By the age of the dinosaurs, animal life had grown pretty huge on this planet. Apatosaurus, Diplodocus, Tyrannosaurus: these and many other giants towered over most other creatures. Yet despite their immense size, they eventually disappeared, and the land would never see their like again. The seas, however, were a different case, for the greatest creature ever to grace this planet was yet to come. And that species still with us today: at up to 180 tons, the blue whale weighs about twice as much as some of the heaviest dinosaurs.
Blue whale (c) CCC
It's hard to imagine just how mighty blue whales are, so here are some comparisons. Their hearts weigh the same as a large cow. They can exceed the length of three double-decker buses. A football team could stand on a blue whale's tongue without falling off. Their aortas are so huge that a human child could crawl through them. And talking of children, at birth, a blue whale baby weighs about the same as an adult hippopotamus. Yet despite these magnificent statistics, blue whales are extremely nimble thanks to their marine environment. Over short bursts, they can achieve astonishing speeds of up to 50 km/hour.
Incidentally, in case you were wondering which is the second largest animal ever to have lived, then, once again, look no further than current times. Fin whales can weigh up to 120 tons and reach an impressive 26 m in length.
That's not to say that all whales and dolphins are giants, though. The lightest of them all are the vaquita and finless porpoise, at around 50 - 55kg. You'd need about 3,000 of them to balance out the weight of a blue whale.
It's easy to work out the age of a dog, or a cat, or a horse. You generally know the exact date of their birth, and you're likely still to be around when they die. Yet when it comes to measuring the lifespans of creatures that live much, much longer than we humans, and in the freezing waters of northern oceans to boot, then the maths becomes much harder.
Somewhere out in the Arctic Ocean, right now, there are elderly bowhead whales swimming around. Not a single living human being on this planet was around when they were born. They are so old that when, as youngsters, they might have swum past Victoria Island, in Canadian Arctic waters, the island would not yet have been so named, for the British Queen herself hadn't even been born. Victoria has lived and died since then, world wars have been fought, and yet another new century has begun. And still those bowheads swim the Arctic waters, their steady pace of life slowed down by their cold environment which they combat with blubber up to 70 cm thick (another record).
Bowhead whale (c) Alan Airey
It is estimated that bowhead whales are able to live for more than 200 years. This makes bowheads the oldest living mammals in the world - in fact, they would even appear to outlive giant tortoises, which have themselves only been known to attain the comparatively youthful age of around 180.
It will be some time before science can more precisely measure a bowhead's age, because it's only comparatively recently that detailed accounts have been made of individuals, and to find out how long they live, we'll all just have to wait. What we do know, however, is that in recent years, bowheads have been found with harpoons and spear points embedded in parts of their bodies that, due to their construction, we know must have been made way back in the 19th century. These survivors of hunts of much more than a century ago would likely have been adults at the time.
Ever since mankind started building walls and creating artificial boundaries, many of the great land migrations of the past have been severely curtailed. Antelopes used to trek back and forth through great swathes of Africa, but have now been restricted to comparatively short trips within game reserves. The bison of North America, which once travelled huge distances in mighty herds, are now confined to a few small groups with little room for ranging.
Yet the seas have no walls, and here, many fish and mammals are still able to follow the extraordinary migratory routes of their ancestors. Few of them travel as far as the great whales. In the southern seas, southern right whales gather in the spring in their calving grounds along the coasts of Africa, South America and New Zealand, before travelling to Antarctica for summer feeding. Blue whales migrate thousands of kilometres from their tropical winter breeding grounds to the cooler waters of the Arctic or Antarctic, often eating virtually nothing during their four-month trip. Humpback whales take similar journeys, those who winter north of the equator swimming slowly towards the Arctic for the summer, while those below the equator go south.
Humpback whale (c) Scott Portelli
Dolphin seasonal movements, meanwhile, can vary greatly, even within a species. Bottlenose dolphins in higher latitudes often travel further south in the winter, such as between New Jersey and North Carolina. Some coastal communities, however, such as the ones that live off the northern Scottish coast around the Moray Firth, do not migrate at all.
Yet the overall record, indeed for any known mammal, lies with a humpback whale who is known to have migrated more than 9,800km from Brazil to Madagascar. That's about a quarter of the way around the world in just one journey.
It's often said that rats are the most successful of all mammals, able to colonise virtually every type of environment across the globe. On land, yes, that's true, but land only makes up around 30% of the world's surface. The rest is water, mainly seas and oceans, and there's barely a single stretch of it in which at least one type of whale or dolphin doesn't spend time.
Bolivian River dolphin (c) Fernando Trujillo
Bowhead whales live in the freezing Arctic waters of the north, as do narwhals and belugas. Several species of whale make their way to Antarctic waters to feed during the summer months. Dozens upon dozens of species are found in the Atlantic, Pacific and Indian Oceans. Even more land-trapped waters, such as the Mediterranean Sea, host a great variety, from Risso's, striped and common dolphins to harbour porpoises and sperm whales.
Not that these far-reaching mammals are confined to the deeper waters. Coastal populations of dolphins and porpoises can be found all round the globe, from Europe to Australia to the Americas. Estuaries are home to several species, too, such as the tucuxi, a South American dolphin that enjoys both salt and fresh water.
But the story doesn't even stop there. If you take a trip along some of the great rivers of the world, such as the Amazon, Ganges or Indus, then you might encounter one of the remaining river dolphins of the world, a final testament to the astonishing adaptability of the whale and dolphin families who have made some 70% of the world's surface their home, a mammalian record.
Not long ago, a researcher from Cornell University discovered something truly astonishing that redrew our thinking about whale calls and song. Using detailed acoustic technology, he worked out just how far whale song can carry beneath the waves. His results were mind-bending, and rather beautiful, too. He was able to reveal that the call of humpback whales, thanks to their deep, resonating boom, can carry from the waters of Puerto Rico to the shores of Newfoundland. In short, across a distance of more than 2,500 km, it is entirely possible for one whale to talk to another.
Humpback whale (c) Duncan Murrell
Whale song itself is not just potent, but extraordinarily complex. Male humpbacks perform their songs during the mating season, so they could be a form of underwater serenade. They are richly structured, too, building into phrases, which are joined together into themes. These themes are then blended together into a song that can be half an hour in length or more, and the final songs are then repeated over and over again, sometimes even for days. They are repeated year after year, often changing in format and always replicated by the whole population. This conjures up the most amazing image. All the large whale species, spread all around the globe, traversing the seas on their migratory journeys, can be in constant communication with each other, networking through calls that criss-cross the seas. However, the advent of shipping vessels, with their own deep underwater sounds made by rotating propellers, has created a sort of acoustic smog, masking the whales' own communication lines. In the way that people who live in cities that are lit at night are unable to see the stars, so whales are increasingly battling to hear their distant companions through the interference with unknown consequences.