# Latest Oligocene (late Chattian) environmental transitions revealed by plant-insect interactions preserved in plant assemblages from Wind Brickyard, Eger, Hungary

Imre Gyökeres, Benjamin Adroit, Árpád Dávid

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Imre Gyökeres, Benjamin Adroit, Árpád Dávid. Latest Oligocene (late Chattian) environmental transitions revealed by plant-insect interactions preserved in plant assemblages from Wind Brickyard, Eger, Hungary. Palaeogeography, Palaeoclimatology, Palaeoecology, 2025, 666, pp.112828. 10.1016/j.palaeo.2025.112828. hal-05136781

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# Latest Oligocene (late Chattian) environmental transitions revealed by plant-insect interactions preserved in plant assemblages from Wind Brickyard, Eger, Hungary

Imre Gyökeres<sup>a, *,</sup>, Benjamin Adroit<sup>b, c</sup>, Árpád Dávid<sup>a</sup>

## ARTICLE INFO

Editor: Howard Falcon-Lang

### Keywords:

- Insect damage

- Fossil leaves

- Late Oligocene

- Palaeoclimate

- Central Paratethys

- CLAMP

## ABSTRACT

Plants and insects are fundamental components of terrestrial ecosystems; evidence of their interactions (preserved as trace fossils on leaves) provides valuable insights into past environments. The Wind Brickyard succession in Hungary (Central Paratethys), of latest Oligocene age, offers a rare opportunity to study well-preserved evidence of plant-insect interactions and palaeoclimate across three plant-bearing intervals. Coinciding with the Late Oligocene Warming Event and the onset of the Miocene Glaciation, the Wind Brickyard assemblages capture palaeoecological responses to climate change, filling a critical knowledge gap in European palaeoecosystems. By integrating herbivory analysis and CLAMP-based palaeoclimate reconstructions, this study contributes to our understanding of how palaeoenvironmental and palaeoclimatic factors shaped latest Oligocene biodiversity over time. In this study, a total of 1310 fossil leaves from three different stratigraphic intervals were analyzed. Thirty-three, mostly generalized, damage types were documented. The greatest damage frequency and richness occurred in the upper of the three levels, which is represented by mainly azonal elements of riparian and swamp vegetation. This higher proportion of specialized insect damage is connected to elements of the zonal vegetation. These findings suggest that environmental changes and host plant zonality influenced the greater damage richness and frequency in the upper layer, highlighting significant ecological shifts close to the Oligocene-Miocene boundary.

## 1. Introduction

Terrestrial plants and insects dominate Earth's biodiversity, with half of the insect species depending on plants as their primary food source (Stork, 1988; Schoonhoven et al., 1998, 2005; Wilf and Labandeira, 1999). These interactions are crucial for terrestrial food webs (Forister et al., 2015). Plant-insect interactions can provide unique insights into past ecological dynamics (Labandeira, 2013a, 2013b; Robledo et al., 2018; Schachat et al., 2018, 2022, 2023; Adroit et al., 2018, 2021; Labandeira and Wappler, 2023). In the absence of insect body fossils, plant-insect associations provide indirect evidence of insect activity, such as herbivory. Studying palaeoenvironmental changes is important for understanding the plausible responses of our modern environments to Global Change (Meehl et al., 2007). In palaeontology, herbivory traces on fossil leaves reveal past plant-insect interactions and

palaeoenvironmental changes. These traces are measured using the guide to insect damage types on compressed plant fossils (Labandeira et al., 2007). Several studies have used fossil insect herbivory data to understand ancient terrestrial ecosystems (Wappler et al., 2012; Wappler and Grímsson, 2016).

The Oligocene is still considered an understudied period in terms of plant-insect interactions (Gunkel and Wappler, 2015). This epoch is marked by significant climate changes, including notable fluctuations of the Antarctic Ice Sheet following its initial formation in the Early Oligocene, as well as eustatic changes driven by variations in Earth's orbital cycles (Wade and Pälike, 2004; Coxall et al., 2005; Pälike et al., 2006). Based on the δ¹⁸O and δ¹³C isotope records of Central Europe, there was a significant decrease in the mean annual temperatures during the Oligocene compared to the Eocene (Eocene Climatic Optimum) (Zachos et al., 2001; Mosbrugger et al., 2005). Plant communities

<footnote><sup>a</sup> Department of Mineralogy and Geology, Institute of Earth Sciences, University of Debrecen, Egyetem tér 1, 4032 Debrecen, Hungary</footnote>

<footnote><sup>b</sup> ISEM, Univ Montpellier, CNRS, EPHE, IRD, Montpellier, France</footnote>

<footnote><sup>c</sup> Swedish Museum of Natural History, Department of Palaeobiology, Box 50007, 10405 Stockholm, Sweden</footnote>

<footnote>* Corresponding author at: Department of Mineralogy and Geology, Institute of Earth Sciences, University of Debrecen, Egyetem tér 1, 4032 Debrecen, Hungary. E-mail address: gyokeres.imre@science.unideb.hu (I. Gyökeres).</footnote>
adapted to climatic shifts, including lower temperatures and reduced seasonal precipitation (Fletcher et al., 2008; Pagani et al., 2009), resulting in European fossil floras dominated by broad-leaved subtropical evergreen rainforests (Mai, 1995; Teodoridis and Kvaček, 2015).

In response to these environmental changes during the Oligocene, thermophilous, predominantly evergreen forests were gradually replaced by temperate deciduous vegetation and mixed deciduous forests (Walther, 1994; Hably and Erdei, 2023). In the Paratethys Province (Alpine-Carpathian-Pannonian region), temperate deciduous elements appeared much later, during the Late Oligocene to Early Miocene, than in the coeval North Bohemian and German floras (Hably and Erdei, 2023). As these elements coexisted with a high diversity of thermophilous species (Kvaček and Hably, 1991; Hably and Erdei, 2023), the decreasing temperature cannot be significantly interpreted by the appearance of temperate taxa (Hably, 1991, 1993).

However, our knowledge of this region is limited in terms of fossil insect herbivory. Section of Wind Brickyard is an important key site in

the Central Paratethys as serves holostratotype of Egerian (Central Paratethys regional stage) (Báldi, 1969; Báldi and Senes, 1975). Plant fossils of Wind Brickyard are well-preserved in three different layers. As the sequence of Wind Brickyard takes place close to the boundary of the Late Oligocene Warming event and the beginning of the Miocene Glaciation, it could show how the ecosystem reacted as a response to the climate change after the Eocene Climatic Optimum. Because of its rare geological conditions, Wind Brickyard offers a unique opportunity to investigate relationships between plant-insect interactions and palaeoclimatic conditions over time to characterize European palaeoecosystems better and provide an opportunity for comparison with other palaeofloras from this region, such as the Early Oligocene Kiseged, Eger (Andreánszky, 1964, 1965, 1967a, 1967b; Novák, 1950; Andreánszky and Novák, 1957; Andreánszky and Cziffery, 1964; Hably and Erdei, 2015) and Late Oligocene flora of the Zsil-Valley (Transylvania, Romania) (Staub, 1887).

By combining analyses of plant-insect interactions with

<figure><img src="image_2.png" /><figcaption>**Fig. 1.** The location of Wind Brickyard from the Late Oligocene. (A) Palaeogeography of the Central Paratethys: Late Rupelian–Chattian. CWC – Central Western Carpathians; ? – assumed short-living sea connection (based on Kováč et al., 2017); in the corner, the map of Hungary shows Eger. (B) The location of Wind Brickyard, in Eger. (C) Stratigraphic section of the Wind Brickyard (based on Báldi, 1966). The figure shows all the 3 levels with fossil leaves in the Wind Brickyard, in Eger. The black star indicates the position of the locality.</figcaption></figure>
palaeoclimatic reconstructions, this study aims to shed light on the ecological and environmental dynamics regarding the three different formations of the locality. These results will not only enhance our understanding of European palaeoecosystems but also contribute valuable data for comparisons with other regional palaeofloras, bridging critical gaps in knowledge about biodiversity and climate-driven changes during the Oligocene.

## 2. Geological background

The Wind Brickyard, located near the city of Eger in northern Hungary (47°53′47.55″N, 20°23′52.20″E) is a key site within the Central Paratethys (Fig. 1A, B). This succession spans the Oligocene-Miocene boundary (dated at 23.03 Ma) encompassing the upper Chattian and lower Aquitanian global stages. Specifically, the Wind Brickyard is situated within nannoplankton zone NP 25, which corresponds to early part of the Egerian (23.3–24.4 Ma) in the uppermost Oligocene (Less, 2020).

Beneath the Wind Brickyard, the Lower Oligocene Kiscell Clay Formation, dating to the Rupelian and early Chattian, consists of grey calcareous clay and clayey marl (Fig. 1C). These deposits are not laminated (Báldi, 1983). The Eger Formation, which is the primary focus of the Wind Brickyard exposure, overlays conformably atop the Kiscell Clay Formation. During the Egerian, a new sea connection was opened towards the Western Tethys and normal marine conditions were returned after the anoxia during the Kiscellian stage (34–25 Ma) (Piller et al., 2007; Kováč et al., 2017). The base of the formation is a deep-sublittoral aleuritic, clayey marl with interbedded glauconitic, tuffitic sandstone, which upward consists of mollusc-rich clay, sandy aleurite then fine-grained sandstone with numerous plant remains, with increasing amounts of sand to the top (Báldi, 1983; Nagymarosy and Báldi-Beke, 1988; Babinszki et al., 2023).

The macroflora of Wind Brickyard occurs in three different stratigraphic intervals (Andreánszky, 1966; Báldi, 1973; Kvaček and Hably, 1991; Erdei and Bruch, 2004; Gyökeres et al., 2022) (Fig. 1C). In the lower part of the section, there is the so-called molluscan clay. This layer includes interbedded silts with numerous plant remains, referred to as the lower flora (LW) (Báldi, 1973). The thickness of these strata is 10 and 30 cm. Above this layer, there is a 5.0–5.5 m thick sequence of sandy clay where the topmost 30 cm contains the fossil leaves of the middle flora (MW). The third is the upper flora (UW) in the uppermost part of the section, with finely stratified friable micaceous sandstone and sandy clay (190 cm). The succession was deposited at decreasing water depth of normal marine (euhaline) salinity. The deep sublittoral mollusc fauna (Nucula, Flabellipecten, Pitar) is gradually replaced by shallow sublittoral to littoral ones (Chlamys, Ostrea, Glycymeris) and higher up by a lagoonal (Tympanotonus, Turritella, Melanopsis) assemblage (Báldi and Sztanó, 2000; Babinszki et al., 2023).

## 3. Material and method

### 3.1. Fossil leaf collection

The fossil leaf collection of Wind Brickyard is stored at the Mátra Museum of the Hungarian Natural History Museum, Hungarian National Museum Public Collection Centre in Gyöngyös (Supplement S1 – S2). It contains more than 2500 fossil leaves (~ 2400 angiosperms’ leaves). Böckh (1867) was the first to report on the locality and its fossil plant remains. Since then, several authors have studied the macroflora of the outcrop, including Andreánszky (1949a, 1949b, 1966), Andreánszky and Kovács (1955), Pálfalvy (1951), Nagy and Pálfalvy (1963), Kvaček and Hably (1991), Erdei and Bruch (2004), and Hably and Erdei (2023).

The following evergreen elements were abundant in the fossil leaf collection of LW: Lauraceae, *Platanus neptuni* (Ettingshausen) Bűzek, Holý et Kvaček, Fagaceae, cf. *Myrica integerrima* Kräusel et Weyland and *Dryophyllum callicomifolium* Andreánszky, which are supposed to

indicate a warm temperate to subtropical mixed mesophilous forest of Eastern Asia (Kvaček and Hably, 1991). The MW assemblage is dominated by fossil pines and Lauraceae suggesting warm temperate subtropical seashore vegetation. Meanwhile, *Ulmus* and *Daphnogene* indicate a possible riparian forest (Erdei and Bruch, 2004). Kvaček and Hably (1991) also suggest that lower formations experienced long-distance transport, which likely led to a strong selection of fossil leaves, as evidenced by the high number of poorly preserved specimens. This taphonomic bias may have influenced the preservation of insect damage, potentially affecting the observed frequency and diversity of interactions (Wilf et al., 2001). The third one (UW layer) is characterized by swamp and riparian elements, including *Alnus oligocaenica* Andreánszky, *Acer hungaricum* Andreánszky, „Rhamnus“ warthae Heer, *Ulmus pyramidalis* Goeppert. Thermophilous elements, such as *Daphnogene*, *Engelhardia*, Leguminosae and palms, are also present. The fossil remains in this layer likely experienced minimal transport, as evidenced by the presence of nearly complete leaf fans of ferns and palms found in small, fragmentary specimens (Kvaček and Hably, 1991).

### 3.2. Interpretation of the palaeoclimate

The palaeoclimate estimation, assuming a Mean Annual Temperature (MAT) of 20–22 °C and a Mean Annual Precipitation (MAP) of approximately 1500 mm, was based on the comparison of fossil taxa with species living in similar climatic conditions (Andreánszky, 1966). However, Kvaček and Hably (1991), who revised the macroflora of Wind Brickyard, estimated that the MAT was lower, around 15 °C, based on the vegetation. They disagreed with Andreánszky (1966), who suggested warming trends between the „lower“ and „upper flora“, as well as with Planderová et al. (1975), who predicted cooling trends due to the appearance of riparian (Arcto-Tertiary) elements, particularly in the „upper flora“. Nevertheless, Nagy (1979) conducted a palynological analysis that identified the Arcto-Tertiary elements at all three levels of Wind Brickyard, which challenged previous assumptions. Furthermore, the Coexistence Approach was used to estimate the palaeoclimate of the three floras and the entire Wind Brickyard section, determining a MAT range of 15.6–18.8 °C and a MAP range of 1096–1260 mm for the entire Wind Brickyard exposure (Erdei and Bruch, 2004).

In light of the varied palaeoclimatological estimates, we employed the Climate Leaf Analysis Multivariate Program (CLAMP) in our research to assess the climatic parameters. CLAMP uses the relationships between leaf morphological-anatomical traits and climatic parameters. The estimated palaeoclimatic parameters were based on the scoring of 31 leaf morphological-anatomical traits, with the major advantage of requiring only morphotypes rather than taxonomic classification (Yang et al., 2011).

In our study, 39 morphotypes containing 97 specimens from the whole Wind Brickyard were scored for CLAMP, including only woody dicotyledon plant remains (Supplements S3 – S6). We used leaf traits to obtain palaeoclimate results, including mean annual temperature (MAT), warmest month mean temperature (WMMT), coldest month mean temperature (CMMT) and mean annual precipitation (MAP). For MAP, CLAMP does not directly estimate its value, but it is possible to calculate the low and high precipitation values using the CLAMP variables for the three wettest months (Three_WET) and the three driest months (Three_DRY), which together provide an interval for MAP (Girard et al., 2019) (Supplement S7).

We employed four calibration datasets in our analysis to facilitate comparisons between these datasets and estimations from previous studies: C1: *Physg3arcAZ GRIDMet3arAZ*, C2: *Physg3arcAZ Met3arAZ*, C3: *Physg3brcAZ GRIDMet3brAZ* and C4: *Physg3brcAZ Met3brAZ* (Supplement S7). C2 contains 173 modern vegetation sites, mostly from the Northern Hemisphere, including samples from regions with winter cold (Yang et al., 2011). C1 corresponds to the gridded meteorological data from C2. C4 includes 144 modern vegetation sites, mainly from the temperate areas of the Northern Hemisphere and this dataset does not
contain samples from regions that experience extreme cold (Yang et al., 2011). C3 is the gridded meteorological data derived from C4.

### 3.3. Identification of the plant-insect interactions

Plant-insect interactions were identified using the 'Guide to Insect (and Other) Damage Types on Compressed Plant Fossils' by Labandeira et al. (2007). Damages were categorized into terrestrial arthropod functional feeding groups (FFGs) based on their feeding modes. Each FFG encompasses numerous Damage Types (DTs), which are documented with photographs and descriptions provided in the guide. In

addition, to apply this method of measuring plant-insect interactions in the fossil record, Schachat et al. (2018) suggested that it is better to consider leaves with a minimum 50 % complete leaf blade. Thus, we used 1310 fossil leaves to analyze plant-insect interactions (Supplements S8–S11).

Furthermore, because we had different amounts of leaves, we used rarefaction data to compare the three different floras subsampled with an amount of 200 leaves. In addition, sample-based rarefaction (Gotelli and Colwell, 2001) was performed to standardize plant species richness to compare the different layers (Gunkel and Wappler, 2015). All statistical analyses were performed on the whole fossil leaf assemblages and

<figure><img src="image_3.png" /><figcaption>**Fig. 2.** Comparison of the temperatures (°C) and precipitation (mm) estimated by CLAMP among the layers. A. In darker blue the mean temperature of the coldest month (CMMT), in light blue the mean annual temperature (MAT) and in red the mean temperature of the warmest month (WMMT). Colored rectangles around the boxplots correspond to the previously determined intervals by CA (based on Erdei and Bruch (2004)). The light blue dashed line corresponds to MAT determined by Kvaček and Hably (1991). B. Blue boxplots represent precipitation data of the 3 layers based on different calibrations (based on Girard et al. (2019)). The colored rectangle around the boxplots corresponds to the previously determined intervals by CA (based on Erdei and Bruch (2004)). The light blue dashed line corresponds to MAP determined by Kvaček and Hably (1991). Red crosses correspond to the MAP of Wind Brickyard based on the calculation of Tanrattana et al. (2020). See details for CLAMP calibrations in Table S7. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
on subsets of them including only taxa with at least 20 specimens. Quantitative analyses were performed using R version 4.3.2 (R Development Core Team, 2020).

# 4. Results

## 4.1. Palaeoclimatic comparison

The so-called 'completeness statistics' provided by the CLAMP analysis are above the 0.6 cut-off for reliability in every case (Supplements S3 – S6), suggesting that our floras should give reliable results (see Yang et al., 2011). The palaeoclimatic estimation range is based on C1 to C4, which is detailed in Supplement S7. As C1 and C4 have the most different values from the four calibrations, thus we interpret the lowest and highest borders of the given palaeoclimatic parameters of CLAMP at Wind Brickyard in Fig. 2A, B. Considering the whole locality, MAT ranges from 12.0 ± 2.8 °C and 14.4 ± 2.0 °C. CMMT is estimated to be 0.1 ± 3.8 °C and 3.5 ± 3.4 °C while WMMT ranges from 24.12 ± 3.0 °C and 26.21 ± 2.7 °C. Precipitation is estimated between 1208 ± 39.8–2271 ± 72.2 mm and 2952 ± 61.7–3837 ± 75.5 mm (Supplement S7).

Palaeoclimate parameters were also estimated for the three distinct formations of the Wind Brickyard. UW appeared to be the coolest palaeoenvironment according to MAT, CMMT and WMMT, while LW was the warmest of the three layers (Fig. 2A, Supplement S7). Almost all

of the CMMT estimations are above 0 °C. According to the temperature values, all layers have a strong seasonality range. LW seems to be the wettest by precipitation values and UW is the driest (Fig. 2B, Supplement S7). The values from C1, which include floras that experienced cold winters, are cooler than those from C4, reflecting significant variations between layers (Spicer et al., 2009; Yang et al., 2011).

## 4.2. Plant-insect interactions

### 4.2.1. Overview of the plant-insect interactions in Wind Brickyard

In Wind Brickyard, 11 % of the 1310 leaves were affected by insect damage, with a total of 237 occurrences. In total, 33 different DTs were observed on at least one leaf (Figs. 3, 4). We observed only a few leaves with specialized insect damage (2 %), but these represent 17 different DTs. Overall, hole-feeding is the most abundant FFG (9 DTs; 156 occurrences). Of the 36 taxa, twenty of them include damaged leaves. Among the taxa which contain at least 20 specimens, the leaves of „Rhamnus” warthae are the most damaged (20 % of 255 specimens) followed by *Alnus oligocaenica* (16 %) and *Acer hungaricum* (15 %). To standardize damage type richness, sample-based rarefaction was performed. Based on rarefaction data, „Rhamnus” warthae (17 DTs), *Acer hungaricum* (11 DTs) and *Daphnogene cinnamomifolia* (9 DTs) have the highest damage richness among the species.

<figure><img src="image_4.png" /><figcaption>**Fig. 3.** Insect damage types on Wind Brickyard leaves. (A) 62.234.1 *Rhamnus* warthae with margin feeding (DT12) from UW, (B) 62.150.1 *Leguminophyllum* sp. with margin feeding (DT12) from UW, (C) 64.078.1 *Dryophyllum callicomifolium* with skeletonization (DT17) from LW, (D) LSZN14 „Rhamnus” warthae with incertae sedis (DT114) from UW, (E) 65.741.1 *Acer hungaricum* with mining (DT94) from UW, (F) enlargement of *A. hungaricum* leaf (see E), (G) 56.1311.1 *Daphnogene cinnamomifolia* with piercing and sucking (DT118 and DT138) from UW, (H) enlargement of *D. cinnamomifolia* (see G). The black scale bar represents 0.5 cm.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Fig. 4.** Insect damage types on Wind Brickyard leaves. (A) enlargement of *A. hungaricum* (see B), (B) 61.169.1 *Acer hungaricum* with skeletonization (DT16) and oviposition (DT76) from UW, (C) 62.010.1 "Rhamnus" warthae with hole feeding (DT01, DT02, DT03) and mining (DT69) from UW, (D) enlargement of "Rhamnus" warthae (see C), (E) 62.041.1 *Acer hungaricum* with surface feeding (DT207) from UW, (F) enlargement of *A. hungaricum* leaf (see E), (G) W1302 "Rhamnus" warthae with hole feeding (DT05), (H) 62.362.1 "Rhamnus" warthae with galling (DT11) from UW, (I) 62.048.1 "Rhamnus" warthae with mining (DT35) from UW, (J) enlargement of "Rhamnus" warthae (see I). The white scale bar represents 1 cm; the black scale bar represents 0.5 cm.</figcaption></figure>

### 4.2.2. Frequency damage comparison among the studied formations of the locality

Of the 1310 leaves, the layer origin of 11 specimens was uncertain. Therefore, only 1299 leaves were used for comparison between the three layers. LW and MW have a similar proportion of damaged leaves (4.6 % and 6.3 %) however, palaeoflora of UW is more damaged (13.8 %) compared to the other layers. Almost all the different DTs appeared on the leaves of UW (30 DTs). In LW and MW, only external DTs (hole feeding, margin feeding and skeletonization) were observed, whereas in the flora of UW, surface feeding, piercing and sucking, oviposition, mining and galling appeared among the FFGs. According to the plant species with at least 20 specimens, *P. neptuni* was the most attacked species by insects in LW, while *U. pyramidalis* was the most damaged in MW. In UW, leaves of „*Rhamnus*” *warthae* have the highest damage frequency.

### 4.2.3. Richness damage comparison among the studied formations of the locality

Among the layers, the fossil leaves of UW have the highest damage type richness (Fig. 5B). This is true even if external and specialized damage are distinguished (Fig. 5C, D). Plant species richness highlights that UW has almost the same number of plant species (19) as LW (16) and MW (18), however, the richness of DTs is significantly higher (Fig. 5A). To minimize bias from species diversity differences between layers, we compared interactions of the same taxa across the layers to determine whether species diversity affected the observed differences in interaction diversity. We compared *Daphnogene cinnamomifolia* (Brongniart) Unger among the different layers because this is the only species

that is abundant in all layers in Wind Brickyard with at least 20 leaves per layer. *D. cinnamomifolia* (264 leaves) has a very low damage frequency (4 %) with 9 DTs. Most of the leaves come from MW (102) but the proportion of damaged leaves is the highest in UW (5.8 %) compared to LW (2.6 %) and MW (3.9 %). Rarefied DT richness based on a subsample of 70 specimens of *D. cinnamomifolia* shows that flora of UW has higher DT richness (6.2 ± 1.1) than LW (2.8 ± 0.6) and MW (3.1 ± 0.9) (Fig. 6). Specialized DT is absent on *D. cinnamomifolia* specimens from LW.

## 5. Discussion

### 5.1. Overview of the palaeoenvironmental conditions of the locality

Our palaeoclimate estimation shows significant differences compared to former studies (Andreánszky, 1966; Kvaček and Hably, 1991; Erdei and Bruch, 2004). CLAMP-based MAT values seem to be lower than those reported by previous authors (15–22 °C) (Andreánszky, 1966; Kvaček and Hably, 1991; Erdei and Bruch, 2004). Our results align with studies on Late Oligocene floras in the Czech Republic and Germany, which indicate a MAT between 9.4 and 13.6 °C while WMMT is consistent with Erdei and Bruch (2004) and Teodoridis and Kvaček (2015) intervals between 20.7 and 27.5 °C. The CMMT obtained by CLAMP is significantly lower than the CA values of Erdei and Bruch (2004). These differences are presumably influenced by the „riparian effect”, as the higher proportion of non-entire-margined species from riparian environments tends to result in colder palaeoclimatic estimates when using physiognomic techniques (Teodoridis, 2004; Mach et al.,
<figure><img src="image_6.png" /><figcaption>**Fig. 5.** Rarefaction curves comparing plant richness (A), damage type richness (B), external damage type richness (C) and specialized damage type richness (D). The grey line for LW, the orange line for MW, and the blue line for UW. The shaded area corresponds to the standard error of the rarefaction calculated after (Heck et al., 1975). The abscissa is reduced to 200 for detail. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

2014). Kowalski and Dilcher (2003) mentioned that the increased proportion of toothed leaves in wetland environments leads to an underestimation of temperature between 2.5 and 10 °C as modern datasets include several sites of dry lands while fossil megafloras mainly deposited in wetlands.

A pronounced seasonality was indicated by CLAMP. The precipitation intervals obtained by CLAMP are higher than those of Andreánszky (1966) and Erdei and Bruch (2004) based on the nearest living relatives and coexistence approach, suggesting greater precipitation than previously thought. In terms of climate classification, we suggest climates ranging from humid continental (Dfb) to oceanic (Cfb) and humid subtropical (Cfa/Cwa), with a trend towards temperate rainforest climates in some layers similar to Eastern Asia, Central and Southeastern China as Kvaček and Hably (1991) previously suggested.

Compared to previous studies on European Late Oligocene localities of Rott, Enspel (Germany) and La Val (Spain) (Wappler, 2010; Gunkel and Wappler, 2015; Moreno-Domínguez et al., 2022), damage frequency of Wind Brickyard (11 %) is relatively lower. Besides different types of vegetation, this might be caused by several reasons such as different depositional environments, taphonomic conditions and palaeogeographical positions. Most insect damage occurred on the most abundant species, which may indicate that mainly polyphagous insects left tracks without significant preferences for particular host plants. Galling is rare in the fossil assemblages of Wind Brickyard. Possible explanation could

be that galling insects survive better in drier environments with nutrient-poor soils than in wetter habitats such as Wind Brickyard due to higher possibility of fungal and pathogenic impact (Julião et al., 2014).

Vegetation of the whole Wind Brickyard is a mix of mesophylous forest and riparian-swampy elements due to the three distinct geological layers representing different types of environments. Hence, it is necessary to examine them separately to detect ecological changes among the layers.

## 5.2. Comparative analysis of the three formations of the locality

CLAMP results show that the UW layer is the coolest, based on MAT, CMMT, and WMMT (Fig. 2A; Supplement S7), with an annual temperature range of about 24 °C, which corresponds to the values suggested by Kvaček and Hably (1991). Lower estimated palaeotemperature values definitively support the riparian character of UW. Environments near water bodies undoubtedly provide unique microclimatic conditions. Palaeotemperature of LW and MW do not differ too much in contrast to the UW, the time interval could not be long enough to reflect a remarkable change in the climatic conditions (Kvaček and Hably, 1991). Subtropical mesophilous zonal forests, although highly biodiverse, may experience more pronounced seasonal effects, limiting certain plant-insect interactions (López-Carretero et al., 2016; Wang et al., 2020). Insects and host plants have seasonal adaptations to environmental
<figure><img src="image_7.png" /><figcaption>**Fig. 6.** Rarefaction curves of all damage types on leaves Daphnogene cinnamomifolia. The grey line for LW, the orange line for MW and the blue line for UW. The shaded area corresponds to the standard error of the rarefaction calculated after (Heck et al., 1975). The abscissa is reduced to 70 for detail. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

conditions during different seasons (Tauber and Tauber, 1981; Wolda, 1988). Higher precipitation levels have been linked to increased nutrient availability in the soil, which can indirectly influence leaf chemistry and herbivory intensity (De La Fuente et al., 2024). In particular, elevated nitrogen and phosphorus levels can enhance leaf palatability, potentially driving higher defoliation rates, especially among generalist herbivores. However, precipitation alone is unlikely to be the sole factor influencing herbivory, as host plant traits, seasonality, and insect feeding specialization also play critical roles in shaping damage patterns. Hence, the wetland vegetation of UW, which might be more in-dependent of the regional climate's seasonality (rainfalls, dry seasons), could continuously provide a larger amount of resources for insect herbivores.

CLAMP results reveal a decreasing palaeotemperature trend across the Late Oligocene at Wind Brickyard (Fig. 2A), potentially biased by riparian and swamp elements that create cooler microclimates despite warmer regional conditions (Kowalski and Dilcher, 2003; Teodoridis, 2004; Spicer et al., 2005; Mach et al., 2014; Peppe et al., 2018). Decreasing precipitation is presented by C4 while C1 shows similar amount of precipitation among the layers (Fig. 2B). However, gridded data of C1 results lower precipitation values compared to ungridded calibration of C4 (Spicer et al., 2009). CLAMP gives usually lower temperature values when used for European fossil megafloras (e.g. Utescher et al., 2000; Uhl et al., 2003, 2006, 2007a, 2007b; Peppe et al., 2011; Thiel et al., 2012). Calibrations based on modern datasets do not include evenly distributed modern flora networks worldwide (Yang et al., 2011).

Generally, damage richness is closely linked to plant diversity across layers. However, plant species richness is relatively similar between layers. Despite this, UW exhibits a higher damage richness compared to LW and MW (Figs. 5B-D). This could be explained by differences in host plant composition: UW is dominated by swamp and riparian elements, while LW and MW primarily represent zonal subtropical mesophilous forest vegetation. Riparian environments provide a high diversity of nutritional resources and habitats for insects (Ramey and Richardson, 2017). Due to resource-abundant conditions, plant communities of riparian zones could have prioritized growth instead of chemical defense, making tender leaves more palatable to herbivores (Herms and Mattson, 1992; Lynn and Fridley, 2019; Silva et al., 2021).

The richness of plant-insect interactions shows the same pattern not only community level (all plant species combined) but also at species

level among the three layers. The herbivory diversity of subtropical species *D. cinnamomifolia* is similar to Wind Brickyard as a whole, with higher damage richness in UW than in the other layers (Fig. 6). It seems to suggest that damage diversity per species shows the same in terms of dynamics than the whole plant-insect interactions diversity dynamics. However, the results of this analysis is limited by the fact that only one species is sufficiently represented across all layers (> 20 specimens), restricting our ability to perform similar comparisons for other taxa.

### 5.3. Influence of host plant zonality on herbivory rates

Fossil plant species of Wind Brickyard can be categorized into groups whether the species are part of the zonal (depending on regional climate) or azonal vegetation (depending more on local climatic conditions) based on Hably and Erdei (2023). The zonality of host plants had a great influence on plant-insect interaction dynamics is one of the main focuses of this study. UW exhibits most of the azonal specimens, representing an association of riparian, swamp environments (Fig. 7A). Proportion of zonal elements is equalized among the flora networks of Wind Brickyard's layers. It appears that the majority of the damage is located on the azonal elements (Fig. 7B), which justifies the need to classify taxa into zonal, azonal, and unknown categories to understand this factor better.

In Fig. 7C, the proportion of specialized damage is higher on zonal elements than on azonal. Higher plant diversity indicates a higher probability of suitable host-plant interactions for generalists (Schuldt et al., 2010). Polyphagous insects can benefit from more diverse environments causing more damage as these ecosystems provide a wider variety of resources for them (Pfisterer et al., 2003; Joshi et al., 2004; Jactel and Brockerhoff, 2007; Unsicker et al., 2008). On the contrary, specialists are expected to prefer those environments that are relatively homogeneous (in space and/or time) (Futuyma and Moreno, 1988; Kassen, 2002; Marvier et al., 2004; Östergård and Ehrlén, 2005). Moreover, open, swampy riparian environments likely attract more generalist insects (Martini et al., 2021) compared to closed-canopy forests, where conditions limit the presence of certain insect groups. Müller et al. (2018) suggested that in central Germany's late Eocene riparian lowland environments, herbivory patterns were largely shaped by local environmental conditions rather than regional climate alone, with riparian vegetation supporting high herbivory levels primarily
<figure><img src="image_8.png" /><figcaption>**Fig. 7.** The proportion of leaves by zonality (A), the proportion of DTs whether occurred on zonal or azonal elements (B) and the proportion of generalized/specialized DT occurrences whether occurred on zonal or azonal elements (C). A means fossil leaves which were part of azonal vegetation, Z means fossil leaves which were part of a zonal vegetation.</figcaption></figure>

through generalized damage. This aligns with our findings at Wind Brickyard, where the UW layer, dominated by azonal riparian and swamp elements, shows higher damage frequency and a greater proportion of generalized herbivory.

Greater specialist damages might be due to monophagous insects preferring less stressful microclimatic conditions, such as closed habitats (subtropical mesophytic forest) (Travieso-Bello and Campos, 2006). In addition, there is a positive relationship between tree species with higher leaf toughness and the proportion of specialized herbivores (López-Carretero et al., 2016; Wang et al., 2020). This could affect also the pattern of higher specialist damage on zonal, tougher leaves. Depending on these facts, specialized damages are likely underrepresented due to the dominance of azonal elements, which create unstable ecological niches, unfavorable for specialist interactions.

Overall, the results of this study may indicate an increasing diversity of plant-insect interactions along with changes in palaeoenvironments over time rather than a decreasing palaeotemperature and precipitation gradient or plant species richness. Despite we detected cooling trends with decreasing precipitation, the wetland character of UW could cause higher frequency and richness of insect damage by providing better conditions for herbivores.

### 5.4. Some limits due to preservation bias

Although the fossil leaves were collected by a private collector (Ferenc Legányi), there is a potential taphonomic bias in the UW layer. The fossil leaf assemblage of the upper formation includes several deciduous species that appear en masse, unlike the other layers. Shorter transportation and waterlogged conditions in swamps and riparian forests slow down destruction, providing better preservational and faster burial circumstances for fossil leaves and their interactions. Underrepresentation of deciduous species in the lower layers might be due to mechanical decomposition during transport in the fluvial system, as well as, faster eradication under humid and warm climate (Ferguson, 1985, 2005). Insect damage could be more frequent on leaves of deciduous species, which might also affect preservation. The strong

selection of fossil leaves in the lower formations due to long-distance transport (Andreánszky, 1966; Kvaček and Hably, 1991) may have affected the observed plant-insect interactions. Certain damage types could be underrepresented if highly damaged or fragile leaves were preferentially lost during transport and deposition. This taphonomic bias has been documented in other fossil floras, where the preservation of herbivory traces depends on leaf toughness and burial conditions (Wilf et al., 2001). Future studies integrating taphonomic filters into quantitative assessments of herbivory would help refine interpretations.

Potential biases may affect the palaeoclimatic results, as CLAMP tends to estimate cooler climates, particularly for fossil assemblages dominated by riparian and swamp vegetation. These habitats create localized microclimates that are naturally cooler than the surrounding regional conditions, which can skew the temperature reconstructions. Previous studies of European fossil floras have noted this systematic tendency of CLAMP to produce lower temperature values (e.g., Girard et al., 2019).

## 6. Conclusion

The Wind Brickyard provides a unique insight into how herbivory patterns changed through time and different palaeoenvironments along three distinct layers during the Late Oligocene. Palaeoclimatic results of this study are significantly different, particularly MAT and CMMT, which are cooler than previous studies indicated. Damage frequency of Wind Brickyard is relatively low compared to other coeval fossil floras. It is interesting to note that decreasing palaeotemperature values are presented across the layers. It appears that UW is the coolest, while there are no remarkable differences between LW and MW. However, it is possible that the “riparian effect” could have caused lower temperature values of UW. Most of the insect damage is on fossil leaves of UW, which contrasts with other studies mentioning higher damage along with increased temperature (Wappler and Grímsson, 2016; Zhang et al., 2018; Ma et al., 2020). Palaeoenvironmental changes of host plants’ habitats might lead to observed differences among the layers as azonal vegetation of UW is characterized by mainly riparian and swamp
elements in contrast to lower layers, which represent mesophytic zonal vegetation with a few seashore elements in MW. The ratio of generalized to specialized damage occurrences highlights the influence of host plant zonality on herbivory dynamics. Generalist herbivores were more abundant in azonal environments like the riparian and swamp vegetation of the UW layer, while specialized damages were more common on zonal elements associated with stable, closed-canopy forests. These findings suggest that ecological stability and plant traits play key roles in shaping herbivory patterns. Moving forward, integrating Wind Brickyard into a broader meta-analysis of European fossil floras across the Cenozoic would place this locality in a wider context and refine our understanding of the evolution of European palaeoforests and their link to modern ecosystems.

### CRediT authorship contribution statement

Imre Gyökeres: Writing – original draft, Visualization, Investigation, Formal analysis, Conceptualization. Benjamin Adroit: Writing – review & editing, Conceptualization. Árpád David: Writing – review & editing.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

### Data availability

The data supporting our results are provided as Supplementary data to this article.

### Acknowledgments

The authors are grateful to Alfred Uchman and an anonymous reviewer for their advice, fruitful comments and suggestions. BA acknowledges support from a Carl Tryggers Stiftelse postdoctoral grant (project no. CTS21: 1585). We are indebted to Rozália Fodor for her assistance in the study of the palaeobotanical collection of the Mátra Museum of the Hungarian Natural History Museum, Hungarian National Museum Public Collection Centre. Special thanks go to Erika Bognár who helped a lot in photographing of fossil plant samples.

### Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.palaeo.2025.112828.

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