生きた化石の最近の同期放射線
N S Nagalingum1, C R Marshall, T B Quental
1Arnold Arboretum of Harvard University, 22 Divinity Avenue, Cambridge, MA 02138, USA. nathalie.nagalingum@rbgsyd.nsw.gov.au
まとめ
かつて生きている化石と考えられていたサイカドは,最近多様化しました. 現代のサイカド種は1200万年未満で,古代の系統の地位に挑戦しています.
科学分野:
- パレオボタニーは古植物学です.
- 進化生物学の進化生物学について
- フィロジェネティクス フィルジェネティクス
背景:
- サイカッドは古代の種子植物で,ジュラ紀・クレタセア紀で多様性のピークに達した.
- 現在の低多様性 (約300種) は,開花植物が増えた後に減少したことを示唆している.
- 形態学的静止状態のため,しばしば"生きている化石"と見なされます.
研究 の 目的:
- サイカードの進化史と多様化を調査する.
- 現存するサイカド種の年齢を決定するために.
- サイカドの"生きた化石"の指定を再評価する.
主な方法:
- 化石で計測された分子フィロゲニーがタイムツリーを構成するために使用されました.
- デッティング方法は,分子のデータに適用して,分岐時間を推論した.
- 多様化パターンを理解するために,系統遺伝学的分析が行われました.
主要な成果:
- サイカッドは,ミオセンの終わりから世界的な再多様化を経験しました.
- 多様化が遅れたのは,近年期に向けてのことである.
- 生きているサイカド種は比較的若く,年齢は1200万年を超えない.
結論:
- サイカッドの再多様化は,最近の進化の出来事です.
- 現存するサイカドの多様性は,恐竜の影響と関連していない.
- 現代サイカド種は,伝統的な意味での"生きた化石"ではありません.
関連する概念動画
The Fossil Record
The fossil record documents only a small fraction of all organisms that have ever inhabited Earth. Fossilization is a rare process, and most organisms never become fossils. Moreover, the fossil record only exhibits fossils that have been discovered. Nevertheless, sedimentary rock fossils of long-lived, abundant, hard-bodied organisms dominate the fossil record. These fossils offer valuable information, such as an organism's physical form, behavior, and age. Studying the fossil record helps...
Diversity of Protists III
Rhizaria are a diverse group of unicellular protists characterized by their threadlike cytoplasmic extensions known as pseudopodia. These structures aid in both locomotion and feeding, giving Rhizaria an amoeboid appearance. Their amoeboid morphology once led to taxonomic confusion, but molecular phylogenetics has clarified their evolutionary placement and emphasized their shared use of pseudopodia despite divergent lineages.This clade comprises diverse lineages such as Chlorarachniophyta,...
Radioactive Decay and Radiometric Dating
Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. The number of disintegrations per unit time is called the activity (A), which is directly proportional to the number of nuclei in the sample. The decay constant (λ) is an average probability of decay per nucleus in unit time.
What is Evolutionary History?
Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and provides evidence for evolution. However, both fossil and living organisms offer evidence that outlines Earth’s evolutionary history.
Speciation Rates
Overview
Other Unique Bacteria
Magnetic bacteria exhibit a directed movement called magnetotaxis, driven by structures called magnetosomes. These magnetosomes consist of chains of magnetic particles made of either magnetite (Fe₃O₄) or greigite (Fe₃S₄) and are organized in a linear conformation by a protein scaffold within invaginations of the cell membrane. The bacteria align along the north–south magnetic field lines, much like a compass needle. They are typically microaerophilic or anaerobic and are commonly found near the...


