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Maiasaura

Wednesday, November 30, 2016

Maiasaura by Alain Beneteau

Maiasaura (from the Greek “μαία” and the feminine form of Latin saurus, meaning “good mother reptile” or “good mother lizard” ) is a large herbivorous hadrosaurid (“duck-billed”) dinosaur genus that lived in the area currently covered by the state of Montana in the Upper Cretaceous Period (mid to late Campanian), about 76.7 million years ago.
 
Illustration of a herd of Maiasaura walking along a creekbed, as found in the semi-arid Two Medicine Formation fossil bed. This region was characterized by volcanic ash layers and conifer, fern and horsetail vegetation. Author: Debivort

The first fossils of Maiasaura were discovered in 1978. In 1979, the genus was named. The name refers to the find of nests with eggs, embryos and young animals, in a nesting colony. These showed that Maiasaura fed its young while they were in the nest, the first time such evidence was obtained for a dinosaur. Hundreds of bones of Maiasaura have been dug up. Evidence suggest the “Maiasaura” was covered rapidly by a global flood. This preserved the nesting site and fossils.

Maiasaura was about nine metres long. Young animals walked on their hind legs, adults on all fours. Maiasaura was probably closely related to Brachylophosaurus.

Maiasaura were large, attaining a maximum known length of about 9 metres (30 ft). They had a flat beak typical of hadrosaurids, and thick noses. They had a small, spiky crest in front of the eyes. This crest may have been used in headbutting contests between males during the breeding season.

Maiasaura peeblesorum skeletal mount, Brussels Natural History museum (2009).

Maiasaura were herbivorous. They were capable of walking both on two (bipedal) or four (quadrupedal) legs. Studies of the stress patterns of healed bones show that young juveniles under four years old walked mainly bipedal, switching to a mainly quadrupedal style of walking when they grew larger. They appeared to have no defense against predators, except, perhaps, its heavy muscular tail and their herd behavior. Herds were extremely large and could have comprised as many as 10,000 individuals. Maiasaura lived in an inland habitat.

Maiasaura lived in herds and it raised its young in nesting colonies. The nests in the colonies were packed closely together, like those of modern seabirds, with the gap between the nests being around 7 metres (23 ft); less than the length of the adult animal. The nests were made of earth and contained 30 to 40 eggs laid in a circular or spiral pattern. The eggs were about the size of ostrich eggs.
Reconstructed nest
 
It appears that young Maiasaura grew quickly. To some researchers, this suggests that they were warm-blooded. The nests that Horner and Makela found also throw light on the social organization of these hadrosaurs. The number and proximity of the nests indicate that females nested in large groups. Some scientists believe that Maiasaura were strongly social animals that lived in herds of many thousands.
 
Maiasaura is a characteristic fossil of the middle portion (lithofacies 4) of the Two Medicine Formation, dated to about 76.4 million years ago. Maiasaura lived alongside the troodontid Troodon and the hypsilophodont Orodromeus, as well as the dromaeosaurid Bambiraptor and the tyrannosaur Daspletosaurus.

10 Facts About Ceratosaurus

Wednesday, November 30, 2016

The large Ceratosaurus at the Natural History Museum of Utah. Photo by Brian Switek.

Ceratosaurus popped up in Jurassic Park III at one point – but what do we know about the dinosaur?

Like a ’56 T-Bird parked in a car park full of hybrids, Ceratosaurus shared its range with several less-archaic carnivores. This primitive predator really stands out in films and in museums, which helps explain the odd dino’s enduring popularity.

1. Ceratosaurus Had an Armored Backside.

A row of bony plates called osteoderms ran down the animal’s spine. They probably didn’t offer much defense, but they sure helped Ceratosaurus score some major style points!

2. It Might Have had Semi-Aquatic Habits.

Like modern gators, Ceratosaurus came with a strong, broad, and flexible tail—and the animal’s teeth are sometimes found scattered near lungfish skeletons. So was it amphibious? According to paleontologist Robert Bakker, the idea has merit. He’s even envisioned Ceratosaurus as a wannabe crocodile of sorts, stealthily lurking beneath Jurassic rivers. But while this dinosaur was likely a halfway-decent swimmer, many feel that Bakker’s very speculative hypothesis can’t keep its head above the water.

3. It’s Been a Movie Star for Over 100 Years.

Audiences watched the bonafide celebrity stalk cavemen in Brute Force (1914), take on Triceratops in One Million Years B.C.(1966), and gag at the sight of Spinosaurus poop in Jurassic Park III (2001).

4. Some Argue that This Creature Directly Competed with the Better-Known Allosaurus.

Both carnivores stalked Utah and Colorado 150 million years ago, and both had nasty jaws designed for slicing (as opposed to crushing bone and all that fun stuff). Because similar bites often mean similar diets, maybe these two titans hunted the same game. Or they might have found separate niches and steered clear of each other—Allosaurus did have proportionately-smaller teeth, after all. Regardless, the late Jurassic was clearly a tough time to be an herbivore.

5. Scientists Still Aren’t Sure About What Ceratosaurus Did With its Dynamic Nasal Horn.

In 1920, an American geologist named Charles Whitney Gilmore wrote that Ceratosaurus’ horn “formed a useful weapon for offense and defense.” Nowadays, however, this thing’s function no longer seems quite so clear-cut.  Thin and probably on the fragile side, most 21st-century specialists hold that Ceratosaurus’ best-known feature was better-suited for display than combat.

6. It Featured Unusually Long Teeth.

Ceratosaurus Juvenile. Author: Deviant Paleoart

One specimen manages to look just as scary with its mouth shut. This dino’s upper teeth are so long that—when the creature’s maw assumes a “closed” position—they extend below the lower jaw!

7. Ceratosaurus was Relatively Rare

Allosaurus seems to have been far more common than Ceratosaurus. The latter, bumpy-snouted predator is only known from a relative handful of skeletons. Meanwhile, very few dinos are as well-represented by the fossil record as Allosaurus: A single quarry contains assorted bones belonging to at least 44 individuals. How many Ceratosaurus specimens has this same site yielded? One.

8. Its Remains Have Been Found on Three Different Continents.

Though frequently cited as a North American creature, Ceratosaurus material has also turned up in Portugal and Tanzania.

9. Size-Wise, Not all Ceratosaurus Were Created Equal.

Ceratosaurus dentisculatus could have really done some damage. While the 18-foot Ceratosaurus nasicornis is, by far, this genus’ most famous species, C. dentisculatus was noticeably longer, with an estimated length of over 23 feet (7 metres)—and it may been twice as massive.

10. Ceratosaurus was Named by One of America’s Greatest Paleontologists.

Skeleton of Ceratosaurus, a theropod dinosaur. Date: 1896 Source: Originally from O. C. Marsh’s book, The Dinosaurs of North America; found in). Author: O.C. Marsh.

Othniel Charles Marsh (1832-1899) also introduced the world to such prehistoric icons as StegosaurusTriceratopsAllosaurusDiplodocus, and Apatosaurus. Plus, he lobbied for Native American rights, regularly corresponded with Charles Darwin, and was among the first to suggest that present-day birds evolved from dinosaurs.

Source: www.mentalfloss.com

Leaellynasaura

Wednesday, November 30, 2016

Leaellynasaura

Leaellynasaura (meaning “Leaellyn’s lizard”) is a genus of small herbivorous ornithischian dinosaurs from the Albian stage of the Early Cretaceous (dated to between 118 and 110 million years ago), first discovered in Dinosaur Cove, Australia. The only known species is Leaellynasaura amicagraphica. It was described in 1989, and named after Leaellyn Rich, the daughter of the Australian palaeontologist couple Tom Rich and Patricia Vickers-Rich who discovered it. The specific name L. amicagraphica translates to “friend writing” and honours both the Friends of the Museum of Victoria and the National Geographic Society for their support of Australian paleontology.
 
Leaellynasaura is a relatively small dinosaur, about 90 centimeters (3 feet) in length. It is known from several specimens including two nearly complete skeletons and two fragmentary skulls. It has been variously described as a hypsilophodontid, a primitive iguanodontian and primitive ornithischian (Genasauria). The most recent assessment describes it as a non-iguanodontian ornithopod.
 
During the early Cretaceous, Victoria was well within the Antarctic polar circle. This means that Leaellynasaura was living, and apparently thriving, at latitudes that no reptile lives at today. The fact that even juveniles had enlarged optic lobes suggests that this dinosaur had large eyes that helped it to see its way through the long, dark polar winters.
 
The type species is Leaellynasaura amicagraphica. It was described in 1989; It was named after Leaellyn Rich, the daughter of the palaeontologist couple Tom Rich and Patricia Vickers-Rich who discovered it. Leaellynasaura was a hypsilophodont, a rather basal ornithopod. Like all ornithopods, it was a herbivore. So far, no complete skeletons have been found of Leaellynasaura. It stood at about one metre (3 feet).
 
Leaellynasaura appeared on the fifth episode of Walking with Dinosaurs. Evolved cold-weather Leaellynasaura appeared in Stephen Baxter’s “Evolution” in the chapter “The Last Burrow.”
 

A female Leaellynasaura feeds her young. Walking with Dinosaurs | BBC Earth

Lambeosaurus

Wednesday, November 30, 2016

Lambeosaurus reconstruction

Lambeosaurus (meaning “Lambe’s lizard”) is a genus of hadrosaurid dinosaur that lived about 75 million years ago, in the Late Cretaceous period (Campanian) of North America. This bipedal/quadrupedal, herbivorous dinosaur is known for its distinctive hollow cranial crest, which in the best-known species resembled a hatchet. Several possible species have been named, from Canada, the United States, and Mexico, but only the two Canadian species are currently recognized as valid.

L. lambei compared to a human by Dinoguy2

Lambeosaurus was belatedly described in 1923 by William Parks, over twenty years after the first material was studied by Lawrence Lambe. The genus has a complicated taxonomic history, in part because small-bodied crested hadrosaurids now recognized as juveniles were once thought to belong to their own genera and species. Currently, the various skulls assigned to the type speciesL. lambei are interpreted as showing age differences and sexual dimorphism. Lambeosaurus was closely related to the better known Corythosaurus, which is found in slightly older rocks, as well as the less well-known genera Hypacrosaurus and Olorotitan. All had unusual crests, which are now generally assumed to have served social functions like noisemaking and recognition.

Restoration of a crouched L. lambei by ДиБгд at Russian Wikipedia Tail and hands fixed by FunkMonk.
 
As in other lambeosaurines, the hollow crest would have formed a resonating chamber for its calls, amplifying them and making a distinctive sound in each species. The shape and patterning of the crest would also have helped individuals to recognize each other in the herd.

Lambeosaurus, best known through L. lambei, was quite similar to Corythosaurus in everything but the form of the head adornment. Compared to Corythosaurus, the crest of Lambeosaurus was shifted forward, and the hollow nasal passages within were at the front of the crest and stacked vertically. It also can be differentiated from Corythosaurus by its lack of forking nasal processes making up part of the sides of the crest, which is the only way to tell juveniles of the two genera apart, as the crests took on their distinctive forms as the animals aged.

Lambeosaurus was like other hadrosaurids, and could move on both two legs and all fours, as shown by footprints of related animals. It had a long tail stiffened by ossified tendons that prevented it from drooping. The hands had four fingers, lacking the innermost finger of the generalized five-fingered tetrapod hand, while the second, third, and fourth fingers were bunched together and bore hooves, suggesting the animal could have used the hands for support. The fifth finger was free and could be used to manipulate objects. Each foot had only the three central toes.

Skull of an adult Lambeosaurus lambei, AMNH. Photo by Ryan Somma

Some Lambeosaurus fossils display detailed impressions of the skin, showing that the skin of the body had a “pebbly” texture and that a weblike sheath of skin joined the fingers. When they were first described, these “webbed hands” were thought to prove the now-out-moded idea that duckbills were aquatic. The “web” actually enclosed a fleshy pad on the palm like that on a camel’s foot.
 
Lambeosaurus is the type genus of the Lambeosaurinae, the subfamily of hadrosaurids that had hollow skull crests. Among the lambeosaurines, it is closely related to similar dinosaurs such as Corythosaurus and Hypacrosaurus, with little separating them but crest form. The relationships among these dinosaur genera are difficult to pick out. Some early classifications placed these genera in the tribe Corythosaurini, which was found by David Evans and Robert Reisz to include Lambeosaurusas the sister taxon to a clade made up of CorythosaurusHypacrosaurus, and the Russian genus Olorotitan; these lambeosaurines, with Nipponosaurus.

Kentrosaurus

Wednesday, November 30, 2016

Kentrosaurus by Mueller Art

Kentrosaurus is a genus of stegosaurian dinosaur from the Late Jurassic of Tanzania. The type species is K. aethiopicus, named and described by German palaeontologist Edwin Hennig in 1915. Often thought to be a “primitive” member of the Stegosauria, several recent cladistic analyses find it as more derived than many other stegosaurs, and a close relative of Stegosaurus from the North American Morrison Formation within the Stegosauridae.

Fossils of K. aethiopicus have been found only in the Tendaguru Formation, dated to the late Kimmeridgian and early Tithonian ages, about 152 million years ago. Hundreds of bones were unearthed by German expeditions to German East Africa between 1909 and 1912. Although no complete skeletons are known, the remains provided a nearly complete picture of the build of the animal.

Kentrosaurus skeleton by nikkitikokathi @Flickr

Kentrosaurus was named by the German paleontologist Edwin Henning in 1915, as World War 1 raged, It is ironic that it became one of the many fossil victims of World War 11. One of the two skeletons of Kentrosaurus that were pieced together from the hundreds of bones taken back to Germany was on display in the Humboldt Museum in Berlin and was destroyed during Allied bombing of the city. it has since been replaced by a copy of the second skeleton, which is still on display in Tubingen. The illustration is based on this skeleton but recent evidence from China places the pelvic spike now on the shoulder.
 
Kentrosaurus generally measured around 4.5 metres (15 ft) in length as an adult, and weighed about one tonne (1.1 tons). It walked on all fours with straight hindlimbs. It had a small, elongated head with a beak used to bite off plant material that would be digested in a large gut. It had a, probably double, row of small plates running down its neck and back. These plates gradually merged into spikes on the hip and tail. The longest spikes were on the tail end and were used to actively defend the animal. There also was a long spine on each shoulder. The thigh bones come in two different types, suggesting that one sex was larger and more stout than the other.

Iguanodon

Wednesday, November 30, 2016

A pair of Iguanodon bernissartensis grazing Belgium Early Cretaceous Period Ardeosaurus in foreground Archaeopteryx in background

Iguanodon (meaning “iguana-tooth”) is a genus of ornithopod dinosaur that existed roughly halfway between the first of the swift bipedal hypsilophodontids of the mid-Jurassic and the duck-billed dinosaurs of the late Cretaceous. While many species have been classified in the genus Iguanodon, dating from the late Jurassic Period to the early Cretaceous Period of Asia, Europe, and North America, research in the first decade of the 21st century suggests that there is only one well-substantiated species: I. bernissartensis, which lived from the late Barremian to the earliest Aptian ages (Early Cretaceous) in Belgium, Spain, and possibly elsewhere in Europe, between about 126 and 125 million years ago. Iguanodon were large, bulky herbivores. Distinctive features include large thumb spikes, which were possibly used for defense against predators, combined with long prehensile fifth fingers able to forage for food.

The genus was named in 1825 by English geologist Gideon Mantell, based on fossil specimens that are now assigned to Therosaurus and MantellodonIguanodon was the second type of dinosaur formally named based on fossil specimens, after Megalosaurus. Together with Megalosaurus and Hylaeosaurus, it was one of the three genera originally used to define Dinosauria. The genus Iguanodon belongs to the larger group Iguanodontia, along with the duck-billed hadrosaurs. The taxonomy of this genus continues to be a topic of study as new species are named or long-standing ones reassigned to other genera.

I. bernissartensis skull and neck. Photo by Ghedoghedo

Scientific understanding of Iguanodon has evolved over time as new information has been obtained from fossils. The numerous specimens of this genus, including nearly complete skeletons from two well-known bonebeds, have allowed researchers to make informed hypotheses regarding many aspects of the living animal, including feeding, movement, and social behaviour. As one of the first scientifically well-known dinosaurs, Iguanodon has occupied a small but notable place in the public’s perception of dinosaurs, its artistic representation changing significantly in response to new interpretations of its remains.

Thumb spike

The thumb spike is one of the best-known features of Iguanodon. Although it was originally placed on the animal’s nose by Mantell, the complete Bernissart specimens allowed Dollo to place it correctly on the hand, as a modified thumb. (This would not be the last time a dinosaur’s modified thumb claw would be misinterpreted; NoasaurusBaryonyx, and Megaraptorare examples since the 1980s where an enlarged thumb claw was first put on the foot, as in dromaeosaurids.)

This thumb is typically interpreted as a close-quarter stiletto-like weapon against predators, although it could also have been used to break into seeds and fruits, or against other Iguanodon. One author has suggested that the spike was attached to a venom gland, but this has not been accepted, as the spike was not hollow, nor were there any grooves on the spike for conducting venom.

Hand of Iguanodon shown in the Natural History Museum. Credit to: Ballista.

 

Hypsilophodon

Wednesday, November 30, 2016

Hypsilophodon skeleton

Hypsilophodon (meaning “Hypsilophus-tooth”) is an ornithopod dinosaur genus from the Early Cretaceous period of England.

The first remains of Hypsilophodon were found in 1849; the type species, Hypsilophodon foxii, was named in 1869. Abundant fossil discoveries were made on the Isle of Wight, giving a good impression of the build of the species. It was a small bipedal animal with an herbivorous or possibly omnivorous diet. Hypsilophodon reached up to 1.8 metres (5.9 ft) in length, weighed about 20 kg (45 lbs), and was an agile runner. It had a pointed head equipped with a sharp beak used to bite off plant material, much like modern day parrots.

Hypsilophodon foxii specimens NHM 28707, 39560-1. Original description: Chief part of the vertebral column, with some bones of the extremities, of a young Iguanodon; nat. size. From the Wealden of Cowleaze Chine, Isle of Wight. In the British Museum, and that of J. S. Bowerbank, Esq., F.R.S.

Older studies have given rise to number of misconceptions about Hypsilophodon: that it would climb trees, were armoured, reached a length of 2.3 metres (7.5 ft) and were also found outside of Wight. During the past decades new research has gradually shown this to be incorrect.

Hypsilophodon was a relatively small dinosaur, though not quite so small as, for example, Compsognathus. For Hypsilophodonoften a maximum length of 2.3 metres is stated. This has its origin in a study of 1974 by Galton, in which he extrapolated a length of 2.28 metres based on specimen BMNH R 167, a thigh bone. However, in 2009, Galton concluded that this femur in fact belonged to Valdosaurus and downsized Hypsilophodon to a maximum known length of 1.8 metres, the largest specimen being NHM R5829 with a femur length of 202 millimetres. Typical specimens are about 1.5 metres long. Hypsilophodon would have reached up to half a metre in height. In 2010, Gregory S. Paul estimated a weight of 20 kilograms (44 lb) for an animal two metres in length.

Hypsilophodon

Like most small dinosaurs, Hypsilophodon was bipedal: it ran on two legs. Its entire body was built for running. A light-weight, minimized skeleton, low, aerodynamic posture, long legs and stiff tail, immobilised by ossified tendons, for balance: all would have allowed it to travel remarkably fast for its size. Galton in 1974 concluded it would have been among the ornithischians best adapted to running.

Heterodontosaurus

Wednesday, November 30, 2016

Heterodontosaurus restoration

Heterodontosaurus was a small, lightly-built dinosaur with three different kinds of teeth (hence its name) and a beak. The sharp, cutting front, upper teeth were used for biting against the horny beak, the cheek teeth were for grinding food, and it also had two pairs of long, canine-like teeth that fit into sockets. It had five-fingered hands with claws, and three-toed feet with claws. Its back legs were longer than its front legs. It had a long, stiff tail.

Size comparison between the ornithischian dinosaur Heterodontosaurus and a human. Silhouette by Jaime A. Headden (User:Qilong), and File:Human (1).png. Compilation by Dropzink – Own work and https://qilong.wordpress.com/2012/10/08/pegomastax-and-the-echinodonts/

Heterodontosaurus was about the size of a turkey, 50 inches long (1.3 m) and 20 inches tall (50 cm). It weighed about 42 pounds (19 kg).
Heterodontosaurus lived in the late Triassic to early Jurassic period, roughly 208 to 200 million years ago. Large predators from that time were: pterosaurs, and  crocodilians. Other dinosaurs from South Africa who lived during the lower Jurassic include: Massospondylus, Thecodontosaurus, Lanasaurus, and Lesothosaurus.

Heterodontosaurus was an herbivore (plant-eater). It had three different kinds of teeth. These teeth were specialized for biting, grinding, and tearing its food. They may have stored food in cheek pouches.
Heterodontosaurus was an ornithopod, whose intelligence (as measured by its relative brain to body weight, or EQ) was midway among the dinosaurs.

African heterodontosaurid localities: Tyinindini, Voyizane, and Tushielaw denote Heterodontosaurus finds Carol Abraczinskas, Paul C. Sereno – Sereno PC (2012) Taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. ZooKeys 226: 1-225. doi:10.3897/zookeys.226.2840.

 

Heterodontosaurus was a relatively fast, bipedal (two-legged) dinosaur. It may have run on two legs and walked on four.
A Heterodontosaurus fossil was first found in South Africa. It was named by Alan J. Charig and Alfred W. Crompton in 1962.

CLASSIFICATION
Heterodontosaurus was a very early Ornithischian dinosaur, the order of bird-hipped, herbivorous dinosaurs. It was an Ornithopod ( the bird-footed, beaked, bipedal, herbivorous dinosaurs), and belonged to the family Heterodontosauridae. The type species is H. tucki.

Herrerasaurus

Wednesday, November 30, 2016

Herrerasaurus skeleton

Herrerasaurus was one the first dinosaurs and was native to South America and was the apex predator of its homeland.

Herrerasaurus was one of the earliest dinosaurs. Its name means “Herrera’s lizard”, after the rancher who discovered the first specimen. All known fossils of this carnivore have been discovered in rocks of Carnian age (late Triassic according to the ICS, dated to 231.4 million years ago) in northwestern Argentina.

Skeletal reconstruction of Herrerasaurus

Oscar Alcober, Ricardo Martinez – Alcober OA, Martinez RN (2010) A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. ZooKeys 63 : 55–81. doi:10.3897/zookeys.63.550

The type species, Herrerasaurus ischigualastensis, was described by Osvaldo Reig in 1963 and is the only species assigned to the genus. Ischisaurus and Frenguellisaurus are synonyms.

For many years, the classification of Herrerasaurus was unclear because it was known from very fragmentary remains. It was hypothesized to be a basal theropod, a basal sauropodomorph, a basal saurischian, or not a dinosaur at all but another type of archosaur. However, with the discovery of an almost complete skeleton and skull in 1988, Herrerasaurus has been classified as either an early theropod or an early saurischian in at least five recent reviews of theropod evolution, with many researchers treating it at least tentatively as the most primitive member of Theropoda.

Herrerasaurus ischigualastensis by Sergey Krasovskiy

It is a member of the Herrerasauridae, a family of similar genera that were among the earliest of the dinosaurian evolutionary radiation. Herrerasaurids may be predatory, but are sometimes considered too primitive to be actual theropods.

Giganotosaurus

Wednesday, November 30, 2016

The night is dark, and full of terrors Art by Giganotosaur (Martin Colombo)

Giganotosaurus is a genus of theropod dinosaur that lived in what is now Argentina, during the early Cenomanian age of the Late Cretaceous period, approximately 99.6 to 97 million years ago. The holotype specimen was discovered in the Candeleros Formation of Patagonia in 1993, and is almost 70% complete. The animal was named G. carolinii in 1995; the genus name translates as “giant southern lizard” and the specific name honours the discoverer, Rubén D. Carolini. A dentary bone, a tooth and some tracks, discovered before the holotype, were later assigned to this animal. The genus attracted much interest and became part of a scientific debate about the maximum sizes of theropod dinosaurs.

Giganotosaurus carolinii vs Tyrannosaurus sizes by Scott Hartman

Giganotosaurus was one of the largest known terrestrial carnivores, but the exact size has been hard to determine due to the incompleteness of the remains found so far. Estimates for the most complete specimen range from a length of 12 to 13 m (39 to 43 ft), a skull 1.53 to 1.80 m (5.0 to 5.9 ft) in length, and a weight of 4.2 to 13.8 t (4.6 to 15.2 short tons). The dentary bone that belonged to a supposedly larger individual has been used to extrapolate a length of 13.2 m (43 ft). Some researchers have found the animal to be larger than Tyrannosaurus, which has historically been considered the largest theropod, while others have found them to be equal in size, and the largest size estimates for Giganotosaurus exaggerated. The skull was low, with rugose (rough and wrinkled) nasal bones and a ridge-like crest on the lacrimal bone in front of the eye. The front of the lower jaw was flattened, and had a downwards projecting process (or “chin”) at the tip. The teeth were compressed sideways and had serrations. The neck was strong and the pectoral girdle proportionally small.

Reconstructed skeleton, Australian Museum, Sydney.

Part of the family CarcharodontosauridaeGiganotosaurus is one of the most completely known members of the group, which includes other very large theropods, such as the closely related Mapusaurus and CarcharodontosaurusGiganotosaurusis thought to have been homeothermic (a type of “warm-bloodedness”), with a metabolism between that of a mammal and a reptile, which would have enabled fast growth. It may have been relatively slow-moving, with a suggested running speed of 14 metres per second (50 km/h; 31 mph). It would have been capable of closing its jaws quickly, capturing and bringing down prey by delivering powerful bites. The “chin” may have helped in resisting stress when a bite was delivered against prey. Giganotosaurus is thought to have been the apex predator of its ecosystem, and it may have fed on juvenile sauropod dinosaurs.

Classification

Coria and Salgado originally found Giganotosaurus to group more closely with the theropod clade tetanurae than to more basal (or “primitive”) theropods such as ceratosaurs, due to shared features (synapomorphies) in the legs, skull, and pelvis. Other features showed that it was outside the more derived (or “advanced”) clade coelurosauria. In 1996, Sereno and colleagues found GiganotosaurusCarcharodontosaurus, and Acrocanthosaurus to be closely related within the superfamily Allosauroidea, and grouped them in the family Carcharodontosauridae. Features shared between these genera include the lacrimal and postorbital bones forming a broad “shelf” over the orbit, and the squared front end of the lower jaw.

Holotype skeleton with reconstructed skull, arm, and feet, on the floor in EBPM

Source: www.wikipedia.org / www.natgeo.com

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