98 CALCAREOUS ALGAE OF THE MIDDLE EAST 



spicuous minority-constituent of calcareous muds. This is the " debris-facies " 

 (Elliott 1958a). 



It must be emphasized that some of the local rock-facies encountered are not 

 easily recognizable in terms of the environments set out above. Diagenesis has 

 sometimes obscured or obliterated part of the evidence, but above all knowledge of 

 the small-scale lateral facies-changes is insufficient for full interpretation of the 

 ecology of the fossil-assemblages seen in hand-specimens. The original surveys were 

 stratigraphical and structural in intent, and only much later were the algae recog- 

 nized by me in thin-sections and hand-specimens of others' collecting, and then put 

 aside for this and other studies. 



The Middle East dasyclad environments reconstructed above are varied in time 

 and space, and in the nature of the rocks which now entomb the fossil evidence. 

 But it is noteworthy that none have yielded any evidence to suggest to me that the 

 ecological requirements of the dasyclads of the past were essentially different to those 

 of their living descendants. 



VII. THE EVOLUTION OF THE DASYCLADACEAE 



From the introductory account given above, it will be remembered that the 

 collection of dasyclads from the Middle East which forms the subject of this work 

 was selected from material collected for general stratigraphical purposes. Excep- 

 tionally it proved rich in species for palaeobotanical study, but much of it yielded 

 only sufficient evidence for identification and age-correlation with species previously 

 described elsewhere. Nevertheless, so much material, dasyclad remains from an 

 Upper Palaeozoic to Lower Tertiary timespan in a mid-Tethyan area favourable to 

 them, inevitably invites the question as to whether any further light is thrown on 

 the evolution of the family as a whole. 



It may be said at once that nothing emerges seriously to modify the general 

 picture of dasyclad evolution sketched by Julius Pia (Pia, see bibliography of : see 

 also Rezak 1959c). The dasyclads, having achieved the verticillate branch-pattern 

 in the Palaeozoic, proceeded to progressive and varied elaboration of the side- 

 branches, and to the progressive shift of the reproductive structures from within the 

 primitive thick stem-cell, into swollen lateral branches, and finally into special 

 structures borne on the laterals, or into the specialized reproductive discs charac- 

 teristic of some genera. The reproductive structures themselves are disappointing : 

 they yield no reasonable evidence of sexual mechanisms as have the fossil Melo- 

 besioids (e.g. M. Lemoine 1961), or the Chaetangiaceae (Elliott 1961). Presumably 

 the dasyclad reproductive bodies known conventionally in the fossils as sporangia, 

 were similar to those of most Recent genera and so contained resting cysts from which 

 gametes were only set free after shedding : this arose as a necessary consequence of 

 the well-developed calcification around these organs. Release of the reproductive 

 elements thus became only possible after the break-up of the calcified layers, and 

 calcification is usually well-developed around the sporangia. The living Dasycladus 

 with restricted stem-cell calcification only, is exceptional in shedding its gametes 

 direct. This condition was regarded by Pia as secondary, Dasycladus thus bearing 



