Spectember/Spectober 2023 #09: Things With Wings

(Apologies for the abrupt absence – I’m okay, just having everything break down at once. This is fine.)

So— back to the speculative evolution request list!

TheBigDeepCheatsy requested a “cactus-dwelling/germinating evolution of introduced rosy-faced lovebirds”:

A shaded sketch of a speculative symbiotic relationship between lovebirds and saguaro cactus. The lovebird is shown on the left, a small parrot that looks very similar to modern rosy-faced lovebird except with hints of a more mottled color pattern. The cactus is shown on the right, a large fasciated saguaro with its top fanning out into a wide "crown", with several nest holes dug into it and multiple lovebirds occupying them.

While Agapornis cheatsyi is still quite physically similar to its introduced ancestors, this lovebird has developed a close symbiotic relationship with the cactus Carnegiea ornipolis, a descendant of the modern saguaro.

Naturally fasciated, this cactus grows a splaying fan-like crown which the lovebirds excavate their shallow nest burrows into. Feeding on the cactus’ fruit in early summer, the lovebirds then disperse the seeds via their droppings – a process that significantly improves propagation chances, both due to the birds commonly foraging and defecating around suitable nurse plants and the passage through their gut speeding up germination.

Someone calling themself “LB” asked for some “flying afrotherians”:

A shaded sketch of a speculative flying tenrec. It's a bat-like animal with membranous wings supported by three elongated fingers, and a large shrew-like head with long toothy jaws and an elephant-shrew-like nose.

Elbeitandraka venenifer is a descendant of tree-climbing Malagasy tenrecs that developed gliding membranes – and its lineage is now just about achieving true powered flight.

About 25cm long (~10″), its proportionally short broad wings require it to fly very fast to generate enough lift for its weight. It mostly only actively flies when traveling between roosts and feeding sites (or when escaping from threats), alternating between gliding to save energy and flapping to recover altitude.

It’s an opportunistic omnivore, crawling around in the tree canopy foraging for vegetation, fruits, fungi, invertebrates, and the occasional smaller vertebrate, using its flexible sengi-like nose to probe around in crevices.

Much like modern common tenrecs it’s capable of hibernating for months at a time through periods of scarce food availability. It also accumulates alkaloid toxins in its body from its arthropod prey, advertising its unpalatability to predators with bold contrasting warning coloration on its wing membranes.

And here’s a combination of a couple of anonymous requests for both “flying heterodontosaurs” and “dragons with hind leg wings, a la sharovipteryx”:

A shaded sketch of a speculative flying predatory heterodontosaurid dinosaur, show both on the ground in a quadrupedal posture and in flight. Its hind legs form its main wings, with elongated outer toes supporting large pterosaur-like flight membranes. It also has a hooked beak at the front of fanged jaws, an s-curved neck, a compact fuzzy body, short forelimbs with taloned hands and small stabilization membranes, and a long vaned tail.

Inversodraco rapax is a highly specialized Jurassic descendant of heterodontosaurids that took to climbing and gliding, developing delta-wing-like membranes on their hindlimbs convergently similar to those of the earlier sharovipterygids.

Around 75cm long (~2’6″), it has unusually flexible hip joints for a dinosaur, able to splay its legs out to the sides to deploy wings supported by an elongated outer toe on each foot. Its arms form small forewings for stability, and its long tail ends in a vane of stiffened feathers that aid in steering.

Unlike its herbivorous-to-omnivorous ancestors it’s primarily a carnivore, swooping down onto small prey and grabbing it with its talon-like forelimbs.

Strange Symmetries #23: Convergent Earvolution

Although it’s not visible externally, owls have one of the most striking modern examples of asymmetry. The ears of many species are uneven, with the right ear opening positioned higher up than the left, giving them the ability to pinpoint the sounds of their prey much more accurately.

But surprisingly this isn’t a unique anatomical trait that only ever evolved once in their common ancestor.

Instead, multiple different lineages of owls have actually convergently evolved wonky ears somewhere between four and seven separate times.

The boreal owl (Aegolius funereus), also known as Tengmalm’s owl, is a small 25cm long (~10″) true owl found across much of the northern parts of both Eurasia and North America. While most other owls’ asymmetrical ear openings are formed just by soft tissue, the boreal owl’s lopsided ears are actually visible in the bones of its skull.

But despite how many times owls have convergently evolved asymmetrical ears, and how successful this adaptation has been for them, for a long time it seemed to be something that no other animals have ever mimicked.

In the early 2000s asymmetric ears were reported in the skulls of some troodontid dinosaurs, which seem to have been nocturnal hearing-based hunters similar to owls, but proper details on this feature still haven’t been formally published.

Then, just a couple of weeks ago, another example was finally announced.

The night parrot (Pezoporus occidentalis) is a small ground-dwelling parrot found in Australia, close to the same size as the boreal owl at around 22cm long (~9″). Critically endangered and very elusive, it’s rarely seen and little is known about it – and it was presumed extinct for much of the 20th century, until more recent sightings of living individuals confirmed that the species is still hanging on.

Recent studies of preserved museum specimens have revealed that it seems to have poor night vision but excellent hearing, and that its right ear opening is noticeably asymmetrical, bulging out sideways from its skull. Much like owls the night parrot relies on acute directional hearing to navigate in darkness, but since its diet consists mainly of seeds it’s probably not using this ability to locate food sources. Instead it may be listening out to keep track of the precise locations of other parrots, and for the approach of predators – so its sharp sense of hearing may be the reason this unique bird has so far just barely managed to survive the presence of invasive cats and foxes.

Island Weirdness #34 — Heracles inexpectatus

New Zealand is probably one of the most famous modern examples of a unique island ecosystem, having been isolated for the last 80 million years. Lacking any living terrestrial mammals, birds instead became the dominant land animals, adapting to a wide range of niches and evolving unusual flightless forms like the modern kiwi and kākāpō.

The St Bathans fossil site on the South Island dates to the early Miocene, about 19 to 16 million years ago, just after a period known as the “Oligocene drowning” when large portions of the landmass were underwater. It gives us a glimpse of an ancient version of New Zealand when the ecosystem was recovering and rapidly diversifying in a then-subtropical climate, and has produced a wide range of new fossil species (including a mysterious mammal).

One of the most recent discoveries from the site is Heracles inexpectatus, a close relative of the modern New Zealand parrots — but significantly larger than any living species, estimated to have stood almost 1m tall (3’3″). Known from just a few leg bones, the fossils were so big that they initially weren’t even recognized as belonging to a parrot, instead being mistaken for a large eagle before their true nature was realized.

At such a size it would likely have been flightless, although it may have still been capable of climbing trees and gliding. Much like the modern kea it was probably an omnivore, using its large curved beak and powerful crunching bite to eat pretty much whatever it wanted.

By the late Miocene, around 13 million years ago, New Zealand’s climate rapidly shifted cooler and drier, and the tropical forests were quickly replaced with temperate ones. This changing habitat may have been too much too fast for the giant parrots to deal with, and they went extinct alongside many of the other St Bathans species.

Island Weirdness #25 – The Broad-Billed Parrot

The dodo wasn’t the only unique bird to evolve on Mauritius. While about eight other endemic bird species still survive today, there were at least twice that many before the arrival of humans in the late 1500s – including the broad-billed parrot Lophopsittacus mauritianus.

Also referred to as the “Indian raven” in historical accounts, it was a fairly large bird measuring between 45 and 65cm in length (1′6″-2′1″). Unusually for a parrot it had a high degree of sexual dimorphism, with males being significantly bigger than females.

Many images depict it as entirely black or blue-grey, but this seems to be based on a misinterpretation. More recent translations of old Dutch descriptions suggest it was actually much more colorful, with a red beak, blue head, and reddish body.

It had a proportionally big head and a flattened skull, and seems to have had a highly specialized diet, using its its large strong beak to crack open hard seeds and nuts like modern hyacinth macaws.

It was near-flightless, capable of taking to the air only with difficulty, and was said to be “bad-tempered”. Attempts to keep individuals in captivity failed, the birds refusing to eat, and while the wild population had apparently learned to be wary of humans by the late 1660s by that point it was already too late. Much like the dodos they lived alongside, a combination of deforestation, hunting, and predation by invasive mammal species sent them into extinction by the 1680s.