Unlocking preservation bias in the amber insect fossil record through experimental decay.

Fossils entombed in amber are a unique resource for reconstructing forest ecosystems, and resolving relationships of modern taxa. Such fossils are famous for their perfect, life-like appearance. However, preservation quality is vast with many sites showing only cuticular preservation, or no fossils. The taphonomic processes that control this range are largely unknown; as such, we know little about potential bias in this important record. Here we employ actualistic experiments, using, fruit flies and modern tree resin to determine whether resin type, gut microbiota, and dehydration prior to entombment affects decay. We used solid phase microextraction gas chromatography-mass spectrometry (SPME GC-MS) to confirm distinct tree resin chemistry; gut microbiota of flies was modified using antibiotics and categorized though sequencing. Decay was assessed using phase contrast synchrotron tomography. Resin type demonstrates a significant control on decay rate. The composition of the gut microbiota was also influential, with minor changes in composition affecting decay rate. Dehydration prior to entombment, contrary to expectations, enhanced decay. Our analyses show that there is potential significant bias in the amber fossil record, especially between sites with different resin types where ecological completeness and preservational fidelity are likely affected

Changes to the Fossil Record of Insects through Fifteen Years of Discovery

The first and last occurrences of hexapod families in the fossil record are compiled from publications up to end-2009. The major features of these data are compared with those of previous datasets (1993 and 1994). About a third of families (>400) are new to the fossil record since 1994, over half of the earlier, existing families have experienced changes in their known stratigraphic range and only about ten percent have unchanged ranges. Despite these significant additions to knowledge, the broad pattern of described richness through time remains similar, with described richness increasing steadily through geological history and a shift in dominant taxa, from Palaeoptera and Polyneoptera to Paraneoptera and Holometabola, after the Palaeozoic. However, after detrending, described richness is not well correlated with the earlier datasets, indicating significant changes in shorter-term patterns. There is reduced Palaeozoic richness, peaking at a different time, and a less pronounced Permian decline. A pronounced Triassic peak and decline is shown, and the plateau from the mid Early Cretaceous to the end of the period remains, albeit at substantially higher richness compared to earlier datasets. Origination and extinction rates are broadly similar to before, with a broad decline in both through time but episodic peaks, including end-Permian turnover. Origination more consistently exceeds extinction compared to previous datasets and exceptions are mainly in the Palaeozoic. These changes suggest that some inferences about causal mechanisms in insect macroevolution are likely to differ as well

Volatile and semi-volatile composition of Cretaceous amber

Chemical analysis of amber, copal, and resin is a valuable tool for interpreting the botanic origin of amber and the ecological role of resin in ancient forests. Here we investigated for the first time the volatile and semi-volatile composition of Cretaceous amber, as well as copal and Defaunation resin produced by trees of the family Araucariaceae (Gymnospermae: Pinidae), via solid-phase microextraction gas chromatography-mass spectrometry. Principal component analysis (PCA) revealed a clear distinction between the Pleistocene copal/Defaunation resin and the much older Cretaceous amber samples. However, even among the younger resin samples whose plant producers were identified to the species level, the PCA did not clearly distinguish the groups, either at the species level or at the genus level. Therefore, even with ideal preservation of original chemistry, PCA of SPME GC/MS data will not differentiate varying botanic origins in the Cretaceous amber samples. There was extensive variation observed in the composition of the amber samples, but no separate groups in the PCA. This amber chemistry was most likely influenced by multiple factors, such as variable original resin chemistry and variable maturation as the most relevant. The Cretaceous amber deposits are proposed to represent forests with multiple taxa (even multiple families) of resin-producing trees, which varied over space and time, rather than representing a widespread and homogenous forest. As resin composition is strongly affected by both taxonomy of the resin-producing tree and ecological factors such as herbivory and pathogens, we propose that these forests were exposed to varying combinations of ecological factors

The taxonomic impediment: A shortage of taxonomists, not the lack of technical approaches

For almost 30 years, there have been active discussions about the taxonomic impediment and the challenge this represents to address the current human-induced biodiversity crisis. From the start (Systematics Agenda 2000, 1994), the term ‘taxonomic impediment’ has been ambiguous, designating both the insufficiency and inadequacy of the resources put to the service of taxonomy (the taxonomic impediment sensu stricto) and its main consequence, the wide discrepancy between the reality of specific biodiversity and our knowledge of it (the taxonomic gap; Dubois, 2010; Raposo et al., 2020). The total number of species on our planet is unknown, and its various estimates (using different methods) are widely divergent, but consensus exists that we are far from having inventoried half, and most likely one-tenth, of the species still present on earth today (González-Oreja, 2008)