Population dynamics of selected species of Brachiopoda and Gastropoda from the Strawn, Canyon, and Cisco groups (Upper Pennsylvanian) of North-Central Texas



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Paleo-community reconstruction and size-frequency analyses of brachiopod and gastropod species from shallow marine embayment facies in the Middle to Upper Pennsylvanian of North-Central Texas suggests that in muddy biotopes community distribution and population dynamics are greatly influenced by substrate limitations. Variation in characteristic patterns of substrate utilization among six paleo-communities identified by cluster analysis indicates that distribution of these primarily suspension feeding forms is controlled by the type of substrate available for habitation. Differences in population dynamics between two major brachiopod groups can be related to adaptations to limited attachment surfaces. Secondarily free-living Chonetids exhibit high but constant juvenile mortality rates and overall higher survival rates. Attached Spiriferids exhibit high juvenile mortality rates punctuated by size-related increases and overall lower survival rates. Exponential population growth and small body size of Glabrocingulum exemplify "r" selection. Linear population growth and high juvenile mortality of Straparollus are imposed by limitations of suspension feeding in a muddy biotope.



Brachiopoda, Fossil--Texas, Gastropoda, Fossil--Texas, Paleontology--Pennsylvanian, Paleontology--Texas