Dinosaur

Saurischia

Scientific study

Fields of study

Information on dinosaurs is gained from a variety of fields of study including Physics, Chemistry, Biology, and the Earth Sciences (which includes Paleontology).

Related Topics:
Physics - Chemistry - Biology - Earth Sciences - Paleontology

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Activities include the discovery, reconstruction and conservation of dinosaur fossils and the interpretation of those fossils to understand better the evolution, classification and behavior of dinosaurs.

Related Topics:
Fossil - Evolution

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Evolution

Dinosaurs split off from their archosaur ancestors during the Triassic period.

Related Topics:
Archosaur - Triassic

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The first known dinosaurs appeared approximately 230 Ma, about 20 million years after the Permian-Triassic extinction event wiped out about 70 percent of all biological diversity on the planet. A few lines of primitive dinosaurs diversified rapidly after the Triassic, and quickly expanded until they filled most of the vacant ecological niches. During the reign of the dinosaurs, which encompassed the ensuing Jurassic and Cretaceous periods, nearly every terrestrial animal larger than 1 m in length (that we know of) was a dinosaur.

Related Topics:
Permian-Triassic extinction event - Biological diversity - Triassic - Jurassic - Cretaceous - 1 m

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The Cretaceous-Tertiary extinction event, 65 Ma at the end of the Cretaceous, caused the extinction of all dinosaurs except for the line that had already led to the first birds.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Classification

Main article: Dinosaur classification

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Dinosaurs are archosaurs, like modern crocodilians. These are set apart by having diapsid skulls, having two holes where jaw muscles attach, called temporal fenestrae. Birds and most reptiles are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Dinosaurs also have teeth that grow from sockets (an archosaur characteristic) rather than as direct extensions of the jaw bones, as well as various other characteristics. Within this group, the dinosaurs are set apart most noticeably by their gait. Instead of legs that sprawl out to the side, as found in lizards and crocodylians, they have legs held directly under their body.

Related Topics:
Archosaur - Crocodilian - Diapsid - Temporal fenestrae - Synapsid - Turtles - Anapsid

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs: these include plesiosaurs (which are not closely related to the dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic.

Related Topics:
Plesiosaur - Pterosaurs

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Dinosaurs are divided into two major orders, the Saurischia and the Ornithischia, on the basis of hip structure.

Related Topics:
Orders - Saurischia - Ornithischia

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Saurischians

Main article: Saurischia

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Saurischians (from the Greek meaning "lizard hip") are dinosaurs that retained the hip structure of their ancestors. They include all the theropods (bipedal carnivores) and sauropods (long-necked herbivores).

Related Topics:
Lizard - Theropods - Carnivore - Sauropod - Herbivore

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Ornithischians

Main article: Ornithischia

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Ornithischians (from the Greek meaning "bird-hip") is the other dinosaurian order, most of which were quadrupedal herbivores.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Areas of debate

Warm-blooded?

Scientists have waged a constant and vigorous debate over the temperature regulation of dinosaur blood—at first over its possibility, then over its method—a debate first popularized by Robert T. Bakker. From the first discovery of dinosaurs, paleontologists posited that they were ectothermic creatures: "terrible lizards" as their name suggested. This axiomatic expectation implied that dinosaurs were mostly slow, sluggish organisms, comparable to modern reptiles, which need the sun to heat their bodies. However, new evidence of dinosaurs in chilly temperate climates, of polar dinosaurs in Australia and Antarctica where they experienced a six-month chilly and dark winter, of feathered dinosaurs whose feathers provided regulatory insulation, and analysis of blood-vessel structures that are typical of endotherms within dinosaur bone, confirmed the possibility that some dinosaurs regulated their body temperature by internal biological methods, some aided partly by their very bulk. Skeletal structures suggest active lifestyles for theropods and other creatures, behavior more suitable for an endothermic cardiovascular system. Sauropods exhibit fewer endothermic characters. Perhaps some dinosaurs were endothermic and others not. Scientific debate over the details continues, although many paleontologists would now agree that endothermic systems are more likely.

Related Topics:
Robert T. Bakker - Ectotherm - Lizard - Polar dinosaurs in Australia - Antarctica - Endotherm

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Complicating this debate, warm-bloodedness can emerge from more than one mechanism. Most discussions of dinosaur endothermia compare them to average birds or mammals, which expend energy to elevate body temperature above that of the environment. Small birds and mammals also possess insulation of some sort, such as fat, fur, or feathers, to slow down heat loss. However, large mammals, such as elephants, face a different problem due to their relatively small surface area to volume ratio (Haldane's principle). This ratio compares the volume of an animal with the area of its skin: as an animal gets bigger, its surface area increases more slowly than its volume. At a certain point, the amount of heat radiated away through the skin drops below the amount of heat produced inside the body, forcing animals to use additional methods to avoid overheating. In the case of elephants, they lack fur, and have large ears which increase their surface area, and have behavioral adaptations as well, such as using the trunk to spray water on themselves and mud wallowing. These behaviors increase cooling through evaporation.

Related Topics:
Insulation - Fat - Fur - Feather - Haldane

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Large dinosaurs would presumably have faced the same situation: their size would dictate that they lost heat relatively slowly to the surrounding air, and so could have been what are called bulk endotherms, animals that are warmer than their environments through sheer size rather than any special adaptations like those of birds and mammals. However, so far this theory fails to explain the vast multitudes of dog- and goat-sized dinosaurs, which made up the bulk of the ecosystem in the mesozoic.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Feathered dinosaurs and the bird connection

Main article: Feathered dinosaurs

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Over a hundred distinct anatomical features are shared by birds and theropod dinosaurs.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Feathers

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The first good specimen of a "feathered dinosaur" was the 1861 discovery of the Archaeopteryx in Germany, in the Solnhofen limestone, which is a lagerstätte; one of the rare and remarkable geological formations known for their superbly detailed fossils. Coming just two years after Darwin's seminal The Origin of Species, the evidence of a transitional fossil between reptiles and birds spurred the debates between evolutionary biology and creationism. This early bird is so dinosaur-like that, without a clear impression of feathers in the surrounding rock, the specimens are commonly mistaken for Compsognathus.

Related Topics:
Archaeopteryx - Solnhofen limestone - Lagerstätte - The Origin of Species - Transitional fossil - Evolutionary biology - Creationism - Compsognathus

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Since the 1990s, a number of feathered dinosaurs have been found, providing clear evidence of the close relationship between dinosaurs and birds. Most of these specimens were local to Liaoning province in northeastern China, which was part of an island continent in the Cretaceous. However, the feathers were only preserved by the lagerstätte of the Yixian Formation; it is therefore possible that dinosaurs elsewhere in the world may have been feathered too, even though the feathers have not been preserved.

Related Topics:
1990s - Feathered dinosaurs - Liaoning - China - Lagerstätte - Yixian Formation

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The feathered dinosaurs discovered so far include Beipiaosaurus, Caudipteryx, Dilong, Microraptor, Protarchaeopteryx, Shuvuuia, Sinornithosaurus, and Sinosauropteryx; and dinosaur-like birds like Confuciusornis; all of which come from the same area and formation in northern China. The dromaeosauridae family in particular seems to have been heavily feathered, and at least one dromaeosaurid, Cryptovolans, may have been capable of flight.

Related Topics:
Beipiaosaurus - Caudipteryx - Dilong - Microraptor - Protarchaeopteryx - Shuvuuia - Sinornithosaurus - Sinosauropteryx - Confuciusornis - Dromaeosauridae - Cryptovolans

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Skeleton

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Because feathers are often associated with birds, feathered dinosaurs are often touted as the missing link between birds and dinosaurs. However, the association of multiple skeletal features also shared by the two groups is the more important link for paleontologists. Furthermore, it is increasingly clear that the relationship between birds, dinosaurs and the evolution of flight is more complex than has been previously realized. For example, while it was once believed that birds simply evolved from dinosaurs and went their separate way, some scientists now believe that some dinosaurs, such as the dromaeosaurs, may have actually evolved from birds, losing the power of flight while keeping the feathers in a manner similar to the Ostrich and other ratites.

Related Topics:
Missing link - Paleontologist - Ostrich - Ratite

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Comparisons of bird and dinosaur skeletons, as well as cladistic analysis, strengthens the case for the link, particularly for a branch of theropods called maniraptors. Skeletal similarities include: the neck, pubis, wrists (semi-lunate carpal), arm and pectoral girdle, shoulder blade, clavicle and breast bone.

Related Topics:
Cladistic analysis - Maniraptor - Neck - Pubis - Wrist - Carpal - Arm - Pectoral girdle - Shoulder blade - Clavicle - Breast bone

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Reproduction biology

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

A recent discovery in a Tyrannosaurus rex skeleton provided more evidence that dinosaurs and birds evolved from a common ancestor and for the first time allowed palentologists to sex a dinosaur. When laying eggs, female birds have a special type of bone, called a medullary bone, that grows in their limbs, forming a layer inside the hard outer bone. It is rich in calcium and used for making eggshells. The presence of endosteally derived bone tissues lining the interior marrow cavities of portions of the Tyrannosaurus rex specimen's hindlimb elements suggested similar reproductive strategies, and revealed the specimen to be female (Schweitzer et al., 2005).

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Lungs

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Big meat-eating dinosaurs had a complex system of air sacs similar to the setup in today's birds, according to an investigation led by Patrick O'Connor of Ohio University. The lungs of theropod dinosaurs—carnivores that walked on two legs and had birdlike feet—likely pumped air into hollow sacs in their skeletons, as is the case in birds. "What was once formally considered unique to birds was present in some form in the ancestors of birds," O'Connor said. The study, funded in part by the National Science Foundation, is detailed in the July 14 issue of the journal Nature. http://news.yahoo.com/s/space/20050713/sc_space/dinosaursbreathedlikebirds;_ylt=AiKKnEF0_n.HLvZUF6ykJloPLBIF;_ylu=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Heart

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Modern computerized tomography (CT) scans of dinosaur chest cavities five years ago found the apparent remnants of complex four-chambered hearts more like mammals and birds. http://news.yahoo.com/s/space/20050713/sc_space/dinosaursbreathedlikebirds;_ylt=AiKKnEF0_n.HLvZUF6ykJloPLBIF;_ylu=X3oDMTBiMW04NW9mBHNlYwMlJVRPUCUl

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Care of young

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The embryo had no teeth, which suggests some parental care was required to feed the young dinosaur. http://www.freep.com/news/nw/dino29e_20050729.htm

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Gizzard

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Both birds and dinosaurs have used gizzard stones. When found in association with fossils, they are called gastroliths.

Related Topics:
Gizzard - Fossil - Gastrolith

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Other

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

A recently discovered troodont fossil demonstrates that the animals slept like birds, with their heads tucked under their arms. http://www.guardian.co.uk/life/news/story/0,12976,1326559,00.html

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Extinction theories

Main article: Cretaceous-Tertiary extinction event

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The extinction of the non-avian dinosaurs is one of the most intriguing problems in paleontology. Only since the 1980s has the nature of this extinction become apparent. The theory first proposed by Walter Alvarez linked the extinction event at the end of the Cretaceous period to a bolide impact about 65.5 Mya, based on a sudden change in Iridium levels in fossilized layers. The bulk of the evidence now indicates that a 10 km wide bolide hit the Yucatan Peninsula 65 Mya, creating the 170 km wide Chicxulub Crater and causing the extinction. Scientists are still disputing whether dinosaurs were in steady decline or still thriving before the meteor struck.

Related Topics:
Extinction - Paleontology - Walter Alvarez - Extinction event - Bolide - Iridium - Yucatan - 170 km - Chicxulub Crater

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Although the speed of extinction cannot be deduced from the fossil record alone, the latest models suggest the extinction was extremely rapid. It appears to have been caused by heat from the meteorite impact and the matter ejected from the crater reentering the Earth's atmosphere around the world. Other theories link the extinction with increased volcanic activity, decreasing oxygen level in the atmosphere and dropping temperatures.

Related Topics:
Heat - Atmosphere

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Other groups as well as the dinosaurs went extinct at the same time, including ammonites (nautilus-like mollusks), mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most kinds of birds, and many groups of mammals.

Related Topics:
Ammonite - Nautilus - Mollusk - Mosasaur - Turtle - Crocodile

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Evidence for Cenozoic non-avian dinosaurs

It has been claimed that fossils from El Ojo, South America, represent remains of non-avian dinosaurs surviving the extinction and still thriving in the Paleocene epoch. There are also other sporadic claims of post-Cretaceous dinosaur fossils (even a very doubtful finding of dinosaur eggs as late as Eocene). While it is certainly not improbable that some scattered population of some (presumably small) dinosaur species could have survived at least some hundreds of years after the mass extinction, evidence now points to El Ojo (and most other) findings as Cretaceous fossils contaminating Paleocene strata. Nevertheless, it is still theorized that some dinosaur population could have survived the main extinction event isolated in Antarctica, and then being killed by the climatic change.

Related Topics:
El Ojo - Paleocene - Eocene - Antarctica

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Bringing dinosaurs back to life

Main article: Molecular paleontology

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

There has been much speculation about the availability of technology to bring dinosaurs back to life. The idea proposed in Michael Crichton's book Jurassic Park, using blood from fossilized mosquitos that have been suspended in tree sap since the Mesozoic and then filling in the gaps with frog genes to create the DNA of a dinosaur, is probably impossible. The main problem is that DNA decays over time by exposure to air, water and radiation. Decay can be measured by a racemization test.

Related Topics:
Michael Crichton - Jurassic Park - Mosquito - Frog - DNA - Racemization

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

There have been two claims about the successful extraction of ancient DNA from dinosaur fossils, but upon further inspection, neither of these reports could be confirmed (Wang et al., 1997). However, a working visual peptide of a (theoretical) dinosaur has been inferred using analytical phylogenetic reconstruction methods on gene sequences of still-living related species (reptiles and birds) (Chang et al., 2002).

Related Topics:
Wang et al., 1997

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Discovery of probable soft tissue from dinosaur fossils

In the March 2005 issue of Science, Mary Higby Schweitzer et al. announced material, after rehydrating, that resembled soft tissue was discovered inside a Tyrannosaurus rex leg bone from the Hell Creek Formation in Montana, from about 68 million years ago.http://www.sciencemag.org/cgi/content/full/sci;307/5717/1952.

Related Topics:
2005 - Science - Mary Higby Schweitzer - Tyrannosaurus rex - Bone - Hell Creek Formation - Montana

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

When the fossilized bone was treated over several weeks to remove mineral content (demineralize) from the fossilized bone marrow cavity, Schweitzer found evidence of intact structures such as blood vessels, bone matrix, and connective tissue (bone fibers). Scrutiny under microscope further revealed the putative dinosaur soft tissue had retained fine structures (microstructures) even at the cellular level. It has not been made clear of what this flexible material is actually composed, although many news reports immediately linked it with the movie "Jurassic Park", and the interpretation of the artifact as well as the relative importance of Dr. Schweitzer's discovery is still undecided.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~