Airborne hearing in non-tympanate tetrapods + climbing salamanders + aerial mammals evolution + Paleocene marine fishes Lagerstätte + sturgeon Cretaceous Arctic migration
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Ben Creisler
Jun 3, 2026, 3:11:22 PM (3 days ago) Jun 3
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Ben Creisler
Jakob Christensen-Dalsgaard, Tanya Bojesen Lauridsen, Grace Capshaw & Catherine E. Carr (2026)
A general mechanism of airborne hearing in recent and early non-tympanate tetrapods
Journal of Experimental Biology 229(11): jeb251719
https://doi.org/10.1242/jeb.251719
https://journals.biologists.com/jeb/article/229/11/jeb251719/371877/A-general-mechanism-of-airborne-hearing-in-recent
Tetrapod tympanic hearing probably emerged in the Triassic with independent origins of middle ear structures in each of the major groups, more than 120 Myr after the origin of tetrapods. During this period, any auditory sensitivity must have been based on non-tympanic mechanisms. We focused on the simplest model for non-tympanic hearing: that sound translates the head, and that this vibration is transduced by the inner ear. This is the mode of human low-frequency bone conduction sensitivity and is also the mode of underwater auditory stimulation for most fishes. The efficiency of translation of an object by sound depends on its density and ka, the product of the acoustic wavenumber (k) and the radius (a) of the head. Analytic and simple finite-element models of translation show that head vibration velocities largely are determined by ka and density (for objects of the same shape and composition), and are almost constant (between 4 and 5 μm s−1 Pa−1; neglecting friction) for objects with ka<1. We compared sensitivity to sound and to head vibrations in animals lacking tympanic middle ears (snakes, salamanders, earless frogs and lungfish) and showed that the low-frequency airborne sound sensitivity in these species is largely consistent with a translation mechanism. Stimulation of the inner ear by sound translation is likely by an inertial system like the otolithic/otoconial ears of fish and early tetrapods, or by fluid inertia in the inner ear generating hydrodynamic waves that stimulate the hair cells, providing a simple mode of sound reception in earless animals.
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Free pdf:
Jonathan M. Huie & Sandy M. Kawano (2026)
Limb kinematics and morphology improve salamander climbing performance
Journal of Experimental Biology jeb.251894.
https://doi.org/10.1242/jeb.251894
https://journals.biologists.com/jeb/article/doi/10.1242/jeb.251894/371696/Limb-kinematics-and-morphology-improve-salamander
Hundreds of plethodontid salamander species can climb vertical structures, despite lacking morphological adaptations typically found in other climbing tetrapods. To compensate, salamanders likely rely more on behavioral modifications to mediate the relationship between their relatively generalist morphologies and climbing performance. Here, we examined four plethodontid species (Aneides aeneus, Aneides lugubris, Aneides hardii, and Plethodon glutinosus) that differ in their habitat preferences, climbing tendencies, and limb morphologies. Using 3D high-speed videography, we compared how these species adjust their gait and limb kinematics while traversing a flat surface inclined at 0°, 45°, 80°, and 90°. We find that all species could climb vertically (or near vertically for A. hardii) using similar gait and kinematic changes that increase stability. For instance, all species used a single-step gait, increased duty factor, reduced stride length, and reduced stride frequency while their bodies were positioned closer to the substrate at the highest inclines compared to 0° or 45° inclines. However, highly scansorial species (A. aeneus and A. lugubris) climbed faster than the other species. The enhanced abilities of scansorial species may be attributable to their longer limbs that enable longer strides as well as their unique foot morphologies - coupled with changes in foot orientation - that facilitate better attachment through grasping. Overall, we propose that behavioral changes are sufficient for adequate climbing, but subtle morphological changes promote exceptional climbing performance. This likely explains the prevalence of climbing abilities across ecologically and morphologically diverse plethodontid salamanders.
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Norberto P. Giannini & Alan Cannell (2026)
The squirrel barrier concept and its bearing on the evolution of aerial mammals
BMC Ecology and Evolution (advance online publication)
doi: https://doi.org/10.1186/s12862-026-02532-w
https://link.springer.com/article/10.1186/s12862-026-02532-w
Some recent tetrapod and fish papers of interest:
Free pdf:
Jakob Christensen-Dalsgaard, Tanya Bojesen Lauridsen, Grace Capshaw & Catherine E. Carr (2026)
A general mechanism of airborne hearing in recent and early non-tympanate tetrapods
Journal of Experimental Biology 229(11): jeb251719
https://doi.org/10.1242/jeb.251719
https://journals.biologists.com/jeb/article/229/11/jeb251719/371877/A-general-mechanism-of-airborne-hearing-in-recent
Tetrapod tympanic hearing probably emerged in the Triassic with independent origins of middle ear structures in each of the major groups, more than 120 Myr after the origin of tetrapods. During this period, any auditory sensitivity must have been based on non-tympanic mechanisms. We focused on the simplest model for non-tympanic hearing: that sound translates the head, and that this vibration is transduced by the inner ear. This is the mode of human low-frequency bone conduction sensitivity and is also the mode of underwater auditory stimulation for most fishes. The efficiency of translation of an object by sound depends on its density and ka, the product of the acoustic wavenumber (k) and the radius (a) of the head. Analytic and simple finite-element models of translation show that head vibration velocities largely are determined by ka and density (for objects of the same shape and composition), and are almost constant (between 4 and 5 μm s−1 Pa−1; neglecting friction) for objects with ka<1. We compared sensitivity to sound and to head vibrations in animals lacking tympanic middle ears (snakes, salamanders, earless frogs and lungfish) and showed that the low-frequency airborne sound sensitivity in these species is largely consistent with a translation mechanism. Stimulation of the inner ear by sound translation is likely by an inertial system like the otolithic/otoconial ears of fish and early tetrapods, or by fluid inertia in the inner ear generating hydrodynamic waves that stimulate the hair cells, providing a simple mode of sound reception in earless animals.
=====
Free pdf:
Jonathan M. Huie & Sandy M. Kawano (2026)
Limb kinematics and morphology improve salamander climbing performance
Journal of Experimental Biology jeb.251894.
https://doi.org/10.1242/jeb.251894
https://journals.biologists.com/jeb/article/doi/10.1242/jeb.251894/371696/Limb-kinematics-and-morphology-improve-salamander
Hundreds of plethodontid salamander species can climb vertical structures, despite lacking morphological adaptations typically found in other climbing tetrapods. To compensate, salamanders likely rely more on behavioral modifications to mediate the relationship between their relatively generalist morphologies and climbing performance. Here, we examined four plethodontid species (Aneides aeneus, Aneides lugubris, Aneides hardii, and Plethodon glutinosus) that differ in their habitat preferences, climbing tendencies, and limb morphologies. Using 3D high-speed videography, we compared how these species adjust their gait and limb kinematics while traversing a flat surface inclined at 0°, 45°, 80°, and 90°. We find that all species could climb vertically (or near vertically for A. hardii) using similar gait and kinematic changes that increase stability. For instance, all species used a single-step gait, increased duty factor, reduced stride length, and reduced stride frequency while their bodies were positioned closer to the substrate at the highest inclines compared to 0° or 45° inclines. However, highly scansorial species (A. aeneus and A. lugubris) climbed faster than the other species. The enhanced abilities of scansorial species may be attributable to their longer limbs that enable longer strides as well as their unique foot morphologies - coupled with changes in foot orientation - that facilitate better attachment through grasping. Overall, we propose that behavioral changes are sufficient for adequate climbing, but subtle morphological changes promote exceptional climbing performance. This likely explains the prevalence of climbing abilities across ecologically and morphologically diverse plethodontid salamanders.
=====
Free pdf:
Norberto P. Giannini & Alan Cannell (2026)
The squirrel barrier concept and its bearing on the evolution of aerial mammals
BMC Ecology and Evolution (advance online publication)
doi: https://doi.org/10.1186/s12862-026-02532-w
https://link.springer.com/article/10.1186/s12862-026-02532-w
Three vertebrate lineages conquered powered flight in different epochs of the Phanerozoic: pterosaurs, dinosaurs (birds) and mammals (bats). The evolutionary mechanisms proposed for the demanding transition to powered flight have been contentious. For mammals, recent evidence suggests that the Darwinian hypothesis of a gliding transition is supported, based on aerodynamic and paleo-atmosphere reconstructions. However, it is surprising that the many (at least 12) confirmed, independent lineages of gliding mammals that existed since the Jurassic to the present never evolved powered flight. To explain this, Pennycuick in 2008 advanced the theoretical concept of the squirrel barrier: gliding mammals face a tradeoff between the cost of abandoning their agile arboreal lifestyle, and the potential gains of powered flight, thereby limiting the evolution of the higher-aspect-ratio wings required for achieving the latter. This concept was seldom discussed, used or tested. Here we examine critically the squirrel barrier concept and its implicit components, contrasting its predictions with available evidence, specifically from morphology, aerodynamics, and fossils. We found the concept highly relevant, and more complex than originally stated. A more nuanced approach to the probable conditions that must be met to transition from the locomotor style of ancestors to flying descendants reveals several intermediate such barriers, of which the squirrel barrier is one requiring profound evolutionary changes. Glide distance is a measure of glide efficiency, because the longer the glide the better the use of the large amount of energy invested in climbing up to the launch point in the canopy. Based on observational data and aerodynamics, we hypothesize that colugos (Dermoptera: Cynocephalidae) are able to maximize glide distance and glide ratio beyond average performance and thus might be beyond the squirrel barrier as proposed by Pennycuick, but still falling too short of reaching sustained powered flight, which constitute an additional, “hard” flight barrier.
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Free pdf:
Sanaa El-Sayed, Matt Friedman, Belal S. Salem, Abdullah S. Gohar, Shorouq F. Al-Ashqar, Mohamed Amin, Hossam El-Saka, Hadeel Saad, Robert P. Speijer, and Hesham M. Sallam (2026)
Sanaa El-Sayed, Matt Friedman, Belal S. Salem, Abdullah S. Gohar, Shorouq F. Al-Ashqar, Mohamed Amin, Hossam El-Saka, Hadeel Saad, Robert P. Speijer, and Hesham M. Sallam (2026)
Rise of modern marine fishes captured in an early Paleocene Lagerstätte
Science Advances 12: eaec8978
DOI: 10.1126/sciadv.aec8978
https://www.science.org/doi/10.1126/sciadv.aec8978
Free pdf:
https://www.science.org/doi/epdf/10.1126/sciadv.aec8978
The Cretaceous-Paleogene (K-Pg) extinction reshaped Earth’s biodiversity, yet its impact on marine fishes remains debated due to gaps in the Paleocene record. Here, we report a paleotropical assemblage from the early Paleocene (Danian) of Egypt that provides a window into this transition. The Qreiya 3 Lagerstätte [62.2 million years ago (Ma)] reveals an offshore marine ecosystem with at least 21 actinopterygian taxa across nine orders, exceeding the diversity of all other Danian skeletal assemblages combined. Most fishes are percomorphs and include the oldest skeleton-based records for at least six ecologically divergent extant groups. These findings reinforce inferences of fish extinction linked to the K-Pg and the rapid establishment of compositionally modern communities, marked by the first occurrences of new lineages no later than ~4 million years (Myr) after the event. Comparisons across sites indicate that percomorphs appear more common at lower paleolatitudes in the Paleocene, expanding into higher paleolatitudes by the Eocene.
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Science Advances 12: eaec8978
DOI: 10.1126/sciadv.aec8978
https://www.science.org/doi/10.1126/sciadv.aec8978
Free pdf:
https://www.science.org/doi/epdf/10.1126/sciadv.aec8978
The Cretaceous-Paleogene (K-Pg) extinction reshaped Earth’s biodiversity, yet its impact on marine fishes remains debated due to gaps in the Paleocene record. Here, we report a paleotropical assemblage from the early Paleocene (Danian) of Egypt that provides a window into this transition. The Qreiya 3 Lagerstätte [62.2 million years ago (Ma)] reveals an offshore marine ecosystem with at least 21 actinopterygian taxa across nine orders, exceeding the diversity of all other Danian skeletal assemblages combined. Most fishes are percomorphs and include the oldest skeleton-based records for at least six ecologically divergent extant groups. These findings reinforce inferences of fish extinction linked to the K-Pg and the rapid establishment of compositionally modern communities, marked by the first occurrences of new lineages no later than ~4 million years (Myr) after the event. Comparisons across sites indicate that percomorphs appear more common at lower paleolatitudes in the Paleocene, expanding into higher paleolatitudes by the Eocene.
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Franklin Duffy, Karen Chin, Steve Cumbaa & Laura Wilson (2026)
Coprolite evidence for marine vertebrate migration in the warm Cretaceous Arctic
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2026.2670771
https://www.tandfonline.com/doi/full/10.1080/08912963.2026.2670771
Vertebrate migrations significantly impact the ecosystems they traverse, yet evidence for migration in the fossil record is difficult to identify. Here we infer the occurrence of seasonally driven marine migration in two exposures of the Upper Cretaceous Kanguk Formation on Devon Island, Nunavut, Canada. Four lines of evidence support the occurrence of migration at these sites: 1) the paleolatitude of Devon Island above the Arctic Circle indicates seasonal extremes in photoperiod, and abundant fossil diatoms in both sediments and coprolites reflect phytoplankton blooms that provided seasonally abundant food sources; 2) the greater abundance of coprolites relative to skeletal fossils suggests temporary vertebrate visitation; 3) coprolite contents and the internal tube-shaped structures we interpret as lumens suggest that at least 45 of the Devon Island coprolites can be attributed to sturgeons, a highly conserved clade with extant members that are predominantly migratory; and 4) paleobiogeographical occurrences of sturgeons and other Cretaceous Devon Island taxa in North America support migratory behaviour. Our analyses suggest sturgeons were migratory visitors that exploited rich food resources supported by seasonal planktonic blooms. This Cretaceous fossil assemblage thus offers rare coprolite evidence that supports the occurrence of migration in the Arctic that likely impacted resource cycling within the Western Interior Seaway.
Coprolite evidence for marine vertebrate migration in the warm Cretaceous Arctic
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2026.2670771
https://www.tandfonline.com/doi/full/10.1080/08912963.2026.2670771
Vertebrate migrations significantly impact the ecosystems they traverse, yet evidence for migration in the fossil record is difficult to identify. Here we infer the occurrence of seasonally driven marine migration in two exposures of the Upper Cretaceous Kanguk Formation on Devon Island, Nunavut, Canada. Four lines of evidence support the occurrence of migration at these sites: 1) the paleolatitude of Devon Island above the Arctic Circle indicates seasonal extremes in photoperiod, and abundant fossil diatoms in both sediments and coprolites reflect phytoplankton blooms that provided seasonally abundant food sources; 2) the greater abundance of coprolites relative to skeletal fossils suggests temporary vertebrate visitation; 3) coprolite contents and the internal tube-shaped structures we interpret as lumens suggest that at least 45 of the Devon Island coprolites can be attributed to sturgeons, a highly conserved clade with extant members that are predominantly migratory; and 4) paleobiogeographical occurrences of sturgeons and other Cretaceous Devon Island taxa in North America support migratory behaviour. Our analyses suggest sturgeons were migratory visitors that exploited rich food resources supported by seasonal planktonic blooms. This Cretaceous fossil assemblage thus offers rare coprolite evidence that supports the occurrence of migration in the Arctic that likely impacted resource cycling within the Western Interior Seaway.
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