Sue" is the nickname given to FMNH PR 2081, one of the largest, most extensive and best-preserved Tyrannosaurus rex specimens ever found.^[2] It has a length of 12.3 metres (40 ft), stands 4 metres (13 ft) tall at the hips, and is estimated to have weighed more than 9 short tons (8.2 t) when alive.^[3][4] It was discovered in the summer of 1990 by Sue Hendrickson, a paleontologist, and was named after her. After ownership disputes were settled, the fossil was auctioned in October 1997 for US $8.36 million,^[5][6] the highest amount ever paid for a dinosaur fossil,^[7] and is now a permanent feature at the Field Museum of Natural History in Chicago, Illinois.
[8]

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Sue

Catalog number	FMNH PR 2081
Common name	Sue
Species	Tyrannosaurus rex
Age	67–65.5 million years[1]
Place discovered	Cheyenne River Indian Reservation, South Dakota
Date discovered	August 12, 1990
Discovered by	Susan Hendrickson

Discovery[edit]

Sue from the front

During the summer of 1990, a group of workers from the Black Hills Institute, located in Hill City, searched for fossils at the Cheyenne River Indian Reservation, in western South Dakota near the city of Faith. By the end of the summer, the group had discovered Edmontosaurus bones and was ready to leave. However, before the group could depart, on August 12, a tire on their truck was deflated.^[9] While the rest of the group went into town to repair the truck, Sue Hendrickson decided to explore the nearby cliffs that the group had not checked. As she was walking along the base of a cliff, she discovered some small pieces of bone. She looked above her to see where the bones had originated, and observed larger bones protruding from the wall of the cliff. She returned to camp with two small pieces of the bones and reported the discovery to the president of the Black Hills Institute, Peter Larson.^[10] He determined that the bones were from a T. rex by their distinctive contour and texture. Later, closer examination of the site showed many visible bones above the ground and some articulated vertebrae.^[11] The crew ordered extra plaster and, although some of the crew had to depart, Hendrickson and a few other workers began to uncover the bones. The group was excited, as it was evident that much of the dinosaur had been preserved. Previously discovered T. rex skeletons were usually missing over half of their bones.^[11] It was later ascertained that Sue was a record 80 percent complete.^[11] Scientists believe that this specimen was covered by water and mud soon after its death which prevented other animals from carrying away the bones.^[2] Additionally, the rushing water mixed the skeleton together. When the fossil was found, the hip bones were above the skull, and the leg bones were intertwined with the ribs. The large size and the excellent condition of the bones were also surprising. The skull was nearly five feet long, and most of the teeth were still intact. After the group completed excavating the bones, each vertebra was covered in burlap and coated in plaster, followed by a transfer to the offices of The Black Hills Institute where preparators began to clean the bones.

Dispute and auction[edit]

McDonald's Fossil Preparation Lab

Soon after the remains were found, a dispute arose over who was the legal owner of the bones. The Black Hills Institute had obtained permission from the owner of the land, Maurice Williams, to excavate and remove the skeleton, and had, according to Larson, paid Williams $5,000 for the remains.^[12] But Williams later claimed that the money had not been for the sale of the fossil and that he had only allowed Larson to remove and clean the fossil for a later sale.^[11] Williams, however, was a member of the Sioux tribe, and the tribe claimed the bones belonged to them. However, the property that the fossil had been found within was held in trust by the United States Department of the Interior. Thus, the land technically belonged to the government. In 1992, the FBI and the National Guard raided the site where The Black Hills Institute had been cleaning the bones and seized the fossil.^[13] The government transferred the remains to the South Dakota School of Mines and Technology, where it was stored until the legal dispute was settled. After a lengthy trial, the court decided that Maurice Williams retained ownership, and the remains were returned in 1995. Williams then decided to sell the remains, and contracted with Sotheby's to auction the property. Many were then worried that the fossil would end up in a private collection where people would not be able to observe it.^[14][15] The Field Museum in Chicago was also concerned about this possibility, and decided to attempt to purchase Sue. However, the organization realized that they might have had difficulty securing funding and decided to request that companies and private citizens provide financial support. The California State University system, Walt Disney Parks and Resorts, McDonald's, Ronald McDonald House Charities, and individual donors agreed to assist in purchasing Sue for The Field Museum. On October 4, 1997, the auction began at $500,000; less than ten minutes later, The Field Museum had purchased the remains with the highest bid of $8,362,500. The winning bid was $7.6 million before Sotheby's commission.^[7]

Preparation and display[edit]

Side view of the display

Sue's original head

The Field Museum hired a specialized moving company, with experience in transporting delicate items, to move the bones to Chicago. The truck arrived at the museum in October 1997. Two new research laboratories funded by McDonald's were created and staffed by Field Museum preparators whose job was to slowly and carefully remove all the rock, or "matrix" from the bones. One preparation lab was at Field Museum itself, the other was at the newly opened Animal Kingdom in Disney World in Orlando. Millions of visitors observed the preparation of Sue's bones through glass windows in both labs. Footage of the work was also put on the museum's website. Several of the fossil's bones had never been discovered, so preparators produced models of the missing bones from plastic to complete the exhibit. The modeled bones were colored in a reddish hue so that visitors could observe which bones were real and which bones were plastic. The preparators also poured molds of each bone. All the molds were sent to a company outside Toronto to be cast in hollow plastic. Field Museum kept one set of disarticulated casts in its research collection. The other sets were incorporated into mounted cast skeletons. One set of the casts was sent to Disney's Animal Kingdom in Florida to be presented for public display. Two other mounted casts were placed into a traveling tour that was sponsored by the McDonald's Corporation.^[2]
Once the preparators finished removing the matrix from each bone, it was sent to the museum's photographer who made high-quality photographs. From there, the museum's paleontologists began the study of the skeleton. In addition to photographing and studying each bone, the research staff also arranged for CT scanning of select bones. The skull was too large to fit into a medical CT scanner, so Boeing's Rocketdyne laboratory in California agreed to let the museum use their CT scanner that was normally used to inspect space shuttle parts.^[16]

Bone damage[edit]

Close examination of the bones revealed that Sue was 28 years old when she died, making her the oldest T. rex known. Her PBS Nova episode reported she died in a seasonal stream bed, which washed away some small bones. During her life, this carnivore received several injuries and suffered from numerous pathologies.^[2] An injury to the right shoulder region of Sue resulted in a damaged shoulder blade, a torn tendon in the right arm, and three broken ribs. This damage subsequently healed (though one rib healed into two separate pieces), indicating Sue survived the incident. The left fibula is twice the diameter of the right one, likely a result of infection. Original reports of this bone being broken were contradicted by the CT scans which showed no fracture. Multiple holes in the front of the skull were originally thought to be bite marks by some, but subsequent study found these to be areas of infection instead, possibly from an infestation of an ancestral form of Trichomonas gallinae, a protozoan parasite that infests birds.^[17] Damage to the back end of the skull was interpreted early on as a fatal bite wound. Subsequent study by Field Museum paleontologists found no bite marks. The distortion and breakage seen in some of the bones in the back of the skull was likely caused by post-mortem trampling. Some of the tail vertebrae are fused in a pattern typical of arthritis due to injury. The animal is also believed to have suffered from gout.^[18] In addition, there is extra bone in some of the tail vertebrae likely caused by the stresses brought on by Sue's great size. Sue did not die as a result of any of these injuries; her cause of death is not known.^[11]
Sue's tendon avulsion was likely caused by contact with struggling prey.^[19]

Display[edit]

Bronze cast of the wishbone of "Sue", Field Museum

Frontal view of Sue's replacement skull.

After the bones were prepared, photographed and studied, they were sent to New Jersey where work began on making the mount. This work consists of bending steel to support each bone safely and to display the entire skeleton articulated as it was in life. The real skull was not incorporated into the mount as subsequent study would be difficult with the head 13 feet off the ground. Parts of the skull had been crushed and broken, and thus appeared distorted. The museum made a cast of the skull, and altered this cast to remove the distortions, thus approximating what the original undistorted skull may have looked like. The cast skull was also lighter, allowing it to be displayed on the mount without the use of a steel upright under the head. The original skull is exhibited in a case that can be opened to allow researchers access for study. When the whole skeleton was assembled, it was forty two feet (twelve meters) long from nose to tail, and twelve feet (four meters) tall at the hips.
The Sue exhibit opened on May 17, 2000, with more than 10,000 visitors.^[20] Paleoartist John Gurche painted a mural of a Tyrannosaurus for the exhibit.^[21]

Ichthyosaurs (Greek for "fish lizard" - ιχθυς or ichthys meaning "fish" and σαυρος or sauros meaning "lizard") were large marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria).
Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 250 million years ago (mya) and at least one species survived until about ninety million years ago,^[1][2] into the Late Cretaceous. During the early Triassic Period, ichthyosaurs evolved from a group of, as yet, unidentified land reptiles that returned to the sea, in a development parallel to that of the ancestors of modern-day dolphins and whales, which they gradually came to resemble in a case of convergent evolution. They were particularly abundant in the later Triassic and early Jurassic Period, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria, in the later Jurassic and Cretaceous Period. In the Late Cretaceous ichthyosaurs became extinct for as yet unclear reasons.
Science became aware of the existence of ichthyosaurs, during the early nineteenth century when the first complete skeletons were found in England. In 1834, the order Ichthyosauria was named. Later that century, many excellently preserved ichthyosaur fossils were discovered in Germany, including soft tissue remains. Since the late twentieth century there has been a revived interest in the group leading to an increased number of named ichthyosaurs from all continents, over fifty valid genera being now known.
Ichthyosaur species varied from one to over sixteen metres in length. Ichthyosaurs resembled both fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges. At least some species possessed a dorsal fin. Their heads were pointed, the jaws often equipped with conical teeth to catch smaller prey. Some species had larger bladed teeth to attack large animals. The eyes were very large, probably for deep diving. The neck was short and later species had a rather stiff trunk. These also had a more vertical tail fin, used for a powerful propulsive stroke. The vertebral column, made of simplified disc-like vertebrae, continued into the lower lobe of the tail fin. Ichthyosaurs were air-breathing, bore live young and were probably warm-blooded.

Ichthyosaurs (Greek for "fish lizard" - ιχθυς or ichthys meaning "fish" and σαυρος or sauros meaning "lizard") were large marine reptiles. Ichthyosaurs belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, although the term is now used more for the parent clade of the Ichthyosauria).
Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 250 million years ago (mya) and at least one species survived until about ninety million years ago,^[1][2] into the Late Cretaceous. During the early Triassic Period, ichthyosaurs evolved from a group of, as yet, unidentified land reptiles that returned to the sea, in a development parallel to that of the ancestors of modern-day dolphins and whales, which they gradually came to resemble in a case of convergent evolution. They were particularly abundant in the later Triassic and early Jurassic Period, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria, in the later Jurassic and Cretaceous Period. In the Late Cretaceous ichthyosaurs became extinct for as yet unclear reasons.
Science became aware of the existence of ichthyosaurs, during the early nineteenth century when the first complete skeletons were found in England. In 1834, the order Ichthyosauria was named. Later that century, many excellently preserved ichthyosaur fossils were discovered in Germany, including soft tissue remains. Since the late twentieth century there has been a revived interest in the group leading to an increased number of named ichthyosaurs from all continents, over fifty valid genera being now known.
Ichthyosaur species varied from one to over sixteen metres in length. Ichthyosaurs resembled both fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges. At least some species possessed a dorsal fin. Their heads were pointed, the jaws often equipped with conical teeth to catch smaller prey. Some species had larger bladed teeth to attack large animals. The eyes were very large, probably for deep diving. The neck was short and later species had a rather stiff trunk. These also had a more vertical tail fin, used for a powerful propulsive stroke. The vertebral column, made of simplified disc-like vertebrae, continued into the lower lobe of the tail fin. Ichthyosaurs were air-breathing, bore live young and were probably warm-blooded.

PREHISTORIC INSECTS

PREHISTORIC SPIDERS              

Evolution of spiders

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A spider in Baltic amber

The evolution of spiders has been going on for at least 400 million years, since the first true spiders (thin-waisted arachnids) evolved from crab-like chelicerate ancestors. Today, there are 42,473 described spider species within the diverse phylum of arthropods.
Major developments in spider evolution include the development of spinnerets and silk secretion.

Early spider-like arachnids

Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids.
Sharing many superficial characteristics with spiders, Trigonotarbida were terrestrial, respired through book lungs, and walked on eight legs with two additional legs adapted to use around their mouth. Arguments still remain open as to whether they possessed the ability to create silk. This had been popular thought for quite some time, until an unpublished fossil was described with distinct microtubercles on its hind legs, akin to those used by spiders to direct and manipulate their silk.
Regardless, Trigonotarbida are not considered true-spiders. They are generally accepted as an independent early offshoot within the Arachnida clade, and not directly ancestral to modern spiders.

Emergence of true spiders[edit]

At one stage the oldest fossil spider was believed to be Attercopus which lived 380 million years ago during the Devonian. Attercopus was placed as the sister-taxon to all living spiders, but has now been reinterpreted as a member of a separate, extinct order Uraraneida which could produce silk, but did not have true spinnerets.

The oldest true spiders are thus Carboniferous in age, or about 300 million years. Most of these early segmented fossil spiders from the Coal Measures of Europe and North America probably belonged to the Mesothelae, or something very similar, a group of primitive spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders. They were probably ground dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were presumably predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction.

As plant and insect life diversified so also did the spider's use of silk.Mygalomorphae and Araneomorphae) appeared more than 250 million years ago, presumably promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline. The oldest mygalomorph, Rosamygale, was described from the Triassic of France and belongs to the modern family Hexathelidae. Megarachne servinei from the Permo-Carboniferous was once thought to be a giant mygalomorph spider and, with its body length of 1 foot (34 cm) and leg span of above 20 inches (50 cm), the largest known spider ever to have lived on Earth, but subsequent examination by an expert revealed that it was actually a middling-sized sea scorpion.

 

Spiders with spinnerets at the end of the abdomen (
By the Jurassic, the sophisticated aerial webs of the orb-weaver spiders had already developed to take advantage of the rapidly diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect "orb" web, the most famous, circular kind one thinks of when imagining spider webs. An examination of the drift of those genes thought to be used to produce the web-spinning behavior suggests that orb spinning was in an advanced state as many as 136 million years ago. One of these, the araneid Nephila jurassica, from about 165 million years ago, recorded from Daohuogo, Inner Mongolia in China, is the largest known fossil spider.^[1]
The 110-million-year-old amber-preserved web is also the oldest to show trapped insects, containing a beetle, a mite, a wasp's leg, and a fly.^[2] The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.
A list of fossil spiders, down to species level, can be found at the American Museum of Natural History's website.[1]

Meganeura

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Meganeura Temporal range: 305–299Ma PreЄ Є O S D C P T J K Pg N Late Carboniferous
Reconstruction
Cast of an original fossil of a Meganeuridae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Superorder:	Odonatoptera
Order:	Meganisoptera
Family:	Meganeuridae
Genus:	Meganeura
Species
Meganeura brongniarti Meganeura monyi Meganeura vischerae

Paleontology portal

Meganeura is a genus of extinct insects from the Carboniferous period approximately 300 million years ago, which resembled and are related to the present-day dragonflies. With wingspans of up to 65 cm (25.6 in), M. monyi is one of the largest known flying insect species; the Permian Meganeuropsis permiana is another. Meganeura were predatory, and fed on other insects.
Fossils were discovered in the French Stephanian Coal Measures of Commentry in 1880. In 1885, French paleontologist Charles Brongniart described and named the fossil "Meganeura" (large-nerved), which refers to the network of veins on the insect's wings. Another fine fossil specimen was found in 1979 at Bolsover in Derbyshire. The holotype is housed in the Muséum national d'histoire naturelle, Paris.

Size[edit]

Controversy has prevailed as to how insects of the Carboniferous period were able to grow so large. The way oxygen is diffused through the insect's body via its tracheal breathing system puts an upper limit on body size, which prehistoric insects seem to have well exceeded. It was originally proposed (Harlé & Harlé, 1911) that Meganeura was only able to fly because the atmosphere at that time contained more oxygen than the present 20%. This hypothesis was dismissed by fellow scientists, but has found approval more recently through further study into the relationship between gigantism and oxygen availability.^[1] If this hypothesis is correct, these insects would have been susceptible to falling oxygen levels and certainly could not survive in our modern atmosphere. Other research indicates that insects really do breathe, with "rapid cycles of tracheal compression and expansion".^[2] Recent analysis of the flight energetics of modern insects and birds suggests that both the oxygen levels and air density provide a bound on size.^[3]
A general problem with all oxygen-related explanations of the giant dragonflies is the circumstance that very large Meganeuridae with a wing span of 45 cm (1.5 ft) also occurred in the Upper Permian of Lodève in France, when the oxygen content of the atmosphere was already much lower than in the Carboniferous and Lower Permian.^[4]

Bechly (2004) suggested that the lack of aerial vertebrate predators allowed pterygote insects to evolve to maximum sizes during the Carboniferous and Permian periods, maybe accelerated by an evolutionary "arms race" for increase in body size between plant-feeding Palaeodictyoptera and Meganisoptera as their predators.^[5]

Ancient 'Frankenstein' Insect Discovered

Wynne Parry, LiveScience Senior Writer   |   July 19, 2011 06:00am ET

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A fossilized Coxoplectoptera larva. Credit: Staatliches Museum für Naturkunde Stuttgart (Germany) View full size image

Insect "Frankensteins" have been discovered among fossils from a deposit in Brazil. The prehistoric creatures had the wings and middle-body segments of a dragonfly's, wing veins arranged like a mayfly and a praying mantis's forelegs.
"It is a very strange mix of characteristics that are otherwise only known for the unrelated insect groups," said one of the researchers to discover this new group of insects, Günter Bechly, a paleontologist at the State Museum of Natural History in Stuttgart, Germany.
From two adult and about 30 larval fossils that came from the Brazilian fossil deposit and are now contained in collections around the world, the researchers created a new order — a broad category that can contain many species — called Coxoplectoptera. This newly named group of insects is long gone; it has no modern descendants, and the fossils date back 120 million years to the early Cretaceous Period. [See image of fossil insect]

A preserved Coxoplectoptera adult.
Credit: Staatliches Museum für Naturkunde Stuttgart (Germany)

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Bechly and fellow discoverer Arnold Staniczek, an entomologist at the museum, realized they had found something special when they came across one of the fossilized adult insects already in the museum's collection while working on a book on the Crato fossil deposit in Brazil from which it came. [Gallery of Colorful Insect Wings]
This deposit has produced tens of thousands of well-preserved fossils during a crucial period for insect evolution, according to Bechly.
Each larva had a body shape that is taller than wide, resembling that of a freshwater shrimp. Based on the larva's shortened mid and hind legs, its thick exoskeleton, beak, large antennae and preying-mantis-like forelimbs, these young insects most likely burrowed part way into the mud underwater and waited to ambush smaller insect prey as they passed, the researchers speculate.
Although it shares characteristics with a number of other insects, Coxoplectoptera's closest living relatives are mayflies. These modern, ephemeral insects die after a brief adult life, of two to three hours to two to three days at most, meant only for reproduction. As adults, they do not eat, said Staniczek. Their ancient relative, however, appears to have been more robust, and like juvenile mayflies, carnivorous.
Coxoplectopterahad forelegs designed for catching and gripping, as well as mouthparts capable of eating — something modern mayflies do not have, he said.
These new insects' anatomy may offer a clue to solving a debate about the origin of insects' wings: Did they start out as stiff outgrowths from plates on the back of the thorax, or midsection, or are insect wings derived from mobile, leg-like appendages? The researchers found evidence in Coxoplectoptera that the wings originated in the back plates; however, these proto-wings appear to have incorporated genes from legs.
The research, with assistance from Roman Godunko, of the University of South Bohemia in the Czech Republic and the State Museum of Natural History in Ukraine, appears in a special issue of the journal Insect Systematics & Evolution.

PREHISTORIC   PLANTS                              
The cladoxylopsids are a group of plants known only as fossils that are thought to be ancestors of ferns and horsetails.
They had a central trunk, from the top of which several lateral branches were attached. Fossils of these plants originate in the Middle Devonian to Early Carboniferous periods (around 390 to 320 million years ago), mostly just as stems.
Cladoxylopsida contains two orders. The order Hyeniales is now included in Pseudosporochnales.
Intact fossils of the Middle Devonian cladoxylopsid Wattieza show it to have been a tree, the earliest identified in the fossil record as of 2007.                                                                                                                                                                                                                   
Gangamopteris is a genus of Carboniferous-Permian, very similar to Glossopteris. Previously, it was classified as fern with reproduction by seed. The genus is usually only applied to leaves, making it an form taxon.^{[verification needed]} Gangamopteris dominates some coal deposits, such as those of the Beacon Supergroup.
In Paleorrota geopark in Rio Grande do Sul, Brazil, were found Gangamopteris obovata. Were located on the Mina Morro do Papaléo in Mariana Pimentel and Quitéria in Pantano Grande. Dating from the Permian and were in the Rio Bonito Formation. In the town of Cachoeira do Sul, met Gangamopteris sulriograndensis were discovered.                                    
Protosalvinia is a prehistoric plant found commonly in shale from shoreline habitats of the Upper Devonian period. The name Protosalvinia is a misnomer. The name literally means early Salvinia, and was given in the erroneous belief that the fossils were an earlier form of the living aquatic fern Salvinia. It is no longer believed that the fossils come from a fern, but deciding exactly what the fossils represent is still a matter of debate. This is surprising when one considers how much is known about the fossils.
The most likely interpretation of Protosalvinia is that it represents either a fossil liverwort or brown alga, although no definitive brown algae have been identified from before the Tertiary period, and examination of the spore structure shows no features in common with living groups of brown algae. The living plant was a thallus with short dichotomous branching. The branches in the largest species were as much as one centimeter across. In some fossils, the branching lobes lie flat, but in others the tips of the branches are curled up over the fossil, giving it a round outline. Embedded in the tissues of the thallus are chambers in which spores (200 micrometre diameter) were produced by meiosis.

Microscope slide mount of Protosalvinia sp. showing bifurcating thallus.

Because Protosalvinia is usually preserved as a compression fossil, it can be difficult to determine whether its anatomy is more like a plant or an algae. Some biochemical evidence favors interpretation as an algae. Lignin and Cutin have been found in the thalli, and sporopollenin in the spore walls. The grouping of the spores found in the thallus favors interpretation as a plant. The absence of any stomata on the surface is inconclusive, as all bryophytes lack stomata on the main body of the plant.
However, the tips of Protosalvinia branches show evidence of conceptacle-like dips.
Protosalvinia is found in association with conodont elements.
For the present, the relationships of Protosalvinia remain uncertain.              SOURCE:WIKIPEDIA

  HELICOPRION:SHARK OR AMMONITE?                                                    Is Helicoprion a shark or an Ammonite? As humans we will ever know, all we can do is imagine. The reason I believe that the Helicoprion tooth spiral isn't a tooth spiral at al  is because. All prehistoric shark teeth have cracks in them from being used to kill their prey. But the fossilized teeth have no cracks in it what so ever. And if you were to take a Helicoprion tooth spiral and turn it on its side(see figure 1.1) it would be in the same shape as an Ammonite's shell. The shell would have sharp barbs all over the shell(see figure 1.2) if it really was a Ammonite shell. The barbs would make a great defense against Hybodus the reason(see figure 1.3) I believe Hybodus would be a predator on Ammonites is because it has teeth that look very similar to that of the Bull shark(see figure 1.4) and that is because the Bull shark's teeth are perfect for crushing shells. And to remind you this is only a theory.                         

Figure 1.1



Figure 1.2

Figure 1.4



Figure 1.3