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DEPOSITIONAL SETTING AND FOSSIL INSECT PRESERVATION: ASTUDY OF THE LATE EOCENE FLORISSANT FORMATION, COLORADOAuthor(s): JENELL THOENE HENNING, DENA M. SMITH, CÉSAR R. NUFIO , and HERBERT W.MEYERSource: PALAIOS, 27(7):481-488. 2012.Published By: Society for Sedimentary GeologyURL: http://www.bioone.org/doi/full/10.2110/palo.2011.p11-084r

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PALAIOS, 2012, v. 27, p. 481–488

Research Article

DOI: 10.2110/palo.2011.p11-084r

DEPOSITIONAL SETTING AND FOSSIL INSECT PRESERVATION: A STUDY OF THE LATE EOCENEFLORISSANT FORMATION, COLORADO

JENELL THOENE HENNING,1 DENA M. SMITH,1* CESAR R. NUFIO,2 and HERBERT W. MEYER 3

1University of Colorado, CU Museum of Natural History—Paleontology, Boulder, Colorado, 80309-0265, USA, Jenell.Thoene@colorado.edu,

Dena.Smith@colorado.edu; 2University of Colorado, CU Museum of Natural History—Entomology, Boulder, Colorado, 80309-0265, USA, nufio@colorado.edu;3Florissant Fossil Beds National Monument, 15807 Teller County Road 1, Florissant, Colorado, 80816, USA, herb_meyer@nps.gov

ABSTRACT

To study how lacustrine depositional environments influence the pre-servation of insects, the abundance, size, and quality of insect specimenswere compared across shale, mudstone, and siltstone within the FlorissantFormation of Colorado. These lithologies were chosen because they reflectdifferences in associated energy, grain size, and presence of diatom layers.Eight hundred and twenty-three fossil insects were collected from a singlestratigraphic section within the lacustrine deposits of the FlorissantFormation (late Eocene). Sampling across these lithologies was associatedwith low specimen collection rates (3.7–5.6 insects collected per collector-day) that did not differ across the sedimentary environments. In addition,the relative abundance of insect orders did not differ across thesedimentary environments. Specimens were significantly smaller and lessvariable in size within the siltstone than they were within the shale andmudstone, likely due to differences in temporal and spatial averaging.Overall, 56% of insect specimens were disarticulated and 66% wereconsidered of low quality. Insect disarticulation levels, preservationquality, and specimen orientation did not differ across all lithologies ingeneral and for the other three insect orders, despite differences incoleopteran (beetles) preservation in siltstone where they were lessdisarticulated and more commonly preserved in a lateral position. Thisindicates that insect specimens of the quality typically associated withshale deposition also can be found in mudstone and siltstone, whichincreases the areas within lakes that can be sampled and compared forpaleoecological studies.

INTRODUCTION

The goal of this study is to address how depositional environmentsinfluence the preservation of insect remains. To study the influence ofsedimentary environment, the abundance, size, completeness, quality,and orientation of fossil insect specimens preserved in three differentlithologies (shale, mudstone, and siltstone) are compared. Studyspecimens come from a single stratigraphic section within the famouslacustrine deposits of the late Eocene Florissant Formation of Colorado.

Insects have a rich fossil record that extends as far back as the earlyDevonian (Grimaldi and Engel, 2005). All extant insect orders arerepresented in the fossil record and are found within a variety ofenvironmental settings, including lake, amber, peat, and tar deposits,and calcium carbonate precipitates (Martınez-Delclos et al., 2004).Lake deposits are particularly important because they are prevalentthroughout geologic time (Labandeira, 1999; Smith and Cook, 2001),and they often yield exceptionally preserved specimens. Withinlacustrine deposits, insects are often preserved as organic remains ofthe cuticle or as a mold when the cuticle is lost during diagenesis orweathering (Martınez-Delclos et al., 1995). Actualistic and assemblage-based studies of lacustrine environments have shown that the ecology

and morphology of insects can influence which taxa will be preserved aswell as their overall quality (Smith, 2000; Smith et al., 2006; Smith andMoe-Hoffman, 2007; Wilson, 1980, 1988). For example, we know thatthe relative abundance of fossil insects within assemblages are notaccurate reflections of the original communities they are thought torepresent, with there being a bias toward those that are smaller,necrophagous, and ground dwelling (Smith, 2000). In turn, the size andhardness of specimens affect their sinking and disarticulation rates,such that small and physically robust specimens are more likely to bepreserved (Smith, 2000; Smith et al., 2006; Smith and Moe, 2007; Smithand Thoene, 2009).

While insect ecology and morphology have been shown to influencetheir preservation, lakes, and even areas within a given lake, may differin their associated types of sediments, sedimentation rates, sedimentsources, levels of energy, water depth, and proximity to source streamsand organic inputs. As such, the heterogeneity between and within lakesmay further filter the types of insects that will be preserved as well as theirpreservation quality. For example, shale deposits, such as those foundwithin the Florissant Formation, are fine-grained, laminated sedimentsthat accumulate in calm lake settings, and deposits like these are oftenconsidered the best environments in which to find fossil insects. Biofilmsassociated with diatoms are thought to further enhance the preservationpotential of fossil specimens within these shales (Harding and Chant,2000; O’Brien et al., 2002, 2008). Still, insect remains also have beendocumented from mudstones and siltstones, areas that lack fissility,biofilms produced by diatoms, and, in regards to siltstone, coarser grainsand potentially greater energy inputs.

In this study, we examine the preservation biases associated withfossil insects found within shale, mudstone, and siltstone deposits froma single stratigraphic section within the Florissant Formation. Bycomparing habitats represented by shale and mudstone, we examinedwhether such lake characteristics as fissility and the presence ofdiatoms, characteristics associated with shale, might be associated withhigher abundance and preservation quality of insect specimens. Byincluding siltstone in our comparison, we are further able to explore theimportance of grain size and energy input on specimen abundance andquality (Table 1). To facilitate comparisons across these ancient lakeenvironments, we quantified collecting rates, relative abundance oftaxa, size, and taphonomic quality of all insect specimens associatedwith each lithology. We also conducted these analyses individuallyacross the four insect orders that are most commonly found withinfossil lake assemblages across each of the lithologies; Hymenoptera(bees, wasps), Coleoptera (beetles), Diptera (flies), and Hemiptera (truebugs) to explore whether certain ecologies or morphological character-istics may influence the preservation of these orders differentially acrossthe preservation environments.

GEOLOGICAL SETTING

The Florissant Formation is well known for its diverse and exceptionallypreserved assemblage of plants, invertebrates and vertebrates, with ,1,570Published Online: July 2012

Copyright G 2012, SEPM (Society for Sedimentary Geology) 0883-1351/12/0027-0481/$3.00

described insect and arachnid species (Meyer, 2003; Meyer et al., 2008).Lacustrine deposition in the Florissant Formation was initiated whenlarge lahars (volcanic debris flow) from the Thirty-Nine Mile VolcanicField dammed and impounded the Florissant drainage basin andformed two stratigraphically and temporally distinct lake episodes(Evanoff et al., 2001; Meyer, 2003). 40Ar/39Ar dating indicates that theupper part of the Florissant Formation was deposited 34.07 6 0.10 Ma(Evanoff et al., 2001). The Florissant Formation is divided into sixinformal units: the lower shale unit, lower mudstone unit, middle shaleunit, caprock conglomerate unit, upper shale unit, and upper pumiceconglomerate (Evanoff et al., 2001, Fig. 1). The three fossiliferousshale units, which include most of the fossil plants and insects, arelithologically heterogeneous and consist of thinly laminated shaleinterbedded with tuffaceous mudstone and siltstone beds, tuffs, andpumiceous sandstone and conglomerate beds (Evanoff et al., 2001).The thinly laminated shale component consists of couplets composedof alternating layers of diatoms and weathered volcanic ash. Thesecouplets average #1 mm thick (O’Brien et al., 2002, 2008), and mayrepresent annual layers (varves) produced by spring diatom blooms(McLeroy and Anderson, 1966) and the influx of ash and clay into thelake from runoff (O’Brien et al., 2002 and 2008). Mudstone, siltstone,and tuffs are interbedded with the thinly laminated shale, and theirsources may have ranged from direct ash fall into the lake to epiclasticsediment from the surrounding landscape.

MATERIALS AND METHODS

Data Collection

Fossil materials were collected from within the Florissant Fossil BedsNational Monument in Teller County, Colorado, by National Parkstaff and interns during the summers of 2009 and 2010. All specimenshave been reposited in the collections of Florissant Fossil BedsNational Monument (FLFO). The specimens were collected fromFLFO Site 9 (equivalent to Inventory and Monitoring site 15) in thenorthwest area of the park (Fig. 2). The collection site was located justwest of the center of ancient Lake Florissant, probably near the openingof a large tributary inlet based on current distribution of the FlorissantFormation, which is thought to closely represent the configuration ofthe ancient lake.

Fossil specimens were collected from a single section within themiddle shale unit of the Florissant Formation. There are 12 informalunits at the site (Fig. 3) composed of shale, siltstone, mudstone, andtuff (Card, 2010). Stratigraphic levels were demarcated at 10 cmintervals along the trench of the collecting site to facilitate documen-tation of sedimentary environments. All insect fossils were collected,regardless of their quality of preservation and levels of disarticulation.Stratigraphic position, collector, and collection date were recorded foreach specimen. Fossil insects were sorted from the samples andidentified to the level of order and family when possible using CSIRO(1991) and Borror et al. (1989) as resources.

Sampling Rate and Relative Abundance

To determine whether there was a difference in the rate at whichinsects were sampled across the different lithologic units, we measured

the number of specimens collected per collector assigned to one of threesedimentary environments over a six-hour field day, for an eleven-dayperiod. Using over 42 six-hour collector days, a nonparametric Wilcoxonsign rank test was used to compare the median rate of insects collectedper six-hour field day across the three sedimentary environments. Todetermine whether the lithologic units differed in their likelihood ofpreserving each of the four most commonly collected orders (Hymenop-tera, Coleoptera, Diptera, and Hemiptera), we compared the frequencyof each order across the lithologic units using chi-squared analysis ofcontingency tables. The relative frequency of the orders across thedifferent units was used, rather than an order-by-order comparison offrequencies across the sediment types, because sampling effort differedacross the sediment types. This sampling effort differed due to the ease ofsampling shale (due to its fissility) rather than an actual difference in therate at which specimens were sampled (see below).

Specimen Size

Digital calipers were used to measure each specimen across the widestpoint of the body and from the top of the thorax to the bottom of theabdomen for length. Specimen size was then calculated by multiplyingthe width by the length. To examine whether there was a bias in the sizeof insects preserved in each sediment type, we compared the size of allspecimens collected from the three different sedimentary lithologies.Levene’s test for equality of variances showed that the variance in bodysizes was unequal across the lithologies. As such, to determine whetherbody sizes differed across sedimentary environments, a one-way analysisof variance was conducted using size data that were log transformed tomeet the assumption of homogeneity of variance and normality. Finally,a Tukey-Kramer HSD was used to determine which differences werestatistically significant. These analyses were then repeated using the log-transformed size data associated with the four dominant insect orders todetermine whether lithology biased the size distributions of each order.

Taphonomic Bias

To study taphonomic bias across the different lithologies, data on thecompleteness (levels of disarticulation), quality, and orientation werecollected for each fossil specimen within each sediment type. Forcompleteness, insects were categorized as complete (100%), incomplete(50%–100%), or fragmented (,50%). The quality of each specimen wasthen determined using a combination of damage and decay level andthe number of morphological characters present that could be used foridentification of a specimen. Each specimen was assigned a quality ofexcellent (no damage and/or decay), good (minor damage and/ordecay), fair (some damage and/or decay), or poor (significant damageand/or decay; Fig. 4). To simplify discussion of these data, specimenswill be referred to as high quality (categorized as excellent to good) orlow quality (categorized as fair to poor). The orientation of each insectwithin the rock was recorded as either dorsal-ventral, lateral, or twisted.Twisted specimens would often have the head pointing in one directionwhile the lower abdomen pointed in the opposite direction. Theorientation of specimens was recorded as it may reflect the level ofturbidity associated with a given environment.

Chi-square analyses of contingency tables were used to determinewhether the completeness, quality, and orientation of specimens were

TABLE 1—Descriptions of shale, mudstone, and siltstone and expectations for fossil insect preservation. Characteristics as defined in Nichols (2009).

Characteristics Depositional environment Expectation of preservation

Shale Clay , mm and siltstone particles, fissile Suspension-settling, abundant diatoms High abundance, high quality

Mudstone Clay , mm and siltstone particles, not fissile Suspension-settling Low abundance, high quality

Siltstone Coarsest: 4–62 mm particles, not fissle Some suspension-settling, and stream run-off Low abundance, low quality

482 THOENE HENNING ET AL. PALAIOS

dependent on lithology. These analyses were conducted using all insectsand then separate similar analyses were conducted that focused on thefour dominant insect orders.

All statistical analyses were performed using JMP IN for Windows(SAS Institute, 1998–2000). All specimen data can be found inSupplementary Data1.

RESULTS AND DISCUSSION

Sampling Rate and Relative Abundance

In total, 823 insects were collected from the section for this study. Forthe two-year collecting period, there were 436 specimens found in shale,62 specimens in mudstone, and 325 in siltstone. Daily collecting rateswere low, with mudstone having the greatest yield of fossil specimensoverall, followed by siltstone and shale (5.6, 4.4, and 3.7 fossil insectsper collector-day, respectively). These sampling rates were notstatistically different from one another (x2 5 2.466, df 5 2, p 5 0.2915).

There were 9 insect orders found in the entire section, with the mostabundant specimens being Hymenoptera (33%), Coleoptera (26%),Diptera (19%), and Hemiptera (9%), and with 15% of specimens notdeterminable to order (Fig. 5). There was no significant difference inthe relative abundance of the four dominant insect orders between theshale, mudstone, and siltstone (x2 5 1.39, df 5 6, p 5 0.97).

Although well known for both exceptional diversity and quality ofinsect specimens, sampling yields at Florissant are actually quite low.Most collectors who study the lacustrine units within the FlorissantFormation focus on the shale units, which are thought to give a higheryield of fossils overall when compared to the other sedimentaryenvironments. Our results show that there is no difference in samplingrate for insects found in the different lithologic units and in fact, insectorders also are sampled in the same proportions in all depositionalsettings. That is, the difference in the overall number of specimenscollected in the different lithologies simply reflects effort and/or timespent collecting in each sediment type and not the actual productivity ofany lithology. Although plants and mollusks appeared to be mostcommon in the shale units, the fissile nature of shale likely made

FIGURE 2—Map showing extent of Florissant Formation (gray shading) and

location of collecting site. Modified from Smith and Moe-Hoffman (2007).

FIGURE 1—General stratigraphy of the Florissant Formation, redrawn from

Evanoff et al. (2001).

1www.palaios.ku.edu

PALAIOS INSECTS AND DEPOSITIONAL ENVIRONMENT 483

collecting much easier and, therefore, sample sizes higher, which is whattruly makes this environment most favored among collectors.

Specimen Size

When examining specimen size in the overall sample of insects, wefound that while the variance in the size of fossil specimens did not differfor specimens found in mudstone or shale (F1, 498 5 0.013, p 5 0.91; SD5 17.04 and 18.08, mudstone and shale, respectively), the variance inspecimen size in siltstone was significantly smaller than that found forspecimens in mudstone or shale (F2, 820 5 17.21, p , 0.0001; SD 5 9.87,siltstone). In turn, mean specimen size did not differ between either shaleor mudstone, but specimen size in siltstone was smaller than thatassociated with the other lithologies (F2, 820 5 29.22, p , 0.0001; Fig. 6).

No differences were found in the size variances associated with shaleand mudstone in the Hymenoptera (F1, 143 5 3.54, p 5 0.062) andDiptera (F1, 93 5 0.058, p 5 0.811), however, the range of specimen sizewas significantly lower for both orders in the siltsone units (Hyme-noptera F2, 241 5 13.21, p , 0.0001; SD 5 17.21 for shale, 9.76 formudstone, and 8.47 for siltstone; Diptera F2, 152 5 7.25, p 5 0.0003; SD5 25.29 for shale, 19.73 for mudstone, and 9.76 for siltstone). ForColeoptera, the size variances differed between all lithologies, withshale having the greatest size range (F2, 208 5 8.63, p 5 0.0003; SD 5

12.86 for shale, 25.89 for mudstone, and 9.30 for siltstone). OnlyHemiptera showed no significant difference in size range between thedifferent sedimentary deposits (F2, 72 5 0.82, p 5 0.44; SD 5 11.30 forshale, 8.19 for mudstone, and 15.14 for siltstone).

Finally, across the different orders, specimens preserved in shale andmudstone were larger than specimens preserved in the siltstone (Fig. 6).This was true for Hymenoptera (F2, 241 5 10.97, p , 0.0001),Coleoptera (F2, 208 5 9.40, p 5 0.0001), and Hemiptera (F2, 72 5 5.75, p5 0.0048). Diptera preserved in shale were among the largest, but werenot significantly different in size than Diptera preserved in mudstone,which were not significantly different from the specimens preserved insiltstone, which were the smallest in size (F2, 152 5 6.58, p 5 0.0018).

Insect size was found to differ depending on sedimentary environ-ment and insects preserved within siltstone were not only significantlysmaller than those preserved in shale or mudstone, but there was lessvariance in the size range of specimens preserved in siltstone. Siltstone isa coarser-grained sediment than shale and mudstone and is depositedduring episodic higher energy events like stream deposition or ashfallinto the lake. Deposition of silt is often precipitated by winter snowmeltand from weathering of allochthonous rock sources (Dean et al., 1999).If specimen size sorting was occurring due to grain size sorting, wewould have expected to see larger specimens in the siltstone than in themudstone and shale, and this was not the case.

Since siltstone was likely the result of episodic higher energy events,these deposits captured insects during brief moments in time, resultingin a sampling interval that was shorter and captured a smallerproportion of the assemblage. In contrast, the sediments that laterbecame shale and mudstone were likely deposited over the duration of ayear in the case of individual diatom couplets or more if multiplecouplets are combined (McLeroy and Anderson, 1966; Wilson andBarton, 1996). These deposits captured insects over a longer time framewhere sediment input tended to be more continuous and for a greaterduration, leading to an insect assemblage that was, therefore, more timeaveraged. In addition, lake basins tend to have a greater sampling areafor capturing insects of varied sizes when compared to the area of asmall, ephemeral fluvial input. Slower sedimentation over a relativelylonger period of time and over a larger catchment area would allow amore diverse fauna to be captured (Behrensmeyer et al., 2000) and,thus, a bigger size range was represented within the mudstone andshale. In general, the sedimentary environments of the FlorissantFormation have captured ranges that represent episodic or seasonalevents, which results in different levels of temporal and spatialaveraging and greater differences in insect size ranges.

This study demonstrates how subtle differences in depositional eventscan impact insect assemblages. Time-averaged assemblages are oftendiscussed on a scale in which hundreds or thousands of years of inputcan occur (Behrensmeyer et al., 2000). For example, Behrensmeyeret al. (2000) estimate that organisms in a lake setting represent a time-averaged assemblage anywhere from 100 years to 10,000 years. At aneven smaller time scale (seasons to decades), however, changes amongassemblages can be captured (see also Barton and Wilson, 1999, 2005).Further, actualistic work on the preservation of insects in an ephemeralplaya lake has shown that specimens accumulated over the duration ofa single season had a significant overrepresentation of smaller insectspecimens (Smith, 2000). Thus, the Florissant Formation appears tohave captured insect assemblages representing both time-averaged

FIGURE 3—Detailed section of the excavation site (FLFO Site 9), redrawn from

Card (2010). Only the shale, mudstone, and siltstone units were fossiliferous.

484 THOENE HENNING ET AL. PALAIOS

events (shale and mudstone) as well as brief moments captured in time(siltstone) and work should be conducted to examine how time-averaged and single event insect assemblages may differ.

Taphonomic Bias

In the overall sample of insects, 56% of specimens were complete andthe majority (66%) had low preservation quality. Completeness of aspecimen and its preservation quality was not dependent on thedepositional environment (x2 5 2.27, df 5 2, p 5 0.32; x2 5 8.49, df 5

6, p 5 0.20; completeness and preservation quality, respectively). Forty-six percent of specimens were oriented in a dorsal-ventral position, 44%

were oriented laterally, and 2% were twisted. Lithology had noinfluence on the orientation of insect specimens (x2 5 5.78,df 5 4, p 5 0.259).

High-quality specimens were far less common than expected,especially given the reputation of the Florissant Formation forexceptional preservation. Thus, unlike some other North Americaninsect Lagerstatten deposits (i.e., Green River Formation, StewartValley), one must excavate many specimens in order to find a few high-quality specimens. The results of this study indicate that while shaleunits are often thought to best preserve insect fossils, given the fine-grained nature of these deposits and current models which state thatpreservation is facilitated by the diatom mats and associated biofilmsfound in these deposits (Harding and Chant, 2000; O’Brien et al., 2002,2008), shale deposits appear to preserve insects in a similar fashion asmudstone and siltstone deposits. Since there were no taphonomicdifferences found between the different sedimentary environments, theco-occurrence of diatom fossils with insect fossils in the shale units islikely due to coincidental timing of deposition. Additionally, weexpected grain size and energy levels to have an effect on the quality of

‹

FIGURE 4—Examples of insect specimens of different preservation qualities. Scale

bar 5 mm. A) Diptera, excellent (no damage, FLFO 7092). B) Hymenoptera, good

(minor damage, FLFO 7320). C) Coleoptera, fair (some damage, FLFO 7743). D)

Indeterminant, poor (significant damage, FLFO 7165).

FIGURE 5—Overall proportion of insect orders found throughout the section at

FLFO Site 9.

PALAIOS INSECTS AND DEPOSITIONAL ENVIRONMENT 485

insect specimens, and thus expected siltstone to have more incomplete,

low-quality, and twisted specimens than the shale or mudstone units.

Again, this was not the case, suggesting that the relative differences in

energy and grain size in siltstones were not enough to negatively impact

preservation in relationship to the other depositional settings.

While these findings were unexpected, they provide welcome news for

researchers who study fossil insects. Searching for quality specimens

does not have to be limited to laminated shale deposits, but instead can

be expanded to sampling a broader range of lakes and sampling within

a greater range of strata within lakes. Being able to collect in a greater

variety of depositional settings will expand insect yields, broaden the

scope of questions that can be asked, and increase our ability to control

for depositional setting in studies that incorporate comparisons across

multiple spatial or temporal scales.

When examining the four dominant insect orders, the levels ofdisarticulation in the three lithologies were not significantly differentfor Hymenoptera (x2 5 0.061, df 5 2, p 5 0.97), Diptera (x2 5 4.98, df5 2, p 5 0.083), and Hemiptera (x2 5 0.423, df 5 2, p 5 0.809). Incontrast, the Coleoptera were found to be significantly less disarticu-lated in siltstone than in shale and mudstone (x2 5 10.012, df 5 2, p 5

0.0067; Fig. 7). This result was unexpected, as siltstone is deposited in ahigher energy setting than shale or mudstone, so specimens wereexpected to have greater levels of disarticulation. Water that has somedegree of surface agitation or energy, however, will result in insects thatsink more quickly (Martınez-Delclos and Martinell, 1993). For beetles,which are relatively robust, sinking times have been shown to have apositive correlation with disarticulation, such that faster sinkingspecimens tend to be less disarticultated (Smith et al., 2006). Inaddition, deposition in siltstone is expected to result in rapid burial ofspecimens, further inhibiting disarticulation.

The preservation quality of specimens from the four dominant orderswas not significantly different depending on lithology (Hymenoptera, x2

5 3.12, df 5 6, p 5 0.794; Coleoptera, x2 5 7.55, df 5 6, p 5 0.273;Diptera, x2 5 5.46, df 5 6, p 5 0.487; Hemiptera, x2 5 4.11, df 5 6, p 5

0.66). Again, this is good news for researchers, as all orders have thesame levels of preservation quality, regardless of lithology.

The orientation of the Hymenoptera (x2 5 2.45, df 5 4, p 5 0.654),Diptera (x2 5 2.58, df 5 4, p 5 0.279), and Hemiptera (x2 5 4.22, df 5

4, p 5 0.378) were not significantly different between the differentlithologies. Interestingly, 90% of Hemiptera were preserved in a dorsal-ventral position. This is likely explained by the dorsal-ventrallyflattened morphology of most Hemiptera, which would have madelanding and remaining positioned on their narrow sides difficult. Theinfluence of morphology on the orientation of specimens also can beobserved in the preservation of the weevils (Curculionidae), which arecommonly preserved in a lateral orientation due to the ventralpositioning of their snout and legs. The Coleoptera had significantlymore laterally oriented specimens in siltstone than in shale and mudstone

FIGURE 6—Size of specimens found in the different sedimentary environments.

Statistical tests were run on log-transformed data, whereas this figure shows the

nontransformed data to make it easier to see mean size and size range of specimens by

each lithology. Letters indicate significance levels at the a 5 0.05 level. Those with the

same letters are not significantly different from each other, whereas those with

different letters are significantly different from each other.

FIGURE 7—Levels of disarticulation in specimens of Coleoptera in the three

lithologic environments. Beetles preserved in siltstone were significantly less

disarticulated (x2 5 10.012, df 5 2, p 5 0.0067).

486 THOENE HENNING ET AL. PALAIOS

(x2 5 14.89, df 5 4, p 5 0.005; Fig. 8). This may have been due in part tothe higher energy contributing to the deposition of siltstone.

CONCLUSIONS

The Florissant Formation is known for its abundant, diverse, andhigh-quality fossil specimens. Counter to our expectations (Table 1),this study shows that fossil insects within the Florissant Formationcan be equally abundant across different sediment types (shale,mudstone, siltstone). In turn, presence of diatoms apparently did notenhance the preservation potential or quality of specimens as thepreservation quality of specimens did not differ between shale (whichcontains diatoms) and mudstone (which is typically not associatedwith diatom layers). The greater turbidity and grain sizes associatedwith the production of siltstone layers also did not negatively impactthe quality of specimens. Still, specimens preserved in siltstone weresmaller than those found in the other sediments and were lessvariable in size than those found within the more temporally andspatially averaged mudstone and shale sediments. This is likely theresult of time averaging, whereby the short episodic events associatedwith the deposition of siltstone may have selectively favored thepreservation of smaller insects, while the longer time periodsassociated with the formation of shale and mudstone may havefavored the capture of larger specimens, which often tend to be lesscommon. Overall, this study shows that researchers can expand theircollecting efforts to include a broader range of lithologies and lakesettings, as shale-quality specimens are equally common in mudstoneand siltstone.

ACKNOWLEDGMENTS

We thank K. Hollis, C. Whitmore, and C. O’Connor for theirassistance with specimen processing, curation, and locality information.The staff at Florissant Fossil Beds National Monument provided awelcoming atmosphere and access to their administrative andcollections spaces during the field portions of the study. We thank K.Card for providing her extensive field notes and detailed measured

section from the site. We greatly appreciate the field assistance wereceived from M. Barton, B. Buskirk, K. Card, R. Carnein, A.Demarest, J. Fearon, K. Hollis, G. Machek, A. Platsky, E. Waite, K.Webster, C. Whitmore, and the Colorado Legends and Legacies YouthCorps. Dr. C. Labandeira and an anonymous reviewer provided greatlyappreciated suggestions for improving an earlier version of thismanuscript. We thank the members of the University of ColoradoInvertebrate Paleontology lab for feedback and support during thecompletion of this project. Specimens were collected under NationalPark Service Research Permit FLFO-2009-SCI-0005, and fundingsupport was provided by the National Park Service through CESUCooperative Agreement Number H1200040001 (Project UCOB56) toPIs D.M. Smith and H.W. Meyer.

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