sloth unleashed

biomedicalephemera:

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]

dailyfossil:

Ambulocetus

Reconstructions by Carl Buell 

When: Eocene (~50 to 48 million years ago)

Where: Pakistan 

What: Ambulocetus is fossil whale relative. This beast was about 10 feet (~3 meters) long, and not very agile in either the land or the water. It was capable of movement on land, but it would have been rather slow and lumbering, as its forelimbs were shortened compared to its fully terrestrial ancestors. In the water it would have been capable of swimming with some speed, but it would not have been able to make quick turns as it chased its prey. Therefore, it has been reconstructed as an ambush-style predator, in the same niche as the modern crocodile. It would have laid in wait in the water, with its relatively dorsal eyes and nose peeking above the sufrace, able to see and smell approaching prey. Once a prey animal got close enough, Ambulocetus would launch itself from the water and try to catch the animal in its powerful jaws, such as is shown above. I think it is some form of basal horse that is trying to avoid the snapping jaws of Ambulocetus. This ambush style strategy could have also worked with aquatic prey, such as schools of fish. Ambush predation is seen in some species of whales today, Orcas (the killer whales) have been recorded ambushing seals on ice flows. 

Ambulocetus lived on the edge of the Tethys Sea (a body of water between India and Asia) in what is now Pakistan. At the time this region was one of many islands off the shore of the island continent of India, which had not yet collided with Asia (this would not happen for tens of millions of years). This warm seaway was full of mammals starting to return to the seas, including other lineages of whale relatives. In the cetacean family tree, Ambulocetus falls between Indohyus and modern whales; it was carnivorous - as all modern whales are-, and far more adapted for aquatic locomotion than Indohyus was, with shortened legs and a much more powerful tail. 

(via scientificillustration)

dailyfossil:

Castorocauda

Art by Mark Klingler

When: Middle Jurassic (~164 million years ago)

Where: China

What: Castorocauda is an aquatic mesozoic mammal. It is known from a very well preserved slab specimen, which shows a suite of features indicating an adaptation to aquatic life. Its limbs were powerful, and easily capable of strong swimming or digging. Its tail was flattened, shown both by the soft tissues preserved on the slab, but also by its flattened caudal vertebrae, which are very simular to that of living swimming mammals, such as the beaver, otter, or platypus. This tail is what gives this Jurassic animal its name: Castorocauda translates to ‘beaver tail’. Its teeth were also specalized for aquatic life; they have primary cusps which curve backwards, which is seen in fish eating animals today, such as the seals. Castorocauda was about 17 inches (~43 cm) long, making it one of the larget Jurassic mammals. 

Castorocauda would have looked somewhat like a platypus lacking a bill, but its diet was more like that of a seal. In the mammal family tree Castorocauda is far far removed from any living taxa. It is a member of a group called the Docodonta, just a few branches removed from one of the first Mammaliforms: Morganucodon. As Castorocauda clearly had fur in life, this puts fur extremely far down on the mammalian lineage. It has been hypothesized previously that even more basal taxa had fur, but there has been no conclusive evidence. As Castorocauda was completely coated in fur, except for much of its tail, it is extremely likely fur originated much deeper in the mammalian lineage, possibly in the non-mammalian synapsids. 

The discovery of Castorocauda also shows that mesozoic mammals were much more ecologically diverse than has been previously proposed. Our ancient kin were not only small rat like insectivorous creatures that ran in the shadows of the dinosaurs; they swam, preyed upon dinosaurs themselves, and even flew (more on that one later)!

(via scientificillustration)

dailyfossil:

Rhynchonkos

Reconstruction by Smokeybjb. 

When: Late Permian (~275 - 270 million years ago)

Where: Oklahoma, USA 

What: Rhynchonkos is a very rare amphibian that lived in the swamp land covering what is now Oklahoma in the Permian. It was about 4.5 inches (~11 cm) long, not counting the tail, with an extremely elongated body and tiny tiny limbs. The elongation of its body compared to other amphibians was accomplished via replication of vertebrae, not elongation of each individual bone.  Rhynchonkos had at least 36 pre-sacral (before the hips) vertebrae. Its mouth was full of rows of tiny teeth, and it is likely that it ate insects and small fish in its swampy home. Older literature about this animal refers to it as Goniorhynchus rather than its current name. This change is due to the fact that the fossil taxon was named in 1970, however, a moth was given the name Goniorhynchus in 1896. Stupid insects. At least it wasn’t a beetle this time! The name  Rhynchonkos was applied in 1981. 

The phylogentic relationships of Rhynchonkos are fairly uncertain. For some time it was held as a close relative of modern caecilians (a group of limbless amphibians), but later fossil finds have cast doubt upon this affiliation. Within other fossil ‘amphbians’ Rhynchonkos has been placed in Lepospondyli (along with our friend Diplocaulus). This group as a whole has a much debated relationship with living amphibians. Some studies have them having nothing to do with living amphibians (lissamphibians), where as others link specific taxa with certain groups of living amphibians. Such as the now disputed Rhynchonkos - caecilian link. It may seem obvious to link this almost limbless fossil with the limbless amphibians, but amphibians (and lizards too!) seem to like to lose their limbs at the drop of a hat. It is very common in swimming and burrowing forms. 

(via scientificillustration)