We have classified them as an extinct order of marine reptiles from the Mesozoic era. We know that they were visibly dolphin-like in appearance and share some other qualities as well. They were warm-blooded, used their colouration as camouflage and had insulating blubber to keep them warm.
Ichthyosaurs are interesting because they have many traits in common with dolphins, but are not at all closely related to those sea-dwelling mammals. We aren't exactly sure of their biology either. They have many features in common with living marine reptiles like sea turtles, but we know from the fossil record that they gave live birth, which is associated with warm-bloodedness. This study reveals some of those biological mysteries.
We find their fossil remains in outcrops spanning the mid-Cretaceous to the earliest Triassic. As we look through the fossils, we see a slow evolution in body design moving towards that enjoyed by dolphins and tuna by the Upper Triassic, albeit with a narrower, more pointed snout.
Johan Lindgren, Associate Professor at Sweden's Lund University and lead author on the paper, described the 180 million-year-old specimen, Stenopterygius, from outcrops in the Holzmaden quarry in Germany.
Both the body outline and remnants of internal organs are clearly visible in the specimen. Remarkably, the fossil is so well-preserved that it is possible to observe individual cellular layers within its skin.
Researchers identified cell-like microstructures containing pigment organelles on the surface of the fossil.
This ancient skin revealed a feature we recognized from marine dwelling animals, the ability to change colour, providing camouflage from potential predators. They also found traces of what might have been the animal's liver.
When they put some of the tissue through chemical analysis, it was consistent with what we'd look for in adipose tissue or blubber. Not surprising as dolphins today use blubber for buoyancy and to help to thermally insulate for thermal regulation in cold seas. It's a highly useful adaptation and one that led me to wonder what other vertebrates might use blubber or some other adaptation to maintain a warmer body temperature independent of icy cold conditions.
Today, blubber is an important part of the anatomy of seals, walruses and whales. It covers the core of their bodies, storing energy, insulating them from cold seas and providing extra buoyancy.
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| Stenopterygius quadriscissus |
This ancient skin revealed a feature we recognized from marine dwelling animals, the ability to change colour, providing camouflage from potential predators. They also found traces of what might have been the animal's liver.
When they put some of the tissue through chemical analysis, it was consistent with what we'd look for in adipose tissue or blubber. Not surprising as dolphins today use blubber for buoyancy and to help to thermally insulate for thermal regulation in cold seas. It's a highly useful adaptation and one that led me to wonder what other vertebrates might use blubber or some other adaptation to maintain a warmer body temperature independent of icy cold conditions.
Today, blubber is an important part of the anatomy of seals, walruses and whales. It covers the core of their bodies, storing energy, insulating them from cold seas and providing extra buoyancy.
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| A rather fetching Walrus, Odobenus rosmarus |
Blubber layers can be incredibly thick. Walruses deposit most of their body fat into a thick layer of blubber — a layer of fat reinforced by fibrous connective tissue that lies just below the skin of most marine mammals.
This blubber layer insulates the walrus and streamlines its body. It also functions as an energy reserve. Blubber covers the core of their bodies but does not grace their fins, flippers and flukes.
They have a few tricks up their sleeves to make this happen. Sharks have evolved specialized physiology to keep their metabolic rate high and their hearts are able to contract in the icy depths because of a special protein. These adaptations allow sharks to enjoy a wide range of habitats and follow their food from warm tropical seas to the icy waters of the North Pacific.
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| Gray Shark, Carcharhinus amblyrhynchos |
In a very cool bit of science, researchers sequenced a shark's heart transcriptome – the messenger molecules produced from the shark’s genome, including those active in making proteins. Then they categorized the proteins based on their functions.
What they found that the proportions of white shark proteins in many categories matched humans more closely than zebrafish. Of particular interest was that white shark had a closer match to humans for proteins involved in metabolism. Great White Sharks have a rare trait in fish called regional endothermy. This allows them to keep the body temperature of some of their organs warmer than the ambient water — a highly useful trait for fast swimming, digestion and hunting in colder waters.
Fancy a read? Check out the work by Michael Stanhope, professor of evolutionary genomics at Cornell’s College of Veterinary Medicine, and scientists at the Save Our Seas Shark Research Center at Nova Southeastern University (NSU). He published the shark genetic study in the November 2013 issue of BMC Genomics. It lays the foundation for genomic exploration of sharks and vastly expands genetic tools for their conservation.
Johan Lindgren, Peter Sjövall, Volker Thiel, Wenxia Zheng, Shosuke Ito, Kazumasa Wakamatsu, Rolf Hauff, Benjamin P. Kear, Anders Engdahl, Carl Alwmark, Mats E. Eriksson, Martin Jarenmark, Sven Sachs, Per E. Ahlberg, Federica Marone, Takeo Kuriyama, Ola Gustafsson, Per Malmberg, Aurélien Thomen, Irene Rodríguez-Meizoso, Per Uvdal, Makoto Ojika, Mary H. Schweitzer. Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature, 2018; DOI: 10.1038/s41586-018-0775-x
North Carolina State University. (2018, December 5). Soft tissue shows Jurassic ichthyosaur was warm-blooded, had blubber and camouflage. ScienceDaily. Retrieved September 7, 2019, from www.sciencedaily.com/releases/2018/12/181205134118.htm
Photo: By Haplochromis - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5825284
