Mesozoic cupules and the origin of the angiosperm second integument

Area of Science:

• Paleobotany
• Evolutionary Biology
• Developmental Genetics

Background:

• The unique second integument of angiosperm ovules distinguishes them from other seed plants.
• Comparing this structure to extinct seed plants is key to understanding angiosperm origins.
• Previous interpretations were limited by insufficient fossil evidence.

Observation:

• Abundant, exceptionally preserved recurved cupules from the Early Cretaceous (approx. 125.6 million years ago) were discovered in Inner Mongolia, China.
• These fossils originated from a newly identified silicified peat deposit.
• Re-examination of potentially related Mesozoic fossils was conducted.

Findings:

• The newly discovered recurved cupules are fundamentally comparable to those of other Mesozoic plants.
• Their structure aligns with the recurved form and development of the second integument in bitegmic, anatropous angiosperm ovules.
• These findings identify potential angiosperm relatives (angiophytes).

Implications:

• Provides a partial answer to the long-standing question of angiosperm origins.
• Guides future research in seed plant phylogenetics.
• Impacts current understanding of angiosperm carpel evolution.