Jacob S. Benner

Macroborings (Gastrochaenolites) in Lower Ordovician Hardgrounds of Utah: Sedimentologic, Paleoecologic, and Evolutionary Implications

Abstract New evidence of fossil macroborings in the Lower Ordovician (Ibexian) of western Utah demonstrates that the macroboring behavioral strategy was firmly established in the earliest stages of the great Ordovician diversification of the marine biosphere. In Utah, borings were excavated in hardgrounds that had developed on sponge-algal mounds and flat-pebble conglomerates in the Fillmore Formation (Ibexian). The most complete specimens possess a neck up to 1 cm in length that opens into a teardrop-shaped chamber with a maximum diameter of 1 cm. The chamber terminates at a depth of 3–4 cm below the hardground surface. These borings belong to the ichnogenus Gastrochaenolites. The organisms responsible for creating the borings are unknown. Sedimentologically, the effect of boring on hardgrounds was to break them into pebble- and cobble-sized clasts. The endolithic lifestyle represented by the borings may have evolved in response to ecologic pressures such as predation or competition for food resources. The macroborings from the Fillmore Formation represent an innovative strategy that may have resulted in the later development of new body plans and the early establishment of endolithic macroinvertebrates.

Late Carboniferous paleoichnology reveals the oldest full-body impression of a flying insect

Insects were the first animals to evolve powered flight and did so perhaps 90 million years before the first flight among vertebrates. However, the earliest fossil record of flying insect lineages (Pterygota) is poor, with scant indirect evidence from the Devonian and a nearly complete dearth of material from the Early Carboniferous. By the Late Carboniferous a diversity of flying lineages is known, mostly from isolated wings but without true insights into the paleoethology of these taxa. Here, we report evidence of a full-body impression of a flying insect from the Late Carboniferous Wamsutta Formation of Massachusetts, representing the oldest trace fossil of Pterygota. Through ethological and morphological analysis, the trace fossil provides evidence that its maker was a flying insect and probably was representative of a stem-group lineage of mayflies. The nature of this current full-body impression somewhat blurs distinctions between the systematics of traces and trace makers, thus adding to the debate surrounding ichnotaxonomy for traces with well-associated trace makers.

Chapter 11 – Glacial Environments

Glacial environments are subject to drastic oscillations in energy regime that rapidly modify the local environment. The impact of glacial phenomena on the distribution, abundance, and evolution of biota based on trace-fossil evidence is the focus of this chapter. Arthropod trackways, shallow horizontal burrows, and fish trails dominate the glacial and periglacial trace-fossil assemblages preserved in terrestrial and glaciolacustrine sedimentary sequences, while nonspecialized feeding burrows that are diminutive when compared to normal-marine settings comprise glaciomarine ichnofaunas. As a consequence of rapid meltwater discharge, freshwater conditions prevail in some fjord settings during deglaciation, allowing for the establishment of suites more typical of freshwater or brackish-water conditions. Despite changes in the composition of the trace making community through time, ichnofacies relationships and ecological niche occupation are similar between the Paleozoic and Cenozoic, an indication of the constancy of the interplay between the biotic community and glacial processes.

COMMENT ON MARDEN (2013): “REANALYSIS AND EXPERIMENTAL EVIDENCE INDICATE THAT THE EARLIEST TRACE FOSSIL OF A WINGED INSECT WAS A SURFACE SKIMMING NEOPTERAN”

Mardens (2013) reanalysis of Knecht et al. (2011) suggesting that specimen SEMC‐F97 is the result of the skimming behavior of a neopteran insect and, more importantly, fossil evidence of “… surface skimming as a precursor to the evolution of flight in insects” (Marden 2013) is found to be deficient on three fronts: (1) the principal specimen was never viewed firsthand which led to significant morphological misinterpretations; (2) poorly designed and executed neoichnological experiments led to incredulous results; and (3) the assumption that this specimen is fossil evidence supporting the surface skimming hypothesis of the origin of insect flight despite the fact that since its induction into the literature that hypothesis has been refuted based on significant paleontological, phylogenetic, genetic, and developmental evidence.

Cochlea Archimedea: Hitchcock's Fish Trail

A specimen figured by Hitchcock (1858) and named Cochlea archimedea presents interesting ichnotaxonomic and paleoecologic issues. The ichnogenus Cochlea is considered to be a preoccupied taxon and therefore invalid. The specimen in question is given its appropriate name, Undichna isp., based on its apparent morphology and is reinterpreted as a trail made by a fish. Two working hypotheses for the construction of the trail are: (A) as a single epichnial groove with side levees made by one fin in contact with the substrate and (B) as a hypichnial trail with two grooves made by two fins in contact with the substrate. A more specific approach cannot be taken without knowledge of the true toponomy of the trace fossil, as none is indicated on the original specimen. Regardless, the identification of the first trails made by fish in the Early Jurassic of the Newark Supergroup of Massachusetts indicates the need for more nondinosaurian trace fossil research in the Mesozoic rift basins of eastern North America. The most likely tracemaker, depending on the correct constructional hypothesis, is either a semionotid with a deeply set anal fin (hypothesis B) or Redfieldius (hypothesis A). Considering the abundance of fish body fossils preserved in rocks of this age in eastern North America, it is likely that once recognized, more Undichna will be discovered in future field explorations.

Enigmatic organisms preserved in early Ordovician macroborings, western Utah, USA

Macroborings in the Lower Ordovician Fillmore Formation, western Utah, USA, occasionally contain fossil remains of enigmatic organisms. In the most complete specimens a common morphology can be observed. The calcified body wall of the animal is vase-shaped, mimicking the shape of the boring itself. An ovoid body leads up to a neck that contains either a single or double cylinder near the aperture of the boring. The incomplete preservation of the specimens is not sufficient to identify the biological affinity of the organism at this time, but a review of potential groups is warranted. While such groups as barnacles, bivalves, mitrates, and a host of worm-like forms are potential boring inhabitants, none fit what is known of the morphology of the specimens from Utah. Regardless, recognition and future identification of these animals will lead to a greater understanding of complex hardground trophic systems during the Ordovician Bioerosion Revolution.