Siver Peter A, Reyes Alberto V, Pisera Andrzej, Buryak Serhiy, Wolfe Alexander P
Botany Department, Connecticut College, New London, CT, USA.
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada.
Ann Bot. 2025 Feb 10. doi: 10.1093/aob/mcaf021.
Phytoliths are microscopic siliceous structures produced in specific tissues by many plant families. The morphological features of phytoliths are diagnostic for many plant taxa, and given their inorganic composition often become part of the fossil record. We use phytolith remains from lacustrine sediments to document the conclusive presence of Arecaceae (palms) in subarctic Canada during the late early Eocene (48 Ma).
Palm phytoliths and aquatic microfossils were extracted from lacustrine mudstones in a drill core taken from the Giraffe kimberlite pipe locality using a combination of acid and oxidation treatments under low heat. Light microscopy and scanning electron microscopy were used to identify, examine, and image the microfossils.
Spherical echinate-shaped palm phytoliths with cone-shaped surface tubercles, likely belonging to the tribe Trachycarpeae (subfamily Coryphoideae), were uncovered in 45 strata over a 37-meter section of core. We further document in-situ linear arrays of phytoliths, or stegmata, from partially-decomposed palm foliage. Additionally, four aquatic organisms, largely restricted to warm subtropical and tropical localities today, were also uncovered in the same strata harboring the palm phytoliths.
The presence of palm phytoliths allows inference of a warm regional climate during the late early Eocene, with mean cold-month temperatures above freezing despite prolonged winter darkness. This conclusion is supported by the presence of multiple warm water aquatic organisms that grew extensively in the maar lake. Our findings will help to document the extent and timing of perennial ice formation in the northern hemisphere during the Cenozoic. Finally, the discovery of stegmata documents that this morphological trait had evolved by early Eocene.
植硅体是许多植物科在特定组织中产生的微观硅质结构。植硅体的形态特征可用于诊断许多植物分类群，并且由于其无机成分，它们常常成为化石记录的一部分。我们利用湖相沉积物中的植硅体遗迹来证明始新世早期晚期（4800万年前）加拿大亚北极地区确凿存在棕榈科（棕榈树）植物。
使用酸处理和低热氧化处理相结合的方法，从长颈鹿金伯利岩管地区采集的岩芯中的湖相泥岩中提取棕榈植硅体和水生微化石。利用光学显微镜和扫描电子显微镜对微化石进行鉴定、检查和成像。
在岩芯37米长的一段中，在45个地层中发现了表面有锥形瘤的球形具刺状棕榈植硅体，可能属于刺葵族（贝叶棕亚科）。我们还进一步记录了来自部分分解的棕榈叶的植硅体原位线性阵列，即植硅体带。此外，在含有棕榈植硅体的同一地层中还发现了四种水生生物，它们如今大多局限于温暖的亚热带和热带地区。
棕榈植硅体的存在表明始新世早期晚期该地区气候温暖，尽管冬季漫长黑暗，但平均冷月温度高于冰点。这一结论得到了在玛珥湖中广泛生长的多种暖水水生生物存在的支持。我们的发现将有助于记录新生代北半球多年生冰形成的范围和时间。最后，植硅体带的发现证明了这种形态特征在始新世早期就已经进化出来。
