Tag: invertebrate

Capinatator

Capinatator praetermissus, an arrow worm from the Mid-Cambrian of Canada (~508 mya). Discovered in the famous Burgess Shale fossil deposits, it was one of the earliest known arrow worms and also much larger than most modern forms, measuring around 10cm in length (4″).

Its mouth was surrounded by 50 hooked spines, which could be extended out to grasp onto its prey – probably feeding on whatever smaller animals it could catch – but when not in use these spines would have been kept folded up inside a fleshy “hood” around its head.

It may have been a transitional form between early large-predator arrow worms and the smaller plankton-feeders that the group later became.

Syringocrinus

Syringocrinus paradoxicus from the Upper Ordovician of North America (~450 mya). Measuring up to around 6cm long (2.3″), it was part of an extinct group of marine animals known as solutes – characterized by irregularly-shaped bodies covered in calcite armor plates, the structure of which suggest they were echinoderms despite their complete lack of any proper symmetry.

It had two appendages, one a short “arm” that was probably used for feeding on food particles suspended in the water, and the other forming a longer stalk-like “tail” that may have served to propel it along the seafloor.

Solutes were once thought to be closely related to the equally weird-looking stylophorans, but some versions of the echinoderm family tree place them much further apart, suggesting their superficial similarities may have been due to convergent evolution instead.

Orthrozanclus

Orthrozanclus elongata, from the mid-Cambrian of China. Only about 2cm long (~0.8″), this tiny creature was covered in both long spines and extensive armor – with tile-like scales on its back, overlapping dagger-shaped plates around its sides, and a small shell on its head.

It’s the second species of Orthrozanclus to be discovered, extending the genus’ range about 10 million years older than the Canadian O. reburrus.

Although it would have been a member of the Lophotrochozoa (the group that contains modern molluscs, annelid worms, and brachiopods), its exact evolutionary relationships are still uncertain. It might have been a transitional form between Wiwaxia and the halkieriids, or it could be closer related to the brachiopods.

Linguamyrmex

Linguamyrmex vladi, an ant from the Late Cretaceous of Myanmar (~99 mya). Part of an extinct group known as the Haidomyrmecini, or “hell ants”, it measured about 5mm long (0.2″) and is known from several individuals in amber.

It had huge scythe-shaped mandibles and a horn-like appendage on its head which together formed a powerful trap-jaw mechanism, snapping vertically shut when a pair of long sensitive trigger hairs touched against a target. One specimen was preserved close to a large soft-bodied beetle larva, which may have been an intended prey item.

When closed, the mandibles formed a tube-like channel to Linguamyrmex’s mouth, allowing it to suck out the “blood” from its impaled victims – and inspiring its species name, referencing Vlad Dracula.

The horn was also reinforced with metal particles in the chitinous exoskeleton, strengthening it against the impact of its closing jaws.

Synophalos

Synophalos xynos, a shrimp-like arthropod from the Early Cambrian of China (~515 mya). Thought to be closely related to stem-crustaceans like Waptia, it was about 2cm long (0.75″) and had a bivalved carapace with a segmented body ending in a forked tail.

Unlike any other known arthropods, however, it formed long “conga line” chains of up to twenty individuals, with the tail of each animal locking securely into the shell of the next. The function of the these chains is unknown, although suggestions include some sort of mating behavior, migration, or defense against predators.

Only one specimen was found completely on its own, and its slightly longer carapace suggests it may represent a different solitary life stage of these strange little creatures.

Unsolved Paleo Mysteries Month #10 – Ambiguous Amiskwia

Amiskwia was a tiny soft-bodied creature from the Middle Cambrian, known from a fairly small number of fossils – about 18 specimens from the Burgess Shale in Canada (505 mya) and an additional one from the Maotianshan Shales in China (515 mya).

Despite only measuring about 2.5cm long (1”), it was one of the larger animals alive at the time. Its body features a head with two tentacles and a small mouth, a pair of stubby fins, and a flattened paddle-shaped tail, suggesting it was an active swimmer. Its internal anatomy has been well-preserved in some specimens, revealing a brain, gut, and traces of what may be blood vessels and a nerve cord.

But we don’t know what type of animal it is. At all.

It was initially thought to be an early arrow worm. However, fossils of Cambrian representatives of that group have since been found, and Amiskwia lacks their characteristic spines and teeth. A relationship to ribbon worms or molluscs has also been suggested, but these hypotheses have the same problems with missing key features.

So, for now, Amiskwia remains one of the “weird wonders” of the Cambrian Explosion with no obvious affinities to any other known group.

[EDIT: As of 2019, Amiskwia seems to have finally been identified as a gnathiferan!]

Unsolved Paleo Mysteries Month #06 – Tricky Trilobites

Trilobites are common and recognizable fossils, found around the world from the Early Cambrian to the Late Permian (521-250 mya), and ranging in size from 1mm to 72cm (0.03″ – 2′4″). They were some of the first organisms on Earth with complex eyes, and some groups also developed ornamentation like spines, horns, and tridents. The image above depicts a particularly elaborate genus known as Dicranurus.

Occasionally fossils have been found showing fine details of trilobite anatomy like antennae, legs, gills, and digestive organs, and we’ve even recently discovered their eggs.

And yet we don’t really know where they came from. Much like the pterosaurs we started the month off with, trilobites appear suddenly in the fossil record with no intermediate or ancestral forms to definitively link them to other groups. We know they were definitely arthropods, but which arthropods they were most closely related to is still uncertain.

They might be related to the chelicerates (arachnids, horseshoe crabs, and eurypterids), or they might be part of the mandibulates (crustaceans, insects, and myriapods). But the exact relationships of these major arthropod groups are still in dispute, too, and phylogenetic results can vary wildly depending on whether trilobites are included in the analysis or not.

It’s probably going to be some time before any sort of consensus is reached.

Unsolved Paleo Mysteries Month #03 – Ammonite Anatomy

Ammonites (or “ammonoids” in technical terms) are one of the most recognizable types of fossil, found in such high abundance that they’re frequently used to precisely date rock layers. They’re absolutely everywhere in fossil collections, and are even made into jewelry.

So we must already know everything we possibly could about them, right?

Except… we really don’t know what their soft parts looked like.

The fossil record for ammonite soft tissue is surprisingly empty for a group that existed for over 300 million years. A possible ink sac and a few organs have been found, but nothing else.

Based on their other cephalopod relatives, they probably had at least ten arms (the two longer tentacles shown on this Collignoniceras are a little speculative), along with a siphon for propulsion – but until we find that elusive exceptional preservation we just don’t know for sure.

[Edit: As of 2022, a few more traces of soft tissue have been found!]