The plesiosaur family was a popular family of marine reptiles in the Mesozoic Era, and recent studies have shown that they have larger red blood cells and are therefore able to dive deeper into the ocean.
The Mesozoic era was the age of dinosaurs and the time of marine reptiles, the image comes from the Internet
During the Mesozoic period, 250 to 066 million years ago, a large number of reptiles lived in the ocean, including the famous plesiosaurs. Plesiosaurs survived for about as long as dinosaurs, and the last plesiosaurs evolved long necks against the sky, such as the famous flakyosaurs.
Image note: Flake dragon with an extra-long neck, image from the Internet
In addition to being able to observe changes directly from the appearance, the researchers tried to explore the evolution of plesiosaurs from a microscopic perspective. Zoologist Kai R. Caspar and others at the University of Bourne found that later plesiosaurs had larger red blood cells, which was the secret of their success in becoming huge and swimming deep into the sea.
To further investigate the adaptability of plesiosaurs to deep-sea life, the researchers made microscopic slices of the skeletons of different species of plesiosaurs, and then compared those large and progressive plesiosaurs with earlier species that lived in shallow offshore environments. The results are consistent with previous speculations, and in the process of spreading into the deep sea, the red blood cells of plesiosaurs gradually became larger, which became a classic evolutionary pattern.
Skeletal slices of plesiosaurs, image from the web
The study's paper, published in Peerj in November 2019, was titled "Hematological convergence between mesozoic marine reptiles (sauropterygia) and extant aquatic." amniotes elucidates diving adaptations in plesiosaurs）
In addition to studying the extinct plesiosaurs, the researchers also analyzed today's marine animals, such as cetaceans, seals and penguins, and found that they had larger and denser red blood cells than their relatives living on land, and the advantage was that they had hemoglobin, which could carry large amounts of oxygen, which supported them to hold their breath and dive in the ocean for long periods of time.
Comparison of the size of red blood cells in different animals, picture from the paper, Chinese: Little Raptor
Kai R. Caspar explains: "It is clear that the ancestors and early members of the plesiosaurs lived in shallow seas before expanding into the open ocean, and in the process the body structure changed accordingly. ”
Plesiosaur evolution, image from the paper, Sinicization; Little Raptor
Plesiosaurs living in shallow waters during the Jurassic period, image from the web
In the repeated diving of plesiosaurs swimming into the deep sea, their red blood cells are getting larger and larger, and the density of red blood cells is becoming higher and higher, so the diving time of plesiosaurs in the later period is getting longer and longer, and the depth of diving is getting deeper and deeper! From an evolutionary perspective, such a change was very beneficial, and the pattern was followed by today's marine life. In today's marine animals (cetaceans, pinnipeds), unusually large red blood cells can be found.
Later plesiosaurs have adapted to life in the deep sea, and the picture comes from the Internet
Today's sperm whales have a strong diving ability, and they have a high density of red blood cells in their blood, pictured from the network
In addition to enlarged red blood cells, later plesiosaurs had more fat, such as aristonectes, which lived in the waters surrounding the Late Cretaceous Antarctica, which could reach 14 meters in length and weigh more than 7 tons. The muscles of the polar plesiosaurs are wrapped in a thick layer of fat, which can play a role in keeping warm, because they are warm-blooded animals!
Polar plesiosaurs are fat-growing plesiosaurs that can survive in cold seas, image from the Internet
Kai Caspar concludes: "This supports our hypothesis that warm-blooded marine organisms are a great adaptation to life in the deep sea. ”
Plesiosaurs diving into the deep sea, image from the Internet
Resources:
1. corinna v. fleischle, p. martin sander, tanja wintrich, kai r. caspar，hematological convergence between mesozoic marine reptiles (sauropterygia) and extant aquatic amniotes elucidates diving adaptations in plesiosaurs，peerj ，november 19, 2019 pubmed 31763069
j.p. o'gorman，s. santillana，r. otero，m.reguero，a giant elasmosaurid (sauropterygia; plesiosauria) from antarctica: new information on elasmosaurid body size diversity and aristonectine evolutionary scenarios，cretaceous research，volume 102, october 2019, pages 37-58
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Text / Paleontological Exploration (Jiang Hong)
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