A study on fern and fern-ally spore composition in Miocene sediments to improve our understanding of the origins of fern diversity in western Amazonia

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A study on fern and fern-ally spore composition in Miocene

sediments to improve our understanding of the origins of fern

diversity in western Amazonia

L. van den Bos – 10829148

Future Planet Studies: Earth Science

University of Amsterdam

Primary advisor: M.C. Hoorn

Secondary advisor: C.N.H. McMichael

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Index

Abstract ... 3 Introduction ... 3 Area description ... 5 Theoretical framework ... 6 Methodology ... 7

Modern fern flora ... 7

Miocene spore determination ... 7

Results ... 9

Discussion ... 12

Relation between the different groups ... 12

The Pebas over time ... 12

Andean genera ... 13 The Várzea ... 14 Conclusion ... 14 Acknowledgement ... 15 References ... 15 Appendix ... 19 Appendix 1 ... 19 Appendix 2 ... 38

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Abstract

There are many different theories about the cause for the high biodiversity of western Amazonia. Andean uplift in the Cenozoic era is believed to be one of the main drivers for the high species-richness in this area. Pteridophytes are important contributors to the species-species-richness of the Amazonian rainforest. Their diversity and distribution patterns, related to specific soils, are a motivation to research their development through time. In this study, the fern composition of Miocene sediments of western Amazonia is analyzed and compared with modern taxa in Amazonia and on the Andean slopes, to increase our understanding of the origin of fern diversity. I used a combination of microscope analysis and a literature study. Through time, an increase in unique genera comes forth and typical Andean genera enter the dataset from the mid- to late-Miocene. The cation-rich Pebas formation, which initiates in the early Miocene, becomes more biodiverse over time. Surprisingly, the similarity of the fern composition between the Miocene Pebas formation and the modern Pebas formation does not seem to be significantly bigger than the similarity between the Miocene Pebas and the modern Nauta formation. This study also suggests that, in relation to overall sporomorph composition throughout the Miocene, the fern spores do not vary much in abundance, but the composition does change over time. I conclude that these changes are most likely due to the increasing influence of the Andes mountain range as sediment provider to western Amazonia, which generated a more enriched soil type and also brings in spores from the mountain forests.

Keywords: Western Amazonia, Andean uplift, pteridophytes, Miocene, spore determination

Introduction

The cause of the species-richness of western Amazonia – the most biodiverse terrestrial ecosystem on our planet (Hoorn et al., 2010) – is a subject much debated over the past decades. In 1969, Haffer proposed the refuge theory to explain the diversity of bird populations. This theory states that during dry climatic periods in the Pleistocene, the Amazonian forest was divided into many smaller forests, thereby isolating animal- and plant species. During the wet climate periods the forests reunited and species dispersed. According to Haffer (1969), this happened several times and this led to the high biodiversity in western Amazonia.

More recent studies suggested that Pleistocene climate change could not have caused forest

fragmentation (Colinvaux, Irion, Räsänen, Bush & De Mello, 2001). Many other articles state that the origin of the high biodiversity of western Amazonia lies in the many dispersal barriers in the form of rivers and subsurface arches (Dinerstein et al., 1995; Olson et al., 2001; Lougheed, Gascon, Jones, Bogart & Boag, 1999; Patton, Da Silva & Malcolm, 2000).

This paper, however, is based on the assumption that the cause of the high biodiversity finds its origin on a far larger timescale: the Andean uplift in the Cenozoic era. Hoorn et al. (2010) explain that the Andean uplift had great effects on the landscape evolution of northern South America. The Andes formed a barrier, changing river drainage patterns as well as climate. The changing environment of the past 65 Ma still divides the Amazonian rainforest on the basis of geological formations and their edaphic properties (Fig. 1).

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Western Amazonia is characterized by different types of landforms that are related to specific types of bedrock. Each of these geological formations have their own characteristic types of soil and plant biomes (Higgins et al., 2011). Most characteristic are the crystalline rocks of the Amazon Craton, the white sand units related to rivers with their source in Amazonia, the Miocene Pebas (or Solimões formation as it is called in Brazil) which are fluvio-lacustrine sediments mostly of clay composition and with their source in sub-Andean areas, and younger fluvial sand/clay units such as the Ica and Nauta formations sourced from the Andes (Hoorn & Wesselingh, 2011; Higgins et al., 2011; Räsänen, Linna, Santos & Negri, 1995).

Worldwide, there are 10,560 different known species divided into 240 genera and approximately 33% of them occur in the American tropics (Christenhusz & Byng, 2016; Tryon & Tryon, 2012). Due to the unique circumstances and edaphic properties, some pteridophytes species are endemic in distinct Amazonian regions (Tryon & Tryon, 2012). The modern fern composition in western Amazonia is well studied by Higgins et al. (2011) and Tuomisto et al. (2016) who presented an inventory of the pteridophyte species composition in their study areas. They related the

characteristic pteridophyte composition to both soil type and geological formation (either Pebas or Nauta formation) and found there was a distinct difference depending on the geological formation on which a soil was formed.

The aforementioned works form an interesting basis for a comparison of the spore fossils found in Miocene sediments, and can give insights in the development of pteridophytes in western Amazonia. This research aims to improve our understanding about the origin of pteridophyte diversity through a palynological study on spores in Miocene sediments. Here we compare the fern spores composition

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on the early- to mid-Miocene cation-rich Pebas formation (25-10 Ma) with fern composition on the associated soils of both Pebas and the late Miocene, cation-poor Nauta formation (10-5 Ma). We also compare these data with the fern composition in the modern, often inundated, várzea and the high altitudes of the modern Andes (Higgins et al, 2011).

Insights into the origins of fern diversification will increase our knowledge about the development of the modern Amazon and may help us preserve this endangered ecosystem in the future. The

following central question will be addressed in this thesis: Is there a close relation between the

current pteridophyte composition on Nauta and Pebas soils and the pteridophyte composition of the Miocene Pebas in western Amazonia?

Furthermore, we will investigate how the relative abundance of fern spores changed through time in comparison to other sporomorphs, whether the composition of the fern flora on the Pebas formation changed through time, at what point in time typical Andean genera reached western Amazonia, and whether the modern várzea resemble the other formations discussed.

This thesis will include theoretical background on the landscapes, a location description, an extensive methodology, results, and lastly a discussion and conclusion.

Area description

Western Amazonia is here defined as the area that extends from the lower Andean slopes (up to 500 m altitude) to the meeting of the Rio Negro and the Solimões River, in the proximities of Manaus. As stated in the introduction, Western Amazonia is the most biodiverse terrestrial ecosystem on our planet (Hoorn et al., 2010; Ter Steege et al, 2006). A lot of biological research has been done in this area, which will be used in this study. All data collected in western Amazonia is somewhat biased as the only form of long distance travel through most parts of western Amazonia is by boat. For this reason, the data is always collected relatively close to a waterbody (Moulatlet, 2017).

Figure 2: Data locations. Fig 2A: Higgins et al., 2011. Fig 2B: Hoorn, 1993 and 1994. Fig 2C: Tuomisto et al., 2016

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The comparison in this research consists of two components: on one side there is information on the composition of the modern-day fern flora (Higgins et al., 2011; Tuomisto et al., 2016), and on the other hand the Miocene samples collected by Hoorn et al. in the early nineties (e.g. Hoorn 1993, 1994) all of which contain spore fossils. Higgins et al. collected their data in Northern Peru along the Tigre, Pucacuro and Pastaza rivers (Fig. 2A). Tuomisto et al. collected their data in western Brazil along the Juruá River (Fig. 2C). The samples collected by Hoorn et al. come from four sections along the Amazon River, very close to the point where the three countries come together. In stratigraphic order from old to young these four sections are situated at La Tagua, Santa Teresa, Mocagua, Santa Sofia (Fig. 2B). Hoorn (1994) shows that the samples at Santa Teresa and La Tagua formed in the early Miocene and that samples collected at Santa Sofia and Mocagua were deposited in the mid- to late-Miocene (Fig. 3).

Theoretical framework

This thesis follows the assumption that different geological formations and their edaphic properties are the cause of the high biodiversity, and that the origin of these landscape is important.

From 31 Ma onwards, Andean uplift is triggered by changes in plate configuration along the west of South America (Parra et al., 2009). Before this event, drainage patterns of the rivers in Amazonia were predominantly directed towards the west (Wanderley‐Filho, Eiras, da Cruz Cunha & van der Ven, 2010). Further Andean uplift created a barrier for these rivers and a large wetland was formed to the east of these young mountains (Hoorn et al., 2010). In this lacustrine environment, the fluvio-lacustrine Pebas formation was deposited. This formation developed between 25 and 10 Ma and consists of poorly weathered cation-rich clay sediments (Räsänen et al., 1995; Hoorn et al., 2010). Overlaying the Pebas formation is the much younger Nauta formation. This formation dates from the late Miocene (10 - 5 Ma) (Higgins et al., 2011). Further Andean uplift drained the wetlands and changed the predominant river flow direction from west to east (Hoorn et al., 2010). Sandy, weathered, cation-poor sediments were deposited in great quantities in the late Miocene (Schobbenhaus et al., 2004). Although the Nauta formation was deposited on top of the Pebas formation, each geological formation lies at the surface in different areas, because further Andean uplift increased orographic rainfall, which in some places eroded the Nauta formation (Roddaz, Baby, Brusset, Hermoza & Darrozes, 2005).

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Subduction of the Nazca Plate is still ongoing today and currently the Andes mountains contain peaks with an altitude of over 5,000 meters (Encyclopaedia Britannica, 2017). The exceptional

circumstances of the Andes make it an excellent environment to home many unique pteridoophyte species. There are over 1,500 different pteridophyte species in the Andes, most of which thrive in cloud forests (Tryon & Tryon, 2012). Some genera are endemic and therefore good indicator genera for the area. However, it must be considered that diagnostic genera of the Andes could have been transported fluvially and may be found in the Miocene Pebas sediments.

Lastly, the várzea forests are floodplains inundated by nutrient-rich rivers. They are flooded up to 210 days per year with water levels that can rise to 15 meters (Parolin, Ferreira, Albernaz & Almeida, 2004). The várzea forests are important for this research, because these forests are flooded with nutrient-rich whitewater rivers originating in the Andes. The soils are very fertile and might contain a lot of pteridophyte species (Richey & Devol, 1986).

Methodology

This study consists of two parts. Firstly, the modern fern flora will be studied in a literature study based on Higgins et al. (2011), Tuomisto et al. (2016) and Tryon & Tryon (2012). Secondly, the early- and mid/late-Miocene fern flora is determined through a palynological microscope study. During this study, the pteridophyte spores are classified by genus, because it is impossible to distinguish all 10,560 different known species based on their appearance under a microscope. The spore classification is done based on morphologic features of the spore with the help of Tryon & Tryon (2012), Henry Hooghiemstra’s PhD thesis (1984), by Solé de Porta & Murillo-Pulido (2005) and the IBED reference collection.

Modern fern flora

To get a clear overview of the modern genera in western Amazonia, table 1 is made in which each row represents a genus and each column a soil type. Red crosses indicate information collected by Higgins et al. (2011) and blue crosses indicate the added information from Tuomisto et al. (2016). A third column represents the várzea, and green crosses are used to represent information gained from Moulatlet, Costa, Rennó, Emilio & Schietti (2014).

In table 2, the altitudes at which the genera from table 1 occur are visualized. Tryon & Tryon (2014) provide growing altitudes of all the genera in the world. Furthermore, genera that only occur at high altitudes are added to table 1 and 2, to include typical modern Andean genera.

Miocene spore determination

The Miocene sediment slides are already prepared for a study by Hoorn (1994). In this study as many slides as possible were examined in the provided time. If a spore is encountered, the section, slide number and microscope coordinates are documented. Subsequently, the spore is photographed at least once (sometimes one photo is not enough to completely visualize the spore). Then the spore morphology is described. To optimize the morphological description, multiple books and articles are used (Playford & Dettmann, 1996; Punt, Hoen, Blackmore, Nilsson, & Le Thomas, 2007;

Hooghiemstra, 1984). The description includes the following aspects if applicable: - Number of laesurae: either monolete or trilete.

- Size: maximum length of the trilete spores/length and width at monolete spores. - Shape: circular, subtriangular convex/concave, triangular, etc.

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- Thickness of the sclerine: actual thickness in micrometer and continuity of the sclerine thickness.

- Details about the laesurae: thickness, distance to sclerine and waviness.

- Surface features and their length: like, but not limited to, the ones described by Playford & Dettmann in 1996 (Fig. 4).

Lastly, the closest related modern genus is determined based on the morphological features. Three sources are used for photo comparison of the spores: Hooghiemstra (1984), Tryon & Tryon (2012) and Solé de Porta & Murillo-Pulido (2005). If there are any contradictions, Tryon & Tryon (2012) is used as the leading literature.

To visualize the data, two extra columns with black crosses are added to table 1. One represents the mid- to late-Miocene (Santa Sophia & Mocagua) and the other represents the early-Miocene (Santa Teresa & La Tagua). Furthermore, extra rows were added to table 1 and 2 where there are genera that did not occur in the modern fern flora. The tables are shown in the results and the data of the fossil spores is added as appendix 1 and 2. In addition, a curve is added to visualize the relative abundance of fern spores through time compared to overall sporomorph abundance (Fig. 5). This curve is based on counting data provided by Hoorn concerning the sections La Tagua, Santa Teresa, Pevas, Los Chorros and Santa Sofia. This abundance through time can clarify the development of fern diversity. For data management purposes, the fossil data is stored as a .pdf file and data about the affinity of spores is stored in a .csv file.

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Results

In tables 1 and 2 the findings of this study are presented. In total, 20 different pteridophyte genera can be distinguished in the Miocene sediment. In the early Miocene sediments, 9 fossil spores of different genera were found. In the mid- to late- Miocene sediments this number increased to 19, and in modern times 37 different genera were identified.

The relative abundance curve does not show a big increase or decrease of fern spores over time compared to the overall sporomorphs (Fig. 5).

Of the different genera found in the Miocene Pebas sediments, 9 appear to be closest related to genera that were also found in modern Pebas soils by Higgins et al. (2011) and Tuomisto et al. (2016), three of which are indicator genera for the modern Pebas formation. The exact same numbers hold for the comparison with the Nauta formation and the Miocene sediments. However, for the Pebas formation, a proportion of 0.3462 genera are shared, and for the Nauta a proportion of 0.4091. The proportion test gives a Z-score of 0.4485, so the null hypothesis is accepted, meaning this is not a significant difference.

Furthermore, when only looking at the Pebas formation through time, an increase in number of genera is visible from the early Miocene to the modern fern flora. When only looking at the first timestep, the mid- to late-Miocene seems to be an expansion of the early Miocene biodiversity. Although, during the second timestep, some genera disappeared.

Table 2 gives more insight into the Andean genera. There are 8 genera that only grow at a minimum altitude of 1000 meters or higher. Of those genera, 5 were not encountered in the literature study and in the microscope study. The other 3 were only found in the Miocene Pebas sediments. Lastly, the várzea seem to be more similar to the Nauta formation than to the Pebas formation. Of the 13 genera, 10 also grow on Nauta soils, compared to the 6 that grow on modern Pebas soils and only 3 that were found in the Miocene sediments.

Figure 5: Fraction of fern spores relative to all sporomorphs for the Amazon River composites, based on counting data provided by Hoorn.

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Table 1: Occurrence of genera. X=Higgins et al. (2011); X=Additions from Tuomisto et al. (2016); X=Moulatlet et al. (2014).

Modern landscapes Mid- to

late-Miocene

Early Miocene Modern fern flora genera The Pebas

formation

The Nauta formation

The várzea Santa Sofia &

Mocagua

Santa Teresa & La Tagua Acrostichum X Adiantum X X X Anetium X Anogramma X Asplenium X X X X Bolbitis X Botrychium X Campyloneurum X Ceratopteris X Cnemidaria X X Ctenitis X X Culcita Cyathea X X X X X Cyclodium X Cystopteris X X Danaea X X X Davalliopsis X Didymochlaena X Diplazium X Elaphoglossum X X X Histiopteris Jamesonia X Lindsaea X X X Lomagramma X Lomariopsis X X Loxsomopsis Lycopodium X X Lygodium X Metaxya X X Mickelia X Microgramma X X X Nephrolepis X Paesia Pecluma X Pityrogramma X X Plagiogyria Polybotrya X X Polypodium X X X X Polytaenium X X Pteridium X Pteris X X Saccoloma X X Salpichlaena X X Schizaea X X X X Selaginella X X X X Stigmatopteris X Tectaria X X Thelypteris X X X Trichomanes X X X Triplophyllum X X Total 26 22 13 20 9

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Table 2: Altitude indication for used genera (Tryon &Tryon, 2012).

Genus Occurring altitude in South-America [m above sea level]

0 500 1000 1500 2000 2500 3000 3500 4000 Acrostichum Adiantum Anetium Anogramma Asplenium Bolbitis Botrychium Campyloneurum Ceratopteris Cnemidaria Ctenitis Culcita Cyathea Cyclodium Cystopteris Danaea Davalliopsis Didymochlaena Diplazium Elaphoglossum Histiopteris Jamesonia Lindsaea Lomagramma Lomariopsis Loxsomopsis Lycopodium Lygodium Metaxya Mickelia Microgramma Nephrolepis Paesia Pecluma Pityrogramma Plagiogyria Polybotrya Polypodium Polytaenium Pteridium Pteris Saccoloma Salpichlaena Schizaea Selaginella Stigmatopteris Tectaria Thelypteris Trichomanes Triplophyllum

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Discussion

First of all, it should be mentioned that the data collected from the Miocene sediments is not complete. Much more data can be collected from other sections (Fig. 3). The scope of this thesis needed to be confined because the microscope research had to be done in one month. Sections Santa Sofia, Mocagua, La Tagua and Santa Teresa were selected, because with those sections and the modern fern composition a clear division in three time periods could be made.

The closeness of the relation between the Miocene Pebas sediments and the modern landscapes as a whole is debatable. The spores found in the Miocene sediments can be affiliated to 20 different genera. Which is not much in comparison to the 240 genera worldwide, of which 119 occur in the American tropics (Tryon & Tryon, 2012). The studies conducted by Higgins et al. (2011), Tuomisto et al. (2016) and Moulatlet (2014) are done on a comparative scale and relatively close to the sampling location of the Miocene sediments. Thus, comparing the data to those papers makes more sense than comparing it to the worldwide dataset.

An assumption is made by Hooghiemstra (2002) based on pollen data: during the Miocene, flora diversity was even higher than today. Therefore, an increase from 20 different genera in the Miocene to 37 genera on these modern landscapes is still against expectations. Especially when taken into account that the Miocene samples represent a far larger area, as the spores of some genera may have been deposited at those sections after fluvial or aerial transport. This mismatch is partially explained by the fact that the collection of the Miocene spore fossils is not complete, and more genera are likely to be identified in expanding studies.

Relation between the different groups

When the modern landscapes are grouped together and all the Miocene samples are too, 32.43% of the genera found in the modern fern flora are also identified in the Miocene samples, with an addition of 8 other genera that were only found in the Miocene samples. It would be wrong to assume that some of those genera have gone extinct, because the fossil spores in this study are all determined by the affiliation to modern day genera. It is however possible that some of the actual taxa that belong to the spores in the Miocene samples are extinct, as there has been a negative evolution-extinction balance since then (Van Der Hammen & Hooghiemstra, 2000).

If the Nauta and Pebas formations are compared separately to the Miocene samples, they each share 9 genera. For the Nauta formation this is 40.91% of its total number of genera and for the Pebas formation this is 34.62%. However, a proportion test shows no significant difference in these

numbers. Therefore, it can be concluded that with this data, the fern flora on Nauta- and the modern Pebas formations differ equally from the Miocene fern composition. This is unexpected because the Miocene sediments are originating from the Pebas system, while the Nauta formation is formed in the late Miocene to early Pliocene (Higgins, 2011). A possible explanation for this is that the spores found in the sediments were transported from more sandy areas, for instance from early Andean areas. The Nauta formation is formed by these sandy units by fluvial transport from the Andes and might therefore resemble the Miocene sediments just as much as the modern Pebas formation (Higgins, 2011).

The Pebas over time

The data clearly shows that the diversity of pteridophyte genera increases within the Pebas formation in stratigraphically younger sediment layers. From the early Miocene to the mid- to

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late-Miocene, the number of different genera increased from 9 to 19. Although 11 new genera were introduced, Ceratopteris (which was relatively abundant in the early Miocene sediments) seems to have disappeared. An explanation for this could be that Ceratopteris only grows at very low altitudes in wet habitats (Tryon & Tryon, 2012). In the early Miocene, the Pebas embayment covered great parts of western Amazonia including our study area (Hovikoski, 2007), while further Andean uplift drained the Pebas embayment, forcing the majority of typical wetland flora and fauna to migrate north along with the retracting brackish water that filled the Pebas embayment (Gingras, Rasanen, Pemberton & Romero, 2002).

Behling, Berrio and Hooghiemstra (1999) and Urrego (1997) collected samples along the Rio Caquetá. These samples were dated back to the late Pleistocene to early Holocene, and contained spores of 3 genera: Cyathea, Selaginella and Polypodium. This puzzle piece fits perfectly in the data collected for this study. Because, these 3 genera were the most encountered genera in the mid- to late-Miocene samples (App. 1 & 2) and are also big contributors to the modern day fern flora (Tryon & Tryon, 2012).

During the second timestep in this study, from the mid- to late-Miocene to modern times, the total number of different genera found in the Pebas formation became 26 - another increase. However, 10 genera from the mid- to late-Miocene did not show up in the data collected from the literature study. A reason that some of the genera supposedly disappeared is because the spores might have been transported over long distances before deposition, whereas the plants identified by Higgins et al. (2011) and Tuomisto et al. (2016) did not move. The genera Botrychium, Cystopteris and

Jamesonia prove this assumption: spores of these genera where found at an altitude of

approximately 100 meter, while Botrychium grows higher than 1000 meters, Cystopteris occurs only above 1500 meters and Jamesonia does not even grow below 3000 meters (Tryon & Tryon, 2012). The relative abundance curve (Fig. 5) shows no big changes in the occurrence of fern spores in comparison to other sporomorphs during the Miocene. Combined with the modern and Miocene spore determination (Table 1), this leads to the insight that the relative size of the fern flora did not increase, but the composition did change, as the number of genera expanded and the composition of genera changed in this study.

Andean genera

When looking at the fern versus altitude table, 8 genera grow at an altitude of 1000 meter or higher. Obviously, these genera where not recorded in the studies of Higgins et al. (2011) and Tuomisto et al. (2016), because these studies were performed at altitudes of respectively 200 and 150 meters. Of those genera, 3 did occur in the mid- to late-Miocene sediments and 1 occurred in the early Miocene sediments. The one Cystopteris spore in the early Miocene samples has probably been transported a long way from the south, where higher peaks were more common at those times (Hoorn et al., 2010).

The Jamesonia spores found in the mid- to late-Miocene are a nice indicator for the uplift of the Andes. In these samples, a lot of Jamesonia was encountered, while this genus only grows at an altitude of at least 3000 meters (Tryon & Tryon, 2012). Therefore, it is safe to assume that mountain peaks of over 3000 meters high, did not occur before 17 Ma close to these latitudes. Other

palynological literature support this statement. Vink et al. (2012) encountered some spores from the indicator taxa Hemitelia in samples representing the late Miocene to the Pliocene (7.15-3.41 Ma).

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et al. (2012) describes a lot of pollen that occur in montane areas and these are all indicator taxa for the same time period.

Approximately 1500 kilometers south of our study area, Andean orogeny was far more developed. High mountain peaks occurred there about 20 million years before they arose west of our study area (Ramos, 2009). For this reason, it is likely that the typical Andean genera that were encountered in this study, first grew 1500 kilometers southwards, before they migrated northwards between the early Miocene and the mid- to late-Miocene.

The Várzea

Lastly, the várzea share only 23.08% of their genera with the Miocene samples. This is somewhat surprising, as one would expect that the inundated states of these ecosystems might be comparable to the wetlands of the early- to mid-Miocene as shown in figure 4. On the other hand, the water in the Pebas embayment contained brackish water and therefore did not resemble the fresh river water of the modern Andean rivers (Gingraset al., 2002). The vegetation in the várzea do, however, very closely resemble the Nauta formation vegetation. Of the várzea vegetation, 76,92% is also found on the Nauta formation. This close resemblance is explained by the fact that the Nauta formation is formed by sandy and weathered material transported by rivers from the Andes and várzea are ecosystems often inundated by whitewater rivers originating in the Andes (Schobbenhaus et al., 2004; Parolin et al., 2004). The close resemblance to the Nauta formation indicates that várzea forests are relatively modern ecosystems.

Conclusion

This pilot study gave some new insights in the origin of the modern fern diversity in western

Amazonia, traced back to the early Miocene. A lot of the early Miocene spores found at La Tagua and Santa Teresa, and mid- to late-Miocene spores found at Mocagua and Santa Sofia are closely

affiliated to genera that occur on modern landscapes in northern Peru and western Brazil. However, if more Miocene samples are included in a follow-up of this study, it is likely that the amount of affiliated genera will be larger.

While the modern Pebas formation is formed in the early- to mid- Miocene, the fern composition on this modern landscape does not resemble the Miocene fern composition better than the much younger Nauta formation does. The modern Pebas and Nauta formations respectively share 34.62% and 40.91% of their fern genera with the Miocene samples, which is no significant difference. This leads to the conclusion that some spores were transported to western Amazonia from much sandier areas, like the early Andes. Furthermore, the Pebas formation itself probably changed trough time. When focusing on the Pebas formation itself, the number of unique genera seems to have been expanding, while the relative abundance of fern spores did not increase in comparison to all sporomorphs. This unexpected expansion of genera is partially explained by the scope of this research and the different methods used for determining Miocene and modern fern composition. However, within the Miocene samples, a northwards migration of Andean taxa into our study area is visible.

In the mid- to late-Miocene samples Botrychium, Cystopteris and Jamesonia were encountered. Because these genera (especially Jamesonia) only occur at high altitudes, they are indicators of further Andean uplift to heights of over 3000 meters between the early Miocene and the mid- to late

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Miocene near our study area. This information is backed up by other palynological research in this area.

Lastly, the várzea ecosystems are assumed to be relatively young landscapes. The fern composition on the often inundated várzea do not resemble the fern composition of the wet Miocene landscapes at all. They are, however, closely related to the relatively young Nauta formation. The Nauta

formation is formed out of sandy material from the Andes and the várzea are often inundated by white water rivers originating in the Andes. This seems to make the edaphic properties of these landscapes, and therefore their fern composition, relatively similar.

As stated before, this is a pilot study and follow-up research is recommended to improve our insight in the origin of fern diversity in western Amazonia even more. In addition, another method to determine the modern fern composition (in the form of surface sediments or a spore trap) is advised to improve the comparison between the Miocene and modern times.

Acknowledgement

I would like to thank Carina Hoorn for her advice, supervision and patience. This study turned out to be a lot more biologically based than I expected and I could not have achieved the same results without her guidance. Furthermore, I would like to thank Annemarie Philip, her attendance during the microscope study made it a lot less monotonous.

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Appendix

Appendix 1

In this study, fossil spores affiliated with 20 different genera were encountered. The spores are distinguished by genus and ordered by taxa. Within some genera spores with varying morphological features were found; these are described separately. The description of all the different genera include taxa, section, slide, coordinates, morphological features, references and scaled photographs. Each description is written on a single page with a maximum of two descriptions per page.

Botrychium Class: Filicopsida Order: Ophioglossales Family: Ophioglossacaea

Sections, slides and coordinates: Moc 3 (99.3/52.2)

Morphological features: Trilete spore, subtriangular convex amb, max length: 50-65 micrometer, verrucate to regulate surface features up to 6 micrometer high, unclear laesurae.

References: Hooghiemstra (1984); Tryon & Tryon (2012) Photographs:

Schizaea

Class: Filicopsida Order: Polypodiales Family: Schizaeaceae

Sections, slides and coordinates: La Tagua 43 (104.7/47.1), Moc 33 (98.8/53)

Morphological features: Monolete spore, max length: 38-52 micrometer, small spherical surface features, laesurae expends to ½ to ¾ of the total spore length.

References: Tryon & Tryon (2012) Photographs:

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Cyathea I Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Ter 9 (94.7/53.7), Ter 10 (105.7/57.6; 104.7/45), Moc 10 (111.4/47.8), Moc 52 (101.6/49.5), Ssof 20 (98.7/59.3; 104.3/57), Ssof 23 (105.4/63.1)

Morphological features: Trilete spore, subtriangular convex amb, max length: 30-60 micrometer, laevigate to scabrate surface features, fine laesurae.

References: Hooghiemstra (1984); Tryon & Tryon (2012) Photographs:

Cyathea II Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Moc 7 (101/57.8), Moc 58 (107.8/51.5), Ssof 23 (99.3/63.4), Ssof 31 (109.7/52.5)

Morphological features: Trilete spore, triangular amb, max length: 45-65 micrometer, some rough scabrate surface elements, fine laesurae, slightly thicker radial sclerine.

References: Hooghiemstra (1984) Photographs:

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Cyathea III Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Ssof 20 (104.2/46.9)

Morphological features: Trilete spore, subtriangular convex amb, max length: 27-41 micrometer, scabrate to micro reticulate surface features, thick laesurae to sclerine.

References: Hooghiemstra (1984) Photographs: Cyathea IV Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Ssof 20 (108.7/56)

Morphological features: Trilete spore, subtriangular convex amb, max length: 35-58 micrometer, fine laesurae to sclerine, verrucate to tuberculae structures up to 6 micrometer high .

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Cyathea V Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Morphological features: Trilete spore, subtriangular convex amb, max length: 55-75 micrometer, thick open laesurae reaching ¾ of the radius, scabrate to reticulate surface features, radially thickend sclerine. References: Hooghiemstra (1984) Photographs: Cyathea VI Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Moc 10 (98/49.2; 109.5/53.3)

Morphological features: Trilete spore, subtriangular convex amb, max length: 36-48 micrometer, fine laesurae reaching ¾ of the radius, verrucate surface features up to 5 micrometer high.

References: Solé de Porta & Murillo-Pulido (2005) Photographs:

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Cyathea VII Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Moc 36 (109.3/56)

Morphological features: Trilete spore, subtriangular convex amb, max length: 38-50 micrometer, thick laesurae reaching ¾ of the radius, verrucate to reticulate surface features.

References: Solé de Porta & Murillo-Pulido (2005) and Hooghiemstra (1984) Photographs:

Cyathea VIII Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Morphological features: Trilete spore, subtriangular concave amb, max length: 43 micrometer, thin wobbly laesurae reaching ¾ of the radius, laevigate to some scabrate surface features.

References: Solé de Porta & Murillo-Pulido (2005) and Hooghiemstra (1984) Photographs:

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Cnemidaria Class: Filicopsida Order: Polypodiales Family: Cyatheaceae

Sections, slides and coordinates: Moc 52 (107.5/46.8), Moc 58 (100.6/60.5; 100.9/60.7) Morphological features: Trilete spore, subtriangular convex to circular amb, max length: 35 micrometer, fine laesurae reaching ¾ of the radius, thick interradial sclerine with 3 big pores in perispore.

References: Solé de Porta & Murillo-Pulido (2005), Tryon & Tryon (2012) and Hooghiemstra (1984) Photographs:

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Pityrogramma Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Sections, slides and coordinates: Ter 10 (107.1/57.8), Ssof 26 (111/55.1; 102.2/54.1), Ssof 31 (97.9/51; 107.1/56.2)

Morphological features: Trilete spore, subtriangular convex amb, length: 40-130 micrometer, thin laesurae reaching ¾ of the radius, scabrate to granulate surface features with folds.

References: Tryon & Tryon (2012) and Hooghiemstra (1984) Photographs:

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Anogramma Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Morphological features: Trilete spore, triangular amb, length: 35 micrometer, thin and wobbly laesurae, reticulate surface features at distal end, interradial thickening up to 4 micrometer. References: Tryon & Tryon (2012)

Photographs:

Jamesonia Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Sections, slides and coordinates: Moc 3 (104.3/61.1), Ssof 5 (112.2/58.5), Ssof 23 (109/55.2), Ssof 26 (101.4/62.1)

Morphological features: Trilete spore, subtriangular convex amb, length: 45-80 micrometer, thick and open laesurae, Scabrate to verrucate surface features on proximal side.

References: Tryon & Tryon (2012), Hooghiemstra (1984) Photographs:

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Ceratopteris Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Sections, slides and coordinates: Ter 10 (104.6/40.9; 106.4/57.3; 107.2/57.8)

Morphological features: Trilete spore, subtriangular convex to circular amb, length: 120 micrometer, unclear laesurae, parallel surface ridges.

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Pteris

Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Sections, slides and coordinates: Moc 58 (105.3/60.6), Ssof 3 (106.8/54.6)

Morphological features: Trilete spore, subtriangular convex to circular amb, length: 36-50

micrometer, fine laesurae, Heavy interradial thickening, laevigate to granulate surface features close to trilete mark. References: Hooghiemstra (1984) Photographs: Acrostichum I Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Sections, slides and coordinates: Ssof 26 (108.9/58.1), Ssof 31 (99.1/50.2)

Morphological features: Trilete spore, subtriangular convex to circular amb, length: 55 micrometer, thin laesurae to spore wall, laevigate surface features.

References: Solé de Porta & Murillo-Pulido (2005) Photographs:

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Acrostichum II Class: Filicopsida Order: Polypodiales Family: Pteridaceae

Morphological features: Trilete spore, subtriangular convex amb, length: 125 micrometer, thick open laesurae ¾ of spore radius, scabrate surface features.

References: Solé de Porta & Murillo-Pulido (2005) Hooghiemstra (1984) and Tryon & Tryon (2012) Photographs:

Saccoloma Class: Filicopsida Order: Polypodiales Family: Dennstaedtiaceae

Sections, slides and coordinates: Moc 30 (107.5/56.4), Ssof 31 (103.6/58)

Morphological features: Trilete spore, subtriangular convex amb, length: 42-65 micrometer, fine laesurae to sclerine, regulate surface features.

References: Hooghiemstra (1984) and Tryon & Tryon (2012) Photographs:

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Thelypteris Class: Filicopsida Order: Polypodiales Family: Thelypteridaceae

Sections, slides and coordinates: La Tagua 47 (96.9/38.6), Moc 3 (102.1/45; 105.8/57.7), Moc 52 (103.5/54.1), Moc 58 (103.2/49.4; 105.3/60.6), Ssof 26 (101.2/51.6)

Morphological features: Monolete spore, length: 32-40 micrometer, width 23-28 micrometer, laesurae unclear, echinate surface features up to 6 micrometer high.

References: Tryon & Tryon (2012) Photographs: Ctenitis Class: Filicopsida Order: Polypodiales Family: Dryopterideceae

Sections, slides and coordinates: Moc 7 (101.2/53.5; 105.3/48)

Morphological features: Monolete spore, length: 50-60 micrometer, width 23-31 micrometer, laesurae ½ to ¾ of the total spore length, spinose to pilate surface features up to 7 micrometer high connected by membranes.

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Cystopteris Class: Filicopsida Order: Polypodiales Family: Dryopterideceae

Sections, slides and coordinates: Ter 5 (108.2/43.2), Moc 3 (98.5/60.3)

Morphological features: Monolete spore, length: 45 micrometer, width 35 micrometer, laesurae ¾ of spore length, baculate to pilate surface features 4 to 6 micrometer high.

Elaphoglossum Class: Filicopsida Order: Polypodiales Family: Dryopterideceae

Morphological features: Monolete spore, length: 39-55 micrometer, width 26-40 micrometer, laesurae ¾ of spore length, surface folds form a pattern.

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Asplenium Class: Filicopsida Order: Polypodiales Family: Aspleniaceae

Sections, slides and coordinates: Ter 9 (109/58.6), Ter 10 (107/58.1), Moc 58 (100.6/61) Morphological features: Monolete spore, length: 39-55 micrometer, width 26-40 micrometer, laesurae ¾ of spore length, surface folds form a pattern.

References: Tryon & Tryon (2012) and Hooghiemstra (1984) Photographs: Polypodium I Class: Filicopsida Order: Polypodiales Family: Polypodiaceae

Morphological features: Monolete spore, length: 70 micrometer, width 50 micrometer, laesurae ½ to ¾ of spore length, scattered verrucate elements.

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Polypodium II Class: Filicopsida Order: Polypodiales Family: Polypodiaceae

Sections, slides and coordinates: La Tagua 47 (108/41.5), Ter 10 (105.2/46), Moc 20 (113.4/54.5), Moc 52 (108.2/52.2), Moc 58 (100.5/60.8), Ssof 26 (111/52)

Morphological features: Monolete spore, length: 40-58 micrometer, width 28-39 micrometer, laesurae ¾ of spore length, tuberculae up to 5 micrometer high.

References: Hooghiemstra (1984) Photographs: Polypodium III Class: Filicopsida Order: Polypodiales Family: Polypodiaceae

Sections, slides and coordinates: Ter 10 (106.1/57.7; 106.4/48.6; 106.6/57.9), Moc 20 (108/60.5), Moc 48 (107.9/55.5)

Morphological features: Monolete spore, length: 48-70 micrometer, width 47 micrometer, laesurae ¾ of spore length, tuberculae up to 4 micrometer high.

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Microgramma Class: Filicopsida Order: Polypodiales Family: Polypodiaceae

Sections, slides and coordinates: Moc 58 (103.3/55.7), Moc 66 (112.3/48.7), Ssof 5 (100.3/45.5) Morphological features: Monolete spore, length: 48-62 micrometer, width 34-50 micrometer, laesurae ½ to ¾ of spore length, verrucate to echinate surface features.

References: Hooghiemstra (1984) and Tryon & Tryon (2012) Photographs: Lycopodium I Class: Lycopodiopsida Order: Lycopodiales Family: Lycopodiaceae

Sections, slides and coordinates: Ter 10 (107/56.8), Ssof 14 (103.2/48.1), Ssof 23 (106.9/62.7) Morphological features: Trilete spore, subtriangular convex amb, max length: 40-50 micrometer, interradial sclerine thickening, thick and open laesurae, scabrate to verrucate surface features. References: Hooghiemstra (1984)

Photographs:

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Lycopodium II Class: Lycopodiopsida Order: Lycopodiales Family: Lycopodiaceae

Sections, slides and coordinates: Moc 33 (104/50), Moc 45 (102/61.4)

Morphological features: Trilete spore, subtriangular convex amb, max length: 40-50 micrometer, much interradial sclerine thickening, thick but closed laesurae, scabrate to regulate surface features. References: Hooghiemstra (1984) and Solé de Porta & Murillo-Pulido (2005)

Photographs: Lycopodium III Class: Lycopodiopsida Order: Lycopodiales Family: Lycopodiaceae

Morphological features: Trilete spore, subtriangular convex amb, max length: 35-50 micrometer, slightly interradial sclerine thickening, thin wavy laesurae to spore wall, foveolate surface features. References: Hooghiemstra (1984) and Solé de Porta & Murillo-Pulido (2005)

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Selaginella I

Class: Lycopodiopsida Order: Selaginellales Family: Selaginellaceae

Sections, slides and coordinates: Moc 3 (113/54.3)

Morphological features: Trilete spore, circular amb, max length: 40-95 micrometer, unclear laesurae, irregular folds up to 10 micrometer high.

Selaginella II

Sections, slides and coordinates: Moc 10 (96.2/46.6), Moc 18 (104.1/53.7)

Morphological features: Trilete spore, subtriangular convex amb, max length: 31-40 micrometer, unclear laesurae, pilate surface features up to 6 micrometer high.

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Selaginella III

Morphological features: Trilete spore, subtriangular convex amb, max length: 35 micrometer, thick laesurae up to sclerine, cristase surface features.

Selaginella IV

Sections, slides and coordinates: Moc 18 (106/47.5), Ssof 20 (109.4/52.1), Ssof 26 (100.5/56.1) Morphological features: Trilete spore, subtriangular convex amb, max length: 30-40 micrometer, unclear laesurae, echinae surface features all over.

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