recursal/Fanatic-Fandom huggingface dataset:
Kronosaurus

***Kronosaurus*** (crow-no-sore-us) was a genus of large Pliosaur that inhabited the Pacific Ocean during the Mid Cretaceous. It is among the largest of all Pliosaurs.

## Characteristics

Upper estimates suggest *Kronosaurus* could reach 10.9 meters in length and 12,100 kg in mass.

*Kronosaurus* had four large flippers for propulsion. It also had a large, powerful head with teeth that could reach 30 cm in length.

## The living creature

*Kronosaurus* was an apex predator. It coexisted with large squid, which it might have fed on. Evidence does suggest that *Kronosaurus* fed on some Plesiosaurs, which were marine reptiles related to the Pliosaurs. *Kronosaurus* is known to have inhabited shallow seas.

## Importance

*Kronosaurus* is perhaps the largest Pliosaur, although, *Pliosaurus* is also a contender for that title.
Top 10 Aquatic Predators

Big thanks to Concaventor Wrangler, DragonSaber73, Michael Benucci, and Therapod King for helping create this list.

In life, *C. megalodon* was an apex predator, feeding primarily on whales. Its bite force has been estimated to have been at least 10 tonnes. It also seems to have rammed prey from below, perhaps to stun them, as the fossilized bones of whales occasionally show signs of serious impact wounds.
Deinonychus

***Deinonychus*** (die-no-nik-us) was a genus of Dromaeosaurid dinosaur that lived in North America during the Early Cretaceous.

## Characteristics

*Deinonychus* could grow to around 3.4 meters in length, 1.1 meter in height, and have a mass in excess of 73 kg, perhaps occasionally reaching 100 kg. It possessed a claw on each foot which could have been used to stab prey.

## The living creature

*Deinonychus* was an effective predator. It had a relatively powerful bite, indicating it could crush bones in its jaw. Its eyes were also facing forward allowing for good depth perception. There is also evidence to suggest it hunted the much larger dinosaur *Tenontosaurus*. If this is true, it would also indicate *Deinonychus* hunted in packs since one could probably not bring down prey that large.

## Importance

The common popular reconstruction of *Velociraptor* is more similar to *Deinonychus* than the former.

The build of *Deinonychus* indicates it had the lifestyle of a fast, agile predator. This seriously suggests it was warm-blooded, further dispelling the dating reconstruction of dinosaurs as massive, sluggish lizards.
Europasaurus

***Europasaurus*** (yer-ope-uh-sore-us) was a genus of Sauropod that lived in what is now Germany during the Late Jurassic.

## Characteristics

*Europasaurus* was fairly small for a Sauropod, reaching around 6.2 meters in length, 2.5 meters in height, and a mass of 800 kg.

*Europasaurus* was a basal, or early, macronarian, related distantly to the North American *Camarasaurus*. As such, its forelimbs were longer than its hind limbs.

## Importance

*Europasaurus* has been studied relatively extensively considering how recently it was described. It is classified as both a Sauropodomorph, an ancestor of the Sauropods, and a Sauropod.

Since Europe during the most of the Mesozoic was largely composed of islands and shallow seas, *Europasaurus* seems to exhibit "insular dwarfism," meaning the species decreased in size over time due to the island habitat. While a similar phenomenon has been observed among other Sauropods, *Europsaurus* is unique as it is the only Sauropodomorph known to have grown smaller instead of larger.
Chasmosaurus

Chasmosaurus by Kevinlaboratory

Chasmosaurus was a genus of Square-like frill and small horned dinosaur that lived in North America during the Late Cretaceous.

It was initially to be called *Protorosaurus*, but this name had been previously published for another animal. All specimens of *Chasmosaurus* were collected from the Dinosaur Park Formation of the Dinosaur Provincial Park of Alberta, Canada. Referred specimens of *C. russelli* come from the lower beds of the formation while *C. belli* comes from middle and upper beds
Baryonyx

***Baryonyx*** (bah-ree-on-icks) was a genus of fish-eating theropod dinosaur that lived in Europe during the Early Cretaceous.

## Characteristics

The holotype, meaning the specimen which the genus is described based on, is thought to have been a juvenile. It was between 7.5 and 10 meters long, and had a mass of between 1,200 and 1,700 kg.

## The living creature

*Baryonyx* had a long, thing snout, roughly comparable to a modern gharial. Its stomach contents also reveal that it ate fish, perhaps wading into a lake, river, or swamp and waiting for a fish to come close enough to snatch.

The stomach contents of *Baryonyx* also reveal that it ate *Iguanodon*, possibly as an active predator, or as a scavenger. *Baryonyx* might have used their large size to intimidate other predators and force them off of kills.

## Importance

When discovered, *Baryonyx* was considered unique due to its gharial-like skull. However, eventually, a skull of *Spinosaurus* was found, which shows that the two genera were related. As a fairly complete Spinosaur, *Barynonyx* has become part of the debate regarding how to reconstruct *Spinosaurus*.

It has been suggested that the African Spinosaur *Suchomimus* is a synonym of *Baryonyx*.
Platybelodon

Two Platybelodon

Platybelodon was a genus of Prehistoric Elephant with a very interesting jaw structure. Its name means "flat spear jaw". This extremely odd structure was probably used for uprooting plants. It could then eat the plants using the channel-like mouth. It may have lived in a swampy environment full of root tubers.

Platebelodon was smaller than modern elephants. It probably lived in more confined spaces in swamps.
Allosaurus

***Allosaurus*** (al-oh-sore-us) was a genus of predatory dinosaur that lived in North America during the Late Jurassic.

## Characteristics

On average, members of the largest *Allosaurus* species were probably around 8.5 meters long, and below 1,000 kg in mass. However, large *Allosaurus* could reach about 9.5 meters in length and 3 meters in height. They could most likely approach 1,500 kg in mass.

The dubious genus *Epanterias*, which might be an *Allosaurus* species or individual, would suggest some could reach around 12 meters on extremely rare occasion. *Saurophaganax*, another roughly 12-meter carnivore, also might be an *Allosaurus* species.

## The living creature

*Allosaurus* was one of the apex predators of its environment. It had a weak bite, roughly comparable to the bite of a lion, but its neck was quite powerful. This suggests to some that it used its head like a "hatchet," slamming its upper jaw into prey. However, not all believe this interpretation.

*Allosaurus* might have fed on Ornithopods like *Camptosaurus* or even *Nanosaurus*. Small Sauropods, perhaps including juveniles belonging to large Sauropod species, might have made up part of the diet of *Allosaurus*. A wound from a tail spike on an *Allosaurus* shows that large Stegosaurs like *Stegosaurus* were also prey, however, these would have been fairly challenging to take down in most cases.

## Importance

*Allosaurus* is one of the most famous predatory dinosaurs. Many specimens have been found, allowing for much research to be conducted on this genus. One specimen, nicknamed "Big Al," was over 95% complete. This individual had vivid evidence of injuries and infections.
Nanosaurus

***Nanosaurus*** (nan-oh-sore-us) was a genus of small Ornithopod dinosaur that lived in North America during the Late Jurassic.

## Characteristics

Most of *Nanosaurus* has been reconstructed. It was small, growing to around 2 meters in length and 60 cm in height. The mass of adults was probably less than 10 kg in most cases.

## The living creature

*Nanosaurus* was a herbivore. Due to its small size, it would have been reasonable prey for many predators in Late Jurassic North America. As such, it probably relied on speed and agility to escape.

## Importance

*Nanosaurus* is best known for the taxonomic debates related to it. Three former genera, *Drinker*, *Othnielia*, and *Othnielosaurus*, as well as a species of *Laosaurus*, are now assigned under *Nanosaurus*.
Saltasaurus

***Saltasaurus*** (saul-tuh-sore-us) was a genus of armored Sauropod that lived in South America during the Late Cretaceous.

## Description

The most recent *Saltasaurus* estimates suggest an upper length of 12.8 meters and a mass of 6,870 kg. While it was a very large animal, it was on the smaller end of the size spectrum for Sauropods.

*Saltasaurus* is known for its osteoderms, meaning it bones that covering part of its skin.

## The living creature

Like all Sauropods, *Saltasaurus* was a herbivore. It has been suggested that the osteoderms acted as "armor," possibly deterring predators such as *Carnotaurus*.

Evidence from a Patagonian sight called "Auca Mahuevo" suggests that hundreds of *Saltasaurus* females congregated to lay large clutches of eggs. This was possibly an annual occurrance.

## Importance

*Saltasaurus* lived during the last stage of the Cretaceous. At this point, the most common large herbivores in North America were Ankylosaurs like *Ankylosaurus*, Ceratopsians like *Triceratops*, and Hadrosaurs like *Edmontosaurus*. However, in South America, Sauropods like *Saltasaurus* were still common at this point.

It has also been suggested that more Sauropods had armor. Other genera such as *Ampelosaurus* have shown this characteristic. It is also possible that it appeared during the later stages of the Cretaceous.
Dilophosaurus

Dilophosaurus

Dilophosaurus was theropod which lived during Early Jurassic period.

## Characteristics

Largest Dilophosaurus found was 6 meters long and 2 meters high. Their mass was around 400 kg. But their most notable feature were two crests on skull. In Jurrssic Park novels and films it was smaller and had things which he hadn't in real life - spitting venom ability and frill around his neck.
Mamenchisaurus

***Mamenchisaurus*** (ma-men-chi-sore-us) was a genus of Asian Sauropod dinosaur that lived during the Late Jurassic and Early Cretaceous. It is best known for its proportionally long neck.

## Characteristics

The most complete specimen indicates a length of about 16 meters for its species. However, some of the other species could probably grow larger. The average length estimate among all the species in the genus is just under 22 meters. The largest species might have reached 35 meters in length and a mass of 80,000 kg.

The neck of *Mamenchisaurus* was around half the length of its body, which stands out even when compared to other Sauropods.

## The living creature

The reason why *Mamenchisaurus* had such a long neck is not certain, but it could have potentially allowed it to feed on multiple trees without having to walk, thus conserving energy.

## Importance

*Mamenchisaurus* is well known for its proportionally long neck. One species known from a small amount of material, *M. sinocanadorum*, is possibly the largest and most massive land animal ever, although there are other contenders, such as *Argentinosaurus*.
Haikouichthys

***Haikouichthys*** (hi-koo-ick-thys) was a genus of vertebrate that lived during the Cambrian period.

## Characteristics

*Haikouichthys* could grow up to about 2.5 cm long. It had a thin body and a prominent dorsal fin running along most of its back. *Haikouichthys* had at least six gills, and possibly as many as nine.

## The living creature

*Haikouichthys* existed during the Cambrian period. As such, nothing is known about its behavior and feeding habits. However, it does seem to have been quite numerous at this time.

## Importance

While the classification of *Haikouichthys* is not certain, it does seem to be one of the first Chordates, the Phyllum containing all dinosaurs, fish, mammals, and reptiles. It is also occasionally termed "the first fish," although it might not have the features required to be termed a "true fish."
Coelacanth

**Coelacanths** (see-lah-canth) are an order of fish that first appeared during the Devonian and are still represented by two known species. Extinct Coelacanth species are known from around the world.

## Characteristics

As the term "Coelacanth" refers to an entire order, the size disparity among the genera is significant. For example, the European genus *Macropoma* grew to around 50 cm. By contrast, *Mawsonia*, a genus that lived in Africa and South America, could grow to around 6.3 meters in length.

As lobe-finned fish, Coelacanths have two sets of large, appendage-like fins. They are very oily in comparison to most other fish.

## The living creature

The lifestyle and habitat of Coelacanth genre is significantly varied. Some genre like *Mawsonia* probably inhabited rivers and lakes. By contrast, *Latimeria*, the only known living genus, lives in extremely deep water.

## Importance

Coelacanths were historically used to explain the evolution of tetrapods. While this is now known not to be the case, Coelacanths are also famous for being thought to have gone extinct during the Late Cretaceous. When living Coelacanths were caught off the coast of Africa in 1938, it raised loads of questions as to what other prehistoric creatures might still be alive. However, it should be remembered that most comparisons between Coelacanths and other prehistoric creatures can easily turn into "weak analogies."
Gorgonopsid

Gorgonopsid was a type of Permian Predator that falls under the former category "mammal like reptile". These reptiles were where all mammals came from, however reptiles also came from the mammal like reptiles, so the term "mammal like reptile" is not used anymore.

Gorgonopsid lived during the late Permian, the period right before the Triassic and the dinosaurs. It is likely that Gorgonopsid died out during the Permian-Triassic Extinction.
Rhamphorhynchus

***Rhamphorhynchus*** (ram-for-inc-us) was a genus of small Pterosaur that lived in Europe during the Late Jurassic.

## Characteristics

*Rhamphorhynchus* was a relatively small Pterosaur. Adults had a wingspan of around 2 meters.

The most famous feature of *Rhamphorhynchus* is its beak, that curves up at the end and possesses relatively few, long, sharp teeth.

## The living creature

Analysis of the scleral rings in the eyes of *Rhamphorhynchus* suggest that it was primarily nocturnal. This might have prevented competition with *Pterodactylus*, which was primarily active during the day.

*Rhamphorhynchus* had a fast growth rate, growing between 130 and 173% during the first year of its life. However, it was nowhere near as fast as some other Pterosaurs. This indicates to some researchers that *Rhamphorhynchus* was cold-blooded, perhaps basking on rocks to warm up as they take longer to lose heat during the night.

Another interesting idea is that *Rhamphorhynchus* dived underwater to hunt like modern cormorants, perhaps accounting for its excellent preservation.

## Importance

*Rhamphorhynchus* has been extensively studied. One interesting specimen contains the remains of a small fish. This specimen was found close to an *Aspidorhynchus*, a Jurassic predatory fish. A possible scenario included the *Rhamphorhynchus* catching the small fish, and then being attacked by the *Aspidorhynchus*, which was "caught" on the wing membrane, and dragged both animals into an anoxic layer of the water and killing them.

*Rhamphorhynchus* was originally named as a different species of *Pterodactylus*.
Amargasaurus

Restoration

***Amargasaurus*** (am-arg-ah-sore-us) is a sauropod from the Early Cretaceous of Argentina which was closely related to *Bajadasaurus*. Only one partial fossil skeleton, discovered in February 1984, is known.

## Characteristics

*Amargasaurus* was a relatively small Sauropod. Based on the currently known remains, the maximum estimated length for *Amargasaurus* is 10 meters. The maximum estimated height is 2.7 meters. The mass of *Amargasaurus* could probably reach 2,600 kg.

The most notable feature of *Amargasaurus* is a series of spines running along the back of its neck.

## The living creature

The use of the spines is not yet known. However, it has been suggested that it turned them toward oncoming predators, perhaps forcing them to abort their attacks.

## Importance

The series of spines made *Amargasaurus* a standout Sauropod. The use of them has been debated. Earlier reconstructions put a sail running between them, comparable to the theropod *Spinosaurus*. However, this is no longer thought to have been present.

If the spines were indeed used against predators, they add to the list of Sauropods that break the "generic" form for protection. Other specializations in other Sauropods include armor in *Saltasaurus* and a tail club in *Shunosaurus*.
Iguanodon

***Iguanodon*** (ig-wah-no-don) was a genus of herbivorous dinosaur that lived in Europe during the Early Cretaceous.

## Characteristics

The only certain species of *Iguanodon* could grow to around 12 meters in length, 4.7 meters in height, and a mass of around 3,080 kg. However, very large individuals might have reached 13 meters in length.

## The living creature

*Iguanodon* was most likely a browser feeding on vegetation at different levels. One of its fingers was well suited to wrapping around objects, meaning that it might have pulled higher branches down to its mouth. It also possessed a "spike" on its thumb. The use of this is uncertain.

*Iguanodon* was large and fairly abundant, indicating that it was the dominant herbivore of its environment. There is evidence that it might have been prey for the Spinosaur *Baryonyx*.

## Importance

*Iguanodon* was the second dinosaur to be named, and the first plant-eating dinosaur. As such, it turned into a wastebasket taxon, receiving a huge amount of species. Today, reclassification has stripped this genus of all except two, of which only one is certain.

Early reconstructions of *Iguanodon* were wrong to an almost comical degree. It was pictured as a large, lumbering, elephantine lizard with a rhino-like horn on its nose (which is now known to be the thumb spike). However, over the years, the genus has been extensively examined, eventually leading paleontologists to our modern reconstructions.
Milo conningia

Milo Conningia is a fish-like creature that existed around 521 million years ago. This creature was significant because it had the very first brain, allowing it to make simple decisions and process basic information. The brain's development was a crucial step in the evolutionary process, setting the stage for more complex organisms and, eventually, humans.
Leedsichthys

***Leedsichthys*** (leads-ick-thiss) was a species of Pachycormid fish that lived during the Jurassic. It is often credited as being the largest fish to have ever lived. *C. megalodon* is also sometimes given this title.

## Characteristics

Size estimates for *Leedischthys* have changed in the past. However, an upper length of 16.5-20 meters is not considered unreasonable. Mass estimates are less certain, but the animal was probably somewhere in the neighborhood of 45,000 kg.

## The living creature

*Leedsichthys* was a filter-feeder. The classification of this genus is not entirely certain, but it was possibly an early form of Teleost fish, the class that contains around 96% of all modern fish species.

## Importance

*Leedsichthys* has been the subject of quite a bit of research and debate. It is also well known due to the fact that it is often credited as the largest fish ever.
Template

Add a brief description of the creature here. Example: "***Spinosaurus*** (spy-no-sore-us) is probably the most famous Spinosaur. It lived in Africa during the Mid Cretaceous."

## Characteristics

Use the first paragraph to discuss size estimates.

Use the next paragraph to discuss other characteristics. This paragraph is optional, but should be added where possible.

## The living creature

Discuss behavior, ecological position, environment, life history, etc. Avoid going into scientific history where possible. If serious debate is ongoing, do not take a side (i.e. semi-aquatic *Spinosaurus* reconstruction).

## Importance

Go over cultural and/or scientific importance
Livyatan

***Livyatan*** (live-ee-ah-tan) was a genus of raptorial sperm and an apex predator. It lived in the oceans of Peru during the Miocene. Some evidence suggests that they also inhabited Australian waters, meaning that this genus might have been more widespread than is currently known.

## Characteristics

Livyatan is thought to have grown to around 17.5 meters. At this size, it would weigh around 50,000 kg. Livyatan had a much shorter, more robust skull than modern sperm whales. It also had a large spermaceti organ which it could have used for communication, echolocation, or to bump other animals.

## The living creature

Livyatan would have been an apex predator of its environment. It is often compared to the killer whale in terms of diet and ecological position. Livyatan probably would have fed primarily on smaller cetaceans and seals.

Livyatan would have faced competition from its infamous contemporary, C. megalodon. While the two predators would almost certainly avoid each other whenever possible, confrontation certainly happened from time to time.

## Importance

Livyatan has become fairly well known due to its large size. On internet forums and social media, it is frequently compared to its rival, C. megalodon in hypothetical battles. It is also possible that Livyatan will topple the claim of C. megalodon's to the highest bite force of any animal as no study has yet been published on the bite of Livyatan.
Pachycephalosaurus

Pachycephalosaurus size comparison from Wikipedia

### Named By:

Charles Gilmore (Troodon) (1931), Barnum Brown and Erich Maren Schlaikjer (1943)

***Pachycephalosaurus*** (Pack-ee-seff-uh-low-sore-us) was a genus of Pachycephalosaurid from Late Cretaceous North America.

## Characteristics

*Pachycephalosaurus* could grow to around 1.5 meters in height and 4.5 meters in length. Large *Pachycephalosaurus* probably had a mass of around 450 kg.

*Pachycephalosaurus* is known for its bony head crest.

## The living creature

*Pachycephalosaurus* was a herbivorous dinosaur.

Pachycephalosaurids possessed distinctive reinforced domes on their heads. The domes are thought by many to have been used for combat between members of the species, similar to horns on bighorn sheep. Support for this hypothesis comes from structural damage to Pachycephalosaurid skulls and the unique bone the made up the crests. This bone contained fibroblasts, which play a critical role in healing damage.

While the reconstruction of Pachycephalosaurids head-butting each other is common, it has also been suggested that the domes were used for flunk-butting. This would have rivals approach each other from opposite sides and stand parallel, striking each other's flanks.

## Importance

*Pachycephalosaurus* is an extremely famous and iconic dinosaur.

*Pachycephalosaurus* also has a somewhat complicated taxonomic history. It was initially assigned to the genus *Troodon*. Pachycephalosaurids in general were seen as Troodonts, which, at the time, were only known from teeth, and, therefore, their striking differences from Pachycephalosaurids were unknown.
Pentaceratops

Pentaceratops ("five-horned face") was a genus of five large horned dinosaur that lived in North America during the Late Cretaceous.

Pentaceratops was about 6 meters (20 feet) long, and has been estimated to have weighed around 5 metric tons (5.5 short tons). It had a short nose horn, two long brow horns, and long horns on the jugal bones. Its skull had a very long frill with triangular hornlets on the edge.
Onchopristis

***Onchopristis*** (on-co-pris-tis) was a genus of giant sawskate that inhabited North Africa, North America, Brazil, and New Zealand, existing from the early to late Cretaceous period. It has been described as a "giant sawfish" in the past, and, while this is no longer thought to have been an accurate description, it likely would have had similar feeding habits.

## Characteristics

*Onchopristis* was a 5-6 meter long giant sawskate with a 2 meter long rostrum or snout.

It has eyes on top of its head that could be used for spotting predators and prey. Like most a bottom-dwelling skate, the mouth and grills of *Onchopristis* were under its body.

Its pelvic fins, the backward set, were probably relatively forward, and were right up against the pectoral fins, the front set.

## The living creature

Modern sawfish typically stun their prey with their rostrum before consuming them. *Onchopristis* is thought to have behaved in a similar way. Like all sawfish and skates, the eyes of *Onchopristis* would have been positioned on top of the animal. However, the rostrum is thought to have had electroreceptors to detect any prey in the water below them like most of modern sharks as well as some rays.

*Onchopristis* first appeared at the beginning of the Cretaceous period, the final of three periods in the Mesozoic. During this period, a warm climate is thought to have resulted in higher sea levels and shallow seas, estuaries, and swampy locations. *Onchopristis* is projected by many to be anadromous, like modern sawfish, meaning that it would migrate into freshwater to spawn.

Evidence does suggest that the theropod *Spinosaurus*occasional preyed on these fishes.

## Importance

Recent analysis revealed that *Onchopristis* probably wasn't a sawfish, but rather, a giant skate with a rostrum. This puts modern *Onchopristis* size estimates at around 5-6 meters long. While they are similar in some ways to sawfishes, they would have looked markedly different.
Pterodactylus

***Pterodactylus*** (tare-oh-dak-till-us) was a genus of small Pterosaur that lived in Europe during the Late Jurassic.

## Characteristics

*Pterodactylus* adults probably had a wingspan of around 1.04 meters.

The beak of *Pterodactylus* was straight, whereas many Pterosaurs had a curved beak. A small crest was present on its head. Impressions have revealed that *Pterodactlyus* possessed a throat pouch.

## The living creature

Analysis of the scleral rings in the eyes of *Pterodactlyus* indicate it was most active during the day, which possibly allowed for it to avoid competition with *Rhamphorhynchus*, another Pterosaur of roughly similar size that was more active during the night.

The growth of *Pterodactlyus* has been studied, indicating the animal reached adulthood in just a few years.

## Importance

*Pterodactlyus* was named in 1809, about 15 years before the first dinosaur known to paleontology, *Megalosaurus*. Pterodactylus turned into a "wastebasket taxon," which means researchers rushed to assign species into its genus without proper study. More recently, *Pterodactlyus* has been reduced to just one species.

Due to how long it has been known to paleontology, *Pterodactylus* has also been studied extensively, perhaps more so than any other Pterosaur. It's name is also the origin of the common term "Pterodactyl." However, the popular Pterodactyl meme is far more akin to *Pteranodon* than *Pterodactylus* itself.
Oldhamina

Oldhamina appears to be a fossil caused by a living organism and was once speculated to be the first complex Precambrian life form. However, this idea was incorrect. The odd leaf-like imprints of Oldhamina were actually made by natural causes. Many other creature-like Precambrian imprints were later proven to be false alarms. Only when Cryptozoon was found, real evidence of larger Precambrian life forms could not be dismissed. Cryptozoon itself was argued over for a little while until living examples were discovered in Shark Bay, Australia.
Anzu

Anzu from "A Dinosaur A Day"

***Anzu*** (an-zoo) was a genus of Oviraptorosaur that lived in what is now the United States during the Late Cretaceous.

## Characteristics

Large ***Anzu*** could reach about 3.5 meters in length and 1.5 meters in height. With larger individuals thought to reach about 300 kg in mass, *Anzu* is the largest known North American Oviraptorosaur. However, it is smaller than the Mongolian genus *Gigantoraptor*.

## The living creature

The specimens of *Anzu* were recovered from mudstone, suggesting they lived in a floodplain, an area quite different from the more arid deposits from which many of the Asian Oviraptorosaurs hail. The animal was probably omnivorous, eating plants and small animals.

*Anzu* had a distinctively large crest. Due to the very thin bones that form it, it was most likely used for display.

## Importance

*Anzu* is unique among North American Oviraptorosaurs for being fairly complete. A skull and a number of fossils representing other parts of the skeleton were recovered.
Acrocanthosaurus

***Acrocanthosaurus*** (ack-row-can-tho-sore-us) was a genus of Carcharodontosaurus that lived in North America during the Early Cretaceous 112 million years ago.

## Characteristics

Growing to around 11 meters long and 4 meters tall, *Acrocanthosaurus* was one of the largest known land predators in North American history.

It is most known for a hump that ran down its back. This may have served as storage for extra fat when food was scarce.

*Acrocanthosaurus* is also known for its relatively powerful arms. While, like most large terrestrial predatory dinosaurs, they look small in comparison to the animal, analysis of their muscular attachments has revealed that they would have been many times stronger than a human's.

## The living creature

*Acrocanthosaurus*, like other members of its family, seems to have been a specialist predator of long-necked Sauropods. Direct evidence suggests a predator-prey relationship between *Acrocanthosaurus* and the enormous herbivore *Sauroposeidon*.

*Acrocanthosaurus* probably also fed on other prey such as ornithopods of varying sizes.

## Importance

The predator-prey relationship between *Acrocanthosaurus* and *Sauroposeidon* is fascinating as the herbivore is far larger.

*Acrocanthosaurus* is the state dinosaur of Oklahoma. This is interesting as Oklahoma already has a state fossil, *Saurophaganax*.
Xiphactinus

***Xiphactinus*** was a genus of large predatory fish that lived in North America's interior seaways during the Late Cretaceous.

## Characteristics

*Xiphactinus* could grow to around 6 meters long. It had a streamlined body, and large fangs.

## The living creature

*Xiphactinus* was a hyper carnivore. One famous specimen of a 4-meter individual contained the remains of a *Gallicus* that was nearly 2-meters long itself. While the ingestion of the *Gallicus* likely killed the *Xiphactinus* as well, it is a testament to the aggression and ferocity of this fish.

## Importance

Xiphactinus is famous for its ferocious appearance. It has been featured multiple times in television, including the *Walking With Dinosaurs* special *Sea Monsters* and the Animal Planet series *River Monsters*.
Basilosaurus

***Basilosaurus*** (bas-ill-oh-sore-us) was a genus of large predatory whale that is known from the United States and regions that were formerly the Tethys Ocean. Possible remains were found in Antarctica, suggesting a wide geographic distribution.

## Characteristics

Estimates suggest that the largest Basilosaurus species could reach about 20 meters in length. It was long and "serpentine," leading to it being initially mistaken for a Mosasaur, hence its name. Therefore, it was not as massive as many shorter whales. However, it was one of the largest mammals to exist before the Miocene, when truly massive whales first appeared. *Basilosaurus* also possesses two hind limbs, showing the transition between early whales and fully aquatic whales.

## The living creature

*Basilosaurus* was an apex predator, probably feeding on smaller whales like *Dorudon*, large fish, and sharks. However, its brain was smaller in comparison to modern toothed whales. As such, it probably lacked social and linguistic capabilities. It also lacked the "melon," which is a large organ in modern toothed whales that is used for echolocation.

## Importance

*Basilosaurus* is one of the most famous prehistoric whales. It was also a "wastebasket taxon" at one point, meaning that other animals were assigned to the *Basilosaurus* genus without serious scientific study, meaning that the genus was later stripped of most of its species.
Tyrannosaurus

A deviant art user's reconstruction of Tyrannosaurus

***Tyrannosaurus rex*** (tie-ran-oh-sore-us) is one of the most famous of all dinosaurs, easily the most famous. It is also one of the largest known predatory dinosaurs.

## Characteristics

The largest mostly complete specimen, nicknamed "Sue," indicates an upper size of 12 meters in length, and 3.6 meters at the hips. Most modern estimates indicate Sue exceeded 8,000 kg, although, most individuals would not be this massive. Isolated remains suggest some could have exceeded "Sue" in size, and possibly reached 10,000 kg.

Scaly skin casts do suggest that *Tyrannosaurus* did not have a feather covering. The arms of *Tyrannosaurus* were proportionally very small, although, muscular attachments indicate they would be significantly stronger than a human's. *Tyrannosaurus* also had excellent 3D vision, and it could probably see even better than modern birds of prey.

## The living creature

*Tyrannosaurus* would have been the apex predator of its environment. It was one of the most intelligent dinosaurs, possessing a relatively large and complicated brain. It also would have been capable of tackling some of the most formidable prey items of the time including *Ankylosaurus*, *Edmontosaurus*, and *Triceratops*, as its bite is thought to have been stronger than any other known land animal.

Some have suggested *Tyrannosaurus* to be a scavenger. Due to its predatory adaptation, it probably was an active predator, however, it would likely also resort to scavenging if it was presented with a chance to.

Much has been learned about the growth curve of *Tyrannosaurus*. Younger individuals were much less robust than adults, even if they attained the same proportions. These younger specimens were once thought to have been males and the stockier individuals were thought to have been females. However, now that analysis from multiple angles has strongly suggested them to represent immature and mature specimens, sexual dimorphism one way or the other cannot be confirmed.

## Importance

Aside from being one of the most famous dinosaurs of all time, *Tyrannosaurus* is probably also the most studied and debated. A particularly interesting case would be the discovery that *Tyrannosaurus* was actually a junior synonym for *Manospondylus*, meaning that material relating to *Tyrannosaurus* was found earlier and named something different. However, the ICZN made an exception to typical nomenclature rules, and *Tyrannosaurus* is still the official name of the genus.

A *Tyrannosaurus* bone was cut open, revealing soft tissue. For a long time, researchers believed that only bones could be preserved. Therefore, this is considered a significant discovery.

*Tyrannosaurus* is also one of the largest predatory dinosaurs of all time, and possibly the most massive. Today, the predatory dinosaur most frequently cited as being the "biggest," *Spinosaurus*, is thought by some to have been quadrupedal and fairly lightly built, although, others strongly disagree with this assessment.
Pterodaustro

***Pterodaustro***  (tear-oh-doss-chrow) was a genus of Pterosaur that lived in South America during the Early Cretaceous.

## Description

Large *Pterodaustro* had a wingspan of around 2.5 meters.

## The living creature

*Pterodaustro* possessed small grinding teeth in its upper jaw and around a thousand bristle like structures it its mouth, which were constructed similarly to normal teeth. This means that *Pterodaustro* was a filter-feeder, possibly living a life similar to modern flamingos, combing for small crustaceans. Some evidence from the scleral rings, a bone found in the eyes, suggests that *Pterodaustro* was nocturnal.

Bacteria picked up by flamingos in their diet leads to their distinctive pink color. This has led to speculation that Pterodaustro was also pink.

*Pterodaustro* seems to have also had stones or gastroliths in its gizzard, which would have aided in digestion.

Research also indicates *Pterodaustro* reached maturity relatively quickly, possibly attaining their adult size in around six years. This growth rate is not remarkable among Pterosaurs, however.

## Importance

The diet of *Pterodaustro* makes it particularly interesting. Its filter feeding mechanisms are, at the time of writing, unique among Pterosaurs.
Brachiosaurus

***Brachiosaurus*** (brak-ee-oh-sore-us) was a large Sauropod that lived in North America, and Asia during the Late Jurassic.

## Characteristics

The remains of *Brachiosaurus* are somewhat incomplete, so the true size of the creature is not certain. However, upper estimates place its length at 21-27 meters and height at 13-15 meters. *Brachiosaurus* also possessed a somewhat distinctive head. Its skull was tall and fairly stout for a Sauropod.

## The living creature

*Brachiosaurus* would have probably been a high browser, capable of feeding on treetops. This would have allowed it to avoid competition with other herbivores such as Stegosaurs and smaller Sauropods. Large predators like *Allosaurus* could have posed a threat to younger individuals, but adult *Brachiosaurus* might not have had any natural predators.

## Importance

*Brachiosaurus* is one of the most famous Sauropods, perhaps only behind *Brontosaurus*. Despite this, limited material has made it hard to determine much about this genus. The species *B. brancai* was moved to the genus, *Giraffatitan*.
Tylosaurus

***Tylosaurus*** (tie-lo-sore-us) was a genus of large Mosasaur that lived in North America during the Late Cretaceous.

## Characteristics

The largest species of *Tylosaurus* could grow to around 14 meters in length. It was fairly lightly built in comparison to *Mosasaurus*, however.

## The living creature

Tylosaurus was an apex predator, feeding primarily on large fish and smaller marine reptiles. It also might have attacked low flying Pterosaurs. It had to coexisted with other Mosasaur apex predators like Mosasaurus through "niche partitioning," meaning that the two animals used their environment differently. However, individuals from the two species certainly confronted each other at times.

## Importance

*Tylosaurus* is one of the largest known Mosasaurs. Plenty of material has been assigned to the *Tylosaurus* genus, which contains eight recognized species.
Sauroposeidon

Sauroposeidon compared to a human

Sauroposeidon was extremely huge, upper estimates put its length at 35 meters. It was more gracile than Giraffatitan in build, however this would actually make it larger since its neck would have to be so long. It would also be longer by around 10 meters.

However, at the same time this gracile build means that it was most likely NOT the largest dinosaur ever. Argentinosaurus was the same length yet it was more heavily built. However, with only some neck vertebrae and ribs found, the exact size cannot be judged. It was probably smaller than Dreadnoughtus, a titanosaur that was 45 percent complete, and 70 percent of it can be reconstructed, therefore, it can have more accurate size estimates. The title of the "largest dinosaur ever" still remains open to debate.
Andrewsarchus

***Andrewsarchus*** (an-drew-sar-cuss) was a genus of mammal that lived during the Eocene.

## Characteristics

Not much is known about *Andrewsarchus*. It was once thought to be a relative of the Mesonychids and the largest terrestrial mammal predator. However, this is no longer certain. What is known is that its skull was nearly a meter long.

## The living creature

Due to its large size, *Andrewsarchus* could probably drive smaller carnivores from their kills. It possibly was also an active predator. It might have had some competitors such as *Hyaenodon* and some species of Enteledont.

*Andrewsarchus* lived during the Eocene epoch, a time where the world was much hotter than today. The Eocene also may have had wet periods, as the Ancient Tethys Sea was in Central Asia at the time.

## Importance

*Andrewsarchus* has become one of the more famous prehistoric animals as it has been historically credited as the largest terrestrial mammalian predator. However, comparisons have been drawn between the skull of *Andrewsarchus* and the skulls of the Enteledonts, a family of predators distantly related to hippopotemi. This would greatly reduce its projected size. Since no other remains are known, the true physiology and taxonomy of this animal are also unknown.
Top 10 Morrison Formation Dinosaurs

Big thanks to Dinosaur action, The Alizarr, and Therapod king for helping create this list.

The Morrison Formation is a Late Jurassic rock formation that lies under much of the Western United States. Not all of it is exposed, but that which is has produced more dinosaur fossils than any other formation in North America. As such, it contains a wealth of iconic dinosaurs, along with other, more recent, but still significant discoveries. Here is a list of the top ten dinosaurs of the Morrison Formation.

*Stegosaurus* is one of a very small group of dinosaurs, including *Triceratops* and *Tyrannosaurus*, that are truly well known by the general public. It is featured extremely often in dinosaur-related books, toys, documentaries, and films.

## **Honorable mention**

*Saurophaganax* - A relative of *Allosaurus* that could grow to around 12 meters long. It was also recommended for first place by a contributor. However, some paleontologists question the validity of this genus, meaning that it did not make the final list.
Microraptor

***Microraptor*** (mike-row-rap-tr) was a genus of small predatory dinosaur that lived in what is now China during the early Cretaceous.

## Characteristics

Growing to between 77 and 120 cm in length, a wingspan of under a meter, and about 1 kg in mass, *Microraptor* was among the smallest dinosaurs.

*Microraptor* is thought to have been covered in iridescent plumage like a modern starling. However, the analysis of the scleral rings, bones in the animal's eyes, have suggested it was nocturnal, and no modern nocturnal birds are known to have had iridescent plumage.

## The living creature

*Microraptor* possessed four wings. Whether or not is was an effective flyer is still debated, but, at the very least it lived in trees, perhaps gliding. Computer analysis from some paleontologists does suggest that *Microraptor* was, in fact, capable of true powered flight.

*Microraptor* probably fed on small mammals. It might have also eaten insects and small reptiles. It seems to have been fairly common in its environment.

## Importance

*Microraptor* was named under somewhat scandalous conditions when a fossilized "creature" composed partially of *Microraptor* pieces was smuggled for sale.

Due to the large number of *Microraptor* remains, it has been studied extensively. The presence of four-winged dromaeosaurids suggests to some that modern birds also went through a four-winged stage in their evolution.
Saurolophus

***Saurolophus*** (sore-ol-oh-fuss) was a genus of very large Hadrosaur that lived in Asia and North America during the Late Cretaceous.

## Characteristics

The Canadian species of *Saurolophus* is estimated to have reached about 8.2 meters in length, 2.5 meters in height, and a mass of around 3,000 kg, a fairly normal size for a Hadrosaur. However, the Mongolian species was much larger, growing to around 13 meters in length, 4 meters in height, and a mass that has been estimated up to 11,000 kg.

*Saurolophus* possessed a small crest on its head that was mostly solid. However, it did have a cavity, which is unusual for its subfamily. Nevertheless, in terms of overall body layout, *Saurolophus* is considered to be a Saurolophine Hadrosaur.

## The living creature

The scleral rings, bones within the eyes, have been analyzed in some Hadrosaurs, showing that they were probably active for a few hours in both the day and the night.

*Saurolophus* was a herbivore. It would have spent most of its time on all fours, where it would be in a position to feed on low vegetation. However, it might have been able to balance on its hind legs to reach plant material higher up.

## Importance

*Saurolophus* is the genus after which the Saurolophine Hadrosaurs are named. This is the group of Hadrosaurs noted for having solid crests or no crests at all. The group contains the famous *Edmontosaurus*.

Several other specimens have been found in China and the United States which might belong to the *Saurolophus* genus.
Wiwaxia

Royal Ontario Museum's Wiwaxia Turntable

***Wiwaxia*** (wih-wacks-eeh-ah) was a genus of bizarre animal that lived during the Cambrian.

## Characteristics

*Wiwaxia* grey to around 5 cm long. How tall the animal got is uncertain. However, it possessed spines sticking out of its back that could reach 5 cm long. Its body was covered in hard "plates" that might have served as protection.

## The living creature

The lifestyle of *Wiwaxia* is uncertain. The spines and plates are thought to have been used for defense against predators. On its bottom, *Wiwaxia* possessed a slug-like "foot" and a mouth. It possibly moved along the seafloor and consumed bacteria that grew in large mats during the Cambrian.

## Importance

*Wiwaxia* fossils have been found in large numbers on several different continents. However, the classification of the animal is uncertain. It is thought to have belonged to Lophotrochoza, a classification containing mollusks and other relatives. However, this area is being debated intensely by paleontologists. *Wiwaxia* is one of the center pieces of the debate.
Dreadnoughtus

***Dreadnoughtus*** (dred-not-us) is a genus of herbivorous Sauropod dinosaur that lived in South America.

## Characteristics

The holotype, the first and only specimen found, indicates a length of 26 meters and a shoulder height of 6 meters. The mass of the animal has been disputed. Estimates range from 21,000-65,000 kg.

## The living creature

*Dreadnoughtus* was an extremely large herbivore. It probably had few natural predators. The holotype does have tooth marks that appear to be from some Megaraptoran predator. However, this was quite possibly scavenging.

## Importance

*Dreadnoughtus* is important as over 45% of the individual was found. This has been used to construct more than 70% of the animal accurately, as some bones can be mirrored (i.e. left thigh and right thigh). This is revolutionary for a large Titanosaur. For comparison less than 3% of *Puertasaurus* is known, and, under 10% of the famous *Argentinosaurus* can be reconstructed. This has led *Dreadnoughtus* to be considered by some to be the largest ever land animal, as it is arguably the largest land animal that can be reconstructed with relative certainty.
Majungasaurus

Majungasaurus was an Abelisaurid Theropod dinosaur from Late Cretaceous Madagascar. It has received a huge surge of popularity in recent years due to extensive evidence suggesting that it was a cannibalistic dinosaur feeding on other Majungasaurus individuals. It has been presented in multiple dinosaur documentaries. Tooth prints in other individuals seem to suggest with very little doubt that this was a secondary food source. Some evidence also suggests that it preyed on the medium-sized Titanosaur Rapetosaurus.