Article

Carpus in Mesozoic anurans: The Early Cretaceous anuran Genibatrachus from northeastern China

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Abstract

The carpus (wrist) of fossil frogs is rarely preserved, because it consists of tiny skeletal elements that ossify only during the postmetamorphic life stage. The structure of the carpus is comparatively well-known in the temnospondyl ancestors of the Anura, but its changes during the transition to their anuran descendents are unknown due to the absence of transitional, presumably paedomorphic forms. The Early Cretaceous Genibatrachus from northeastern China is among the best-documented Mesozoic anurans, both regarding the number of preserved individuals and the representation of developmental stages. The latter aspect is especially important, because in its early developmental history, the anuran carpus is represented by cartilaginous nodules which may be the subject of various, often multiple fusions. Only later do the nodules or the fused elements ossify, enabling them to be preserved in fossils. This is why the carpus of adult fossil frogs is simpler than the foregoing larval period of cartilaginous carpus, not recordable in fossils. Nevertheless, the early development of the carpus may be reconstructed from the morphological details of its ultimate constituents. In this way, Genibatrachus may fill the gap in the evolutionary sequence of the carpus between Paleozoic temnospondyl amphibians and modern frogs.

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... Late skeletogenesis of the mesopodium, however, has received scant attention in anamniote tetrapods, because the carpus and tarsus are typically the last limb structures to ossify or remain cartilaginous throughout life, such as that in neotenic salamander families/ clades (Amphiumidae, Pancryptobrancha, Proteidae, and Sirenidae) (17,26,(28)(29)(30)(35)(36)(37). Specimens in a handful of tetrapod taxa (see Discussion) reveal preaxial dominance in the ossification of distal tarsals of the Early Permian temnospondyl Gerobatrachus hottoni (35) and postaxial dominance in the mesopodium of amniotes (28), anurans (26,37), and "lepospondyls" (29). ...
... Late skeletogenesis of the mesopodium, however, has received scant attention in anamniote tetrapods, because the carpus and tarsus are typically the last limb structures to ossify or remain cartilaginous throughout life, such as that in neotenic salamander families/ clades (Amphiumidae, Pancryptobrancha, Proteidae, and Sirenidae) (17,26,(28)(29)(30)(35)(36)(37). Specimens in a handful of tetrapod taxa (see Discussion) reveal preaxial dominance in the ossification of distal tarsals of the Early Permian temnospondyl Gerobatrachus hottoni (35) and postaxial dominance in the mesopodium of amniotes (28), anurans (26,37), and "lepospondyls" (29). ...
... An even more primitive stem tetrapod, Whatcheeria deltae, was recently shown to have ossified distal tarsals 1, 4, and 5, with distal tarsal 4 being the largest in the digital arch (68). Such a size difference in the digital arch of Whatcheeria likely indicates the existence of postaxial dominance, because the distal carpal/tarsal 4 is typically the first to ossify in amniotes and anurans and remains larger than other distal carpals/tarsals during development (28,37). The preaxial dominance is present in the fin development of the Australian lungfish Neoceratodus, in which the preaxial fin radials form earlier than postaxial fin radials following a corresponding anterior-toposterior shift in expression patterns of Hoxd13 (11). ...
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... The frogs, referred to a single species Genibatrachus baoshanensis (Gao and Chen, 2017) are abundant and represent individuals from late metamorphosed youngs to large and fully grown adults (Fig. 3a, f). This provides a unique opportunity in the world to study the ontogeny of a fossil frog from the Early Cretaceous in detail, such as the ossification sequence of the carpals in Genibatrachus (Roček et al., 2022). Many specimens of the salamander Nouminerpeton aquailonaris (Fig. 3c) were recovered together with frogs but much fewer in number than the frogs. ...
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B. 2007. A review of Neusibatrachus wilferti, an Early Cretaceous frog from the Montsec Range, northeastern Spain. Acta Palaeontologica Polonica 52 (3): 477–487. Neusibatrachus wilferti is an anuran from the late Berriasian–early Valanginian fossiliferous lacustrine limestones that are exposed in the eastern part of the Montsec Range, province of Lleida, Spain. It was originally described by Seiffert in 1972 and its phylogenetic position has since been discussed. Neusibatrachus has been considered an undeterminable fos− sil, an abnormal individual, or a primitive palaeobatrachid. Here we redescribe the only available specimen, and clarify features, such as absence of palatines, nine presacrals, and procoelous vertebral centra, that have been the subject of previ− ous debates. We consider the specimen to be a postmetamorphic individual and make developmental interpretations of some of its characters. In particular, we provide evidence of a living anuran (Rana iberica) that resembles Neusibatrachus in the development of intervertebral articulations. Neusibatrachus is considered a valid genus, which differs from other anurans, except for the pipoids, in the joint presence of an azygous frontoparietal and a parasphenoid lacking the subotic alae, although it differs from the pipoids in having nine presacral vertebrae. Morphological evidence indicates that Neusi− batrachus is related to Xenoanura, the pipoid branch in the living Amphibia Tree of Life based on molecular data. More− over, it might be a member of the pipoid clade proper, which presently includes the Pipidae, Rhinophrynidae, and several fossil taxa, including the Palaeobatrachidae, although the evidence is not conclusive.
Article
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A new temnospondyl amphibian Balanerpeton woodi gen. et sp. nov. is represented by over 30 complete or partial skeletons from the Viséan limestones, shales and tuffs in East Kirkton Quarry, Bathgate, near Edinburgh, Scotland. It is the commonest tetrapod represented in the East Kirkton assemblage and grew to about half a metre in length. Although superficially like the later Dendrerpeton , it is more advanced in possessing small premaxillaries each bearing a pronounced alary process, large external nares, large rounded interpterygoid vacuities, broadly bordered by the vomers anteriorly, a narrow vomer-pterygoid suture and a rod-like stapes. It is characterised by an unusual dental configuration in which each dentary bears a smaller number of larger teeth than the corresponding upper jaw ramus. A second probable temnospondyl is represented by two straight ribs of a much larger form. The relationships of basal temnospondyls and other amphibian groups are discussed and it is proposed that the sister-group of the temnospondyls is the Microsauria and that neither colosteids nor Caerorhachis can be considered to be temnospondyls, as both fall outside the temnospondyl-microsaur clade. A preliminary study of character distribution across a selection of primitive temnospondyls, including Balanerpeton , suggests that it is more advanced than the long-snouted Edopoidea and the Dendrerpetontidae despite its Viséan age. This implies that by the Viséan, significant diversification of temnospondyls had taken place.
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The unity and diversity of developmental processes in the vertebrate limb have singular importance in the interpretation of evolutionary hypotheses of tetrapod diversification. In anurans, the intraordinal diversity of forelimbs seems to be related to the fusion of distal carpals, whereas proximal carpals are invariable. However, there are different ontogenetic pathways involved in the differentiation of proximal carpals. This study presents a comparative analysis of early developmental features in one archeobatrachian and 23 neobatrachian species representing five families and explores the variability in the differentiation of carpal cartilages. We found new evidence supporting the presence of an embryonic intermedium that incorporates with the ulnare. Difference between the pipid Xenopus and the neobatrachians is interpreted as a change in the rate of differentiation of Distal Carpal 5 that does not affect the developmental pattern of digits. The developmental variability exhibited by the intermedium, radiale, and Element Y is combined in patterns that converge on the same adult carpal morphology among neobatrachians; these patterns appear to contain potentially useful phylogenetic information.
The early fossil record of frogs: a review of the evidence
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Die Entwicklung des Skelettes der vorderen Extremität der Anuren Amphibien
  • Schmalhausen
Branchiosaurs: Larvae, metamorphosis and heterochrony in temnospondyls and seymouriamorphs
  • J A Boy
  • H.-D Sues
Untersuchungen zur vergleichenden Anatomie der Wirbelthiere. Erstes Heft: Carpus und Tarsus
  • C Gegenbaur
The carpus of Eryops and the structure of the primitive chiropterygium
  • Gregory
The components of the carpus in Palaeobatrachus and their development in two related recent species
  • Jarošová
Recherches sur l’ostéologie et la myologie des batraciens a leurs différens âges
  • A Dugès
Zur Morphologie des Hand- und Fussskeletts
  • Emery
Branchiosaurs: Larvae, metamorphosis and heterochrony in temnospondyls and seymouriamorphs (Chapter 9)
  • Boy