Cretaceous angiosperm leaf floras from Antarctica

Late Cretaceous angiosperm leaf floras from the Antarctic Peninsula have been studied and described for the first time. The Hidden Lake Formation (Coniacian) and Santa Marta Formation (Santonian-early Campanian) floras were preserved within shallow marine strata exposed on James Ross Island. This area was located at approximately 65°S during the Late Cretaceous. These fossils represent the remains of vegetation growing in the southern high latitudes on an emergent volcanic arc. The plants probably grew on the delta top and along the edge of streams.
The leaf fossils are preserved as isolated and fragmentary impressions and although cuticular anatomy is not present, the angiosperm leaves show the well-preserved fine detail of leaf architecture. These leaves have been drawn and described using Hickey's (1979) terminology. Attempts were made to group the leaves into morphotypes to allow reconstruction of floral composition and palaeoclimates. Several methods of grouping leaves were used, including visual grouping, Single character classification, and multivariate approaches. Multivariate statistical analysis allowed many characters to be considered simultaneously and even allowed fragmentary specimens, which were harder to deal with visually, to be evaluated. Clustering analysis was performed and dendrograms were produced for the Hidden Lake Formation and Santa Marta Formation floras, which were used in conjunction with visual assessments to group leaves with distinct morphologies into morphotypes.
A total of 41 morphotypes were identified, 30 in the Hidden Lake Formation flora and 31 in the Santa Marta Formation flora, with 20 in common. Detailed descriptions of each morphotype and representative illustrations are presented. Comparisons have been drawn with fossil and living angiosperm leaves. Architectural characteristics suggest that some of the leaves may have affinities with the Cunoniaceae, Lauraceae, Sterculiaceae, Nothofagaceae, Myrtaceae and Elaeocarpaceae. If botanical affinities can be confirmed, many of these occurrences would extend the ranges of angiosperm taxa on the Antarctic Peninsula.
Palaeoclimatic interpretation of the leaf floras included comparisons with possible nearest living relatives, analysis of leaf margins, shapes and sizes, and the application of simple linear regression and multiple linear regression models. The climate is considered to have been warm and moist. Mean annual temperature estimates of 12-21°C were provided for the Hidden Lake Formation flora and 14-23°C for the Santa Marta Formation flora. Evaluation of published data suggests that these Coniacian-early Campanian leaf floras may reflect the warmest time during the Cretaceous in Antarctica.