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The Chondricthyans (including the sharks and rays) have been around and keeping the ocean's ecosystems healthy for about 420 Million Years. Today, in celebration of this, I've decided to do a little fun post and list the eight times in Earth's history truly massive chondricthyans have emerged. Hope you all enjoy!!! The First is the Devonian, where there is at least one confirmed fossil (CMNH 5238) of a large currently unnamed Ctenacanthiform shark that reached lengths of 4.2-5 meters (13-16 feet) in length. https://www.mdpi.com/1424-2818/15/3/318 The Second is the Mississippian stage of the Carboniferous (358.9-323.2 Million Years ago), a golden age for chondricthyans. The Early Carboniferous saw the emergence of Giant Ctenacanthiform sharks like Saivodus striatus, which grew up to 10-11 meters (32-36 feet) in length. https://www.uky.edu/KGS/fossils/fossil-of-the-month_2022-07_Saivodus.php https://www.uky.edu/KGS/fossils/fossil-of-the-month_2022-07_how-big.php https://www.nps.gov/articles/000/fossils-of-the-2023-national-fossil-day-artwork.htm The Third is the Pennsylvanian stage of the Carboniferous (323.2-298.9 Million Years ago). Like the Mississippian, the Pennsylvanian was also a golden stage for Chondricthyans where large Ctenacanthiforms continued to thrive and large Eugeneodontida edestoids like Edestus (which could grow up to 6.7 meters (22 feet) in length) emerged. Large Ctenacanthiforms from this time include the unnamed Graham Formation Gilkmanius sp., which grew up to 7 meters (22 feet) in length. https://bioone.org/journals/journal-of-vertebrate-paleontology/volume-37/issue-3/02724634.2017.1325369/A-Pennsylvanian-Supershark-from-Texas/10.1080/02724634.2017.1325369.short The Fourth is the Permian (298-252 Million years ago). There were some large sharks, like the Ctenacanthiform Kaibabvenator (which grew up to 4.8-5.48 meters (16-18 feet) in length). But Eugeneodontida by this point contained the largest Chondricthyans alive at this time including Helicoprion (which grew up to 7.6 meters (25 feet) in length) and Parahelicoprion (which could grow up to 12 meters (36 feet) in length). https://www.academia.edu/29941296/Chondrichthyan_and_actinopterygian_remains_from_theLower_Permian_Copacabana_Formation_of_Bolivia https://doi.org/10.1002%2Far.24046 The Fifth is the Early Cretaceous (145-100 Million Years ago). Though the time's aquatic ecosystems was dominated by large marine reptiles, large sharks managed to emerge and fill ecological niches from time to time. This includes the Early Cretaceous Shark Leptostyrax, which grew up to 6.3 meters (20 feet) in length. https://www.researchgate.net/publication/277782424_A_Gigantic_Shark_from_the_Lower_Cretaceous_Duck_Creek_Formation_of_Texas The Sixth is the Late Cretaceous (100-66 Million years ago). Aquatic ecosystems still were dominated by marine reptiles, but large sharks were indeed present. This includes Cretodus crassidens (which grew up to 9-11 meters (29-36 meters) in length) and Ptychodus (which grew up to 10 meters (32 feet) in length). https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0231544 https://www.cambridge.org/core/journals/journal-of-paleontology/article/morphology-and-paleobiology-of-the-late-cretaceous-largesized-shark-cretodus-crassidens-dixon-1850-neoselachii-lamniformes/A670012A44DDC68FC098BB8C73368408 The seventh is the Miocene-Early Pilocene (23-3.6 Million Years ago). This period saw the rise and reign of some of the largest sharks known currently in the fossil record, including Carcharocles (Otodus) megalodon (which grew up to 17 meters (55 feet) in length). https://www.uv.es/everlab/PUBLICACIONES/2017/2017 Martinez-Perez et al HB miocene sharks.pdf https://www.science.org/doi/10.1126/sciadv.abl6529 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9385135/ The eighth is the Early Pliocene-Late Pleistocene (3.6-0.012 Million Years ago). This period saw the last remnants of the large 20 foot + in size carnivorous sharks from the Miocene-Pilocene mega shark era not including the non-Great White shark (Carcharodon carcharias) and not including the large plankton eating sharks make their final stand. These include Hemipristis serra (which grew up to 6 meters (20 feet) in length) and Parotodus benedeni (which grew up to 7.6 meters (24 feet) in length). https://www.app.pan.pl/archive/published/app63/app004542018.pdf https://www.researchgate.net/publication/364591134_A_previously_overlooked_highly_diverse_early_Pleistocene_elasmobranch_assemblage_from_southern_Taiwan https://www.cambridge.org/core/journals/paleobiology/article/chondrichthyan-fossil-record-of-the-florida-platform-eocenepleistocene/2835CCEC27DC8EE0B24A5B62B1416618 I hope this is helpful?