Tag: convergent evolution

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.

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.

Island Weirdness #58 — Candiacervus ropalophorus

The island of Crete has been isolated since about 5.3 million years ago, when the dried-out Mediterranean Sea refilled — but at that time it started off as several much smaller islands, and only gained its larger modern shape thanks to tectonic uplift in the Pleistocene.

It only had a small number of endemic land mammals during the Pleistocene, whose ancestors all seem to have reached the island by swimming or rafting from southern Greece: dwarf elephants, a small hippo, an otter, a shrew, large mice, and several deer.

Deer are surprisingly good swimmers, and seem to have colonized Crete by the mid-to-late Pleistocene 300,000 years ago. They were by far the most diverse mammals on the island, with eight species in six size classes, each living in different types of habitat and specializing in their own ecological niche in a similar situation to the older Italian Hoplitomeryx. Their anatomy was modified so much that it’s unclear what their original ancestors actually were, or even if they were all descended from a single colonization or multiple arrivals, but they seem to have been close relatives of the huge Megaloceros.

All eight species are usually classified in the genus Candiacervus, and the smallest and weirdest of them all was Candiacervus ropalophorus.

Ironically for a cousin of the giant deer it was tiny, just 40-50cm tall at the shoulder (1’4″-1’8″), with proportionally short stocky legs more like a goat. It seems to have convergently evolved to occupy the same niche as wild goats do elsewhere, clambering over steep rocky mountainous terrain and eating tough prickly vegetation.

The antlers of the males were huge for their body size, around 77cm long (2’6″), and they were simplified into a long straight beam with only a single small spike at the base. The far ends were wider and rounded, described as club-like or spatula-like, and their odd shape suggests they probably weren’t much use for fighting and wrestling like in other deer. Instead they seem to have been more just for show and visual display.

Meanwhile a second dwarf species, Candiacervus reumeri, had more standard-looking antlers and probably still fought each other.

The largest species, Candiacervus major, was as big as a modern wapiti, with a shoulder height of around 1.65m (5’5″) and body proportions much more like a normal long-legged deer. Its antler shape isn’t actually known yet, but since it lived in thickly forested areas of Crete the stags may have had more streamlined antlers to avoid getting snagged on low branches.

The various Candiacervus species went extinct towards the end of the Pleistocene, around the start of the Last Glacial Maximum 21,500 years ago. Originally this was thought to be long before humans ever reached the island, but more recent discoveries have brought that into question.

Humans do actually seem to have encountered living Candiacervus ropalophorus, since petroglyphs in Asphendou Cave appear to depict the dwarf deer and so must be at least 21,500 years old. Additionally, even older stone tools on the southern coast of Crete from at least 130,000 years ago match those made by archaic humans (probably Homo erectus) who may have arrived over sea from northern Africa.

So it’s possible the weird Cretan deer survived alongside humans for some time, but then their habitat started to degrade as the climate shifted rapidly colder and drier. Some remains show that many individuals were suffering from secondary hyperparathyroidism and metabolic bone disease, signs of severe nutritional deficiencies, and their weakening population may have ultimately been unable to deal with both the malnutrition and the additional pressures of human hunting.

Island Weirdness #50 — Caracara tellustris

Jamaica is unusual among the Caribbean islands for having had relatively few predatory birds.

One of the few known fossil species is Caracara tellustris, a close relative of the modern crested caracaras that probably evolved in the mid-Pleistocene between about 1.2 and 0.4 million years ago.

About 60-65cm long (2′-2’2″), it was similar in body size to larger individuals of its living relatives but was heftier built and had slightly longer legs, and its wings were reduced enough that it was either a very weak flier or entirely flightless.

It lived only in the dry scrubland around the southern coast of the island, and probably mainly preyed on reptiles, small rodents, and crabs using its strong legs — a lifestyle very similar to the modern secretarybird. Like other caracaras it would have also opportunistically scavenged on carrion, which there would have been little competition for.

The known remains of Caracara tellustris date to as recently as 100 CE, showing that it existed well into the Holocene and survived through the initial arrival of humans on its island home (about 4000 BCE). This is likely due to its inhospitable hot, arid, and thorny habitat, where it would have been left relatively undisturbed, and it may even have persisted until the time of European colonization in the 1500s.

Unfortunately the scrubland was also very limited in size and the Jamaican caracara would have always been quite a rare species. If it was still around by then it would have faced a combination of introduced predatory mammals and habitat destruction by agriculture, which would have driven it into extinction so quickly its existence was never even noticed by naturalists at the time.

Island Weirdness #49 — Sloth-Monkeys & Fighting Ibises

Jamaica is the third largest island in the Caribbean, and much like Cuba it originated as part of a Late Cretaceous volcanic island arc. It began to subside during the Eocene and was completely submerged for a large portion of the Cenozoic, then was uplifted again in the early-to-mid Miocene, reaching close to its present-day size around 13 million years ago.

Few land mammals ever colonized the island prior to human influence, and most of the known remains are from rodents. But another group did make it onto Jamaica, and became something especially weird.

A stylized illustration of an extinct titi monkey. It has long soft fur and a very long tail.
Xenothrix mcgregori

Xenothrix mcgregori is a primate only known from fragmentary remains, but what is known of its skeleton shows a unique combination of features for a New World monkey. It had a reduced number of teeth in its jaws, with enlarged molars, and oddly-shaped heavily-built leg bones that resemble those of slow quadrupedal climbers like lorises.

It was probably about 70cm long in total (2’4″), including the tail, and is thought to have lived a lot like a tree sloth, spending most of its time moving slowly around in the trees and possibly even feeding while hanging upside down.

Its anatomy was so ununsual that its evolutionary relationships were a mystery until ancient DNA was recovered from subfossil bones and confirmed it was actually a titi monkey very closely related to the genus Cheracebus. Its ancestors probably arrived on Jamaica in the late Miocene, around 11 million years ago, and it had some close relatives on a couple of other Caribbean islands — the terrestrial Paralouatta on Cuba, and Antillothrix and Insulacebus on Hispaniola — although they likely all independently colonized the Caribbean via different rafting events from South America.

A stylized illustration of an extinct flightless ibis. It has stout legs, and has its wings raised as if threatening to hit something with its heavy club-like arm bones.
Xenicibis xympithecus

Another inhabitant of Jamaica was an equally strange bird.

Xenicibis xympithecus was one of only two lineages of ibis ever known to have become completely flightless (the other being Apteribis from Hawaii).

Around 60cm tall (2′), it had some of the most unique wings of any bird. The hollow bones were thickened, its forearm was proportionally short, and the hand was modified into a large heavy “club” — and blunt-force injuries on some of these birds’ remains suggest that they used their wings as weapons when fighting, clobbering each other with powerful blows.

Radiocarbon dating suggests the Xenothrix monkeys survived well into the Holocene, until around 1100 CE. Since various groups of humans had been present on Jamaica since about 4000 BCE the sloth-monkeys must have coexisted with them for several millennia, and their extinction may have been caused by more of a “slow fuse” of gradual habitat destruction than direct exploitation.

Dating on Xenicibis‘ extinction is less precise, with the youngest known remains being somewhere between 10,000 and 2200 years old. It may have still been around when the earliest humans arrived, but unlike the native monkeys it seems like it didn’t last long beyond that point.

Island Weirdness #42 — Tall Owls & Short Ibises

The complete lack of land mammals on the Hawaiian islands left the terrestrial predator niches available to birds — and it was owls who ended up taking advantage of that role in the ecosystem.

The Grallistrix owls were found on Kauaʻi, Oʻahu, Molokaʻi, and Maui, with each island having its own endemic species. They were a type of true owl, probably descended from a species of Strix, and developed especially long legs that led to their nickname of “stilt-owls”.

A stylized illustration of an extinct owl. It has short wings and very long stilt-like legs.
Grallistrix geleches

The Molokaʻi stilt-owl (Grallistrix geleches) was the largest of the four known species, about 60cm tall (2′). Although it had proportionally short wings it was still capable of flying, and probably specialized in stalking and ambushing smaller birds like Hawaiian honeycreepers in the dense forests.

(These owls were also the inspiration for the pokémon Decidueye!)

A stylized illustration of an extinct flightless ibis. It has a downward-curving beak, small wings, and relatively short thick legs compared to other ibises.
Apteribis glenos

Meanwhile the forest floor insectivore niche was occupied by Talpanas on Kauaʻi, but on the other main islands a different type of bird took up the same role.

Apteribis was an ibis closely related to the modern white ibis and scarlet ibis, with three different species found on the islands of Maui, Molokaʻi, and Lānaʻi.

The Moloka’i flightless ibis (Apteribis glenos) was a typical example of the genus, about 50cm long (1’8″). It was flightless, with reduced wings, and had unusually short stocky legs that gave it proportions much more like a kiwi than an ibis. And it probably lived very much like a kiwi, too, probing around in the forest litter with its beak searching for snails and other invertebrates.

We even have an idea of the coloration of these birds, thanks to subfossil remains with preserved feathers. They seem to have been brown and beige, similar to the juvenile plumage of their close relatives.

The arrival of humans at least 1000 years ago would have unfortunately been devastating to both the stilt-owls and the flightless ibises. The combination of hunting, habitat destruction, and invasive dogs, pigs, and rats attacking them and their ground-based nests probably drove them all into extinction very quickly.

Antilohyrax

This is not a deer.

In Africa during the Eocene and Oligocene, the main terrestrial herbivores were a different type of mammal entirely: hyraxes, the close relatives of elephants and manatees. Although their only modern representatives are small climbing rodent-like animals, hyraxes were once a much more diverse and widespread group, filling a variety of ecological niches and ranging from the size of rats up to the size of rhinos.

Antilohyrax pectidens was a mid-sized example of these diverse hyraxes, standing about 50cm tall at the shoulder (1′8″) and living around 34-28 million years ago in Egypt. It had a deer-like snout and long slender limbs adapted for running and leaping, with leg bones incredibly similar in size and proportion to modern springbok.

Its incisor teeth were comb-shaped and resembled those of colugos, so it was probably a similar sort of selective browser eating soft leaves and shoots.

Island Weirdness #23 – The Bibymalagasy

One of the most mysterious members of Madagascar’s pre-human ecosystem was a creature known as Plesiorycteropus, or the “bibymalagasy”.

It’s known only from fragmentary remains, including a few limb bones, vertebrae, partial skulls, and partial pelvises – with two different species identified, the larger Plesiorycteropus madagascariensis and the smaller Plesiorycteropus germainepetterae. For a long time it was it was unclear what type of mammal it even was and the best guess seemed to be “some sort of small aardvark-relative” based on anatomical similarities, but various studies disagreed and some even considered it to represent a completely unique order of mammals.

In 2013 an analysis of preserved collagen from one bone finally gave a better answer – Plesiorycteropus was most closely related to tenrecs, which arrived in Madagascar via ocean rafting during the mid-Cenozoic, and the skeletal resemblance to aardvarks was due to convergent evolution.

It was built for scratch-digging, using its strong forelimbs and claws to dig while bracing itself with its hindlimbs and long thick tail. Its snout had large nasal cavities, indicating a good sense of smell, and similarities to the skulls of armadillos suggest it had the same sort of diet of insects, grubs, worms, and other soft foods. It may also have fed on ants and termites.

Since it’s only known from fragments its full size is hard to determine, but rough estimates suggest Plesiorycteropus madagascariensis was “small dog-sized” – possibly having a head-and-body length of 60-80cm (2′-2′7), and a total length of over 1m (3′3″).

Unlike some other extinct Malagasy animals there are no historical or folkloric accounts of anything resembling the bibymalagasy. One bone has been carbon dated to just over 2000 years ago, shortly after the arrival of human settlers, and it seems to have gone extinct very soon after that date.