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Evolution of Sharks
93
Transcript
Evolution of Sharks
450-400 million years ago
Events Leading Up
- Laurasia and Gondwanaland were the two main land masses along with a low-lying early ocean
- Ostracoderms predated sharks roughly 60 million years earlier
Events Leading Up
Illustration by: Stephen Greb
Extinction Survival
- Recent evidence hints that sharks were able to survive five mass extinctions by diving to deeper ocean depths
- Although some types of shark had died off due to the extinctions, the species itself was able to survive ... unlike that of the dinosaurs
- This caused scientists to rethink the cause of the many mass extinctions and to what had been the dinosaurs' demise
Adaptations
- Some evolved to eat plankton like the huge Whale Shark known today
- Others had jaws adapted for eating on the ocean floor like the Ptychodus mortoni
- Many early sharks adapted to living in early freshwater oceans as opposed to the sharks of today that live in saltwater environments
- Many prehistoric sharks had strange appendages that may have been used for protection or reproduction purposes
- Not all sharks were fast and fierce predators, some were slower
First Known Sharks
- New research proves that sharks had evolved from a type of bony fish categorized as an Acanthodian, which appeared during the Silurian Period
- These fish are the first known to have developed the cartilaginous body structure of the sharks known today
- The first recognizable sharks appeared in the fossil record during the Paleozoic Era
- Leonodus sharks appeared during the Devonian Period
- The Carboniferous Period is when many sharks began to appear in the fossil record , thus scientists deem it as the "Golden Age" for sharks
Body Structure Evolution
Goblin Shark Jaw Extended
Body Structure Evolution
- Sharks are recognizable throughout the fossil record due to the slow process of evolution (Goblin Shark)
- New evidence hints that sharks evolved much differently than most species - they began with bone skeletons (Gogo Shark)
Credit: Dianne Bray / Museum Victoria
Goblin Shark Jaw Retracted
Examples
- Great Whites had long been thought to be living relatives of Megalodons, but are now known to be related to Mako sharks
Examples
Mako Shark
Megalodon Shark
Evidence
- Due to their body structure being mostly made of cartilage, it is difficult for researchers to find evidence of prehistoric sharks
- The many teeth that they lose frequently have the ability to fossilize, which allow researchers to develop a better understanding of the species
- The first shark skin evidence was found of Elegestolepis
- Shark skin, which is made up of millons of scales called "placoid scales" or "dermal denticles," allow for the animal's speed in the ocean ... of which few pieces of evidence have been found
- Few shark vertebrae and tissue has been recorded
- Radiocarbon dating used on sharks living today has allowed scientists to figure out the sharks' ages as well as sexual maturity, which allows for better understanding of early shark life
Teeth
- Originally thought to be petrified dragon tongues in the Middle Ages
- Used for weapondry
- Assumptions have been made to determine the size of the shark
- Have often been compared to one another
- Radiocarbon dating recently had begun to be used to age-date teeth
Fossils
- Impressions on rocks from shark corpses
Fossils
"Squalicorax shark"
Credit: Michael Brett-Surman, Smithsonian Institution
Aftermath
- Overfishing is threatening the species, having a negative affect on the ecosystem as a whole
- The Great White is considered vulnerable
- Population growth is slow due to a higher age for reproductive maturity as well as low quantity of pups produced each season
Aftermath
Why Sharks Matter
- The keep ecosystems in balance
- Studies of sharks and their evolution allows scientists to have a greater understanding of the Earth's history and evolution as a whole
Citations
Information
- Aidan, Martin R. “Evolution of a Super Predator.” Introduction to Shark Evolution, Geologic Time and Age Determination: Biology of Sharks and Rays, World Wide Web Publication, 2003, www.elasmo-research.org/education/evolution/evol_s_predator.htm.
- Dickerson, Kelly. “Solved: When Earth's Largest Shark Disappeared.” LiveScience, Purch, 22 Oct. 2014, www.livescience.com/48405-megalodon-shark-extinction-date.html.
- Fergusson, I., Compagno, L.J.V. & Marks, M. “Carcharodon Carcharias .” The IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources, 2009, www.iucnredlist.org/details/3855/0.
- Frost, Emily. “Sharks.” Ocean Portal: Find Your Blue, Smithsonian's National Museum of Natural History, 6 Mar. 2018, ocean.si.edu/sharks.
- Gishlick, Alan D., et al. “Triggering Adaptive Radiation.” Understanding Evolution, University of California Museum of Paleontology, 2018, evolution.berkeley.edu/evolibrary/article/adaptiveradiation_01.
- Milman, Oliver. “'Missing Link' in Shark Evolution Found in 380m-Year-Old Australian Fossil.” The Guardian, Guardian News and Media, 29 May 2015, www.theguardian.com/science/2015/may/29/missing-link-in-shark-evolution-found-in-380m-year-old-australian-fossil.
- News Staff / Source. “New Study Confirms Sharks Arose from Acanthodian Fishes.” Science News, Sci-News, 16 Mar. 2017, www.sci-news.com/paleontology/sharks-acanthodians-04706.html.
- Pimiento, Catalina, and Meghan A. Balk. “Body-Size Trends of the Extinct Giant Shark Carcharocles Megalodon: a Deep-Time Perspective on Marine Apex Predators.” US National Library of Medicine National Institutes of Health: Paleobiology, Cambridge University Press, June 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4541548/.
- “Prehistoric Sharks.” Discovery: Shark Week, Discovery Communications, LLC, 18 Sept. 2014, www.discovery.com/tv-shows/shark-week/about-this-show/prehistoric-sharks/.
- Reese, Devin. “Choose Your Weapon: Shark or Vending Machine.” Q?Rius, Smithsonian's National Museum of Natural Histor, 4 Aug. 2014, qrius.si.edu/blog/choose-your-weapon-shark-or-vending-machine#.U-EVykgozMl.
- Rogers, Michael. “A Timeline Of Shark Evolution.” Welcome To SharkSider.com!, Welcome To SharkSider.com!, 10 June 2016, www.sharksider.com/timeline-shark-evolution/.
- Sattler, Brian. “LU Scientists Explore Novel Fossil Dating Method.” Lamar.edu, Lamar University, 2 Apr. 2013, www.lamar.edu/news-and-events/news/2013/04/lu-scientists-explore-novel-fossil-dating-method-.html.
- Saxena, Shalini. “Radiocarbon Dating Finds a Greenland Shark That Could Be 400 Years Old.” Ars Technica, WIRED Media Group, 12 Aug. 2016, arstechnica.com/science/2016/08/radiocarbon-dating-finds-a-greenland-shark-that-could-be-400-years-old/.
- “Shark Evolution.” The Shark Trust, Shark Trust, 2018, www.sharktrust.org/en/shark_origins.
- “Shark Teeth.” Shark Savers: WildAid, WildAid, 2018, www.sharksavers.org/en/education/biology/shark-teeth1/.
- Smithsonian Ocean Team. “Great White Shark.” Ocean Portal: Find Your Blue, Smithsonian's National Museum of Natural History, 27 Dec. 2017, ocean.si.edu/great-white-shark.
- Various Authors. “How Did Prehistoric Sharks Escape Mass Extinction.” Prehistoric Sharks: Sharkopedia Sharkopedia, Discovery, 2018, sharkopedia.discovery.com/shark-topics/prehistoric-sharks/#how-did-prehistoric-sharks-escape-mass-extinction.
- Various Authors. “The Creature That Feasted On Prehistoric Sharks.” Prehistoric Sharks: Sharkopedia Sharkopedia, Discovery, 2018, sharkopedia.discovery.com/shark-topics/prehistoric-sharks/#the-creature-that-feasted-on-prehistoric-sharks.
- Waters, Hannah. “Shark Teeth Tell Great White Shark Evolution Story.” Ocean Portal: Find Your Blue, Smithsonian's National Museum of Natural History, 11 Jan. 2018, ocean.si.edu/ocean-news/shark-teeth-tell-great-white-shark-evolution-story.
- “450 Million Years of Sharks.” Shark Savers: WildAid, WildAid, 2018, www.sharksavers.org/en/education/biology/450-million-years-of-sharks1/.
Images
- https://cdn.thinglink.me/api/image/668642736189997056/1024/10/scaletowidth
- https://cdn.zmescience.com/wp-content/uploads/2018/02/Kurzflossen-Mako.jpg
- http://marinebio.org/oceans/threatened-endangered-species/
- http://ocean.si.edu/ocean-photos/goblin-shark
- http://ocean.si.edu/ocean-photos/squalicorax-shark-fossil
- http://pluspng.com/img-png/shark-png-shark-png-1011.png
- https://www.uky.edu/KGS/education/images/ord_jawless1.jpg
- http://weirdass.co.uk/goblin-shark/
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