Tag: arthropod

Almost-Living Fossils Month #08 – A Lot Of Lobsters

Hoploparia was a type of clawed lobster that first appeared in the fossil record in the Early Cretaceous about 140 million years ago. Many many different species within this genus have been found all over the world – over 100 of them have been described! – with quite a lot of anatomical diversity between them, showing that these lobsters were very good at adapting to a wide range of habitats and climates.

Although the vast majority of Hoploparia species lived just in the Cretaceous period, a small number of them did survive the end-Cretaceous mass extinction 66 million years ago. Hoploparia stokesi here was one of them, known from both the Late Cretaceous and Early Paleocene of Antarctica (~70-61 mya) – and was actually one of the first fossils ever described from the continent.

Specimens of this species are usually about 13cm long (5″), and show an evolutionary shift over time, developing much stronger claws and jaws, suggesting they were adapting their diet towards hard-shelled prey.

Various species of Hoploparia persisted on in North America, Europe, and Antarctica for the first half of the Cenozoic, but they never recovered to anywhere close to their Cretaceous levels of diversity. By the Early Miocene (~23-16 mya) there was just one known species left hanging on in Antarctica, and then they were gone.

(However, some modern lobster genera may in fact have originated from somewhere within the huge Hoploparia lineage back in the Cretaceous, so they might at least still have some close living relatives!)

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 #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.