The Colors of Sea Monsters Revealed
By Megan Pinaire
The age of the dinosaurs is famous for the Tyrannosaurus Rex, king of all land dwelling dinosaurs. Yet the ocean, at the same time, was ruled by terrifyingly large sea monsters like mosasaurs and ichthyosaurs. Around 245–90 million years ago, Ichthyosaurs controlled the oceans, averaging six to thirteen feet, with the largest at seventy-five feet. Despite their aesthetic resemblance to fish, they were in fact reptiles. Mosasaurs had their reign of terror 98–66 million years ago. They too were marine lizards that grew, on average, to be about fifty feet long, with the longest recorded at fifty-seven feet. During the later years of their existence, they actually resembled dolphins as a result of convergent evolution. While not a great source of trepidation, the leatherback turtle was actually the most fit out of the majority of these ancient species, in the context of evolution, because this species still exists today. Leatherbacks can grow to eight and half feet long and weigh up to 700 kilograms.
But what did these creatures look like? A study was conducted at SP Technical Research Institute of Sweden and MAX IV Laboratory, Lund University, Sweden regarding these ancient sea monsters. Previously, scientists could only guess at the outer color schemes and markings of such extinct animals. However, soft tissue (which is prone to decay) was found fossilized, preserved by an “organic film.” This discovery of such an organic film belonging to mososaurs, ichthyosaurs, and ancient leatherback turtles gave scientists the first glimpse into the skin colors of these species.
During the initial analysis of the skin cells, micrometer-sized organic bodies were found. Therefore, before scientists were able to study the tissue in regard to which color scheme they represented, they had to analyze these bodies and determine their identities. There was debate over whether the bodies were fossilized melanosomes (which would represent the pigment containing organelles the monsters had) or microbes (which would suggest the fossils found were merely of bacteria that had aided the decomposition process). By studying the content of the soft tissue and comparing it to extant lizards, it was proved that the microscopic bodies were indeed remnants of the animals themselves.
The sea monster soft tissue discovered and studied was found to be densely packed with melanosomes. Melanin is a general term for the group of pigments that are responsible for the coloration of organisms. The melanin of a cell is contained in organelles called melanosomes. Therefore, skin darkness is related to the density of melanosomes in skin cells. The more dense the melanosomes, the darker the skin color.
The researchers were able to determine from the fossilized organic film that the reptiles all had either completely or partially dark skin as a result of the high density of melanosomes. Ichthyosaurs probably had uniformly dark coloration because they were deep divers, and such dark skin allowed camouflage in the deep water where there is little to no light. This is unlike many sharks and marine mammals, which are typically darker on top and lighter on their bellies, a technique known as countershading. The extant, deep diving sperm whale, however, has a similar scheme as the ichthyosaurs are thought to have had. While this similarity would be due to convergent evolution, such similarities between an ancient and an extant animal might reveal clues about the ichthyosaurs’ life history.
The leatherback turtle’s color scheme was analyzed and it was observed that the ancient turtles had the same color as they do today. They have a completely black back which allows them to survive in cold water. This coloring absorbs maximum heat from the sun while they bask at the surface of the ocean. The densely packed melanin in their cells (causing dark color), in addition to their large body mass, helps keep a high enough body temperatures. It appears they have had the same coloring for the majority of their existence, showing the evolutionary significance of such a color scheme in the species. This ability to absorb light and utilize the subsequent heat from the sun in cold waters contributes to the leatherback’s worldwide abundance.
Knowing the color scheme of extinct species is a major piece of the evolutionary time puzzle scientists are trying to put together. Pigmentation and coloration have many functions, including camouflage, sexual display, and warmth. Studies that reveal the color of ancient monsters allow us to peek into other portions of their lives, behavior, and survival techniques.
Read more at: http://www.nature.com/nature/journal/v506/n7489/full/nature12899.html
