New study suggests ‘hyperdense’ Eocene air aided the origin of bat flight
Giannini et al 2024 reported,
“Here a gliding performance gradient emerged of decreasing sink rate with increasing AR that eventually allowed applying available muscle power to achieve level flight using flapping, which is greatly facilitated in hyperdense air. This gradient strongly supports a gliding (trees-down) transition to powered flight in bats.”
The study looked at Onychonycteris bats (Fig 1) from the Green River Formation (Early Eocene), widely considered the – warmest – period in the Cenozoic. Warmer air is always – less – dense. That’s a pilot’s concern on hot summer days when longer runways are needed to takeoff due to less dense hot air.
So ‘hyper-dense air’ is unexpected in the Early Eocene.
This bat flight study was hampered by taxon exclusion.
The authors reported, “the origin of bat flight remains obscure, with currently no theory satisfactorily explaining its early evolution.”
That is incorrect. The LRT provides bat ancestors back to Ediacaran worms.
Figure 1. From Giannini et al 2024, Onychonycteris specimens laid out. The smaller, more primitive undescribed Green River bat is added here to scale.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=143″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=488″ class=”size-full wp-image-85619″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=584&h=1226″ alt=”Figure 1. From Giannini et al 2024, Onychonycteris specimens laid out. The smaller, more primitive undescribed Green River bat is added here to scale. ” width=”584″ height=”1226″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=584&h=1226 584w, https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=71&h=150 71w, https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg?w=143&h=300 143w, https://pterosaurheresies.files.wordpress.com/2024/04/onychonycteris.holotype.diagram588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. From Giannini et al 2024, Onychonycteris specimens laid out. The smaller, more primitive undescribed Green River bat is added above them to full scale on a 72-dpi monitor). They are all tiny and lightweight, much smaller than the first birds or pterosaurs.
In trait analysis
(the LRT, subset Fig 6 ), the traditional ‘smallest primate’, Microcebus (Fig 2), nests basal to bats. In the LRT bats and primates are sister clades close to the middle Mesozoic origin of placentals. Oodectes is a larger last common ancestor.
So there’s a phylogenetic starting point missing from the bat study.
Microcebus is a small nocturnal
frugivore and insectivore (primarily beetles) that leaps between jungle branches in Madagascar today.
With few exceptions, living bats are typically either frugivores or insectivores.
Extant Microcebus evolved from a more plesiomorphic Cretaceous microcebid,
so keep that in mind.
Figure 2. Microcebus, the basalmost bat in the LRT, compared to fossil bats.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=146″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=498″ class=”size-full wp-image-68876″ src=”https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=584&h=1202″ alt=”Figure 2. Microcebus, the basalmost bat in the LRT, compared to fossil bats.” width=”584″ height=”1202″ srcset=”https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=584&h=1202 584w, https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=73&h=150 73w, https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg?w=146&h=300 146w, https://pterosaurheresies.files.wordpress.com/2022/05/microcebus_basal-bats588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Microcebus, the basalmost bat in the LRT, compared to fossil bats from a few years ago.
An undescribed Green River bat,
(Figs 1, 2) posted on FaceBook by Fossil Butte Museum in 2022, is smaller than Onychonycteris (Fig 1) by a third, and more primitive. The skull is half as long as that of Microcebus, Phylogenetic miniaturization was present at the origin of bats. All three Green River bats are much smaller than any of the Solnhofen birds (e.g. Archaeopteryx) and much smaller than the most primitive pterosaur, Bergamodactylus, and its nonvolant relatives. These first bats were the size and weight of the smallest living bats.
So hyperdense air was not necessary.
Even so, remember night air is cooler and thus more dense than warm, sunlit air.
Gliding never leads to flapping flight.
An indicator of flapping in birds and pterosaurs is the slender, elongate and locked down coracoid (Fig 6). In bats, lacking such a coracoid, an elongate clavicle serves as the same structural member (Figs 4, 5). The authors did not mention the words, ‘coracoid’ or ‘clavicle’ in their text. The bat expert authors missed this key factor to flapping flight in all three flying vertebrate clades.
The transition from non-volant to volant is the question here.
The authors indicate gliding in ‘hyperdense air’ was necessary or at least helpful.
Why do bat experts search for other solutions while avoiding the relatively easy task of simply adding taxa to their cladograms? Answers to enigmas appear in cladograms. Unfortunately, this is common to all paleontologists: pterosaur experts, whale experts, turtle experts, fish experts, amniote experts, etc. Longtime readers know this.
A competing hypothesis
posits an arboreal nocturnal jungle origin, based on Microcebus, listening inverted on a branch or tree trunk for beetles or insect larvae rustling in the leaf litter below. When the moment in right the microcebid pre-bat would drop down to capture and feed. The distance from branch to ground need not have been more than 20-50cm. Greater heights are always possible. Greater auditory acuity leads to echolocation.
Today
Microcebus feeds by grabbing fruit or prey, then shoving that food into its mouth (see video above). In a pre-bat microcebid, a larger grasping hand led to further predatory success.
Figure 1. Bat embryo wing shape compared to Pterodactylus. Note the ability to fold (relax) the wings until they virtually disappear in both cases. Also note the origin of bat wings paralleling those of pterosaur wings in that during embryology the bat wing also has a narrow chord that more deeply develops long after birth.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=142″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=484″ class=”size-full wp-image-22220″ src=”https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=584&h=1237″ alt=”Figure 1. Bat embryo wing shape compared to Pterodactylus. Note the ability to fold (relax) the wings until they virtually disappear in both cases. Also note the origin of bat wings paralleling those of pterosaur wings in that during embryology the bat wing also has a narrow chord that more deeply develops long after birth.” width=”584″ height=”1237″ srcset=”https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=584&h=1237 584w, https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=71&h=150 71w, https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg?w=142&h=300 142w, https://pterosaurheresies.files.wordpress.com/2016/03/myotis-embryo-wingshape588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Bat embryo wing shape compared to Pterodactylus. Note the ability to fold (relax) the wings until they virtually disappear in both cases. Also note the origin of bat wings paralleling those of pterosaur wings in that during embryology the bat wing also has a narrow chord that more deeply develops long after birth.
A larger grasping webbed hand
(retained from the embryo stage) led to even further success, both in grabbing prey and cushioning the landing. The ability to fold away that large grasping web was also a key step. Only the thumb remained a grasping organ in bats. We see this phylogenetic development replayed ontogenetically in bat embryos, where the brachiopatagirum first extends only to the elbows, as in pterosaurs (Fig 3), then later joins to the fuselage fillet between the elbow and ankle.
The authors did not mention the word ‘fold’ in their text, but they did discuss webbed fingers originating in mammal embryos. This webbing usually disappears in all other mammals other than bats, colugos and marine taxa.
Figure 4. Tadarida skeleton and soft tissue. The large clavicle is highlighted. Note the long tail and short fingers.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=198″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=584″ class=”size-full wp-image-85635″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=584&h=887″ alt=”Figure 4. Tadarida skeleton and soft tissue. The large clavicle is highlighted. Note the long tail and short fingers.” width=”584″ height=”887″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=584&h=887 584w, https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=99&h=150 99w, https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg?w=198&h=300 198w, https://pterosaurheresies.files.wordpress.com/2024/04/tadarida_invivo_skeleton.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 4. Tadarida skeleton and soft tissue. The large clavicle is highlighted. Note the long tail, a primitive trait. The ears here as as large as the skull. The hind limbs are relatively shorter than Eocene bats in figure 1.
Dropping from low branches onto leaf litter at a smaller size and mass
(e.g. the unnamed Green River specimen) led to further success due to less damage to the pre-bat and less disruption when hitting the leaf litter. Flapping on the way down (= controlled parachuting) slowed the descent and made hitting the target more precise, and that led to further success. This was likely a gradual process.
Figure 5. Eocene Onychonycteris had long clavicles, but not as relatively long as in Tadarida (figure 4).
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=584″ class=”size-full wp-image-85637″ src=”https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=584&h=540″ alt=”Figure 5. Eocene Onychonycteris had long clavicles, but not as relatively long as in Tadarida (figure 4).” width=”584″ height=”540″ srcset=”https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=584&h=540 584w, https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=150&h=139 150w, https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg?w=300&h=278 300w, https://pterosaurheresies.files.wordpress.com/2024/04/bat_clavicle_onychonycteris.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 5. Eocene Onychonycteris had long clavicles, but not as relatively long as in Tadarida (figure 4).
The strong hind limbs of Microcebus,
(Fig 2) ideal for leaping, were gradually reduced and extended laterally (a reversal to the early synapsid orientation) as parachuting with flapping gradually gained dominance over leaping between branches during phylogenetic miniaturization. Rather than leaping back into the branches to repeat the attack, as in Microcebus, leaping enhanced with flapping was gradually employed. This was the vigorous and energetic origin of the bat Bauplan – not passive, inactive gliding in hyper-dense air. Note the longer hind limbs of Eocene bats (Fig 1) compared to living Tadarida (Fig 4).
Figure 2. Subset of the LRT focusing on bats and their ancestor, Microcebus, a mouse lemur.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=300″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=584″ class=”size-full wp-image-69914″ src=”https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=584&h=229″ alt=”Figure 2. Subset of the LRT focusing on bats and their ancestor, Microcebus, a mouse lemur.” width=”584″ height=”229″ srcset=”https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=584&h=229 584w, https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=150&h=59 150w, https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg?w=300&h=118 300w, https://pterosaurheresies.files.wordpress.com/2022/06/bats-cladogram588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 6. Subset of the LRT focusing on bats and their ancestor, Microcebus, a mouse lemur. From 2022.
On a side note,
the authors reported, “While the origin of pterosaur flight remains obscure…” This is incorrect. Peters 2000, 2002, 2007 recovered pterosaur ancestors among the flapping bipedal clade that includes Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama (Fig 6), four phylogenetically miniaturized, increasingly bipedal tanystropheid lepidosaurs with increasingly locked down coracoids and gradually longer ring fngers.
These pre-pterosaur taxa
(Fig 6) had an increasing number of traditional pterosaur synapomorphies such that the hyper elongation of the fourth manual digit was the last pterosaur trait to develop (Peters 2002).
Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.
” data-medium-file=”https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=266″ data-large-file=”https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=584″ class=”size-full wp-image-9326″ src=”https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=584&h=657″ alt=”Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.” width=”584″ height=”657″ srcset=”https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=584&h=657 584w, https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=133&h=150 133w, https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg?w=266&h=300 266w, https://pterosaurheresies.files.wordpress.com/2013/02/pterosaur-pectoral-girdle5881.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 7. Pre-pterosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex. Note the elongate, locked-down coracoid on the flapping taxa, derived from the disc-like alternately sliding coracoid of the quadrupedal ancestor, Huehuecuetzpalli.
The fact that these pterosaur ancestors are not more widely recognized
goes back to the SC Bennett curse, “You will not be published and if you are published, you will not be cited.” Academics either hate it or ignore it when independent researchers get published. In this case citation is not the problem. Omitting pertinent taxa is the problem. Time after time this is what is holding back paleontologists from rising out of the muck of the paleo dark ages. Not sure why an outsider has to remind them to add taxa, but that has been the pattern now for at least two decades.
Consider this your peek behind the bat curtain.
Paleontology is not like physics, chemistry and anstronomy where scientists test each others’ ideas. Remember, Archaeopteryx was not given its due status until 130 years after its discovery. Huxley’s lectures in the 1870s argued for the theropod-bird connection, and Ostrom followed a century later with more bird-like taxa in evidence. Even with these professors’ backing this hypothesis was not widely accepted until just before the first Jurassic Park movie.
So don’t hold your breath for this one either.
References
Giannini NP, Cannell A, Amador LI and Simmons NB 2024. Palaeoatmosphere facilitates a gliding transition to powered flight in the Eocene bat, Onychonycteris finneyi. Nature communications biology. https://doi.org/10.1038/s42003-024-06032-9
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. – Historical Biology 15: 277–301.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
http://reptileevolution.com/reptile-tree.htm
http://reptileevolution.com/microcebus.htm
http://reptileevolution.com/pterosaur-wings.htm
The origin and evolution of bats part 4: distance vs. accuracy
Source: https://pterosaurheresies.wordpress.com/2024/04/28/new-study-suggests-hyperdense-eocene-air-aided-the-origin-of-bat-flight/
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