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, 99 (4), 2061-6

Impact of the Terminal Cretaceous Event on Plant-Insect Associations

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Impact of the Terminal Cretaceous Event on Plant-Insect Associations

Conrad C Labandeira et al. Proc Natl Acad Sci U S A.

Abstract

Evidence for a major extinction of insect herbivores is provided by presence-absence data for 51 plant-insect associations on 13,441 fossil plant specimens, spanning the Cretaceous/Paleogene boundary in southwestern North Dakota. The most specialized associations, which were diverse and abundant during the latest Cretaceous, almost disappeared at the boundary and failed to recover in younger strata even while generalized associations regained their Cretaceous abundances. These results are consistent with a sudden ecological perturbation that precipitated a diversity bottleneck for insects and plants.

Figures

Figure 1
Figure 1
A spectrum of plant–insect associations from the Williston Basin of southwestern North Dakota. Associations range from the earliest Paleocene at upper left, 14.4 m above the K/T boundary, and continue to the older associations of the latest Cretaceous at lower right, 85.5 m below the boundary. All material is from the Denver Museum of Nature and Science (DMNH) or the Yale Peabody Museum (YPM). Following each plant host are, respectively, morphotype number (indicated by the prefixes HC or FU) (17), specimen number, DMNH locality number (loc.), and ± meter distances from the K/T boundary as in Fig. 2 (17). Damage types are indicated by the prefix DT (Fig. 2). (Scale bars: solid = 1 cm, backslashed = 0.1 cm.) (a) Two linear mines with oviposition sites (arrows), following secondary and then primary venation, terminating in a large pupation chamber (DT59), on the dicot Paranymphaea crassifolia (FU1), DMNH 20055, loc. 563, +14.4 m. (b) Single gall (DT33) on primary vein of Cercidiphyllum genetrix (Cercidiphyllaceae, FU5), DMNH 20042, loc. 562, +8.4 m. (c) Free feeding (DT26) on Platanus raynoldsi (Platanaceae, FU16), DMNH 20035, loc. 2217, +1.3 m. (d) Skeletonization (DT61) on a probable lauralean leaf (HC32), DMNH 19984, loc. 2097, −31.4 m. (e) Multiple galls (DT33) on Trochodendroides nebrascensis (Cercidiphyllaceae, HC103), DMNH 19976, loc. 1489, −33.7 m. (f) Initial phase of a serpentine mine (DT45) on Marmarthia pearsonii (Lauraceae, HC162), DMNH 7228, loc. 2087, −36.9 m. (g) Cuspate margin feeding (DT12, arrow) on Metasequoia sp. (Cupressaceae, HC35), DMNH 13108, loc. 567, −56.8 m. (h) Serpentine leaf mine (DT43) assigned to the Nepticulidae (Lepidoptera), on unidentified Rosaceae (HC80), YPM 6367a, loc. 567, −56.8 m. (i) Hole feeding pattern (DT57) on an unknown genus of Urticales (HC81), DMNH 19539, loc. 2203, −56.8 m. (j) General skeletonization (DT16) on Erlingdorfia montana (Platanaceae, HC57), DMNH 11013, loc. 571, −61.7 m. (k) Large scale-insect impressions (DT53) centered on primary veins of E. montana, DMNH 18829b. loc. 571, −61.7 m. (l) Slot hole feeding (DT8) on an unidentified genus of Platanaceae (HC109), DMNH 18658, loc. 434, −88.5 m. See Table 1, which is published as supporting information on the PNAS web site, www.pnas.org, for additional descriptions of damage types.
Figure 2
Figure 2
Stratigraphic and sampling data for the 51 insect-mediated damage types from a 183-m composite section straddling the K/T boundary (orange bar), from the Williston Basin of southwestern North Dakota (Table 1 and Table 2, which is published as supporting information on the PNAS web site). The estimated time duration for this interval is 2.2 million years (my) before present, of which 0.8 my are assigned to the postboundary interval and 1.4 my are allocated to the preboundary interval (2). The Cretaceous strata are within the Hell Creek and Fort Union formations, and the Paleocene strata are entirely within the Fort Union Formation (2, 17). Placement of the zero datum is at the K/T boundary, not the Hell Creek/Fort Union formational contact, because the contact is diachronous with respect to the K/T boundary timeline (17). Depicted are the raw presence/absence data for damage types, categorized by functional feeding group and subgroup at the bottom, and representing 106 discrete horizons. Eight damage types have single stratigraphic occurrences (dots); the ranges of those with multiple stratigraphic occurrences are shown as vertical shaded bars, categorized by host specificity from the color scheme at upper left (see text). Confidence intervals of 50% are provided for the 14 damage types whose regional last appearances occur before the boundary, using a method that accommodates nonrandom distributions of fossil horizons and sampling intensity by allowing recovery potential to vary stratigraphically (39) (see text). Of the 14 specialized damage types with multiple stratigraphic occurrences that disappear at or below the K/T boundary, six (42.9%) reappear during the latest Paleocene to middle Eocene of Wyoming and Utah (27, 30). All associations are extant today. Four confidence intervals that exceed our sampling range are shown without end bars. Total specimen frequencies are given at right, including all plant organs; note logarithmic scale. The gray horizontal lines in the main figure and corresponding gray squares at right indicate the 14 horizons with more than 200 specimens of identified dicot leaves, used in Fig. 3; meter levels for these floras are: −75.0, −65.0, −56.8, −47.8, −36.9, −34.6, −31.4, −15.0, −3.6, +0.2, +1.3, +30.9, +42.4, +50.0. Abbreviations: mar., margin feeding; skel., skeletonization; spl., specialized external feeding types; p., piercing and sucking; o., oviposition. Limitations on graphical presentation cause the flora at +0.2 m, which is Paleocene, to appear within the orange line representing the K/T boundary.
Figure 3
Figure 3
(a) Frequency analyses (percentage basis) of insect damage for the 14 discrete horizons with at least 200 specimens of identified dicot leaves. The vertical scale shows the meter level with respect to the K/T boundary (orange bar). The horizontal scale is the percentage of leaves bearing insect damage. Binomial error bars of ±1 σ are placed on frequency data based on the number of specimens (30). In green are all damage types; black, generalized damage types only; and purple, lumped intermediate and most specialized damage types. Because some individual leaves contain more than one damage type, the total percentage (green) is usually less than the sum of the two other data series. (b) Damage diversity analysis of insect damage, with raw data bootstrapped to 5,000 replicates (27). Vertical scale and zero datum as in a; the data series shows the mean number of damage types for 200 specimens. The data labels show the number of leaves in each sample and also pertain to a. Limitations on graphical presentation result in the data from +0.2 m (500 specimens), which are Paleocene, to appear within the orange line representing the K/T boundary. Error bars represent ±1 σ around the mean and are mathematically forced to be small when the total number of specimens only slightly exceeds 200. Poor preservation is probably responsible for the lack of recovered insect damage around the 30- to 40-m interval. See Table 3.

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