lissamphibia – Nix Illustration

Palaeoplethodon

There are no salamanders living in the Caribbean today, but one tiny fossil shows that this wasn’t always the case.

Palaeoplethodon hispaniolae was discovered in a chunk of amber from the Dominican Republic on the island of Hispaniola. The exact age of this type of amber is uncertain, but it most likely dates to the early-to-mid Miocene, about 20-15 million years ago.

The only known specimen is a hatchling, just under 2cm long (0.8″). It’s unclear what its full adult size could have been, but based on its modern relatives it may have grown to anywhere between 4.5cm and 20cm long (~2-8″).

Its strongly webbed hands and feet suggest it was very closely related to modern tropical climbing salamanders – but Palaeoplethodon had a unique webbing arrangement, with its feet relatively elongated and its hands fully fused into small rounded pads.

Funcusvermis

Biofluorescense is the term for when living organisms “glow” under certain types of light. Although it’s not usually directly visible to human eyes, wavelengths such as ultraviolet can reveal it – and we’re still only just starting to discover how widespread it really is in nature.

This phenomenon has been found in all major groups of modern amphibians, with most of them glowing green under UV, suggesting that it originated in their ancestors at least 300 million years ago.

So, ancient species like Funcusvermis gilmorei here could probably glow green, too!

Living during the late Triassic (~220 million years ago), fossils of Funcusvermis were found in what is now Arizona, USA. It’s only known from fragmentary remains, but those pieces are distinctive enough to identify it as the earliest known relative of modern caecilians.

It had a caecilian-like jaw with two rows of teeth, but unlike its worm-like modern relatives it still had small legs and wasn’t as highly specialized for burrowing. The shape of its vertebrae suggest it had a tubular body, and while its exact proportions and full length are unknown it may have been comparable in size to the smallest modern caecilians, around 10cm long (~4″).

Its combination of anatomical features gives further support to the idea that all modern amphibians share a common ancestor among the dissorophoid temnospondyls. The more distantly related but also caecilian-like Chinlestegophis may be a case of convergent evolution, representing a separate branch of temnospondyls that were coincidentally exploring a similar sort of lifestyle at around the same time.

Almost-Living Fossils Month #25 – Europe’s Fully Aquatic Frogs

The palaeobatrachids were a group of frogs, part of a fairly “primitive” lineage that also includes the living pipids. They first appeared in the fossil record about 70 million years ago in the Late Cretaceous, but may have actually originated much earlier, perhaps as far back as the Late Jurassic (~145 mya).

These frogs lived mainly in Europe, with a few possible remains also known from North America in the Cretaceous. They were fully aquatic, spending their entire lives in water, and fully-grown adults looked similar to modern Xenopus clawed frogs, with slightly flattened egg-shaped bodies, upwards-facing eyes, and long fingers and toes.

Some fossils preserve soft-tissue impressions, showing internal organs such as unusual bag-shaped lungs. Eggs and juveniles have also been found, and while most species’ tadpoles usually reached lengths of around 6cm (2.4″), a few were comparatively gigantic, growing to over twice that size.

The end-Cretaceous extinction (~66 mya) had little overall effect on the palaeobatrachids, and they continued to thrive in the warm wet environments of Europe during the early Cenozoic. But as climates in Western Europe gradually became drier and cooler starting in the Early Oligocene (~33 mya) they mostly disappeared from that region and instead shifted east towards Central and Eastern Europe, ranging as far as Russia.

By the Late Pliocene (~3 mya) they were struggling to cope with the ongoing cooling and drying, and the onset of the Pleistocene glaciations made things even worse for them.

Palaeobatrachus langhae was probably the last species of these frogs, known from the Early Pliocene to the mid-Pleistocene (~5 mya – 500,000 years ago). Growing to about 10cm long (4″), it lived in some of the final refuges of the palaeobatrachids in Eastern Europe, inhabiting inland temperate areas where winter temperatures weren’t too harsh.

Unfortunately the palaeobatrachids didn’t quite manage to make it through the Ice Age, ending up trapped by their fairly specialized habitat preferences. During repeated glacial periods the temperatures became too cold for them, freezing the water they depended on, but the warmer climates to the south were also too dry for them to migrate into – and with nowhere to go, they finally went completely extinct just half a million years ago.

Almost-Living Fossils Month #13 – Some Long Salamanders

A group of salamanders called batrachosauroidids first appeared in the fossil record at the very end of the Jurassic, about 145 million years ago, originating in Europe and quickly spreading to North America. Long snake-like bodies and reduced vestigial limbs gave these amphibians a very similar appearance to modern amphiumas or sirens, but they weren’t actually very closely related to each other – instead, the batrachosauroidids’ closest living relatives are thought to be mudpuppies and the blind cave-dwelling olm.

They were probably fully aquatic, living in wetlands with slow-moving currents, and the structure of their jaws suggest they were active predators that would have fed on other smaller animals in the water.

After surviving the end-Cretaceous mass extinction fairly well, with fossils of a couple of species known from both sides of the Cretaceous-Paleogene boundary, the batrachosauroidids continued on for most of the Cenozoic. They seem to have disappeared from Europe first, with the last known record in the mid-Eocene (~40 mya), but they persisted in North America for at least another 25 million years, well into the Miocene.

One of the last known members of the group was Batrachosauroides dissimulans from the mid-Miocene of Florida and Texas, USA (~16-13 mya). It was also one of the largest of the batrachosauroidids, similar in size to modern amphiumas at around 1m long (3′3″).

Past that point in time there’s no further evidence of batrachosauroidids, although due to the rather poor fossil record of salamanders it’s possible they may have survived for a while longer – but since amphiumas and sirens began to develop larger body sizes from the Late Miocene onwards, it’s likely that they were evolving to fill the ecological niches left vacant by the extinction of the last batrachosauroidids.

Almost-Living Fossils Month #07 – Scaly Amphibians

Although there are just three main types of modern amphibians alive today – the frogs, salamanders, and caecilians, collectively known as “lissamphibians” – they weren’t always the only ones.

A fourth major lineage called albanerpetontids originated in the Middle Jurassic, about 166 million years ago. They’re usually thought to be slightly closer related to frogs-and-salamanders than to caecilians, but they also might not quite be true lissamphibians and instead belong just outside the group as evolutionary “cousins”. It’s a little complicated since we’re still not actually sure which group of ancient amphibians the lissamphibians even evolved from.

Resembling tiny salamanders, usually only around 5cm long (2″), albanerpetontid fossils have been found in North America, Europe, Africa, and Asia. In some places their remains are actually quite common, suggesting they were one of the more numerous small vertebrates in their ecosystems. They’re thought to have lived mostly in leaf litter, similarly to some small modern lizards like ground skinks, wriggling and burrowing through the loose material and preying on small invertebrates.

Their most notable feature was their body being covered in a mosaic of small scales – although unlike reptile scales these were bony structures formed under a layer of skin, structurally much more like fish scales, and they probably weren’t particularly visible in life. They also had very flexible necks for amphibians, with a convergently mammal-like joint between their skull and vertebrae.

After surviving the end-Cretaceous extinction alongside their lissamphibian relatives the albanerpetontids ended up mostly restricted to just Europe, but they seem to have continued on there for pretty much the entire Cenozoic.

Albanerpeton pannonicus here was one of the very last known members of the group, living just 2.5 million years ago in the late Pliocene and early Pleistocene. Despite the albanerpetontids’ 160-million-year history and having made it through multiple mass extinctions, it seems to have been the cooling Ice Age climate that finally sent these scaly little amphibians into extinction.

Habrosaurus

Sirens are part of the salamander branch of the lissamphibians, and are some of the most unusual members of the group. They have an eel-like body shape, with small forelimbs and no hindlimbs at all, and have functional external gills as adults. Their main diet is carnivorous, with palatal teeth and a keratinous beak at the front of their jaws adapted for eating hard-shelled prey – but they’ve also been observed feeding on plant material, a rarity among amphibians.

Habrosaurus here was one of the earliest known sirens, living during the Late Cretaceous and Early Paleocene of North America (~84-58 mya). Reaching lengths of around 1.6m (5′3″), it was one of the largest known lissamphibians of all time, comparable in size to some modern giant salamanders.

It lacked the beak seen in its modern relatives, instead having specialized chisel-like teeth at the edges of its jaws that convergently served the same purpose of delivering a crushing bite.