Amphibians

As creatures of the moist and warm, amphibians may seem unfit for the world of ice and desiccation. Without waterproof skins on their bodies and eggs, and largely intolerant of the ocean, they ought to be left behind as the evolutionary relics they appear to be. However, though their range is now spotty across the world, and though many lineages did die, they have a surprisingly bright future as a whole.

For one, the cooled waters of the world are rich in oxygen, giving these animals' way of life an edge that they did not have before. For another, the quick cooling of lakes and rivers did not affect them so much as it did fish, for unlike them, they can walk off to new bodies of water, often warmer and shallower ones caused by seasonal rains as opposed to a more dependable yearly quota. Finally, though their realm is indeed patchy, their hold on these areas allows them to diversify independently from one another. The two great lineages will go on — two only, for the aberrant and fascinating caecilians perished.

It is not uncommon to see amphibians in niches that freshwater fish once filled. Various salamanders in the Americas and Asia swim in rivers and lakes; long, thin, and eel-like, they nab fish, aquatic insects, and tadpoles from the water column. These tadpoles are plentiful when the time is right, but even out of season, sizeable specimens can be seen scraping algae or hunting zooplankton, their adults only appearing for a short window for reproduction. But as is common with amphibians, much of their identity has to do with how they interact with the land.

Amphibians hunt flying and walking animals regularly, either while in the water themselves or ambling upon its surface. These have appeared in various forms. In North America's deciduous forests, grand riverside toads can be seen ambushing prey on land or in water. In west equatorial Africa, sharp-eyed targetfrogs float at the surface, leaping upward or onto the shore upon smaller animals. These behaviors may seem vaguely crocodilian at times. However, the resemblance is not at all vague in one lineage of large carnivorous salamanders, the mandermaws, which carry the suchomorphic torch into the future.

Comparing them to other animals directly is oversimplifying, however, and indeed, there is nothing quite like a mandermaw. They are incredibly wrinkly, with flat bodies, long tails, and giant heads set with seemingly sunken eyes. And they are huge, with the largest species measuring 3.5 m long from nose to tail, larger than any other amphibian living or dead.

These titanic creatures are derived from Andrias, a genus of giant salamanders that lived in East Asia and contained some truly giant species. Tolerant of cold water in a variety of environments, from caves to rocky streams to forested waterways, they were prepared for a dip in temperature. Adult salamanders did not move much from their small territories, so their survival was largely through the relocation of young to new areas. These young would live for many years and required very little food to stay alive, allowing them to wait out the cold until the perfect time to breed. Still, these giants' survival was a struggle, requiring all remaining species to interbreed as they were forced into each other's spaces. A scene only a few hundred thousand years into the event would feature only one hybrid species, Andrias totum.

As the world stabilized, they found themselves in broadleaved forests and woodlands roughly around southeastern China, following the coast loosely. Some continued to eat crustaceans, fish, other amphibians, small mammals — basically anything they could nab — either from the water or while trekking on land. However, others found new uses for these adaptations. Their ancestors had unusually flexible lower jaws, the left and right of which could move independently of each other. This, along with slight flexibility in their skulls, allowed them to bite with only one side of their mouths, keeping the other firmly closed. This allowed them to target prey precisely, their broad heads sucking a large volume of water only in the direction needed, drawing the target into the mouth where they were clamped with innumerable small, sharp teeth. While the salamanders had strong bites, their skulls did not connect under their eyes; in technical terms, their maxillae are only connected anteriorly. Thus, they tended to clamp prey using the frontmost teeth only, transferring force through the bony bridge connecting the upper jaw to the braincase.

Typical mandermaws hunt much the same, lying on a lake or river's bottom with eyes staring upward. Their vision, while much improved from the weak eyes of their ancestors, is still poor. They rely instead on sensory nodes distributed on their wrinkly skin, especially along their sides like the lateral line of a fish. These beasts will wait on the bottom for an impressively long time, with slow metabolisms that will keep them going for months. Even breathing is not an urgent matter, for their incredibly wrinkled, contorted skins provide them with plenty of oxygen from the cool water around them, allowing them to stay submerged for potentially hours before needing to surface for air. This is a major change from their ancestors, which relied on their lungs primarily. When a big enough animal approaches, the mandermaw will not strike until the creature makes contact with the water, perhaps to drink, take a dip, or find fish to eat.

When the time is right, the mandermaw strikes; the mud and stone of the bottom suddenly shoots out in the form of a spectacularly camouflaged amphibian, charging out in a fraction of a second with a quick swipe of the tail. Its great mouth opens, hinging much further back along the skull then before, and the broad head draws in an immense amount of water in the direction of the prey only. This suction is only secondary, however, for the mandermaw can snap its jaws around the animal even if both parties have left the water. The prey may struggle, but the predator's flexible jaws conform to its body, each reinforced tooth biting into its flesh. The prey may fight back, but the mandermaw's skin serves yet another purpose: It is rubbery, thick, and only loosely attached to its body, so strikes often deal little damage as its hide simply gives way. The beast manipulates its catch so the prey's bulk is at the tip of the predator's snout, right where the upper jaw connects via the bone bridge to the rest of the skull. It then clamps down, crushing the ribcage, vertebrae, or even the skull. The predator may wrench off parts to swallow, but more often consumes the prey whole. It may not need to feed again for weeks.

Mandermaws have done splendidly for themselves. Compared to crocodilians, they have higher population densities thanks to their lower metabolism, kill prey faster, are less conspicuous, and can wait far longer than them. However, they certainly have their troubles. Mandermaws cannot take prey as large as crocodilians could, for their small teeth and flexible bones would be more easily damaged. They also bear an evolutionary quirk they must find a way to compensate for: Mandermaws have no eyelids. This proves to be a serious concern when handling violently lashing prey, and makes dispersal to new feeding grounds over water more complicated. It has found solutions to these, however. Mandermaw maxillae and prefrontal bones have grown a ridge that runs close to the skin above, while their eyes have sunken somewhat into their heads. This provides a bony barrier for their delicate eyes. Losing one or both eyes, while uncommon, is not a death blow, for the animals can hunt via their mechanoreceptors alone.

These long-bodied, short-legged creatures are capable of walking and hunting on land, though adults rarely do. When they do, it is usually after a rain, and often when forced out by territorial neighbors. On land they eat small to medium-sized vertebrates, though with less success than they would in their watery domain. Their young, however, have proportionately bigger eyes and longer legs, allowing them to disperse and hunt in water and on land alike. Both adults and young find a handy use for their eye guards on dry ground, for they allow water to be held in a little pool over the eyes. This often makes the salamander look like it is wearing glasses. One smaller species in particular has obvious rounded pools over each eye when out on land, hence their name, spectacled mandermaws.

Curiously, the way of the mandermaw is closely mimicked by a South American frog, the geriatric pancake frog. Descended from Telmatobius, which contained several wrinkly, aquatic frogs, they have very large feet and hunt in a quite similar fashion. They are, however, far smaller.

With dryness abounding, other amphibians have instead taken terrestriality to further extremes, reducing their dependency on water. Unfortunately, much of the diversity of aridity-resistant amphibians was lost in the age of cold, for they tended to bury themselves in the earth to wait out particularly dry times, and they were often prepared for high temperatures, not low. But with loss comes new niches for others to fill, and no amphibian was better prepared to jump at the opportunity than toads. Adaptable, unspecialized, and resilient to dry conditions as a rule, nearly all the borders of the amphibian realm are inhabited solely by these toxic frogs.

For example, take southern Africa, once home to such creatures as the odd shovelnose frogs and the adorable rain frogs. Both of these had effective adaptations to live in parched habitats, most impressively that they lacked a tadpole stage, instead producing little frogs from their eggs. They are succeeded by a toad with its own odd adaptations, the sandscale toad.

Sandscale toads might warrant a double-take upon first glance. They appear to have surpassed the most characteristic feature of amphibians, covered head to toe in dry scales that allow them to live in dry grasslands and deserts with ease. In truth, however, it is not a scaly covering that camouflages them so well against the sandy soil in which they live, but it is the sandy soil itself.

When spring is here and temporary ponds sit in the warm sun, these toads can be seen enjoying a swim or a rest on the water's edge. They are hardly recognizable as sandscale toads, for their yellow skins are moist and glisten in the sun. They do have an odd texture up close, though, with shallow pores that dot their skins. These are used to armor themselves in dirt. When the water has yielded to mud in the heat of the sun, sandscale toads prepare for the long, arid days ahead. They leave what is left of the water and come to a patch of dry dirt or sand, them roll themselves around in it, covering themselves thoroughly. The small pore-like structures they are covered in are in fact minute cups, each of which catches a grain of sand or dirt. As the frog's skin goes from shiny and wet to only partly damp, the cups contract as water leaves them. This holds the grain tightly, allowing the toad to venture off into the arid unknown.

The toads will not see liquid water again for some time. Unlike virtually all dry-adapted frogs, they will not burrow into the ground and wait for rain to return. Instead, they travel forth. Sandscale toads rely on their marvelous armor to protect them as they travel, usually at night, feeding on insects and spiders. But the armor is more than just a shield against dehydration. It provides them very convincing camouflage, for the grains against their yellow skin make them virtually indistinguishable from the soil. Their abrasive coverings, too, are very offputting to predators; one that nabs a sandscale toad will feel as if its mouth is full of sand and dirt, which may not be worth a snack that is only 4-7 cm long. If pressed further, the covering allows the frog to escape a grabbing mouth or claw, wrestling itself away and leaving the predator with only loose grains. This is risky, for it is much more difficult to reapply the protective coating without soaking in standing water first, but the toad does what it must. Last, sandscale toads have warty skin that produce copious bufotoxin, the characteristic poison of toads. All this greatly increases their survivability in the open, leaving dehydration as their greatest enemy.

Being tied to rain to reproduce is unfortunate in an environment that is so arid, giving them only one small window in spring to do it. However, they can do at least some of the work earlier to make it as quick as possible. A mature male sandscale toad will croak loudly at night, sounding like "guac guac" or sometimes more of a squeaking noise, to attract a female. These two can do what few frogs can: they can mate without water, practicing internal fertilization by pressing their cloacas together, as opposed to fertilizing the eggs once they are in water as most frogs do, called external fertilization. Just as remarkable, female sandscale toads will hold not eggs within them when they are ready to lay, but fully-formed tadpoles - they give live birth! This combination of traits, external fertilization and viviparity, are rare indeed among frogs, though, perhaps because of their tendency to resist arid environments, this is the third time these traits have co-appeared in toads.

Barring chance windfalls of rain, winter comes without the toads seeing even a drop of water. Though they can last a bit longer above ground thanks to the ability to bask without fear of dehydration, they are forced to weather the bitter cold underground in torpor. When spring arrives, the toads arise, and the downpour they have been waiting for is nigh. The toads will smell water from an impressive distance, whiffing the scent of algae and petrichor. A scene of a growing seasonal pool is a magical event as parched sandscale toads shuffle in from all directions, dressed in old hides with patches of dirt missing from their backs. They lay their eyes upon standing water for the first time in an entire year. They eagerly soak themselves and drink up, then remove their sandy exterior by rubbing with their long back legs. This is easy now that the cups are wet and supple again. The degraded skin itself follows soon after, for this is the only time they can shed. The females waste no time in entering labor, spilling the well-developed tadpoles into the precious water. They will grow quickly on a diet of plankton and occasional mosquito larvae, becoming subadults by the time the water yields to mud, and later, parched earth. This they can do at breakneck speed, becoming independent of standing water within 8 weeks. However, because they cannot grow without shedding their skins, sandscale toads will burrow beneath the pool they were born in for their first dry season, reaching adult size at the end of the following spring.