Paul C. Nascimbene

Fossiliferous Cretaceous amber from Myanmar (Burma): Its rediscovery, biotic diversity, and paleontological significance

Abstract Amber from Kachin, northern Burma, has been used in China for at least a millennium for carving decorative objects, but the only scientific collection of inclusion fossils, at the Natural History Museum, London (NHML), was made approximately 90 years ago. Age of the material was ambiguous, but probably Cretaceous. Numerous new records and taxa occur in this amber, based on newly excavated material in the American Museum of Natural History (AMNH) containing 3100 organisms. Without having all groups studied, significant new records and taxa thus far include the following (a † refers to extinct taxa): For Plants: An angiosperm flower (only the third in Cretaceous amber), spores and apparent sporangia of an unusual but common fungus, hepatophyte thalli and an archegoniophore of Marchantiaceae, and leafy shoots of Metasequoia (Coniferae). Metasequoia is possibly the source of the amber. For Animals: Mermithidae and other Nematoda; the oldest ixodid tick (a larval Amblyomma); bird feathers; and the only Mesozoic record of the Onychophora (“velvet” worms), described as †Cretoperipatus burmiticus, n. gen., n. sp. (Peripatidae). Poinars classification of the Onychophora is substantially revised. Still largely unstudied, the fauna of mites (Acari) and spiders (Araneae) appears to be the most diverse ones known for the Mesozoic. For Insecta: Odonata indet. (wing fragment); Plecoptera indet.; new genera of Dermaptera, Embiidina, and Zoraptera (the latter two as the only definitive Mesozoic fossils of their orders). Within Hemiptera, there are primitive new genera in the Aradidae, Hydrometridae, Piesmatidae, Schizopteridae, and Cimicomorpha (Heteroptera), as well as in †Tajmyraphididae (Aphidoidea), and †′otopsyllidiidae. An adult snakefly (Raphidioptera: †Mesoraphidiidae) is the smallest species in the order, and new genera occur in the Neuroptera: Coniopterygidae, Berothidae, and Psychopsidae, as well as larvae of apparent Nevrorthidae. Coleoptera are largely unstudied, but are probably the most diverse assemblage known from the Cretaceous, particularly for Staphylinidae. An adult lymexylid, the most primitive species of Atractocerus, is the first Mesozoic record of the family. In Hymenoptera there are primitive ants (Formicidae: Ponerinae n. gen., and †Sphecomyrma n.sp [Sphecomyrminae]), the oldest record of the Pompilidae, and significant new records of †Serphitidae and †Stigmaphronidae, among others. Diptera are the most diverse and abundant, with the oldest definitive Blephariceridae and mosquito (Culicidae), as well as new genera in the Acroceridae, Bibionidae, Empidoidea; a new genus near the enigmatic genus Valeseguya, and an unusual new genus in the †Archizelmiridae. †Chimeromyia (Diptera: Eremoneura), known previously in ambers from the Lower Cretaceous, is also represented. The stratigraphic distribution of exclusively Mesozoic arthropods in Burmese amber is reviewed, which indicates a probable Turonian-Cenomanian age of this material (90–100 Ma). Paleofaunal differences between the NHML and AMNH collections are discussed, as is the distinct tropical nature of the original biota. Burmese amber probably harbors the most diverse biota in amber from the Cretaceous, and one of the most diverse Mesozoic microbiotas now known.

Biogeographic and evolutionary implications of a diverse paleobiota in amber from the early Eocene of India

For nearly 100 million years, the India subcontinent drifted from Gondwana until its collision with Asia some 50 Ma, during which time the landmass presumably evolved a highly endemic biota. Recent excavations of rich outcrops of 50–52-million-year-old amber with diverse inclusions from the Cambay Shale of Gujarat, western India address this issue. Cambay amber occurs in lignitic and muddy sediments concentrated by near-shore chenier systems; its chemistry and the anatomy of associated fossil wood indicates a definitive source of Dipterocarpaceae. The amber is very partially polymerized and readily dissolves in organic solvents, thus allowing extraction of whole insects whose cuticle retains microscopic fidelity. Fourteen orders and more than 55 families and 100 species of arthropod inclusions have been discovered thus far, which have affinities to taxa from the Eocene of northern Europe, to the Recent of Australasia, and the Miocene to Recent of tropical America. Thus, India just prior to or immediately following contact shows little biological insularity. A significant diversity of eusocial insects are fossilized, including corbiculate bees, rhinotermitid termites, and modern subfamilies of ants (Formicidae), groups that apparently radiated during the contemporaneous Early Eocene Climatic Optimum or just prior to it during the Paleocene-Eocene Thermal Maximum. Cambay amber preserves a uniquely diverse and early biota of a modern-type of broad-leaf tropical forest, revealing 50 Ma of stasis and change in biological communities of the dipterocarp primary forests that dominate southeastern Asia today.

Arthropods in amber from the Triassic Period

The occurrence of arthropods in amber exclusively from the Cretaceous and Cenozoic is widely regarded to be a result of the production and preservation of large amounts of tree resin beginning ca. 130 million years (Ma) ago. Abundant 230 million-year-old amber from the Late Triassic (Carnian) of northeastern Italy has previously yielded myriad microorganisms, but we report here that it also preserves arthropods some 100 Ma older than the earliest prior records in amber. The Triassic specimens are a nematoceran fly (Diptera) and two disparate species of mites, Triasacarus fedelei gen. et sp. nov., and Ampezzoa triassica gen. et sp. nov. These mites are the oldest definitive fossils of a group, the Eriophyoidea, which includes the gall mites and comprises at least 3,500 Recent species, 97% of which feed on angiosperms and represents one of the most specialized lineages of phytophagous arthropods. Antiquity of the gall mites in much their extant form was unexpected, particularly with the Triassic species already having many of their present-day features (such as only two pairs of legs); further, it establishes conifer feeding as an ancestral trait. Feeding by the fossil mites may have contributed to the formation of the amber droplets, but we find that the abundance of amber during the Carnian (ca. 230 Ma) is globally anomalous for the pre-Cretaceous and may, alternatively, be related to paleoclimate. Further recovery of arthropods in Carnian-aged amber is promising and will have profound implications for understanding the evolution of terrestrial members of the most diverse phylum of organisms.

Cretaceous African life captured in amber.

Amber is of great paleontological importance because it preserves a diverse array of organisms and associated remains from different habitats in and close to the amber-producing forests. Therefore, the discovery of amber inclusions is important not only for tracing the evolutionary history of lineages with otherwise poor fossil records, but also for elucidating the composition, diversity, and ecology of terrestrial paleoecosystems. Here, we report a unique find of African amber with inclusions, from the Cretaceous of Ethiopia. Ancient arthropods belonging to the ants, wasps, thrips, zorapterans, and spiders are the earliest African records of these ecologically important groups and constitute significant discoveries providing insight into the temporal and geographical origins of these lineages. Together with diverse microscopic inclusions, these findings reveal the interactions of plants, fungi and arthropods during an epoch of major change in terrestrial ecosystems, which was caused by the initial radiation of the angiosperms. Because of its age, paleogeographic location and the exceptional preservation of the inclusions, this fossil resin broadens our understanding of the ecology of Cretaceous woodlands.

Ectomycorrhizas from a Lower Eocene angiosperm forest.

The development of mycorrhizal associations is considered a key innovation that enabled vascular plants to extensively colonize terrestrial habitats. Here, we present the first known fossil ectomycorrhizas from an angiosperm forest. Our fossils are preserved in a 52 million-yr-old piece of amber from the Tadkeshwar Lignite Mine of Gujarat State, western India. The amber was produced by representatives of Dipterocarpaceae in an early tropical broadleaf forest. The ectomycorrhizas were investigated using light microscopy and field emission scanning electron microscopy. Dissolving the amber surrounding one of the fossils allowed ultrastructural analyses and Raman spectroscopy. Approx. 20 unramified, cruciform and monopodial-pinnate ectomycorrhizas are fossilized adjacent to rootlets, and different developmental stages of the fossil mycorrhizas are delicately preserved in the ancient resin. Compounds of melanins were detectable in the dark hyphae. The mycobiont, Eomelanomyces cenococcoides gen. et spec. nov., is considered to be an ascomycete; the host is most likely a dipterocarp representative. An early ectomycorrhizal association may have conferred an evolutionary advantage on dipterocarps. Our find indicates that ectomycorrhizas occurred contemporaneously within both gymnosperms (Pinaceae) and angiosperms (Dipterocarpaceae) by the Lower Eocene.

Crown Group Lejeuneaceae and Pleurocarpous Mosses in Early Eocene (Ypresian) Indian Amber

Cambay amber originates from the warmest period of the Eocene, which is also well known for the appearance of early angiosperm-dominated megathermal forests. The humid climate of these forests may have triggered the evolution of epiphytic lineages of bryophytes; however, early Eocene fossils of bryophytes are rare. Here, we present evidence for lejeuneoid liverworts and pleurocarpous mosses in Cambay amber. The preserved morphology of the moss fossil is inconclusive for a detailed taxonomic treatment. The liverwort fossil is, however, distinctive; its zig-zagged stems, suberect complicate-bilobed leaves, large leaf lobules, and small, deeply bifid underleaves suggest a member of Lejeuneaceae subtribe Lejeuneinae (Harpalejeunea, Lejeunea, Microlejeunea). We tested alternative classification possibilities by conducting divergence time estimates based on DNA sequence variation of Lejeuneinae using the age of the fossil for corresponding age constraints. Consideration of the fossil as a stem group member of Microlejeunea or Lejeunea resulted in an Eocene to Late Cretaceous age of the Lejeuneinae crown group. This reconstruction is in good accordance with published divergence time estimates generated without the newly presented fossil evidence. Balancing available evidence, we describe the liverwort fossil as the extinct species Microlejeunea nyiahae, representing the oldest crown group fossil of Lejeuneaceae.

A new Dominican amber fossil of the derived fern genus Pleopeltis confirms generic stasis in the epiphytic fern diversity of the West Indies

One of the grand objectives in the integration of fossils and phylogenetics is to obtain support for macroecological and macroevolutionary hypotheses. Here, we provide new evidence from Dominican amber fossils, which supports a likely stasis in the generic composition of epiphytic plant communities in the West Indies for at least 16 million years. The proposed hypothesis is based on the discovery of the first fossil of the Neotropical fern genus Pleopeltis. The relationships of this specimen to extant genera are studied using a dated phylogenetic framework to reconstruct the evolution of the characters preserved in the fossil, as well as by exploring the phylomorphospace of Pleopeltis. The fossil corroborates divergence time estimates obtained independently and also suggests the conservation of the generic composition of epiphytic communities. We discovered evidence for conserved morphotypes in the genus Pleopeltis occurring from the mid-Miocene to the present. The innovative use of phylomorphospace reconstruction provided crucial information about the affinities of the fossil. Rather than relying on reconstructing the evolution of single characters, this analysis integrates the evolution of all informative characters observed to evaluate relationships of the fossilized morphotype to extant morphotypes.

Seeking carotenoid pigments in amber-preserved fossil feathers

Plumage colours bestowed by carotenoid pigments can be important for visual communication and likely have a long evolutionary history within Aves. Discovering plumage carotenoids in fossil feathers could provide insight into the ecology of ancient birds and non-avian dinosaurs. With reference to a modern feather, we sought chemical evidence of carotenoids in six feathers preserved in amber (Miocene to mid-Cretaceous) and in a feather preserved as a compression fossil (Eocene). Evidence of melanin pigmentation and microstructure preservation was evaluated with scanning electron and light microscopies. We observed fine microstructural details including evidence for melanin pigmentation in the amber and compression fossils, but Raman spectral bands did not confirm the presence of carotenoids in them. Carotenoids may have been originally absent from these feathers or the pigments may have degraded during burial; the preservation of microstructure may suggest the former. Significantly, we show that carotenoid plumage pigments can be detected without sample destruction through an amber matrix using confocal Raman spectroscopy.

The termites of Early Eocene Cambay amber, with the earliest record of the Termitidae (Isoptera)

Abstract The fauna of termites (Isoptera) preserved in Early Eocene amber from the Cambay Basin (Gujarat, India) are described and figured. Three new genera and four new species are recognized, all of them Neoisoptera – Parastylotermes krishnai Engel & Grimaldi, sp. n. (Stylotermitidae); Prostylotermes kamboja Engel & Grimaldi, gen. et sp. n. (Stylotermitidae?); Zophotermes Engel, gen. n., with Zophotermes ashoki Engel & Singh, sp. n. (Rhinotermitidae: Prorhinotermitinae); and Nanotermes isaacae Engel & Grimaldi, gen. et sp. n. (Termitidae: Termitinae?). Together these species represent the earliest Tertiary records of the Neoisoptera and the oldest definitive record of Termitidae, a family that comprises >75% of the living species of Isoptera. Interestingly, the affinities of the Cambay amber termites are with largely Laurasian lineages, in this regard paralleling relationships seen between the fauna of bees and some flies. Diversity of Neoisoptera in Indian amber may reflect origin of the amber deposit in Dipterocarpaceae forests formed at or near the paleoequator.

Variation in the Deterioration of Fossil Resins and Implications for the Conservation of Fossils in Amber

ABSTRACT The deterioration of fossil resins (crazing, cracking, and darkening) was investigated by comparing the effects of one year of accelerated aging—specifically intensive exposure to light, heat, and fluctuating humidity, both individually and in combination—on samples from several natural resin deposits. These included two Cretaceous ambers (from Myanmar [Burma] and central New Jersey), two Tertiary ambers (from the Baltic and the Dominican Republic), and Holocene copal from Zanzibar. The five resins were chosen for their disparate ages and botanical origins (and thus chemical and physical properties), as well as their paleontological significance. In all cases, pronounced deterioration occurred under combined exposure to light and fluctuating humidity, based on surface crazing and a decrease in absorbance of light in the UV region (360–400 nm). While crazing did not visibly occur in cases of fluctuating humidity in dark conditions, or UV exposure alone, spectrophotometric evidence indicates that some deterioration did take place. Yellowing after exposure to elevated temperatures occurred in all samples tested, with the exception of Burmese amber. All four true ambers exhibited a decrease in UV absorbance after exposure to heat (while copal actually showed an increase). The samples from the five deposits represent three chemical subclasses of fossil resins, and each of the resins reacted differently to the various aging conditions, with New Jersey amber particularly unstable. Based on these results, amber collections should be stored in an environment with stable humidity, relatively low heat, and minimal exposure to light. Anoxic sealing and storage, and particularly embedding amber samples in a high-grade epoxy, may be beneficial, and further investigation is indicated.