Sunday 13 November 2016

Following Insect feeding traces across the Cretaceous-Palaeocene boundary in Patagonia.

The End Cretaceous Extinction Event is generally thought to have been caused by the impact of a large extra-terrestrial object (asteroid or comet) into the Yucatan Peninsula in Mexico. this is reflected in a slightly less sever extinction being recorded in high latitude Southern Hemisphere deposits than in their equivalents in the Northern Hemisphere. In Australia otherwise exclusively Mesozoic Plant groups such as the Corystosperms and Bennettitaleans are known to have survived into the early Cainozoic, while marine invertebrate faunas in New Zealand appear to have been less severly impacted by the event than those in the Northern Hemisphere, and a lowere severity extinction is seen in the pollen record in both New Zealand and Patagonia. Plant-Insect interactions are a major driver of terrestrial ecosystems, which are known to have been strongly disrupted by the End Cretaceous Extinction in North America, requiring new relationships to evolve between Plant and Insect groups before complex ecosystems could reappear. However to date such relationships have not been studied across the Cretaceous-Palaeocene boundary in other parts of the world.

In a paper published in the journal Nature: Ecology & Evolution on 7 November 2016, Michael Donovan of the Department of Geosciences at Pennsylvania State University, Ari Iglesias of the Instituto de Investigaciones en Biodiversidad y Medioambiente at the Universidad Nacional del Comahue, Peter Wilf, also of the Department of Geosciences at Pennsylvania State University, Conrad Labandeira of the Department of Paleobiology at the National Museum of Natural History, Department of Entomology and Behavior, Ecology, Evolution, and Systematics Program at the University of Maryland and the School of Life Sciences at Capital Normal University and Rubén Cúneo of the Museo Paleontológico Egidio Feruglio, describe the results of a study of insect feeding traces across the Cretaceous-Palaeocene boundary in Chubut Province in Central Patagonia in Argentina.

Donovan et al. examined fossil leaves from four sites in central Patagonia, Lefipán East, where 606 specimens dated to between 67 and 66 million years ago were recovered from the Late Cretaceous Lefipán Formation, Palacio de los Loros 1, where 1089 spcimens dated to between 65.58 and 64.86 million years ago were recovered from the Late Cretaceous Salamanca Formation, where 1132 specimens dated to between 64.67 and 63.49 millon years ago were recovered from the Early Palaeocene Salamanca Formation, and Las Flores, where 571 specimens dated to beteen 62.52 and 62.22 million years ago were recovered from the Early Palaeongene Peñas Coloradas Formation.

These leaves were examined for different types of Insect-damage, paying particular attention to leaf-mines, which tend to be distinctive at the species level. They were able to identify a total of 49 different damage types from the Cretaceous and 60 damage types from the Palaeocene. This is remarkable as it represents more damage types than have been identified from either period than in the entire of North America, where numerous studies of this type have been carried out. In addition each of the Patagonian sites has a greater diversity of damage types than any similar site in North America, other than the exceptional Palaeocene Mexical Hat site of Montana, which has produced more individual damage types than either of the Patagonian Palaeocene sites.

Insect damage on latest Cretaceous and early Palaeocene leaves from Chubut, Argentina. (a–l) Latest Cretaceous samples from the Lefipán Formation (a–c), and early Palaeocene samples from the Salamanca (d–i) and Peñas Coloradas (j–l) formations. (a) Multiple, overlapping blotch mines containing centralized frass on leaf. (b) Spheroidal galls with striated surfaces. (c) Margin feeding with thickened reaction tissue. (d) Serpentine mine with spheroidal terminal chamber on Cissites patagonica. (e) Elliptical gall positioned on the primary vein at the intersection with secondary veins on Laurophyllum piatnitzkyi. (f) Row of parallel-sided holes near the leaf margin on Dryophyllum australis. (g) Spheroidal galls with distinct outer rims positioned on the primary vein of Cissites patagonica. (h) Concentric rings of piercing and sucking marks surrounded by dark reaction tissue. (i) Hole feeding surrounded by a wide rim of blotched reaction tissue. (j) Serpentine mines that transition to blotch mines with internal, intestiniform trails on Fagophyllum duseni. (k) Elongate, curvilinear patches of skeletonized tissue. (l) Deeply incised margin feeding damage on Dryophyllum australis. Donovan et al. (2016).

This sample set showed a more diverse assemblage of Insect herbevores than has previously been observed on either side of the Cretaceous-Palaeocene boundary. A decrease in diversity was observed across the boundary, with maximum diversity not reached until four million after the event. This was accompanied by a 30% drop in leaf-type across the boundary. All of the major feeding damage types (hole feeding, margin feeding, skeletonization, surface feeding, piercing and sucking, mining, galling and oviposition) continue across the boundary, though 21.8% of more specialized forms died (compared to a 55.6% decline in North Dakota), and no trace could be confidently assigned to a single species persisted across the boundary.

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