Category: science illustration

Spectember #06: Aquatic Afrosoricidans

(The submitted prompt here was “some kind of fully aquatic non cetacean or dugong mammal with a different bodyplan”.)

Transcript for the text on the image under the cut:

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Spectember #01: Land Dolphins

Welcome to SPECTEMBER!

This month we’ll be taking a break from real creatures to instead explore some “what if” scenarios for the evolution of life.

If you’re unfamiliar with speculative evolution, it’s basically a biology-focused type of science fiction exploring hypothetical evolutionary paths, whether as alternate histories for the ancient past, possible far future descendants of modern species, or even completely alien life on other worlds. The concept has been around for well over a century at this point, but Dougal Dixon’s 1981 book After Man was probably the biggest influence.

All this month, on weekdays I’ll be posting my own work based on the suggestions from earlier in the year, and on weekends I’ll highlight some of the history of the spec evo genre.

So let’s have some fun – and if you want to join in, #spectember is an open concept and anyone is welcome to take part!

Transcript for the text on the image under the cut:

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Thylacares

Thylacocephalans were a bizarre group of extinct marine arthropods that often looked like tiny alien creatures – and whose evolutionary relationships are still uncertain. Despite existing in oceans around the world for at least 350 million years, their fossil record is rather spotty and their internal anatomy is often poorly preserved, making it difficult to figure out anything more specific than “probably some sort of crustacean“.

Possible thylacocephalans are known from as far back as the Cambrian, but one of the earliest definite members of the group was Thylacares brandonensis.

Living during the early Silurian, around 436 million years ago, in the region that today is part of Wisconsin, USA (found in the same fossil formation as last week’s Venustulus), this species measured up to about 7.5cm long (3″). Its body was enclosed by a large bivalved carapace, with protruding stalked eyes and what may have been a pair of antennae, along with smaller raptorial limbs than its later relatives.

While it was less specialized than other thylacocephalans it was probably a similar sort of swimming predator, catching prey with its spiny limbs.

Venustulus

The synziphosurines were ancient marine chelicerate arthropods that were traditionally thought to be early representatives of the horseshoe crab lineage. But more recent studies have shown them to occupy a slightly more basal position on the chelicerate evolutionary tree, instead being related to the common ancestor of sea scorpions, horseshoe crabs, and arachnids.

(Also horseshoe crabs might actually be part of the arachnids, closely related to ricinuleids!)

Venustulus waukeshaensis was one of the earliest known synziphosurines, living in what is now Wisconsin, USA during the early Silurian, about 436 million years ago. It grew to around 8cm long (~3.2″) and had six pairs of appendages on the underside of its body, with the first pair modified into chelicerae and the rest being walking legs.

It also appears to have been blind, lacking any evidence of eyes despite its fossils being fairly well-preserved – suggesting it lived in conditions where vision wasn’t much use, such as dark murky water or burrowing around in seafloor sediment.

Tridenaspis

Although the only surviving agnathans in modern times are the lampreys and hagfish, back in the early-to-mid-Paleozoic these “jawless fish” were much more diverse. Many of them were heavily armored with large bony head shields – a feature eventually inherited by early jawed fish like the placoderms – which protected their heads, gills, and some of their internal organs.

And some of the oddest-looking of these armored agnathans was a lineage known as the galeaspids.

Known from southern China, Tibet, and Vietnam, these small fish were bottom-dwellers living in the shallow waters of lagoons and river deltas. Their most distinctive feature was a single large opening on the upper side of their head shields – and despite looking like a particularly goofy mouth this hole was actually a nostril, used for both a sense of smell and as a water intake for their gills. The actual mouth and the gill openings were on the underside of the head.

While early galeaspids had rounded head shields, later forms developed some more unusual shapes, with long spines sticking out to each side and pointed or spatula-shaped snouts.

Tridenaspis magnoculus here lived during the early Devonian in Southwest China, about 407-393 million years ago, and was only about 5cm long (2″). It wasn’t the most extremely pointy of its kind, but still had a weird kite-shaped head shield, a long vertical slit-shaped nostril opening, and rather large upwards-facing eyes.

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.