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This blog has featured posts concerning saber-toothed seals and saber-toothed marsupials but did you know that the oceans around South America once contained a saber-toothed whale? Odobenocetops lived during the Pliocene era (around 2.5 to 5 million years ago). Two similar species are known in the genus from fossils discovered in coastal Peru. An early member of the dolphin superfamily, Odobenocetops was probably more closely related to narwhals and belgugas then to modern dolphins and killer whales.
Measuring only a little longer than 2 meters (6 feet) in length, Odobenocetops was remarkable (at least among whales) for its flexible neck–which could turn 90 degrees. The powerful blunt snout of the endearing little whale suggests that it fed from beds of mollusks and other bottom dwelling shellfish, which it rasped from their shells with a muscular tongue. Additionally, the Odobenocetopsidae had echolocation abilities like modern dolphins–although probably not so amazingly precise, since the extinct whales’ echolocation melons were much smaller than those of living dolphins.
Of course the most distinctive features of Odobenocetops were their long spiky teeth running parallel along their sides. Scientists speculate that these tusks could have been used to seek food or as a sensory organ–like the narwhal’s sensitive tusk. Perhaps male whales used their tusks to battle for females, like walruses do (although they seem awfully brittle for such battles). Some males had uneven tusks. The sole known skull of a male Odobenocetops leptodon features a right-hand tusk 1.2 m (4 ft.) long, while the left-hand tusk is only 25 cm (10 in.) long. Since this is the only male O. leptodon skull currently known, it is unclear whether such asymmetry was normal.
It is striking that the whales’ saber teeth were held next to the body and it makes one think that the whale did not execute many sharp turns. A humorous but somewhat sad cartoon which I found unattributed on the web demonstrates the potential drawbacks of the Odobenocetops’ striking saber toothed design.
I have always been fascinated by saber-toothed animals. Only a few saber toothed creatures remain in today’s world (like the estimable walruses and a few tiny saber-toothed deer) but in fearsome ages past, the design was widespread. Most readers are probably familiar with the smilodons, the magnificent saber-toothed cats which hunted the megafauna of Pleistocene North and South America, however the story of the saber-toothed cats intersects the story of another giant saber-toothed predator which was nearly as fearsome and even stranger. Thylacosmilus was a genus of saber toothed marsupial predators which ruled South America during the Miocene and Pliocene. Like the smilodons, Thylacosmilidae were large, agile predators which used their long fangs to slash the throats of huge prey. Unlike Smilodons, Thylacosmilidae were marsupials which gave birth to a tiny helpless larva which they then nurtured in a pouch.
The prominent teeth of Thylacosmilus were a result of convergent evolution and the creatures did not share any direct ancestors with cats since the divergence of placental and marsupial mammals (deep in the depths of the Mesozoic). Thylacosmilus’ teeth were also different in that they continuously grew throughout the animal’s life. The teeth were probably worn down as the predators gnawed on bones. Additionally Thylacosmilidae possessed scabbard-like bone flanges built into its lower jaw to protect its teeth (a feature missing entirely from Smilodons). Who knows what sort of noises Thylacosmilidae made with these peculiarly shaped mouths? For millions of years Thylacosmilidae lorded over the strange mammals of South America. The glyptodonts (and possibly other armadillos) developed their armor to ward off the mighty beasts. However the fickle play of tectonics undid the mighty killers.
In the beginning of the Pliocene, a land bridge joined North America and South America and suddenly the true cats arrived on what had been an island continent. As the climate dried out, Smilodons competed directly with Thylacosmilidae. Strange new herbivores appeared to displace the old prey animals. The Great American Interchange of long sundered mammalian lineages proved too much for the saber toothed marsupials. Thylacosmilidae were giant and fierce but they were no match for invasive cats.
Today we feature one of everyone’s favorite animals–the great toothwalkers of the northern oceans, the mighty walruses (Odobenus rosmarus). Adult Pacific male walruses can weigh more than 2,000 kg (4,400 pounds) and grow to lengths exceeding 13 feet. The huge pinnipeds live in vast colonies ringed around the Arctic Ocean. Females separate themselves from the fractious males in order to protect their calves from the squabbling and dueling of the bulls. The tusks (which can grow to 1 m (3 ft 3 in) in length) are also used by both genders to leverage their great weight out of the water—hence the name “toothwalker.” The word walrus comes from the Old Norse word “hrossvalr” which means horsewhale.
The distinctive face of the walrus is a mass of large coarse bristles properly known as vibrissae. Like the barbells of a catfish, these vibrissae are extremely sensitive tactile organs which help the walrus find shellfish on the dark and turbid ocean bottom. Walruses are capable of diving deep to find the invertebrates they like to eat. Scientists have recorded dives of 113 meters (371 feet) which lasted for about 25 minutes. Once the walruses have located a food source to their liking, they dislodge their prey with jets of water and then suction up the creatures. Apparently they are most partial to bivalve mollusks, snails, sea cucumbers, and crabs, but in extreme circumstances they can hunt large fish or even smaller seals.
Walruses can sleep in the water, their heads supported by an inflatable pouch which allows them to bob comfortably in the choppy near-freezing water. Additionally they change color with the temperature—their surface skin can be pink, as blood rushes near to the surface when they are hot, or they can turn grey brown when cold.
All pinnipeds, including walruses, are in the order Carnivora where they seem to most closely share a common ancestor with bears back in the Oligocene. Walruses are the only species in the only genus of the family Odobenidae. Once the Odobenidae were a sprawling family with at least twenty species spread across three several subfamilies (the Imagotariinae, Dusignathinae and Odobeninae), but something went wrong and walruses are all that’s left of the saber-toothed seals.
Walruses’ only natural predators are polar bears and killer whales, but even the world’s largest land predator and the most formidable ocean predator find adult walruses intimidating. Except in extraordinary circumstances the huge predators only hunt calves or weakened walruses. Predictably, humans are the walruses’ main problem. In the 18th, 19th, and 20th century immense numbers of walruses were killed for blubber, skin, meat, and ivory. Today this commercial exploitation has ended and worldwide populations have rebounded somewhat–though certain geographic areas remain depopulated.
Perhaps because they move ponderously on land and because their whiskers suggest comic uncles, some people underestimate walruses. I have been fortunate enough to see a young adult walrus in captivity (he was orphaned as a pup and would have died if not taken in by an aquarium) and it is a mistake to underestimate these animals. The walrus (whose name was Ayveq) was as large as a midsized truck, yet he could move with shark-like speed but ballet-like grace in the water. Bull walruses come into maturity at the age of 7, but they don’t usually get to mate with cows until they are 15 or so and have bested many competitors in savage sword duels with their tusks. Ayveq had access to a harem of walrus cows from a much younger age, and his comic attempts to understand himself and his relation to the females was a source of much surprised astonishment among aquarium-goers. As a peripheral point, I neglected to mention that male walruses have a uniquely large baculum which can measure up to 63 cm (25 inches)—larger than that of any other land mammal. The apparatus supported by this bone is similarly oversized.
Ayveq could produce a remarkable series of shrieks, grunts, whistles, bellows—apparently communication is important in the teaming masses of walrus colonies. Whether drinking herring through a straw, mugging for a crowd, or using his back flippers to amuse himself, Ayveq was always remarkable. His death saddened me considerably and I could not write about walruses without mentioning his extravagant personality. Knowing Ayveq also left me convinced that walruses might be perverts but they are also highly intelligent and gregarious beings. This conviction is born out by the painstaking work of biologists and zoologists who are just beginning to recognize how complicated walrus society is. It is no wonder, that so many poets, artists, and musicians have referenced the remarkable tusked creatures.