Microbioerosion structures are a common sign of microbial activity known mainly from marine environments and calcareous substrates, or from pollen records. However, the same phenomenon has been overlooked in animal fossils preserved in lake sediments. We studied 430 fragments of chitinous microfossils from three central European glacial lakes and detected microboring structures in approximately 10%. The microfossils belong to two size groups: (1) spherical objects with lengths ranging from 50 to 300 µm that are probably microturbelarian (Turbellaria: Rhabdocoela) cocoons, and (2) larger remnants (up to 2 mm long) of caddisfly (Insecta: Trichoptera) frontoclypeal apotomes. Four microbioerosion morphotypes were distinguished: (1) small holes (< 0.6 µm) oriented perpendicular to microfossil walls, likely produced by bacteria or fungi; (2) simple meandering tunnels and; (3) asterisk-like tunnel structures produced by fungi and/or fungus-like organisms; and (4) abrasions caused by biofilms. The maximum diameter of the simple holes and both tunnel structures depended on host-microfossil size: a higher diversity of microbioerosions was found on larger chitinous fragments. We propose that the good preservation of microfossils in the studied sediment samples might be due to rapid transport to the anoxic profundal zone or by rapid burial in anoxic sediments.

The Ordovician (485–444 Ma) saw a global shift from microbial- to skeletal-dominated reefs, and the rise of corals and bryozoans as important reef-builders. Hypothetically, increasingly morphologically diverse and abundant reef-building metazoans increased spatial habitat heterogeneity in reef environments, an important component of reefs' capacity to support diverse communities. Quantifying the spatial scale and extent of this heterogeneity requires three-dimensional exposures of well-preserved reefs whose composition and spatial arrangement can be measured. The Darriwilian (c. 467–458 Ma) carbonate sequence of the Mingan Archipelago, Quebec, presents such exposures, and also provides an opportunity to establish how the distribution of skeletal-dominated metazoan reefs contributed to, and was influenced by, seafloor relief. This study includes two transects through a 200–300 m wide paleo-reef belt, which developed along a rocky paleo-coast line. The reefs are typically micrite-rich, meter-scale mounds, locally forming larger complexes. Here, we present quantitative evaluations of the composition of these reefs, and detailed mapping of reef distributions. There is high compositional heterogeneity between reefs at spatial scales ranging from meters to kilometers, contributed by differences in the volumetric contribution of skeletal material to the reef core, and in the identity of the dominant reef-builders. We suggest that the abundance and morphological diversity of Middle Ordovician reef building metazoans made them important contributors to environmental and substrate heterogeneity, likely enhancing the diversity of reef-dwelling communities.

A distinctive burrow form, Reniformichnus australis n. isp., is described from strata immediately overlying and transecting the end-Permian extinction (EPE) horizon in the Sydney Basin, eastern Australia. Although a unique excavator cannot be identified, these burrows were probably produced by small cynodonts based on comparisons with burrows elsewhere that contain body fossils of the tracemakers. The primary host strata are devoid of plant remains apart from wood and charcoal fragments, sparse fungal spores, and rare invertebrate traces indicative of a very simplified terrestrial ecosystem characterizing a ‘dead zone’ in the aftermath of the EPE. The high-paleolatitude (∼ 65–75°S) setting of the Sydney Basin, together with its higher paleoprecipitation levels and less favorable preservational potential, is reflected by a lower diversity of vertebrate fossil burrows and body fossils compared with coeval continental interior deposits of the mid-paleolatitude Karoo Basin, South Africa. Nevertheless, these burrows reveal the survivorship of small tetrapods in considerable numbers in the Sydney Basin immediately following the EPE. A fossorial lifestyle appears to have provided a selective advantage for tetrapods enduring the harsh environmental conditions that arose during the EPE. Moreover, high-paleolatitude and maritime settings may have provided important refugia for terrestrial vertebrates at a time of lethal temperatures at low-latitudes and aridification of continental interiors.