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Chitons are back in international headlines again! Or, to be more technically accurate, the overlooked armored mollusks at least made it into the news (perhaps for the first or second time in their 400-500 million year history). These remarkable miniature tanks consist of a muscular mollusk which lives encased in 8 interlocking pieces of hard aragonite armor. The armor is not only a shell–it contains integral parts of the chiton such as aragonite eyes and other sensory cells. Thanks to this robust design, chitons are extremely successful and they can be found living in intertidal zones worldwide. Although they lack the pizzazz of their flamboyant mollusk cousins such as bobtail squid or giant clams, chitons are of enormous interest to a new generation of materials scientists who have been studying the natural world to get fresh ideas for molecular engineering. This weekend’s news story comes from such scientists who discovered that a brown rectangular chiton, Cryptochiton stelleri, (aka the “gumboot chiton”, or “the wandering meatloaf”) contains an esoteric mineral named santabarbaraite never before found in a living creature. Santabarbaraite is an extremely hard and tough mineral (itself only discovered by scientists in the year 2000) which contains a surprising amount of water. In the parlance of chemists, it is an amorphous ferric hydroxy phosphate mineral hydrate. The gumboot chitons manufacture this material as part of their long rows of rock-hard teeth (with which they scrape algae from marine rocks). Coincidentally, gumboot chitons are the largest chitons out there, with a maximum possible length of 36 centimeters (14 inches).
This is undoubtedly fascinating to people with advanced understanding of the chemical structures and properties of matter, but it is somewhat abstruse. The study’s lead author, scientist Derk Joester of Northwestern helps contextualize the importance of the finding by noting that “mechanical structures are only as good as their weakest link, so it’s interesting to learn how the chiton solves the engineering problem of how to connect its ultrahard tooth to a soft underlying structure.” The researchers are already planning how to use the secrets they have gleaned from the chiton to print hard santabarbaraite structures onto soft papers.
During the Mesozoic, the age of dinosaurs, mammals were widespread, but they kept a low profile so as to avoid the baleful attention of the great reptiles. A fossil of one of these furtive early mammals was discovered last November (2011) in Argentina. The creature was christened as Cronopio dentiacutus, and not only does the animal’s partial skull give us a window into mammalian form in the late Cretaceous it also provides a special treat for regular readers of Ferrebeekeeper, for like the Smilodon, the walrus, and the Odobenocetops, Cronopio has distinctly pronounced saber teeth (despite being a small scurrying squirrel-like creature).
A model of the Cronopio dentiacutus–which was only 10 to 15 cm (4 to 6 inches) long.
Cronopio dentiacutus was probably actually more shrew-like than squirrel-like and used its saber teeth for hunting insects. Based on its large eye sockets, Cronopio most likely hunted its prey at night (when it could also more easily escape the attention of the dinosaurs and other larger predators.
Julio Cortázar, Argentine Surrealist author
Cronopio dentiacutus takes its species name from a Greek phrase meaning sharp teeth, but the origin of its genus name is rather more literary. The Argentine surrealist writer Julio Cortázar wrote several books about abstracted categories of fictional entities and the Cronopio was the idealistic but disorganized type of being (as opposed to rigid, highly-organized “famas” and indolent, dull “esperanzas”). It is unclear what creative/idealistic features of this insectivorous early mammal struck the fancy of the discovering paleontologist to provoke such a name, but it is nice to see scientists pay Argentine belles-lettres such an acknowledgement.
A Smilodon fends off the vulture-like Teratornis at what would later be called the Rancho La Brea tar pits, situated in Los Angeles, California (Painting by Charles R. Knight)
Lately this blog has been fixated on magnificent saber-toothed mammals. We have featured the extinct saber-toothed whale, a saber-toothed marsupial predator, the little saber-toothed deer, and even the familiar walrus (in reality, a giant saber-toothed seal), but we realize that everyone has really been looking forward to the most famous saber-toothed animal of them all, Smilodon, the saber toothed cat. Smilodon was actually a genus of several large cats, the biggest of which, Smilodon populator, weighed 360 to 470 kg (790 to 1,000 lb) and was larger than modern tigers or lions. In fact Smilodon species are sometimes known as “saber toothed tigers” or “saber toothed lions,” however taxonomists tell us such names are off the mark since the Smilodons belonged to the extinct Machairodontinae genus of felines rather than the familiar Panthera genus of big cats so familiar today.
About two and a half million years ago, Smilodon evolved in North America from an earlier genus of saber toothed cat Megantereon (there were a lot of other earlier genera of saber-toothed cats, not to mention even more genera of saber toothed carnivores which were not exactly felines—the whole story is complicated). During the Great American Interchange with South America the big predators invaded South America at the same time armadillos were making their way up into North America. Yikes, that’s a pretty lopsided exchange.
In addition to long razor sharp teeth, Smilodons possessed immense neck and forelimb muscles. Using the muscles of their front torso they would pull down and pin the great grazing metafauna of the American plains. Prey animals almost certainly included bison, tapirs, deer, American camels, and ground sloths. Additionally Smilodons might have opportunistically killed juvenile mastodons and mammoths. To dispatch such large prey Smilodons employed their fearsome canine teeth with which they bit through the prone creatures’ necks.
Smilodon fatalis (reconstruction/specimen at the Page Museum)
Paleontologists have collected a great deal of fossil evidence concerning Smilodons, which suggest that the big cats were sophisticates social predators like today’s lions or wolves. The number and nature of saber-toothed cat fossils recovered from tar pits suggests that Smilodon prides would converge together on prey animals caught in the petrochemical ooze–only to become trapped themselves. Also some fossilized smilodons have shown evidence of badly broken bones healing—a rarity in carnivores which is generally only possible for pack/pride animals which can (sometimes) rely on a support network.
Thanks to their size, ferocious appearance, and highly characteristic teeth, Smilodons have a special place in human culture to the extent that few other extinct animals do. The Flintstones had a pet smilodon named “Baby Puss” which evicted Fred from his house in the title sequence and the moral struggles of Diego the saber tooth constituted the moral hook of “Ice Age” a cartoon movie. Ironically for all of our apparent fondness for the great cats, it seems that human migration into the Americas may have been the downfall of the great cats (which vanished 10,000 years ago) but whether their extinction was the result of humans overhunting their prey, shifting climate, or some other factor remains an open question.
Smilodon by Knight
Musk Deer
Continuing our series of posts about saber toothed mammals we come to a second family of living creatures. Half way between the primitive chevrotains (mouse deer) and the familiar true deer (cervids) are the Moschidae, a family of small artiodactyls consisting of one genus with several similar species. The musk deer are small delicate grazers which live in the forested mountains or alpine scrubland of Asia. Musk deer weigh between 7 and 17 kilograms (15 and 37 lb) depending on gender, age, and species. Unlike true deer, the little creatures lack antlers, but male musk deer make up for this absence with a pair of elongated canine teeth which they use to fight for breeding rights.
Alpine Musk Deer (Moschus chrysogaster)
Like true deer, musk deer eat the tender shoots of trees and grasses, as well as berries, lichens, and mosses. Females live in small territories of approximately 100 to 200 acres. The territory of a dominant male will overlap several of the females’ territories. Female musk deer give birth to a single fawn. Musk deer are nocturnal or crepuscular. They use their acute hearing and excellent sense of smell to flee from predators at the slightest hint of danger.
The skull of a male Siberian Musk Deer (Moschus moschiferus)
Male adult musk deer have a musk pouch located between their genitals and their umbilicus which they use to attract mates. Unfortunately for the little saber toothed deer this pouch also attracts human hunters. For centuries (or longer) musk has been a prized luxury good, so much so that, at times, prices have soared to $45,000/kg on the black market. The musk is said to have an incredibly complex aroma but the main notes are earthy, woody, and “animalic” (i.e. fecal). Dried musk grain must be substantially tinctured with alcohol before it produces a perfume which is pleasant to humans. The resultant substance however served as a mainstay of the perfume industry and as a cure-all nostrum in ayurvedic medicine until the creation of synthetic musk. Poor musk deer from several species were nearly wiped out because of whatever mysterious power their sexual marking fluid has on humankind.
The Dwarf Musk Deer (Moschus berezovskii)
Thylacosmilus digital illustration
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.
Thylacosmilidae (artist unknown)
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.
Thylacosmilidae and Smilodons were not closely related (click on this picture to visit "Understanding Evolution" an excellent site where I found this helpful image)
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.
Thylacosmilus atrox (digital art by viergacht)
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