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My favorite mammals are the mighty proboscideans—elephants, mammoths, mastodons, gomphotheres, moeritheriums, and so on. I have not written about them more because the only proboscideans we know a lot about are the elephants–and elephants are complicated—they are smart and they have human length lives of great social complexity, all of which makes them hard to write about. Additionally elephants are tragic—their populations keep shrinking away as humankind grasps for ever more land and poachers kill the great sentient giants for their ivory. Yet elephants still have a perilous chance to keep on living. What is even sadder than the senseless slaughter of the magnificent elephants are the other proboscideans, which have vanished one by one from earth. Everyone knows about the woolly mammoth and Cuvieronius, the new world gomphothere, but the last non-elephant proboscideans to have died out were even more contemporary.
The stegodons (from the extinct subfamily Stegodontinae) evolved in Southeast Asia approximately eleven and half million years ago. They lived in large swaths of Asia throughout the Pliocene and Pleistocene epochs and they survived in Indonesia deep into the Holocene epoch. Radio-carbon dating has dated the last living stegodons to 2,150 BC. The giants died after the pyramids were built at Giza and great cities had begun to sprout up in Mesopotamia and along the Indus valley.
Stegodons looked much like elephants—a resemblance which has caused much taxonomical confusion. Paleontologists once believed elephants descended from stegondons but It seems now that both stegodons and modern elephants descended from Gomphotheriidae (a sister group to the mammoths). Stegodons had different molars and their tusks were so close together that their long trunks draped over the sides. There were many species of stegodons, the largest of which were among the largest of proboscideans, far more immense than today’s two elephant species. The biggest stegodont were 4 m (13 ft) high at the shoulders and had a body length of 8 m (26 ft) which does not even count their 3 meter (10 foot) tusks!
Modern humans reached Southeast Asia 50,000 years ago so we lived in proximity with the stegodons for some time before they vanished. Certain species of stegodons reached isolated Indonesian islands where, over generations, they shrank into dwarf forms. These tiny stegodons were hunted by Homo floresiensis, which seems to have been a dwarf species of human (although the scientific community has not reached consensus concerning the nature of Homo floresiensis). Imagining tiny versions of humans hunting tiny versions of huge elephant-like creatures boggles the mind! I am profoundly sorry the stegodons dwarf, giant, or otherwise could not have held on for a few more millennia. I would love to have seen them—or by 4000 years ago were they already as the Saola is now—ever retreating from a world that did not seem to fit them?
The world’s largest hornet is the Asian giant hornet (Vespa mandarinia). An individual specimen can measure up to 5 cm (2 inches) long and has a wingspan of 7.6 cm (3 inches). Giant hornets have blunt wide heads which look different from those of other wasps, hornets, and bees and they are colored yellow orange and brown.
The Asian giant hornet ranges from Siberia down across the Chinese coast into Indochina and lives as far west as India, however the hornet is most common in the rural parts of Japan where it is known as the giant sparrow bee. The sting of the Asian giant hornet is as oversized as the great insect is. Within the hornet’s venom is an enzyme, mastoparan, which is capable of dissolving human tissue. Masato Ono, an entomologist unlucky enough to be stung by the creature described the sensation a “a hot nail through my leg.” Although the sting of a normal honey bee can kill a person who is allergic to bees, the sting of an Asian giant hornet can kill a person who has no allergies–and about 70 unfortunate souls are killed by the hornets every year.
Armed with their size and their fearsome sting, Asian giant hornets are hunters of other large predatory insects like mantises and smaller (i.e. all other) hornets. The giant hornets do not digest their prey but masticate it into a sticky paste to feed to their own offspring. A particular favorite prey is honey bee larvae, and since European honey bees have no defense against the giant wasps, all efforts by Japanese beekeepers to introduce European bees have met with failure. Japanese honey bees however have evolved a mechanism (strategy?) to cope with hornet incursion. When a hive of Japanese honey bees detects the pheromones emitted by hunting hornets, a crowd of several hundred bees will form a gauntlet (carefully leaving a space for the hornet to enter). Once the hornet walks into the trap the bees rush on top of it and grasp it firmly. They then begin to vibrate their flight muscles which raises the temperature and produces carbon dioxide. Since giant hornets cannot survive the CO2 levels or high temperatures that honey bees can, the hornets put up a titanic struggle to overcome the mass of bees, killing many in the process. However honey bees have a fanaticism which would do credit to the most ardent practitioner of Bushido, and they usually kill the invaders.
We boldly continue armor week with an overview of the magnificent armadillo family. This order of armored mammals (Cingulata) is more diverse than any other sort of armored mammals–outshining even the scaled pangolins. Today the only living members of the Cingulata order are the armadillo family (a successful group consisting of more than 20 living species) but the armadillos’ extinct cousins were once far more widespread and bizarre. These relatives included the pampatheres–long plantigrade browsing creatures covered in banded armor who roamed the continent from one end to the other. Even more impressive were the glyptodonts, massive tank-like creatures bigger than a compact car.
The Cingulata order is part of the superorder Xenarthra. Separated from all other placental mammals for over 100 million years (due to South America’s unique isolation after the breakup of the southern supercontinent Gondwana), xenarthrans evolved in different directions from other mammals. The unique challenges and opportunities of their island continent resulted in bony domed giants like the pampatheres and glyptodonts, both of which are characterized by tortoise-like body armor composed of bone segments (osteoderms). The glyptodonts were unlike tortoises in that they could not draw their head beneath their shells: instead their heads were protected by bony caps atop their skulls. The largest glyptodonts could grow to 4 metres long, 1.5 metres high and have a mass of 3 tons (Ferrebeekeeper has already written about the smallest known Cingulata species—the pink fairy armadillo, which can still be found living in the central dry lands of Argentina).
Thanks to convergent evolution the herbivorous glyptodonts resembled other armored giants like cryptodire turtles and ankylosaurs. One species of glyptodont, Doedicurus clavicaudatus, even had a heavy spiked tail (although it is unclear whether this was used against predators or to compete for territory and mates).
When the first members of the Cingulata order emerged in the Myocene, the top predators of South America were giant running predatory birds–the Phorusrhacidae, which resembled giant dashing eagles up to 3.2 metres (10 ft) high. The glyptodonts, pampatheres, and armadillos outlasted these terror birds and they then outlasted the carnivorous metatherian mammals (with terrible saber teeth) which followed. When the Isthmus of Panama connected South America with North America (and therefore with an entirely new universe of ultra-competitive mammals), the armored cingulatans competed just fine with the newcomers. Some glyptodonts and pamphatheres wandered up through Central America and found new homes in North America. The armadillos are still there. However at the end of the last ice-age, a new African species arrived and brought a devastating and final end to the glyptodonts, the pampatheres, and most of the armadillos. But even this newly arrived predator seemed impressed by the greatest of armored mammals. An Argentine anthropologist even reports discovering a site twenty leagues from Buenos Aires where early human hunters had used glyptodont shells as dwelling places.
There are about 120 living species of marine mammals (although that total may tragically become much smaller in the very near future). Of this number, only one species is herbivorous. The mighty dugong (Dugong dugon) is the last animal of its kind, a gentle lumbering remnant of the giant herds of sirenian grazers which once graced the world’s oceans. Dugongs are distinct from the three extant species of manatees (the world’s other remaining sirenians) in that they never require fresh water at any point of their lives. Additionally dugongs possess fluked tails in the manner of dolphins and whales.
Dugongs live in shallow tropical waters of the Indian Ocean and the Pacific Ocean. They range from Madagascar to the Philippines, but are only common along the north coast of Australia (where conservation efforts and a limited human population have allowed them to live in peace). Dugongs can swim in deep oceans for a limited time, but prefer to stay on continental shelves where they can feed on seagrass and marine algae. Their all-salad diet does not prevent them from growing to substantial size: some individuals have been known to reach more than 3.5 meters in length (11 feet) and weigh over 950 kilograms (nearly a ton). Although Dugongs can live more than seventy years, they reproduce extremely slowly. Females gestate for over a year and then suckle their calf for around 18 months. Calves may stay with their mothers for many years after being weaned and need almost contact with their mothers for security and affection until they are almost grown. Young dugongs swim with their short paddle-like flippers, but adults use their tail for propulsion and only steer with their flippers.
Dugongs have a variety of vocalizations with which they communicate. Usually they live in small family units. Great herds are not unknown but seagrasses do not grow in sufficient quantity to support such numbers together for long.
Like the other sirenians, Dugongs have dense bones with almost no marrow (a feature known as pachyostosis). It has been speculated that such heavy skeletons help them stay suspended just beneath the water in the manner of ballast. The lungs of dugongs are extremely elongated, as are their large elaborate kidneys (which must cope with only saltwater). Additionally, the blood of dugongs clots extremely rapidly.
Dugongs face a number of natural threats, particularly storms, parasites, and illnesses. Because of their large size they are only preyed upon by alpha predators such as large sharks, killer whales, and salt-water crocodiles. As with other marine animals, the greatest dangers facing dugongs come from humankind. For millennia Dugongs have been hunted for meat, oil, and ivory. Traditional medicine from various portions of their range (wrongly) imputes magical properties to parts of their bodies. Worst of all, dugongs are frequent victims of boat collisions or are killed as by-catch by fishermen trying to catch something else.
Today we celebrate the world’s largest bivalve mollusk, the magnificent and world-famous giant clam (Tridacna gigas). Native to shallow coral reefs of the South Pacific and Indian oceans, giant clams can weigh up to 500 lbs and measure 50 inches across. Huge specimens can be very ancient and some have lived for more than a century. Giant clams are hermaphrodites: every individual possesses both male and female sex organs–however a clam is incapable of mating with itself. They are broadcast spawners producing vast numbers of gametes which they release in response to certain chemical transmitter substances. During these spawning events (which usually occur in conjunction with certain lunar phases) a single clam can release over 500 million eggs in one evening. Giant clam larvae then swim free among the plankton. They pass through several mobile transition phases before settling down in one favorite home (as can be seen in the comprehensive life cycle drawing below).
As usual for sea creatures, the giant clam has a troubled relation with humankind. Fabulists have asserted that the great bivalves chomp down on divers for food or out of spite (the clams do slowly shut when harassed, but the movement is a defense mechanism and happens gradually). They are considered delicacies on many South Pacific islands and naturally the insatiable Japanese pay a premium to eat them as “Himejako”. Their shells also command a premium from collectors. Across the South Pacific, giant clams are dwindling away thanks to overfishing, reef destruction, and environmental factors.
It is sad that the gentle and lovely giant clam is suffering such a fate (although aquaculture is now bringing a measure of stability to some populations). In addition to being beautiful and useful to ecosystems, they are remarkable symbiotic creatures. A unique species of algae flourishes in the mantle of the giant clam and the clam gains much of its energy and sustenance from these photosynthetic partners. The clam possesses iridophores (light sensitive circles) on its flesh which allow it to gauge whether its symbiotic algae is getting enough sunlight–and perhaps watch for predators. It can then alter the transparency of its mantle flesh accordingly. According to J. H. Norton, giant clams have a special circulatory system to keep their symbionts alive and happy. The happy and beneficial relationship between a clam and its algae allows the former to attain great size and the latter to remain alive in the ever-more competitive oceans. I have concentrated on writing about T. Gigas, but there are many other members of the Tridacninae subfamily which lead similar lives (although they do not attain the same great size). To my eye they are all remarkable for their loveliness.
Leedsichthys (Leedsichthys problematicus) was the largest known bony fish. It lived during the middle Jurassic (155 million years ago), feeding on algae, plankton, and small shrimp & fish—much like a modern whale shark or baleen whale. Leedsichthys had over 40,000 teeth with which to skim its meal from the water. Although most of these huge fish were around 12 meters (approximately 40 feet) or smaller in length, many scientists believe that Leedsichthys was capable of growing much larger. Fragmentary specimens suggest they attained lengths greater than 17 meters (about 55 feet) and even larger individuals might be found.
Leedsichthys is named after Alfred Nicholson Leeds, who discovered its fossilized remains in 1886 in England. He had so much trouble piecing the bones together that he gave the fish the species name of “problematicus”. Leedsicthys was most likely a global species with a presence in all of the open oceans of the Jurassic world. It is unclear why the species went extinct, but paleontologists have speculated that it was out-competed by the teleosts–the modern bony fish–which lay vastly more eggs than pachycormids like Leedsichthys.