Evidence for an amphibian sixth digit

Hayashi, S.; Kobayashi, Takuya; Yano, Tohru; Kamiyama, Namiko; Egawa, Shiro; Seki, Ryohei; Takizawa, Kazuyasu; Okabe, Masataka; Yokoyama, Hitoshi; Tamura, Koji

doi:10.1186/s40851-015-0019-y

Cited by 25 publications

(21 citation statements)

References 56 publications

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“…In its first two years, comparative morphology and embryology in evolutionary developmental contexts have been major themes of interest (ex. Hirasawa and Kuratani, 2015;Hojo et al, 2015;Tada and Kuratani, 2015;Hayashi et al, 2015;Nakano, 2015;Onai et al, 2015a, b;Oisi et al, 2015;Shigeno et al, 2015;Kaji et al, 2016;Takeuchi et al, 2016;Suzuki et al, 2016;Hirasawa et al, 2016), a clear trend dating to the launch year, as we reported in a previous review (Fukatsu and Kuratani, 2014). Nonetheless, ZL is open to all areas of basic zoology, and many of the top cited and most frequently accessed papers have been from fields other than evo-devo (Holland, 2015;Kishida et al, 2015;Inoue et al, 2015;Mizunami et al, 2015;Hosokawa et al, 2015;Moriyama and Numata, 2015).…”

Section: Introductionmentioning

confidence: 50%

Launch of Zoological Letters

Fukatsu

Kuratani²

2016

Zoological Science

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Section: Introductionmentioning

confidence: 50%

Launch of Zoological Letters

Fukatsu

Kuratani²

2016

Zoological Science

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“…Thus, the most accepted perspective is that the prepollex in these mammal taxa would be the radial sesamoid (for an alternative interpretation of the identity of a predigit in anurans see Hayasi et al. ). A closer look at the anatomy of this structure in Ctenomys allows us to stress that this sesamoid underwent a radical change on its morphology in this genus.…”

Section: Discussionmentioning

confidence: 99%

“…Schmitt et al (2009) mentioned recently a similarly enlarged prepollex and prehallux in the giant mole-rat, Fukomys mechowii, and interpreted them also as an adaptation for its digging lifestyle. Thus, the most accepted perspective is that the prepollex in these mammal taxa would be the radial sesamoid (for an alternative interpretation of the identity of a predigit in anurans see Hayasi et al 2015). A closer look at the anatomy of this structure in Ctenomys allows us to stress that this sesamoid underwent a radical change on its morphology in this genus.…”

Section: Discussionmentioning

confidence: 99%

Functional morphology and identity of the thenar pad in the subterranean genus Ctenomys (Rodentia, Caviomorpha)

et al. 2019

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As in many other fossorial tetrapods, the most obvious adaptations to scratch‐digging in the subterranean tuco‐tuco (Rodentia, Ctenomyidae, Ctenomys) are found in the hands, which among other adaptations, present the mesaxonic condition; i.e. the central digits are more developed, and also their claws, which are curved and elongated. The thumb is atrophied and aligned with the rest of the digits, showing a small and flat claw. This configuration of digits and claws seems to be in accordance with what it is expected for rodents: rudimentary movements when handling food items. However, on the palmar side of the hand, tuco‐tucos have several pads, the thenar (located under the thumb) being the most developed. In this study, we investigated the functional morphology of the thenar pad through different approaches: musculoskeletal anatomy, histology and functionality. The analysis of radiographs and clarified and double‐stained hand samples of Ctenomys talarum and C. australis showed that the thenar pad is supported by a paddle‐shaped bone that articulates with a protrusion in the scapholunate bone. This bone, flat and long, continues in a flat cartilaginous structure, with a shape similar to a claw. Dissections showed that the thenar pad has several associated muscles: the m. palmaris longus, the m. abductor pollicis longus, and a massive muscular complex located between the thumb and the thenar pad. By topology it might be inferred that this complex is formed by the m. abductor pollicis brevis, the m. flexor pollicis brevis and the m. adductor pollicis brevis. Longitudinal histological sections of the thenar pad stained with hematoxylin‐eosin showed a thick layer of keratin at the distal end, external face. The observation of live specimens of C. talarum foraging on two food items of different size and filmed at 300 fps showed that the thenar pad acts as an opposable thumb, with digit‐like movements. Tuco‐tucos are able to perform more precise movements than expected, and to grasp and manipulate the food with one hand. In previous studies, it was suggested that the thenar pad was supported by a ‘palmar ossicle’, or ‘prepollex’ (= radial sesamoid bone). Our results suggest that this sesamoid underwent a radical change on its morphology, making the thenar pad a part of the food handling system in Ctenomys, so the thenar pad might be considered a ‘false thumb’, rather than a palmar pad. It is suggested to advance on the description and functional analysis of the thenar pad, redefining the structure, since the terms used so far to define it would not be accurate.

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“…See Hayashi et al [11] for details of EVG + AB staining. We made some modifications for staining: coloring times for Weigert’s hematoxylin solution, alcian blue solution and van Gieson’s solution were for 3 min, 10 min and 3 min, respectively, in this study.…”

Section: Methodsmentioning

confidence: 99%

Flight feather development: its early specialization during embryogenesis

et al. 2018

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BackgroundFlight feathers, a type of feather that is unique to extant/extinct birds and some non-avian dinosaurs, are the most evolutionally advanced type of feather. In general, feather types are formed in the second or later generation of feathers at the first and following molting, and the first molting begins at around two weeks post hatching in chicken. However, it has been stated in some previous reports that the first molting from the natal down feathers to the flight feathers is much earlier than that for other feather types, suggesting that flight feather formation starts as an embryonic event. The aim of this study was to determine the inception of flight feather morphogenesis and to identify embryological processes specific to flight feathers in contrast to those of down feathers.ResultsWe found that the second generation of feather that shows a flight feather-type arrangement has already started developing by chick embryonic day 18, deep in the skin of the flight feather-forming region. This was confirmed by shh gene expression that shows barb pattern, and the expression pattern revealed that the second generation of feather development in the flight feather-forming region seems to start by embryonic day 14. The first stage at which we detected a specific morphology of the feather bud in the flight feather-forming region was embryonic day 11, when internal invagination of the feather bud starts, while the external morphology of the feather bud is radial down-type.ConclusionThe morphogenesis for the flight feather, the most advanced type of feather, has been drastically modified from the beginning of feather morphogenesis, suggesting that early modification of the embryonic morphogenetic process may have played a crucial role in the morphological evolution of this key innovation. Co-optation of molecular cues for axial morphogenesis in limb skeletal development may be able to modify morphogenesis of the feather bud, giving rise to flight feather-specific morphogenesis of traits.

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Evidence for an amphibian sixth digit

Cited by 25 publications

References 56 publications

Launch of Zoological Letters

Launch of Zoological Letters

Functional morphology and identity of the thenar pad in the subterranean genus Ctenomys (Rodentia, Caviomorpha)

Flight feather development: its early specialization during embryogenesis

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