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Black Piranha - Serrasalmus rhombus
The black piranha (also known as the redeye or rhombeus piranha) has recently been discovered to have a bite force as strong as the estimated force of the extinct Megapiranha.
Though the negative stigma towards piranhas is largely undeserved, the mature black piranha is one of the most aggressive fish. This is especially true recently, with the over-fishing of the Amazon and Orinoco rivers, depleting the food sources of the adult fish.
Most species of juvenile piranhas feed on the scales and fins of others fish. Yes, they will swim up to, and rip the fins off of big fish, especially as they near maturity, but are not yet large enough to reliably hunt down other fish.
Despite their huge size (up to 1 m long, four times longer than adult black piranhas) and extremely strong bite force, the Megapiranha of the Pleistocene era (8-10 mya) wasn’t believed to have a solely carnivorous diet. Their saw-shaped teeth bear similarities to the Serrasalmus genus, but also to the teeth of the Pacu, or “vegetarian piranha”.
Expédition dans les parties centrales de l’Amérique du Sud, de Rio de Janeiro à Lima et de Lima au Para. Under direction of Le Comte Francis de Castelnau, 1856.
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Some other drawings I did at the Zoology Museum.
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Ways to Die: Snake Venom
The vast majority of snakes that one encounters in the wild (unless you live in Australia or India) are either non-venomous to humans or want nothing to do with you.
However, should you stumble upon a rattlesnake nest or coral snake hole while texting in the middle of nowhere, there will probably be a combination of different enzymes and polypeptides pumped into your body, via the modified parotid salivary glands (right below the ear in humans) that snakes have evolved over the ages, to disable their prey. Of course, you’re not prey, but you stepped on a snake while texting. It has every reason to envenomate you.
While all snakes have multiple active enzymes in their venom, all snakes dangerous to humans have either neurotoxins or cytotoxins as a significant component in their venom. For the most part, elapids (such as the cobras and mambas) create neurotoxins, while the viperids (such as vipers, adders, and rattlesnakes) create cytotoxins.
Neurotoxins
- Dendrotoxins: Inhibit neurotransmission by blocking the exchange of positive and negative ions across the pre-synaptic neuronal membrane, causing paralysis. Found in some rattlesnakes (such as the Mojave) and mambas.
- Fasciculins: Destroys acetylcholinesterase (AChE) in synaptic clefts of nerves. Without AChE, acetylcholine (ACh) is not broken down, and remains bound to the postsynaptic vesicles of the nerve, leading to constant contraction of the related muscles. This is called tetany or tetanic paralysis. Found only in mambas.
- α-neurotoxins: Very large group of toxins that mimic ACh and bind to post-synaptic vesicles, leading to numbness and paralysis. Found in cobras, kraits, and sea snakes.
Cytotoxins
- Cardiotoxins: Target muscle cells and cause depolarization. If enough of these components reach the heart, the depolarization can cause irregular heartbeat or spontaneous stopping of the heart. Can cause fasciculations in skeletal muscles. Found in the Naja genus, and in King Cobras. Minor but important component of mamba venom.
- Phospholipases: Proteins that target the phospholipid bilayer of cells, causing cellular rupture. Can cause extreme blistering at site of bite. Relatively uncommon, found in the Japanese Habu.
- Hemotoxins: Burst red blood cells (hemolysis), causing thin blood, internal bleeding, and blood clots due to the massive clotting response. Found to some degree in almost all vipers, as well as some cobras.
Images:
Top: Bungaris fasciatus - Banded Krait. An elapid, and the largest of the kraits. Has neurotoxic venom. [source]
Center Right: Hydrophis robusta [now Hydrophis spiralis] - Yellow Sea-Snake. The longest sea snake, at 3 m (9.8 ft). A member of the Hydrophiinae, separate from other elapids. Though they have some of the most toxic venom in the world, bites are extremely uncommon and often unnoticed. [source]
Center Left: Vipera russellii - Russell’s Viper. A particularly aggressive viperid. Necrosis and amputation following envenomation not uncommon, due to hemolysis and local cell damage. [source]
Bottom: Vipera caudisona [now Crotalus horridus] - Timber Rattlesnake. A venomous viperid endemic to the United States. Primarily hemotoxic venom, very low fatality rate, but very painful bites. [source] -
Illustration for PocketWatch, a product that allows consumers to check for gingivitis. I did most of this in Photoshop, but the basic structure of the dental implant hardware was done in Illustrator.
Thanks for the submission Kristin!
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Age estimation from teeth
Eruption of deciduous (baby or milk) teeth and permanent (adult) teeth occurs at fairly regular intervals during the subadult years of development (see the figure above, deciduous teeth are shaded). Therefore, age estimation of subadults based dental eruption is quite accurate.
While tooth wear and permanent tooth loss can occur in subadults, these degenerative changes are usually associated with adults. Loss of permanent teeth and accompanying bone resorption of the alveolar bone of the maxilla and/or mandible are often associated with old age. Tooth wear or dental attrition most often occurs in adults, but the age of onset depends on diet and other environmental factors. This process leads to loss of outer white tooth enamel and exposure of the yellowish dentine of the pulp cavity, especially on the cusps of the teeth. The older an individual is, the more dentine is exposed due to tooth wear.
Image is scanned from Tim D. White, Michael T. Black & Pieter A. Folkens: Human Osteology, Academic Press, 3 ed. (2011)
Posted on December 10, 2012 via Academia with 164 notes
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megalodon teeth in graphite, by Karsyn deGast
Thanks for the submission karsyndegast
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1950’s German Educational Chart, published by the Deutsches Museum Dresden.
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Deer Skull Sketch by bparker321 on Flickr.
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Binturong skull
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Form and Skull of Sus scrofa moupinensis - North China wild boar
Piggers! The wild boar was domesticated in China at some point between 7000-8000 BCE, after dogs, sheep, and cats, but before cattle, horses, and camels. Wild swine are native to most of Asia, Central Europe, and North Europe, but at this point have formed feral herds throughout every continent but Antarctic. In the wild, most Suidae are very aggressive in protecting themselves and their territory, and uncastrated domestic males (boars) tend to display the same characteristics in many breeds.
As one can tell by the sharp canines and incisors, and broad canines good for grinding food, Suidae are extremely omnivorous, and find food by digging through the dirt with their snouts. In males, the canine teeth grow through their entire life, though at different rates in each genus. In feral boars (Sus scrofa), the canines don’t often reach more than a few inches long, but they are razor-sharp and expertly wielded. In some other species, such as the babirusa, the overgrown canines (tusks) are much longer than those of Sus scrofa, reaching the point of growing so long they curve backwards and into the cranial cavity.
Tusk-brains aside, all Suidae are extremely intelligent when it comes to domestic animals. As omnivores, they’re both hunted and hunters in the wild, and need to have an effective and developed brain to balance both.
Elemens de zoologie. Henri Milne-Edwards, for M. Alphonse Milne Edwards. 1840.
