Perhaps no living creature is quite as spectacularly stupendous as the big blue whale. With a maximum, verified size of 30 metres and 200 tonnes, it is the largest animal on the planet by a ridiculously huge margin. Some reports even indicate the largest blue whales may have reached a titanic 33 metres in length and weighed up to 273 tonnes, though these claims are unverified. Nevertheless, at such unfathomably enormous sizes, the blue whale is possibly the largest animal to have ever existed in the history of the planet! Now, it is worth mentioning that there have been challengers to this title in recent years. Many long necked dinosaurs, such as Supersaurus, were much longer than any blue whale and could reach lengths of 35 to 45 metres or more.Some long necked dinosaurs, such as Bruhathkayosaurus, as well as some specimens of prehistoric marine reptiles called ichthyosaurs, such as the Aust Colossus, have even been estimated to be as large as or larger than the biggest blue whales. The rarity of fossilisation also means it’s very unlikely that we’ve discovered the largest dinosaurs or ichthyosaurs ever to exist.
That being said, most giant dinosaurs and ichthyosaurs are only known from fragmentary remains and so estimating their size is still quite difficult. Therefore, at 30 metres and 200 tonnes, the blue whale remains the largest animal whose size can be estimated with some certainty and that’s an exceptionally impressive record. The blue whale’s size only becomes even more impressive with further details. For instance, a blue whale’s tail is almost as wide as the length of a double-decker bus! The tongue of a blue whale is as heavy as an elephant while its heart can weigh over 180 kilograms! Adult blue whales can also blast water up to 12 metres tall and are the loudest animals ever known, capable of producing sounds as loud as a jet plane! While all these records are certainly impressive, perhaps the most impressive thing is that blue whales didn’t start out so spectacular. In fact, when we look through their evolutionary history, it becomes clear that even the big blue whale began with the most humble of origins.
Whales are mammals and belong to a group of mammals called the artiodactyls; the same group that includes giraffes, deer, cattle, pigs and hippos. In fact, the earliest ancestors of whales were actually small, terrestrial mammals! While this might be very surprising at first, the skeletons of modern whales actually show evidence of this since whale skeletons still retain tiny hindlimbs. These bones are so small and reduced that they are no longer visible from the outside and have become vestigial. However, these bones clearly show us that modern whales are descended from four legged ancestors and this becomes easier to understand when we take things step by step. Some of the earliest whale ancestors are known from Pakistan and are approximately 50 million years old. A good example of this is Ichthyolestes; a fox sized animal that resembled a cross between a dog and a deer, even possessing long legs and a terrestrial lifestyle. However, Ichthyolestes is indeed among the earliest ancestors of whales and this becomes clear when we look at its skull.
Ichthyolestes and similar whale ancestors all possess features in their inner ear that are only observed in modern whales and this is a clear sign of their evolutionary relationship. It’s even been hypothesised that animals like Ichthyolestes were already spending time close to the water, hunting fish and other aquatic organisms. This is based on features in the skull and limbs that indicate they had adaptations for a semi-aquatic lifestyle. These adaptations would become even more pronounced with animals like Ambulocetus; another extremely important whale ancestor from Pakistan whose name literally means ‘walking whale’.
Ambulocetus and its close relatives literally looked like the mammal version of crocodiles, being powerful predators with massive jaws and large teeth. However, the skeleton of Ambulocetus suggests that it was built more like an otter and probably used a similar method of swimming. Ambulocetus had eyes on the top of its skull, a feature seen in crocodiles and other aquatic animals, but also possessed features in the inner ear only seen in whales. Crucially, Ambulocetus and its relatives have only been found in marine deposits, indicating they spent much of their life around marine habitats. However, oxygen isotope values indicate that Ambulocetus and its relatives were also consuming fresh water, suggesting they were free to move between water bodies of different levels of salinity. While its limbs were not as long as those of Ichthyolestes, Ambulocetus may have been able to walk on land for brief periods, though it probably spent the vast majority of its time in water.
Some studies have even found that Ambulocetus’s limbsmay not have been able to support its body on land at all and that it would have been completely aquatic. Overall, Ambulocetus is among the best studied whale ancestors and it is an exceptionally important animal as it showcases how whales gradually transitioned from land to water. Rodhocetus is yet another important whale ancestor from Pakistan and it largely resembled Ambulocetus in outward appearancebut had even more adaptations for a life at sea, with even shorter limbs and more skeletal adaptations for swimming. These features would eventually lead to true whales that were completely adapted for life in the open ocean, with flippers instead of limbs and a powerful, fluked tail. Yet, even the history of marine whales is just as fascinating.
Some of the first fully marine whales were the basilosaurids and these were completely marine animals, with fully developed flippers and a fluked tail. However, they also differed from modern whales in some key ways. Most notably, they had an extremely streamlined, almost serpentine build. Their skulls were also very small in comparison to their total body length and their reduced hindlimbs would likely have been visible outside the body. Basilosaurids also lacked the melon organ seen in toothed whales today, which is used for echolocation and communication. They also had proportionately smaller brains, which suggests they weren’t as intelligent or as socially complex as modern whales. While many basilosaurids, such as Cynthiacetus and Dorudon, were quite small in size, other basilosaurids were truly enormous.
For instance, the mighty Basilosaurus; known from Asia, Africa and the Americas; was between 15 and 20 metres long and would have been the most powerful predator on the planet during its time. There are even Basilosaurus bite marks in the fossils of smaller whales like Dorudon, and fossilised stomach contents from Basilosaurus actually contained remains of both Dorudon and large sharks. These discoveries suggest that Basilosaurus was truly the apex predator of its time.The name Basilosaurus even means ‘king reptile’, since its huge size and serpentine build originally led to it being mistaken for some kind of dinosaur or sea monster! Meanwhile, another giant basilosaurid called Perucetus, meaning ‘whale of Peru’, was even more massive and may have weighed between 60 and 114 tonnes, making it the largest whale to have ever evolved up until that point.
It was only between 17 and 34 million years ago that whales finally split into the two groups we have today. One group is the toothed whales; which includes sperm whales, beaked whales, dolphins and porpoises; while the other group is the baleen whales; the giant, filter feeding whales that includes the big blue whale itself. Baleen whales are notable for having lost their teeth and having replaced them with plates of bristle like structures called baleen. Baleen is made of keratin, the same material as hair and fingernails, and this forms a comb like structure on the whales’ jaws, allowing them to filter out water when feeding. Baleen whales are also well known for being the largest living animals, with many baleen whales being considerably larger than any other animal on the planet.
However, the first baleen whales didn’t start out as giants. Some of the earliest baleen whales, such as Cetotherium,were only slightly larger than a large dolphin and were extremely fast swimmers, using their speed to escape predators. In fact, it’s only within the last 4 or 5 million years that truly gigantic, baleen whales evolved. It’s worth mentioning at this point that being in water doesn’t automatically mean animals can achieve huge sizes. While it’s generally known that it’s physically easier to support a larger body mass in water than on land, due to buoyancy, this doesn’t automatically mean marine animals frequently grew to huge sizes.
For example, aside from the prehistoric ichthyosaurs and some whales, giant marine animals are quite rare in the fossil record. The only other marine animals known to have reached huge sizes are the prehistoric fish Leedsichthys, the filter feeding sharks of today like the whale shark and basking shark, and the extinct, predatory shark Megalodon. Meanwhile, the giant, long necked dinosaurs continuously grew to gigantic sizes on land across a period of almost 100 million years. Therefore, despite it being physically easier to grow larger in water, it seems massive, marine animals aren’t as common as we’d expect. It’s also notable that most of the giant marine animals, such as baleen whales, filtering feeding sharks and Leedsichthys, were all filter feeders that fed on swarms of tiny organisms. In fact, it’s this very method of feeding that eventually led to the big blue whale of today.
Small, early baleen whales like Eobalaenoptera lived in very dangerous waters. They were ideal prey for the giant shark Megalodon as well as huge, predatory sperm whales like Livyatan. Thus, small whales like Eobalaenoptera had to rely on their speed to escape these threats. At this point in time, very few baleen whales reached over 10 metres in length and it was only around 4 or 5 million years ago that a notable change occurred. Around this time, populations of krill and other tiny organisms began to shift around the globe and started accumulating in huge numbers in various parts of the world’s oceans. This new change in marine ecosystems allowed baleen whales to grow big. The baleen whales’ filter feeding lifestyle allowed them to make the best possible use of these vast swarms of krill and they grew enormous on this diet.
Many baleen whales, like the blue whale, use a method of feeding called lunge feeding, where they engulf an enormous amount of krill and water in one, gigantic gulp. A single blue whale can engulf over 200 tonnes of water in a single mouthful! They then use their sheets of baleen to filter out the water, allowing them to swallow only the krill. With this very successful lifestyle, the big baleen whales of today evolved within the evolutionary blink of an eye, eventually culminating in the titanic, 30 metre, 200 tonne blue whale itself. After over 50 million years of evolution, the big blue whale has broken all records and swims as among the largest animals to have ever existed. It is an impossibly huge privilege that we’re able to share the planet with such an awe-inspiring animal! Sri Lanka is particularly blessed in this regard as it is among the best places in the world to observe blue whales! However, it’s crucially important that we do not take such blessings for granted.
For all their might and majesty, even blue whales are now endangered and are facing serious threats. Prior to the 19th century, there were around half a million blue whales and they were abundant across the planet. However, following the excessive whaling that occurred over the next century, this population was decimated and blue whales were almost completely hunted to extinction. This is also one of the reasons why few blue whales today approach or exceed 200 tonnes in size. It was only following the ban of international whaling in 1966 that blue whale populations finally began to increase, with between 10,000 and 25,000 individuals recorded in 2018. However, this is still a depressingly small portion of their original numbers. More worryingly, despite the ban of whaling, blue whales today still face considerable threats that shouldn’t be ignored. For instance, ship strikes pose significant danger to blue whales today and are among the leading causes of death for current populations.
This is a serious threat for blue whale populations around Sri Lanka too and shouldn’t be overlooked. Entanglement in fishing gear is another notable cause of death, while sound pollution or artificial, underwater noise can disrupt the whales’ feeding patterns. Therefore, the brilliant blue whale is still extremely vulnerable and it would be a tragic shame if we were to let such a magnificent and majestic animal disappear forever. However, there is thankfully still hope. With the ban of whaling, blue whale numbers did increase and the threats they face today are all threats that we can solve. Unlike dinosaurs or even the whales’ prehistoric ancestors, the whales of today are living legends that we can still see and appreciate in their entirety. We don’t have to wait for their fossils to make us recognise their amazing size and power, so let’s make sure we don’t let the privilege of sharing this world with them go to waste! Let’s ensure that we continue to coexist with the largest animal ever known and make sure we never take that blessing for granted!
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