Data from: Mesozoic cupules and the origin of the angiosperm second integument

The second integument of the angiosperm ovule is unique among seed plants,
with developmental genetics that are distinct from those of the inner
integument. Understanding how the second integument should be compared to
structures in other seed plants is therefore crucial to resolving the
long-standing question of the origins of angiosperms. Attention has
focused on several extinct plants with recurved cupules that are
reminiscent of the anatropous organization of the basic bitegmic ovules of
angiosperms, but interpretations have been hampered by inadequate
information on the relevant fossils. Here we describe abundant
exceptionally well-preserved recurved cupules from a newly discovered
silicified peat dating to the Early Cretaceous epoch (around 125.6 million
years ago) in Inner Mongolia, China. The new material, combined with
re-examination of potentially related fossils, indicates that the recurved
cupules of several groups of Mesozoic plants are all fundamentally
comparable, and that their structure is consistent with the recurved form
and development of the second integument in the bitegmic anatropous ovules
of angiosperms. Recognition of these angiosperm relatives (angiophytes)
provides a partial answer to the question of angiosperm origins, will help
to focus future work on seed plant phylogenetics and has important
implications for ideas on the origin of the angiosperm carpel.