The majority of known fossils of Cambrian crustaceans are in the form of minuscule microfossils with “Orsten-type preservation” – formed in oxygen-poor seafloor mud and exceptionally well-preserved in three-dimensional detail. They can only be discovered and studied after dissolving away the rock around them with acid and picking through the residue under a microscope, then they’re scanned with an electron microscope to see their fine details.
And it turns out some of these tiny early crustaceans looked really weird.
Continue reading “Cambrian Explosion #59: Stem-Crustacea – Actual Ancient Aliens & Bivalved Buddies”
Life seems to have existed on Earth for over 4 billion years, but for much of that time it was primarily microscopic. And although multicellularity is known to have independently evolved multiple times, large complex forms didn’t really get started until around 600 million years ago, with the strange Ediacarans being some of the most famous early examples.
But that may not have been the first time such an evolutionary experiment happened.
A collection of fossils discovered near the city of Franceville in Gabon appear to represent an even earlier example of large multicellular life. Known as the “Francevillian biota” or “Gabonionta”, these fossils are over three times older then the Ediacarans, dating to a staggering 2.1 billion years ago during the Paleoproterozoic Era.
Over 400 specimens have been collected, representing a variety of different forms — including discs with ruffled edges, rods, rounded clusters of blobs, and elongated shapes that are sometimes attached to long “strings of beads” — with the largest reaching lengths of about 17cm (6.5”). Their age places them somewhere around the origin point of the earliest eukaryotes, and they may represent a completely unique kingdom of life unlike anything alive today.
These organisms’ appearance in the fossil record came shortly after the Great Oxygenation Event, suggesting the evolutionary development of large complex bodies is directly linked to the amount of available oxygen for aerobic respiration. Later, atmospheric oxygen dropped again, and the Francevillian biota disappeared into extinction, leaving us with only these mysterious fossils hinting at a surprisingly diverse and alien-looking period in life’s deep past.
Found only in the Carboniferous-aged Bear Gulch Limestone (~318 mya) in Montana, USA, Typhloesus wellsi is such a confusing animal that it’s been nicknamed “the alien goldfish”.
It was one of the first body fossils found containing conodont elements, leading to it initially being identified in the 1970s as the then-unknown conodont animal – until actual conodont animals were discovered a few years later, looking nothing like it. The elements were reassessed as actually being Typhloesus’ gut contents, indicating it was actually a conodont-eating predator or scavenger.
Reaching sizes of almost 10cm long (4″), it was vaguely fish-shaped with a pair of ventral fin folds and a stiffened vertical tail paddle. No obvious sensory structures are preserved, but there are impressions of a large gut cavity in the front half of its body, along with a pair of strange unidentified organs known as “ferrodiscus” that contained a high concentration of iron deposits.
And despite being known from over 50 specimens, we still don’t know where to classify it. At all. It lacks evidence of features like gill openings or a notochord that could associate it with chordates. Its gut appears to be a blind sack with no anus, a condition usually seen only in cnidarians and flatworms, and finned active swimmers are known in other invertebrate groups like molluscs and arrow worms, but Typhloesus doesn’t resemble anything like those either.
With the similarly mysterious Tullimonstrum recently getting a lot of attention and a possible identification as a lamprey-relative, perhaps somebody will eventually have another look at this strange little creature, too.