泥盆纪（英语：Devonian，符号D）是地球地质历史中显生宙古生代中的第四个纪，开始于4.19亿年前（同位素年龄419.2 Ma），结束于3.59亿年前（358.9 Ma），上承志留纪，下启石炭纪。
Why the Devonian period first saw the rise of land plants, the appearance of the first forests, and the emergence of early tetrapods (four-limbed vertebrates)? (ChatGPT, 2025-5-18)
The Devonian Period (419–359 million years ago), often called the “Age of Fishes,” was a transformative era in Earth’s history that also witnessed three major evolutionary milestones:
- The rise of land plants,
- The appearance of the first forests, and
- The emergence of early tetrapods (four-limbed vertebrates).
These events were interconnected, and several key environmental, atmospheric, and evolutionary factors made them possible:
1.
Atmospheric Oxygen Levels Rose Significantly
- Photosynthesis by early land plants (which first appeared in the Silurian) gradually increased oxygen levels in the atmosphere.
- By the Devonian, this buildup supported more complex ecosystems and made terrestrial environments more hospitable.
- Importantly, higher oxygen levels allowed for:
- The development of larger body sizes,
- More efficient aerobic respiration, and
- The survival of animals exploring land.
2.
Evolutionary Innovation in Plants
- Vascular tissue (xylem and phloem) evolved, allowing plants to transport water and nutrients efficiently.
- This adaptation enabled plants to grow upright and colonize drier, upland environments, leading to:
- The formation of the first true forests with trees like Archaeopteris,
- Complex root systems that stabilized soil and contributed to soil formation and carbon cycling.
3.
New Terrestrial Niches and Food Webs
- The growth of forests and terrestrial vegetation created microhabitats, food sources, and shade cover on land and near freshwater environments.
- This encouraged the evolution of arthropods (insects, spiders, etc.) and, eventually, vertebrates to exploit these new niches.
4.
Freshwater Ecosystem Complexity
- The Devonian is known for diverse fish lineages: placoderms, early sharks, lobe-finned fishes (Sarcopterygii), and ray-finned fishes (Actinopterygii).
- Among them, the lobe-finned fishes (e.g., Tiktaalik) developed limb-like fins, lungs, and neck mobility.
- In shallow, oxygen-poor waters, these features offered survival advantages:
- Fleshy fins helped move through vegetation or mudflats,
- Primitive lungs allowed gulping air when water oxygen was low.
This pre-adapted them for partial terrestrial locomotion—the crucial evolutionary step toward tetrapods.
5.
Climate and Geological Stability
- The Devonian had warm, stable climates and extensive coastal and swampy environments—ideal for amphibious life.
- Continental drift created large landmasses (e.g., Gondwana, Euramerica), promoting varied ecological zones and speciation.
Summary:
The Devonian saw a co-evolutionary cascade:
- Plants colonized land → forests formed → oxygen increased → new terrestrial niches emerged → arthropods thrived → lobe-finned fish adapted → tetrapods evolved.
This chain reaction shaped the terrestrial biosphere we still live in today.
Would you like a timeline or visual diagram to trace this evolutionary cascade?
