The Oldest Known Digestive System Consisting of Both Paired Digestive Glands and a Crop From Exceptionally Preserved Trilobites of the Guanshan Biota (Early Cambrian, China)

Abstract

The early Cambrian Guanshan biota of eastern Yunnan, China, contains exceptionally preserved animals and algae. Most diverse and abundant are the arthropods, of which there are at least 11 species of trilobites represented by numerous specimens. Many trilobite specimens show soft-body preservation via iron oxide pseudomorphs of pyrite replacement. Here we describe digestive structures from two species of trilobite, Palaeolenus lantenoisi and Redlichia mansuyi. Multiple specimens of both species contain the preserved remains of an expanded stomach region (a "crop") under the glabella, a structure which has not been observed in trilobites this old, despite numerous examples of trilobite gut traces from other Cambrian Lagerstätten. In addition, at least one specimen of Palaeolenus lantenoisi shows the preservation of an unusual combination of digestive structures: a crop and paired digestive glands along the alimentary tract. This combination of digestive structures has also never been observed in trilobites this old, and is rare in general, with prior evidence of it from one juvenile trilobite specimen from the late Cambrian Orsten fauna of Sweden and possibly one adult trilobite specimen from the Early Ordovician Fezouata Lagerstätte. The variation in the fidelity of preservation of digestive structures within and across different Lagerstätten may be due to variation in the type, quality, and point of digestion of food among specimens in addition to differences in mode of preservation. The presence and combination of these digestive features in the Guanshan trilobites contradicts current models of how the trilobite digestive system was structured and evolved over time. Most notably, the crop is not a derived structure as previously proposed, although it is possible that the relative size of the crop increased over the evolutionary history of the clade.

Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period

“…Cambrian guts are typically preserved either as carbonaceous films 45 , sediment infillings 46 , or via phosphatization 44 , the latter of which is potentially reflective of the organism's digestive physiology. However, there are limited (and perhaps contentious) examples of gut pyritization 47 (but see also ref. 48 ) as well as gut-content pyritization 46 .…”

Microbial decay analysis challenges interpretation of putative organ systems in Cambrian fuxianhuiids

“…Accordingly, the bulbous expansion in the head region of the fuxianhuiids is interpreted here as a microbial biofilm, which developed principally around the biomass concentrated in the foregut region located beneath the head shield and of connective and muscle tissues. It is not known how extensive the gut was in this region-some arthropods have an expanded area such as a 'crop' here [26]. We propose that following consumption of the foregut tissue, bacteria extended into the head region to consume more labile material, such as nervous, vascular and muscle tissue, eventually also metabolizing more durable connective tissues with typical structures such as inter gnathal ligaments leading to a 'brain-like' appearance [25].…”

The trouble with trilobites: classification, phylogeny and the cryptogenesis problem

“…Zhang et al 2007;Mayers et al 2019) as opposed to trilobites (cf. Lerosey-Aubril et al 2012, 2017aGutiérrez-Marco et al 2017;Hopkins et al 2017;Wang et al 2018). The results of the phylogenetic analysis conducted by Moysiuk & Caron (2019) show that Agnostina (Agnostus + Peronopsis) is sister to the polymerid trilobites, which is mainly supported by shared features such as the calcified tergites, style of tergal articulation, and a dorsally segmented cephalon (including the occipital lobe).…”