Retro vs Modern #09: Hallucigenia sparsa

If just one single species had to represent how our reconstructions of prehistoric animals can drastically change, it would have to be Hallucigenia sparsa.

1970s

First discovered in the 1910s in the Canadian Burgess Shale fossil deposits, specimens of Hallucigenia were initially categorized as being a species of the early polychaete worm Canadia. It wasn’t until the 1970s that they were recognized as being something else entirely, and the first reconstruction of this tiny animal was bizarre.

It was depicted as a long-bodied creature with a single row of tentacles along its back, and several pairs of long sharp spines that were interpreted as being stilt-like “legs” used to walk. The tentacles were thought to catch food from the water and pass it forwards to the bulbous “head” – and at one point it was even proposed that all the tentacles had their own additional “mouths” at their tips!

It’s easy to look back on this version now and laugh at how ridiculous and obviously wrong it was, but it’s important to remember the historical context here. This was coming from a point when the incredible animal diversity of the Cambrian Explosion was only just starting to be understood, revealing a range of poorly-understood bizarre and alien-looking forms like Opabinia – “weird wonders” that were considered to be representatives of previously unknown ancient branches of life.

At the time, Hallucigenia‘s utter weirdness and impractical body plan seemed to almost make sense as a unique evolutionary “failed experiment” that had left no living relatives.

1990s

Discoveries of legged-and-armored lobopodian “worms” in the Chinese Chengjiang fossil deposits during the 1980s prompted a re-interpretation of Hallucigenia in the early 1990s. Speculatively reconstructing it as a lobopodian with the spines on its back and with the tentacles as a set of paired clawed legs started to make it seem a lot less alien and a lot more like a real velvet-worm-like animal – and just a year later the “missing” other half of the leg pairs was confirmed to be present in some of the fossil specimens.

But it was still unclear which end was actually the head, and whether the large blob-like structure was a real part of Hallucigenia‘s anatomy or just an artifact of the fossilization process.

2020s

New research in the mid-2010s finally settled the head problem and clarified a lot of Hallugicenia‘s anatomy, discovering that the slender elongated end had a pair of simple eyes and a mouth with a throat ringed with tiny teeth.

We now know Hallucigenia sparsa lived all around the world during the mid-Cambrian, about 518-508 million years ago, with body fossils known from Canada and China and isolated spines found in numerous other similarly-aged locations. Instead of an evolutionary dead-end “weird wonder” it was actually an early member of the vast arthropod lineage, just one of a highly diverse collection of successful Cambrian lobopodians, and its closest living relatives are probably velvet worms and tardigrades.

It grew up to about 5cm long (2″) and had seven pairs of long sharp defensive spines along its back, covered with a microscopic surface texture of tiny triangular “scales”. It had seven pairs of clawed walking legs, with most of its feet tipped with two claws each but the final two pairs having just one, and its body ended right at the final pair of limbs – the “blob” structure in some fossils was actually just an artifact the whole time, formed by Halligenia‘s innards being forcefully squeezed out during its burial in the seafloor sediment.

Its neck region bore three pairs of long delicate tendril-like limbs, which may have been covered in feathery hair-like structures for filter-feeding similar to some other lobopodians. A small pair of velvet-worm-like antennae may also have been present on its head, and could have been a sexually dimorphic feature.

Retro vs Modern #08: Helicoprion davisii

First discovered in Western Australia in the mid-1880s, the bizarre-toothed eugeneodont cartilaginous fish Helicoprion davisii was initially mistaken for a species of the equally weird Edestus. It was eventually recognized as part of a separate genus over a decade later, when similar fossils of its close relative Helicoprion bessonowi were found in the Ural Mountains.

1890s-2000s

With Helicoprion only known from strange buzzsaw-like spiral whorls, the function and location of this structure in the fish’s body was a huge source of confusion for over a century.

The earliest interpretation was a defensive structure curling upwards from the snout, then as part of the tail or dorsal fins. It was soon realized to probably be part of the lower jaw instead, but the exact arrangement was still a mystery.

A downward-curling position was popular in reconstructions for much of the 20th century. From the 1960s onwards, however, discoveries of preserved skull cartilage and soft-tissue body outlines of other eugeneodont species began to give a better idea of what these fish were and what they looked like. They were identified as being related to modern chimaeras, but with a very different appearance – they had streamlined shark-like bodies with large triangular pectoral fins, a single dorsal fin, no pelvic or anal fins at all, and broad keels along the sides of their tails.

A single tooth whorl sat in the middle of the lower jaw, with its sides covered by skin, and the largest and youngest teeth formed at the back before spiralling forwards, downwards, and inwards.

In the 1990s a “pizza-cutter” reconstruction gave Helicoprion long narrow jaws with the whorl positioned very far forwards, sawing and crushing prey against the underside of the snout. A version with the whorl very deep inside the throat was also proposed in 2008, but only a year later a new variant of the pizza-cutter saw-jaw model suggested the presence of a specialized “pocket” in the upper jaw lined with teeth.

2020s

Finally, in 2013, CT scanning of a Helicoprion specimen originally discovered in the 1960s revealed something incredibly special – an almost complete three-dimensionally preserved and articulated set of jaws. It showed narrow jaws that were shorter than the previous reconstructions, with the whorl occupying the entire lower jaw and braced by cartilage on each side.

We now know Helicoprion davisii was found worldwide during the early-to-mid Permian, about 272-268 million years ago, and based on some of the biggest known tooth whorls it may have reached sizes of up to 8m long (~26′), similar in size to modern basking sharks. It continuously added new and larger teeth to its whorl throughout its life, with the smaller older teeth being retained instead of shed, slowly pushed into a tight spiral deep inside the lower jaw.

The upper jaw formed a sheath-like pocket lined with a “pavement” of numerous tiny rounded teeth, and as Helicoprion closed its jaws the various parts of the whorl simultaneously grabbed, sliced, and pulled prey further into its mouth – a mechanism possibly specialized for efficiently de-shelling cephalopods like ammonites and nautiloids.

Retro vs Modern #07: Mosasaurus hoffmannii

The first scientifically documented mosasaur fossils were skulls discovered in the Netherlands during the 1760s and 1770s, but these remains were initially interpreted as belonging to a fish, crocodile, or whale. In the late 1790s their resemblance to monitor lizards was noted, and the fossils were soon recognized as belonging to giant marine reptiles unlike any known living species – a revolutionary concept at the time, and influential in the early development of ideas about extinction.

In the 1820s Mosasaurus hoffmannii was the first species officially described. For several decades it was thought to be a giant amphibious lizard with either webbed feet or flipper-like legs, with one of the earliest popular reconstructions being the 1850s Crystal Palace statue.

By the 1870s more complete fossil discoveries in North America had revealed the paddle-like flippers and fully aquatic nature of mosasaurs. Skin impressions showed overlapping keeled diamond-shaped scales resembling those of rattlesnakes, but proportionally much smaller compared to their body size.

1890s

Then, in the late 1890s, one mosasaur specimen was interpreted as having a mane-like “fringe” of soft tissue along its back.

Only a few years later this was realized to be a mistake, actually being preserved tracheal cartilage, but it was too late. The idea had already caught on in artistic depictions and quickly became a paleoart meme, with mosasaurs frequently portrayed with elaborate frills for the majority of the next century.

2020s

Early arguments about whether mosasaurs’ closest relatives were monitor lizards or snakes had settled down by the 1920s, with the consensus at the time being monitor lizards, and the first half of the 20th century saw little mosasaur research beyond the naming of a few new species. Much like the ichthyosaurs and plesiosaurs it was only really in the wake of the Dinosaur Renaissance that interest in these marine reptiles and their paleobiology really began to pick up again.

Rather than sea-serpent-like creatures we now recognize that mosasaurs actually looked more like lizards converging on whales or ichthyosaurs, with smooth streamlined bodies and vertical tail flukes. The size and shape of their scales varied across different parts of their bodies, parts of their bodies had dark coloration (likely with a countershaded pattern), and they probably had forked tongues.

They had a higher metabolic rate than most modern lizards, and may even have been warm-blooded. They probably also gave birth to live young, although a recently-discovered fossil soft-shelled egg found in Antarctica has been suggested to have come from a large mosasaur.

The debate about their evolutionary relationships has been reignited, too, with some recent studies once again supporting a very close relationship to snakes – although there’s currently no clear consensus.

Our modern view of Mosasaurus hoffmannii is a large chunky mosasaur that grew to at least 11m long (~36′). It lived during the end of the Cretaceous period, about 70-66 million years ago, and inhabited a wide range of climates across much of the ancient Atlantic Ocean and various connected shallow seaways, with fossils known from Europe, Africa, and North and South America.

Its long jaws had a powerful bite force and it seems to have been a more visual hunter than some other mosasaurs, with relatively large eyes and a less well-developed sense of smell. It was one of the largest marine animals of its time and was probably a generalist apex predator, feeding on a wide variety of prey such as fish, ammonites, and other marine reptiles.

Retro vs Modern #06: Plesiosaurus dolichodeirus

Plesiosaurs were first recognized as a distinct group of fossil animals in the early 1820s, only a few years after ichthyosaurs. Initially they were perceived as being closer in form to reptiles in the “chain of being” than the more fish-like ichthyosaurs were, and so the group’s scientific name ended up reflecting that early interpretation – “plesiosaur” roughly translates to “near to reptiles”.

The first named species of plesiosaur was Plesiosaurus dolichodeirus, based on a near-complete skeleton discovered by Mary Anning that revealed the strange long-necked proportions of these animals for the first time.

1830s-1850s

Early reconstructions of plesiosaurs in the 1830s compared them to “a snake threaded through a turtle”, giving them highly sinuous necks and a turtle-like body. Much like ichthyosaurs they were assumed to be amphibious, using their flippers to crawl up onto the shore like a sea turtle.

The 1850s Crystal Palace plesiosaur statues show a variant of this design with smooth skin textures and fairly flexible reptilian bodies, with powerful shoulders and flipper postures that give them an overall almost seal-like appearance.

1860s-1990s

From the 1860s onwards a more upright S-shaped neck pose became the most common depiction of plesiosaurs. The writhing snake-like necks persisted in some reconstructions of the extremely long-necked elasmosaurids, but the overall design for these animals that caught hold for the next century was an egg-shaped body with oar-like flippers and a swan-like neck – a body plan that would end up so influential in pop culture that it was incorporated into modern lake monster folklore, with the Loch Ness Monster being the most famous example.

During this period plesiosaurs were often portrayed as floating or swimming at the water’s surface, rowing along with their flippers and using their long necks to snatch up prey. They were generally assumed to still haul out turtle-style to lay their eggs on the shore, although it wasn’t clear how the very largest species would have been able to support their own weight.

2020s

Since the 1990s a boom of new plesiosaur species and biomechanical studies have brought a lot of changes to our understanding of these marine reptiles.

Their necks are now considered to have been less flexible, capable only of more gentle curving, and were probably much thicker and more streamlined with the body than previously depicted. Rather than oar-like rowing all four of their flippers were probably used in more of an “underwater flying” vertical motion similar to modern sea turtles – which is pretty fitting, considering that their closest living relatives are now thought to actually be turtles.

They gave live birth and were probably warm-blooded, with a thick layer of insulating blubbery fat and a teardrop-shaped body outline. Their skin texture was smooth, but one exceptionally well-preserved specimen shows a covering of tiny thin millimeter-sized scales that wouldn’t have been visible in life except in extreme closeup.

We now know Plesiosaurus itself was a fairly small species, around 3.5m long (~11’6″), with a broad body and a short thick tail that probably had a rudder-like fin – usually assumed to be vertically-oriented, but possibly horizontal instead. It lived during the Early Jurassic, about 201-183 million years ago, in the shallow tropical sea that covered what is now southern England, and had a rather small head compared to other plesiosaurs, with its eyes facing upwards and to the sides.

It had sharp needle-like teeth that would have been used to catch soft-bodied aquatic prey like fish and cephalopods. It’s not known whether it had extensive fleshy lips, croc-like snaggletoothed jaws, or something in-between, so the facial soft tissue on this particular reconstruction is rather speculative.

Retro vs Modern #05: Ichthyosaurus communis

Fossilized ichthyosaur bones have been found for centuries, but were initially misidentified as being the remains of fish, dolphins, and crocodiles. More complete skeletons began to be discovered in the early 19th century – particularly by pioneering paleontologist Mary Anning – and Ichthyosaurus communis was one of the first species of these ancient “fish lizards” to be scientifically recognized.

1830s-1870s

Early reconstructions of ichthyosaurs in the 1830s depicted flippered crocodile-like animals with long straight eel-like tails and strangely shrinkwrapped features, showing the sclerotic rings of their eyes and the internal bones of their flippers as highly visible externally. They were also frequently portrayed as being amphibious, hauling themselves out of the water to bask.

By the late 1830s impressions of smooth scaleless skin had been found, and specimens with tail-tips that were always “broken” in the exact same place were interpreted as evidence of the presence of some sort of paddle-like tail fin. The 1850s Crystal Palace Ichthyosaurus statues show this slightly updated version, along with a low dorsal ridge on their backs reminiscent of a beluga whale.

2020s

From the 1880s onwards the discovery of exceptional ichthyosaur specimens preserving whole body outlines revealed a fully aquatic streamlined shape, a triangular dorsal fin, and a crescent-shaped vertical tail fluke. Numerous examples of fossilized pregnant females also showed that ichthyosaurs gave live birth rather than laying eggs.

This highly dolphin-like version of ichthyosaurs quickly caught on and became the standard depiction into the early 20th century, frequently showing them as highly active animals – swimming in groups, chasing fish and ammonites, and leaping dramatically out of the water like their modern cetacean counterparts. While we don’t actually know if they were social or acrobatic like dolphins, it was still a surprising and refreshing contrast to the increasingly lumpy and sluggish depictions of non-avian dinosaurs that were happening around the same time.

Actual further paleontological study on ichthyosaurs was scarce for decades, however, with a general attitude that the group was already scientifically “complete” and there wasn’t much new or interesting left to learn about them anymore. It wasn’t until the late 20th century that they began to have their own “ichthyosaur renaissance” alongside the dinosaurs, with a sharp rise in research in the last few decades bringing us a lot of new information about their diversity and biology.

Ichthyosaurus communis was just one of several species in the Ichthyosaurus genus, living during the Early Jurassic, about 196-183 million years ago, in the shallow tropical seas of what is now Europe. About 3.3m long (~11′), it was adapted for high-speed long-distance swimming like a modern tuna, and it probably had a large keeled peduncle on the sides of its tail.

Bone structure and isotope analysis show that ichthyosaurs were all warm-blooded. One exceptional specimen also preserves an insulating layer of cetacean-like blubber, along with some evidence of its coloration: overall darker on the top and lighter on the underside in a countershaded pattern.

(I’ve given this reconstruction some speculative disruptive camouflage, too.)

Some of the preserved pigmentation has enough microscopic detail to show what appear to be branched melanophore cells associated with the ability to change color – suggesting that ichthyosaurs may have been able to actively darken and lighten their coloration like some modern lizards.

Retro vs Modern #04: Archaeopteryx lithographica

Archaeopteryx lithographica was first discovered in the 1860s, still in the early days of our understanding of dinosaurs, and was a timely example of the sort of transitional form first proposed by Charles Darwin only a couple of years earlier. For over a century it was a famous icon of evolution, and has been part of a lot of weird drama over the years – it’s been central to arguments about bird origins, was accused of being a fake, and one specimen even vanished under mysterious circumstances.

1860s-1970s

At the time of its discovery Archaeopteryx was actually fairly quickly accepted as demonstrating an evolutionary link between dinosaurs and birds… but sadly this view wasn’t to last.

In the early 20th century opinion shifted towards birds not being dinosaurs but instead descended from “thecodont” reptiles (what we’d now call early archosaurs and pseudosuchians). And so for a long time Archaeopteryx ended up being depicted as simply the “first bird”, a half-reptile half-avian curiosity.

Reconstructions of it from this time period varied from very good to kind of awkward depending on how much the artist was trying to emphasize its reptilian ancestry, commonly featuring wonky-fingered wings and a scaly lizard-like face. It was also frequently depicted with bright gaudy parrot-like coloration, with a specific yellow-and-blue color scheme becoming a “paleoart meme” so prolific that it would eventually inspire the design of a Pokémon.

2020s

After decades of stagnation the dinosaur-bird link was resurrected in the early 1970s, with the discovery of the bird-like Deinonychus kicking off the Dinosaur Renaissance. Along with the explosion of spectacularly feathered dinosaur fossils from China in the mid-1990s, Archaeopteryx finally began to be properly presented as a feathered dinosaur again.

Continued study of the known Archaeopteryx specimens in the last couple of decades has vastly improved our knowledge of what this animal would have looked like, revealing previously unknown features like the exact plumage arrangement on its wings and legs, and even potentially some details about its coloration.

Living in southern Germany during the Late Jurassic, about 150-148 million years ago, Archaeopteryx inhabited what was then an island archipelago in a shallow tropical sea. It grew to around 50cm long (~1’8″) and was almost entirely covered with pennaceous feathers, externally probably just looking like a long-tailed bird.

It had broad wings, with asymmetrical flight feathers similar to those of modern birds but with more extensive coverts, some of which were probably a matte black color. Its legs also sported long “feather trousers” and a “raptor“-like hyperextensible second toe, and there was a slight forked shape to the tip of its tail.

Arguments have gone back and forth about how well it was actually able to fly, with current thinking being that it made short bursts of active flapping flight a little like a modern pheasant – but since its shoulder joints were less mobile than those of modern birds it must have used a different sort of flight stroke to generate lift.

It’s no longer always considered to have been the “first bird”, or even to have been the direct ancestor of any modern birds. Instead it represents an offshoot lineage of early birds (or very-bird-like dinosaurs) that was just one part of a still-expanding flock of feathery fossil discoveries.

Retro vs Modern #03: Hylaeosaurus armatus

Despite being the third-ever scientifically named dinosaur genus, and being used in the first official definition of dinosaurs as a group, Hylaeosaurus armatus has ended up as a much less well-known name than Iguanodon or even Megalosaurus.

It was also the very first ankylosaur to be discovered, found as a partial skeleton in Southeast England in the early 1830s. Its large bony spikes were quickly recognized as being some sort of defensive armor, initially thought to be arranged in a vertical row along the animal’s back and tail.

1850s

The Victorian Crystal Palace statue of Hylaeosaurus is surprisingly decent for such an early attempt at reconstructing something as weird as an ankylosaur. It gives the impression of a slower and much more lizard-like animal than Iguanodon or Megalosaurus, showing it as a large squat quadruped with hoof-like claws and heavily armored scaly skin, with long spines running along its back and numerous smaller bony bumps over its head and sides.

1860s-1920s

Discoveries of other more complete armored dinosaurs began to give a better picture of what ankylosaurs actually looked like. But although Hylaeosaurus was soon recognized as having had multiple rows of spikes rather than just one, actual reconstructions of it seem to have been scarce during this period – mostly all derivative of a single 1869 image that depicted it as a sort of fat sprawling pinecone-lizard bristling with spikes.

2020s

Still only known from fragmentary material, Hylaeosaurus has remained rather obscure for a long time. In the 21st century it’s started to get a bit more attention, however, with the original specimen being further prepared and examined – and 2020 was Hylaeosaurus’ big year, with both a redescription of the genus being published and it also being featured on a special-edition British 50p coin.

Hylaeosaurus was probably around 4m long (~13′), and lived in southeast England about 140-136 million years ago. It may have also ranged further across Europe, with possible remains known from Germany and some more dubious records from France, Spain, and Romania. Generally classified as an early nodosaurid, most of our modern knowledge of what it would have looked like comes from other discoveries of much better-known ankylosaurian relatives, including some exquisitely well-preserved examples in the last few years like Borealopelta and Zuul.

It would have had a low triangular head, with a toothless beak at the front of its jaws and leaf-shaped teeth further back, and a pair of short horns on the back of its skull behind its eyes. Rows of spiky osteoderm armor ran along is body, with longer curving spines over its shoulders, all covered in thick keratin sheaths that would have made them look even larger in life. Numerous smaller bony nodules in its skin filled in the gaps between the armor, forming a tough protective shield over its entire back. Its short powerful limbs had hoof-like claws, and if it was indeed a nodosaurid its tail would have lacked the famous club of its ankylosaurid cousins.

Based on Borealopelta we even now know a little bit about the potential coloration and patterning of these animals – some of them were reddish-colored, with a countershaded camouflage pattern, darker on top and lighter on the underside.

Retro vs Modern #02: Iguanodon bernissartensis

Named just a year after Megalosaurus, in 1825, Iguanodon has remained a fairly iconic dinosaur ever since.

Discovered in a different region of Southeast England, its fossilized teeth were soon recognized as being similar to those of modern iguanas – but much much larger. Partial skeletal remains were initially reconstructed as belonging to a gigantic herbivorous lizard, with what was thought to be a horn placed on the tip of its nose.

1850s

The Victorian Crystal Palace statues of Iguanodon depicts a more bulky reptile with a nose horn, a toothless beak at at the front of its jaws, scaly skin, thick upright legs and hoof-like claws. Much like the Megalosaurus of the time it’s really not nearly so bad of a reconstruction as it’s often accused of being, showing a surprisingly naturalistic and almost mammal-like interpretation of these animals compared to later portrayals.

Technically the particular “Iguanodon” species at Crystal Palace has more recently been renamed Mantellisaurus atherfieldensis, but it was considered to be Iguanodon at the time so it’s included here anyway.

1880s-1960s

A massive discovery of the remains of nearly 40 Iguanodon individuals in a coal mine in Bernissart, Belgium, revealed the full anatomy of these dinosaurs for the first time. Much more well-preserved and complete than the patchy English material, these larger Iguanodon bernissartensis eventually became the official type species for the whole genus – a standard used to help determine whether similar-looking fossils are Iguanodon or not.

The Bernissart specimens were restored as bipedal animals in an upright kangaroo-like pose, with their tails dragging behind them acting like a tripod to prop them up. What had previously been the single “horn” was finally realized to instead be a thumb spike on each hand, interpreted as a defensive weapon against predators.

This image of Iguanodon persisted for decades, with a giraffe-like long prehensile tongue sometimes also depicted (including a particularly bizarre interpretation of it sticking out through a hole in the lower jaw!).

2020s

The Dinosaur Renaissance in the late 20th century corrected Iguanodon‘s posture to hold its body horizontally, and it was eventually recognized as being capable of both bipedal and quadrupedal movement. Juveniles were found to have walked more on their hindlimbs, while adults spent more time on all fours but were still capable of running bipedally when they needed to.

We now have fossils of Iguanodon from across much of Europe during the Early Cretaceous, about 126-122 million years ago. Our modern view of this animal is a heavily built ornithopod that grew to around 9m long (~30′), with a horse-like head, a large keratinous beak at the front of its jaws, chewing teeth further back, and cheeks covering the sides of its mouth. Its chunky forelimbs each had a large thumb spike, hoof-like claws, and a prehensile grasping pinky finger, while its powerful hindlimbs ended in three-toed vaguely bird-like feet.

Soft tissue preservation discovered in related hadrosaurs suggests it probably also had a very bulky body with a thick heavily muscled neck and tail, and possibly an ornamental “frill” running along its back. Skin impressions show a covering of numerous tiny pebbly scales, generally too small to have been visible from a distance.

Retro vs Modern #01: Megalosaurus bucklandii

It’s time for Retro vs Modern Month!

Every weekday this March we’ll be looking at some examples of how our paleontological understanding and visual depiction of various fossil creatures has evolved over the years.

Starting with…

Retro vs Modern #01: Megalosaurus bucklandii

Fragmentary fossil remains of dinosaurs have been found in Southeast England for hundreds of years, but it wasn’t until the 1820s that they were properly recognized as belonging to an ancient “great lizard” given the name Megalosaurus bucklandii – the very first non-avian dinosaur known to science, almost two decades before the term “dinosaur” would even be created to categorize these extinct animals.

1850s

The Victorian Crystal Palace reconstruction of Megalosaurus is often mocked for its inaccurate bulky appearance, but for its time it was actually an incredibly progressive vision of a predatory dinosaur. It was depicted as an alert, active, bear-like beast with upright muscular limbs, and a humped back based on what later turned out to actually be remains of a different dinosaur species.

1890s-1960s

Discoveries of other large theropod dinosaurs revealed their bipedal posture, and Megalosaurus reconstructions were revised to show an upright kangaroo-like stance. But despite some other early portrayals of active agile dinosaurs, the overall opinion of these animals began to drift during the first half of the 20th century towards sluggish tail-dragging reptiles: depicting them as slow, stupid, cold-blooded, awkward and obsolete evolutionary failures whose extinction had been inevitable.

2020s

Starting in the late 1960s the Dinosaur Renaissance finally began to shift thinking back towards active and warm-blooded dinosaurs, recognizing theropods’ close evolutionary relationship to modern birds and correcting their posture into a horizontal stance with a counterbalancing tail. And while Megalosaurus itself is still only known from fragments, discoveries of more completely preserved relatives like Torvosaurus have given us a much better idea of what it was probably like.

We know know Megalosaurus lived on what at the time was a subtropical island in the shallow western Tethys Sea, about 166 million years ago during the Mid Jurassic. It would have been around 8m long (~26′), with a long narrow snout, and short muscular arms with enlarged meathook-like thumb claws. Its legs and tail would have been fairly thick and bulky, and it may have had a covering of hair-like protofeathers on its body.

Utaurora

Ever since the bizarre anatomy of Opabinia was first recognized in the 1970s, it’s been a persistently unique “weird wonder” of the Cambrian period. Over the decades we’ve figured out that it was an early type of arthropod in an evolutionary position between lobopodians and radiodonts, but this whole time it’s still been sitting there alone as the only known representative of a weird stem-lineage with no other known close relatives.

…Until now!

A fossil from the Wheeler Shale in Utah, USA (~507 million years ago) that was originally thought to be a tiny radiodont has been re-studied, and now we finally have another member of the opabiniid family: Utaurora comosa.

Only about 3cm long (1.2″), Utaurora had 15 pairs of swimming flaps along the sides of its body, and a tail region with a 7-part fan and a pair of serrated spines. Hair-like gill blades covered both its back and the bases of its swimming flaps, and although its head region was poorly preserved it probably had an arrangement of 5 eyes and a long flexible claw-tipped proboscis similar to that of Opabinia.

Its discovery extends both the geographical and temporal known range of opabiniids, and suggests that their continued scarcity in other Cambrian fossil sites compared to other soft-bodied arthropods may simply be because they were just incredibly rare animals in those habitats at the time.