Vertebrate coprolites from Middle Triassic Chang 7 Member in Ordos Basin, China: Palaeobiological and palaeoecological implications

https://doi.org/10.1016/j.palaeo.2022.111084Get rights and content

Highlights

  • •
    The most detailed coprolite record from the early Ladinian of Ordos Basin, China.
  • •
    Diverse large carnivorous predators with varying dietary habits are retrieved.
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    The first Mesozoic-type, trophically multileveled (> 6) lacustrine ecosystem.
  • •
    Rebuilding the top-predator trophic structure in the paleolake after the EPME.

Abstract

The early Ladinian lacustrine ecosystem of the Chang 7 Member in the Ordos Basin was proposed as the earliest known Mesozoic-type, trophically multileveled lacustrine ecosystem after the end-Permian mass extinction (EPME). However, limited evidence of higher-order trophic levels represented by predatory fish has made this conclusion elusive. In this study, we investigated the external morphology, food inclusions, and geochemical composition of 54 vertebrate coprolites from organic-rich lacustrine sediments of Chang 7 Member, Yanchang Formation, in the Bawangzhuang section, Tongchuan City, Shaanxi Province, China. These coprolites were identified as seven morphotypes in three groups: three heteropolar spiral forms, two amphipolar spiral forms, and two non-spiral forms. Preserved inclusions (fish scales, bone fragments, teeth) indicated that the producers of these coprolites were piscivorous animals. Compared with coprolites previously researched, all coprolites described herein were inferred to be produced by fish: three heteropolar types of spiral coprolites derived from three types of hybodonts, two amphipolar spiral coprolites from coelacanth or Saurichthys with simple spiral valves, and non-spiral coprolites from at least two predatory actinopterygians. Thus, the biodiversity of the lacustrine paleoecosystem, particularly that of predators with upper trophic levels, was substantially enriched. The existence of large carnivorous predators of different taxa as apex predators in a trophically multileveled (at least six levels) lacustrine ecosystem indicates that the early Ladinian lacustrine ecosystem of the Ordos Basin marks the rebuilding of the top-predator trophic structure in the lacustrine ecosystem after the EPME.

Introduction

The Chang 7 Member consists of exceptionally abundant lacustrine organic-rich shales and mudstones that account for the dominant high-quality hydrocarbon source rocks of the Mesozoic oil pools in the Ordos Basin (Qiu et al., 2015; Liu et al., 2021a, Liu et al., 2021b). Recently, a Mesozoic-type, trophically multileveled lacustrine ecosystem was recovered from the early Ladinian Chang 7 Member, and Zhao et al. (2020) proposed that it is the earliest known complex lacustrine ecosystem after the end-Permian mass extinction (EPME). However, little is known of the upper trophic level predators of such a lacustrine ecosystem, except that ‘higher-order trophic levels being represented by predatory fish’ was mentioned (Zhao et al., 2020). Large predators at upper trophic levels are highly susceptible to environmental fluctuations and stress (Steneck, 2012); thus, the recovery dynamics of large predators provides a key proxy for evaluating ecosystem recovery after extinction events (Chen and Benton, 2012; Scheyer et al., 2014).
Coprolites (fossilised faeces) always possess partially digested or undigested food remains, which provide a valuable palaeobiological source for interpreting the diet (herbivore, carnivore, or omnivore), feeding behaviours, and digestive physiology of the host animals (e.g. Chin et al., 1998; Prasad et al., 2005; Hunt et al., 2007; Eriksson et al., 2011; Zatoń and Rakociński, 2014; Zatoń et al., 2015). Thus, coprolites may reveal predator-prey interactions among animals, allowing for the reconstruction of the diversity and trophic structure of ancient ecosystems (e.g. Luo et al., 2017; Qvarnström et al., 2017, Qvarnström et al., 2019a, Qvarnström et al., 2019b, Qvarnström et al., 2021; Dentzien-Dias et al., 2021; Rummy et al., 2021). Abundant and diverse vertebrate coprolites that were associated with body fossils of plants (Ji et al., 2010), notostracans (Xie et al., 2015), ostracods, insects (Zhao et al., 2020), bony fishes, and shark teeth (Liu, 1962) were obtained from the Chang 7 Member in the Ordos Basin. However, well-preserved vertebrate coprolites have not been systematically described, except for a brief description by You et al. (2020) and a sporadic mention in some publications (Yang et al., 2016; Zhao et al., 2020).
This study aimed to investigate the external morphology, food inclusions, and geochemical composition of vertebrate coprolites from organic-rich mudstones of the Chang 7 Member in the Bawangzhuang section to infer their possible producers and predator-prey relationships and explore their palaeobiological and palaeoecological significance in the early Ladinian lacustrine ecosystem of the Ordos Basin.

Section snippets

Geological setting

The Bawangzhuang section (35°14′2.83″N, 109°2′28.86″E) is located in the Yintai District of Tongchuan City, close to the southern margin of the Ordos Basin in Shaanxi Province, China (Fig. 1A). The Ordos Basin, the second largest sedimentary basin in China, is a continental basin that developed in the Palaeozoic epicontinental sea (Jiang et al., 1992). The Triassic succession therein represents a transition from sporadically distributed, purple-coloured fluvially dominated deposits of the Lower

Material and methods

The material comprised 54 coprolites: 35 complete coprolites of different shapes and sizes and 19 incomplete coprolites. These coprolites were preserved in massive organic-rich mudstones. A large bulk of mudstones (ca. 2000 kg) was split into pieces during the fieldwork of November 2020 and April 2021, and coprolites were collected when some bump-like appearances were observed on the rock surface; they are highly phosphate-fossilised and often have a sharp outer contact with clear separation

Coprolite descriptions

The coprolites studied were described in detail and classified into seven morphotypes, mainly based on their morphology, size, and surface features. First, they were categorised into non-spiral and spiral forms based on whether they have spirals (Hunt and Lucas, 2012). Second, the spiral forms were further recognised as heteropolar or amphipolar: heteropolar coprolites have a variable number of closely spaced spirals concentrated at one end of the specimen, while amphipolar coprolites have a

Coprolite producer

Deciphering coprolite producers in palaeocoprology is of paramount importance (Chin, 2002; Hunt et al., 2007; Smith and Botha-Brink, 2011; Qvarnström et al., 2019a) because it provides new insights into the diversity and trophic structure of past ecosystems. Although coprolites are not directly associated with their potential producers, multiple indicators, including size, shape, undigested inclusions, and body fossil taxa of host strata allowed us to recognise their potential producers and

Conclusions

Exceptionally rich coprolites have been documented in Chang 7 Member of the Yanchang Formation in the Bawangzhuang section, Tongchuan City, Shaanxi Province, China. The external morphology, food inclusions, and elemental composition of coprolites were examined. Seven morphotypes were identified: three heteropolar spiral forms, two amphipolar spiral forms, and two non-spiral forms. The sizes (larger than 5 mm), chemical compositions (primarily calcium phosphate), and preserved inclusions (e.g.

Author contributions

ZY Sun and QQ Meng conceived the study and the development of the manuscript, and supervised experiment analyses. ZY Sun and JC Li made the sample collections. MT Yao ran all experiments, drew all figures, and wrote the initial manuscript supervised by ZY Sun and QQ Meng. All authors revised the manuscript and contributed to the interpretation of the results and the writing of the final manuscript.

Author statement

The authors that they have no financial and personal relationships with other people or organizations that can inappropriately influence this work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in the manuscript entitled as “Vertebrate coprolites from Middle Triassic Chang 7 Member in Ordos Basin, China: Palaeobiological and palaeoecological implications”.

Declaration of Competing Interest

None.

Acknowledgements

We thank Dai Yanlin (the graduate student of Peking University), Zhang Chuanwen (the graduate student of China University of Geosciences, Beijing), Yao Zhixiao and Wang Junshe (local farmers of the Bawangzhuang village) for fossil collections in the fieldwork; Hu Tianfen and Wang Mingcui for fossil preparation. We are grateful to Dr. Michał Zatoń (University of Silesia) and an anonymous reviewer for their constructive reviews. The study was financially supported by grants from the National

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