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Fossil discoveries proved that Chondrichthyes have lived million years ago and that some had eventually evolved.

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The first chondrichthyans (cartilaginous fishes), distant ancestors of modern sharks and rays, may be indicated by isolated scales and teeth from the Upper Ordovician and Silurian. The first definitive remains containing prismatic calcified cartilage date from the Early Devonian Period.

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421 MYA (Silurian Period) - Holocephali Chimaera

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421 MYA (Silurian Period) - Holocephali Chimaera

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During the Silurian period, the Holocephali and Elasmobranchii classes diverged, differentiating the chimeras of sharks and rays. In the Carboniferous period (358 – 298 million years ago) sharks and rays separated completely.

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Chimaeras are cartilaginous fishes, but not technically sharks. It is thought that sharks and chimaeras may have diverged up to 420 million years ago. Today, many chimaera species are limited to the deep ocean.

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The earliest confirmed monodontoid chondrichthyan order, the Elegestolepidida (Lower Silurian to the Lower Devonian), is known only from scales that lack enamel and basal bone osteons and possess a distinctive neck canal formation. It is the stratigraphically oldest chondrichthyan taxon to develop monodontode scales, which, in contrast to the 'placoid' scales of euselachians, are growing structures.

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An early shark, Cladoselache, from the Upper Devonian of Ohio, reached a length of 2 meters. The skin does not seem to have borne scales, although small multi-cusped tooth-like scales have been found on the edges of the fins, in the mouth cavity, and around the eye.

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380 MYA (Middle of the Devonian) - Cladoselache

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380 MYA (Middle of the Devonian) - Cladoselache

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Cladoselache is the first group to evolve that we would recognise as sharks, but they may in fact have been a type of chimaera. As active predators they had torpedo-shaped bodies, forked tails and dorsal fins.

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359 MYA (Carboniferous Period) - Golden Age of Shark

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359 MYA (Carboniferous Period) - Golden Age of Shark

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The Carboniferous Period is known as the 'golden age of sharks'. An extinction event at the end of the Devonian killed off at least 75% of all species on Earth, including many lineages of fish that once swam the oceans. This allowed sharks to dominate, giving rise to a whole variety of shapes and forms. Some of the most bizarre prehistoric 'sharks' to appear during this time actually evolved out of the chimaera lineage. These include Stethacanthus, which had a truly peculiar anvil-shaped fin on its back.

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358 MYA (Carboniferous Period) - Osteichthyes

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358 MYA (Carboniferous Period) - Osteichthyes

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The Chondrichthyes diversified at different points and achieved high diversity at times. The Osteichthyes (bony fishes) also radiated several times and they have become a major element of marine and freshwater life today.

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The Delphyodontos, a possible early chimaera, seems to have no fins at all and a spherical body covered with small denticles.

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Another chimaera, Echinochimaera, has denticles in different parts of its body. The male also has pelvic claspers and forehead ‘claspers’, short spines over the eyes, as in some modern forms.

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201 MYA (Early Jurassic Period) - Mesozoic Sharks

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201 MYA (Early Jurassic Period) - Mesozoic Sharks

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Some of the sharks from the Paleozoic period survived into the Mesozoic era. During the Jurassic period there was another rapid increase in the number of shark species. This is when all modern shark families and the skates and rays first evolved.

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195 MYA (Early Jurassic Period) - The origin of sharks' fearsome jaws

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195 MYA (Early Jurassic Period) - The origin of sharks' fearsome jaws

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By the Early Jurassic Period, the oldest-known group of modern sharks, the Hexanchiformes or sixgill sharks, had evolved. It was at this point that they evolved flexible, protruding jaws, allowing the animals to eat prey bigger than themselves, while also evolving the ability to swim faster.

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150 MYA (Lower Jurassic) - Rays and Skates

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150 MYA (Lower Jurassic) - Rays and Skates

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The fossil record of rays and skates dates back to the Lower Jurassic period. In contrast to the bony fishes, cartilaginous fishes leave behind little fossil records with the exception of teeth and scales.

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66 to 23 MYA (Palaeogene) - Great white shark evolution

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66 to 23 MYA (Palaeogene) - Great white shark evolution

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Sharks soon began to increase in size once again, and continued to evolve larger forms. It was during this time that Otodus obliquus, the ancestor to megalodon (Otodus megalodon), appeared. O. megalodon is the biggest shark ever to have lived, and scientists consider it one of the most powerful predators to have evolved.

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23 MYA (Neogene) - Hammerhead shark evolution

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23 MYA (Neogene) - Hammerhead shark evolution

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The youngest living group of sharks are thought to be the distinctive hammerhead sharks. The strange shape of their head is thought to mainly help in electroreception (the detection of naturally occurring electric fields or currents) as they hunt for prey. It may also improve their vision, enhance their swimming and refine their ability to smell.

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Current manta rays evolved about 5 million years ago. One of the most distinctive features of manta rays are their enormous and triangular pectoral fins that were developed over the course of the years until they differentiated clearly from other “wingless” bodies of other species of rays.

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He published De aquatilibus duo, cum eiconibus ad vivam ipsorum effigiem quoad ejus fieri potuit, ad amplissimum cardinalem Castilioneum. He attempted the first comparative analysis of sharks and presented 110 species of fish in a much more realistic light.

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He provided an illustration of Great White, under the name De Lamia (a child-eating demon in Greek mythology). He also proposed that it was this fish, and not a whale, that was the culprit behind Jonah’s biblical plight. He postulated that a whale did not have a throat wide enough to swallow a man whole.

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He depicted the Ziphius in his 1560 work Icones Animalium. Researchers believe that the drawn beast may be a great white shark. He published many mythical beasts and in it he included illustrations of Great White and then he studied sharks based on dried specimens thus accounting for the rather desiccated appearance.

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His sailors brought home a shark specimen that was exhibited in London. Afterwards, the name “Sharke” finally finds its place in the English language.

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Italian botanist who published an article, De glossopetris dissertatio, in which he postulated that the mystical glossopetrae were actually fossilized shark teeth.

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Published a comparative study of shark teeth, theorizing for the first time that fossils are the remains of living animals and again suggesting that glossopetrae were indeed fossilized shark teeth after the dissection of a Great White shark head.

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Classified sharks in the group Condropterygii, along with lampreys and sturgeon. Linnaeus continued expanding his classification system, and in 1758 he published the tenth edition of Systema Naturae—the work we consider the beginning of zoological nomenclature. Within this edition, Linnaeus introduced binomial nomenclature, a naming scheme that identifies organisms by genus and species, with an attempt to reflect ranked hierarchies. Linnaeus identified 14 shark species.

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French zoologist that grouped sharks, rays, and chimaeras as "cartilaginous fish," He describes the "white shark" as the largest shark.

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Proposed the generic name Carcharodon in a work by Johannes Müller and Fredrich Henle (here in Smith's later 1840s publication), pulling together the Greek "carcharos" (meaning ragged and used in the association by Belon nearly 300 years earlier) and "odon" (Greek for "tooth"). Thus, Smith was proposing a name meaning "ragged tooth."

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In 1934, William Beebe and Otis Barton Descended 923 m/3,028 ft below the surface off the coast of Bermuda in a bathysphere that was designed and funded by Barton. Here, Beebe observed deep-sea life in its own environment rather than as a captured specimen without being crushed by tremendous underwater pressure.

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Pioneer in shark biology and researched on shark behavior. She theorized that some shark species do not have to swim continuously to breathe.

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1953 - ROV (Remotely Operated Vehicles) 

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1953 - ROV (Remotely Operated Vehicles) 

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The poodle by Dimitri Rebikoff is the first ROV ever built in the year 1953. Rebikoff is a French pioneer in dive equipment and photography. The poodle was an adaptation from his dive scooter equipped with a tether and surface controls. ROVs are cheaper and safer than sending humans deep underwater for sea exploration. Today ROVs utilizes remote sensing and satellite communication technology to connect to researchers in real-time.

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The Trieste is another submersible built by Auguste Piccard, his son Swiss explorer Jean Ernest-Jean Piccard and U.S. Navy Lieutenant Don Walsh. This submersible was used to descend in the Challenger Deep, the deepest known point in the ocean located at the Mariana trench. The Trieste was used for several oceanographic research projects and biological observations.

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Through continuous research, new species of the Chondrichthyan family are being discovered. Current species are also being cultured and protected.

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There are approximately 630 different species of rays and skates that are divided into 18 families when scientifically classified.

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Today, many experts agree that manta rays are the most developed elasmobranches of all in terms of morphology or physical characteristics.

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Recently, the Monterey Bay Aquarium Research Institute launched a project they called the Shark Café Camera Project. Their goal is to research the activities of the Great white sharks at the “Shark Café”, a remote place in the Pacific where they migrate to each year. Since the Shark Café is thought to be the counterpart of a dessert in the ocean, the team is curious about the reasons why the predators go there. The team experimented on using ReplayXD cameras that are used in off road racing and bicycling, customized it so that it can survive being deep underwater and attached it to the dorsal fins of the sharks. Fin cameras provide a clear, stable video from the shark’s perspective.

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Her team has discovered Squalus clarkae from the Gulf of Mexico. Before, it was just another species of dogfish shark but after genetic testing and morphology, it was considered to be a new species and they named it after the “shark lady”, Eugenie Clark.

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Acoustic tags, also called sonic tags, emit sound waves that researchers can track on a ship or shore using a hydrophone. They allow for direct tracking of the tagged animal, which reveals their traveling behavior. However, acoustic tags are more difficult to use in fishes that can shed them like in stingrays. Acoustic telemetry is like improved acoustic tags that are more resilient to tag shedding and can collect information from the tagged animal for multiple years using long-life transmitters. In 2016-2018, a group of ATAP researchers used acoustic telemetry to track the traveling behaviors of stingrays and found that duckbill rays were incredibly mobile, traveling kilometers at high speed and being detected from far away distances while blue stingrays exhibit extreme resident behavior, staying in a fixed area for 3 years

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Modern sharks and toothed whales continued to flourish at the top of the food chain. Hammerheads were the last of the modern shark families to evolve, and did so in the Cenozoic era.

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2020 - Pliotrema kajae and Pliotrema annae

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2020 - Pliotrema kajae and Pliotrema annae

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Two new species of sawsharks discovered in the West Indian Ocean. These species were discovered during research investigating small-scale fisheries operating off the coasts of Madagascar and Zanzibar. The lead author of the research is Simon Weigmann.

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2020 – Fossil discovery of Mennerotodus mackayi and Mennerotodus parmleyi

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2020 – Fossil discovery of Mennerotodus mackayi and Mennerotodus parmleyi

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Estimated to have lived 65 million years ago and 35 million years ago, respectively. These fossil shark specie discoveries were from Georgia and Alabama in the United States, lead by a team of palaeontologists headed by David Cicimurri. They are closely related to modern sand tiger sharks.

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Future direction of the the Chondrichthyan species according to current researches.

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The IUCN/SSC Shark Specialist Group (SSG) has prepared a  status survey containing an attempt to illustrate the threats that sharks and rays face in certain regions of the world to provide comprehensive resource documentations for global action for the conservation of Chondrichthyan fishes.

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Dulvy and co-authors then developed the first global sawfish conservation strategy to combat the endangering species of sharks and rays.

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Species Diversity and Conservation Status of Chondrichthyes of Russian Waters

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Species Diversity and Conservation Status of Chondrichthyes of Russian Waters

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The conservation status of cartilaginous fishes in the waters of Russia is assessed according to the criteria of the International Union for Conservation of Nature. The current state of individual threatened species is briefly characterized.

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Of the 1,041 known species of chondrichthyan (cartilaginous) fishes—sharks, rays, and deep-sea chimaera (aka ghost sharks)—more than 30 percent are endangered, threatened, vulnerable to extinction, or near threatened.

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The large, shallow-water species of the endangered Mekong freshwater stingray (Dasyatis laosensis)—are generally at the greatest risk.

On the Mae Klong River in Thailand, cyanide-containing waste discharged from an ethanol plant in 2016 killed at least 70 giant stingrays, with few large rays having been seen there since.

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Sawfish populations are likely declining due to overharvesting and entanglement in fishing gear, as their long, toothed rostrums become very easily entangled with fishing line and nets.

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One of the most endangered fish in European waters. This family of elasmobranchs (sharks and rays) are particularly susceptible to the combined impacts of fishing and habitat degradation, due to their coastal location and biology (large, flat-bodied animals with low fecundity).

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The Northern River Shark (Glyphis garricki) is one of the rarest species of shark in the world. It is known only from a small number of locations in Western Australia, the Northern Territory and Papua New Guinea. Discovered in Australia in 1986, only 36 specimens have been recorded here since.

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Giant devil rays are ovoviviparous and they often inhabit the deep pelagic waters where they feed on planktons. The giant devil ray is listed as Endangered on the IUCN Red list. Some researchers also considered giant devil rays as  extremely rare due to scarce data about them.

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Ganges shark is only found in rivers and possibly estuaries, with no confirmed records from oceans or seas. It is amongst the 20 most threatened shark species and is listed as a Critically Endangered species in the IUCN Red List. Its population has been steadily decreasing due to overfishing, habitat degradation, increasing river utilisation, and building of dams.

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This specie is rare and catches are almost never reported. Their low numbers combined with habitat destruction have made them critically endangered. In some accounts, the Irrawaddy river sharks are also considered potentially extinct due to the lack of present studies about them.

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The white-spotted Izak or African spotted catshark is a catshark of the family Scyliorhinidae. It is found in the western Indian Ocean off the coasts of Natal, South Africa. The only specimens of this species that have been collected since this date have been those from Madagascar in the late 1980s and early 1990s.