#vendia

Most animals are bilaterally symmetric, having body plans with mirrored left and right sides – which also allows them to have a defined head end, rear end, top side, and underside.

It's not entirely clear what evolutionary advantage this type of symmetry gave to the first bilaterians, which would have been been small "simple" worm-like animals living sometime during the Ediacaran Period between 600 and 560 million years ago. The current generally accepted explanation is that it probably allowed for better active locomotion – clustering sense organs at the head end and directing body movement more efficiently towards food sources and away from threats.

However, this sort of symmetry is never completely perfect. Internal structures like organs are often arranged nonsymmetrically, and the realities of genetics, physical development, and environmental influences always result in external small deviations.

Zebra From The Back by Lynn Greyling | CC0 Public Domain

…But not every bilaterian has stayed roughly symmetrical.

Over the last half-billion years or so some bilaterians have abandoned their roughly-mirror-image body plans in favor of something distinctly wonkier. Asymmetry has evolved multiple times in various different lineages, and so every weekday this month we'll be looking at some examples.

And we might as well start way back near the beginning:

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Strange Symmetries #01: Almost Bilateral

Living in the Ediacaran between about 567 and 550 million years ago, the proarticulatans were flattened rounded organisms with two rows of soft "quilted" rib-like segments (known as isomers) and sometimes a larger fused "head" section at the front. The left and right isomers weren't perfectly mirrored, instead being offset from each other in a glide reflection pattern – but the presence of a clear central body axis suggests these animals may have had some sort of relation to the earliest bilaterians, possibly even being a very early stem group that was experimenting with a not-quite-totally-bilateral body plan.

Discovered in what is now northwest Russia, and dating to around 555 million years ago, Vendia sokolovi was a small proarticulatan measuring about 1.1cm long (0.4"). It had a rather small number of isomers compared to some of its relatives, only 7 per side, and seems to have had a simple digestive tract that branched into each isomer.

(The superficial resemblance to trilobites was coincidental – while we might not be entirely sure what these things were, we do at least know they weren't closely related to early arthropods.)

Very little overall is known about these animals' lifestyles. Trace fossils suggest they were able to move around, feeding on microbial mats on the seafloor, and they may also have been able to firmly stick themselves onto the spots they were currently grazing.

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Vendia sokolovi, a 1 cm-long enigmatic* organism from the upper Ediacaran of Russia (displaying the 'glide symmetry' characteristic of many Ediacaran forms), feeding (?) on the bacterial mats that used to be widespread before the Cambrian explosion.

*as Ediacaran organisms tend to be, alas

Some art I made a long time ago but still find kind of neat.

References:

Well, when I said I was going to start drawing every day, I’d intended to draw something new every day, not just refine drawings I made on previous days; and of course I intended to post them earlier in the day, not just before midnight.  (Well, technically I only said I’d draw something new every day; I didn’t say I’d post it; but I mean...)

But right now, with the end of the semester nigh and as busy as I am catching up with grading and writing exams, I’ll give myself some slack and count this.

Okay, I said I was going to draw something every day, so in keeping with that goal... and on the topic from yesterday of character redesigns—here’s one of the main characters from the animated pilot pitch I’ve been (sporadically) working on.  I posted a drawing of her before, but I really wasn’t happy with it, and had been meaning to give her a redesign for some time, so... here it is.  Still not sure I’d call this definitely finalized, but I think it’s a vast improvement on the previous design.

(Previous design here, for comparison.)