amphibian – 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.

Kermitops

Despite being named after the famous Muppet frog, Kermitops gratus here wasn’t actually a frog itself. Instead it was a close relative of the common ancestor of all modern amphibians, part of a grouping of amphibian-like animals known as amphibamiform temnospondyls.

Living in what is now Texas, USA, during the mid-Permian, about 275 million years ago, Kermitops would have resembled a chunky salamander. Only its fossil skull is known, so its full body size is uncertain, but based on the proportions of related amphibamiformes it was probably around 15-20cm long (~6-8″).

Although its discovery helps to fill in the very sparse fossil record of the early evolution of modern amphibians, it’s also complicated matters more than expected. Previously it was thought that the characteristic skull anatomy of modern amphibians evolved in a clear sequence, but Kermitops has a unique mix of features that doesn’t fit this idea – suggesting that there was a lot of convergent evolution going on in amphibamiformes at the time.

Crystal Palace Field Trip Part 1: Walking With Victorian Monsters

This past week I’ve been out of town and unable to work on much art, but instead here’s something a little different. I finally got the chance to go visit some familiar old faces out in the wilds of south London, so let’s go on a little tour of these iconic Victorian-era retrosaurs…

A photograph of an informational sign in London's Crystal Palace Park. The text on it reads, "The Crystal Palace Dinosaurs 1854, a journey through time and science". Three of the iconic Victorian dinosaur statures are also pictured below the title, showing the Iguanodon, Hylaeosaurus, and Megalosaurus.

The Crystal Palace Dinosaurs take their name from the original Crystal Palace, a glass-paned exhibition building originally constructed for a World’s Fair in Hyde Park in 1851.

In 1854 the structure was relocated 14km (~9 miles) south to the newly-created Crystal Palace Park, and a collection of over 30 life-sized statues of prehistoric animals were commissioned to accompany the reopening – creating a sort of Victorian dinosaur theme park – sculpted by Benjamin Waterhouse Hawkins with consultation from paleontologist Sir Richard Owen.

The Palace building itself burned down completely in 1936, and today only the ruins of its terraces remain in the northeast of the park grounds.

Two images of Victorian London's Crystal Palace building. On the left an old black-and-white photograph from around 1854 shows the original structure, a grand glass-paned building with ornate terraced gardens in front of it. On the right a more modern photo from 2011 shows what little remains today – just the ruins of the terraces and stairs. — *The Crystal Palace building then and now*
Left image circa 1854 (public domain)
*Right image circa 2011 by Mark Ahsmann (CC BY-SA 3.0)*

Six sphinx statues based on the Great Sphinx of Tanis also survive up among the Palace ruins, flanking some of the terrace staircases. They fell into serious disrepair during the latter half of the 20^th century, but in 2017 they all finally got some much-needed preservation work, repairing them and restoring their original Victorian red paint jobs.

A photograph of one of the surviving sphinx statues in the Crystal Palace ruins, reclining on a plinth beside some stone steps. It's recently renovated with a coat of terracotta red paint to match its original Victorian-era appearance. In the background the huge Arqiva Crystal Palace telecom tower can be seen.

…But let’s get to what we’re really here for. Dinosaurs! (…And assorted other prehistoric beasties!)

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.

Keraterpeton

Keraterpeton galvani here was part of a group of amphibian-like early tetrapods called lepospondyls.

Living in what is now southern Ireland during the Late Carboniferous, about 318-314 million years ago, this 30-40cm long (~1′-1’4″) fully aquatic animal was the earliest known member of the diplocaulid lineage (although its skull was much less elaborately modified than its famous boomerang-headed relative Diplocaulus).

It had a broad short-snouted head with eyes set far forward, and a pair of backwards-pointing bony “horns” at the back of its skull. Its forelimbs were smaller than its hindlimbs, and unlike most other diplocaulids it had five fingers on its hands instead of four.

Its vertically flattened paddle-like tail was also around twice as long as the rest of its body, and was probably its main source of propulsion in the water.

Keraterpeton seems to have been quite numerous in the coal swamps it inhabited, representing the most common species preserved in the Irish Jarrow Assemblage site – a location where fossil specimens were uniquely “cooked” and partially replaced with coal during the fossilization process.

Strange Symmetries #08: A Different Diplocaulus

With its bizarre boomerang-shaped skull, Diplocaulus is probably the most iconic ancient amphibian. (It even inspired the design of the pokémon Dragapult!) It was part of the lepospondyls, a diverse collection of early tetrapods mainly found in Europe and North America between the Early Carboniferous and the mid-Permian, about 350-270 million years ago.

But one species hung on a bit longer into the late Permian, about 259-254 million years ago, and this late-surviving lepospondyl was perhaps the oddest of them all.

Diplocaulus minimus was the only lepospondyl known from the supercontinent of Gondwana, found in what is now Morocco in northern Africa. About 70cm long, around half of which was its long tail, it had the distinctive elongated skull of a diplocaulid – but in a bizarrely asymmetrical shape.

The left prong of its skull was long and tapering, but the right was shorter and more rounded. This doesn’t seem to have been due to individual deformity or distortion of the fossil material, since more than one skull has been found with the same features, but the reason for such a striking amount of asymmetry in this species is unknown.

Diplocaulids’ head shapes are thought to have acted as hydrofoils, providing lift while they were swimming. Perhaps Diplocaulus minimus‘ much more wonky skull means this species wasn’t relying on that hydrodynamic function as much as its relatives, and something else was going on with its ecology.

…Although, that weird head does bear a surprising resemblance to a proposed asymmetric “flying wing” aircraft design from the 1950s, so it might have worked better for underwater flight than it seems at first glance.

Platycepsion

Platycepsion wilksoni was a temnospondyl amphibian that lived during the early-to-mid Triassic (~251-242 million years ago) in what is now New South Wales, Australia.

A single partial skeleton discovered in the 1880s is the only known record of this species, and represents a juvenile that would have been around 15-20cm long (6-8″). We don’t know exactly what it would have looked like as an adult, but it was probably quite similar to other closely-related members of the brachyopid family – mostly-aquatic salamander-like animals with short but wide toothy jaws, eyes set towards the front of the head, small limbs, and paddle-like tails.

A recent re-analysis of the Platycepsion specimen found evidence of soft-tissue preservation of external gills, showing that it wasn’t just a juvenile but a true larva, a sort of temnospondyl “tadpole”.

Distinct larval stages have been found in a few other types of temnospondyls, but this is the first definite example from the stereospondyls, a major Mesozoic lineage that survived all the way into the Early Cretaceous.

Brachydectes

The lysorophians were a group of Carboniferous and Permian tetrapods with highly elongated bodies and tiny limbs, usually thought to be part of the lepospondyl amphibians – but some recent studies have instead placed them and some of their close relatives as possibly being very early members of the reptile branch of amniotes.

Brachydectes newberryi here is one of the best-known lysorophians, represented by a good amount of fossil material compared to many of its relatives. Living in the Midwestern United States during the late Carboniferous and early Permian, around 310-290 million years ago, it had a proportionally tiny head and reached lengths of around 60-70cm (2′-2’4″).

Its wide shovel-shaped snout and thickened reinforced bones around its braincase suggest it was adapted for headfirst digging, and some specimens have actually been found preserved inside their burrows. The roof of its skull also developed extensive “sculpturing” as individuals aged, with juveniles having smooth bone surfaces and larger adults having a distinct rough bumpy texture.

So I’ve depicted it here with a speculative keratinous “head shield”.

Lethiscus

Ever since the earliest tetrapods crawled onto land and developed limbs and digits, some lineages have just… decided the whole “legs” thing was overrated and lost them entirely.

And the earliest known group to do this were the aïstopods. These highly elongated amphibian-like animals had specialized lightly-built skulls with large jaw muscles, and they may have filled a similar ecological niche to modern snakes, hunting small terrestrial invertebrates.

Lethiscus stocki was one of the first members of this snake-like group, living in Scotland during the Early Carboniferous about 340 million years ago. Growing to at least 50cm long (~20″), it was already a very specialized animal despite its basal position among the aïstopods, with eyes set far forward on its face and no trace of vestigial limbs.

CT scans of its skull have shown some surprisingly fish-like anatomy, especially in its braincase, features that were lost very early in tetrapod evolution. This suggests that aïstopods weren’t part of the lepospondyl amphibians like previously thought, but actually originated much much earlier in the tetrapod evolutionary tree – potentially placing them somewhere among the “fishapods” between Ichthyostega and Crassigyrinus.

Temnospondyl Toes

The evolutionary origins of modern amphibians are still a bit murky, but one of the most likely possibilities is that they evolved from a group of temnospondyls known as amphibamiformes. (Or, at least, that frogs-and-salamanders evolved from them. Caecilians might be a different type of temnospondyl.)

And a recent discovery adds a little bit more evidence to that hypothesis.

A new specimen from the 309-million-year-old Late Carboniferous Mazon Creek fossil deposits in Illinois, USA, shows some soft-tissue impressions around the body of a terrestrial amphibamiform* — most notably showing its toes, with chunky rounded fleshy pads at the end like those seen in many modern amphibians.

Fossil trackways already suggested that some terrestrial temnospondyls had chunky toes, but up until now all known soft-tissue impressions only showed the slender tapering toes of aquatic forms. This is the first direct fossil evidence of toe pads, and hints that a lot of modern amphibians’ soft-tissue features may have actually had a very ancient origin.

(*A more precise identification couldn’t be made, but it shows some similarities to both Doleserpeton and Pasawioops.)