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Monday April 22nd, 2024

Lanka’s Blue Whale: Eight Evolutionary Stages (Part I)

Nothing…nothing…THERE!! A distant white smudge blurs a space on the horizon: spray from a blue whale coming to surface. Our boat moves toward it and soon we can see more and more whale above the waves. Biggest animals ever, blue whales abound on Lanka’s southern porch. I spent a morning watching as three blues separately dove, tail up, then re-surfaced minutes later, spouting exhalations to catch breath. They were foraging and dining on balls of krill: thumb-size orange crustaceans congregating in their millions along the edge of the continental shelf. Krill is virtually the entire blue whale diet.

A typical blue feeding dive is an athletic and physiological marvel. Strokes from huge tail flukes power her downward against her own buoyancy through the first 25 meters. As she descends, pressure from the water above forces her flexible rib cage inward, decreasing her volume and increasing her density so that her buoyancy dissipates and she begins to fall rapidly with gravity toward the sea bed. She turns and heaves herself upward in a strenuous lunge through krill balls, fighting not only gravity but also the hydrodynamic drag created by her own gaping jaws. She shudders to a halt, having gulped maybe 60 tons of seawater. With a gelatinous tongue the weight of an elephant, she spews the water out through her baleen—cartilaginous sieves that line her mouth—retaining countless krill then to swallow. She does this all again and again, upward toward the surface, holding her breath all the while of course. After gasping in the waves for several minutes, her tail goes up again in her next dive.

Lankan waters teem with organic nutrients washed from the rain-drenched land. They sink by the ton into cold deep waters just beyond the shelf. Winds sweep surface water away in mighty currents and this pulls oxygen-rich, nutrient-laden cold water up from the deep in a process called ‘upwelling.’ When sunlight hits this fertile slurry, photosynthesis goes crazy. Tiny plants called ‘phytoplankton’ grow and multiply by the billion. Micro-animals (‘zooplankton’) dine on this sumptuous buffet and likewise proliferate. Feeding on both, krill blooms turn the sea to orange.

That, in a nutshell, is why blues visit Lankan waters. Science is learning more and more about how these astonishing animals came to exist in the first place. Shall we take it from the top? In this essay’s Part I here, I recount the first five of eight key evolutionary stages. In a later Part II, I shall recount the remaining three.

One: Origins

It all began in Lanka’s general neighborhood. It has long been known that cetaceans (whales and dolphins) are mammals and therefore evolved from exclusively land-going animals. Amazingly enough, recent science assures us that they sprang from the order of artiodactyls!!! Artiodactyls? Oh, of course, you know them by their street name: even-toed ungulates!!! OK, OK, so even-toed ungulates are mammals with hooves formed from two (or sometimes four) of their five toes. Present-day representatives include deer, pigs, sheep, camels, cattle, giraffes and hippos (the closest living cousins of cetaceans).

Herbivorous artiodactyls found themselves roaming Asian savanna as the Indian subcontinent broke away from Africa and raced across the ancient Tethys Sea until it collided 50 million years ago (mya) with Eurasia’s southern flank and began pushing the Himalayas up toward the sky. Coincidentally, or probably not, cetacean evolution dates from that same time. A deer-size creature called ‘Pakicetus’ began taking dips in shallow water, perhaps when streams flooded seasonally or perhaps to dodge predators. Its fossils now lie high in the mountains of India and Pakistan.

By and by, it learned to fish, launching the speedy 10-million year cetacean journey from land-going herbivores to sea-bound carnivores. There must have a day early on when a frustrated mommy growled the Pakicetus equivalent of ‘Yes, you ARE going to eat this and you’re going to eat it right NOW!’ as she spat some regurgitated fish down her pup’s throat, and then a moment later the pup chirped back the equivalent of ‘MommyMommy, I actually like it!’

Two: Fresh Water to Salt

Rains, possibly early monsoons, poured themselves on the rising Himalayas, creating streams flowing down toward the Tethys, itself shrinking down as its floor got squeezed up into hills. This would have created varying riverine habitats that perhaps fueled rapid emergence of new cetacean species. Some developed hippo-like heavy bones, providing ballast against buoyancy, allowing them to wade and bottom-walk while submerged. Some supplemented their diet with underwater grasses. For a while they hunted in water but returned to land for sleep, mating, calving and nursing, like present-day seals and walrus.

Some learned to swim of course. First came an awkward dog-paddle with limbs moving in a gait easily adaptable from trotting on dry land. Later, front paws thrust out motionlessly forward and webbing emerged on back-pushing hind feet, alternating left and right. Then hind legs came into simultaneous strokes, which continued down through a stiffening tail undulating downward and upward, providing propulsion both ways. Cetaceans migrated quickly into deeper and broader freshwater streams, then into brackish swamps and marshlands where they had to tolerate salty water, drastically altering their metabolisms in so doing. In an incredibly brief time of perhaps only one million years from their first emergence, cetaceans reached the sea. It had never been that far away but getting there required arduous metamorphosis.

Like a furry 400-pound crocodile, ‘Ambulocetus’ skulked in shallow bays, marsh and estuaries. Comfortable in both fresh and salt water, it could also shamble awkwardly on land if need be. With eyes high on its head, it could stay concealed while swimming. Squat, powerful web-footed hind legs launched its massive head and jaws in ambush takedowns. Its time was brief, however. New cetaceans departed the land entirely to spend their whole lives at sea, including sleeping, mating, calving, nursing and rearing young. Land-linked cousins they left behind fell extinct, out-competed by other carnivores. (Today’s freshwater dolphins and porpoises later migrated back from the sea.)

Three: Ocean Radiation

Physiology again transformed quickly as cetaceans made oceans their home. Genes for producing hind legs sputtered into quietude. Eyesight, useless in deep darkness, lost primacy, yielding to accelerated hearing acuity, exploiting sound’s superior transmissibility in water. Sound could help detect both predators and prey as their changes of speed and direction generated noise. Nostrils migrated to head-top blowholes, facilitating breathing at the surface. Body shapes moved toward hydrodynamic tubularity. With enlarging bodies, surface to volume ratios shrank, fostering heat conservation. Forelegs became flippers, enhancing maneuverability, and keel-like fins grew, providing stability. Backs acquired flexibility and tails sprouted flat broad flukes providing powerful up-and-down propulsion from the rear.

Kidneys got better dealing with salty seawater. Buoyant and drag-inducing fur disappeared in favor of buoyancy-neutral blubber, making dives easier and proving useful for reserve energy and heat maintenance needed for energy-expensive warm blood. With oxygen stored in blood rather than lungs, long dives on a single breath became feasible. Learning to sleep with half their brains at a time, they could maintain conscious control of their breath with the other half.

Drawing on mammalian smarts and social bonding, cetaceans became top predators, rivaling sharks who had ruled since the dinosaur extinction event (65 mya) that ushered sea-going reptiles to their doom. By 40 mya, cetaceans broke out of the shrinking Tethys and colonized all the seas, proliferating westward across the widening Atlantic, then through a gap between North and South America into the vast Pacific.

New species took up positions in the variegated niches they explored. By 35 mya, cetaceans poised for their next great transformation. ‘Modern’ cetaceans peeked between the curtains, then confidently took center stage.

Four: Echolocators and Filter-Feeders

Antarctica split from South America, isolating itself at the South Pole. A cold water current now circled it through southerly reaches of the Pacific, Atlantic and Indian Oceans. It obstructed flows of warm air and water to Antarctica, turning a previously subtropical climate to an icy one. In this so-called ‘Southern Ocean,’ cold water upwelling proliferated, fueling massive blooms of phytoplankton, zooplankton, krill and other organisms. Ocean productivity rose exponentially and cetaceans moved in to take advantage.

Deep-diving hunters with teeth (‘odontocetes’: the name referring to, well, teeth) emerged by steering their excellent hearing in a new direction. High-frequency clicks echoing back to them off increasingly abundant prey allowed them to ‘see’ with sound. This new sonogram sense colonized and re-wired their visual cortex, providing precision ‘sight,’ comparable in acuity with human vision, far outstripping the best human-made sonar. It all stemmed from a genetic shift identical to what propelled echolocation in bats, a stunning example of ‘convergent evolution’ if ever there was one. Echolocation feeds the charismatic bottlenose and spinner dolphins, orca and sperm whale found around Sri Lanka today.

Other cetaceans, however, found a different way to exploit oceanic abundance. They swam through balls of small animals, gulped them with seawater, then forcefully expelled the water from their mouths, leaving teeming prey stuck to the insides of their teeth, thereafter to be swallowed. This ‘filter-feeding’ also proved an excellent way to make a living.

They soon kicked it up a notch, sprouting cartilaginous bristles between their teeth, allowing them to filter more efficiently. These strips, known as ‘baleen,’ grew longer and more numerous through time and the teeth vanished, being necessary no longer. The great cetacean sub-order of ‘mysticetes’ (referring to mustache-like rows of filtering baleen hanging from upper jaws in their mouths) came fully into its own, right around the same time as echolocation perfected itself among their odontocete cousins.

That is the usual story at least. A minority view, however, holds that mysticetes emerged much later than the odontocete radiation 35-30 mya. This view contends that mysticetes sprang from odontocetes themselves, maybe around 25 mya, tracking another uptick in ocean productivity. A line of odontocetes found that they could abandon the expensive machinery of echolocation and learn to live by filter-feeding alone, as sketched above. Echolocation confers no great advantage in finding large balls of fish or krill. Normally acute cetacean hearing can fill the bill. To make room for more and more baleen, their skulls needed to change shape and this disallowed effective echolocation. The theory goes that baleen whales radiated quickly as they exploited a previously-underutilized feeding technique.

It seems counter-intuitive that a cetacean cluster would give up a tool as useful as  echolocation, but evolution brims with strange pathways and reversals. Lanka’s huge ‘fruit bats,’ for example, forsake echolocation because their stationary food source doesn’t require or reward it. They use eyes and nose to find their fruit. And cetaceans, after all, returned to the sea millions of centuries after their ancestors wiggled out of it onto dry land.

Five: Pouch and Lunge

In any case, mysticetes weren’t done yet. Around 15 mya, cooling seas boosted prey abundance yet again. To take advantage, some mysticetes developed large pouches extending from their mouths back toward their navels. Longitudinal folds in these pouches and changes in head morphology helped these so-called ‘rorquals’ open their jaws in a widening gape so as to hoover up heavier mouthfuls of prey.

Rorquals combined this new physiology with a novel style of feeding: ‘lunging’ at high speed through balls of prey, jaws magnificently wide, drawing massive gulps of food and seawater into their mouths. They developed soft fleshy tongues capable of licking their lunches efficiently off their baleen plates after spitting the water back into the sea. Swallow and repeat.

Close ancestors of today’s blue whale, early rorquals conspicuously lacked its size. They were in fact outsized by a contemporary odontocete, ‘Livyatan,’ extinct forebear of today’s sperm whale. A massive mammal hunter with bigger teeth than any other animal ever, it undoubtedly relished rorqual for breakfast.

As indicated above, Part II of this essay will address three more blue whale evolutionary stages.

 

(Writer, lawyer and former law professor, Mark Hager lives with his family in Pelawatte. mark.hager@gmail.com; https://www.linkedin.com/in/mahager/)

Further Reading:

Small, The Blue Whale

Zimmer, Fish With Fingers, Whales With Legs

Rice, Marine Mammals of the World

Berta, Return to the Sea

Whitehead & Rendell, The Cultural Lives of Whales and Dolphins

Mann, Deep Thinkers

Pyenson, Spying on Whales

Martenstyn, Out of the Blue

 

Organizations and Resources:

Centre for Research on Indian Ocean Marine Mammals (CRIOMM) (Sri Lanka)

Sri Lanka’s Amazing Maritime (SLAM) (Sri Lanka)

NOAA Fisheries, National Oceanic and Atmosphere Administration (USA)

Whale and Dolphin Conservation (WDC) (UK)

Marine Mammal Institute, Oregon State University (USA)

Wildlife and Nature Protection Society (Sri Lanka)

Sri Lanka Wildlife Conservation Society (Sri Lanka)

Department of Wildlife Conservation (Sri Lanka)

 

Whale Watching:

Borderlands, Weligama

Mirissa Water Sports, Mirissa

Raja and the Whales, Mirissa

Royal Tours, Mirissa

 

 

        

 

        

 

        

 

            

 

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