Taphonomy

A detailed understanding of the taphonomy is a crucial matter (Fig 4). How were the bryophyte fragments transported to the discovery site leading to preservation? The narrow, shallow rocky gully, in which the mummified corpse was discovered, is a sediment trap (Fig 4). The organic remains were transported either by melt water (hydrochory), wind (anemochory) or animal/human activity (zoochory/anthropochory) into the hollow. Remains carried by melt water to the site, could only have arrived from the hydrological catchment of the site. The catchment is small (about 3000m²), due to the location just below the main Alpine ridge. Remains of plants growing in this area can be considered of local origin. Other remains are blown into the site by wind or are transported by human or animal activity. Their provenances might exceed the local catchment and may even derive from the valley bottoms. Such remains are defined as extra-local. The representativeness of a bryophyte fragment recovered from the hollow depends on abundance in the vegetation, distance from the growing area and its preservability over thousands of years after deposition.

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Fig 4. Taphonomic processes.

These led to the deposition of flowering plant remains at the Ötzi discovery site according to Heiss and Oeggl [14].

https://doi.org/10.1371/journal.pone.0223752.g004

Radiocarbon dating

Eleven of the radiocarbon dates relevant to the Iceman pertain to the mosses. They fall between about 4, 000 and 2,500 BC. Details are in S2 Appendix.

Excavations and sampling

The samples with bryophytes from the Iceman site were recovered in the course of two archaeological excavations at the discovery site conducted by Andreas Lippert, University of Vienna. The first excavation took place immediately after the discovery and lasted only three days due to bad weather conditions in autumn 1991. It was restricted to the south-eastern part of the gully, where the body had lain [32, 33]. The second excavation took place in the summer of 1992and focused on the bottom ice layer incorporating the most of the finds [34]. During this campaign the complete southern part of the gully was unearthed. The sun mainly melted the ice; only if artefacts appeared in the ice was a steam jet used to thaw out the objects. All melt-water from the gully was collected and directed with a system of gutters into a set of sieves, which collected all small finds carried with water. At the beginning of the excavation, a 1 m grid covering the gully was surveyed from the surface and coordinates were measured for detailed documentation and precise spatial information to ensure the exact location of all material retrieved from the site. After all the ice had been removed from the gully, the sediment of each quadrant was also sampled and taken to the Institute of Botany in Innsbruck for further analysis.

All discoveries were listed in a catalogue and ordered by the following categories of finding types [34]: 1. Equipment: comprising the wooden tools and weapons, such as the bow and the axe, quiver, backpack, birch bark vessels containing charcoal and maple leaves, retouching tool, wood; 2. Clothing: including twisted and sewn leather, fur, hat, shoes; 3. Netting: grass cape, twisted grasses, cords, animal hair, grass leaves, 4.Stray finds: summarize all finds, that could not be assigned to any of the categories mentioned;. 5. Sediment: all remains—mainly minerogenic but also organic—retrieved from the bottom of the gully. We use this classification also in our multivariate analyses. For further details on the samples (position at the discovery site, designation, finding type, etc.) see S1 Table.

Field survey of bryophytes

With emphasis on those species recovered with the Iceman, the present day bryoflora has been extensively recorded in one km squares in the region as shown in a few distribution maps already published [18, 22].These maps are now greatly augmented by the number of recorded squares much increased to 200.The bryophytes growing in the nival zone, above 3000m a.s.l, are listed in S3 Appendix.

Multivariate analyses

Two multivariate statistical approaches using the computer program CANOCO 4.5 for Windows were used for the analysis of the data set: Principal Component Analysis (PCA) and Redundancy Analysis (RDA), both with linear response models [35]. Two exploratory Detrended Correspondence Analyses (DCA) using the data sets for the PCA and RDA show gradient lengths between 2–3 SD (standard deviation units = taxonomic turnover units) indicating that the linear models PCA and RDA were appropriate for the bryophyte data-set [36].

The PCA Ordination is based on square root transformed count data including 200 samples with 70 different bryophyte species from the Iceman discovery site at 3210 m above sea level and 1 sample including 4 different mosses from the Iceman´s intestines. The two variables “moss stems” and “Hepaticae” were included in the analysis as supplementary parameters. The reduction of the complex multivariate dataset to 2 Principal Components (PC) highlights the relationship among the bryophyte species.

For the bryophyte distribution in relation to explanatory parameters a Redundancy Analysis (RDA) was performed [35] to find out the power of the explanatory parameters. The bryophyte data-set for the Redundancy Analysis comprises the same 200 samples and the analysis is based on square root transformed raw count data. Apart from the 70 bryophyte species also 14 types of macrofossils showing in part high frequency (animal hair, Brachypodium spikelets, cord, Corylus wood, Picea/Larix wood, Poaceae/Cyperaceae/Juncus leaves, leather twisted, Tilia bast, Tilia wood, charchoal sum, crops, aves (bird) feathers, faeces, Acer platanoides leaves) were included in the analysis. The following explanatory variables following 0/1 coded parameters were used: sediment, clothing, netting, equipment and stray finds. These parameters indicate the site of retrieval or collection of the samples. Since collinearity among the parameters poses a problem for multivariate analysis an examination of the correlation matrix between these variables was carried out to detect redundant variables. Apart from the low correlations between the variables sediment, clothing, netting, equipment and stray finds, they are also characterised by low variance inflation factor values (VIF < 20) implying that they were less redundant among each other [35]. The statistical significance of the canonical axes and the explanatory variables were determined using Monte Carlo permutation tests with 499 random permutations [35, 37].

Apart from the Iceman intestine samples (red square) the sample numbers are not shown in both figures of the PCA and RDA to avoid overcrowding of the graphs. In the RDA ordination the direction and the length of the explanatory variables (bold red arrows) indicate the importance and the correlation of the variables to each other and to the first two RDA axes. The position (angle) of the species scores (blue arrows) to the explanatory variables (bold red arrows) shows the relationship of the species to the explanatory variables.

Differential preservation

The Iceman site is unique in Quaternary and archaeological bryology, whither in North America or Europe where such work has been carried out for many decades since the 19^th century [38, 39, 40]. No other site has been investigated at such a great altitude with bryophytes preserved by freezing over thousands of years. The rich bryophyte assemblage is especially outstanding in the large number of liverworts and the suite of rock-loving species such as Andreaea spp. and particularly Grimmia spp. Seven species of the latter genus is an unparalleled discovery from a Quaternary site.

The under-representation of liverworts in Quaternary and archaeological assemblages has been a recurrent topic and the Iceman bryophytes bear greatly on this matter. Subfossil bryophyte assemblages totalling many species often include not a single liverwort. In this case the implication is that rapid freezing has allowed the preservation of more than ten species of liverworts. The presence of frozen fragments of liverworts in samples taken from two rock glaciers, one in Switzerland and one in South Tyrol, supports the freezing theory for good representation of liverworts, better revealing the former abundance in the vegetation [41, 42].

Anthropochory

Endoanthropochory is indisputable for a small number of mosses. That the Iceman carried mosses unintentionally to the discovery site is certain because there are very small fragmentary remains of several mosses in his alimentary tract, most notably Neckera complanata, Anomodon viticulosus, Hymenostylium recurvirostre and two species of bogmosses, Sphagnum sp. and Sphagnum affine [16, 21, 22]. See S4 Appendix. The most intriguing among these species is Sphagnum affine which occurred in only one of the colon samples. Hymenostylium recurvirostre and Sphagnum affine are unexpected discoveries, discussed at length by Dickson et al. [21, 22]. Sphagnum affine is unknown now in South Tyrol but could well have grown in Vinschgau where formerly there were extensive mires. Had he known its absorbent, antiseptic properties, the Iceman could have gathered it there at 800m above sea level. Often lime-encrusted, Hymenostylium recurvirostre, found growing in only three squares (Fig 8), occurs in abundance only on wet, basic rock. How it came to be in the Iceman’s lowermost gut is a difficult matter to explain; perhaps in drinking water?

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Fig 8. Moss distribution.

Map showing the present distribution of the four mosses Anomodon viticulosus, Hymenostylium recurvirostre, Neckera complanata and Sphagnum teres in the region of the Iceman site.

https://doi.org/10.1371/journal.pone.0223752.g008

The Iceman is not alone in having moss fragments internally. The alimentary tracts of the two most famous Danish Iron Age bog bodies both have Sphagnum fragments as does Lindow Man from England [5]. Long Ago Person Found, a glacier mummy from British Columbia, had Sphagnum cf Acutifolia as well as Andreaea and several other mosses in the innards [5, 43]. In none of these cases were the mosses ingested deliberately. Neither nutritious nor palatable mosses are not knowingly ingested and certainly not as staples [44]. With bogmoss leaves and a few other mosses in her faeces, perhaps an exception is the late 15^th century Greenlandic frozen mummy of a woman who may have been starving to death which the Iceman certainly was not [5].

Before the moss fragments were known from the Iceman’s alimentary tract [16], that he had deliberately carried Neckera complanata was beyond reasonable doubt from the large mass of that species from the sample 91/124 (“sewn leather, fur, grasses”, belonging to his clothing; [17]). Another example is 91/137 leather, grasses, hairs from clothing had Neckera complanata, Neckera crispa, Hylocomium splendens Pohlia sp and Andreaea probably nivalis. This is the earliest known example of both ectoanthropochory and endoanthropochory.

Zoochory

That large mammals such as alpine ibex or chamois traversing or lingering at the Iceman site brought bryophyte fragments on feet or hair is surely very likely. That was ectozoochory and, furthermore, endozoochory is proven by the discovery of moss fragments in caprine droppings from the site. One dropping contained a fragment of Heterocladium dimorphum and another contained a fragment of Polytrichum piliferum. See S5 Appendix. Heterocladium dimorphum is not known to grow now in the Austrian Alps at higher than 2,800m [45] being a height 200m short of the nival zone and some 400m short of the Iceman site. Because of its habitat often being crevices in rock, it is not a particularly expected moss to have been inside a large grazer. In contrast Polytrichum piliferum is no surprise, this being a very common moss over a great altitudinal range and very frequent in the nival zone. Remains of mosses have been recovered from archaeological caprine droppings elsewhere, but only very sparsely, for example Akeret and Jacomet [46] and Jacomet, Leuzinger and Schibler [47]. Goats and sheep do not deliberately eat bryophytes and therefore few in quantity or variety are to be expected. Even larger herbivores such as muskoxen and reindeer/caribou eschew mosses if the preferred lichens are available [48].

Hydrochory

This was important only for local species. However, the catchment of the Iceman site is small and movement by water can only have taken place during the summer melt of snow and ice; the thousands of fragments Polytrichum. piliferum, Polytrichastrum sexangulare and Racomitrium lanuginosum may well have been carried by meltwater. At present, however, there are no constantly fast-flowing streams in the catchment. In the late summer meltwater merely seeps into the hollow.

Anemochory. Among the many wind-blown mosses listed in the papers by Miller and Howe Ambrose [29, 30] and McDaniel and Miller [31] are the nival or alpine zone mosses found with the Iceman such as Polytrichum piliferum, Hypnum revolutum, Hypnum vaucheri and Ditrichum flexicaule. Wind could have blown fragments of local bryophytes to lodge in the snow in or on top of the snow-filled hollow not just in summer but at other seasons. Flø and Hägvar found moss fragments including bulbils to be “common” in sticky traps very close to a glacier in southern Norway. Such aerial transport was mainly below 0.5m [49].

There is little evidence that bryophyte leafy fragments are transported over very large distances as distinct from microscopic spores which certainly are but of no relevance here. Even if a fragment of any of the 75 species had arrived from very far off there is no way that that could be known.

Last journey

An ascent along the lower Schnalstal was suggested by Lippert [32] and is in congruence with the reconstruction of his last itinerary by pollen and moss fragments from his intestines [5, 15]. The small tree Hophornbeam (Ostrya carpinifolia), the pollen of which was identified in big quantities in the large bowel, occurs in the lower Schnalstal in the forests. It seems puzzling that he took the most stressful track through a gorge, but considering scenarios that he was on the run [2, 50] a gorge provided most opportunities to hide. There are five mosses of especial importance in this matter (Fig 8): Neckera complanta, Anomodon viticulosus, Hymenostylium recurvirostre, Sphagnum teres and Sphagnum affine.

To the north of the Iceman site, Neckera complanata has not been recorded in Ventertal nor even in Ötztal; it is known in the very distant Inntal, about 50 km north of the site as the crow flies and longer on the ground. These five are low to moderate altitude mosses. Mainly of woodlands, the Neckera and the Anomodon often grow together in the bryosociologial category Neckerion complanatae, as do other Iceman mosses Neckera crispa, Anomodon curtipendula, Leucodon sciuroides and Amalystegium serpens. Today these mosses thrive in the lower Schlandraunertal, the lower Schnalstal and in the surroundings of the Vernagt reservoir (Fig 8). They are most frequent from the gorge of the Schnalstal to the mouth of the Pfossental. This strengthens the claim that the Iceman went up Schnalstal on his very last ascent, though no Hymenostylium has been found there: that calcicole moss of wet rock is known very near Schlandraunertal and in Pfelderertal too (Fig 8). A journey from the distant Pfelderertal seems very unlikely but the possibility of Schlandraunertal cannot be totally excluded.

Like most species of Sphagnum, Sphagnum teres grows in mires. There is an area with this species in several contiguous squares at the northwest (Kurzras and nearby, Fig 8). The aquatic/mire species Warnstorfia exannulatus (Sarmenthypnum exannulatum) and W. fluitans both grow near Kurzras. Perhaps this indicates that the Iceman was in that vicinity just before the ascent to 3,210m and his violent death. For this very last climb either Finailtal or Tisental would have been possible. Before all that, the fragment of the low altitude, mire species Sphgnum affine taken from the colon is an indication that Ötzi had been in the Vinschgau valley bottom, conceivably as low as 600m; that after his first descent and just before the final ascent to the nival zone [2,5,15].

Palaeoecology

In the bryophyte assemblage there are rock-loving species, aquatic species, mire species, bare ground species and shade-loving woodland species. The local species are mainly acidophytes and cryophytes, both chionophile and chionophobe [51].

The subfossil bryophyte record from the hollow suggests that the bryoflora between 4,000 and 2,000 years BC was very similar to that growing now (S1 Appendix and S1 Table). With over 3,000 recovered fragments wide ranging Polytrichum piliferum in 182 samples out of 200 was abundant then as now, the same for the chionophilous Polytrichastrum sexangulare in 137 samples. This correspondence can be claimed also for the chionophobous Paraleucobrym enerve in 74 samples. As now there was a boulder strewn landscape with much bare rock and summer snow melt but plenty snow lying late into summer and through the year.

However, there are some marked contrasts. Forming merely small tufts here and there, this present scarcity of Racomitrium lanuginosum in the vegetation contrasts with the thousands of fragments from 148 samples. Even more of a contrast is the good subfossil representation of Grimmia mollis in 53 samples with a total lack from the hydrological catchment now; it is a species of more or less constantly wet rock and sides of rivulets. That type of habitat similarly suits Andreaea nivalis in 48 samples while being very sparse in the catchment now. It also suits Apomaruspella revoluta in 11samples; that liverwort is not in the catchment now. However, it is known in the nival zone or very close to it elsewhere in Austria and Italy, Switzerland and France. All that suggests that the catchment was wetter for much or all of the time covered by the subfossils. If that is a correct deduction then the case for hydrochory is supported.