The blue whale is the largest animal on Earth today
Image note: Restoration of a crested tooth whale, picture from the internet
The origin of baleen whales has always been a confusing mystery, but recent discoveries have given us a key to solving this puzzle, and this key is the crown tooth whale!
Illustration: Blue whales that swim in the ocean, which belong to baleen whales, the image comes from the Internet
Caption: Flocks of large-winged whales, also belonging to baleen whales, are imaged from the Internet
Today's baleen whales in the ocean are the largest animals on earth, including the blue whales, fin whales, large-winged whales and so on that we are familiar with. Although baleen whales are docile, the ancestors of these big guys are basically the same fierce predators, how did they gradually change from predatory to filter feeding? A fossil of an ancient whale from South Carolina in the United States shows us the amazing evolution of it. The research paper was published in the journal Contemporary Biology in July 2017 titled "The Origin of Filter Feeding in Whales." The ancient whale was named coronodon havensteini, the genus name means "coronal teeth", and the species name is taken from the discoverer Mark Havenstein. This ancient whale lived in the Oligocene period about 30 million years ago, and it is not a very old cetacean chronologically, but it has become a key link in the evolutionary relationship between modern cetaceans and the suborder Cetaceans.
Note: Fossils of the crested tooth whale, picture from the paper
The fossil of the crown-toothed whale includes a less complete skull with some of its teeth, the oddly shaped teeth from which it got its name. The crown-toothed whale has two different shapes of teeth, the teeth in front of the head are conical, similar to the teeth of the toothed whale, which are typical of predators' teeth and begin with punctures. Serrated, gear-like teeth located at the back of the head are another type of tooth, and this uniquely structured tooth was first found in whales, similar to the structure of pinnipeds that are far away, such as crab-eating seals.
Image note: Teeth of a crown-toothed whale, image from the web
Crab-eating seals are known to resemble grates in teeth, thanks to their long-term krill-feeding habits. The teeth of crab-eating seals have a certain degree of filtration in structure, and this set of equipment is completely unsavory in the krill-rich Antarctic Sea. Crown-toothed whales have some tiny scratches on their molars, which should be left behind when they close their mouths and squeeze the water to allow them to filter food out of their mouths, and the more tiny and solid foods that pass through these narrow crevices. Crested whales also have wear marks on their sharper teeth at the front, suggesting that they are not entirely filter-eaters, but at least catch some of the larger prey. From the perspective of tooth structure and wear, the teeth of the crown-toothed whale began to evolve gradually so that it is not as good at hunting large prey in the ocean as the original close relatives, and their daily life mode should be a combination of filter feeding and predation, both catching some relatively easy to catch large prey, but also eating some smaller foods through filter feeding.
Image note: Crab-eating seal, image from the web
The teeth of the crab-eating seal are very similar to those of the crown-toothed whale. Image from the web
Image note: Fossil skull of a crested tooth whale, image from the Internet
Illustration: Schematic diagram of the feeding pattern of the crested whale, picture from the paper
Illustration: Schematic diagram of the evolution of whale baleen, picture from the paper
The discovery of the crown-toothed whale gives us an idea of how baleen whales evolved from predators, the beginning of their evolution, and how these big guys who made a living from filter feeding evolved. In fact, the evolution path of cetaceans is more diverse and complex than we think, and every discovery and study of ancient whales will serve as an accumulation of understanding this magical evolutionary path, allowing us to see the evolution of cetaceans more clearly.
Note: Close-up of tooth restoration of a crested whale, image from the web
Note: Whale baleen actually evolved from teeth, image from Wikipedia
Resources:
geisler, jonathan h; boessenecker, robert w; brown, mace; beatty, brian l (2017). "the origin of filter feeding in whales". current biology. 27 (13): 2036–2042.e2. doi:10.1016/j.cub.2017.06.003. pmid 28669761. lay summary – sciencedaily (june 29, 2017).