Mystacina: a walking, climbing, scraping micro-bat

The little New Zealand bat, Mystacina
(Figs. 1, 2), provides a living example for the earlier drop and hover hypothesis for the origin of bat flight. Most bats hang by their feet and observe what is below when they are not flying. This one, not so much.

Figure 1. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey.

Figure 4. The false vampire bat hovering before attacking a mouse in dry fallen leaves, listening to locate is prey. Flapping is key. Pre-bats were not gliders. Prebats flapped their parachute-like forelimbs.

Distinct from other bats,
Mystacina spends about thirty percent of its time on the ground on all fours (see YouTube video link below), wings folded, digit 2, the ventral one, reduced to a bumper.

Figure 1. Skeleton of Mystacina tuberculata from Digimorph.org and used with permission. The large head size is a derived trait.

Figure 2. Skeleton of Mystacina tuberculata from Digimorph.org and used with permission. The large head size is a derived trait. Note the two large incisors, used for scraping away burrows in soft hollow trees, co-copted by vampire bats to scrape away cattle skin.

The sharp incisor teeth
are used to scrape away soft tree interiors to create arboreal burrows. This trait is co-opted by related and sometimes terrestrial vampire bats to scrape away cattle skin to start  bleeding.

Figure 2. Mystacina skull from Digimorph.org and colorized here.

Figure 3 Mystacina skull from Digimorph.org and colorized here.

The propatagium is small
to aid in terrestrial locomotion. Mystacina has a large brain. A YouTube video (click to view) shows Mystacina in action.

Based on its performance,
and location, I wondered if Mystacina would be one of the most primitive of bats. It is not. So it may have reverted to a more primitive way of getting along (walking on all fours) after earlier achieving inverted bipedality and flight. Perhaps isolation on New Zealand as the only endemic mammal permitted this to happen.

Can you think of another set of animals
that reverted to quadrupedal locomotion after achieving flight? (Answer below).

FIgure 3. Subset of the LRT focusing on bats and kin including Mystacina.

FIgure 4. Subset of the LRT focusing on bats and kin including Mystacina. No, Mystacina does not nest at the base of all bats. Manis is the extant pangolin. Cynocephalus is the extant colugo or flying lemur.

Mystacina tuberculata (Gray 1843; 6-7cm snout-vent length) is the extant New Zealand lesser short-tailed bat. The tail extends beyong the uropatagia. It sometimes feeds on nectar with a long hairy tongue, but is considered omnivorous because it eats beetles and larvae. Today’s post was inspired by the discovery of a fossil relative from the Miocene of New Zealand, Vulcanops jennyworthyae.

Be wary of NatGeo.com stories
with headlines about burrowing bats. Mystacina bats burrow their way into the cores of rotting trees using their scraping incisors, a point missed by the author of the story from 2018, but cited by her in another online story here. Bats did not create small caves in the ground. At best they disturbed or ran into dense leaf litter to locate their prey.

Earlier we looked at the origin of large wings/hands
as holders of fruit hanging from trees (Fig. 5), either for the fruit itself or for the insects boring through it. This allows fruit bats and micro bats to have a phylogenetic common ancestor (Fig. 4 in clawed bats like Icaronycteris and Onychonycteris.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Figure 5. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Hanging upside down is something
many, if not all basal placentals did and do (Fig. 5). Those who don’t, like humans, horses and elephants, are derived. In contrast, bats rely only on their feet to hang upside down. The tail is no longer involved and disappears in some taxa.

Figure 1. GIF animation thought experiment on the origin and evolution of bats from a Ptilocercus-like omnivore.

Figure 6. GIF animation thought experiment on the origin and evolution of bats from a Ptilocercus-like omnivore. A change is warranted in this illustration. Abdominal membranes were probably present in pre-bats, extending from the torso to the fingers. These created a flapping steerable  parachute for bat decent to the leaf litter forest floor.

If you’re still wondering about
the other animals that reverted to a quadrupedal configuration after learning how to fly, think of the pterodactyloid-grade pterosaurs, which did so four times by convergence (Figs. 7, 8) according to the large pterosaur tree (LPT). Based on the extreme small size of hatchlings due to phylogenetic miniaturization at the genesis of these clades, these baby pterosaurs were probably relegated to clambering through dense, moist leaf litter until reaching a size that enabled flight without rapid desiccation due to a high surface-to-volume ratio.

Figure 8. Click to enlarge. The descendants of Sordes in the Dorygnathus clade and their two clades of pterodactyloid-grade descendants.

Figure 7. Click to enlarge. The descendants of Sordes in the Dorygnathus clade and their two clades of pterodactyloid-grade descendants.

I have to say,
putting together these cladograms of vertebrates, pterosaurs and therapsids has taught me more about the theory of evolution and the way things work than dissecting a frog ever did in high school, or picking matrix off a fossil later on. Comparative anatomy gives one an appreciation and understanding of micro-evolution, not only what happened, but often why it happened over a wide range of taxa, some of which have never been compared to one another before.

The base of the Scaphognathia

Figure 8. Click to enlarge. The base of the Scaphognathia illustrating the size reduction that preceded the size increase in the transition from Scaphognathus to several later, larger “pterodactyloid”-grade clades.

By contrast,
the focus of paleontology textbooks seems to be showing chapter after chapter of skeletons, too often without making such distant comparisons with a freedom not often enough permitted in academia.


References
Gray JE 1843. List of the Specimens of Mammalia in the Collection of the British Museum, George Woodfall and Son, London.

wiki/Mystacina
wiki/Vulcanops

2 thoughts on “Mystacina: a walking, climbing, scraping micro-bat

  1. Interesting stuff – but misleading. For starters, the Pteropodidae do NOT feed by enfolding the fruit with their wings. For grasping, they typically use their elongated thumbs /thumb claws. Secondly, they often eat in a non-inverted position, sometimes holding a large-ish piece of fruit with a foot. Trust me – I’ve lived with Pteropus conspicillatus for nearly two years.

    • Talia, thank you. According to the LRT, Pteropodidae are derived from bats that already have volant wings. I’m looking back to the origin of ‘the big hand’ and suggesting new hypotheses that someday will be confirmed or refuted. Richard Feynman said, science begins with a guess.

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