Tag: rodent

Spectember/Spectober 2024 #10: Nosey Sea Monkey & Louse Mouse

Okay, let’s finish up this year’s round of speculative evolution concepts with one last post before we get back to normal paleoart content.

(…what do you mean it’s November 3rd? how did that happen?)

Belial Lyka asked for a “marine proboscis monkey with a somewhat buoyant nose”:

A shaded sketch of a speculative semiaquatic descendant of proboscis monkeys. It has a large trunk-like nose, a fat body, long arms ending in flipper-like hands, short legs with webbed feet, and a short thick tail. A second image shows its head with its nose inflated into a balloon-like display structure.

A descendant of modern proboscis monkeys, Phusarhinus beliallykae is a large semiaquatic primate found in shallow marshy coastal areas of what was once Southeast Asia. Around 4m long (~13′) it has a lifestyle somewhat similar to ancient early sirenians, feeding on soft aquatic plants and hauling out onto land to rest.

Its dense rib bones and long flipper-like grasping forelimbs make it rather front-heavy, allowing it to naturally float with its head and arms hanging down closer to the bottom for energy-efficient foraging. When it needs to resurface to breathe it shunts air from its lungs into its large inflatable nasal sacs, altering its buoyancy enough to tip its head back up towards the surface.

Unlike its ancestors the elaborate nasal structures are found on both males and females – although they’re more brightly colored in males and are also used for visual courtship displays and as resonating chambers for loud booming calls.

And somebody who only gave their name as “bunny” suggested a “parasitic rodent”:

A shaded sketch of a speculative parasitic descendant of semiaquatic rats. It has a wide flattened body with thick armor-like bands running down its back, a small head, stubby limbs tipped with long hooked claws, and a short fat tail.

Sanguichelonamys bunnyi is a highly unusual descendant of a rakali-like semiaquatic rodent that had a symbiotic relationship with early members of the Phusarhinus lineage. The rodents initially just removed algae and external parasites from the bodies of the increasingly bulky aquatic monkeys, but things have recently started to turn more parasitic.

At just 3cm long (~1.2″) Sanguichelonamys is one of the smallest mammals to ever exist, with a wide flattened body and sharp hooked claws used to cling onto its host monkey’s thick skin. Although it still does remove other parasites, during haul-out periods it will also use its sharp incisors to deliberately enlarge the wounds left behind – or even open up new ones – and directly feed on fresh blood from its host.

The thickened keratinous skin along its head and back has a specialized hydrophobic surface that traps a layer of air while underwater, acting as a “rebreather” bubble similar to that of water anoles. Along with the ability to drastically slow down its metabolism and respiration rate, this allows Sanguichelonamys to survive being submerged during its host’s lengthy foraging dives.

Bathyergoides

Blesmols, or African mole-rats, are a group of rodents adapted for mole-like burrowing. Closely related to the more famous naked mole-rat, these little mammals have reduced eyes and ears along with incisors that protrude out even when their mouths are closed, allowing them to excavate tunnels primarily using their teeth.

One of the earliest known fossil blesmols is Bathyergoides neotertiarius here, from the early Miocene of Namibia about 20 million years ago. For almost a century this species was known only from teeth and partial skull remains, but recently a partial skeleton was described giving us a better idea of its overall appearance and lifestyle.

Bathyergoides was a fairly large blesmol, around 25cm long (~10″), and was already specialized for tooth-digging with a skull very similar to modern forms. It had powerful muscular forelimbs that would have been used to push back loose soil while burrowing, but unlike its living relatives it also had a long tail and relatively slender hindlimb bones – with anatomy suggesting its legs were used more for stabilizing its posture than for actively digging.

It may have had a less subterranean lifestyle than modern blesmols, digging out extensive burrows but still foraging for food above ground in a similar manner to modern semi-fossorial rodents like giant pouched rats.

Leithia melitensis

During the mid-Pleistocene, between about 900,000 and 500,000 years ago, the Mediterranean islands of Malta and Sicily were connected and shared a unique ecosystem made of up a mix of weird endemic species. While the tiny elephants and giant swans are probably the most famous, there were also several other unusual animals such as dwarf hippos, huge owls, large cranes, giant tortoises, and big lizards.

And also massive rodents.

Leithia melitensis, the Maltese giant dormouse, was descended from garden dormice, but thanks to the lack of large land predators on Siculo-Malta it was able to evolve a much much larger body size – about 60-70cm long (2′-2’4″), almost the size of a cat.

Recent reconstructions of its skull have shown it was also proportioned differently compared to its tiny modern relatives, more chunkily built with a shorter and wider snout, bigger teeth, and thicker cheekbones that must have anchored some incredibly powerful muscles for chewing. It may have been eating a much more herbivorous diet than other dormice, processing a lot of tough fibrous vegetation.

Island Weirdness #51 — Tainotherium valei

Like much of the Caribbean, Puerto Rico originated as part of a Mesozoic volcanic island arc. While in theory this could have resulted in the region retaining some relict populations of weird Cretaceous species, there’s a major reason this didn’t actually happen: the asteroid impact event 66 million years ago. The proximity to Chicxulub would have been devastating to the proto-Caribbean at the time, with tsunamis as high as 500m (1640′) battering the islands and destroying practically everything that lived there at the time.

Afterwards subsidence in the early Cenozoic submerged many of the islands and drowned whatever was left, so it wasn’t until later tectonic uplifting that land re-emerged and was able to be recolonized by species via rafting and island hopping (or possibly via a short-lived land bridge).

Caviomorph rodents arrived from South America around the start of the Oligocene, about 33 million years ago, and became very successful due to being some of the only land mammals present on many of the islands. The only modern survivors of this lineage are a handful of hutias, but in the past they were much more diverse — and some of them were giants. 

Tainotherium valei lived in Puerto Rico during the Late Pleistocene and early Holocene, and while it wasn’t quite the largest of the giant hutias it was still enormous. It’s only known from a single partial leg bone, so its full size is difficult to estimate, but it was probably somewhere around 80cm tall at the shoulder (2’7″) and weighed about 100kg (220lbs) – similar in size to a modern black bear.

And that leg bone is especially unusual, showing anatomical adaptions associated with tree-climbing. This is strange for such a huge heavy mammal, but it may have been an ecological equivalent of something like the giant Malagasy lemurs, a slow-moving animal that climbed up trees to feed and regularly traveled over the ground from one feeding site to another.

During the Pleistocene lower sea levels meant most of the Puerto Rican archipelago was part of a much larger landmass that also included most of the nearby Virgin Islands, and the predominate climate at the time was a dry savanna. As sea levels rose at the start of the Holocene the climate shifted wetter and Puerto Rico became densely forested. This would have been advantageous for a tree-climbing animal like Tainotherium, so it was likely still around when the first humans arrived in around 3000-2000 BCE.

Unfortunately these early settlers appear to have burned large amounts of the forests for the first few centuries of their presence, and such widespread habitat destruction would have driven this giant rodent extinct very quickly.

Josephoartigasia

The biggest known rodent of all time, Josephoartigasia monesi from the Pliocene and early Pleistocene of Uruguay, South America (~4-2 mya). Similar in size to a modern bison, it stood about 1.5m tall at the shoulder (4′11″) and weighed around 900kg (~2000lbs).

Despite looking like an extra-large capybara, it was only distantly related to the modern giant rodents. Its closest living relative is actually the much smaller pacarana.

Its 30cm long (12″) incisors could produce a large amount of bite force, and it may have used them in a similar manner to elephant tusks – rooting in the ground for food, stripping trees and branches, or defending itself from predators.