From ScienceDaily:
Molecular and microstructural analysis of a Stenopterygius ichthyosaur from the Jurassic (180 million years ago) reveals that these animals were most likely warm-blooded, had insulating blubber and used their coloration as camouflage from predators.
“Ichthyosaurs are interesting because they have many traits in common with dolphins, but are not at all closely related to those sea-dwelling mammals,” says research co-author Mary Schweitzer, professor of biological sciences at NC State with a joint appointment at the North Carolina Museum of Natural Sciences and visiting professor at Lund University. “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.”
Johan Lindgren, associate professor at Sweden’s Lund University and lead author of a paper describing the work, put together an international team to analyze an approximately 180 million-year-old Stenopterygius fossil from the Holzmaden quarry in Germany.
“Both the body outline and remnants of internal organs are clearly visible,” says Lindgren. “Remarkably, the fossil is so well-preserved that it is possible to observe individual cellular layers within its skin.”Paper. (paywall) – 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 More.
Soft tissue analysis seems to have brought oddities to life. Although considered a reptile, the ichthyosaur had features that remind one of a mammal. New Scientist offers:
A 180-million-year-old fossil, found in Germany, is so extraordinarily well preserved that pieces of the skin removed for analysis were still flexible. It shows that at least some ichthyosaurs had smooth, scaleless skin underlain by blubber, making them even more like dolphins than we thought.
All modern sea animals with blubber either maintain a constant body temperature, like whales and seals, or keep their body well above the water temperature, like the leatherback turtle, says team member Johan Lindgren of Lund University in Sweden. “At the very minimum, it’s what you see in the leatherback turtle today,” he says. Michael Le Page, “Fossil blubber shows ichthyosaurs were warm blooded reptiles” at New Scientist
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See also: Soft tissue find shows dinosaurs had birdlike lungs
and
Developing story: Young Earth creationist microscopist, fired in wake of finding soft tissue from dinosaurs, sues (2014)