Dinosaur

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Today's episode is from a Wikipedia article titled,

Dinosaur.

Dinosaurs are a diverse group of reptiles of the clade Dinosauria.

They first appeared during the Triassic period between 245 and 233.

23 million years ago,

MYA,

Although the exact origin and timing of the evolution of dinosaurs is the subject of active research.

They became the dominant terrestrial vertebrates after the Triassic-Jurassic extinction event 201.

3 million years ago,

And their dominance continued throughout the Jurassic and Cretaceous periods.

The fossil record shows that birds are feathered dinosaurs,

Having evolved from earlier theropods during the late Jurassic epoch,

And are the only dinosaur lineage known to have survived the Cretaceous-Paleogene extinction event approximately 66 million years ago.

Dinosaurs can therefore be divided into avian dinosaurs,

Birds,

And the extinct non-avian dinosaurs,

Which are all dinosaurs other than birds.

Dinosaurs are varied from taxonomic,

Morphological,

And ecological standpoints.

Birds at over 10,

700 living species are among the most diverse groups of vertebrates.

Between fossil evidence,

Paleontologists have identified over 900 distinct genera and more than 1,

000 different species of non-avian dinosaurs.

Dinosaurs are represented on every continent by both extant species,

Birds,

And fossil remains.

Through the first half of the 20th century,

Before birds were recognized as dinosaurs,

Most of the scientific community believed dinosaurs to have been sluggish and cold-blooded.

Most research conducted since the 1970s,

However,

Has indicated that dinosaurs were active animals with elevated metabolisms and numerous adaptations for social interaction.

Some were herbivores,

Others carnivores.

Evidence suggests that all dinosaurs were egg-laying,

And that nest-building was a trait shared by many dinosaurs,

Both avian and non-avian.

While dinosaurs were ancestrally bipedal,

Many extinct groups included quadrupedal species,

And some were able to shift between these stances.

Elaborate display structures such as horns or crests are common to all dinosaur groups,

And some extinct groups developed skeletal modifications such as bony armor and spines.

While the dinosaurs' modern-day surviving avian lineage birds are generally small due to the constraints of flight,

Many prehistoric dinosaurs,

Non-avian and avian,

Were large-bodied.

The largest sauropod dinosaurs are estimated to have reached lengths of 39.

7 meters and heights of 18 meters,

And were the largest land animals of all time.

The misconception that non-avian dinosaurs were uniformly gigantic is based in part on preservation bias,

As large,

Sturdy bones are more likely to last until they are fossilized.

Many dinosaurs were quite small,

Some measuring about 50 centimeters in length.

The first dinosaur fossils were recognized in the early 19th century with the name dinosaur,

Meaning terrible lizard,

Being coined by Sir Richard Owen in 1842 to refer to these great fossil lizards.

Since then,

Mounted fossil dinosaur skeletons have been major attractions at museums worldwide,

And dinosaurs have become an enduring part of popular culture.

The large sizes of some dinosaurs,

As well as their seemingly monstrous and fantastic nature,

Have ensured their regular appearance in best-selling books and films such as Jurassic Park.

Persistent public enthusiasm for the animals has resulted in significant funding for dinosaur science,

And new discoveries are regularly covered by the media.

Definition.

Under phylogenetic nomenclature,

Dinosaurs are usually defined as the group consisting of the most recent common ancestor,

MRCA,

Of triceratops and modern birds,

And all its descendants.

It has also been suggested that dinosauria be defined with respect to the MRCA of Megalosaurus and Iguanodon,

Because these were two of the three genera cited by Richard Owen when he recognized the dinosauria.

Both definitions result in the same set of animals being defined as dinosaurs.

Dinosauria equals Ornithischia plus Saurischia.

This definition includes major groups such as Ankylosaurians,

Armored herbivores,

Quadrupeds,

Stegosaurians,

Plated herbivores,

Quadrupeds,

Ceratopsians,

Bipedal or quadrupedal herbivores with neck frills,

Pachycephalosaurians,

Bipedal herbivores with thick skulls,

Ornithopods,

Bipedal or quadrupedal herbivores including Tugbills,

Theropods,

Mostly bipedal carnivores and birds,

And Sauropodomorphs,

Mostly large herbivores,

Quadrupeds with long necks and tails.

Birds are now recognized as being the sole surviving lineage of theropod dinosaurs.

In traditional taxonomy,

Birds were considered a separate class that had evolved from dinosaurs,

A distinct superorder.

However,

A majority of contemporary paleontologists concerned with dinosaurs rejected the traditional style of classification in favor of phylogenetic taxonomy.

This approach requires that,

For a group to be natural,

All descendants of members of the group must be included in the group as well.

Birds are thus considered to be dinosaurs,

And dinosaurs are,

Therefore,

Not extinct.

Birds are classified as belonging to the subgroup Maniraptora,

Which are colorosaurs,

Which are theropods,

Which are ceriscians,

Which are dinosaurs.

Research by Matthew G.

Barron,

David B.

Norman,

And Paul M.

Barrett in 2017 suggested a radical revision of dinosaurian systematics.

Phylogenetic analysis by Barron et al.

Recovered the Ornithischia as being closer to the Theropoda than the Sauropodomorpha,

As opposed to the traditional union of theropods with sauropodomorphs.

They resurrected the clade Ornithischolida to refer to the group containing Ornithischia and Theropoda.

Dinosauria itself was redefined as the last common ancestor of Triceratops auritis,

Passar domesticus and Diplodocus carnegie,

And all of its descendants,

To ensure that sauropods and kin remain included as dinosaurs.

General Description Dinosaurs can be generally described as archosaurs with hind limbs held erect beneath the body.

Other prehistoric animals including pterosaurs,

Mosasaurs,

Ichthyosaurs,

Plesiosaurs,

And dimetrodon,

While often popularly conceived of as dinosaurs,

Are not taxonomically classified as dinosaurs.

Dinosaurs are distantly related to dinosaurs being members of the clade Ornithischia.

The other groups mentioned are,

Like dinosaurs and pterosaurs,

Members of Sauropsida,

The reptile and bird clade,

Except Dimetrodon which is a synapsid.

None of them had the erectile limb posture characteristic of true dinosaurs.

Dinosaurs were the dominant terrestrial vertebrates of the Mesozoic era,

Especially the Jurassic and Cretaceous periods.

Other groups of animals were restricted in size and niches.

Mammals,

For example,

Rarely exceeded the size of a domestic cat and were generally rodent-sized carnivores of small prey.

They have always been recognized as an extremely varied group of animals.

Over 900 non-avian dinosaur genera have been identified with certainty as of 2018,

And the total number of genera preserved in the fossil record has been estimated at around 1,

850,

Nearly 75% of which remain to be discovered,

And 1,

124 species by 2016.

A 1995 study predicted that about 3,

400 dinosaur genera ever existed,

Including many that would not have been preserved in the fossil record.

In 2016,

The estimated number of dinosaur species that existed in the Mesozoic was 1,

543 to 2,

468.

In 2021,

The number of modern-day birds,

Avian dinosaurs,

Was estimated to be at 10,

806 species.

Some are herbivorous,

Others carnivorous,

Including seed-eaters,

Fish-eaters,

Insectivores,

And omnivores.

While dinosaurs were ancestrally bipedal,

As are all modern birds,

Some prehistoric species were quadrupeds,

And others,

Such as ankyosaurs and iguanodon,

Could walk just as easily on two or four legs.

Cranial modifications like horns and crests are common dinosaurian traits,

And some extinct species had bony armor.

Although known for large size,

Many Mesozoic dinosaurs were human-sized or smaller,

And modern birds are generally small in size.

Dinosaurs today inhabit every continent,

And fossils show that they had achieved global distribution by at least the early Jurassic epoch.

Modern birds inhabit most available habitats,

From terrestrial to marine,

And there is evidence that some non-avian dinosaurs could fly or at least glide,

And others,

Such as spinosaurids,

Had semi-aquatic habits.

Distinguishing Anatomical Features While recent discoveries have made it more difficult to present a universally agreed-upon list of their distinguishing features,

Nearly all dinosaurs discovered so far share certain modifications to the ancestral archosaurian skeleton,

Or are clearly descendants of older dinosaurs showing these modifications.

Although some later groups of dinosaurs featured further modified versions of these traits,

They are considered typical of Dinosauria.

The earliest dinosaurs had them and passed them on to their descendants.

Such modifications originating in the most recent common ancestor of a certain taxonomic group are called the synapomorphies of such a group.

A detailed assessment of archosaur interrelations by Sterling Nesbitt confirmed or found the following twelve unambiguous synapomorphies,

Some previously known.

In the skull,

A supratemporal fossa excavation is present in front of the supratemporal fenestra,

The main opening in the rear skull roof.

Hippophyses,

Obliquely backward-pointing processes on the rear top corners of the anterior front neck vertebrae behind the atlas and axes,

The first two neck vertebrae.

Apex of a deltopectoral crest,

A projection on which the deltopectoral muscles attach,

Located at or more than 30% down the length of the humerus,

Upper arm bone.

Medius,

A lower arm bone,

Shorter than 80% of humerus length.

Fourth trochanter,

Projection where the caudofomeralis muscle attaches on the inner rear shaft,

On the femur,

Thigh bone,

Is a sharp flange.

Fourth trochanter asymmetrical,

The distal,

Lower margin forming a steeper angle to the shaft.

On the astragalus and calcineum,

Upper ankle bones,

And the proximal articular facet,

The top connecting surface for the fibula occupies less than 30% of the transverse width of the element.

Exocipitals,

Bones at the back of the skull,

Do not meet along the midline on the floor of the intercranial cavity,

The inner space of the brain case.

In the pelvis,

The proximal articular surfaces of the ischium,

With the ilium and the pubis are separated by a large concave surface.

On the upper side of the ischium,

A part of the open hip joint is located between the contacts with the pubic bone and the ilium.

Nemial crest,

On the tibia,

Protruding part of the top surface of the shin bone,

Arcs anterolaterally,

Curves to the front and the outer side.

Ridge proximodistally oriented,

Vertical,

Ridge present on the posterior face of the distal end of the tibia,

The rear surface of the lower end of the shin bone.

Concave articular surface of the fibula of the calcaneum,

The top surface of the calcaneum,

Where it touches the fibula,

Has a hollow profile.

Nesbitt found a number of further potential synapomorphies and discounted a number of synapomorphies previously suggested.

Some of these are also present in silosaurids,

Which Nesbitt recovered as a sister group in Dinosauria,

Including a large anterior trochanter.

Metatarsals 2 and 4 of sub-equal length,

Reduced contact between ischium and pubis,

The presence of anemiocrest on the tibia and of an ascending process on the astragalus,

And many others.

A variety of other skeletal features are shared by dinosaurs.

However,

Because they are either common to other groups of archosaurs or were not present in all early dinosaurs,

These features are not considered to be synapomorphies.

For example,

As diapsids,

Dinosaurs ancestrally had two pairs of infratemporal fenestri,

Openings in the skull behind the eyes,

And as members of the diapsid group Archosauria,

Had additional openings in the snout and lower jaw.

Additionally,

Several characteristics once thought to be synapomorphies are now known to have appeared before dinosaurs,

Or were absent in the earliest dinosaurs and independently evolved by different dinosaur groups.

These include an elongated scapula or shoulder blade,

A sacrum composed of three or more fused vertebrae,

Three are found in some other archosaurs,

But only two are found in Heraurosaurus,

And a hip socket with a hole at the center of its inside surface.

Another difficulty of determining distinctly dinosaurian features is that early dinosaurs and other archosaurs from the late Triassic epoch are often poorly known and were similar in many ways.

These animals have sometimes been misidentified in the literature.

Dinosaurs stand with their hind limbs erect in a manner similar to most modern mammals,

But distinct from most other reptiles,

Whose limbs sprawl out to either side.

This posture is due to the development of a laterally facing recess in the pelvis,

Usually an open socket,

And a corresponding inwardly facing distinct head on the femur.

Their erect posture enabled early dinosaurs to breathe easily while moving,

Which likely permitted stamina and activity levels that surpassed those of sprawling reptiles.

Erect limbs probably also helped support the evolution of large size by reducing bending stresses on limbs.

Some non-dinosaurian archosaurs,

Including Rhysuchians,

Also had erect limbs,

But achieved this by a pillar-erect configuration of the hip joint,

Where instead of having a projection from the femur insert on a socket on the hip,

The upper pelvic bone was rotated to form an overhanging shelf.

History of Study Pre-scientific History Dinosaur fossils have been known for millennia,

Although their true nature was not recognized.

The Chinese considered them to be dragon bones and documented them as such.

Villagers in central China have long unearthed fossilized dragon bones for use in traditional medicines.

In Europe,

Dinosaur fossils were generally believed to be the remains of giants and other biblical creatures.

Early Dinosaur Research Scholarly descriptions of what would now be recognized as dinosaur bones first appeared in the late 17th century in England.

Part of a bone,

Now known to have been the femur of a Megalosaurus,

Was recovered from a limestone quarry at Cornwell near Chipping Norton,

Oxfordshire,

In 1676.

The fragment was sent to Robert Plott,

Professor of chemistry at the University of Oxford and first curator of Ashmolean Museum,

Who published a description in his The Natural History of Oxfordshire,

1677.

He correctly identified the bone as the lower extremity of the femur of a large animal and recognized that it was too large to belong to any known species.

He therefore concluded it to be the femur of a huge human,

Perhaps a titan or another type of giant featured in legends.

Edward Lude,

A friend of Sir Isaac Newton,

Published Lysophilacea Britannicae Echinographia,

1699,

The first scientific treatment of what would now be recognized as a dinosaur,

When he described and named a sauropod tooth,

Rutellum impiccatum,

That had been found in Caswell near Whitney,

Oxfordshire.

Between 1815 and 1824,

The Reverend William Buckland,

The first reader of geology at the University of Oxford,

Collected more fossilized bones of Megalosaurus and became the first person to describe a non-avian dinosaur in a scientific journal.

The second non-avian dinosaur genus to be identified,

Iguanodon,

Was discovered in 1822 by Mary Ann Mantle,

The wife of English geologist Gideon Mantle.

Gideon Mantle recognized similarities between his fossils and the bones of modern iguanas.

He published his findings in 1825.

The study of these great fossil lizards soon became a great interest to European and American scientists,

And in 1842 the English paleontologist Sir Richard Owen coined the term dinosaur,

Using it to refer to the distinct tribe of suborder of Saurian reptilis that were then being recognized in England and around the world.

The term is derived from ancient Greek dinos,

Terrible,

Potent,

Or fearfully great,

And Sauros,

Lizard or reptile,

Though the taxonomic name has often been interpreted as a reference to dinosaurs' teeth,

Claws,

And other fearsome characteristics.

Owen intended it to also evoke their size and majesty.

Owen recognized that the remains that had been found so far,

Iguanodon,

Megalosaurus,

And Haleosaurus,

Shared a number of distinctive features,

And so decided to present them as a distinct taxonomic group.

As clarified by British geologist and historian Hugh Torrens,

Owen had given a presentation about fossil reptiles to the British Association for the Advancement of Science in 1841.

The reports of the time show that Owen did not mention the word dinosaur,

Nor recognize dinosaurs as a distinct group of reptiles in his address.

He only introduced the dinosauria in the revised text version of his talk published in April of 1842.

With the backing of Prince Albert,

The husband of Queen Victoria,

Owen established the Natural History Museum London to display the National Collection of Dinosaur Fossils and other biological and geological exhibits.

Discoveries in North America In 1858,

William Parker Foulke discovered the first known American dinosaur in Marl Pits in the small town of Haddonfield,

New Jersey.

Although fossils had been found before,

Their nature had not been correctly discerned.

The creature was named Hadrosaurus Foulke.

It was an extremely important find.

Hadrosaurus was one of the first nearly complete dinosaur skeletons found.

The first was in 1834 in Maidstone,

England,

And it was clearly a bipedal creature.

This was a revolutionary discovery as,

Until that point,

Most scientists had believed dinosaurs walked on four feet like other lizards.

Foulke's discoveries sparked a wave of interest in dinosaurs in the United States known as dinosaur mania.

Dinosaur mania was exemplified by the fierce rivalry between Edward Drinker Cope and Osniel Charles Marsh,

Both of whom raced to be the first to find new dinosaurs in what came to be known as the Bone Wars.

This fight between the two scientists lasted for about 30 years,

Ending in 1897 when Cope died after spending his entire fortune on the dinosaur hunt.

Many valuable dinosaur specimens were damaged or destroyed due to the pair's rough methods.

For example,

Their diggers often used dynamite to unearth bones.

Modern paleontologists would find such methods crude and unacceptable,

Since blasting easily destroys fossil and stratigraphic evidence.

Despite their unrefined methods,

The contributions of Cope and Marsh to paleontology were vast.

Marsh unearthed 86 new species of dinosaur,

And Cope discovered 56,

A total of 142 new species.

Cope's collection is now at the American Museum of Natural History in New York City,

While Marsh's is at the Peabody Museum of Natural History at Yale University.

Dinosaur Renaissance and Beyond World War II caused a pause in paleontological research.

After the war,

Research attention was also diverted increasingly to fossil mammals rather than dinosaurs,

Which were seen as sluggish and cold-blooded.

At the end of the 1960s,

However,

The field of dinosaur research experienced a surge in activity that remains ongoing.

Several seminal studies led to this activity.

First,

John Ostrom discovered the bird-like dromaeosaurid Theropod denunicus and described it in 1969.

Its anatomy indicated that it was an active predator that was likely warm-blooded,

In marked contrast to the then-prevailing image of dinosaurs.

Concurrently,

Robert T.

Bakker published a series of studies that likewise argued for active lifestyles in dinosaurs,

Based on anatomical and ecological evidence,

Which were subsequently summarized in his 1986 book,

The Dinosaur Heresies.

New revelations were supported by an increase in dinosaur discoveries.

Major new dinosaur discoveries have been made by paleontologists working in previously unexplored regions,

Including India,

South America,

Madagascar,

Antarctica,

And most significantly,

China.

Across theropods,

Sauropodomorphs,

And ornithischians,

The number of named genera began to increase exponentially in the 1990s.

As of 2008,

Over 30 new species of dinosaurs were named each year.

At least sauropodomorphs experienced a further increase in the number of named species in the 2010s,

With an average of 9.

3 new species having been named each year between 2009 and 2020.

As a consequence,

More sauropodomorphs were named between 1990 and 2020 than in all previous years combined.

These new localities also led to improvements in overall specimen quality,

With new species being increasingly named not on scrappy fossils,

But on more complete skeletons,

Sometimes from multiple individuals.

Better specimens also led to new species being invalidated less frequently.

Asian localities have produced the most complete theropod specimens,

While North American localities have produced the most complete sauropodomorph specimens.

Prior to the dinosaur renaissance,

Dinosaurs were mostly classified using the traditional rank-based system of Linnean taxonomy.

The renaissance was also accompanied by the increasingly widespread application of cladistics,

A more objective method of classification based on ancestry and shared trades,

Which has proved tremendously useful in the study of dinosaur systematics and evolution.

Cladistic analysis,

Among other techniques,

Helps to compensate for an often incomplete and fragmentary fossil record.

Reference books summarizing the state of dinosaur research,

Such as David B.

Y.

Shampel and colleagues,

The Dinosauria,

Made knowledge more accessible and spurred further interest in dinosaur research.

The release of the first and second editions of The Dinosauria in 1990 and 2004,

And of a review paper by Paul Sereno in 1998,

Were accompanied by increases in the number of published phylogenetic trees for dinosaurs,

Soft tissue,

And molecular preservation.

Dinosaur fossils are not limited to bones,

But also include imprints or mineralized remains of skin coverages,

Organs,

And other tissues.

Of these,

Skin coverings based on keratin proteins are most easily preserved because of their cross-linked hydrophobic molecular structure.

Fossils of keratin-based skin coverings,

Or bony skin coverings,

Are known from most major groups of dinosaurs.

Dinosaur fossils with scaly skin impressions have been found since the 19th century.

Samuel Beckles discovered a sauropod forelimb with preserved skin in 1852 that was incorrectly attributed to a crocodile.

It was correctly attributed by Marsh in 1888 and subject to further study by Reginald Hooley in 1917.

Among ornithiscians,

In 1884 Jacob Wortmann found skin impressions on the first known specimen of Edmontosaurus anectens,

Which were largely destroyed during the specimen's excavation.

Owen and Hooley subsequently described skin impressions of Hypsilophodon and Iguanodon in 1885 and 1917.

Since then,

Scale impressions have been most frequently found among hadrosaurids,

Where the impressions are known from nearly the entire body across multiple specimens.

Starting from the 1990s,

Major discoveries of exceptionally preserved fossils and deposits,

Known as Conservation Lagerstätten,

Contributed to research on dinosaur soft tissues.

Chiefly among these were the rocks that produced the J-hole early Cretaceous and Yanliao mid-to-late Jurassic biotas of northeastern China,

From which hundreds of dinosaur specimens bearing impressions of feather-like structures,

Both closely related to birds and otherwise,

Have been described by Jing Zhu and colleagues.

In living reptiles and mammals,

Pigments storing cellular structures known as melanosomes are partially responsible for producing coloration.

Both chemical traces of melanin and characteristically shaped melanosomes have been reported from feathers and scales of J-hole and Yanliao dinosaurs,

Including both theropods and ornithischians.

This has enabled multiple full-body reconstructions of dinosaur coloration,

And similar techniques have also been extended to dinosaur fossils from other localities.

However,

Some researchers have also suggested that fossilized melanosomes represent bacterial remains.

Stomach contents in some J-hole and Yanliao dinosaurs closely related to birds have also provided indirect indications of diet and digestive system anatomy,

E.

G.

Crops.

More concrete evidence of internal anatomy has been reported of Italy.

It preserves portions of the intestines,

Colon,

Liver,

Muscles,

And windpipe.

Concurrently,

A line of work by Mary Higbee Schweitzer,

Jack Horner,

And colleagues reported various occurrences of preserved soft tissues and proteins within dinosaur bone fossils.

Various mineralized structures that likely represented red blood cells and collagen fibers had been found by Schweitzer and others in Tyrannosaurid bones as early as 1991.

However,

In 2005,

Schweitzer and colleagues reported that a femur of Tyrannosaurus preserved soft,

Flexible tissue within,

Including blood vessels,

Bone matrix,

And connective tissue,

Bone fibers,

That had retained their microscopic structure.

This discovery suggested that original soft tissues could be preserved over geological time.

Later in 2009,

Schweitzer and colleagues reported that a Brachylophosaurus femur preserved similar microstructures,

And immunohistochemical techniques based on antibody binding demonstrated the presence of proteins such as collagen,

Elastin,

And laminin.

Both specimens yielded collagen protein sequences that were viable for molecular phylogenetic analyses,

Which grouped them with birds,

As would be expected.

The extraction of fragmentary DNA has also been reported for both of these fossils,

Along with a specimen of Hypacrosaurus.

In 2015,

Sergio Bertazzo and colleagues reported the preservation of collagen fibers and red blood cells in eight Cretaceous dinosaur specimens that did not show any signs of exceptional preservation,

Indicating that soft tissue may be preserved more commonly than previously thought.

Suggestions that these structures represented bacterial biofilms have been rejected,

But cross-contamination remains a possibility that is difficult to detect.