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The colors of many animals arise from ordered nanometer-scale variations in tissue structure. Such structural colors—especially those with metallic optical effects—are widespread among modern insects but are preserved rarely in insect fossils. This suggests that a specific set of taphonomic circumstances is required for preservation of structural colors. Here we present the results of the first systematic investigation of the controls on the preservation of structurally colored tissues in fossil insects. Approximately 700 specimens of beetle taxa known to exhibit metallic structural colors were studied from seven Lagerstätten: Randecker Maar (early Miocene), Clarkia (early Miocene), Enspel (late Oligocene), Florissant (late Eocene), Eckfeld (middle Eocene), Messel (middle Eocene), and Green River (middle Eocene). The quality of preservation of metallic colors varies among, and within, these biotas; colors are well preserved in most specimens from Clarkia, Enspel, Eckfeld, and Messel, but are typically poorly preserved in specimens from Randecker Maar and absent in Florissant and Green River. These differences are independent of taxonomy and the age and depositional context of the biotas. Instead, variation among biotas is attributed to differences in their late diagenetic history, in particular the maximum depth to which sediments were buried and the nature of fluid flow, as well as recent weathering. Variations in the quality of structural color preservation among specimens from individual biotas are independent of precise stratigraphic and sedimentological context. These intrabiota variations usually result from differences in the extent of microbial degradation of the cuticle and of recent weathering, but also the mode of curation of specimens. The last of these has important implications for curatorial practice.
The discovery of fossil bird tracks from the Cenomanian Kerker Member (Zebbag Formation) in southern Tunisia represents the oldest report of fossil birds from the Cretaceous of continental Africa. Three small bird tracks were discovered in a track-bearing surface dominated by tridactyl dinosaur footprints and are attributed to the ichnogenus Koreanaornis. This represents the first occurrence of this ichnogenus in Africa and indicates a worldwide distribution of these shorebirdlike tracks, previously known only from Asia and North America. Tracks described in this study are also smaller than any other fossil bird track known to date, thus they can be included in the minute size class following modern bird track groups. A comparison with present-day shorebird tracks indicates strong similarities in size, morphology, and environment with extant members of the Actitis genus, commonly known as sandpipers, which inhabit arid central African tidal flats. The occurrence of bird tracks in the early Late Cretaceous of Tunisia also brings important new insight into the paleoecology of an area previously thought to be a site of exclusively marine deposition.
The crinoid fossil record is dominated by isolated ossicles, pluricolumnals, arm segments, and other fragmentary remains resulting from postmortem skeletal disarticulation; however, few studies to date have focused on dissociated crinoid elements in taphonomic and/or paleoenvironmental analysis. A diverse, abundant, and taphonomically variable crinoid fauna recovered from a thin mudstone interval within the Upper Pennsylvanian Barnsdall Formation in northeastern Oklahoma presents a unique opportunity to test the value of incomplete crinoid remains in reconstructing paleoenvironmental conditions and understanding taphonomic patterns. Isolated radial plates were identified to the most precise level possible, commonly genus or species, and used to calculate the minimum number of completely disarticulated individuals; this value was then compared to the number of articulated specimens representing that same taxon to determine the proportion of individuals with cups that have undergone disarticulation into separate ossicles. Cladid taxa are shown to be particularly prone to total disarticulation, with disparid microcrinoids and, somewhat surprisingly, flexibles demonstrating more resistance to disarticulation. Genus-level taphonomic trends among cladid taxa indicate that genera with large but thin cup plates, short anal sacs, and arms capable of adopting a trauma posture are less prone to total disarticulation. Analysis of fragmentary crinoid material recovered from disaggregation of bulk mudstone slabs reveals that thin horizons containing abundant articulated crinoid crowns are enriched in skeletal material and encrusted ossicles relative to thicker subjacent and superjacent intervals, providing further evidence that such horizons represent periods of sediment starvation on the distal shelf that were episodically punctuated by storm events.
To study how lacustrine depositional environments influence the preservation of insects, the abundance, size, and quality of insect specimens were compared across shale, mudstone, and siltstone within the Florissant Formation of Colorado. These lithologies were chosen because they reflect differences in associated energy, grain size, and presence of diatom layers. Eight hundred and twenty-three fossil insects were collected from a single stratigraphic section within the lacustrine deposits of the Florissant Formation (late Eocene). Sampling across these lithologies was associated with low specimen collection rates (3.7–5.6 insects collected per collector-day) that did not differ across the sedimentary environments. In addition, the relative abundance of insect orders did not differ across the sedimentary environments. Specimens were significantly smaller and less variable in size within the siltstone than they were within the shale and mudstone, likely due to differences in temporal and spatial averaging. Overall, 56% of insect specimens were disarticulated and 66% were considered of low quality. Insect disarticulation levels, preservation quality, and specimen orientation did not differ across all lithologies in general and for the other three insect orders, despite differences in coleopteran (beetles) preservation in siltstone where they were less disarticulated and more commonly preserved in a lateral position. This indicates that insect specimens of the quality typically associated with shale deposition also can be found in mudstone and siltstone, which increases the areas within lakes that can be sampled and compared for paleoecological studies.
Microfacies analysis of five patch reefs from the Martin Bridge Formation (Upper Triassic/Norian, Summit Point, Oregon, United States) reveals that microbialite fabrics dominate reef construction versus corals or other large metazoans. Other reef bioconstructors include characteristic Late Triassic branching corals and diminutive calcifiers (solenoporacean red algae, foraminifera, and sponges). The patch reefs exhibit dense growth fabrics and had elevation above the seafloor, making them ecological reefs or true reefs. Robust binding and encrusting organisms inhabited higher-energy areas, whereas red algae, followed by phaceloid coral colonies, inhabited zones of decreasing water energy, defining a subtle zonation consistent with wave energy in the paleoenvironment.
The dominance of microbial fabrics and diminutive bioconstructors make the Summit Point reefs distinct among Upper Triassic reefs from northeastern Panthalassa. Summit Point was originally identified as a Dachstein-type reef (e.g., high diversity, dominated by corals and sponges, massive bedding, large reef cavities). However, the dominance of microbial fabrics over larger metazoans, the (comparatively) modest faunal diversity, and lack of abundant, multigenerational epibionts or cements clearly differentiates the Summit Point reefs from the Dachstein reefs of northern Europe. The Summit Point reefs do, however, bear a striking resemblance to some Middle Triassic (Anisian) reefs from the Tethys, particularly with the abundance of microbialite fabrics and diminutive, binding or encrusting bioconstructors.
Short chains of discoidal, rarely spheroidal, structures, recovered by acid maceration of Lower Devonian (Lochkovian) siltstones from the Welsh Borderland are interpreted as coprolites because they comprise comminuted or homogenized tissues. They are placed in a new species of the ichnogenus Lancifaex. Tissues include the smooth and banded tubes of Nematasketum, a close ally of Prototaxites, and rarer cuticles of Nematothallus and Cosmochlaina. All these taxa have been assigned to an extinct class, Nematophytales Lang 1937, which Lang thought was intermediate between higher plants and algae. More recently, there is more compelling evidence, particularly from Prototaxites, that the class had fungal affinities. We thus conclude that the producers of the coprolites were selective feeders on nematophytes, and hence on fungi. Prior evidence for the reconstruction of terrestrial ecosystems in the mid-Paleozoic has been dominated by mega- and mesofossils of primary producers because body fossil records of consumers, whether carnivores, herbivores, or detritivores, are rare. Coprolites previously described from the locality that contain spores and residues of higher plants provide indirect evidence, based on consideration of comparative body size of coeval animals recorded elsewhere, for detritivory, probably in millipedes. In a similar approach involving mites, collembolans and millipedes—animals known to be mycophagous today—it is concluded that millipedes were the most likely producers of the coprolites described here.