Multivariate analysis of Lower Cretaceous monosulcate pollen from central-western Argentina

Monosulcate pollen grains are an important component of the Mesozoic palynofloras around the world. These type of grains are produced by several groups of plants and because of the morphological similarities among them, their taxonomic determination is difficult. Currently, there is scarce information about morphological differences of monosulcate pollen grains and this makes their botanical affinity in fossil specimens challenging. In this work, we analyzed statistically the morphological features of monosulcate fossil pollen grains recovered from six palynological assemblages from the Lower Cretaceous Lagarcito Formation of central-western Argentina. We used our own fossil dataset and data from the description of monosulcate pollen grains published from Cretaceous cycadalean in situ male cones from Patagonia. Furthermore, morphological variables from selected living species were added to support the analysis. According to our results, two main groups with clear morphological features were characterized among fossils. The use of an extant dataset allowed us to support the exine sculpture as an important variable when characterizing fossil pollen grains. Finally, our fossil dataset showed similarities with the in-situ pollen grains from the cycadalean cone species Androstrobus munku and Androstrobus patagonicus. This work is the first attempt to identify different morphological types among fossil monosulcate pollen grains recovered from the Lagarcito Formation of central-western Argentina. Our results will contribute to elucidate morphological variations in fossil pollen grains and may improve future taxonomic studies.

单槽花粉粒（monosulcate pollen grains）是全球中生代孢粉植物群（Mesozoic palynofloras）的重要组成部分。此类花粉粒由多类植物产生，且因彼此形态相似，其分类鉴定颇具难度。当前，关于单槽花粉粒形态差异的研究资料较为匮乏，这使得化石标本中该类花粉的植物亲缘关系判定极具挑战性。
本研究对阿根廷中西部下白垩统拉加尔西托组（Lagarcito Formation）6个孢粉组合（palynological assemblages）中产出的单槽化石花粉粒的形态特征进行了统计分析。本研究采用了自建的化石数据集，以及来自巴塔哥尼亚地区白垩纪苏铁目（cycadalean）原位雄球花（in situ male cones）中单槽花粉粒的已发表描述数据。此外，本研究还纳入了选定现生类群的形态变量以辅助分析。
根据分析结果，化石样品中可划分为两个具有显著形态特征的主要类群。通过使用现生类群数据集，本研究证实了花粉外壁纹饰（exine sculpture）是化石花粉粒分类特征中的重要变量。最后，本研究的化石数据集与苏铁目球果物种Androstrobus munku及Androstrobus patagonicus的原位花粉粒具有相似性。
本研究是首次针对阿根廷中西部拉加尔西托组产出的单槽化石花粉粒开展不同形态类型划分的尝试。本研究结果有助于阐明化石花粉粒的形态变异规律，可为未来的分类学研究提供参考与支撑。