[Paleontology • 2025] Eotephradactylus mcintireae • Unusual Bone Bed reveals A Vertebrate Community with Pterosaurs and Turtles in equatorial Pangaea before the end-Triassic Extinction

Eotephradactylus mcintireae 

 Kligman, Whatley, Ramezani1, Marsh, Lyson, Fitch, Parker & Behrensmeyer, 2025

 DOI: doi.org/10.1073/pnas.2505513122 

artwork: Brian Engh.

 

Significance: 

PFV 393 is the first radioisotopically dated (209.187 ± 0.083 Ma old) high-diversity continental vertebrate fossil assemblage to fill a 12-Ma fossil gap preceding the end-Triassic extinction. The taphonomy and depositional setting of this assemblage show that key members of post–Triassic Mesozoic vertebrate communities, including frogs, lepidosaur reptiles, pterosaurs, and turtles, coexisted with archaic lineages such as metoposaurid amphibians, trilophosaurid archosauromorphs, Vancleavea, doswelliids, phytosaurs, and aetosauriforms in the mesic fluvial environments of aridifying equatorial Pangaea approximately 7 Ma prior to the end-Triassic extinction. A member of this paleocommunity and one of the earliest few pterosaurs found outside of Europe, the newly described Eotephradactylus mcintireae gen. et sp. nov., reveals novel aspects of pterosaur mandibular evolution, ecology, and biogeography.

Abstract

Temporally constrained microvertebrate bone beds are powerful tools for understanding continent-scale biotic change. Such sites are rare globally in nonmarine settings during the 12 million years (Ma) preceding the end-Triassic extinction (ETE; ~201.5 Ma), obscuring patterns of faunal change across this interval. A vertebrate assemblage from Arizona, USA, provides unique insights into community composition and ecology prior to the ETE. PFV 393 is a macro- and microvertebrate bone bed preserved in a volcaniclastic fluvial channel-fill with a high-precision U-Pb zircon age of 209.187 ± 0.083 Ma. The fossil assemblage consists of three-dimensionally preserved, delicate, and small skeletal elements of known and new taxa that document a local paleocommunity including hybodontiformes, actinopterygians, actinistians, metoposaurids, salientians, synapsids, lepidosaurs, testudinatans, trilophosaurids, Vancleavea, doswelliids, Revueltosaurus, loricatans, phytosaurs, and pterosaurs. The new early-diverging pterosaur is one of the few Triassic pterosaurs found outside of Europe and the only one with a documented precise radioisotopic age. The testudinatan material shows the rapid dispersal of terrestrial stem-turtles across the Pangaean supercontinent in the Norian and refines temporal constraints on the origin of the turtle shell. The presence of vertebrate lineages endemic to the Triassic highlights their persistence in a mesic, fluvial paleocommunity through a prolonged phase of environmental change preceding the ETE. These lineages coexisted with frogs, lepidosaurs, turtles, and pterosaurs- all key elements of post–Triassic Mesozoic communities. The arrival of turtles and pterosaurs in west-central Pangaea therefore may have been driven by the northward drift of Laurentia from humid equatorial conditions into more arid subtropical latitudes.

life restoration of Eotephradactylus mcintireae catching a fish in the Chinle Formation environment.
An artist's reconstruction of the fossilized landscape, plants and animals found preserved in a remote bonebed in Petrified Forest National Park in Arizona. Researchers led by paleontologist Ben Kligman,, present the fossilized jawbone of a new pterosaur species and describe the sea gull-sized flying reptile along with hundreds of other fossils they unearthed from the site. These fossils, which date back to the late Triassic period around 209 million years ago, preserve a snapshot of a dynamic ecosystem where older groups of animals lived with evolutionary upstarts.
The newly described pterosaur Eotephradactylus mcintireae is seen eating an ancient ray-finned fish alongside an early species of turtle and an early frog species, with the skeleton of an armored crocodile relative lying on the ground and a palm-like plant growing in the background.

artwork: Brian Engh.

Eotephradactylus mcintireae gen. et sp. nov.

Ben T. Kligman, Robin L. Whatley, Jahandar Ramezani1, Adam D. Marsh, Tyler R. Lyson, Adam J. Fitch, William G. Parker and Anna K. Behrensmeyer. 2025. Unusual Bone Bed reveals A Vertebrate Community with Pterosaurs and Turtles in equatorial Pangaea before the end-Triassic Extinction. Proceedings of the National Academy of Sciences. 122 (29) e2505513122. DOI: doi.org/10.1073/pnas.2505513122 [July 7, 2025]

[PaleoMammalogy • 2025] Bone Microstructure supports A Mesozoic Origin for a semiaquatic burrowing lifestyle in Monotremes (Mammalia)

Kryoryctes cadburyi  Pridmore, Rich, Vickers-Rich & Gambaryan, 2005

in Hand, Wilson, López-Aguirre, Houssaye, Archer, ... et Beck, 2025. 

DOI: doi.org/10.1073/pnas.2413569122

  facebook.com/PNASNews

Artwork by Peter Schouten.

Significance

The egg-laying monotremes have played a central role in our understanding of mammalian evolution, but their fossil record is poor and their evolutionary history is controversial. Living monotremes are ecologically very distinct from each other: The platypus is well adapted for a semiaquatic lifestyle, whereas echidnas are fully terrestrial. Here, we show that an isolated mammal humerus from the Early Cretaceous of Australia, from a species called Kryoryctes cadburyi, belongs to a monotreme, and that microscopic features of this bone indicate that this monotreme was a semiaquatic burrower. This suggests that the amphibious lifestyle of the modern platypus had its origins at least 100 Mya, during the Age of Dinosaurs, and that echidnas evolved from semiaquatic ancestors.

Abstract

The platypus and four echidna species are the only living egg-laying mammals and the sole extant representatives of Order Monotremata. The platypus and echidnas are very disparate both morphologically and ecologically: The platypus is a specialized semiaquatic burrowing form that forages for freshwater invertebrates, whereas echidnas are fully terrestrial and adapted for feeding on social insects and earthworms. It has been proposed that echidnas evolved from a semiaquatic, platypus-like ancestor, but fossil evidence for such a profound evolutionary transformation has been lacking, and this hypothesis remains controversial. Here, we present original data about the Early Cretaceous (108 to 103 Ma) Australian mammal Kryoryctes cadburyi, currently only known from a single humerus, that provides key information relating to this question. Phylogenetic analysis of a 536-character morphological matrix of mammaliaforms places Kryoryctes as a stem-monotreme. Three-dimensional whole bone comparisons show that the overall shape of the humerus is more similar to that of echidnas than the platypus, but analysis of microstructure reveals specializations found in semiaquatic mammals, including a particularly thick cortex and a highly reduced medullary cavity, present in the platypus but absent in echidnas. The evidence suggests Kryoryctes was a semiaquatic burrower, indicating that monotremes first evolved an amphibious lifestyle in the Mesozoic, and providing support for the hypothesis that this is ancestral for living monotremes as a whole. The lineage leading to the modern platypus appears to have been characterized by extremely long term (>100 My) niche conservatism, with echidnas representing a much later reversion to a fully terrestrial lifestyle.

 

An artist’s impression of Kryoryctes cadburyi.

Artwork by Peter Schouten.

 

Suzanne J. Hand, Laura A. B. Wilson, Camilo López-Aguirre , Alexandra Houssaye, Michael Archer, Joseph J. Bevitt, Alistair R. Evans, Amalia Y. Halim, Tzong Hung, Thomas H. Rich, Patricia Vickers-Rich and Robin M. D. Beck. 2025. Bone Microstructure supports A Mesozoic Origin for a semiaquatic burrowing lifestyle in Monotremes (Mammalia). PNAS. 122 (19) e2413569122. DOI: doi.org/10.1073/pnas.2413569122 

 facebook.com/PNASNews/posts/1088669536623961

[Herpetology • 2025] Iguanas rafted more than 8,000 km from North America to Fiji

 

A Fijian crested iguana (Brachylophus vitiensis) resting on a coconut palm on the island of Fiji in the South Pacific. The four species of iguanas that inhabit Fiji and Tonga today are descended from ancestors that colonized the island within the past 34 million years, probably by rafting 5,000 miles across the Pacific Ocean from western North America.

in Scarpetta, Fisher, Karin, Niukula, Corl, Jackman et McGuire, 2025. 

DOI: doi.org/10.1073/pnas.2318622122

Abstract

Founder-event speciation can occur when one or more organisms colonize a distant, unoccupied area via long-distance dispersal, leading to the evolution of a new species lineage. Species radiations established by long-distance, and especially transoceanic, dispersal can cause substantial shifts in regional biodiversity. Here, we investigate the occurrence and timing of the greatest known long-distance oceanic dispersal event in the history of terrestrial vertebrates—the rafting of iguanas from North America to Fiji. Iguanas are large-bodied herbivores that are well-known overwater dispersers, including species that colonized the Caribbean and the Galápagos islands. However, the origin of Fijian iguanas had not been comprehensively tested. We estimated the phylogenetic relationships and evolutionary timescale of the iguanid lizard radiation using genome-wide exons and ultraconserved elements (UCEs). Those data indicate that the closest living relative of extant Fijian iguanas is the North American desert iguana and that the two taxa likely diverged during the late Paleogene near or after the onset of volcanism that produced the Fijian archipelago. Biogeographic models estimate North America as the most probable ancestral range of Fijian iguanas. Our analyses support the hypothesis that iguanas reached Fiji via an extraordinary oceanic dispersal event from western North America, and which spanned a fifth of the earth’s circumference (>8,000 km). Overwater rafting of iguanas from North America to Fiji strengthens the importance of founder-event speciation in the diversification of iguanids and elucidates the scope of long-distance dispersal across terrestrial vertebrates.

A Fijian crested iguana (Brachylophus vitiensis) resting on a coconut palm on the island of Fiji in the South Pacific. The four species of iguanas that inhabit Fiji and Tonga today are descended from ancestors that colonized the island within the past 34 million years, probably by rafting 5,000 miles across the Pacific Ocean from western North America.

photo: Nicholas Hess

A map of the world 34 million years ago, showing hypothesized scenarios for the colonization of Fiji by Brachylophus. Based on new research, the most likely scenario is represented by the dark blue arrow from western North America to Fiji. The small red stars represent sites in North America where fossil iguanids have been found. The ranges of modern iguanids — in the Americas and Fiji and Tonga — are shown in light blue.

Simon G. Scarpetta, Robert N. Fisher, Benjamin R. Karin, Jone B. Niukula, Ammon Corl, Todd R. Jackman and Jimmy A. McGuire. 2025. Iguanas rafted more than 8,000 km from North America to Fiji. Proceedings of the National Academy of Sciences. 122 (12) e2318622122. DOI: doi.org/10.1073/pnas.2318622122 [March 17, 2025]

Iguanas floated to Fiji millions of years ago on an unprecedented raft journey, scientists say

https://news.berkeley.edu/2025/03/17/iguanas-floated-one-fifth-of-the-way-around-the-world-to-colonize-fiji/

https://www.universityofcalifornia.edu/news/iguanas-floated-fiji-millions-years-ago-unprecedented-raft-journey-scientists-say

 

Significance: Transoceanic dispersal to far-away islands is an important mechanism for the generation of new species lineages and biotas and has captivated scientists since at least the time of Darwin. Determining whether and how such events occur is challenging, particularly for hypothesized dispersals spanning thousands of kilometers. We addressed the enigmatic occurrence of Fijian iguanas via phylogenomic and biogeographic analyses, providing strong evidence that iguanas rafted >8,000 km from North America as early as the Paleogene. This represents the longest documented transoceanic dispersal in terrestrial vertebrates. Our findings elaborate on the importance of long-distance dispersal in the diversification of iguanids. Iguanid lizards display a propensity for overwater dispersal, which could stimulate further research into the predictability of these incredible biogeographic events.

[Paleontology • 2024] Extremely rapid, yet noncatastrophic, Preservation of the Flattened-feathered and 3D Dinosaurs of the Early Cretaceous of China

  

 Extremely rapid preservation of the flattened-feathered and 3D Dinosaurs of the Early Cretaceous, Yixian Formation in China

in MacLennan, Sha, Olsen, Kinney, Chang, Fang, Liu, Slibeck, Chen et Schoene, 2024.

DOI: doi.org/10.1073/pnas.2322875121

Significance: 

Traditionally, the spectacular preservation of fossils of feathered dinosaurs and early birds and other animals found in sedimentary strata of the Yixian Formation in northeast China has been attributed to Pompeii-like volcanic catastrophes. We provide high-resolution geochronology and sedimentological analysis challenging this model and show that these strata instead record normal life and death processes preserved in a succession of depositional environments that span less than 100 thousand years.

Abstract

Northeast China’s Early Cretaceous Yixian Formation preserves spectacular fossils that have proved extraordinarily important in testing evolutionary hypotheses involving the origin of birds and the distribution of feathers among nonavian dinosaurs. These fossils occur either flattened with soft tissue preservation (including feathers and color) in laminated lacustrine strata or as three-dimensional (3D) skeletons in “life-like” postures in more massive deposits. The relationships of these deposits to each other, their absolute ages, and the origin of the extraordinary fossil preservation have been vigorously debated for nearly a half century, with the prevailing view being that preservation was linked to violent volcanic eruptions or lahars, similar to processes that preserved human remains at Pompeii. We present high-precision zircon U-Pb geochronology from cores and outcrops, demonstrating that Yixian Formation accumulation rates are more than an order of magnitude higher than usually estimated. Additionally, we provide zircon provenance and sedimentological data from 3D dinosaur fossils, which imply that their death and burial occurred in collapsed burrows, rather than via a catastrophic volcanogenic mechanism. In the studied area, the three principal fossil-rich intervals of the Yixian occur as a cyclic sequence that correspond to periods of high precipitation. Using Bayesian–Markov Chain Monte Carlo approaches, we constrain the total duration of the sequence to less than ~93,000 y and suggest that climatic precession paced the expression of these cyclic sediments. Rather than representing multiple, Pompeii-like catastrophes, the Yixian Formation is instead a brief snapshot of normal life and death in an Early Cretaceous continental community.

Two perfectly articulated skeletons of the sheep-size dinosaur Psittacosaurus, found in China's Yixian Formation. New research suggests they died in burrow collapses, not via volcanism, as previously thought.

by Jun Liu, IVPP, Chinese Academy of Sciences

Artist's rendition of a Psittacosaurus dinosaur with babies being hunted by Repenomamus, a mammal. One fossil assemblage from the Yixian Formation preserved the remains of these species in mortal combat, frozen in mid-action. The dinosaur here is shown with bristly proto-feathers on its tail.

artwork by Alex Boersma

 Scott A. MacLennan, Jingeng Sha, Paul E. Olsen, Sean T. Kinney, Clara Chang, Yanan Fang, Jun Liu, Bennett B. Slibeck, Elaine Chen, and Blair Schoene. 2024. Extremely rapid, yet noncatastrophic, Preservation of the Flattened-feathered and 3D Dinosaurs of the Early Cretaceous of China. PNAS. 121 (47) e2322875121. DOI: doi.org/10.1073/pnas.2322875121

[Paleontology • 2024] Theropod Trackways as indirect evidence of Pre-avian Aerial Behavior

The animal responsible for Dromaeosauriformipes rarus tracks is believed to be a small microraptorine related to the ancestors of birds.

in Dececchi, Kim, Lockley, Larsson, Holtz, Farlow et Pittman, 2024.

DOI: 10.1073/pnas.2413810121 

facebook.com/PalaeoPittman  cmns.UMD.edu

artwork: Julius Csotonyi.  

Abstract

Body fossils set limits on feasible reconstructions of functional capacity and behavior in theropod dinosaurs, but do not document in-life behaviors. In contrast, trace fossils such as footprints preserve in-life behaviors that can potentially test and enhance existing reconstructions. Here, we demonstrate how theropod trackways can be used as indirect evidence of pre-avian aerial behavior, expanding the approaches available to study vertebrate flight origins. This involved exploring the behavioral implications of a two-toed Cretaceous-aged theropod trackway produced by a small, bird-like microraptorine moving at high speed. Applying first principle running biomechanics, we were able to conclude that the trackway is atypical, indirectly evidencing pre-avian aerial behavior. This trackway documents the evidence of wing-assisted aerodynamic force production during locomotion, supporting a broader distribution of this behavior than currently known. These findings support previously proposed aerial behavior in early bird-like theropods, showing how trackways will help to deepen our understanding of theropod flight origins.

Illustrated reconstruction of Dromaeosauriformipes rarus running along the muddy shore of an ancient lake.

artwork: Alex Boersma

The animal responsible for Dromaeosauriformipes rarus tracks is believed to be a small microraptorine related to the ancestors of birds.

artwork: Julius Csotonyi.  

 T. Alexander Dececchi, Kyung Soo Kim, Martin G. Lockley, Hans C.E. Larsson, Thomas R. Holtz Jr., James O. Farlow and Michael Pittman. 2024. Theropod Trackways as indirect evidence of Pre-avian Aerial Behavior. PNAS. 121 (44) e2413810121. DOI: doi.org/10.1073/pnas.2413810121 

facebook.com/PalaeoPittman/posts/1955746624888160

   facebook.com/JuliusCsotonyi/posts/10159909081901396

Researchers Solve Mystery of ‘Dinky’ Dinosaur’s Unusually Long Stride 

UMD paleontologist Thomas R. Holtz Jr. helped recreate the movements of a bird-sized raptor, shedding new light on the origin of flight.

https://cmns.UMD.edu/news-events/news/thomas-holtz-helps-solve-mystery-microraptorine-footprints

[Ornithology • 2024] Patagona chaski • Extreme Elevational Migration spurred Cryptic Speciation in Giant Hummingbirds (Apodiformes: Trochilidae)

 

Patagona chaski   

Patagona gigas  (Vieillot, 1824)

in Williamson, Gyllenhaal, Bauernfeind, Baumann, Gadek, Marra, Ricote, Valqui, Bozinovic, Singh & Witt, 2024. 

DOI: 10.1073/pnas.2313599121 

  twitter.com/JL_Williamson

 

Significance: 

Biodiversity varies from place to place because the range of climates suitable for any one species tends to be limited. The giant hummingbird appears to defy this tendency, occurring across the broadest range of environments of any hummingbird. We asked whether its migration, physiology, or genetics explain its climate generalism, potentially illuminating mechanisms of niche breadth evolution. Microtracking devices revealed an epic migration from the Chilean coast to the Peruvian Andes, with an extreme, >4,100-m elevational shift and corresponding performance trade-offs. Genomes revealed that migrant and resident populations diverged in the Pliocene and have since evolved under phenotypic stasis. A migratory shift enabled climatic niche expansion, leading to speciation and niche subdivision, consistent with diversification by niche breadth oscillation.

Abstract

The ecoevolutionary drivers of species niche expansion or contraction are critical for biodiversity but challenging to infer. Niche expansion may be promoted by local adaptation or constrained by physiological performance trade-offs. For birds, evolutionary shifts in migratory behavior permit the broadening of the climatic niche by expansion into varied, seasonal environments. Broader niches can be short-lived if diversifying selection and geography promote speciation and niche subdivision across climatic gradients. To illuminate niche breadth dynamics, we can ask how “outlier” species defy constraints. Of the 363 hummingbird species, the giant hummingbird (Patagona gigas) has the broadest climatic niche by a large margin. To test the roles of migratory behavior, performance trade-offs, and genetic structure in maintaining its exceptional niche breadth, we studied its movements, respiratory traits, and population genomics. Satellite and light-level geolocator tracks revealed an >8,300-km loop migration over the Central Andean Plateau. This migration included a 3-wk, ~4,100-m ascent punctuated by upward bursts and pauses, resembling the acclimatization routines of human mountain climbers, and accompanied by surging blood-hemoglobin concentrations. Extreme migration was accompanied by deep genomic divergence from high-elevation resident populations, with decisive postzygotic barriers to gene flow. The two forms occur side-by-side but differ almost imperceptibly in size, plumage, and respiratory traits. The high-elevation resident taxon is the world’s largest hummingbird, a previously undiscovered species that we describe and name here. The giant hummingbirds demonstrate evolutionary limits on niche breadth: when the ancestral niche expanded due to evolution (or loss) of an extreme migratory behavior, speciation followed.

  

  

 

Jessie L. Williamson, Ethan F. Gyllenhaal, Selina M. Bauernfeind, Matthew J. Baumann, Chauncey R. Gadek, Peter P. Marra, Natalia Ricote, Thomas Valqui, Francisco Bozinovic, Nadia D. Singh, and Christopher C. Witt. 2024.  Extreme Elevational Migration spurred Cryptic Speciation in Giant Hummingbirds. PNAS. 121 (21); e2313599121. DOI: 10.1073/pnas.2313599121 

  twitter.com/JL_Williamson/status/1790397976550011094

The proposed scientific name for the resident northern population is Patagona chaski. “Chaski” is the word for messenger in Quechua, a family of Indigenous languages that spread from Peru to other neighboring countries.

 news.cornell.edu/stories/2024/05/worlds-largest-hummingbird-actually-two-species

[PaleoEntomology • 2022] Archaboilus musicus • High Acoustic Diversity and Behavioral Complexity of Katydids in the Mesozoic Soundscape

 

Archaboilus musicus Gu, Engel & Ren, 2012

in Xu, Wang, Wappler, Chen, ... et Engel, 2022.

  pnas.org/doi/10.1073/pnas.2210601119

Significance: 

Extinct animals usually had complex acoustic behavior, but fossils reveal little of these details. Here, we report the earliest insect ears and sound-producing system found in Mesozoic katydids. These katydids evolved unexpectedly high acoustic diversity. Our analysis shows that katydids are the earliest known animals to have evolved complex acoustic communication, acoustic niche partitioning, and high-frequency musical calls. Our results not only suggest that acoustic communication might have been an important driver for the early radiation of katydids but also support the hypothesis of the acoustic coevolution of mammals and katydids. These findings unveil acoustic behavioral complexity and evolutionary adaption amongst Mesozoic katydids and contribute to understanding the evolution of Mesozoic soundscape thus far mostly inaccessible from the paleontological record.

Abstract

Acoustic communication has played a key role in the evolution of a wide variety of vertebrates and insects. However, the reconstruction of ancient acoustic signals is challenging due to the extreme rarity of fossilized organs. Here, we report the earliest tympanal ears and sound-producing system (stridulatory apparatus) found in exceptionally preserved Mesozoic katydids. We present a database of the stridulatory apparatus and wing morphology of Mesozoic katydids and further calculate their probable singing frequencies and analyze the evolution of their acoustic communication. Our suite of analyses demonstrates that katydids evolved complex acoustic communication including mating signals, intermale communication, and directional hearing, at least by the Middle Jurassic. Additionally, katydids evolved a high diversity of singing frequencies including high-frequency musical calls, accompanied by acoustic niche partitioning at least by the Late Triassic, suggesting that acoustic communication might have been an important driver in the early radiation of these insects. The Early—Middle Jurassic katydid transition from Haglidae- to Prophalangopsidae-dominated faunas coincided with the diversification of derived mammalian clades and improvement of hearing in early mammals, supporting the hypothesis of the acoustic coevolution of mammals and katydids. Our findings not only highlight the ecological significance of insects in the Mesozoic soundscape but also contribute to our understanding of how acoustic communication has influenced animal evolution.

Ecological restoration of singing katydids from the Middle Jurassic Daohugou Konservat-Lagerstätte of China. 

Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences: NIGPAS

Chunpeng Xu, Bo Wang, Torsten Wappler, Jun Chen, Dmitry Kopylov, Yan Fang, Edmund A. Jarzembowski, Haichun Zhang and Michael S. Engel. 2022. High Acoustic Diversity and Behavioral Complexity of Katydids in the Mesozoic Soundscape. PNAS. 119 (51) e2210601119

  pnas.org/doi/10.1073/pnas.2210601119

 phys.org/news/2022-12-fossil-katydids-insights-evolution-mesozoic.html

[Paleontology • 2023] Evidence for Heterothermic Endothermy and Reptile-like Eggshell Mineralization in Troodon, A Non-avian Maniraptoran Theropod

Troodon

in Tagliavento, Davies, Bernecker, Staudigel, Dawson, ... et  Fiebig, 2023. 

  DOI: 10.1073/pnas.2213987120

artwork: Alex Boersma

Abstract

The dinosaur–bird transition involved several anatomical, biomechanical, and physiological modifications of the theropod bauplan. Non-avian maniraptoran theropods, such as Troodon, are key to better understand changes in thermophysiology and reproduction occurring during this transition. Here, we applied dual clumped isotope (Δ47 and Δ48) thermometry, a technique that resolves mineralization temperature and other nonthermal information recorded in carbonates, to eggshells from Troodon, modern reptiles, and modern birds. Troodon eggshells show variable temperatures, namely 42 and 29 ± 2 °C, supporting the hypothesis of an endothermic thermophysiology with a heterothermic strategy for this extinct taxon. Dual clumped isotope data also reveal physiological differences in the reproductive systems between Troodon, reptiles, and birds. Troodon and modern reptiles mineralize their eggshells indistinguishable from dual clumped isotope equilibrium, while birds precipitate eggshells characterized by a positive disequilibrium offset in Δ48. Analyses of inorganic calcites suggest that the observed disequilibrium pattern in birds is linked to an amorphous calcium carbonate (ACC) precursor, a carbonate phase known to accelerate eggshell formation in birds. Lack of disequilibrium patterns in reptile and Troodon eggshells implies these vertebrates had not acquired the fast, ACC-based eggshell calcification process characteristic of birds. Observation that Troodon retained a slow reptile-like calcification suggests that it possessed two functional ovaries and was limited in the number of eggs it could produce; thus its large clutches would have been laid by several females. Dual clumped isotope analysis of eggshells of extinct vertebrates sheds light on physiological information otherwise inaccessible in the fossil record.

Several Troodon females laid their eggs in communal nests.

artwork: Alex Boersma/PNAS

 

Significance: The dinosaur–bird transition is among the most fascinating events in evolutionary history, but several biological aspects such as changes in reproductive system, nesting strategy, and body temperature are still poorly understood. Dual clumped isotope thermometry (Δ47 and Δ48) can shed light on these biological aspects in fossils. Our results show that eggshells of modern reptiles and birds differ in their isotopic compositions. Interestingly, analyses of eggshells of Troodon, a non-avian theropod, reveal that it retained a slower, reptile-like mineralization to produce its eggs, despite having already evolved the capacity of changing its body temperature (heterothermic endothermy) like modern birds. Our findings also suggest that Troodon possessed two functional ovaries and that their nests were shared by multiple females.

 

Mattia Tagliavento, Amelia J. Davies, Miguel Bernecker, Philip T. Staudigel, Robin R. Dawson, Martin Dietzel, Katja Götschl, Weifu Guo, Anne S. Schulp, François Therrien, Darla K. Zelenitsky, Axel Gerdes, Wolfgang Müller and Jens Fiebig. 2023. Evidence for Heterothermic Endothermy and Reptile-like Eggshell Mineralization in Troodon, A Non-avian Maniraptoran Theropod. Proceedings of the National Academy of Sciences. 120 (15) e2213987120. DOI: 10.1073/pnas.2213987120

phys.org/news/2023-04-analysis-dinosaur-eggshells-bird-like-troodon.html

[Paleontology • 2022] Marmorerpeton wakei • Middle Jurassic Fossils (Caudata: Karauridae) document An early Stage in Salamander Evolution

Marmorerpeton wakei  

 Jones, Benson, Skutschas, Hill, Panciroli, Schmitt, Walsh & Evans, 2022

DOI: 10.1073/pnas.2114100119

 twitter.com/MarcEHJones

Artwork: Brennan Stokkermans

Significance: 

Little is known about stem-lineage salamanders, limiting understanding of their early evolution and of the origins of modern amphibian diversity. We report new, three-dimensionally preserved skeletons of the stem-salamander Marmorerpeton, from 166 million-year-old rocks in Scotland, documenting many phylogenetically informative anatomical traits. High resolution computed tomography (CT) scans reveal unprecedented three-dimensional anatomical detail, illuminating anatomical changes during early salamander evolution. Phylogenetic analysis provides evidence for an anatomically diverse radiation of early stem salamanders distributed across Eurasia during the Middle Jurassic and Early Cretaceous. Our findings highlight the morphological variety of stem-salamanders, undermining the use of single exemplars (e.g., Karaurus; the “Archaeopteryx” of salamanders) to represent early evolutionary transitions.

Abstract

Salamanders are an important group of living amphibians and model organisms for understanding locomotion, development, regeneration, feeding, and toxicity in tetrapods. However, their origin and early radiation remain poorly understood, with early fossil stem-salamanders so far represented by larval or incompletely known taxa. This poor record also limits understanding of the origin of Lissamphibia (i.e., frogs, salamanders, and caecilians). We report fossils from the Middle Jurassic of Scotland representing almost the entire skeleton of the enigmatic stem-salamander Marmorerpeton. We use computed tomography to visualize high-resolution three-dimensional anatomy, describing morphologies that were poorly characterized in early salamanders, including the braincase, scapulocoracoid, and lower jaw. We use these data in the context of a phylogenetic analysis intended to resolve the relationships of early and stem-salamanders, including representation of important outgroups alongside data from high-resolution imaging of extant species. Marmorerpeton is united with Karaurus, Kokartus, and others from the Middle Jurassic–Lower Cretaceous of Asia, providing evidence for an early radiation of robustly built neotenous stem-salamanders. These taxa display morphological specializations similar to the extant cryptobranchid “giant” salamanders. Our analysis also demonstrates stem-group affinities for a larger sample of Jurassic species than previously recognized, highlighting an unappreciated diversity of stem-salamanders and cautioning against the use of single species (e.g., Karaurus) as exemplars for stem-salamander anatomy. These phylogenetic findings, combined with knowledge of the near-complete skeletal anatomy of Mamorerpeton, advance our understanding of evolutionary changes on the salamander stem-lineage and provide important data on early salamanders and the origins of Batrachia and Lissamphibia.

 

Marmorerpeton wakei  

 

Marc E. H. Jones, Roger B. J. Benson, Pavel Skutschas, Lucy Hill, Elsa Panciroli, Armin D. Schmitt, Stig A. Walsh and Susan E. Evans. 2022. Middle Jurassic Fossils document An early Stage in Salamander Evolution. PNAS. 119 (30) e2114100119. DOI: 10.1073/pnas.2114100119

 twitter.com/MarcEHJones/status/1546802860519833601

 

 Marmorerpeton wakei (mar-more-ER-pet-on WAY-kee), 

 twitter.com/gsciencelady/status/1546807472706437120

 

[Mammalogy • 2021] Mammalian Face as An Evolutionary Novelty

in Higashiyama, Koyabu, Hirasawa, ... et Kurihara, 2021. 

DOI: 10.1073/pnas.2111876118

 twitter.com/H_Higashiyama

Significance: 

The anatomical framework of the jaw has traditionally been thought to be highly conserved among vertebrates. However, here we show that the therian-unique face (muzzle) evolved via a drastic alteration of the common pattern of the tetrapod jaw. Through comparative morphological and developmental analyses, we demonstrated that the therian mammal’s premaxilla (rostral-most upper jawbone) is derived from the maxillary prominence of the mandibular arch. The developmental primordium that produces the premaxilla in nonmammalian tetrapods rarely contributes to the upper jaw in therian mammals but rather forms a motile nose. We propose that these previously unrecognized rearrangements allowed key innovations such as the highly sensitive tactile perception and olfactory function in mammalian evolution.

Abstract

The anterior end of the mammalian face is characteristically composed of a semimotile nose, not the upper jaw as in other tetrapods. Thus, the therian nose is covered ventrolaterally by the “premaxilla,” and the osteocranium possesses only a single nasal aperture because of the absence of medial bony elements. This stands in contrast to those in other tetrapods in whom the premaxilla covers the rostral terminus of the snout, providing a key to understanding the evolution of the mammalian face. Here, we show that the premaxilla in therian mammals (placentals and marsupials) is not entirely homologous to those in other amniotes; the therian premaxilla is a composite of the septomaxilla and the palatine remnant of the premaxilla of nontherian amniotes (including monotremes). By comparing topographical relationships of craniofacial primordia and nerve supplies in various tetrapod embryos, we found that the therian premaxilla is predominantly of the maxillary prominence origin and associated with mandibular arch. The rostral-most part of the upper jaw in nonmammalian tetrapods corresponds to the motile nose in therian mammals. During development, experimental inhibition of primordial growth demonstrated that the entire mammalian upper jaw mostly originates from the maxillary prominence, unlike other amniotes. Consistently, cell lineage tracing in transgenic mice revealed a mammalian-specific rostral growth of the maxillary prominence. We conclude that the mammalian-specific face, the muzzle, is an evolutionary novelty obtained by overriding ancestral developmental constraints to establish a novel topographical framework in craniofacial mesenchyme.

Keywords: evolution, craniofacial, skull, mammals

Evolutionary transitions of upper jaw bones in the fossil synapsids.

 

 Hiroki Higashiyama, Daisuke Koyabu, Tatsuya Hirasawa, Ingmar Werneburg, Shigeru Kuratani, and Hiroki Kurihara. 2021. Mammalian Face as An Evolutionary Novelty. PNAS. 118 (44); e2111876118. DOI: 10.1073/pnas.2111876118

 twitter.com/H_Higashiyama/status/1455700921254481924

[Paleontology • 2020] Kongonaphon kely • A Tiny Ornithodiran Archosaur from the Triassic of Madagascar and the Role of Miniaturization in Dinosaur and Pterosaur Ancestry

Kongonaphon kely 

Kammerer, Nesbitt, Flynn, Ranivoharimanana & Wyss, 2020

  DOI: 10.1073/pnas.1916631117 

Illustration: Alex Boersma 

  twitter.com/Synapsida

Abstract

Early members of the dinosaur–pterosaur clade Ornithodira are very rare in the fossil record, obscuring our understanding of the origins of this important group. Here, we describe an early ornithodiran (Kongonaphon kely gen. et sp. nov.) from the Mid-to-Upper Triassic of Madagascar that represents one of the smallest nonavian ornithodirans. Although dinosaurs and gigantism are practically synonymous, an analysis of body size evolution in dinosaurs and other archosaurs in the context of this taxon and related forms demonstrates that the earliest-diverging members of the group may have been smaller than previously thought, and that a profound miniaturization event occurred near the base of the avian stem lineage. In phylogenetic analysis, Kongonaphon is recovered as a member of the Triassic ornithodiran clade Lagerpetidae, expanding the range of this group into Africa and providing data on the craniodental morphology of lagerpetids. The conical teeth of Kongonaphon exhibit pitted microwear consistent with a diet of hard-shelled insects, indicating a shift in trophic ecology to insectivory associated with diminutive body size. Small ancestral body size suggests that the extreme rarity of early ornithodirans in the fossil record owes more to taphonomic artifact than true reflection of the group’s evolutionary history.

Keywords: body size, evolution, Dinosauria, Triassic, phylogeny

Anatomy of the maxilla of Kongonaphon kely gen. et sp. nov. (UA 10618).
Right maxilla in right lateral and palatal views. 

Systematic Paleontology

Archosauria Cope, 1869 

Avemetatarsalia Benton, 1999 

Lagerpetidae Arcucci, 1986 

sensu Nesbitt et al., 2009 

Kongonaphon kely gen. et sp. nov. 

Etymology. Name meaning “tiny bug slayer,” derived from kongona (Malagasy, “bug”) and φoν (variant of ancient Greek φoνeύς, “slayer”), referring to the probable diet of this animal; kely (Malagasy, “small”), referring to the diminutive size of this specimen.

Illustration of Kongonaphon kely, a newly described reptile near the ancestry of dinosaurs and pterosaurs, in what would have been its natural environment in the Triassic (~237 million years ago).

Illustration: Alex Boersma 

  twitter.com/Synapsida

Significance: 

Reptiles of the Mesozoic Era are known for their remarkable size: dinosaurs include the largest known land animals, and their relatives, the pterosaurs, include the largest creatures to ever fly. The origins of these groups are poorly understood, however. Here, we present a species (Kongonaphon kely) from the Triassic of Madagascar close to the ancestry of dinosaurs and pterosaurs, providing insight into the early evolution of those groups. Kongonaphon is a surprisingly small animal (estimated height, ∼10 cm). Analysis of ancestral body size indicates that there was a pronounced miniaturization event near the common ancestor of dinosaurs and pterosaurs. Tiny ancestral body size may help explain the origins of flight in pterosaurs and fuzzy integument in both groups.

Christian F. Kammerer, Sterling J. Nesbitt, John J. Flynn, Lovasoa Ranivoharimanana and André R. Wyss. 2020. A Tiny Ornithodiran Archosaur from the Triassic of Madagascar and the Role of Miniaturization in Dinosaur and Pterosaur Ancestry. PNAS. DOI: 10.1073/pnas.1916631117

twitter.com/Synapsida/status/1280220348944957440

A tiny ancient relative of dinosaurs and pterosaurs discovered

phys.org/news/2020-07-tiny-ancient-relative-dinosaurs-pterosaurs.html