Triassic amber
Previously unrecorded, the oldest Southern Pangea amber occurs in the Upper Triassic terrestrial deposits of the Fingal Valley Coal Measures (‘Fingal Tier’) of the Upper Parmeener Supergroup of Tasmania, where it was discovered in 2015 (Figs. 2A,C and S1) (see also the Supplementary Text). The amber is found as small (≤1.5 mm long), mostly clear fragments with inclusions representing bark fragments, plant pieces, miniscule organic debris, and microbe-like inclusions within the top of the sequence in Unit 4, which is characterized by volcanic lithic sandstone and coal measures, containing distinct Late Triassic Dicroidium floras of inferred Carnian age (~230 Ma), dated by palynomorph biostratigraphy; these remains were deposited with sediments of high sinuosity rivers in a temperate climate with favorable seasonal growth14. The Fingal Valley deposits reveal stark links with palynological assemblages of the Carnian in Europe, i.e. coeval taxa in the Dolomites in Italy, which comprise spores of inferred hygrophytic environments (Annulispora, Aulisporites, and tricassate spores, likely Camarozonosporites). The resin that Fingal Valley amber represents was probably secreted by conifers (e.g., Cheirolepidiaceae), comparable to other Late Triassic deposits containing amber. The distinctive cheirolepidiacean palynomorph, Classopollis, shares an approximately coeval first appearance in southeastern Australia15. It is unlikely to be a coincidence that the oldest Mesozoic ambers are dated as Carnian in age, an interval represented by the ‘Carnian Pluvial Event’16, a time of major climatic shifts, seemingly worldwide, associated with major volcanism that saw increased rainfall during the late early Carnian and lower rainfall at the end of this age. It was a perfect climatic recipe for the secretion of resins and the associated sedimentary regimes of fluvial cycles that preserve amber in the geologic record17,18. Whilst most Carnian amber has been found in a narrow low northern paleolatitude band, the new Carnian-aged amber from Fingal Valley, Tasmania, provides tantalizing new evidence of Pangean-wide, increased resin production during the Late Triassic.
Late Triassic to early Paleogene ambers of Southern Pangea and Southern Gondwana with representative amber specimens and site images from the Late Triassic, Late Cretaceous and early Paleogene. (A to C) Fingal Valley, northeastern Tasmania, Fingal Valley Coal Measures, Carnian, Upper Triassic. (A) Several amber pieces <2 mm from the coal measures. (B) 2 mm piece of amber with preserved bark and microbe-like inclusions. (C) Photograph of Fingal Valley Triassic amber site. (D to F) Waihere Bay, western Pitt Island, Chatham Islands, Tupuangi Formation, upper Cenomanian, lower Upper Cretaceous. (D) Conducting fieldwork in the richly fossiliferous sections of the southern Waihere Bay. (E) Well preserved in situ amber droplet 3.2 mm long. (F) Seed cone scales of Protodammara reimatamoriori Mays & Cantrill, 2019, image depicting in situ resin canals within the dispersed ovuliferous complexes. (G to I) Strahan, Macquarie Harbour, Macquarie Harbour Formation, Western Tasmania, lower Eocene. (G) Inclusion–rich amber piece. (H) Section of Macquarie Harbour Formation along Macquarie Harbour near Strahan with fossiliferous strata. William De Silva for scale. (I) Clear, glassy amber specimen. (J to L) Anglesea Coal Measures, Alcoa Mine, Victoria, Australia, upper middle Eocene. (J) Collecting samples at main amber site. (K) Piece of clear yellow Anglesea amber with inclusion of new dipteran (Ceratopogonidae). (L) In situ amber piece at primary site with Estwing rock pick for scale.
Cretaceous amber
Significant amounts of early Late Cretaceous (late Cenomanian–Turonian, ~96–92 Ma) amber19 have been recently recovered in 2015–2016 from the Tupuangi Formation of Pitt Island, Chathams Islands, eastern Zealandia (Fig. 2D–F) (see also the Supplementary Text). In contrast to the small tubular ambers reported previously as in situ resin canals within fossils of cupressaceous conifers (Fig. 2F)2, these Chatham ambers represent relatively large droplets, blebs and fragmented pieces (≤2 cm in diameter) throughout over 300 m of section. The base of the Tupuangi Formation consists of a sandstone to granule conglomerate facies, but the majority of the strata (>300 m thick) comprises a facies association of fine- to medium-grained sandstone interbedded with carbonaceous siltstone facies. The latter facies association hosts abundant organically-preserved plant fossil remains, including rare horizons of amber. Multiple paleosols with densely-spaced tree trunks in growth positions were observed, and numerous horizons of well-preserved vegetative remains that were dominated by conifers (primarily Cupressaceae, Podocarpaceae and Araucariaceae), but locally abundant ginkgos, seed ferns, angiosperms and ferns, and rare lycophytes and bryophytes20,21,22,23,24. These strata represent deposition in fluviodeltaic alluvial and coastal plains with intermittent swamps, oxbow lakes and/or mires19,20. The fossils represent south-polar (~80–70°S)25 forests thriving during a global greenhouse interval, while still attached to the West Antarctic sector of Gondwana prior to Late Cretaceous continental break-up26. Significantly, these terrestrial ecosystems are the most southerly recorded Cretaceous forests and the most southern occurrence of Cretaceous amber. The potential of finding arthropods in the Tupuangi Formation amber is high, especially given a recent report27 that describes three species of beetles as compression fossils from these deposits.
Late Cretaceous amber pieces (N = 5) from the Santonian (~86–84 Ma) Tuna-1 petroleum well in the Gippsland Basin of southern Victoria (see also the Supplementary Text), bolster the Cretaceous Australian record, represented by a sole report1 on the Otway Basin Turonian amber. The Tuna-1 amber is dated by its occurrence in the Golden Beach subgroup of the Latrobe Group and spore-pollen in the Tricolporites apoxyexinus Zone28. The Tuna-1 amber is represented by a dominance of mostly transparent with rare semi-opaque orange and rare red amber that ranges from lenticular, angular, wedge-shaped, and irregularly shaped pieces. Possible filamentous inclusions have been noted in amber pieces obtained at 2668.1 m depth; otherwise, only minor amounts of pyrite, pseudoinclusions sensu Thiel et al.29 and particulate debris have been noted in the amber. The lowermost levels containing amber at 2673.1 m is characterized by siltstone with dispersed organic matter, which is overlain by sandy siltstone with coalified wood fragments, massive siltstones with coal laminations and organic matter, and capped by partially sideratized siltstone with poorly developed laminations and minor bioturbation.
Paleogene amber
Early to mid-Paleocene (~66–62 Ma) amber has been recovered from the Department of Primary Industries (DPI) Core Lab in small amounts (N = 6) in 2013–2015 from drill cores in the Gippsland Basin of southern Victoria, Australia, in the petroleum well Barracouta-1 (spudded in December 1964; originally named the Gippsland Shelf-1 well) at 1967.9 m depth. This record is represented by translucent to semi-opaque orange and red amber devoid of inclusions to date, apart from particulate debris and pseudoinclusions29. This Paleocene amber from the lower Lygistepollenites balmeii spore-pollen Zone was deposited in sediments of the mid-Cretaceous to Eocene Latrobe Group, which mostly comprises fluvial, floodplain and coastal plain siliciclastics interspersed with thin coal beds30. Amber-bearing wells of the Gippsland Basin are located in the western portion of the Central Deep: an elongate, east-west striking depocenter that developed in response to rifting throughout the Late Cretaceous31. Bathymetry maps indicate that the amber-bearing wells only occur in the shallow portions of the Central Deep, with the most prolific deposits of the Tuna-1 well located along the shelf edge.
Early Eocene amber has been discovered recently in 2014 from the lower Paleogene Macquarie Harbour Formation of western Tasmania cropping out near and in the town of Strahan and along Macquarie Harbour (Figs. 2G–I and S1) (see also the Supplementary Text, discussing the primary collecting sites, including the Regatta Point Tavern and Railway Workshop areas). Our research indicates that this formation is much more extensive that previously reported and the base could well extend into the Paleocene. Entire droplets, runnels and variously shaped and sized fragmental pieces have been analyzed for inclusions. Most of the pieces are within the 1–2 mm range, but some exceed 20 mm. Palynological assessment has shown that the deposition of the resiniferous lignitic strata occurred during the Ypresian (middle to upper Malvacipollis diversus spore-pollen Zone; ~54–52 Ma)32, which marked a global and protracted greenhouse climate that saw a low to moderate thermal gradient from pole to equator33 and a possible increase in precipitation levels at high latitudes. Many ancestors of the modern tropical flora were able to disperse polewards and proliferate in areas that straddled the southern most regions of Gondwana. Strahan (42°S, 145°E), which is currently settled on the Macquarie Harbour, western Tasmania, was once situated at a latitude near the Antarctic Circle (66–64°S)34. During this time, the landscape was dominated by an interplay of channel and tidal systems, although the production, and consequent deposition, of resin potentially occurred within a freshwater swamp or estuary; this is evident from fine, highly carbonaceous silts and sand, the presence of sulphides that had subsequently oxidized, and the occurrence of mangrove Nypa and abundant dinoflagellates in the fossil record3. The early Eocene Tasmanian amber represents Class 1b ambers sensu Anderson et al.35. The botanic provenance of the amber is most likely to have been the conifer families Araucariaceae and/or Cupressaceae, as supported by FTIR and NMR analyses36, whilst macrofossils and pollen inclusions indicate the genera Agathis or Araucaria.
Abundant amber and associated diverse bioinclusions have been discovered in 2014 in the Anglesea Coal Measures near the town of Anglesea, Victoria, Australia. Late middle Eocene (~42–40 Ma; middle Nothofagidites asperus Zone)37 arthropods, plant matter, and fungal inclusions in amber have been identified from a single, continuous brown coal seam ~2 m thick directly overlying a paleosol with rootlets preserved (Figs. 2J–L and S1) (see also the Supplementary Text). The inclusions have been recovered from the ‘A Group Coal Seam’ in the middle–upper Eocene Eastern View Group, which comprises mostly non-marine claystone, sandstone and brown coal. The depositional environment of the Eastern View Group has been interpreted as a meandering river on a coastal plain with an indication of increasing marine influence up succession38,39. The preservation of the amber recovered from Anglesea varies from diagenetically altered pieces to well-preserved, vitreous examples with easily seen inclusions (Fig. 2K). The amber is mostly commonly light green or dark yellow and translucent with less common orange and red amber and rare white and brown amber. Most resin pieces are 1–2 mm long, but some exceed 40 mm with most being angular to subangular with fewer pieces being spherical and tabular in nature. Amber droplets are encountered within coal hand samples. Both Class Ib and Class II ambers35 were encountered at Anglesea. FTIR and NMR spectral data indicate that, as with the Tasmanian Macquarie Harbour Formation amber, Cupressaceae and/or Araucariaceae were primary botanical sources, but the Anglesea ambers also include one or more angiosperm groups with a chemical signature similar to Dipterocarpaceae36.
Animal, plant and fungi inclusions in Paleogene amber
Diverse inclusions of arthropods, plants and fungi have been discovered in both the Macquarie Harbour Formation (MHF) of western Tasmania, dated as early Eocene (~54–52 Ma), and the ‘A Group Coal Seam’ of the Anglesea Coal Measures (ACM), which is late middle Eocene in age (~42–40 Ma) (see also the Supplementary Text).
More than 2,530 amber pieces, representing a dominance of translucent pieces from deep red to clear, were assessed for bioinclusions in the MHF amber. Notably, two complete arthropods (an insect and a mite) have been identified along with an another decayed arthropod, possible evidence of termites, pieces of arthropods (femur, wing), coprolites, and nematodes; these nematodes (Fig. S1) are the oldest record of this group in the Southern Hemisphere, and the only previous occurrence being from the Miocene of New Zealand9. Palynological inclusions are observed, including an araucariacean pollen grain, along with fungal hyphae and probable fungal spores. Filamentous structures are detected in a number of specimens, as was disseminated organic material and potential plant structures, in addition to fungal mycelia. Many spherical inclusions of varying sizes are common with a high proportion being attributed to a different plant exudation that did not mix with the coeval resin exudation (named as pseudoinclusions by other authors). The complete insect is a coccoidean 1st instar, possibly of the family Eriococcidae (Fig. 3A), thus representing a major group of scale insects with a fossil record extending back into the mid-Cretaceous of Australasia40. The mite (Fig. 3B,C) is an oribatid nymph and probably belongs to the Enarthronota (most likely Hypochthoniidae or Brachychthoniidae, being both cosmopolitan edaphic families).
Arthropod bioinclusions in western Tasmania amber of Strahan, early Eocene. (A) Light photograph of a coccoidean 1st instar (Hemiptera: Sternorryncha: Coccoidea), possibly of the family Eriococcidae. (B to C) Light photograph in dorsal view and camera lucida drawing (Adobe Photoshop CS2, version 9.0; www.adobe.com) in lateral view of an oribatid nymph, probably belonging to the Infraorder Enarthronota (Arachnida: Acari: Acariformes; most likely family Hypochthoniidae or Brachychthoniidae).
The ACM amber biota comprises a multitude of animal, plant and fungal groups from a total of 3,291 amber pieces and the most bioinclusion-rich, in situ deposit recorded from Australia (Fig. 4). Fungi include hyphomycetean remains similar to the extant anamorphic genus Monotosporella (Fig. S1). Plant inclusions comprise well preserved non-vascular plants (i.e., bryophytes) of liverworts and mosses (the first in amber in the far south), a trichome, a petal, leaf bract, possible seeds, and a possible megaspore. Significantly, two species of the liverwort Radula (Radulaceae) have been recognized along with two moss species attributed to Racopilum (Racopilaceae) (Fig. 4A–C). Several arthropods (arachnids and hexapods) have been identified in the ACM amber, which include juvenile spiders in a cluster most likely formed after hatching for safety reasons until the next moult (Fig. 4D) and immature mites belonging to the Trombidiformes (Erythraeidae, Leptus Latreille, 1796). Hexapods are represented by some collembolans and diverse insect groups, as lepidopterans represented by diverse and abundant, isolated scales (Fig. S1), and flies of the families, Ceratopogonidae (or biting midges; Fig. 4H), Dolichopodidae (or long-legged flies, two of them in copula; Fig. 4I), and Tipulidae (or craneflies). Dolichopodidae have a fossil record extending to the Cretaceous with several records in the Paleogene in amber deposits worldwide. These predatory flies today eat springtails (also recorded in the ACM amber), aphids and a variety of larvae in a wide range of habitats near water or in meadows and woodland edges. Some are restricted to wet places including sands on the banks of water bodies, including saline water and also the intertidal zone adjacent to seashores. Significantly, the mating flies represent an extremely rare example of frozen behavior in the Australian fossil record. Ceratopogonidae is a globally distributed family. Its fossil record extends back into the Jurassic. Adults feed on nectar, but many females are haematophagous (blood suckers). Larvae live usually in moist environments. In Australia, the oldest record of this family is a poorly preserved compression fossil in the Early Cretaceous Koonwarra beds of Victoria, most likely belonging to the pantropical and relict genus Leptoconops Skuse, 188941. In our amber, the family is represented by two complete specimens, a male and a female, plus an incomplete specimen, all present in the same small portion of amber, representing the cosmopolitan genus Culicoides Latreille, 1809. More significant is a complete female specimen of the genus Meunierohelea Szadziewski, 1988 (Fig. S1), which persists in the Recent fauna with one extant species in Australia while its past distribution was wider, including Baltic, Bitterfeld, Rovno and Indian Cambay ambers42. Some other ceratopogonid relict genera are found as fossils in the Northern Hemisphere, revealing limited modern distributions in the Southern Hemisphere as Austroconops Wirth and Lee, 1958 (Australia), Metahelea Edwards, 1929 (Philippines and Australia) and Physohelea Grogan and Wirth, 1979 (Patagonia)43. Borkent and Craig44 proposed one hypothesis in which competition with Ceratopogonini (especially Culicoides) have replaced Austroconops from most of its historical range explaining this type of present distribution. Other degraded and partial insects include several other dipterans, a probable member of Tingidae or ‘lace bugs’ and a confirmed cockroach (Blattodea). Two collembolans belong to the so-called ‘slender springtails’ (Hexapoda: Entomobryidae) that, until now, had no fossil record in Australia, but are found elsewhere in the Eocene, including many specimens in Baltic amber. One of these specimens has been classified in the living genus Coecobrya (Fig. 4E,F). The fossil record of springtails is notably poor in the Southern Hemisphere, but Entomobryidae have already been recorded as amber inclusions from the late Oligocene–early Miocene of New Zealand9. Exquisitely preserved specimens of collembolans belonging to Symphypleona have been also recovered from the new ACM amber locality (Fig. 4G). Most significant are several winged and worker ants belonging to the myrmicine genus Monomorium, according to the current status of this non-monophyletic genus (they are very similar to the synonymized Chelaner), or a “Monomorium-like” lineage. The specimens exhibit a unique combination of characters indicating that most likely this is the fourth known fossil species of Monomorium (Figs. 4J, 5, 6 and S2) and the first recorded in the Southern Hemisphere45. In the Recent biota, Monomorium mostly inhabits the Old World, particularly the tropics, and Australia is considered one of the two main centers of speciation. These new fossil ants are the oldest from Southern Gondwana and unveil the antiquity of many elements in the modern Australian biotas.
Significant bioinclusions of plants and animals in Southern Gondwana late middle Eocene amber of Anglesea, Victoria. (A to B) Liverworts of the genus Radula (Marchantiophyta: Radulaceae). (C) Two stems with perfectly preserved phyllids or leaf-like structures of mosses of the genus Racopilum (Bryophyta: Racopilaceae). (D) Juvenile individuals of spiders. (E to F) Springtail of the living genus Coecobrya (Entomobryomorpha: Entomobryidae) in two views. (G) A Symphypleona springtail. (H) Light photograph of large piece of yellow amber with two dipterans, Dolichopodidae at left and Ceratopogonidae at right, and at top of image a mite of the living genus Leptus (Arachnida: Acari: Trombidiformes: Erythraeidae). (I) Dipterans of the family Dolichopodidae (long-legged flies) in copula. (J) Worker ant of the living genus Monomorium or a “Monomorium-like” lineage (Hymenoptera: Formicoidea: Formicidae) (see Fig. S2).
Reconstruction with anatomical features of the second fossil ant discovered in Australasia and the oldest from Southern Gondwana. The reconstruction of this worker ant corresponds to a new myrmicine species belonging to the extant genus Monomorium or a “Monomorium-like” lineage discovered in late middle Eocene amber of Anglesea, Victoria (see Fig. 4J). It is based on several specimens (also see Fig. S2), and the body color pattern is conjectural, but aligns with the common pattern found in extant Monomorium ants. Performed using Light-Wave 3D computer graphics program (NewTek; www.newtek.com/lightwave/) (Artist: J.A. Peñas).
Paleobiological reconstruction of the new “Monomorium” ant and the liverwort Radula sp. The ants and liverwort are represented on a resiniferous conifer tree trunk, and this scenario is reconstructed from the assemblage preserved in late middle Eocene amber of Anglesea, Victoria. Performed using Light-Wave 3D computer graphics program (NewTek; www.newtek.com/lightwave/) (Artist: J.A. Peñas).
Source: Ecology - nature.com
