GROUP RELATIONSHIPS 



25 



RELATION OF MAZOCARPON TO AFFILIATED GROUPS OF PLANTS 



The genera to be considered are : 

 (1) Sigillaria, a g-roup of plants identi- 

 fied by diagnostic characteristics of 

 their stems; (2) Sigillariosirohus, a 

 group of plants identified by certain 

 features of their cones, generally dis- 

 cernable when preserved as impressions 

 and coalified compressions; and (3) one 

 section of the genus Triletes, the Apha- 

 nozonati, a group of lycopods identified 

 by certain characteristics of their iso- 

 lated megaspores. Mazocarpon is a group 

 of plants identified by certain special- 

 ized characteristics of cones and spo- 

 rangia which may be distinguished only 

 when well preserved. The groups over- 

 lap in a biological sense and can be 

 represented as members of the Sigillar- 

 iaceae during a considerable part of 

 Carboniferous time. However, the de- 

 gree of overlap between the genera or 

 species is not precisely definable. The 

 relationships of the late Devonian and 

 early Mississippian antecedants are ob- 

 scure, and post-Carboniferous represen- 

 tatives are also inadequately known. 

 Chiefly because of the inadequacy of 

 knowledge of specific interrelationships 

 during Pennsylvanian time and generic 

 and suprageneric interrelationships dur- 

 ing the late Devonian and early Car- 

 boniferous time it appears necessary to 

 classify the diverse fossils separately, 

 in different specific and generic groups 

 at least. Treated thus, the minor stages 

 of the evolutionary sequence may be 

 discussed more readily and accurately; 

 nomenclatorial confusion can be reduced 

 to a minimum because probable interrela- 

 tionships are referred to more precisely. 



Information obtained from the study 

 of Mazocarpon oedipternum supports 

 the belief that the different genera men- 

 tioned above are all members of an 

 intimately related series. It seems that 

 the major line of phylogenetic affinity 

 is reasonably certain even though the 

 minor stages of evolution are imperfect- 

 ly known. The object of further study 

 should be the recognition of these minor 

 stages of the evolutionary sequence, key- 

 ing them carefully with the time se- 



quence represented by the sedimentary 

 strata. Study of the abundant mega- 

 spores will aid greatly. In the past, 

 sigillarian fructifications have been 

 identified less frequently than their 

 stems, and it has been a question 

 whether some of them were most inti- 

 mately allied with Lepidostrohus and 

 other lepidodendrids rather than the 

 sigillarians. If this were the case, an 

 interlocking phylogenetic relationship 

 between the lepidodendrids and sigillar- 

 ians might be indicated. The two groups 

 are for the most part easily distinguish- 

 ed by characters of the leaf bolsters, 

 but there has always been some question 

 whether these distinctions were of ac- 

 tual generic importance, and if so, at 

 what point in the geological history 

 generic segregation took place. The 

 presence of Mazocarpon at a position 

 rather high in the Pennsylvanian shows 

 that the characters which distinguish 

 Mazocarpon from Lepidostrohus were 

 important and persistent, and shows 

 that direct phyletic connection between 

 these two lines in Pennsylvanian time 

 is improbable. It is more likely that 

 the two groups diverged in the early 

 Mississippian. 



In the following discussion, impor- 

 tant characters in classification of the 

 sigillarian alliance are considered. The 

 object is to illustrate the relationship of 

 these forms in the light of reconsidera- 

 tion of certain of the significant bio- 

 characters. It seems that more emphasis 

 may reasonabl^^ be placed on some of 

 them, such as mode of fructification and 

 character of the megaspores, than has 

 been generally recognized. On the other 

 hand, the characters of cone phyllotaxis 

 appear to have been overemphasized. 



The manner in which the cones are 

 borne on these plants seems to be a 

 character of major importance in defi- 

 nition of the sigillarian alliance. Both 

 Mazocarpon and Sigillariostro'bns cones 

 are pedunculate, and stems of SigUlaria 

 bore fructifications on the main trunks 

 by means of peduncles. A primary 



