Draft:Original research/Paleontology

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

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
Def. the study "of the forms of life existing in prehistoric or geologic times" 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.)"

Fossils
Def. "the mineralized remains of an animal or plant" or any "preserved evidence of ancient life, including shells, imprints, burrows, coprolites, and organically-produced chemicals" is called a fossil.

Derived terms include "ichnofossil, index fossil, living fossil, "mesofossil, microfossil," and trace fossil".

Colors
"On December 9, 1833, the English fossil collector Elizabeth Philpot sent a letter to naturalist William Buckland. In addition to requesting back some vertebrae of a marine reptile Buckland had borrowed, Philpot also included notes on a recent trip with a young upstart fossil hound—the pioneering paleontologist Mary Anning. But what made the note special was an illustration Philpot had included with the letter. It depicted the toothy smile of an Ichthyosaurus skull, drawn after one of the many such fossils that Philpot, her sisters and Anning were finding in the ancient rocks of England’s southern coast. And it wasn’t drawn in any ordinary ink. The sepia tones were made from the preserved ink of a squid-like creature found in the same deposits as the ichthyosaur, revitalized after 200 million years."

"On the surface, Philpot’s drawing might only seem to be a neat fossiliferous trick. In 2009, another drawing made from ancient ink kicked up renewed attention for the surprising fact that traces of prehistoric color could persist to the 21st century. But the fact that such primordial shades can be recovered at all opens up a realm of scientific possibility. With the right specimens, experts can start to color in the fossil record."

"Researchers have known about fossil insect color patterns and mollusk color patterns all the way back to the Victorian era."

"The biological key to solving the coloration puzzle comes down to miniscule structures called melanosomes. These are tiny, blobby organelles that contain pigment, or melanin, and are present in soft tissues such as skin, scales, and feathers. And while these details were often cast aside as fossil bacteria in decades past, renewed efforts in the 21st century have been able to find the relationship between these tiny structures and colors."

"The discovery of preserved melanosomes opens up the possibility of interpreting the colour of extinct birds and other dinosaurs."

"Pulling color from the past requires a combination of lucky finds with advanced imaging techniques."

"First, paleontologists need a fossil which is likely to have preserved melanin—a fossil not just with bones, but feathers, skin or hair. These fossils often contain both melanosomes as well as chemically-degraded melanin pigment, and when paleontologists find such a fossil, then they can use modern technology to take a closer look."

"You start by looking for the microbodies using instruments like scanning electron microscopes."

"Once those characteristic shapes turn up, chemical analysis can confirm the presence of melanin pigment."

"This was particularly critical early on in fossil melanin studies because there was still some doubt that the microbodies were in fact melanosomes and not other similar structures, like bacteria. From there, comparisons of the physical and chemical signatures of the melanosomes and melanin can be compared to those of living animals, for which color is known, to reconstruct the look of creatures long dead."

"When paleontologists announced the discovery of the feathered dinosaur Anchiornis in 2009, the preserved plumage surrounding the skeleton was a dark, carbon-colored shade. But analysis of another Anchiornis fossil [...] the following year revealed a striking color pattern that had previously been invisible. The distribution and details of the preserved melanosomes indicated that Anchiornis was covered in feathers of black and white—not dissimilar from a magpie—with a splash of red feathers on the top of its head. For the first time, a dinosaur had been fully restored in living color."

"The week before the Anchiornis paper came out, the small, fuzzy dinosaur Sinosauropteryx was shown to have a vibrant, red-and-white banded tail. In 2012, the stacked arrangement of melanosomes found in the feathers of four-winged dinosaur Microraptor was shown to create an iridescent sheen similar to that of a modern raven. (Avian dinosaurs joined the list, too, with giant fossil penguins bearing color patterns of black, red and gray.) And while early studies focused on feathers, paleontologists soon found that melanosomes can reveal the hues of scaly dinosaurs, too. The beaky, horned dinosaur Psittacosaurus was countershaded dark above and light below to help with camouflage, and the immense armored dinosaur Borealopelta sported reddish-brown tones."

"Comparison [is] of melanosome proportions and body contour feather morphology in extinct penguins Inkayacu paracasensis (A and B) and representative extant penguins (C and D)."

"In the case Borealopelta, for example—with a pattern of rusty red on top, light on bottom—the shading might have been a way for the low-slung dinosaur to hide from the ravenous tyrannosaurs of the time. Other dinosaurs were flashier. The candy-cane tail of Sinosauropteryx was likely a social signal, used by these dinosaurs to communicate with each other when they met."

"The dinosaur [Sinosauropteryx] is portrayed in the predicted open habitat in which it lived around the Jehol lakes, preying on the lizard Dalinghosaurus."

Micropaleontology
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
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
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
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
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
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
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
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). 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.

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

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

People appear.

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

"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)."

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

"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."

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

Miocene Epoch
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."

"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."

"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."

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

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

"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."

“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.”

Fossils "from the Early Miocene St Bathans Fauna of New Zealand [attest] to the former existence of a giant psittaciform, which is described as a new genus and species [image on the left]. The fossils are two incomplete tibiotarsi from a bird with an estimated mass of 7 kg, double that of the heaviest known parrot, the kakapo Strigops habroptila. These psittaciform fossils show that parrots join the growing group of avian taxa prone to giantism in insular species, currently restricted to palaeognaths, anatids, sylviornithids, columbids, aptornithids, ciconiids, tytonids, falconids and accipitrids."

"Insular avifaunas are renowned for the evolution of novelties, usually in the form of extraordinarily large and flightless members of widespread and well-known lineages [1–4]. Preeminent among these is the columbid Dodo Raphus cucullatus of Mauritius [5], but the list includes giant Sylviornithidae on New Caledonia (Sylviornis) and Fiji (Megavitiornis) [6–8], other giant columbids on Rodrigues (Pezophaps) and on Fiji (Natunaornis) [5,9], giant waterfowl on Hawaii [10] and Malta [11], a giant ciconiid stork on Flores, Indonesia [12], and giant tytonid owls and other raptors in the Caribbean [13–16]. Insular rails (Rallidae) tend to be larger than mainland relatives, but the largest, the Takahe (Porphyrio hochstetteri) from New Zealand (NZ), at up to 3.2 kg, is smaller than these insular giants [17,18]."

"Since moa were first reported in 1839 [22], NZ has become recognized as the epitome of the phenomenon of island giantism in birds. In addition to nine moa species (Dinornithiformes), two flightless anserines (Cnemiornis, Anatidae), two gruiforms (Aptornis, Aptornithidae) and a huge eagle (Hieraaetus moorei, Accipitridae) evolved from small ancestors into giant elements of the Holocene avifauna [23–28]."

"The fossils, catalogued in the Museum of New Zealand Te Papa Tongarewa collections, are shafts of left and right tibiotarsi probably of one individual [image on the left]. [...] Tibiotarsi of Heracles inexpectatus gen. et sp. nov., left, holotype (a,b,f) NMNZ S.51083 and right, paratype (g), compared to (d,e) left tibiotarsus of Strigops habroptila (Canterbury Museum Av45277), in craniolateral (a) and cranial (b–g) views. (c) Silhouettes of a human and Heracles for scale. Scale bars are 20 mm. Abbreviations: ccl, crista cnemialis lateralis; cl, condylus lateralis; cm, condylus medialis; dtl, distal insertion scar for transverse ligament; fc, fibular crest; lfr, lateral scar for fibular retinaculum; lic, linea intermuscularis cranialis; mfr, mediocranial scar for fibular retinaculum; pons, pons supratendineus; ptl, proximal insertion scar for transverse ligament; se, sulcus extensorius; sf, sulcus m. fibularis; trf, tuberculum retinaculi m. fibularis. Human silhouette from PhyloPic, by T. M. Keesey."

Fossils of Heracles inexpectatus are from a "conglomerate, 9.5–9.58 m above base of Bannockburn Formation, Early Miocene, 19–16 Ma [32]".

"The holotype of Heracles inexpectatus is the largest fossil bone known among several thousand specimens in the fauna and adds a giant psittaciform to it."

"The St Bathans Fauna has already revealed evidence for an Early Miocene radiation of parrots (Psittaciformes) in NZ, with three small nestorids described in Nelepsittacus, and another the size of Nestor notabilis [34]. Extant nestorids are grouped in Nestor as the sister taxon to Strigops habroptila; the two groups combined form the NZ endemic clade Strigopoidea that is the sister taxon of remaining psittaciforms [39]. Strigops habroptila is the heaviest and only flightless psittaciform [38,40], with legbones the largest among parrots [35]. Heracles inexpectatus has similar proportions and morphology to S. habroptila, but is much larger, differing qualitatively in greater medial projection of the proximomedial scar of the transverse ligament and less projection of the lateral fibular retinaculum scar [image on the left], the last relating to less climbing ability [34]. All known fossil parrots are much smaller than Strigops [34]. Given this similarity and its provenance, the affinity of Heracles inexpectatus may lie with Strigopoidea. The short separation of the mediocranial fibular retinaculum scar from the condyle suggests closer affinity to strigopids than nestorids [34]."

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

The Oligocene Epoch covers 34 - 23 Mya.

"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."

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

"Death came suddenly for the young fish darting through a lake roughly 50 million years ago."

A "stone slab [in the image on the left] from the western United States [...] includes the fossils of 257 now-extinct fish (Erismatopterus levatus) bunched together in a dense swarm."

Each "fish’s orientation and position" have been analyzed.

The "ancient fish followed two rules used by their modern counterparts. An individual was repelled by its closest companions — to avoid collisions — and attracted to those farther away, which encouraged clumping. Like a modern-day school, the fossilized grouping had an elongated shape that might have helped to ward off predators."

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

Mesozoic Era
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."

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
"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."

Late Cretaceous
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
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.

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. This seems to underscore a higher diversity of terminal Cretaceous pterosaurs than previously thought.

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. In a paper published in 2016, Hainosaurus was considered congeneric with Tylosaurus.

Campanian
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.

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.

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."

"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."

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

"Only its forelimbs are completely missing."

"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)."

"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."

“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!”

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

Santonian
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.

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

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.

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

Coniacian
The holotype of the type species, Futalognkosaurus dukei, was originally estimated at 32 - 34 m in length. In 2008 this was down-sized to 26 m. Holtz estimated it at 28 m. An estimate by Gregory S. Paul was that Futalognkosaurus had a maximum length of 30 m. Its weight has been estimated between 38.1 - 50 tonnes. 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 m.

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".

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. Malawisaurus is the sister group of this new clade. Another, much later member of Lognkosauria is the colossal Puertasaurus,

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

An unnamed Enantiornithes bird is of northern Gondwana

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.

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

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.

Neuquenraptor may be a junior subjective synonym of Unenlagia.

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, and a length of just two metres on the other.

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

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.

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.

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.

Unenlagia was a member of the Dromaeosauridae. 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. Rahonavis was found be the sister taxon of Unenlagia.

But, Unenlagiidae was positioned within Avialae.

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."

"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".

"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."

"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."

Aptian
The Aptian stage of the Lower Cretaceous lasted from ~125.0 Ma until ~113.0 Ma.

Fossils of Microraptor and Jeholornis are from the Jiufotang Formation, with an Early Cretaceous, Aptian age of 120.3 +/-0.7 Ma, which overlies the Yixian Formation and underlies the Fuxin Formation and the Shahai Formation.

Wulong (meaning "dancing dragon") is a genus of Microraptoria Dromaeosauridae dinosaurs from the Early Cretaceous (Aptian) Jiufotang Formation (Jehol group) of China that includes one species, Wulong bohaiensis, where the skeletal remains shown in the third down image on the right represent a juvenile.

"The specimen of Wulong is a gorgeous fossil. With the feathers and claws, I think it would have been beautiful and just a little bit scary. I'd love to see one alive."

"Wulong bohaiensis, was a bantamweight meat-eater - a bit bigger than a crow - residing in a lakeside environment, researchers said. It possessed a scaly face, a mouth full of pointy teeth and one particularly dangerous toe claw, and probably hunted small mammals, lizards, birds and fish."

"Birds evolved from small feathered dinosaurs roughly 150 million years ago."

"Living birds shoot up to adult size very quickly, mainly as a way of getting strong enough to fly as soon as they can. But they may delay getting their adult feathers for a long time. Gulls, for example, don't look like adults for three or four years even though they learn to fly in only three months."

"Here is an animal that has all kinds of signals of being a juvenile, outside its bones, inside its bones, in its joints. And it has long, isolated plumes extending from its already-very-long tail. This is quite different from living birds and tells us that these decorative feathers preceded adulthood in dinosaurs. Of course, perhaps they're using these feathers in a very different way from living birds, too."

It has a narrow head that carries thin jaws filled with small and sharp teeth and its closest relative is microraptor that is a genus of tiny, feathered paravian dinosaurs.

"There was a lot of flying, gliding, and flapping around these ancient lakes. As we continue to discover more about the diversity of these small animals it becomes interesting how they all might have fit into the ecosystem. [...] It was an alien world, but with some of the earliest feathers and earliest flowers, it would have been a pretty one."

Valanginian
"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."

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

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."

Berriasian
"This femur [in the centered image] is huge! And in an exceptional state of conservation. It's very moving."

Jurassic Period
"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."

"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."

The first modern mammals evolved during the Jurassic Period.

Tithonian
The Tithonian is the latest age of the Late Jurassic epoch or the uppermost stratigraphy stage of the Upper Jurassic series, spanning the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma, preceded by the Kimmeridgian and followed by the Berriasian stage (part of the Cretaceous).

Kimmeridgian
Lithacosphinctes achilles is from the Kimmeridgian.

The Kimmeridgian is a geology age or stratigraphy stage in the Late or Upper Jurassic geology epoch or stratigraphy series spanning the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma, following the Oxfordian and preceding the Tithonian.

Oxfordian
The Oxfordian, in the International Commission on Stratigraphy (ICS) geologic timescale, the earliest age of the Late Jurassic epoch, or the lowest stage of the Upper Jurassic series, spans the time between 163.5 ± 4 Ma and 157.3 ± 4 Maand is preceded by the Callovian and followed by the Kimmeridgian.

Callovian
On the right is an image of Peltoceras solidum, an ammonite from the Matmor Formation (Jurassic, Callovian), Makhtesh Gadol, Israel.

On the left is an example of Kosmoceras medea.

Another species of Kosmoceras is on the lower right, specifically Kosmoceras proniae.

The Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma and 163.5 ± 4.0 Ma, the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian.

Bathonian
The Bathonian is an age and stage of the Middle Jurassic, lasting from approximately 168.3 Ma to around 166.1 Ma which succeeds the Bajocian age and precedes the Callovian age.

Bajocian
The Bajocian in the Middle Jurassic lasted from approximately 170.3 Ma to around 168.3 Ma and succeeds the Aalenian age and precedes the Bathonian age.

Aalenian
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.

Toarcian
The Toarcian, in the International Commission on Stratigraphy (ICS) geologic timescale, an age and stage in the Early or Lower Jurassic, spans the time between 182.7 Ma and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.

The base of the Toarcian is defined as the place in the stratigraphic record where the ammonite genus Eodactylites first appears, a GSSP for the base is located at Peniche, Portugal. The top of the stage is at the first appearance of ammonite genus Leioceras.

In the Tethys Ocean domain, the Toarcian contains the following ammonite biozones:
 * zone of Pleydellia aalensis
 * zone of Dumortieria pseudoradiosa
 * zone of Phlyseogrammoceras dispansum
 * zone of Grammoceras thouarcense
 * zone of Haugia variabilis
 * zone of Hildoceras bifrons
 * zone of Harpoceras serpentinum
 * zone of Dactylioceras tenuicostatum

"The genus Mystriosaurus, established by Kaup in 1834, was one of the first thalattosuchian genera to be named. The holotype, an incomplete skull from the lower Toarcian Posidonienschiefer Formation of Altdorf (Bavaria, southern Germany), is poorly known with a convoluted taxonomic history. For the past 60 years, Mystriosaurus has been considered a subjective junior synonym of Steneosaurus. However, our reassessment of the Mystriosaurus laurillardi holotype demonstrates that it is a distinct and valid taxon. Moreover, we find the holotype of “Steneosaurus” brevior, an almost complete skull from the lower Toarcian Whitby Mudstone Formation of Whitby (Yorkshire, UK), to be a subjective junior synonym of M. laurillardi. Mystriosaurus is diagnosed in having: a heavily and extensively ornamented skull; large and numerous neurovascular foramina on the premaxillae, maxillae and dentaries; anteriorly oriented external nares; and four teeth per premaxilla. Our phylogenetic analyses reveal M. laurillardi to be distantly related to Steneosaurus bollensis, supporting our contention that they are different taxa. Interestingly, our analyses hint that Mystriosaurus may be more closely related to the Chinese teleosauroid (previously known as Peipehsuchus) than any European form."

"A prehistoric crocodile [Mystriosaurus laurillardi] that lived 180 million years ago has finally been identified – nearly 250 years after its fossil was unearthed in Germany."

Second down on the right is a photograph "of teleosauroid thalattosuchian specimen (UH 7), lower Toracian of Holzmaden (southwestern Germany), which was described by Mueller-Töwe (2006) as “Steneosaurus” brevior Blake, 1876, and which we herein refer to tentatively as ?Mystriosaurus sp."

Pliensbachian
The Pliensbachian, an age of the geologic timescale and stage in the stratigraphic column, is part of the Early or Lower Jurassic epoch or series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma. The Pliensbachian is preceded by the Sinemurian and followed by the Toarcian.

The base of the Pliensbachian is at the first appearances of the ammonite species Bifericeras donovani and genera Apoderoceras and Gleviceras, with The Wine Haven profile near Robin Hood's Bay (Yorkshire, England) has been appointed as global reference profile for the base (GSSP).

The Pliensbachian contains five ammonite biozones in the boreal domain:
 * zone of Pleuroceras spinatum
 * zone of Amaltheus margaritatus
 * zone of Prodactylioceras davoei
 * zone of Tragophylloceras ibex
 * zone of Uptonia jamesoni

In the Tethys Ocean domain, the Pliensbachian contains six biozones:
 * zone of Emaciaticeras emaciatum
 * zone of Arieticeras algovianum
 * zone of Fuciniceras lavinianum
 * zone of Prodactylioceras davoei
 * zone of Tragophylloceras ibex
 * zone of Uptonia jamesoni

Sinemurian
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).

The Sinemurian is preceded by the Hettangian and is followed by the Pliensbachian.

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.

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

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."

"(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)."

"(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."

"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."

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

Hettangian
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.

"The dinosaur's remains, which were found in South Africa in 1978 and were being kept in a collection at the University of Witwatersrand in Johannesburg, had been identified as a Massospondylus -- a dinosaur from the Early Jurassic period."

The "dinosaur was in fact not what it seemed by comparing the specimen with other Massospondylus fossils."

"It differed in a large number of ways in terms of the appearance of its skull, and in the shape of its skull bones, and one or two other features -- enough to suggest that it's actually a completely different kind of dinosaur."

"The new dinosaur, which would have measured around 10 feet long and eaten plants and small animals, is thought to have had a chunky body, a long slender neck and a small, boxy head."

"The specimen has now been renamed "Ngwevu intloko," which means "gray skull" in the Xhosa language and was chosen to honor South Africa's heritage."

The "transition between the Triassic and Jurassic periods -- around 200 million years ago -- [suggests] more complex ecosystems were thriving during the period than previously thought."

On the left is a Micro-CT scan of the Ngwevu intloko skull on the right. Inumerating and comparing skull bones between various specimens of Massospondylus such as the one lowest left allowed sufficient differentiation to indicate that Ngwevu intloko was a distinct species.

Triassic Period
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
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.

Geckoes are the earliest crown group squamates, not Iguanomorpha (iguanians).

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

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

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

Olenekian Age
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 recognized (Zakharov, 1997; Zakharov et al., 2004)."

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

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

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

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

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

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

In "the eastern Anti-Atlas Mountains of Morocco [...] several skulls and an almost complete skeleton from two species of Phoebodus, a primitive shark genus that, until now, was known only from its three-cusped teeth [have been found]."

The "fossils reveal that Phoebodus had an eel-like body and a long snout, which makes it look a lot like the frilled shark that still roams the deep sea today."

"The fossilized Phoebodus remains were found in a layer estimated to be about 360 to 370 million years old, in what used to be a shallow sea basin. When the sharks died there, the limited water circulation and low oxygen levels created an environment in which their bodies were largely left alone by bacteria, scavengers, and currents, preserving them for posterity."

"The [CT] scans revealed some striking similarities to the frilled shark, not just in body shape, but in the teeth as well, which offers some clues to how the more ancient predators might have hunted."

"The frilled shark is a specialized predator, with the ability to suddenly burst forward to catch its prey. The inward-pointing teeth then help to make sure the prey can only go one way: into its throat. Maybe Phoebodus did something similar.”

For "a better understanding of how Phoebodus may have gotten its food, [...] another unrelated species with a surprisingly similar skull, jaw, and teeth, [was looked at]], a large freshwater fish called the alligator gar. Like Phoebodus, the alligator gar has long jaws and a flat skull, which limit its bite force. Yet there are also benefits to having a head like that."

"They hunt in open water, where they don’t have the luxury of choosing which direction their next meal will come from. And flat heads and long jaws are great for snapping sideways at prey."

"When a certain structure or strategy is effective, there is a tendency for it to show up time and time again—both in living creatures and in the fossil record. While a lot has changed since Phoebodus swam the Devonian oceans, the physics of feeding in water have not.”

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

Ordovician Period
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
"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".

The Sandbian was the last stage of the Upper Ordovician

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

Eurypterids
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.

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

Guzhangian Stage
"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)."

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

Middle Cambrian
The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At 508 Ma (Wuliuan, middle Cambrian) old, it is one of the earliest fossil beds containing soft-part imprints.

"Cambroraster was similar in some ways to lampreys, stingrays and horseshoe crabs."

"We really didn't know what to make of it."

The "creature's formal scientific name is now Cambroraster falcatus. (The first part of the name refers to the fact that it lived during a time period called the Cambrian and had rake-like claws)."

"Cambroraster was about the size of a painted turtle or a medium pizza — making it huge by Cambrian standards. At that time, most animals were smaller than your little finger."

"It was an arthropod, a distant relative of crabs, insects and spiders and other animals with jointed legs, although it didn't have any legs itself."

"Like a horseshoe crab (not a true crab but a distant relative of spiders), Cambroraster dug in the muddy bottom for food such as worms, researchers think, although it did so with a set of rake-like claws studded with hooked spines — something horseshoe crabs definitely do not have, but some relatives of real crabs do."

"Cambroraster devoured its prey with a circular, toothy lamprey-like mouth that was the calling card of the extinct group it's part of: the radiodonts (named for their round, toothy mouths), which died out about 350 million years ago."

Proterozoic Eon
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" is called the Proterozoic.

First era of prehistoric multicellular life.

Neoproterozoic
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" is called the Neoproterozoic.

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

"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."

"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."

Archeon Eon
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
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
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.