Month: February 2023

Paucipodia

Lobopodians were some of the earliest known panarthropods, closely related to velvet worms, tardigrades, and the ancestors of all the true arthropods. They were small soft-bodied worm-like animals with multiple pairs of fleshy legs, and some species also bore elaborate spikes, armor plates, and fleshy bumps all over their bodies – with the spiny Hallucigenia being the most famous example.

But unlike its more charismatic relative Paucipodia inermis here didn’t seem to have any ornamentation at all.

Known from the Chinese Chengjiang fossil deposits, dating to about 518 million years ago, Paucipodia lived in what was then a shallow tropical sea. Its 13cm long (~5″) tubular body had nine pairs of legs, with each foot tipped with a pair of hooked claws, and the inside of its mouth was ringed with tiny sharp teeth.

Several specimens have been found preserved in association with the weird gummy-disc animal Eldonia, which may indicate Paucipodia either preyed on them or scavenged on their carcasses.

Some Paucipodia fossils also have enigmatic tiny “cup-like” organisms attached to their legs. It’s currently unknown what exactly these were, or whether they were parasitic in nature or simply opportunistically “hitching a ride” similar to the Inquicus found on armored palaeoscolecid worms in the same fossil beds.

Noripterus

Noripterus complicidens was a pterosaur that lived in what is now Mongolia and northwest China during the early Cretaceous, about 140 million years ago.

It had a wingspan of up to 4m (~13′), with a head-and-body length of around 1.2m (~4′), and like other dsungaripterids it had a distinctively reinforced skull, with a toothless beak at the front of its jaws and strong widely-spaced teeth further back – an arrangement that was probably used to catch and then powerfully crack open hard-shelled prey.

Unlike other pterosaurs, however, Noripterus also had some very unusual feet.

All other known pterosaurs seem to have had plantigrade hindlimbs, standing and walking with the whole foot on the ground. But Noripterus had toe joints that looked more like those of theropod dinosaurs than other pterosaurs, with a higher level of upward flexibility and potentially a more digitigrade posture standing on just its toes.

With dsungaripterids already having fairly stout body proportions that suggest they spent a lot of time walking around on the ground, Noripterus may have been even more agile and adept at terrestrial locomotion. Digitigrady is generally more efficient for moving at higher speeds, so this pterosaur might have been a runner behaving similarly to modern ground birds, preferring to sprint away from threats on foot rather than launch itself into the air.

Tropidosuchus

Proterochampsids were a group of Triassic archosauriformes, closely related to the true archosaurs (crocodilians, pterosaurs, and dinosaurs/birds).

Known only from South America between about 242 and 205 million years ago, these reptiles’ heads were wide at the back but very narrow along the snout, often with prominent bony bumps and ridges on their skulls, and they had less osteoderm armor on their bodies than other archosauriformes.

They’ve traditionally been interpreted as very crocodile-like and semi-aquatic, but their long slender limbs and presence in rather arid paleoenvironments suggest they may have been more terrestrial fast-running predators.

Tropidosuchus romeri here lived about 235 million years ago in what is now Argentina. It was one of the smaller proterochampsids, only about 50cm long (1’8″), with just a single row of osteoderms along its back, and had larger and lower-set eyes compared to its relatives.

CT scans of its braincase indicate it had a particularly good sense of smell, and it may have relied mainly on scent to locate prey.

Antaecetus

Antaecetus aithai was an early whale that lived during the late Eocene (~40 million years ago) in what is now Morocco, at a time when northern Africa was covered by a warm shallow sea.

It was part of the “basilosaurids“, some of the first fully aquatic cetaceans – traditionally considered to be a single defined group, but more recently found to be more of an “evolutionary grade” of multiple early whale lineages – and much like Basilosaurus it had elongated back vertebrae that would have given it a very long slender body shape.

Antaecetus also had a proportionally smaller head and smaller teeth than other basilosaurids, along with much denser bones and a stiffer spine that would have made it a rather slow swimmer with reduced maneuverability. It was also fairly small overall compared to most of its relatives, probably around 6m long (~20′).

It was probably a slow-moving coastal water animal somewhat like modern sirenians – except unlike manatees and dugongs it was carnivorous. Its relatively delicate teeth suggest it was feeding on soft-bodied prey like cephalodpods, and with its lack of speed it must have been some sort of ambush predator, waiting around for potential prey to come within striking range.