Alopias grandis may have reached lengths of 13 m (42 ft)

Alopias grandis was an absolutelely enormous  iocene thresher shark. Normal thresher sharks have teeth that are around 10 mm long, the teeth of Alopias grandis are stunning 2 inches long which is around 50mm!!! Scale this up and you end up with a true monster of a shark, although I dont really think that this shark would pose a real danger to humans if it would be alive today as thresher sharks are fish hunters, thrashing them together with their enormous tail although I wouldnt want to be whipped by one.

Hybodontiform (Hybodontiformes)

The largest hydontiformid is Ptychodus was about 32 feet long (10 meters).

Ptychodus is a genus of extinct hybodontiformshark which lived from the Cretaceous to the Paleogene.Ptychodus was about 32 feet long (10 meters) and was unearthed in Kansas, United States.It was covered in placoid scales like other members of Hybodontoidea, reinforced with a large cartilaginous skeleton, and was a bearer of large serrated spines along the dorsal fin.It was a molluscivore predator that dined upon the extremely large bivalves and crustaceans inhabiting the Western Interior Seaway. While there is no solid evidence of members of the Ptychodus species living among other durophagous sharks like members of Heterodontidae (bullhead sharks), it is believed that this Cretaceous macropredator was the precursor to crushing plate teeth seen in many similar sharks and rays.
Ptychodus would have been a benthic predator, straying from the upper layers of the oceans that would have been inhabited by Mosasaurs, Pliosaurs, other sharks such as the Cretoxyrhina, which it was ill-equipped to tackle or compete with. It was capable of growing to enormous size because of this, decreasing the contact it had with macropredatory organisms, and securing a vast food source with little to no competition. Its biological range was linked to the Western Interior Seaway, where it was restricted to the middle and southern end, away from the highly concentrated remains of Cretoxyrhina and Squalicorax in the same period. It is believed that Ptychodus species not only preferred this area because of the subtropical environment, but due to the higher concentration of their prey source Cremnoceramus, Volviceramus and other members of the inoceramids.
Unlike the colossal nektonic planktivores Rhincodon (whale sharks) and Cetorhinus (basking sharks) which relied upon gill rakers to acquire their food, the Ptychodus had a massive arrangement crushing plate teeth. The Ptychodus diet was probably restricted to slow-moving or sessile shellfish, mollusks, invertebrates, larvae, and the occasional sunken carrion of Cretaceous megafauna that it could manipulate into its mouth. One of the largest bivalves at the time was the 9 foot Platyceramus, a shelled mollusk that would have provided a difficult meal for any other creature, but with its crushing palate Ptychodus could have broken though this durable mollusk with ease.Giant ammonites such as the Parapuzosia seppenradensis, members of the Belemnite family, squid, and a variety of Cretaceous crustaceans would also make up the majority of the shark"s food. The Genus name Ptychodus comes from the Greek words ptychos (fold/layer) and odon (tooth), describing the shape of their crushing and grinding teeth that were recovered in deposits around the Niobrara Formation.

Cretoxyrhina mantelli

Cretoxyrhina mantelli was a large shark that lived about 100 to 82 million years ago, during the late Cretaceous period. It is nicknamed the Ginsu shark in reference to the Ginsu knife,since it fed by slicing into its victims with its knife-sharp teeth.It had no common name in the early literature, although over 30 synonyms were assigned to it.Its genus name is creto- (for "Cretaceous") prefixed to Oxyrhina ("sharp-nosed"), its original name.
This shark was first identified by the famous Swiss Naturalist Louis Agassiz, in 1843, as Cretoxyhrina mantelli. However, the most complete specimen of this shark was discovered in 1890, by the fossil hunter Charles H. Sternberg, who published his findings in 1907. The specimen comprised a nearly complete associated vertebral column and over 250 associated teeth. This kind of exceptional preservation of fossil sharks is rare, because a shark"s skeleton is made of cartilage, which is not prone to fossilization. Charles dubbed the specimen Oxyrhina mantelli. This specimen represented a 20-foot-long (6.1 m) shark. It was excavated from Hackberry Creek, Gove County, Kansas.
In later years, several other specimens have also been found. One such specimen was discovered in 1891 by George Sternberg, and was stored in a Munich museum. This specimen was also reported to be 20 feet long, but was destroyed during a bombing raid on Munich in World War II.
Cretoxyrhina is among the most well-understood fossil sharks to date. Several preserved specimens have revealed a great deal of insight about the physical features and lifestyle of this ancient predatory shark.
The fossil teeth of C. mantelli are up to 7 cm long,curved, and smooth-edged, with a thick enamel coating.
The jaws of Cretoxyrhina contained up to seven rows of teeth, with 34 teeth in each row of its upper jaw and 36 in each row of its lower jaw.
Cretoxyrhina mantelli grew up to 7 metres (23 ft) long and rivaled the extant great white shark, Carcharodon carharias, in size.
This shark lived in Cenomanian–Campanian seas worldwide, including in the Western Interior Seaway of North America.
Cretoxyrhina was the largest shark in its time and was among the chief predators of the seas. Fossil records revealed that it preyed on a variety of marine animals, such as mosasaurs like Tylosaurus,plesiosaurs like Elasmosaurus, bony fish like Xiphactinus, and protostegid turtles like Archelon.

Hemipristiis  serra

Hemipristis is a genus of weasel shark which includes the extinct species H. serra, H. curvatus and H. wyattdurhami, although the most popular species by far is H. serra. The last surviving member of the Hemipristis genus is H. elongata, better known as the Snaggletooth shark. H. serra seems to have been a particularly large species of Hemipristis, with the size of the teeth and jaw reconstructions of H. serra being roughly three times larger than the modern species H. elongata. Ergo, if the bite of a large H. serra was three times larger than a big H. elongata, then it is within the realms of possibility that a large H. serra would also be three times as long as a large H. elongata. With a large H. elongata measuring about two hundred and forty centimetres long, this would make a large H. serra a little over seven meters long, bigger than the largest recorded great white shark. In all seriousness though this is not that much a stretch of the imagination, as H. serra was swimming in the oceans at the same time as even bigger sharks such as C. angustidens, C. chubutensis, and of course the mighty C. megalodon!
Hemipristis sharks are noted for having slim pointed teeth in their lower jaws and having broader triangular teeth in the upper jaws. Although this may seem curious it is actually a simple arrangement that allows the lower teeth to pierce the flesh of prey and holding it in place while the upper teeth saw through with their serrations. This allows Hemipristis to remove bite sized chunks from the bodies of large prey. The large size of H. serra meant that it could prey upon larger animals, a statement that is corroborated by the presence of Hemipristis tooth marks upon the bones of mammalian sirenians such as manatees.
Hemipristis serra teeth are very popular collectors’ items on the fossil market due to their colouration which makes them quite unique when compared with the teeth of other shark species.

Squalicorax

Squalicorax is a genus of extinct lamniformshark known to have lived during the Cretaceous period.The name Squalicorax is derived from the Latin "squalo" for shark and the Greek "corax" for raven.
These sharks are of medium size, up to 5 meters  in length. As a lamniform shark, Squalicorax probably would have resembled a modern Great White shark. Aside from swimming the northern oceans between North America, Europe and North Africa, an articulated skeleton of Squalicorax, S. falcatus, has been recovered from the US state of Kansas. This indicates that Squalicorax was also swimming in the Western Interior Seaway that once submerged the mid US, along with much of Canada. These would have been dangerous waters for even a fully grown Squalicorax, as giant mosasaurs such as Tylosaurus were also swimming these waters at the time. The body were similar to the modern gray sharks, but the shape of the teeth is strikingly similar to that of a tiger shark. The teeth are numerous, relatively small, with a curved crown and serrated, up to 2.5 – 3 cm in height (the only representative of the Mesozoic Lamniformes with serrated teeth
Squalicorax is a confirmed dinosaur eater, with evidence of this coming from a metatarsel (foot bone) of a hadrosaurid that has a Squalicorax tooth embedded in it. The general consensus is that the dinosaur had been swept out to sea and had its body scavenged by a wandering Squalicorax that may have picked up on its scent in the water. Other food sources included turtles, mosasaurs, ichthyodectes and other bony fishes and sea creatures.

Leptostyrax macrorhiza may have reached lengths of 12 m (40 ft) and are estimated to have weighed in at 5 tonnes.

A giant shark the size of a two-story building prowled the shallow seas 100 million years ago.
The massive fish, Leptostyrax macrorhiza, would have been one of the largest predators of its day, and may push back scientists" estimates of when such gigantic predatory sharks evolved.
By analyzing ecosystems from the Mesozoic Era, the Leptostyrax macrorhiza ichange the picture of the Early Cretaceous seas.
Previously, researchers thought the only truly massive predators of the day were the fearsome pliosaurs, long-necked, long-snouted relatives to modern-day lizards that could grow to nearly 40 feet (12 m) in length. Now, it seems the oceans were teeming with enough life to support at least two top predator.
As for the ancient shark"s feeding habits, they might resemble those of modern great white sharks, who eat whatever fits in their mouth. If these ancient sea monsters were similar, they might have fed on large fish, baby pliosaurs, marine reptiles and even full-grown pliosaurs that they scavenged.

Cosmopolitodus hastalis was a giant mako shark, up to 8 metres long.

Cosmopolitodus is an extinct genus of sharks  known in the fossil records from the Cretaceous to the Quaternary (age range: from 20.43 to 3.6 million years ago). Fossils are found in the marine strata in the Pliocene of Libya, the Netherlands, Portugal,india,Italy and in the Miocene of Chile, the Czech Republic, France, Malta, the Netherlands, Peru and Portugal.

Paratodus benedeni