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Cambrian Explosion #32: Rise of the Arthropods

The world of the Cambrian Period was a strange combination of both familiar and alien. The land would have seemed rather barren, populated mainly by microbes and algae, yet the oceans teemed with creatures already identifiable as sponges, comb jellies, jellyfish, acorn worms, vertebrates, echinoderms, arrow worms, annelids, molluscs, and brachiopods – small and primitive-looking in some cases but still recognizable enough.

But at the same time there were “weird wonders” everywhere, things much harder to identify, with shapes so bizarre that their initial discovery was met with laughter.

Animal life was exploring so many different possibilities for body plans and ecologies, and one lineage in particular dominated this explosion of evolutionary experimentation: the arthropods.

Arthropods are represented today by the chelicerates (sea spiders, horseshoe crabs, and arachnids), myriapods (millipedes and centipedes), crustaceans, and insects, and together these groups make up over 80% of all known living animal species and are vital parts of almost every ecosystem on the planet.

Styxosaurus

Styxosaurus snowii here was one of the largest known elasmosaurids, named after the mythological river separating the worlds of the living and the dead.

Reaching around 11m long (36′), with half of that being entirely neck, it lived during the late Cretaceous period about 83-80 million years ago in what is now the American Midwest – a region that at the time was submerged under a large inland sea.

With pointy interlocking teeth in its proportionally tiny head, Styxosaurus would have fed on slippery aquatic animals like fish and cephalopods, possibly using its long neck to get up close to its targets while the bulk of its body remained out of sight in dark murky waters. Large numbers of gastroliths found in the stomach regions of some specimens would have been used to grind up the hard parts of prey items after they were swallowed whole.

Phiomicetus

Named after the canine-headed Ancient Egyptian god, Phiomicetus anubis is the first fossil cetacean to discovered, described, and named entirely by a team of Arab paleontologists.

Living during the mid-Eocene, about 43 million years ago, in a shallow sea-covered region that is now part of Egypt‘s Western Desert, Phiomicetus was an early protocetid – an amphibious foot-powered swimmer, at a transitional point in the evolution of whales from deer-like terrestrial animals to fully aquatic screaming torpedoes.

About 3m long (~10′), it had large jaw muscles and sharp teeth with wear patterns that suggest it was a raptorial hunter grabbing and snapping at prey with powerful bites. It would have probably tackled fairly big prey compared to other protocetids, hunting things like large fish, turtles, and even smaller whales in an ecological role similar to that of modern orcas.

Along with the distantly-related long-snouted Rayanistes it’s one of the earliest known whales from Africa, giving us further glimpses at a time period when early cetaceans were first dispersing out from the South Asian subcontinent via the ancient Tethys Sea.

Joermungandr

Named after a legendary Scandinavian serpent, Joermungandr bolti here was a recumbisrostran “microsaur” – part of a group of animals that were traditionally considered to be lepospondyl amphibians, but more recently have been proposed to in fact be a lineage of early reptiles.

Discovered in the Mazon Creek fossil beds in Illinois, USA, this species dates to the late Carboniferous period around 310 million years ago. A single near-complete specimen about 5cm long (~2″) preserves impressions of the body outline and numerous tiny scales, giving us a pretty good idea of what it looked like in life.

Joermungandr had a long streamlined tubular body with small limbs and a short tapering tail, and a stubby snout with fused bones heavily reinforcing its skull. Along with microscopic ridges on its body scales that resemble the dirt-repelling scales of some modern reptiles, this combination of features suggest it was a headfirst burrower that wriggled its way through soil with snakelike motions.

Spectember 2021 – Reedstilt Redesign

(This was originally supposed to be a final-day-of-#Spectember bonus post, but it got much longer than I expected so it’s a few days late.)

To finish off this year’s diversion into speculative evolution, instead of pulling from my ~~still-rather-long~~ list of unused submissions I’m doing something a little different – trying to give an idea of how I go through the actual process of designing a speculative species.

And for today’s example I’m going to do a “redesign” of sorts for a classic Dougal Dixon After Man creature: the reedstilt.

For several reasons:

It was on the cover of the old edition of After Man I first discovered as a kid in the local library, it immediately caught my attention, and as a result it’s always been one of my favorite species from the book.
But some of its anatomy doesn’t really hold up.
I really really Do Not Like the “official” redesign that replaced the original art in the 2018 reprint. It’s shrinkwrapped.
I just think it’s neat.

Reedstilt in both original flavor and 2018 revamp style.

Spectember 2021 – Dimorphic Tunicates

As we come to the end of the month, here’s another #Spectember concept from an anonymous submission:

Spectember 2021 – Slime Snouters & Megaphone Birds

Today’s #Spectember concept is brought to you by @thecreaturecodex , who wanted to see a depiction of something from The Snouters: Form and Life of the Rhinogrades:

Spectember 2021 – Quadrupedal Pachycephalosaurs

Today’s #Spectember concept comes from an anonymous submitter:

Spectember 2021 – Marsupial Predators

It’s September, the Cambrian series has been delayed until later this year, so instead let’s get speculative – it’s time for the return of #Spectember! I can’t manage daily content this time around, but I still have plenty of submitted concepts left over from last time.

So let’s get started with some marsupials suggested by someone crediting themselves only as Bruno Drundridge:

Qinornis

66 million years ago, the end-Cretaceous mass extinction wiped out all dinosaurs except for the avian bird lineage.

…Or did it?

But I’m not talking about the dubious claims of non-avian dinosaur fossils found in places they shouldn’t be. This is about something else entirely: an unassuming little bird known as Qinornis paleocenica.

Living in Northwest China during the mid-Paleocene, about 61 million years ago, Qinornis was roughly pigeon-sized at around 30cm long (12″). It’s known only from a few bones from its legs and feet, but those bones are unusual enough to hint that it might have been something very special.

Uniquely for a Cenozoic bird, some of its foot bones weren’t fully fused together. This sort of incomplete fusion is seen in both juvenile modern birds and in adults of non-avian ornithurine birds from the Cretaceous – and the Qinornis specimen seems to have come from an adult animal.

If it was fully grown with unfused feet, then that would suggest it was actually part of a “relic” lineage living 5 million years after the mass extinction, surviving for quite some time longer than previously thought.

The last known non-avian dinosaur.