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A Re-Analysis of the Late Cretaceous Flora of the Two Medicine Formation in Montana
Using Digital Leaf Physiognomy
Ann Marie
1University
1,2
Prue ,
3
Chin ,
Karen
Garland
2
Upchurch
of Wisconsin-River Falls Plant and Earth Science Department/Geology, 2Texas State University Department of Biology, 3University of Colorado Boulder Department of Geological Sciences
Purpose Comparison The purpose of this study was to: •  Use previously studied fossil leaves to determine paleoclimate •  Determine the reliability of previous es:mates •  Test the credibility of new clima:c methods for leaves •  Compare new es:mates to other fossil locali:es •  Determine the consistency of previous published climate es:mates Paleoclimatological Comparison
Formation
1 2 3 In 1987, David Crabtree studied Late Cretaceous fossil dicot leaves of the lower Two Medicine Forma:on in Montana (Fig. 1 and Fig. 2) During the study, he made preliminary paleoclimate es:mates using Leaf Margin Analysis (LMA), the percent of untooth leaves that correlates with temperature. There was no quan:ta:ve method at the :me for precipita:on es:mates, but he made a qualita:ve es:mate. Two Medicine climate es:mates of Crabtree (1987): 2 Averages of each parameter for all 29 dicots of the Two Medicine Formation
Blade
DLP MAP
(cm)
LAA MAP
(cm)
Fox Hills
66.5
49.7
21.6
14.8
141
152
Two Medicine
79.6
48
17.1
10.2
108.1
91.3
Both the Two Medicine Forma:on and the Fox Hills Forma:on have fewer than 30 species, which is the minimum number needed for reliable temperature es:mates with LMA. In both cases DLP gives warmer values than LMA. These warmer values are more congruent with other temperature es:mates from the northern Western Interior of North America (Wolfe and Upchurch, 1987; Upchurch et al., in press). Methods and Results Margin
LMA MAT
(°C)
Table 3 U:lizes the data from Peppe et al.’s (2011) Fox Hills Forma:on in the Dakotas. This site was climatologically compared to the Two Medicine Forma:on. These two sites are of similar paleola:tudes in the similar region. C. EnCre (Untoothed) DMNH 16426 loc. 1902 Dicot 28 Figure 3 Examples of fossil leaves we digitally repaired from this assemblage. These are the original specimens that Crabtree collected and described (1987). Almost all of the specimens were obtained by the Denver Museum of Nature and Science from the University of Montana. Many of these were prepped with nail polish and hairspray to enhance vena:on, margins, and cu:cles. While this prepara:on helped retain valuable scien:fic informa:on, it was a glaring problem during the photographic sessions. A1. Shows well preserved teeth in the upper right hand por:on. This preserva:on helped in the interpreta:on of the broken sec:ons of the margin as seen in the repaired specimen digitally removed from the matrix as in A2. The final, A3, shows the specimen with the teeth removed as called for in DLP. B1. Shows a heavily damaged leaf with only half the leaf preserved. This half por:on was digitally extracted from the matrix and had the pe:ole and teeth removed as seen in B2 and B3. In order to use such “half” leaves for paleoclimate reconstruc:on, the leaf parameters were doubled to make a full leaf. C1. Shows a great example of a preserved en:re leaf (untoothed). Since this leaf specimen had no visible teeth, the specimen only needed to be digitally extracted from the matrix as seen in C2. # of
Morphotypes
DLP MAT
(°C)
2 1 3 B. Toothed Half DMNH 16430 loc. 1902 Dicot 33 A. Toothed DMNH 16366 loc. 1902 Dicot 12 IntroducCon 1 Age (Ma) Paleolatitude
Internal
Other
•  Mean Annual Temperature (MAT) was 7-­‐10°C •  Mean Annual Precipita:on (MAP) was ~High~ **Portion of
Tooth Area Area (BA) Perimeter Major Axis
# of Teeth
[cm2]
[cm]
[cm]
Untoothed
(TA) [cm2]
Shape
Factor
Feret
Diameter
[cm]
Area
[cm2]
Perimeter
(IP) [cm]
Petiole
Area [cm2]
Leaf Area
[mm2]
0.52
5.4
27.8
24.0
0.05
279.5
29*
27.6 %
Untoothed
Cut Bank 43
0.14
27.9
25.4
7.2
Table 2 These are the described parameters used in Peppe et al. (2011) regression equa:ons and univariate regression plots. Tooth Area (TA) is the total area of the teeth. Blade Area (BA) is the area of the leaf before teeth are removed. Leaf Area is the combined area of the Blade and the area of the pe:ole. *Crabtree (1987) originally described 28 morphotypes. While analyzing the fossils at the Denver Museum of Nature and Science, we came across more morphotypes than Crabtree (1987) described. ** The Por:on of untoothed is not an average. It is the percentage of untoothed leaves in an assemblage. 40Ar/39Ar
Method for Digital Leaf Physiognomy 1.Took pictures of specimens at the Denver Museum of Nature and Science Fig. 1 The map gives a generalized posi:on of the United States during the Early Campanian, which is the deposi:onal sewng of the Two Medicine forma:on. As the paleola:tudinal lines indicate, Montana was located at about the 50 degree North paleola:tudes. Map modified from the work Crabtree (1987). N (b)
(a)
Fig. 2 This is a geologic map and a simple stra:graphic column of the Two Medicine Forma:on. The blue star is the approximate loca:on of Crabtree (1987) fossil locality, while the red circle is the loca:on of the 40Ar/39Ar da:ng sample. The age es:ma:on is ~79.6 Ma. a. Modified from the work of Rogers et al. (1993), b. Modified from the work of Foreman et al. (2008) By 2005, the new method of Digital Leaf Physiognomy (DLP) had been developed to reconstruct climate through leaf physiognomy (e.g. Royer et al., 2005). DLP is a mul:variate method that uses computer photo-­‐edi:ng sopware and algorithms to measure different leaf parameters (Table 1). The calcula:ons used in this study are those proposed by Peppe et al. (2011). Mean Annual Temperature (MAT, in °C)
Leaf Margin Analysis (LMA) MAT = 4.6 + ( % of Untoothed x 0.204 )
Digital Leaf Physiognomy (DLP) MAT = -16.004 + ( % Untoothed x 0.21 ) + ( FDR x 42.296 ) + [ (# Teeth / IP ) x - 2.609 ]
Mean Annual Precipitation (MAP, in cm)
Leaf Area Analysis (LAA) MAP = 2.92 + [ ln ( Leaf Area in mm) x 0.283 ]
DLP MAP = 3.033 + [ ln (Leaf Area in mm) x 0.298 ] + [ ln ( PR ) x - 2.717 ] + [ ln (# Teeth / IP ) x 0.279]
Table 1 Peppe et al.’s (2011) proposed regression equa:ons calculated from 92 global extant calibra:on sites. Feret Diameter Ra:o (FDR) is the ra:o of the Feret diameter and leaf length. Feret diameter is the diameter of a circle with the same area as the leaf. Perimeter Ra:o (PR) is the ra:o between the perimeter of the leaf with teeth and the Internal Perimeter (IP) of the leaf aper the teeth are digitally removed. MAT temp: ~ 8°C Number of teeth
MAT temp: ~ 16°C
Leaf area MAT temp: Off the Graph MAP Amount: ~ 3.3 (loge) = 27.1 cm # Teeth / IP
TA/ BA* TA / BA*
MAP amount: Off the graph MAT temp: ~ 21°C 2
Shape factor
Perimeter ratio
MAT temp: ~ 27°C 0
10
20
30
Mean annual temperature (°C)
Our data Results •  Our calculated MAT from LMA was similar to Crabtree’s (1987) as seen in Fig. 6 •  The MATs inferred from superimposed points on Peppe et al.’s (2011) univariate regressions show a wide range, which DLP falls into (Fig. 6) •  Map calculated from LAA is comparable to MAP calculated from DLP as seen in Fig. 7 •  The MAPs inferred from superimposed points on Peppe et al.’s (2011) univariate regressions give the lowest and highest es:mates for MAP (Fig. 7) 3
4
5
6
7
Mean annual precipitation
(loge, mm2)
Analyses of the Two Medicine Forma:on leaves indicate the following: •  Mean Annual Temperature (MAT) calculated from Leaf Margin Analysis (LMA) of ~ 10 °C is similar to Crabtree’s (1987) findings of 7-­‐10 °C •  MAT calculated from the Digital Leaf Physiognomy (DLP) equa:on in Peppe et al. (2011), is 7 degrees warmer at 17 °C , and is more congruent with published temperature es:mates for the northern Western Interior (Wolfe and Upchurch, 1987) •  Mean Annual Precipita:on (MAP) calculated from Leaf Area Analysis (LAA) and DLP equa:ons is 91 and 108 cm/
yr., respec:vely, and is congruent with qualita:ve es:mates of Wolfe and Upchurch (1987) Our data MAT temp: ~ 22°C Figure 5 Our data when superimposed on to Peppe et al.’s (2011) univariate regression MAP plots gives a very wide range of es:mates. The leaf area gives a very low es:mate, and the TA/BA ra:o is extremely high. *TA/BA ra:o is erroneous for both MAP and MAT, mostly likely caused by the amount of teeth preserved in the fossils. These analyses suggest that the apparently enhanced predic:ve power of DLP makes it the “go to” method for using fossil leaves to reconstruct paleoclimate. Works Cited and Acknowledgements Works Cited: Estimated MAT for the Two Medicine Formation during the Campanian 30
25
20
15
10
5
0
> 29
Estimated MAP for the Two Medicine Formation during the Campanian MAP estimation (cm)
Cut Bank 2. Digitally repaired fossils in Adobe® Photoshop® Elements 7.0 3. Uploaded edited fossils into ImageJ to digitally calculate parameters suggested by Peppe et al. (2011) (Table 2) 4. Compiled data in Excel and took averages of the parameters of all morphotypes (Table 2) 5. Averaged data was superimposed onto Peppe et al.’s (2011) univariate regression plots (Fig. 4-­‐5) to get MAT and MAP es:mates 6. Equa:ons from Table 1 were used to calculate MAT and MAP from the data in Table 2 Percent untoothed
Temperature °C
40Ar/39Ar
Figure 4 These plots are Peppe et al.’s (2011) univariate regression plots calculated from 92 global extant calibra:on sites. Our data when superimposed on to these plots and the es:ma:ons of MAT are read directly down. With the excep:on of TA/BA, most es:ma:ons are on par with each other. *TA/BA ra:o is erroneous for both MAT and MAP, mostly likely caused by the amount of teeth preserved in the fossils. Conclusions >665 cm
200
150
100
50
0
Calculated
LAA
DLP
LAA
Tooth Area /
Blade Area
MAP estimation methods
Type of MAT method
Crabtree (1987)
Calculated univariate
DLP
Superimposed points
Figure 6 These show the temperatures of the different methods. When comparing the temperatures, Crabtree’s es:mate and calculated LMA are similar to each other but much lower than the other methods’ es:mates. The DLP method falls into the range of the fiwng point plots. Calculated univariate
DLP
Superimposed points
Figure 7 This histogram shows the varia:on in MAP es:mates for each method. The two fiwng point plot parameters make the minimum and maximum of the es:ma:ons. DLP’s es:mate is congruent with the calculated LLA. Adobe® Photoshop® Elements 7.0, 2008. Adobe Systems Inc., Jan Jose, CA., USA Crabtree, D., 1987. The Early Campanian flora of the Two Medicine Forma:on, Northcentral Montana: Unpublished Ph.D. Disserta:on, The University of Montana, Missoula, 357 p. Foreman, B.Z., Rogers, R.R., Deino, a. L., Wirth, K.R., Thole, J.T., 2008. Geochemical characteriza:on of bentonite beds in the Two Medicine Forma:on (Campanian, Montana), including a new 40Ar/39Ar age. Cretac. Res. 29, 373–385. doi:10.1016/ j.cretres.2007.07.001 Rasband, W.S., 2007-­‐2014. ImageJ, U.S. Na:onal Ins:tutes of Health, Bethesda, Maryland, USA, hmp://imagej.nih.gov/ij/. Peppe, D.J., Royer, D.L., Cariglino, B., Oliver, S.Y., Newman, S., Leight, E., Enikolopov, G., Fernandez-­‐Burgos, M., Herrera, F., Adams, J.M., Correa, E., Currano, E.D., Erickson, J.M., Hinojosa, L.F., Hoganson, J.W., Iglesias, A., Jaramillo, C. a., Johnson, K.R., Jordan, G.J., Krap, N.J.B., Lovelock, E.C., Lusk, C.H., Niinemets, Ü., Peñuelas, J., Rapson, G., Wing, S.L., Wright, I.J., 2011. Sensi:vity of leaf size and shape to climate: Global pamerns and paleoclima:c applica:ons. New Phytol. 190, 724–739. doi:10.1111/j.1469-­‐8137.2 010.03615.x Rogers, R.R., Swisher III, C.C., Horner, J.R., 1993. Ar age and correla:on of the nonmarine Two Medicine Forma:on (Upper Cretaceous), northwestern Montana, U.S.A. Can. J. Earth Sci. 30, 1066–1075. doi:10.1139/e93-­‐090 Royer, D.L., Wilf, P., Janesko, D. a., Kowalski, E. a., Dilcher, D.L., 2005. Correla:ons of climate and plant ecology to leaf size and shape: Poten:al proxies for the fossil record. Am. J. Bot. 92, 1141–1151. doi:10.3732/ajb.92.7.1141 Wolfe, J.A., Upchurch, G.R., 1987. North American nonmarine climates and vegeta:on during the Late Cretaceous. Palaeogeogr. Palaeoclimatol. Palaeoecol. 61, 33–77. doi:10.1016/0031-­‐0182(87)90040-­‐X Upchurch, G.R., Kiehl, J., Shields, C., Scherer, J., 2015. La:tude temperature gradients and high-­‐la:tude temperatures during the latest Cretaceous: Congruence of geologic data and climate models, in press. Acknowledgements: Thanks to UNAVCO and their support for the RESESS program. A very special thank you to NSF and USGS for funding this summer’s research and to Exxon Mobil for their con:nued support for the educa:on of geosciences. Thank you Denver Museum of Nature and Science staff, for access to imaging equipment and specimens, and CU-­‐Boulder Museum Collec:ons staff for help and encouragement. Lastly, A.M.P. would like to thank the University of Wisconsin-­‐River Falls’ Geology Department for all the years of encouraging support and educa:on. This material is based upon work supported by the Na:onal Science Founda:on under Award No. EAR 1261833.