A mid-Cretaceous embryonic-to-neonate snake in amber from Myanmar

Fossil-informed biogeographic analysis suggests Eurasian regionalization in crown Squamata during the early Jurassic

Background

Squamata (lizards, snakes, and amphisbaenians) is a Triassic lineage with an extensive and complex biogeographic history, yet no large-scale study has reconstructed the ancestral range of early squamate lineages. The fossil record indicates a broadly Pangaean distribution by the end- Cretaceous, though many lineages (e.g., Paramacellodidae, Mosasauria, Polyglyphanodontia) subsequently went extinct. Thus, the origin and occupancy of extant radiations is unclear and may have been localized within Pangaea to specific plates, with potential regionalization to distinct Laurasian and Gondwanan landmasses during the Mesozoic in some groups.

Methods

We used recent tectonic models to code extant and fossil squamate distributions occurring on nine discrete plates for 9,755 species, with Jurassic and Cretaceous fossil constraints from three extinct lineages. We modeled ancestral ranges for crown Squamata from an extant-only molecular phylogeny using a suite of biogeographic models accommodating different evolutionary processes and fossil-based node constraints from known Jurassic and Cretaceous localities. We hypothesized that the best-fit models would not support a full Pangaean distribution (i.e., including all areas) for the origin of crown Squamata, but would instead show regionalization to specific areas within the fragmenting supercontinent, likely in the Northern Hemisphere where most early squamate fossils have been found.

Results

Incorporating fossil data reconstructs a localized origin within Pangaea, with early regionalization of extant lineages to Eurasia and Laurasia, while Gondwanan regionalization did not occur until the middle Cretaceous for Alethinophidia, Scolecophidia, and some crown Gekkotan lineages. While the Mesozoic history of extant squamate biogeography can be summarized as a Eurasian origin with dispersal out of Laurasia into Gondwana, their Cenozoic history is complex with multiple events (including secondary and tertiary recolonizations) in several directions. As noted by previous authors, squamates have likely utilized over-land range expansion, land-bridge colonization, and trans-oceanic dispersal. Tropical Gondwana and Eurasia hold more ancient lineages than the Holarctic (Rhineuridae being a major exception), and some asymmetries in colonization (e.g., to North America from Eurasia during the Cenozoic through Beringia) deserve additional study. Future studies that incorporate fossil branches, rather than as node constraints, into the reconstruction can be used to explore this history further.

An earliest Triassic age for Tasmaniolimulus and comments on synchrotron tomography of Gondwanan horseshoe crabs

Constraining the timing of morphological innovations within xiphosurid evolution is central for understanding when and how such a long-lived group exploited vacant ecological niches over the majority of the Phanerozoic. To expand the knowledge on the evolution of select xiphosurid forms, we reconsider the four Australian taxa: Austrolimulus fletcheri, Dubbolimulus peetae, Tasmaniolimulus patersoni, and Victalimulus mcqueeni. In revisiting these taxa, we determine that, contrary to previous suggestion, T. patersoni arose after the Permian and the origin of over-developed genal spine structures within Austrolimulidae is exclusive to the Triassic. To increase the availability of morphological data pertaining to these unique forms, we also examined the holotypes of the four xiphosurids using synchrotron radiation X-ray tomography (SRXT). Such non-destructive, in situ imaging of palaeontological specimens can aid in the identification of novel morphological data by obviating the need for potentially extensive preparation of fossils from the surrounding rock matrix. This is particularly important for rare and/or delicate holotypes. Here, SRXT was used to emphasize A. fletcheri and T. patersoni cardiac lobe morphologies and illustrate aspects of the V. mcqueeni thoracetronic doublure, appendage impressions, and moveable spine notches. Unfortunately, the strongly compacted D. peetae precluded the identification of any internal structures, but appendage impressions were observed. The application of computational fluid dynamics to high-resolution 3D reconstructions are proposed to understand the hydrodynamic properties of divergent genal spine morphologies of austrolimulid xiphosurids.

A new Early Cretaceous lizard in Myanmar amber with exceptionally preserved integument

We here report on a well-preserved juvenile lizard specimen in Albian amber (ca. 110 mya) from the Hkamti site (Myanmar). This new taxon is represented by an articulated skull and the anterior portion of the trunk, including the pectoral girdle and forelimbs. The scleral ossicles and eyelid are also visible, and the specimen exhibits pristine detail of the integument (of both head and body). In a combined molecular and morphological analysis, it was consistently recovered as a scincoid lizard (Scinciformata), as sister to Tepexisaurus + Xantusiidae. However, the phylogenetic position of the new taxon should be interpreted with caution as the holotype is an immature individual. We explored the possibility of miscoding ontogenetically variable characters by running alternative analyses in which these characters were scored as missing data for our taxon. With the exception of one tree, in which it was sister to Amphisbaenia, the specimen was recovered as a Pan-xantusiid. Moreover, we cannot rule out the possibility that it represents a separate lineage of uncertain phylogenetic position, as it is the case for many Jurassic and Cretaceous taxa. Nonetheless, this fossil offers a rare opportunity to glimpse the external appearance of one group of lizards during the Early Cretaceous.

The First Ptilodactyla Illiger, 1807 (Coleoptera: Dryopoidea: Ptilodactylidae) Described from Eocene Baltic Amber

The beetle family Ptilodactylidae contains more than 500 extant species; however, its fossil record is scarce and remains understudied. In this study, we describe a new species of Ptilodactylidae, Ptilodactyla eocenica Kundrata, Bukejs and Blank, sp. nov., based on a relatively well-preserved specimen from Baltic amber. We use X-ray microcomputed tomography to reconstruct its morphology since some of the principal diagnostic characters have been obscured by opaque bubbles. It is the third ptilodactylid species described from Baltic amber, and the first one belonging to the subfamily Ptilodactylinae. Additionally, we summarize the classification, diversity, and distribution of both extinct and extant Ptilodactylidae.

Paleontology: It's a bird, it's a plane, it's Oculudentavis!

Few animals have experienced such jarring taxonomic whiplash as has Oculudentavis, a tiny tetrapod preserved in amber. A new specimen of this perplexing lineage now shows that it is a lizard unlike any ever discovered.

Assessing ontogenetic maturity in extinct saurian reptiles

Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life-history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least-inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260-million-year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. 'juvenile', 'mature') and provide routes for better clarity and cross-study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method-specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, 'Ontogenetic Assessment', be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well-represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well-constrained, empirically tested methods.

Cretaceous Blind Snake from Brazil Fills Major Gap in Snake Evolution

Blind snakes (Scolecophidia) are minute cryptic snakes that diverged at the base of the evolutionary radiation of modern snakes. They have a scant fossil record, which dates back to the Upper Paleocene-Lower Eocene (∼56 Ma); this late appearance conflicts with molecular evidence, which suggests a much older origin for the group (during the Mesozoic: 160–125 Ma). Here we report a typhlopoid blind snake from the Late Cretaceous of Brazil, Boipeba tayasuensis gen. et sp. nov, which extends the scolecophidian fossil record into the Mesozoic and reduces the fossil gap predicted by molecular data. The new species is estimated to have been over 1 m long, much larger than typical modern scolecophidians (<30 cm). This finding sheds light on the early evolution of blind snakes, supports the hypothesis of a Gondwanan origin for the Typhlopoidea, and indicates that early scolecophidians had large body size, and only later underwent miniaturization.

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Boipeba tayasuensis is the oldest fossil blind snake from the Late Cretaceous of Brazil

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A new phylogenetic analysis places the taxon within living typhlopoids

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Boipeba is estimated to be ∼1 m in length, larger than any living blind snake

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The small body size of extant blind snakes is due to subsequent miniaturization

X-ray micro-computed tomography reveals a unique morphology in a new click-beetle (Coleoptera, Elateridae) from the Eocene Baltic amber

Beetle fossils are a rich source of information about the palaeodiversity and evolutionary history of the order Coleoptera. Despite the increasing rate of fossil research on click-beetles (Coleoptera: Elateridae), the most diverse group in the superfamily Elateroidea, their fossil record has remained largely unstudied. This may be caused by the combination of their rather uniform external morphology and the suboptimal state of preservation and visibility in most fossil specimens. Here, we used X-ray micro-computed tomography to reconstruct the morphology of an interesting click-beetle from Eocene Baltic amber, which had some principal diagnostic characters obscured by opaque bubbles and body position. Our results suggest that the newly described Baltelater bipectinatus gen. et sp. nov. belongs to tribe Protelaterini within subfamily Lissominae. Since Protelaterini have a predominantly Gondwanan distribution, our discovery is of a great importance for the historical biogeography of the group. Very distinctive are the bipectinate antennae with 11 antennomeres and with rami beginning on antennomere IV, which are not found in any recent Elateridae. The discovery of a new click-beetle lineage from European Eocene amber sheds further light on the palaeodiversity and historical diversification of the family as well as on the composition of the extinct amber forest ecosystem.

Fossils reshape the Sternorrhyncha evolutionary tree (Insecta, Hemiptera)

The Sternorrhyncha, which comprise about 18,700 described recent species, is a suborder of the Hemiptera, one of big five most diverse insect orders. In the modern fauna, these tiny phytophages comprise insects of great ecological and economic importance, like aphids (Aphidomorpha), scale insects (Coccidomorpha), whiteflies (Aleyrodomorpha) and psyllids (Psylloidea). Their evolutionary history can be traced back to the Late Carboniferous, but the early stages of their evolution and diversification is poorly understood, with two known extinct groups-Pincombeomorpha and Naibiomorpha variously placed in classifications and relationships hypotheses. Most of the recent Sternorrhyncha groups radiated rapidly during the Cretaceous. Here we report the new finding of very specialised sternorrhynchans found as inclusions in mid-Cretaceous amber from Kachin state (northern Myanmar), which represent another extinct lineage within this hemipteran suborder. These fossils, proposed to be placed in a new infraorder, are revealed to be related to whiteflies and psyllids. We present, also for the first time, the results of phylogenetic analyses covering extinct and extant lineages of the Sternorrhyncha.

Megaevolutionary dynamics and the timing of evolutionary innovation in reptiles

The origin of phenotypic diversity among higher clades is one of the most fundamental topics in evolutionary biology. However, due to methodological challenges, few studies have assessed rates of evolution and phenotypic disparity across broad scales of time to understand the evolutionary dynamics behind the origin and early evolution of new clades. Here, we provide a total-evidence dating approach to this problem in diapsid reptiles. We find major chronological gaps between periods of high evolutionary rates (phenotypic and molecular) and expansion in phenotypic disparity in reptile evolution. Importantly, many instances of accelerated phenotypic evolution are detected at the origin of major clades and body plans, but not concurrent with previously proposed periods of adaptive radiation. Furthermore, strongly heterogenic rates of evolution mark the acquisition of similarly adapted functional types, and the origin of snakes is marked by the highest rates of phenotypic evolution in diapsid history.

Discovery of the oldest South American fossil lizard illustrates the cosmopolitanism of early South American squamates

Squamates have an extremely long evolutionary history with a fossil record that extends into the Middle Triassic. However, most of our knowledge of their early evolutionary history is derived from Laurasian records. Therefore, fundamental questions regarding the early evolution of squamates in the Southern Hemisphere, such as the origins of the extremely diverse and endemic South American fauna, remain unanswered. Here, we describe a new lizard species that represents the oldest fossil squamate from South America, demonstrating that squamates were present on that continent at least 20 million years earlier than previously recorded. The new species represents the first occurrence of the extinct squamate family Paramacellodidae in South America and displays an unusual limb morphology. Finally, our findings suggest early South American squamates were part of a much broader distribution of their respective clades, in sharp contrast to the high levels of endemicity characteristic of modern faunas.

New fossil lizard specimens from a poorly-known squamate assemblage in the Upper Cretaceous (Campanian) San Juan Basin, New Mexico, USA

Recent collection efforts in the upper Campanian (∼76-73.5 Ma) Fruitland and Kirtland formations of northwestern New Mexico have significantly increased the taxonomic diversity of lizards in this historically poorly understood squamate assemblage. New lizard specimens from the “Hunter Wash Local Fauna” of the upper Fruitland and lower Kirtland formations include: (1) new specimens referable to Chamopsiidae; (2) new material belonging to Scincomorpha, (3) new material belonging to Anguidae; and (4) the first reported predatory lizard (Platynota) material from the Campanian of New Mexico. The increase in lizard diversity in the “Hunter Wash Local Fauna” expands our understanding of Late Cretaceous squamate taxonomy, distribution, and diversity in the Western Interior of North America (Laramidia). Collectively, the described specimens represent family-level diversity similar to that seen in other Campanian foreland basin deposits of the Western Interior, such as the mid-paleolatitude Kaiparowits Formation of southern Utah, the higher paleolatitude Dinosaur Park Formation of southern Alberta, and the lower paleolatitude Aguja Formation of southwestern Texas. The lizards of the “Hunter Wash Local Fauna” represent crucial mid-paleolatitude data from a coastal plain depositional setting in Laramidia—allowing for comparisons to more well-studied assemblages at different latitudes and in different depositional settings.

The structural origins of brittle star arm kinematics: An integrated tomographic, additive manufacturing, and parametric modeling-based approach

Brittle stars are known for the high flexibility of their arms, a characteristic required for locomotion, food grasping, and for holding onto a great diversity of substrates. Their high agility is facilitated by the numerous discrete skeletal elements (ossicles) running through the center of each arm and embedded in the skin. While much has been learned regarding the structural diversity of these ossicles, which are important characters for taxonomic purposes, their impact on the arms' range of motion, by contrast, is poorly understood. In the present study, we set out to investigate how ossicle morphology and skeletal organization affect the flexibility of brittle star arms. Here, we present the results of an in-depth analysis of three brittle star species (Ophioplocus esmarki, Ophiopteris papillosa, and Ophiothrix spiculata), chosen for their different ranges of motion, as well as spine size and orientation. Using an integrated approach that combines behavioral studies with parametric modeling, additive manufacturing, micro-computed tomography, scanning electron microscopy, and finite element simulations, we present a high-throughput workflow that provides a fundamental understanding of 3D structure-kinematic relationships in brittle star skeletal systems.

New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan

Snakes represent one of the most dramatic examples of the evolutionary versatility of the vertebrate body plan, including body elongation, limb loss, and skull kinesis. However, understanding the earliest steps toward the acquisition of these remarkable adaptations is hampered by the very limited fossil record of early snakes. Here, we shed light on the acquisition of the snake body plan using micro-computed tomography scans of the first three-dimensionally preserved skulls of the legged snake Najash and a new phylogenetic hypothesis. These findings elucidate the initial sequence of bone loss that gave origin to the modern snake skull. Morphological and molecular analyses including the new cranial data provide robust support for an extensive basal radiation of early snakes with hindlimbs and pelves, demonstrating that this intermediate morphology was not merely a transient phase between limbed and limbless body plans.

Land Snail with Periostracal Hairs Preserved in Burmese Amber

Excellently preserved fossils often provide important insights into evolutionary histories and adaptations to environmental change in Earth's biogeologic record. Mid-Cretaceous Burmese amber, for example, is a proven reservoir for spectacular findings. Here we document the first record of a fossil land snail with periostracal hairs preserved in amber. We interpret the development of hairs as an adaptation to the tropical forest environment, serving as a mechanism to increase adhesion of the snail to plants during foraging while collecting and transporting seeds in the process. The present record coincides with a major global radiation of angiosperms, a main food resource for terrestrial snails. As such, the expansion of flowering plants likely triggered this evolutionary adaptation and, thus, the diversification of land snails in the Cretaceous.

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We document the oldest fossil record of a hairy land snail

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The hairs are interpreted as adaptation to a tropical forest environment

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Hairs are suggested to increase adhesion to plants during foraging

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The adaptation was potentially caused by the coeval radiation of flowering plants

A unique camouflaged mimarachnid planthopper from mid-Cretaceous Burmese amber

Predation is a major driving force for the evolution of functional forms. Avoidance of visual predators has resulted in different kinds of anti-predator defences, such as: camouflage, crypsis, disruptive coloration, and masquerade or mimesis. Camouflage is one of the forms involving shape, colouration, structure and behaviour when the visual pattern and orientation of an animal can determine whether it lives or dies. Inferring the behaviour and function of an ancient organism from its fossilised remains is a difficult task, but in many cases it closely resembles that of its descendants on uniformitarian grounds. Here we report and discuss examples of morphological and behavioural traits involving camouflage named recently as a flatoidinisation syndrome, shown by the inclusion of a planthopper in mid-Cretaceous Burmese amber. We found a new genus and species of an extinct Cretaceous planthopper family Mimarachnidae showing peculiar complex morphological adaptations to camouflage it on tree bark. Due to convergence, it resembles an unrelated tropiduchid planthopper from Eocene Baltic amber and also a modern representatives of the planthopper family Flatidae. Flattening of the body, the horizontal position of the tegmina at repose, tegmina with an undulating margin and elevated, wavy longitudinal veins, together with colouration and more sedentary behavioral traits enable these different insects to avoid predators. Our discovery reveals flatoidinisation syndrome in mid-Cretaceous Burmese amber which may provide insights into the processes of natural selection and evolution in this ancient forest.

A New Enantiornithine Bird with Unusual Pedal Proportions Found in Amber

Recent discoveries of vertebrate remains trapped in middle Cretaceous amber from northern Myanmar [1, 2] have provided insights into the morphology of soft-tissue structures in extinct animals [3-7], in particular, into the evolution and paleobiology of early birds [4, 8, 9]. So far, five bird specimens have been described from Burmese amber: two isolated wings, an isolated foot with wing fragment, and two partial skeletons [4, 8-10]. Most of these specimens contain the remains of juvenile enantiornithine birds [4]. Here, we describe a new specimen of enantiornithine bird in amber, collected at the Angbamo locality in the Hukawng Valley. The new specimen includes a partial right hindlimb and remiges from an adult or subadult bird. Its foot, of which the third digit is much longer than the second and fourth digits, is distinct from those of all other currently recognized Mesozoic and extant birds. Based on the autapomorphic foot morphology, we erect a new taxon, Elektorornis chenguangi gen. et sp. nov. We suggest that the elongated third digit was employed in a unique foraging strategy, highlighting the bizarre morphospace in which early birds operated.

A fully feathered enantiornithine foot and wing fragment preserved in mid-Cretaceous Burmese amber

Over the last three years, Burmese amber (~99 Ma, from Myanmar) has provided a series of immature enantiornithine skeletal remains preserved in varying developmental stages and degrees of completeness. These specimens have improved our knowledge based on compression fossils in Cretaceous sedimentary rocks, adding details of three-dimensional structure and soft tissues that are rarely preserved elsewhere. Here we describe a remarkably well-preserved foot, accompanied by part of the wing plumage. These body parts were likely dismembered, entering the resin due to predatory or scavenging behaviour by a larger animal. The new specimen preserves contour feathers on the pedal phalanges together with enigmatic scutellae scale filament (SSF) feathers on the foot, providing direct analogies to the plumage patterns observed in modern birds, and those cultivated through developmental manipulation studies. Ultimately, this connection may allow researchers to observe how filamentous dinosaur 'protofeathers' developed-testing theories using evolutionary holdovers in modern birds.

The Core Eudicot Boom Registered in Myanmar Amber

A perfect flower in a mid-Cretaceous (early Cenomanian) Myanmar amber is described as Lijinganthus revoluta gen. et sp. nov. The fossil flower is actinomorphic and pentamerous, including calyx, corolla, stamens, and gynoecium. The sepals are tiny, while the petals are large and revolute. The stamens are dorsifixed, filamentous, and each has a longitudinally dehiscing bisporangiate anther. The gynoecium is in the centre of the flower, composed of three fused carpels with a stout style. Lijinganthus revoluta gen. et sp. nov. demonstrates a great resemblance to the flowers of Pentapetalae (Eudicots), adding new information to the enigmatic early evolutionary history of Pentapetalae and Eudicots.