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CONIFER POLLEN CONES FROM THE CRETACEOUS OF ARKANSAS: IMPLICATIONS FOR DIVERSITY AND REPRODUCTION IN THE CHEIROLEPIDIACEAE

Authors
Publisher
The Paleontological Society
Publication Date
Disciplines
  • Biology

Abstract

Abstract Cheirolepidiaceous conifer pollen cones (Classostrobus arkansensis new species) from the Lower Cretaceous (Aptian/Albian) Holly Creek Formation of Arkansas, some still attached to Pseudofrenelopsis parceramosa Fontaine, shoots, bear helically arranged, semipeltate to dorsiventral microsporophylls with abaxially situated pollen masses. The in situ Classopollis Pflug, 1953 pollen and orbicule outer sculpturing consists of short spinules. The abaxial epidermis of the microsporophyll head consists of a stomatiferous central region of isodiametric cells bearing hollow papillae with rounded apices and a nonstomatiferous marginal area of elongate, nonpapillate cells. The head abaxial cuticles are thin relative to those of the shoot internodes. A cutinized hypodermis is lacking. Previously described pollen cones of Classostrobus comptonensis (Alvin et al., 1994) from the English Wealden (Barremian) are also associated with P. parceramosa shoots; however, they differ substantially from the Arkansas cones in possessing peltate microsporophylls with the abaxial surfaces bearing conical papillae, a cutinized hypodermis, and cuticles as thick as those of the shoot internodes. Therefore, at least two morphologically distinct pollen cones were produced on ultimate shoots conforming to P. parceramosa as presently circumscribed. Most cheirolepidiaceous conifers possess extremely thick cuticles on the abaxial surface of the microsporophyll head, which may suggest an unusual pollination biology entailing the production of fewer, relatively long-lived pollen cones. However, the thin cuticles and relatively abundant material of Classostrobus arkansensis n. sp. are more consistent with the typical coniferous pollination system, which includes production of numerous, ephemeral cones. Apparently, the Cheirolepidiaceae possessed a diversity of reproductive strategies.

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