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The fossil insect assemblage associated with the Toarcian (Lower Jurassic) oceanic anoxic event from Alderton Hill, Gloucestershire, UK - PubMed

  • ️Mon Jan 01 2024

The fossil insect assemblage associated with the Toarcian (Lower Jurassic) oceanic anoxic event from Alderton Hill, Gloucestershire, UK

Emily J Swaby et al. PLoS One. 2024.

Abstract

Extreme global warming and environmental changes associated with the Toarcian (Lower Jurassic) Oceanic Anoxic Event (T-OAE, ~183 Mya) profoundly impacted marine organisms and terrestrial plants. Despite the exceptionally elevated abundances of fossil insects from strata of this age, only assemblages from Germany and Luxembourg have been studied in detail. Here, we focus on the insect assemblage found in strata recording the T-OAE at Alderton Hill, Gloucestershire, UK, where <15% of specimens have previously been described. We located all known fossil insects (n = 370) from Alderton Hill, and used these to create the first comprehensive taxonomic and taphonomic analysis of the entire assemblage. We show that a diverse palaeoentomofaunal assemblage is preserved, comprising 12 orders, 21 families, 23 genera and 21 species. Fossil disarticulation is consistent with insect decay studies. The number of orders is comparable with present-day assemblages from similar latitudes (30°-40°N), including the Azores, and suggests that the palaeoentomofauna reflects a life assemblage. At Alderton, Hemiptera, Coleoptera and Orthoptera are the commonest (56.1%) orders. The high abundance of Hemiptera (22.1%) and Orthoptera (13.4%) indicates well-vegetated islands, while floral changes related to the T-OAE may be responsible for hemipteran diversification. Predatory insects are relatively abundant (~10% of the total assemblage) and we hypothesise that the co-occurrence of fish and insects within the T-OAE represents a jubilee-like event. The marginally higher proportion of sclerotised taxa compared to present-day insect assemblages possibly indicates adaptation to environmental conditions or taphonomic bias. The coeval palaeoentomofauna from Strawberry Bank, Somerset is less diverse (9 orders, 12 families, 6 genera, 3 species) and is taphonomically biased. The Alderton Hill palaeoentomofauna is interpreted to be the best-preserved and most representative insect assemblage from Toarcian strata in the UK. This study provides an essential first step towards understanding the likely influence of the T-OAE on insects.

Copyright: © 2024 Swaby et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1

(A) Global palaeogeographical map of the Early Toarcian (modified from [22] under a CC BY license), showing the location of the Karoo and Ferrar large igneous provinces (LIPs) in South Gondwana [91]; the box shows B. (B) Palaeogeography of NW Tethys, modified from [92] under a CC BY license, showing the likely distribution of the Toarcian palaeo-landmasses superimposed on the present-day coastline, and the location of: (1) Alderton Hill, UK and (2) Strawberry Bank, UK.

Fig 2
Fig 2. Fauna associated with the insect horizon at Alderton Hill, Gloucestershire, UK.

Scale = 1 cm unless otherwise stated. (A) Leptolepis concentricus Egerton, 1849 [63], BGS 114078–79 (Actinopterygii: Leptolepiformes); (B) L. normandica Nybelin, 1962 [100], NHMUK PV P.7621, in association with indeterminate insect; (C) L. coryphaenoides Bronn, 1830 [101], NHMUK PV P.28855; (D) Pachycormus macropterus de Blainville, 1818 [102], CAMSM J.61246 (Pachycormiformes: Pachycormidae), scale = 2 cm; (E) Hooklets of Geoteuthis Münster, 1843 [103], BGS GSM 117962–63 (Cephalopoda), scale = 5 mm); (F) Pseudomytiloides dubius Sowerby, 1823 [104], BGS Geol. Soc. 4147 (Bivalvia: Myalinida); (G) Hildaites murleyi Moxon, 1841 [93], BGS GS.32040, genotype (Cephalopoda: Ammonitida); (H) Coelodiscus minutus Schübler, 1833 [105], BGS GSM 114054 (Gastropoda: Coelodiscidae), scale = 2.5 mm; (I) Chondroteuthis wunnenbergi Bode, 1933 [106], NHMUK PI C.5257a,b (Cephalopoda: Belemnitida); (J) Chondroteuthis wunnenbergi Bode, 1933 [106], NHMUK PI C.59301 (Cephalopoda: Belemnitida); (K) Proeryon richardsoni Woodward, 1911 [98], CHAGM F.685, holotype (Decapoda: Eryonidae), scale = 2 cm.

Fig 3
Fig 3. Fossil insect orders Odonata,? Dermaptera, Reculida, Blattodea and Orthoptera from the Toarcian of Alderton Hill, Gloucestershire.

(A) Heterophlebia buckmani Brodie, 1845 [62] (Odonata: Heterophlebiidae), NHMUK PI I.11310; (B) Heterothemis brodiei Buckman, 1843 [60] (Odonata: Liassogomphidae), NHMUK PI I.3552 (holotype); (C) H. brodiei Buckman, 1843 [60], NHMUK PI I.11288; (D) Protomyrmeleon sp. Geinitz, 1887 [112] (Odonata: Protomyrmeleontidae), NHMUK PI In.59065; (E)? Dermaptera De Geer, 1773 [113], NHMUK PI I.11403; (F) Geinitzia carpentieri Zeuner, 1937 [71] (Reculida: Geinitziidae), NHMUK PI In.36200 (holotype); (G) Liadoblattina blakei Scudder, 1886 [67] (Blattodea: Raphidiomimidae), NHMUK PI I.3574 (holotype); (H) Blattodea Latreille, 1810 [114], undescribed, BRSMG Cg2374; (I) Locustopsis sp. Handlirsch, 1906 [115] (Orthoptera: Locustopsidae), NHMUK PI I.11370; (J) “Elcana” cf. geinitzi (Heer, 1880) [116] (Orthoptera: Elcanidae), NHMUK PI I.11295; (K) “Elcana” cf. geinitzi (Heer, 1880) [116], NHMUK PI I.3560; (L) Protogryllus magnus Zeuner, 1937 [71] (Orthoptera: Protogryllidae), NHMUK PI I.11324 (holotype); (M) Orthoptera Olivier, 1789 [117], incertae sedis, NHMUK PI I.11405 (leg). Scale bars = 2.5 mm.

Fig 4
Fig 4. Fossil insect orders Hemiptera, Coleoptera, Necrotrichoptera, Mecoptera from the Toarcian of Alderton Hill, Gloucestershire.

(A) Fulgoridium sp. Handlirsch, 1906 [115] (Hemiptera: Fulgoridiidae), NHMUK PI I.11328; (B) Margaroptilon brodiei Handlirsch, 1906 [115] (Hemiptera: Fulgoridiidae), NHMUK PI I.3561 (holotype); (C) M. brodiei Handlirsch, 1906 [115], NHMUK PI I.11266 (holotype of M. bulleni); (D) Archijassus heeri Geinitz, 1880 [116], (Hemiptera: Archijassidae), NHMUK PI I.11458; (E) Progonocimicidae Handlirsch, 1906 [115] (Hemiptera), NHMUK PI I.11465; (F) Engynabis tenuis Bode, 1953 [46] (Hemiptera), NHMUK PI I.3313; (G) Hemiptera Linnaeus 1758 [118], incertae sedis, NHMUK PI I.11446; (H) Hemiptera Linnaeus, 1758 [118], undetermined, CHAGM F.643.1; specimen photographed and reproduced with permission; (I) Hemiptera Linnaeus, 1758 [118], incertae sedis, NHMUK PI I.11317; (J) Coleoptera Linnaeus, 1758 [118], incertae sedis, NHMUK PI I.69; (K) Coleoptera Linnaeus, 1758 [118], incertae sedis, NHMUK PI I.11345; (L) Coleoptera Linnaeus, 1758 [118], incertae sedis, NHMUK PI I.3077; (M) Coleoptera Linnaeus, 1758 [118], incertae sedis, NHMUK PI I.11355; (N) Necrotaulius parvulus (Geinitz, 1884) [66] (Necrotrichoptera: Necrotauliidae), NHMUK PI I.15014; (O) N. parvulus (Geinitz, 1884) [66], NHMUK PI I.11389; (P) Protobittacus handlirschi Tillyard, 1933 [70] (Mecoptera: Bittacidae), composite photograph of the part (NHMUK PI I.11406) and counterpart (NHMUK PI I.11335) (holotype); (Q) Orthophlebia brodiei Tillyard, 1933 [70] (Mecoptera: Orthophlebiidae), NHMUK PI I.15019 (holotype); (R) Orthophlebia sp. Westwood, 1845 [62] NHMUK PI I.11225. Scale bars = 2.5 mm.

Fig 5
Fig 5. Fossil insect orders neuroptera and diptera from the Toarcian of Alderton Hill, Gloucestershire.

(A, B) Actinophlebia intermixta Scudder, 1885 [119] (Neuroptera: Osmylopsychopidae), NHMUK PI I.3577 & NHMUK PI I.11346 (holotype, part and counterpart); (C) Paractinophlebia curtisii Scudder, 1886 [67] (Neuroptera: “Familia nova A”), NHMUK PI I.3585 (holotype); (D) “Prohemerobius”aldertonensis Whalley, 1988 [68] (Neuroptera: “Prohemerobiidae”), NHMUK PI I.11304 (holotype); (E) “Archeosmylus” alysius Whalley, 1988 [68] (Neuroptera: “Prohemerobiidae”), NHMUK PI I.3318 (holotype); (F) “A.” complexus Whalley, 1988 [68] (Neuroptera: “Prohemerobiidae”), NHMUK PI I.11412 (holotype); (G) Architipula anglicana (Tillyard, 1933) [70] (Diptera: Limoniidae), NHMUK PI I.11298 (holotype); (H) Grimmenia tillyardi Kopeć et al., 2017b [76] (Diptera: Limoniidae), NHMUK PI I.3328 (holotype). Scale bars = 2.5 mm.

Fig 6
Fig 6

Individual-based rarefaction curves for Alderton Hill and Strawberry Bank at the following taxonomic ranks: (A) order level; (B) family level; (C) genus level; (D) species level. The rarefaction curves show the expected richness (y-axis) for a given number of specimens (x-axis). The green and orange curves represent the Alderton Hill and Strawberry Bank insect assemblages respectively. Shaded areas represent 95% confidence intervals.

Fig 7
Fig 7

Pie-charts showing the number and percentages of taxonomically identifiable insect specimens within each order, grouped by abundance from (A) Alderton Hill, Gloucestershire and (B) Strawberry Bank, Somerset: Note that the ‘winged insects’ Amphiesmenoptera and Panorpida are superorders, but are still included within this comparison.

Fig 8
Fig 8

The frequency of individual insect specimens in each taphonomic grade for: (A) Alderton Hill, Gloucestershire (n = 291); (B) Strawberry Bank, Somerset (n = 518). The number and percentage in each primary taphonomic grades are given in red boxes, and the secondary taphonomic grade counts and percentages are stated above each individual bar. The solid green and orange bars denote complete specimens or element, and the paler green and orange bars denote partial specimens or elements.

Fig 9
Fig 9. Calculated Pearson residuals for each entry in the Chi-squared contingency table at order level, used to determine the degree to which each primary taphonomic grade contributed to the total Chi-squared score for the Alderton Hill palaeoentomofauna.

The colour of each circle represents its residual value: positive residuals are blue and negative residuals are red, indicating a positive and negative association respectively between taxonomy and taphonomy. The size of the circle is proportional to the degree of cell contribution to the relationship. Note: Ephemeroptera was not included in this analysis as the specimen attributed to this order (WARMS G 8084) was not available for re-examination and therefore could not be assigned a taphonomic grade.

Fig 10
Fig 10

Preserved length and width of all insect elements recorded from: (A, C) Alderton Hill, Gloucestershire; (B, D) Strawberry Bank, Somerset.

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Grants and funding

ES Grant number NE/S007350/1] Natural Environmental Research Council (NERC) through the Central England NERC Training Alliance (CENTA) Doctoral Training Partnership https://www.ukri.org/councils/nerc/ The sponsors did not play any role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.