Hippos of the Sea

The ocean has diverse creatures and to further understand them it helps to compare them to creatures commonly observed on land. Manatees could be considered to be the cows of the ocean, seals are comparable to dogs and hippopotamus may lack some similar characteristics but they would be the land equivalent to whales. Whales may not be using legs to walk on the ocean floor or laid the mud but they share a recent common ancestor with Hippopotamus amphibius or hippos.

The Ancient Greeks believed that the hippopotamus was closely related to horses and in slightly more recent studies hippos were linked to pig-like animals. The general shape of the animals, along with some of their features like 4 legs, lead to the misconception that pigs evolved from hippos. This is an incorrect assumption for many reasons. Hippos and pigs do share a common ancestor but the introduction of the modern day hippopotamus 16 million years ago has not changed form to introduce the pig as we know it. The common ancestor of the hippo and pig is believed to the be Indohyus, or Indian pig that lived 48 million years ago but is now extinct. The new fossil discovery of Indohyus in 2004 led people to assume the link between pigs and hippos that was previously assumed 200 years ago by morphologists. The molars of hippos and pigs resemble each other but it is now known that teeth are easily altered with age and environmental factors so this evidence was deemed unreliable. The morphology of the fossils seem to suggest a linkage between the two but the use of DNA proves that the common ancestor of the whale and hippo was more recent.

Aesthetically, hippos and Cetacea or whales, don’t have much in common but this is expected because the common ancestor of the two is dated back 40 million years ago. It is inferred that these species had a water-loving ancestor that evolved to split into two groups: aquatic and semi-aquatic. Because of this linkage whales, dolphins and porpoises are able to be categorized into the same group as giraffes, sheep, cows and other land mammals, Artiodactyla. This combines cetaceans and even toed ungulate. Cetaceans are aquatic, finned mammals (whales, dolphins and porpoises) and even toed ungulate are animals that distribute their weight evenly between the third and fourth toes (camels, moose, sheep, giraffes and hippos).

A University of California Berkeley professor analyzed blood samples of hippos and whales and was able to find a close relationship between the two. Furthering testing was carried out on the mitochondrial, ribosomal and nuclear DNA and it provided more evidence to solidify the claim. In last two decades there has more and more evidence to prove that the hippo’s closest existing relative is the whale. At this point in time the study lacks some fossil evidence to back of the claims but the DNA evidence and existing fossil evidence suggests that researchers are on the correct path.

The lack of visible homologous structures and preconceived knowledge can lead people to draw false conclusions. The advancement of technology provides more opportunities to the solidify the Theory of Evolution and how it has impacted the world we live amongst or the creatures in the depths of the ocean that remain hidden.

Sources

About Mr. Mohn

Biology Teacher

This entry was written by Alexis J. and tagged . Bookmark the permalink.

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