FOSSIL BRYOPHYTES

1. The rapid increase in the knowledge of the early geological history of bryophytes which has taken place in recent years is emphasized. 2. An explanation for this unexpected development is sought in a consideration of the conditions necessary for the preservation of bryophytes as fossils. 3. It is concluded that the chances of preservation depend not so much on the conditions suitable for the growth of bryophytes or the possession of resistant structures (although both can be important contributory factors) but on the occurrence of the right kind of sedimentation in the right place at the right time. 4. The fossil history of the main Orders of the Bryophyta is then systematically reviewed, with special reference to first records in the Palaeozoic and Mesozoic. 5. A number of problematic bryophyte-like fossils of Palaeozoic age are also reviewed. Four (Protosalvtnia Dawson, Sporogonites Halle, Tetrapterites Sullivan and Hibbert, and a Dicranum-like plant from South Africa) are accepted as probably bryophytic; three (Musciphyton Greguss, Hepaticaephyton Greguss, and an alleged bryalean sporogonium from the Rhynie Chert) are rejected on the grounds of insufficient evidence. 6. The bearing of the fossil evidence on bryophyte evolution is briefly considered. 7. It is shown that the principal groups of both liverworts and mosses had already been differentiated before the end of the Palaeozoic. 8. A polyphyletic origin of the Bryophyta is therefore highly probable. 9. Beyond this, the early fossil evidence as yet gives no unequivocal answers and more detailed phylogenetic speculation based on the present state of knowledge of fossil bryophytes has little value. 10. Further knowledge of the early fossil history of bryophytes is needed and it is suggested that this is most likely to be obtained by patient systematic search in finegrained freshwater sediments by bulk maceration techniques.