3 Mb2k.

Carboniferous Period[edit]

The Carboniferous began 359.2 ± 2.5 Mb2k and ended 299.0 ± 0.8 Mb2k. The first reptiles evolved during this period.

Devonian Period[edit]

The Devonian spanned 416.0 ± 2.8 to 359.2 ± 2.5 Mb2k.

Silurian Period[edit]

The Silurian spanned 443.7 ± 1.5 to 416.0 ± 2.8 Mb2k.

Ordovician Period[edit]

The Ordovician spanned 488.3 to 443.7 Ma. It is divided into three Epochs, the Upper Ordovician, Middle Ordovician, and Lower Ordovician. The Upper Ordovician is sometimes referred to as Late.

Sandbian Stage[edit]

Nemagraptus gracilis, Sandbian graptolites, are from the Caparo Formation, Venezuelan Andes. Credit: J.C. Gutiérrez-Marco, D. Goldman, J. Reyes-Abril, and J. Gómez.

"The Lower Sandbian Nemagraptus gracilis Zone comprises one of the most widespread, and easily recognizable graptolite faunas in the Ordovician System. The base of the N. gracilis Zone also marks the base of the Upper Ordovician Series".[73]

The Sandbian was the last stage of the Upper Ordovician

Middle Ordovician Epoch[edit]

This is an image of Amplexograptus sp., probably A. perexcavatus (Lapworth, 1876), from the Middle Ordovician near Caney Springs, Tennessee. Credit: Wilson44691.

On the right is an image of Amplexograptus sp., probably A. perexcavatus (Lapworth, 1876), from the Middle Ordovician near Caney Springs, Tennessee USA.

Paleontologist have no strong agreement of the timespan considered as the Middle Ordovician Epoch, but an approximation is from about 471.8 to about 460.9 Ma.

Lower Ordovician Epoch[edit]

The Lower Ordovician Epoch lasted from about 488.3 to about 471.8 Ma.

Eurypterids[edit]

This is an image of an Eurypterus lacustris fossil, Muséum national d'histoire naturelle, Paris. Credit: FunkMonk.

Although present in the Ordovician around 460 million years ago, about 410 million years ago, the first large marine predators (eurypterids), an order of arthropods, experienced a dramatic decline and are extinct.[74]

Cambrian Period[edit]

The Cambrian lasted from 542.0 ± 1.0 to 488.3 ± 1.7 Mb2k.

Guzhangian Stage[edit]

The image shows an exoskeleton of the cosmopolitan agnostoid trilobite Lejopyge laevigata. Credit: Shanchi Peng et al.

"The GSSP level [for the Guzhangian] contains the lowest occurrence of the cosmopolitan agnostoid trilobite Lejopyge laevigata [in the image on the left] (base of the L. laevigata Zone)."[75]

The Guzhangian Stage of the Cambrian Period lasted from about 500.5 to about 497 Ma.


Proterozoic Eon[edit]

Def. the "eon from 2,500 Ma to 541.0±1.0 Ma, the beginning of the Phanerozoic, marked by the build up of oxygen in the atmosphere and the emergence of primitive multicellular life"[76] is called the Proterozoic.

First era of prehistoric multicellular life.

Neoproterozoic[edit]

Def. "a geologic era within the Proterozoic eon; comprises the Tonian, Cryogenian and Ediacaran periods from about 1000 to 544 million years ago, when algae and sponges flourished"[77] is called the Neoproterozoic.

Ediacaran[edit]

Dickinsonia is a 558-million-year-old oval-shaped creature that may have borne a superficial resemblance to a segmented jellyfish. Credit: Ilya Bobrovskiy.{{fairuse}}
Amongst the depositional sequences of the Ediacaran and Cambrian is the Ediacaran base GSSP. Credit: James G. Gehling and Mary L. Droser.

"The fossils [of Dickinsonia] were unearthed at Zimnie Gory in the White Sea area of north-west Russia."[78]

"The fossil fat molecules that we've found prove that animals were large and abundant 558 million years ago, millions of years earlier than previously thought."[79]

"Scientists have been fighting for more than 75 years over what Dickinsonia and other bizarre fossils of the Ediacaran Biota were. The fossil fat now confirms Dickinsonia as the oldest known animal fossil, solving a decades-old mystery that has been the Holy Grail of palaeontology."[79]

Archeon Eon[edit]

The Archeon Eon lasted from about 4 billion to about 2500 million years ago. It was during the early Archean that life first appeared on Earth.

Hadean Eon[edit]

The Hadean Eon lasted from the formation of the Earth to about 4 billion years ago. It is the only major division of the geologic time scale without life, and so of little interest to paleontologists.

Hypotheses[edit]

To construct an hypothesis in paleontology requires statements of generalization usually using universals. Establishing that a phenomenon has occurred may require a proof of concept. Demonstrating a change from contemporary knowledge needs a control group for comparison.

  1. Ammonites are alive today.

See also[edit]

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External links[edit]

{{Archaeology resources}}{{Gene project}}