Sauropsid columella (=stapes) variation + formation of feather follicles (free pdf)
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Ben Creisler
May 5, 2026, 5:53:19 PM (11 days ago) May 5
to DinosaurMa...@googlegroups.com
Ben Creisler
Recent papers:
Free pdf:
John Peacock, Serjoscha W. Evers, Tiago R. Simões, Garth M. Spellman & Daniel J. Field (2026)
Clade-wide morphological and functional variation of the sauropsid columella
The Anatomical Record (advance online publication)
https://doi.org/10.1002/ar.70215
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70215
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.70215
The columella (=stapes) is the middle ear bone of reptiles that transmits vibrations from the environment to the inner ear. It has been shown to exhibit extensive interspecific morphological disparity in several clades; however, its morphological variation and associated functional consequences remain poorly described. Using published micro-computed tomography data of turtle, lepidosaur, crocodilian, and bird columellae, as well as images of non-avian dinosaur columellae, we provide qualitative and quantitative descriptions, and explore how phylogeny and function influence columellar morphology between and within sauropsid clades. Scaling relationships illustrate that birds have proportionally smaller columellae than other sauropsids, which may facilitate higher-frequency hearing. Columellar length scales proportionally with head width in both birds and turtles, whereas in lepidosaurs it increases disproportionately with head size. The sizes of other columellar features show varying degrees of negative allometry when compared to columellar length. Birds show high morphological lability in distal end and shaft shape but are conservative in footplate morphology, whereas lepidosaurs and turtles show more variability in footplate size and shape but more conservative shafts and distal structures. Snakes display multiple differences from non-ophidian squamates including longer columellae and similar relative footplate sizes to turtles and birds. Ecological signal appears evident in the footplate of the sea snake, Aipysurus laevis, which may have convergently evolved a mosasaur-like condition, as well as a derived columellar morphology in fossorial snakes that may be convergent in multiple lineages. Our findings show that columellar disparity reflects ecological, functional, and phylogenetic factors, and provide a framework for further investigations into the evolution of the sauropsid ear.
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John Peacock, Serjoscha W. Evers, Tiago R. Simões, Garth M. Spellman & Daniel J. Field (2026)
Clade-wide morphological and functional variation of the sauropsid columella
The Anatomical Record (advance online publication)
https://doi.org/10.1002/ar.70215
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70215
Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.70215
The columella (=stapes) is the middle ear bone of reptiles that transmits vibrations from the environment to the inner ear. It has been shown to exhibit extensive interspecific morphological disparity in several clades; however, its morphological variation and associated functional consequences remain poorly described. Using published micro-computed tomography data of turtle, lepidosaur, crocodilian, and bird columellae, as well as images of non-avian dinosaur columellae, we provide qualitative and quantitative descriptions, and explore how phylogeny and function influence columellar morphology between and within sauropsid clades. Scaling relationships illustrate that birds have proportionally smaller columellae than other sauropsids, which may facilitate higher-frequency hearing. Columellar length scales proportionally with head width in both birds and turtles, whereas in lepidosaurs it increases disproportionately with head size. The sizes of other columellar features show varying degrees of negative allometry when compared to columellar length. Birds show high morphological lability in distal end and shaft shape but are conservative in footplate morphology, whereas lepidosaurs and turtles show more variability in footplate size and shape but more conservative shafts and distal structures. Snakes display multiple differences from non-ophidian squamates including longer columellae and similar relative footplate sizes to turtles and birds. Ecological signal appears evident in the footplate of the sea snake, Aipysurus laevis, which may have convergently evolved a mosasaur-like condition, as well as a derived columellar morphology in fossorial snakes that may be convergent in multiple lineages. Our findings show that columellar disparity reflects ecological, functional, and phylogenetic factors, and provide a framework for further investigations into the evolution of the sauropsid ear.
=====
Free pdf:
Hans I-Chen Harn, Ting-Xin Jiang, Chih-Han Huang, Wen-Tau Juan, Tzu-Yu Liu, Tsao-Chi Chuang, Wan-Chi Liao, Yingxiao Wang, Ji Li, Cornelis J Weijer, Ping Wu, Chin-Lin Guo & Cheng-Ming Chuong (2026)
Novel tissue mechanics-guided cellular flows drive the formation of feather follicles
The EMBO Journal (advance online publication)
doi: https://doi.org/10.1038/s44318-026-00771-7
https://link.springer.com/article/10.1038/s44318-026-00771-7
Complex tissue architecture is achieved through multiple rounds of morphological transitions. Here, we analyzed cellular flows and tissue mechanics during avian skin development by employing chicken and transgenic quail skin explant models. We demonstrate how novel cellular flows initiate chemo-mechanical circuits that guide epithelial protrusion, folding, invagination, and spatial cell fate specification. During initial feather bud formation, stiff dermal condensates protrude vertically from the locally softened epithelial sheet. As the bud elongates, it stretches the epithelial cells at the base, thus mechanically activating YAP, which causes the epithelial sheet to fold downward and form a stiff cylindrical wall that invaginates into the skin. This stiff epithelial tongue is essential for the compaction and formation of the tightly packed dermal papillae. These topological transformational events are mechanically interconnected, and the completion of one circuit initiates the next. In contrast, during scale development, the rigid epithelial sheet restricts dermal cell flows, preventing further topological transformation. Based on these findings, we developed a topological transformation model describing how this process enabled the evolution of feather follicles from scales.
Synopsis
Mechanical and biochemical signalling events are involved in shaping developing skin appendages, such as scales and feathers. This study reveals how tissue mechanics-guided cellular flows between dermis and epidermis induce signalling events mediating feather follicle development and evolution from scales.
Dermal condensates stiffen and protrude through locally softened epidermis to initiate bud formation during early morphogenesis.
Mechano-transduction during bud elongation activates YAP and MMPs, leading formation of the cylindrical follicle wall that compartmentalizes dermal cell fates.
Mechanical sealing of the follicle base is mediated by coordinated epidermal invagination and TGF-β dependent activation and compaction of SMA⁺ dermal cells.
Biomechanical properties regulate scale-to-feather conversion, with epidermal softening enabling cellular flows required for feather follicle formation.
===
Hans I-Chen Harn, Ting-Xin Jiang, Chih-Han Huang, Wen-Tau Juan, Tzu-Yu Liu, Tsao-Chi Chuang, Wan-Chi Liao, Yingxiao Wang, Ji Li, Cornelis J Weijer, Ping Wu, Chin-Lin Guo & Cheng-Ming Chuong (2026)
Novel tissue mechanics-guided cellular flows drive the formation of feather follicles
The EMBO Journal (advance online publication)
doi: https://doi.org/10.1038/s44318-026-00771-7
https://link.springer.com/article/10.1038/s44318-026-00771-7
Complex tissue architecture is achieved through multiple rounds of morphological transitions. Here, we analyzed cellular flows and tissue mechanics during avian skin development by employing chicken and transgenic quail skin explant models. We demonstrate how novel cellular flows initiate chemo-mechanical circuits that guide epithelial protrusion, folding, invagination, and spatial cell fate specification. During initial feather bud formation, stiff dermal condensates protrude vertically from the locally softened epithelial sheet. As the bud elongates, it stretches the epithelial cells at the base, thus mechanically activating YAP, which causes the epithelial sheet to fold downward and form a stiff cylindrical wall that invaginates into the skin. This stiff epithelial tongue is essential for the compaction and formation of the tightly packed dermal papillae. These topological transformational events are mechanically interconnected, and the completion of one circuit initiates the next. In contrast, during scale development, the rigid epithelial sheet restricts dermal cell flows, preventing further topological transformation. Based on these findings, we developed a topological transformation model describing how this process enabled the evolution of feather follicles from scales.
Synopsis
Mechanical and biochemical signalling events are involved in shaping developing skin appendages, such as scales and feathers. This study reveals how tissue mechanics-guided cellular flows between dermis and epidermis induce signalling events mediating feather follicle development and evolution from scales.
Dermal condensates stiffen and protrude through locally softened epidermis to initiate bud formation during early morphogenesis.
Mechano-transduction during bud elongation activates YAP and MMPs, leading formation of the cylindrical follicle wall that compartmentalizes dermal cell fates.
Mechanical sealing of the follicle base is mediated by coordinated epidermal invagination and TGF-β dependent activation and compaction of SMA⁺ dermal cells.
Biomechanical properties regulate scale-to-feather conversion, with epidermal softening enabling cellular flows required for feather follicle formation.
===
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