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Grasses and dinosaurs
The picture just might be changing. Grasses -- wheat, corn, rice, etc. -- "rule", so to speak, 20% of the surface of the earth, and, as monocotyledons, are related to palms, pineapples, orchids, and lillies. The fundamental research is being conducted by 13 scholars, the Grass Phylogeny Working Group <www.virtualherbarium.org/CPWG/>, intensive exegesis of restriction site maps of chloroplast genome. Grass -- I use the term botanically, not recreationally vis-a-vis Frank Zappa -- has nearly circular pollen, with one pore, tiny foramina entering the outer covering of the pollen walls only. The oldest known, clearly recognizable grass pollen is from the Paleocene of Africa and South America, 55-60mya (cf. B.F. Jacobs, J.D. Kingston, L.L. Jacobs, 1999, The origin of grass-dominated ecosystems, Annals Missouri Botanical Garden 86:590-643). An!
yet. Jacobs et al. noted the 1987 study by H.P. Linder, 1987, The evolutionary history of the Poales/Restionales: a hypothesis, Kew Bulletin 42:297-318, a paper virtually forgotten but worth perusing. Linder reported Maastrichtian grass-like pollen grains, although the fossils are not preserved well enough to determine if they had the foramina penetrating the pollen outer wall. Perhaps not. Perhaps so. No definite fossils have been found to prove that dinosaur herbivores were eating grass. Unlike other monocotyledons, grasses differ in the sequence of embryonic development, and DNA evidence points to a period of change in their common ancestors 55-70mya. These ancestors had an ovary consisting of three fused carpels, each creating one locule with one ovule (cf. Elizabeth Kellogg & H.P. Linder 1995, Phylogeny of the Poales). In some taxa related to grasses, two of the ovules fail to develop, one reaching maturation. Among grasses, however, only one ovule and!
ocule develop, the ovule forming an outer cover fusing to the inner ovary wall -- this being the caryopsis, the grain, the grasses's fruit, unknown among all other angiosperms.
I am willing to wager that grasses were appearing in scattered areas during the late Cretaceous, some being consumed by dinosaurs. Plants have remarkable arrays of toxicological defenses against herbivores -- could some have been poisonous to dinosaurs?