science illustration – Page 37

Puijila

We have a fairly good picture of the evolutionary origins of most groups of aquatic mammals – except for the pinnipeds. The fossil record of early seals is still rather sparse, and for a long time the earliest known species was Enaliarctos, an animal that was already very seal-like and didn’t help much in figuring out whether seals’ closest living relatives are bears or musteloids.

But then Puijila darwini was found in the late 2000s, a transitional form with a near-complete skeleton, filling in a gap in our understanding so conveniently it almost seems too good to be true.

This is the equivalent of Archaeopteryx for seals.

Discovered in Nunavut, Canada, Puijila dates to the early Miocene, about 23-20 million years ago. It was a small freshwater otter-like animal, about 1m long (3’3″), with a long tail and webbed feet adapted for paddling with all four of its limbs.

It lived at around the same time as the more specialized Enaliarctos, so it wasn’t a direct ancestor of modern seals, instead being part of an early offshoot lineage that retained more basal characteristics – but it does gives us a clue as to what the earliest pinnipeds looked like. Along with genetic studies it also helped to clarify that seals’ closest relatives are indeed the musteloids, although they’re estimated to have last shared a common ancestor around 45 million years ago so there’s still a lot of time unaccounted for in the proto-seal fossil record.

Several other fossil species that were previously thought to be musteloids have now also been recognized as close relatives of Puijila, and it seems that they were a fairly widespread group basically filling the ecological niche of otters at a time before true otters existed.

Most surprising and frustrating of all, however, is that some of these other otter-seals actually survived all the way into the Pleistocene, only going completely extinct sometime in the last 2 million years.

We barely missed having them still alive today!

Bambolinetta

Between about 9 and 7 million years ago, the modern regions of Tuscany, Corsica, and Sardinia were once part of a single island in the ancient Mediterranean Sea.

And since evolution often goes in weird directions on isolated islands, it’s no surprise that some unusual species developed there.

One of which was a very odd duck.

A map of the Mediterranean region during the Late Miocene, showing the location of the Tusco-Sardinian island. — From fig 4 in Williams, M. F. (2008). Cranio-dental evidence of a hominin-like hyper-masticatory apparatus in Oreopithecus bambolii. Was the swamp ape a human ancestor?. Bioscience Hypotheses, 1(3), 127-137. https://doi.org/10.1016/j.bihy.2008.04.001

Bambolinetta lignitifila lived during the Late Miocene, about 7.5 million years ago. Known from a single partial skeleton discovered in the mid-1800s, it was initially thought to be a fairly normal dabbling duck and wasn’t properly re-examined until 2014, when its strange features were finally recognized.

It was a medium-sized duck, probably around 50cm long (1’8″), but it had much chunkier wing bones than its relatives, with noticeably shortened forearms – looking much more like the wings of an auk or penguin, and suggesting that it was a similar sort of wing propelled diver. This is incredibly weird for a duck, since every other known diving species uses feet for propulsion instead, and so Bambolinetta may be the only known waterfowl to ever develop this type of underwater locomotion.

It’s not clear whether it was still capable of flying or not. There were few predators in its habitat, so it may well have become completely flightless – and that could also be the reason it later went extinct. Sea levels in the region began to drop around 7 million years ago, reconnecting the Tusco-Sardinian island to the European mainland, and Bambolinetta‘s high level of ecological specialization and its potential island tameness would have given it little defence against an influx of new unfamiliar predators.

Holopterygius

Coelacanths are represented today by just two surviving species, one in East Africa and one in Indonesia, both very similar in appearance and ecology to each other.

For a long time their lineage was thought to be all “living fossils“, retaining the same basic body plan for the last 400 million years – but more recent discoveries have revealed that these fish were actually much more diverse over the course of their evolutionary history.

Holopterygius nudus was a fairly early member of the group, living during the mid-Devonian about 385 million years ago. The only known fossil specimen was discovered in Germany in the 1970s, but it was originally thought to be a different type of fish entirely and wasn’t identified as being a coelacanth until over 30 years later.

And compared to its living relatives it was tiny, just 7cm long (2.75″), with a distinctive tapering eel-like tail. Its convergent close resemblance to modern cusk-eels suggest it may have occupied a similar ecological niche, living near the sea floor and hiding in tight spaces like crevices and burrows.

Tiarajudens

Synapsids just keep evolving saber teeth.

Both proto-mammals and true mammals have independently evolved oversized fangs quite a few different times in a lot of different lineages over the last few hundred million years (even in some modern ones), and one of the first to experiment with such a feature was Tiarajudens eccentricus.

Living in southern Brazil towards the end of the Permian period, about 265-260 million years ago, Tiarujudens was an early member of a group of known as anomodonts. These chunky herbivorous synapsids weren’t directly ancestral to modern mammals, but were instead evolutionary cousins, and their lineage eventually included tusked dicynodonts like the world-conquering Lystrosaurus.

Tiarajudens was around 1-1.2m long (3’3″-3’11”) and sported a pair of very long blade-like canine teeth in its upper jaw. Since the rest of its teeth were clearly adapted for eating plants – with one of the the earliest known examples of flat grinding molars that would have allowed it to chew up tough vegetation – these fangs probably served more of a display or defensive function.

The saber teeth may even have been a sexually dimorphic feature like in modern musk deer. Another anomodont from South Africa, Anomocephalus africanus, is incredibly similar to Tiarajudens except for a lack of fangs – and since South America and Africa were connected as part of Pangaea at the time, it’s possible that these two actually represent males and females of the same species.

Without finding a larger number of fossils we can’t know for certain, but it’s an interesting possibility at least.

Hovasaurus

The Permian-Triassic extinction 252 million years ago was the most severe mass extinction in Earth’s history, so incredibly devastating that it’s been nicknamed the “Great Dying” – but there were still some animals that somehow just… didn’t seem to really notice it at all.

And one of these surprisingly resilient species was Hovasaurus boulei.

It was part of a group known as the tangasaurids, a fairly early evolutionary branch of diapsid reptiles from Madagascar and East Africa that originated sometime in the mid-Permian, just before the common ancestor of modern lizards and archosaurs.

Hovasaurus lived in Madagascar both just before and for some time after the Great Dying, dating to around 252-247 million years ago. Growing up to about 90cm long (~3′), it was one of the largest tangasaurids and was also highly specialized for aquatic life in freshwater rivers, with an eel-like tail twice the length of the rest of its body and heavy thickened ribs.

Hundreds of fossils have been found representing life stages from hatchling to adult, and juvenile Hovasaurus actually seem to have been almost fully aquatic – they had proportionally shorter limbs and may have behaved similarly to modern sea turtles, crawling into the water shortly after hatching and only returning to land as adults once they had longer better-developed legs.

Many fossils also preserve clusters of pebbles in their abdominal cavities, which are thought to have been used as extra ballast to help weigh them down in the water when hunting small fish and invertebrates.

It’s not entirely clear why these odd little aquatic reptiles were apparently unaffected by the Great Dying. Perhaps, much like the many freshwater species that survived though the later end-Cretaceous mass extinction, Hovasaurus was simply very good at dealing with sudden changes in its environment and food availability due to the variability of river habitats, and was able to weather though the worst of the extinction without much trouble.

Or maybe it was just one of the lucky ones.

Atlasaurus

Sauropod dinosaurs were just generally weird animals, but there’s something… not quite right about Atlasaurus imelakei.

Named after the Atlas Mountains of Morocco where its fossil remains were discovered, Atlasaurus lived during the mid-Jurassic period, around 168-165 million years ago. While it wasn’t the strangest–looking sauropod by any means, compared to other species its body proportions still show a particularly bizarre combination of features, with a slightly bigger head, unusually short neck, and very long slender legs that made up nearly half of its 9m height (29’6″).

It’s sort of the uncanny valley of sauropods. Everything about it is just a tiny bit wrong.

A photograph of an Atlasaurus model. Its been reconstructed very skinny, which only serve to emphasize its weird proportions. — And more shrinkwrapped depictions really don’t help with that. [image source]

Its tall shoulders and sloping back resemble the body plan of brachiosaurids so closely that it was initially thought to be an early member of that group, but more recent studies suggest it may have been part of an earlier evolutionary branch of sauropods known as the turiasaurs – which would mean its brachiosaur-like shape was actually the result of convergent evolution.

But what was it doing with such weird proportions?

…We really don’t know. Other short-necked sauropods seem to have been adapted for feeding on lower vegetation only a couple of meters off the ground, but Atlasaurus’ leggy build would have made it a high browser like the brachiosaurids it was mimicking. Its long legs may also have allowed it to move faster, or given it some advantage navigating over rough terrain, but since no other sauropod ever seemed to evolve this way it must have been doing something particularly unique.

Or perhaps it was just an evolutionary fluke. Maybe part of a lineage that had started adapting to short-necked low browsing, then moved back towards the high browsing niche – and happened to end up lengthening their legs instead of their necks to get the necessary height back.

Eons Roundup 5

Some more recent commission work for PBS Eons!

The lemurs Archaeolemur and Pachylemur, from “When Giant Lemurs Ruled Madagascar”
https://www.youtube.com/watch?v=1hTJh8W0khU

The meridiungulates Notiolofos and Antarctodon, from “When Antarctica Was Green”
https://www.youtube.com/watch?v=cC4WiBCoVeo

The Near Eastern wildcat Felis silvestris lybica, from “How We Domesticated Cats (Twice)”
https://www.youtube.com/watch?v=CYPJzQppANo

Maiabalaena

The earliest baleen whales didn’t actually have any baleen plates in their mouths, and the evolutionary origin of these unique filter-feeding structures is still poorly understood.

It was thought to have been a fairly simple linear process from toothed ancestors to a mix of teeth and baleen and then to fully toothless with just baleen, but more recent discoveries have begun to cast doubt on that idea. The teeth of ancestral baleen whales weren’t suited to filter-feeding at all, instead still being adapted for predatory piercing and chewing – actions which would have been constantly interfering with and damaging any proto-baleen forming alongside them, and making it seem much more unlikely that there would have ever been a transitional form that had both teeth and baleen at the same time.

But then how did baleen whales get their baleen?

Maiabalaena nesbittae here provides a possible solution. Discovered in Oregon, USA, this early baleen whale dates to the early Oligocene, around 33 million years ago, and compared to most of its modern relatives it was comparatively tiny, only about 4.6m long (15′).

And it had no teeth at all, but possibly also no baleen.

Baleen rarely fossilizes, so it’s unclear whether Maiabalaena actually had any or not, but the shape of its skull suggests it probably didn’t – it lacked the broad thickened upper jaw associated with supporting racks of baleen plates. It instead seems to have been adapted for suction feeding similar to modern belugas and beaked whales, using muscular cheeks and tongue to manipulate water pressure and pull small prey like fish and squid straight into its mouth.

Since it lived at a time when the Antarctic Circumpolar Current was forming and cooling the oceans, changing ecosystems and prey availability, it may represent a previously unknown stage in baleen whale evolution – a point when they’d moved towards specializing for suction feeding and lost their teeth entirely, before transitioning again over to filter-feeding with baleen in a completely separate evolutionary development a few million years later.

Cryodrakon

Fragmentary fossils of huge azhdarchid pterosaurs have been found in Canada since the early 1970s, and for a long time they were assumed to belong to Quetzalcoatlus. But more recently these remains were re-examined and shown to actually represent an entirely new genus and species.

Cryodrakon boreas – an excellent name meaning “icy dragon of the north wind” – was officially described in late 2019. With a wingspan of around 10m (32’10”) it was similar in size to its close relative Quetzalcoatlus, but it dates to about 10 million years earlier making it one of the oldest azhdarchids ever found in North America.

It lived about 76 million years ago in Alberta, with its fossils coming from the Dinosaur Park Formation, an area that at the time would have been a coastal plain near the northern parts of the Western Interior Seaway. Despite Alberta being located somewhat closer to the Arctic Circle than it is today, the climate was warm-temperate and temperatures rarely dipped below freezing, with short nights in the summers and only a few hours of daylight in the winters.

Like other azhdarchids Cryodrakon would have spent a lot of its time on all fours on the ground. While moving like that it would have been almost 5m tall (16’5″), similar in size to a modern giraffe, stalking smaller animals and eating whatever it could catch and fit into its mouth.

Lophialetes

Much like how hyraxes were once far more diverse than their modern representatives, some ancient members of the tapir lineage were similarly weird.

Lophialetes expeditus was one of these odd tapir-relatives, living in Mongolia and China during the mid-Eocene about 48-37 million years ago. Standing around 50cm tall at the shoulder (1’8″) it had a build more resembling a deer or a horse than its pig-like modern cousins, and it was adapted for fast running in open plains, with long slender legs and three-toed hoofed feet that bore most of its weight on the middle digit.

Its skull had a nasal region similar to both modern tapirs and saiga antelope, suggesting the presence of a short trunk-like nose – but since some of its closest relatives didn’t have nearly such well-developed snouts, it seems that Lophialetes evolved its trunk separately to modern tapirs.