Porpoisely Quiet?

Way back in the early 19th century, the naturalist Karl Ernst von Baer, better known for his work on embryology, made an interesting discovery that seems fairly obvious to us in hindsight: the blowhole of a porpoise is, in fact, its nostril. Other anatomists followed up on this, leading to the further discovery that a number of air sacs appear to be connected to the nasal cavity. They can hold a fair amount of air when fully inflated, but nothing like as much as the lungs, so exactly what they were for wasn't clear.

Fast forward to 1956, and scientific research confirmed another interesting fact about such animals: they can echolocate by sending out sonar pings. In 1968, the two facts were put together when it was demonstrated how the unusual structure of the porpoise's head allows it to transmit the necessary sound pulses, which are initially generated somewhere in the nasal passages.

Pliocene (Pt 16): The Pliocene Oceans

Bohaskaia

Over the last two and a half years, I have talked about a range of mammal species found across the Pliocene world. So far, I have only looked at the continents, and the various animals that lived on land. But the Pliocene seas were, of course, equally teeming with animal life. Much of this naturally consisted of either fish (most famously the giant "megalodon" shark) or invertebrates of various kinds. Sea turtles also existed, including some quite large ones, but, in keeping with the scope of this blog, I'm going  to focus on the mammals.

While we often tend to think that prehistoric animals tended to be larger than those alive today, this, was however, rather less true of whales, which have grown more or less steadily in size over the course of their evolution, perhaps in part to make it increasingly difficult for anything else to eat them. So, for example, the Pliocene killer whale (Orcinus citoniensis) was around 4 metres (12 feet) in length, barely more than half that of the modern species - although still quite impressive on a human scale.

Fossil Porpoises Muddy the Waters

Harbour porpoise

Dolphins and porpoises belong to two separate families, and there are clear differences between them. However, this isn't immediately obvious at first glance: they're both small cetaceans, with flippers, tail flukes, and so on. A comparison between, say, a bottlenose dolphin (Tursiops truncatus) and a harbour porpoise (Phocoena phocoena) does show a number of differences that are broadly true of their respective relatives - but not entirely so.

Porpoises, for instance, are smaller than dolphins, on average. But only 'on average', because, in fact, the smallest dolphin is smaller than the smallest porpoise. Similarly, dolphins usually have a 'beak' - a narrow snout projecting forward from the front of the head - that is missing in the more rounded heads of porpoises. But, once again, there are dolphins that don't have the beak, such as Risso's dolphin (Grampus griseus).