Enigmatic origin of massive Late Cretaceous-to-Neogene coprolite-like deposits in North America: a novel palaeobiological alternative to inorganic morphogenesis

Abstract

Innumerable coprolite specimens, alternatively pseudo‐coprolites, are distributed in several Late Cretaceous‐to‐Neogene continental deposits hosted by the Whitemud Formation (Maastrichtian) in southern Saskatchewan, Canada, Golden Valley Formation (Paleocene) in western North Dakota and the Wilkes Formation (Miocene) in Washington State, USA. These massive accumulations of excrement‐shaped specimens also include multi‐decimetre‐long specimens previously interpreted as casts of intestinal organs by an unknown zoology, possibly reptilian. The possible vertebrate zoology origin of these has been widely disputed because of the lack of any skeletal remains or any other definitive evidence of palaeobiology. Alternative originations suggest non‐zoological processes, such as sideritic muds extruded by biogenic gas‐driven flows during diagenesis. Multi‐decimetre‐long intestine‐like casts recovered from the three deposits differ from the more widely distributed faeces‐like specimens because their elongated forms have bilateral symmetry in cross‐section and surface textures consisting of sub‐mm‐wide longitudinal parallel striations extending without interruption along the looped and coiled surfaces. These possible impressions of musculature are not present on smaller specimens having coprolite‐like shapes. A novel interpretation proposes that these multi‐decimetre‐long specimens may be gut casts of a previously unrecognized giant terrestrial earthworm (Oligochaeta) that existed from the Late Cretaceous to the Neogene. The possibility of this Annelida zoology provides palaeobiological resolution for the lack of any evidence of vertebrate skeletal remains or other evidence of origination and further suggests that the innumerable excrement‐like specimens may also have palaeobiological affinity.

Ferruginous casts of bromalites in kaolin beds: microbial ferrihydrite‐goethite transformation as early stage taphonomy in lacustrine and riparian sediments

“…The kaolin-dominated beds are stratigraphically higher eastward into the area of the Readlyn deposit, where the deposits have been interpreted as a facies of the lower Frenchman Formation (Broughton 1977(Broughton , 1979Pruett & Murray 1991). The strata consist of as much as 20 m of upward fining silty kaolin fills of fluvial channels and fluvial-margin lacustrine or riparian areas (Berry 1935;Bell 1949;Broughton et al 1977;Binda & Nambudiri 1983;Broughan 1984;Broughton 2017). The kaolin-rich deposits vary from relatively pure clay to silty and sandy sediments derived from diagenetic alteration of feldspathic sediments (Pruett & Murray 1991).…”

“…The depositional environment of the Readlyn coprolite deposit has been interpreted as being abandoned channel and oxbow lake complex characterized by kaolin-rich oozy bottom sediments and adjacent riparian terrains (Broughton 1981(Broughton , 2017. This facilitated excrement of herbivores grazing lacustrine bottom plants to have been suspended and rapidly buried in the water-saturated kaolin-rich bottom silt.…”

“…Multi-metre thick kaolin beds of the Whitemud Formation (Maastrichtian) in southern Saskatchewan (Broughton et al 1978;Broughton 2017) and the Wilkes Formation (Miocene) in Washington State (Mustoe 2001;Yancey et al 2013) host two of the largest known terrestrial accumulations of coprolites or alternatively pseudo-coprolites. The distribution of these innumerable coprolites associated with each formation is constrained to a single narrowly defined deposit, one in Maastrichtian strata in southern Saskatchewan at the Readlyn deposit (Fig.…”

“…2). The morphogenesis of these ferruginous faecal (or faecal-like) specimens has been controversial for decades, resulting in polarized interpretations as to representing faecal by-products of animal activity, albeit of unknown taxonomic affinity (Broughton 2017), or entirely inorganic products resulting from concretionary siderite diagenesis and thereby pseudo-coprolites (Spencer 1993;Mustoe 2001;Yancey et al 2013).…”

“…Both deposits accumulated specimens having identical sinuous extruded faecal-like morphologies, hence coprolites, but otherwise would not be necessarily exceptional. The exceptionality results from discoveries at each deposit of identical specimens of gut-like soft-tissue organs (cololites), each as much as 1-1.5 m long (Seilacher et al 2001;Broughton 2017). These metre-long 3-D forms enigmatically lack any associated evidence of skeletal remains.…”