A diverse insect assemblage of exceptionally preserved debris carriers is reported from Cretaceous Burmese, French, and Lebanese ambers.

Amber is fossilized tree resin, and inclusions usually comprise terrestrial and, rarely, aquatic organisms. Marine fossils are extremely rare in Cretaceous and Cenozoic ambers. Here, we report a record of an ammonite with marine gastropods, intertidal isopods, and diverse terrestrial arthropods as syninclusions in mid-Cretaceous Burmese amber. We used X-ray–microcomputed tomography (CT) to obtain high-resolution 3D images of the ammonite, including its sutures, which are diagnostically important for ammonites. The ammonite is a juvenile Puzosia (Bhimaites) and provides supporting evidence for a Late Albian–Early Cenomanian age of the amber. There is a diverse assemblage (at least 40 individuals) of arthropods in this amber sample from both terrestrial and marine habitats, including Isopoda, Acari (mites), Araneae (spiders), Diplopoda (millipedes), and representatives of the insect orders Blattodea (cockroaches), Coleoptera (beetles), Diptera (true flies), and Hymenoptera (wasps). The incomplete preservation and lack of soft body of the ammonite and marine gastropods suggest that they were dead and underwent abrasion on the seashore before entombment. It is most likely that the resin fell to the beach from coastal trees, picking up terrestrial arthropods and beach shells and, exceptionally, surviving the high-energy beach environment to be preserved as amber. Our findings not only represent a record of an ammonite in amber but also provide insights into the taphonomy of amber and the paleoecology of Cretaceous amber forests.

Burmese amber represents the world’s most diverse biota in the Mesozoic. Previous studies have focused on the biodiversity of its inclusions, as well as pholadid borings. Here we report a variety of marine animals symbiotic with or adhere to Burmese amber or the amber deposits, including crinoid columns, corals and oysters. We propose that there is no distinct evidence indicating the secondary transportation of Burmese amber over long distances. The ancient sedimentary environment was likely located in the coastal area. The hardening time of the resin was not long after secretion. The resin has been mixed with fragments of marine organisms in the ancient sediments, and has been deposited for a long time. The zircon age in the sediments surrounding amber approximately represents the age of Burmese amber, but due to limits of the method, the current zircon U-Pb SIMS age may be younger. Therefore, as far as the situation is concerned, the age of Burmese amber may be close to the boundary between the Albian and Cenomanian, or even late Albian. We suggest that it is plausible to generally refer to the age of Burmese amber as mid-Cretaceous, and a precise age requires further biostratigraphic and chronological studies.

Camouflage and mimicry are staples among predator-prey interactions, and evolutionary novelties in behavior, anatomy, and physiology that permit such mimesis are rife throughout the biological world [1, 2]. These specializations allow for prey to better evade capture or permit predators to more easily approach their prey, or in some cases, the mimesis can serve both purposes. Despite the importance of mimesis and camouflage in predator-avoidance or hunting strategies, the long-term history of these traits is often obscured by an insufficient fossil record. Here, we report the discovery of Upper Cretaceous (approximately 100 million years old) green lacewing larvae (Chrysopoidea), preserved in amber from northern Myanmar, anatomically modified to mimic coeval liverworts. Chrysopidae are a diverse lineage of lacewings whose larvae usually camouflage themselves with a uniquely constructed packet of exogenous debris, conveying greater stealth upon them as they hunt prey such as aphids as well as evade their own predators [3, 4]. However, no lacewing larvae today mimic their surroundings. While the anatomy of Phyllochrysa huangi gen. et sp. nov. allowed it to avoid detection, the lack of setae or other anatomical elements for entangling debris as camouflage means its sole defense was its mimicry, and it could have been a stealthy hunter like living and other fossil Chrysopoidea or been an ambush predator aided by its disguise. The present fossils demonstrate a hitherto unknown life-history strategy among these "wolf in sheep's clothing" predators, one that apparently evolved from a camouflaging ancestor but did not persist within the lineage.

Understanding the genealogical relationships among the arachnid orders is an onerous task, but fossils have aided in anchoring some branches of the arachnid tree of life. The discovery of Palaeozoic fossils with characters found in both extant spiders and other arachnids provided evidence for a series of extinctions of what was thought to be a grade, Uraraneida, that led to modern spiders. Here, we report two extraordinarily well-preserved Mesozoic members of Uraraneida with a segmented abdomen, multi-articulate spinnerets with well-defined spigots, modified male palps, spider-like chelicerae and a uropygid-like telson. The new fossils, belonging to the species Chimerarachne yingi, were analysed phylogenetically in a large data matrix of extant and extinct arachnids under a diverse regime of analytical conditions, most of which resulted in placing Uraraneida as the sister clade of Araneae (spiders). The phylogenetic placement of this arachnid fossil extends the presence of spinnerets and modified palps more basally in the arachnid tree than was previously thought. Ecologically, the new fossil extends the record of Uraraneida 170 million years towards the present, thus showing that uraraneids and spiders co-existed for a large fraction of their evolutionary history.