Fossil Frogs Research Articles

A new fossil frog (Lissamphibia: Anura) from the Late Cretaceous of Brazil and the early evolution of neobatrachians

Abstract Although neobatrachians represent about 95% of anuran diversity, their fossil record, especially during the Mesozoic, remains scarce and often limited to a few damaged specimens with uncertain affinities. In South America, fossil neobatrachians have been identified from the Cretaceous deposits in Chile, Argentina, and Brazil. Here, we describe a new species of fossil neobatrachian from the Late Cretaceous (Campanian) Bauru Basin, south-eastern Brazil, based on several well-preserved specimens. The morphology of the new species was described in detail using high-resolution micro-CT, and its taxonomic affinities were investigated through a phylogenetic analysis encompassing both living and extinct taxa. The new taxon was recovered among hyloids, more specifically as closely related to other well-ossified taxa. However, due to the lack of any synapomorphies with extant families, we were unable to assign the new species to a more specific group within Neobatrachia. The discovery of a new fossil frog in the Late Cretaceous Bauru Basin significantly enhances our understanding of neobatrachian early morphology during the Late Cretaceous of South America.

Frog limbs in deep time: is jumping locomotion at the roots of the anuran Bauplan?

AbstractThe unique body plan of frogs (Lissamphibia: Anura) has been largely conserved from at least 200 Myr, and its evolution from a more generalized tetrapod condition is still poorly understood, in part due to the scarce early fossil record of Salientia, the anuran total-group. The origin of the anuran Bauplan has been classically explained as an adaptation to jumping, but recent studies incorporating new data in a phylogenetic context have challenged the popular jumping hypothesis. Here we revisit and test this hypothesis from a paleobiological perspective by integrating limb data from a wide range of extant and fossil frogs. We first explored the evolution of limb proportions from the Jurassic to the Paleogene to understand when the present limb diversity originated and whether, and to what extent, limb proportions have been conserved over the last 200 Myr. We then inferred the locomotor capabilities of extinct species by phylogenetic flexible discriminant analysis, and from these inferences, we studied the locomotor diversity of frogs over geological time and reconstructed the ancestral state for frog-like salientians. The evolution of limb proportions is characterized by an early diversification that was underway in the Jurassic, followed by a repeated convergence over a limited area of the morphospace that was already explored by the Early Cretaceous. In agreement with this early limb diversity, the Jurassic stem species were also locomotory diverse, and their inferred locomotor modes do not support the jumping hypothesis. We propose that the patterns found herein of repeated convergent evolution of both limb proportions and locomotor capabilities over geological time hamper any attempt to confidently infer the ancestral locomotion mode and, it therefore might be time to start focusing on other hypotheses on the origin of the anuran Bauplan that are not related to locomotion.

A new fossil frog crab (Brachyura, Lyreididae) from the Eocene of northeastern Pacific

A new fossil frog crab (Brachyura, Lyreididae) from the Eocene of northeastern Pacific

First fossil evidence for a new frog from the Early Cretaceous of the Jiuquan Basin, Gansu Province, north-western China

Based on a well-preserved incomplete skeleton, a new frog, Gansubatrachus qilianensis gen. et sp. nov., is described from the Lower Cretaceous Zhonggou Formation of Jiuquan Basin, Gansu Province, north-western China. This species differs from other frogs in a unique combination of characteristics, such as a robust and non-bifurcated alary process on the premaxilla, a ‘V’-shaped parahyoid, a paired sphenethmoid, eight presacral vertebrae, three pairs of free ribs, and unexpanded sacral diapophyses. Phylogenetic analysis based on parsimony suggests that Gansubatrachus is a basal Lalagobatrachia. This discovery of a new frog fossil from the Early Cretaceous of north-west China expands the diversity of fossil frogs in East Asia and provides new material for further studies on the distribution and evolutionary history of Cretaceous Asian anurans. http://zoobank.org/urn:lsid:zoobank.org:pub:A80B417A-F9C6-4704-B473-FBBA6CDC8C2B

Fossil frogs from the upper Miocene of southwestern Brazilian Amazonia (Solimões Formation, Acre Basin).

ABSTRACT Much of what we know about late Miocene vertebrates from the Brazilian Amazonia is based on the fossil record from several sites in the Solimões Formation. The Talismã site, one of the most important for vertebrate fossils in the formation, has produced an abundant and diverse fauna dominated by crocodylians, mammals, and turtles, but small vertebrates are still underrepresented. We report some isolated bones recovered from this site, providing the first Neogene records of anurans in Brazil. Two taxa are recognized, a distinct species of Pipa, and an unidentified species of the Rhinella clade, both of which are members of the extant Amazonian batrachofauna. These new fossils expand our knowledge of the late Miocene anuran assemblages from the region and contribute to the paleoenvironmental reconstruction of the site.

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

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.

Fossil frogs from the early Campanian of West Texas, USA, with comments on Late Cretaceous anuran diversity in southern Laramidia

A rare early Campanian (Aquilan) assemblage consisting of disarticulated anuran bones is described from the Aguja Formation of West Texas, USA. Many specimens within the assemblage pertain to taxonomically informative elements (maxillae, urostyles, and ilia). Morphological variety among specimens pertaining to each suggests high local species richness comparable with that seen elsewhere among frogs from similarly well-sampled localities of the Late Cretaceous Western Interior. Comparison between environmentally and temporally analogous microvertebrate assemblages in southern Utah, USA, reveals that anurans in both areas exhibit morphological similarities consistent with regionally allied ‘southern’ faunas. Among their differences, one character (dorsal protuberance of the ilium) consistently exhibited among some ilial morphotypes from Utah is conspicuously absent among those of West Texas. Two ostensibly exclusive ilial morphs in West Texas add additional support to the presence of taxonomically segregated, sub-regional populations of anurans in southern Laramidia during early to middle Campanian time.

A new genus of fossil frog (Anura) from lower Cretaceous deposits in South America.

The frog clade Neobatrachia or "advanced frogs" represents more than 95% of the diversity within Anura. The neobatrachian fossil record is incomplete due to the small size and fragile nature of their bones but provides some clues on the time and rate of the current diversification of modern-day amphibians. The Crato Formation (Aptian) of northeastern Brazil is known for the presence of, at least, five species of neobatrachian fossils. Herein, we describe a well-preserved fossil that represents a new neobatrachian taxon from the Crato Formation (Cretaceous) in the Araripe Basin, northeastern Brazil, and perform phylogenetic analysis to assess its higher-level relationships. The new specimen is an almost complete and articulated skeleton with soft tissue preservation. Phylogenetic analysis recovered the specimen nested in the clade Hyloidea and our results highlight the remarkable value of the Crato Formation as a Laggerstätte.

A new fossil frog crab (Brachyura, Raninoidea) from the Paleogene of northeastern Pacific

One new genus and two new species of fossil frog crabs from the Eocene to Oligocene deposits of Washington State (USA) and Vancouver Island (British Columbia, Canada) of the north-eastern Pacific are described, based upon several well- preserved specimens. The studied specimens are herein described as Amphoranina blandi n. gen., n. sp. and A. multispinata n. gen, n. sp. (Raninidae De Haan, 1839) respectively. Amphoranina n. gen. appears to be endemic to the middle to upper Paleogene of the northeastern Pacific.

The earliest record of Caribbean frogs: a fossil coquí from Puerto Rico.

The nearly 200 species of direct-developing frogs in the genus Eleutherodactylus (the Caribbean landfrogs, which include the coquís) comprise an important lineage for understanding the evolution and historical biogeography of the Caribbean. Time-calibrated molecular phylogenies provide indirect evidence for the processes that shaped the modern anuran fauna, but there is little direct evidence from the fossil record of Caribbean frogs about their distributions in the past. We report a distal humerus of a frog from the Oligocene (approx. 29 Ma) of Puerto Rico that represents the earliest known fossil frog from any Caribbean island. Based on its prominent rounded distal humeral head, distally projecting entepicondyle, and reduced ectepicondyle, we refer it to the genus Eleutherodactylus. This fossil provides additional support for an early arrival of some groups of terrestrial vertebrates to the Greater Antilles and corroborates previous estimates based on molecular phylogenies suggesting that this diverse Caribbean lineage was present in the islands by the mid-Cenozoic.

Index to Titles and Authors/Editors of Books Reviewed

Index to Titles and Authors/Editors of Books Reviewed

Fossil Frogs and Toads of North America. Life of the Past. By J. Alan Holman. Bloomington (Indiana): University of Indiana Press. $30.00 (paper). xv + 246 p. + 48 pl.; ill.; general, taxonomic, and site indexes. ISBN: 978-0-253-03174-7. [This book was originally published in 2003. This is the first paperback edition.] 2018.

<i>Fossil Frogs and Toads of North America. <i>Life of the Past</i></i>. By J. Alan Holman. Bloomington (Indiana): University of Indiana Press. $30.00 (paper). xv + 246 p. + 48 pl.; ill.; general, taxonomic, and site indexes. ISBN: 978-0-253-03174-7. [This book was originally published in 2003. This is the first paperback edition.] 2018.

Inter-amphibian predation in the Early Cretaceous of China

For most fossil taxa, dietary inference relies primarily on indirect evidence from jaw morphology and the dentition. In rare cases, however, preserved gut contents provide direct evidence of feeding strategy and species interaction. This is important in the reconstruction of food webs and energy flow through ancient ecosystems. The Early Cretaceous Chinese Jehol Biota has yielded several such examples, with lizards, birds, small dinosaurs, and mammals as both predator and prey. Here we describe an Early Cretaceous fossil frog specimen, genus Genibatrachus, that contains an adult salamander within its body cavity. The salamander is attributed to the hynobiid-like genus Nuominerpeton. The salamander skeleton is complete and articulated, suggesting it was caught and swallowed shortly before the frog itself died and was buried.

Non-integumentary melanosomes can bias reconstructions of the colours of fossil vertebrates

The soft tissues of many fossil vertebrates preserve evidence of melanosomes—micron-scale organelles that inform on integumentary coloration and communication strategies. In extant vertebrates, however, melanosomes also occur in internal tissues. Hence, fossil melanosomes may not derive solely from the integument and its appendages. Here, by analyzing extant and fossil frogs, we show that non-integumentary melanosomes have high fossilization potential, vastly outnumber those from the skin, and potentially dominate the melanosome films preserved in some fossil vertebrates. Our decay experiments show that non-integumentary melanosomes usually remain in situ provided that carcasses are undisturbed. Micron-scale study of fossils, however, demonstrates that non-integumentary melanosomes can redistribute through parts of the body if carcasses are disturbed by currents. Collectively, these data indicate that fossil melanosomes do not always relate to integumentary coloration. Integumentary and non-integumentary melanosomes can be discriminated using melanosome geometry and distribution. This is essential to accurate reconstructions of the integumentary colours of fossil vertebrates.

A novel kinematics analysis method using quaternion interpolation–a case study in frog jumping

Spherical Linear Interpolation (SLERP) has long been used in computer animation to interpolate movements between two 3D orientations. We developed a forward kinematics (FK) approach using quaternions and SLERP to predict how frogs modulate jump kinematics between start posture and takeoff. Frog limb kinematics have been studied during various activities, yet the causal link between differences in joint kinematics and locomotor variation remains unknown. We varied 1) takeoff angle from 8 to 60°; 2) turn angle from 0 to 18°; and 3) initial body pitch from 0 to 70°. Simulations were similar to experimentally observed frog kinematics. Findings suggest a fundamental mechanism whereby limb elevation is modulated by thigh and shank adduction. Forward thrust is produced by thigh and proximal foot retraction with little contribution from the shank except to induce asymmetries for turning. Kinematic shifts causing turns were subtle, marked only by slight counter-rotation of the left versus right shank as well as a 10% timing offset in proximal foot adduction. Additionally, inclining initial body tilt influenced the centre of mass trajectory to determine direction of travel at takeoff. Most importantly, our theory suggests firstly that the convergence of leg segment rotation axes toward a common orientation is crucial both for limb extension and for coordinating jump direction; and, secondly, the challenge of simulating 3D kinematics is simplified using SLERP because frog limbs approximately follow linear paths in unit quaternion space. Our methodology can be applied more broadly to study living and fossil frog taxa as well as to inspire new control algorithms for robotic limbs.

The earliest direct evidence of frogs in wet tropical forests from Cretaceous Burmese amber

Frogs are a familiar and diverse component of tropical forests around the world. Yet there is little direct evidence from the fossil record for the antiquity of this association. We describe four fossil frog specimens from mid-Cretaceous (~99 mya) amber deposits from Kachin State, Myanmar for which the associated fauna provides rich paleoenvironmental context. Microcomputed tomographic analysis provides detailed three-dimensional anatomy for these small frogs, which is generally unavailable for articulated anurans in the Mesozoic. These crown-group anuran specimens provide the earliest direct evidence for anurans in a wet tropical forest. Based on a distinct combination of skeletal characters, at least one specimen has clear similarities to living alytoid frogs as well as several Mesozoic taxa known from the Jehol Biota in China. Whereas many Mesozoic frogs are from seasonal and mesic paleoenvironments, these fossils provide the earliest direct evidence of anurans in wet tropical forests.

A new pelobatoid frog from the lower Eocene of southern China

A new frog with pelobatoid affinities is described from the lower Eocene of southern China based on 11 individuals at different developmental stages. Comparative analysis reveals that this anuran shares osteological characters with the rather diverse family Megophryidae. In particular, intervertebral discs are present between the anterior vertebral centra and the lamella alaris of the squamosal is widely separated from the maxilla, which lacks a zygomaticomaxillar process. The new frog also shares features with the genus Pelodytes and especially with its most primitive extant species, P. caucasicus. Particularly given that Pelodytidae and Megophryidae are grouped in the Pelobatoidea, and that the new fossil frog existed almost 50 Ma ago, these comparisons suggest that the new frog represents a Paleogene member of the Pelobatoidea. Phylogenetic analysis supports this conclusion, but relationships within the superfamily Pelobatoidea remain unstable across different analyses, as do the positions of fossil frogs of similar geological age in Mongolia (Prospea) and USA (Aerugoamnis). Nevertheless, this new discovery represents the first record of a Paleogene frog from China as well as the first fossil anuran from South China, filling the large gap between Chinese Cretaceous and Neogene anurans. The new frog also opens an important window on the early evolutionary history of the Pelobatoidea, which presumably originated in East Asia.

Modeling warming predicts a physiological threshold for the extinction of the living fossil frog Calyptocephalella gayi

Global climate change will have a greater impact on ectotherms in tropical and subtropical communities than at higher latitudes, because ambient temperatures are closer to the upper thermal limits of species. Amphibian species are highly dependent on external weather conditions, and the effect of global warming on these has been evaluated recently. The Great Chilean frog (Calyptocephalella gayi) is an endemic, monotypic species and genus whose conservation status is considered Vulnerable because of high extraction pressure for human consumption, lack of regulatory measures and comprehension by its consumers. Their populations have also declined due to the loss and destruction of their habitats. C. gayi has not been considered as an object of physiological study, so this large species is not known as one that can adapt to current environmental changes. In this study we analyze the thermoregulatory capacity and thermal efficiency of C. gayi to determine its potential for climatic adaptation. The results indicate that this species is strictly a thermal-conformer; its thermal efficiency and its ability to withstand high temperatures allow it to sustain itself under a climate change scenario, however, it has thermal constraints that do not allow it to withstand temperatures greater than 30°C. By modeling its ontogenetic conditions mathematically, we project that the larvae are not in danger, although there is a group of around 4% which is very close to 30°C, which is the highest temperature recorded for the species. However, about 40% of subadults and approximately 47% of adult frogs will not survive the change of ~7°C projected for the following 85 years, which will affect future generations.

Palaeoenvironmental and evolutionary implications of fossil frog assemblages from the South African west and south coasts

The oxidative depolymerizations of Shenfu subbituminous coal (SSBC) and its thermal dissolution insoluble (TDI), which obtained by thermal dissolution (TD) in 1-methylnaphthalene at 320 °C, were investigated with H2O2 aqueous solution as oxidant under different conditions. Their products were characterized by FTIR, ultimate analyses and acidic functional groups determination. Further, the detailed comparison of oxidative depolymerizations of SSBC and its TDI was carried out with 20% H2O2 at 60 °C. The water solubles (WSs) were esterified, and subsequently analyzed by GC/MS in order to understand the macromolecular structural features of SSBC. The results revealed that compared with SSBC, the TDI contained more phenolic hydroxyls and showed higher oxidation reactivity. It suggested that the phenolic hydroxyl should be the active site of oxidative depolymerization, and thermal dissolution generated substantial phenolic hydroxyls in TDI by the rupture of Cal–OAr. The WS from the oxidation of SSBC mainly consists of monocyclic aromatic acids, while the WS from TDI contains much amount of alkanoic acids and α,ω-dicarboxylic acids. Especially the substantial oxalic acid and malonic acid identified in the WS from TDI suggested that significant amount of the aromatic rings in the macromolecules of SSBC could be coupled directly or connected by monomethylene bridge.

A burrowing frog from the late Paleocene of Mongolia uncovers a deep history of spadefoot toads (Pelobatoidea) in East Asia.

Fossils are indispensible in understanding the evolutionary origins of the modern fauna. Crown-group spadefoot toads (Anura: Pelobatoidea) are the best-known fossorial frog clade to inhabit arid environments, with species utilizing a characteristic bony spade on their foot for burrowing. Endemic to the Northern Hemisphere, they are distributed across the Holarctic except East Asia. Here we report a rare fossil of a crown-group spadefoot toad from the late Paleocene of Mongolia. The phylogenetic analysis using both morphological and molecular information recovered this Asian fossil inside the modern North American pelobatoid clade Scaphiopodidae. The presence of a spade and the phylogenetic position of the new fossil frog strongly support its burrowing behavior. The late Paleocene age and other information suggestive of a mild climate cast doubt on the conventional assertion that burrowing evolved as an adaptation to aridity in spadefoot toads. Temporally and geographically, the new fossil provides the earliest record of Scaphiopodidae worldwide, and the only member of the group in Asia. Quantitative biogeographic analysis suggests that Scaphiopodidae, despite originating in North America, dispersed into East Asia via Beringia in the Early Cenozoic. The absence of spadefoot toads in East Asia today is a result of extinction.