Determination of Anthracene Derivatives in Baltic Amber Using SERS.

The article describes the results of Raman spectroscopy and SERS for the study of fluorescent components of Baltic amber via the extraction method. Using SERS, it was possible to confirm the presence of anthracene derivatives in amber: tetracene and benzanthracene. It has been shown that SERS methods are effective for the detection of aromatic compounds; they increase the registered Raman signal and make it possible to identify peaks characteristic of the compounds under study. By combining experimental methods with DFT simulations, anthracene derivatives were modeled and confirmed to be present in the structure of Baltic amber. A combination of the proposed methods can be used to distinguish between different types of amber and isolate the necessary amber components. The obtained results are promising for compiling spectral maps of ambers for their possible classification by their place of origin.

An Eocene army ant.

Among social insects, army ants are exceptional in their voracious coordinated predation, nomadic life history and highly specialized wingless queens: the synthesis of these remarkable traits is referred to as the army ant syndrome. Despite molecular evidence that the army ant syndrome evolved twice during the mid-Cenozoic, once in the Neotropics and once in the Afrotropics, fossil army ants are markedly scarce, comprising a single known species from the Caribbean 16 Ma. Here we report the oldest army ant fossil and the first from the Eastern Hemisphere (EH), Dissimulodorylus perseus, preserved in Baltic amber dated to the Eocene. Using a combined morphological and molecular ultra conserved elements dataset spanning doryline lineages, we find that D. perseus is nested among extant EH army ants with affinities to Dorylus. Army ants are characterized by limited extant diversification throughout most of the Cenozoic; the discovery of D. perseus suggests an unexpected diversity of now-extinct army ant lineages in the Cenozoic, some of which were present in Continental Europe.

Synchrotron X-ray imaging of a dichasium cupule of Castanopsis from Eocene Baltic amber.

PREMISE OF THE STUDY: The Eocene Baltic amber deposit represents the largest accumulation of fossil resin worldwide, and hundreds of thousands of entrapped arthropods have been recovered. Although Baltic amber preserves delicate plant structures in high fidelity, angiosperms of the "Baltic amber forest" remain poorly studied. We describe a pistillate partial inflorescence of Castanopsis (Fagaceae), expanding the knowledge of Fagaceae diversity from Baltic amber. METHODS: The amber specimen was investigated using light microscopy and synchrotron-radiation-based X-ray micro-computed tomography (SRµCT). KEY RESULTS: The partial inflorescence is a cymule, consisting of an involucre of scales that surround all four pistillate flowers, indicating a dichasium cupule. Subtending bracts are basally covered with peltate trichomes. Flowers possess an urecolate perianth of six nearly free lobes, 12 staminodia hidden by the perianth, and a tri-locular ovary that is convex-triangular in cross section. The exceptional three-dimensional preservation suggests that the fossil belongs to the extant East Asian genus Castanopsis. The amber inclusion represents the first record of Castanopsis from Baltic amber and the first pistillate inflorescence of Fagaceae from Eurasia. CONCLUSIONS: The partial female inflorescence reported here provides an important addition to acorns of Castanopsis described from middle Eocene strata of Europe. Furthermore, the intercontinental distribution of Castanopsis in the Eocene is confirmed. The amber fossil also broadens the picture of the Baltic amber source area, indicating oligotrophic, sandy, bog-like habitats. Finally, this study underscores the great benefit of SRµCT as a powerful tool to investigate plant inclusions from amber in a nondestructive way.

Diverse early dwarf mistletoes (Arceuthobium), ecological keystones of the Eocene Baltic amber biota.

PREMISE OF THE STUDY: Extant dwarf mistletoes (Arceuthobium M. Bieb., Viscaceae) are hemiparasites with complex roles in nature. They are one of the most severe pests in northern hemisphere conifer forests, but they also enhance the structural complexity and species diversity of the forests. Here, we describe the first pre-Miocene macrofossils of dwarf mistletoes. The fossils from Eocene Baltic amber provide new insights into the morphological evolution of the Arceuthobium lineage and its paleobiogeography. METHODS: The amber inclusions were investigated with light microscopy and compared with extant Viscaceae and to historic descriptions of lost Baltic amber fossils with affinities to Viscaceae. KEY RESULTS: Six fossil species of the Arceuthobium lineage, A. johnianum comb. nov., A. mengeanum comb. nov., A. conwentzii sp. nov., A. groehnii sp. nov., A. viscoides comb. nov. and A. obovatum sp. nov., occurred in source forests of Baltic amber, representing the oldest macrofossil evidence of dwarf mistletoes. They share morphological features of their bracts, internodes, fruits, and stomata with extant Arceuthobium. Differences from extant dwarf mistletoes, such as the perianth merosity, the nonfusion of squamate bracts and presence of oblanceolate expanded leaves, indicate their affiliation to an ancient lineage of the genus. CONCLUSIONS: The occurrence of six species of dwarf mistletoes in a single amber deposit suggests Arceuthobium was a keystone taxon of the Baltic amber source area. As in extant conifer forests, they probably influenced the structural complexity of the forest, not only leading to more open woodlands but also increasing species diversity, at least at a microhabitat scale.

Microtomography of the Baltic amber tick Ixodes succineus reveals affinities with the modern Asian disease vector Ixodes ovatus.

BACKGROUND: Fossil ticks are extremely rare and Ixodes succineus Weidner, 1964 from Eocene (ca. 44-49 Ma) Baltic amber is one of the oldest examples of a living hard tick genus (Ixodida: Ixodidae). Previous work suggested it was most closely related to the modern and widespread European sheep tick Ixodes ricinus (Linneaus, 1758). RESULTS: Restudy using phase contrast synchrotron x-ray tomography yielded images of exceptional quality. These confirm the fossil's referral to Ixodes Latreille, 1795, but the characters resolved here suggest instead affinities with the Asian subgenus Partipalpiger Hoogstraal et al., 1973 and its single living (and medically significant) species Ixodes ovatus Neumann, 1899. We redescribe the amber fossil here as Ixodes (Partipalpiger) succineus. CONCLUSIONS: Our data suggest that Ixodes ricinus is unlikely to be directly derived from Weidner's amber species, but instead reveals that the Partipalpiger lineage was originally more widely distributed across the northern hemisphere. The closeness of Ixodes (P.) succineus to a living vector of a wide range of pathogens offers the potential to correlate its spatial and temporal position (northern Europe, nearly 50 million years ago) with the estimated origination dates of various tick-borne diseases.

A swarm of whiteflies--the first record of gregarious behavior from Eocene Baltic amber.

A new whitefly Snotra christelae gen. et sp. n. is characterized, illustrated, and described from the Baltic amber. It represents the first record of gregarious behavior of Aleyrodinae (Aleyrodidae) whiteflies in fossil state. Implications of this finding on interpretation of whiteflies and their host-plant relationships and evolutionary traits of the group are discussed.

Unexpected Diversity of Xenoscelinae in Priabonian European Amber: The Third Xenosceline Species from Rovno Amber.

Xenophagus simutniki sp. n. is described from a late Eocene Rovno amber specimen. The new species is similar to the fossil Xenophagus popovi Lyubarsky et Perkovsky, 2017 from the late Eocene Baltic amber (W Russia), differing in the medially notched anterior margin of the pronotum. The Rovno xenosceline fauna is the richest among both extant and extinct faunas. This fauna includes the extinct genera Xenophagus Lyubarsky & Perkovsky, 2017 and Xenohimatium Lyubarsky & Perkovsky, 2012, which are closest to the extant Mediterranean Xenoscelis Wollaston 1864 and the representative of the extant boreal genus Zavaljus Reitter, 1880. A key to extinct species of the subfamily Xenoscelinae is presented. The possible reasons of xenoscelines abundance in European amber forests are discussed.

Impact of increasing morphological information by micro-CT scanning on the phylogenetic placement of Darwin wasps (Hymenoptera, Ichneumonidae) in amber.

The correct interpretation of fossils and their reliable taxonomic placements are fundamental for understanding the evolutionary history of biodiversity. Amber inclusions often preserve more morphological information than compression fossils, but are often partially hidden or distorted, which can impede taxonomic identification. Here, we studied four new fossil species of Darwin wasps from Baltic and Dominican amber, using micro computed tomography (micro-CT) scans and 3D reconstructions to accurately interpret and increase the availability of morphological information. We then infer their taxonomic placement in a Bayesian phylogenetic analysis by combining morphological and molecular data of extant and fossil Darwin wasps and evaluate the impact and usefulness of the additional information from micro-CT scanning. The results show that although we gained significant morphological information from micro-CT scanning, especially concerning measurements and hidden dorsal and ventral structures, this did not impact subfamily-level placement for any of the four fossils. However, micro-CT scanning improved the precision of fossil placements at the genus level, which might be key in future dating and diversification analyses. Finally, we describe the four new fossil species as Rhyssa gulliveri sp. nov. in Rhyssinae, Triclistus levii sp. nov. in Metopiinae, Firkantus freddykruegeri gen. et. sp. nov. in Pimplinae and Magnocula sarcophaga gen. et sp. nov. in Phygadeuontinae. The first two species are the first known representatives of the subfamilies Rhyssinae and Metopiinae in amber. Supplementary Information: The online version contains supplementary material available at 10.1186/s13358-023-00294-2.

A fossil "Social Stomach": Micro-CT imaging unearths first fossil record of ant proventriculi and comparative analysis with recent species.

Eusociality is an extreme form of social behavior found in some invertebrates, especially in ants, which allows them to thrive and dominate the environment through their cooperative and organized behavior. Their complex colony structure and social behavior is provided, among other things, by morphological adaptations, such as the unique structure and a huge variety of proventriculi relative to other insect groups. Here, we report the first discovery of proventriculus by X-ray microcomputed tomography (µCT) in the fossil ants †Oecophylla brischkei Mayr, 1868 and †Oecophylla crassinoda Wheeler, 1922. This is a remarkable fossil find, as it opens up new perspectives for research on phylogeny, the evolution of ant sociality and feeding behavior. We present a 3D model of the proventriculus in Oecophylla smaragdina (Fabricius, 1775) and a 3D model of the proventriculus in †Oe. brischkei and compare them. Fossil proventriculi are not fundamentally different in structure from the recent. Apparently, already in the late Eocene, the lifestyle and sociality of ants of the genus Oecophylla were similar to the one we are currently observing.

The First Fossil Record of the Genus Manica Jurine, 1807 from Late Eocene Baltic Amber and Discussion of the Early Evolution of Myrmicini (Hymenoptera: Formicidae: Myrmicinae).

The Holarctic genus Manica Jurine, 1807 are mysterious and primitive ants from the tribe Myrmicini of the subfamily Myrmicinae. The first fossil species of this genus, †Manica andrannae Zharkov and Dubovikoff, sp. n. is described from the Baltic amber (ca. 33.9-37.8 million years ago). X-ray microcomputed tomography (µCT) was used to access morphological features and accurately measure the new species. A straightened and painted 3D model is also proposed as a reconstruction of the worker. The new species differs from all extant species of the genus by the propodeum with a weakly convex dorsum and short, blunt tubercles, and by more angular petiolar node. These features bring it closer to sister genus Myrmica Latreille, 1804. The phylogenetic relationships of the new species with other species of the genus are discussed. Based on the studied morphological features, the species is closest to the species Manica yessensis Azuma, 1955. The early evolution and paleobiogeography of the tribe Myrmicini are discussed. This finding confirms the origin of the genus Manica at least in the Eocene epoch.

Taxonomic description and phylogenetic placement of two new species of Spalangiopelta (Hymenoptera: Pteromalidae: Ceinae) from Eocene Baltic amber.

Spalangiopelta is a small genus of chalcid wasps that has received little attention despite the widespread distribution of its extant species. The fossil record of the genus is restricted to a single species from Miocene Dominican amber. We describe two new fossil species, Spalangiopelta darlingi sp. n. and Spalangiopelta semialba sp. n. from Baltic amber. The species can be placed within the extant genus Spalangiopelta based on the distinctly raised hind margin of the mesopleuron. 3D models reconstructed from µCT data were utilized to assist in the descriptions. Furthermore, we provide a key for the females of all currently known Spalangiopelta species. The phylogenetic placement of the fossils within the genus is analyzed using parsimony analysis based on morphological characters. Phylogenetic and functional relevance of two wing characters, admarginal setae and the hyaline break, are discussed. The newly described Baltic amber fossils significantly extend the minimum age of Spalangiopelta to the Upper Eocene.

Allocordyceps baltica gen. et sp. nov. (Hypocreales: Clavicipitaceae), an ancient fungal parasite of an ant in Baltic amber.

An ancient fungal parasite of a Camponotus ant (Formicidae: Hymenoptera) in Baltic amber is described as Allocordyceps baltica gen. et sp. nov. (Hypocreales: Clavicipitaceae). The new genus is characterized by an orange, stalked, cup-shaped ascoma with partially immersed perithecia that emerges from the rectum of the ant, two separate stromata with septate mycelium that emerge from the base of the neck and the abdomen of the ant, respectively, and free-standing putative perithecia bearing putative asci with putative multicellular ascospores fragmented into one-celled partspores. This oldest known fossil fungus of an ant could represent a precursor of the genus Ophiocordyceps, which at present is the only fungal lineage parasitizing ants of the genus Camponotus. The fossil shows unique morphological features that existed in the Hypocreales some 35-55 MYA.

A Baltic amber species of the diving beetle genus Coptotomus Say, 1830 (Coleoptera: Dytiscidae: Coptotominae).

We provide the first report of the Nearctic diving beetle subfamily Coptotominae Van den Branden, 1885 for the Paleactic Region, based on † Coptotomus balticus sp. n. from Baltic amber. Coptotomus Say, 1830 is otherwise distributed with five extant species and one subspecies in the Nearctic Region. The new species is the smallest species of the genus and thus readily separated from the extant taxa.

A new species of Proneuronema (Neuroptera: Hemerobiidae) from late Eocene Rovno amber.

Proneuronema sidorchukae sp. nov. (Neuroptera: Hemerobiidae: Drepanepteryginae) is described from the late Eocene Rovno amber, Ukraine. It is most similar to P. minor from Baltic amber, but easily distinguished from it by some crossveins in the third gradate series of the forewing broadly margined with dark brown, the proximal part of the costal space narrower, and proximal subcostal veinlets more oblique. The new species is the smallest known of the genus, with a forewing length of 5.9 mm. Rovno amber hemerobiids show a tendency to decrease in size compared to congeneric or conspecific specimens from Baltic amber. The morphology and terminology of the mesonotum in Hemerobiidae is discussed.

Entomopathogenic fungi (Hypocreales: Ophiocordycipitaceae) infecting bark lice (Psocoptera) in Dominican and Baltic amber.

Ophiocordyceps dominicanus Poinar & Vega sp. nov. in Dominican amber and Polycephalomyces baltica Poinar & Vega sp. nov. (Hypocreales: Ophiocordycipitaceae) in Baltic amber are described as entomopathogenic fungi of bark lice (Psocoptera). The specimens possess several features unknown in extant synnematous entomopathogenic fungi such as a tubular dark synnema with a straight, pointed tip bearing spores over the entire surface in O. dominicanus, and a globular yellowish synnema developing on the tip of the host's antenna in P. baltica. These are the only known fossil entomopathogenic fungi of bark lice, making them unique not only for their characters but also in respect to their selection of developmental sites on their bark lice hosts.

Poisonous setae on a Baltic amber caterpillar.

The knobbed setae on a small caterpillar in 45-55 million years old [Eocene] Baltic amber were studied and characterized as urticating, with evidence of liquid release implying the production of poisons. It is presumed that the caterpillar had been disturbed just prior to falling into the resin, as some of its setae showed defensive responses. The swollen tips of the setae are equipped with "trip hairs" and when disturbed, the tips release liquid deposits, some of which contain rod-like bodies. These setal responses to a disturbance are the first report of poisonous setal defense mechanisms in a fossil insect.

Neotype designation and re-description of Prolachlanius resinatus (Hagen) (Neuroptera, Hemerobiidae) from Baltic amber, with the first record of the species from Rovno amber.

Prolachlanius resinatus (Hagen) is re-described, based on five specimens from late Eocene Baltic amber (including the neotype designated herein) and the first recorded specimen from contemporaneous Rovno amber (Klesov locality). This is the most common species of Hemerobiidae in Baltic amber. The forewing venation of Prolachlanius is most similar to that of Sympherobius, and, therefore, its assignment to Sympherobiinae is confirmed. The genus differs from other Sympherobiinae by the distal branch of RP being not deeply forked, and the presence of crossvein 4r-m in the forewing. The male genitalia of Prolachlanius are sufficiently dissimilar from those of other Sympherobiinae to distinguish it as a separate genus, particularly by the structure of the ectoprocts, and the 8th and 9th sternites. The extremely short eighth sternite of Prolachlanius is especially noteworthy.

A new species of Succinoraphidia Aspöck amp; Aspöck, 2004 (Raphidioptera: Raphidiidae) from the late Eocene Rovno amber, with venation characteristics of the genus.

Succinoraphidia radioni sp. nov. (Raphidiidae) is described from the late Eocene Rovno amber, Ukraine. The genus also includes two species from contemporaneous Baltic amber, i.e., S. exhibens Aspöck Aspöck, 2004 and S. baltica (Carpenter, 1957), comb. nov. The venation of Succinoraphidia is analysed. It possesses several plesiomorphic character states at the family level, and the monotypic subfamily Succinoraphidinae represents a basal group within the family or possibly even a potential stem group of Raphidiidae. All diagnostic character states of Succinoraphidia (except the structure of the pterostigma) are found in a few Cretaceous species of the paraphyletic Mesoraphidiidae, but some of these are not found in the extant Raphidiidae.

The last batrachideine of Europe: A new genus and species of pygmy grasshopper (Orthoptera: Tetrigidae) from Eocene Baltic amber.

A new genus and species of pygmy grasshopper (Orthoptera: Tetrigidae) is described from Eocene Baltic amber. Danatettix hoffeinsorum gen. et sp. nov. is assigned to the subfamily Batrachideinae based on antennae with more than 19 antennomeres, sulcate mesofemora, and rectangular paranota. This species is readily distinguished from other batrachideines by a markedly produced vertex, pronotum with divergent internal and external lateral carinae, and highly setiferous female lateral basivalvular sclerite with scabrose integument. The morphology of Danatettix suggests placement within the here defined Tettigidea genus group (comprising Eutettigidea Hancock, 1914, Paurotarsus Hancock, 1900, and Tettigidea Scudder, 1862) and suggests that the latter had diverged from the new Scaria genus group (comprising Eotetrix Gorochov, 2012, Rehnidium Grant, 1956 and Scaria Bolívar, 1887) by the Early Eocene.

A new fossil soldier beetle (Coleoptera: Cantharidae: Malthininae) from Baltic amber.

The very abundant representatives of the genus Malthodes Kiesenwetter, 1852 from the Eocene amber forests show a remarkable diversity of body forms, especially regarding the last abdominal segments, both tergites and sternites. These structures are important during the mating. In the present work, we describe a new species, Malthodes gedanicus sp. nov. characterized by the last sternite elongated and apically divided into two long and flat squarish lobes with three tips of which the central is longest, and by the last tergite elongated and spatuliform apically. The phylogenetic relationships based only on the shape of the last abdominal segments remain unclear and the new species is very vaguely similar to M. trifurcatus Kiesenwetter, 1852.