Graptolite reconstructions and interpretations

Graptolites can be identified as a group of clonal, colonial pterobranchs with numerous extinct members and a few extant ones, secreting a characteristic housing structure, the tubarium. The zooids of the extant genus Rhabdopleura can be regarded as a general model to reconstruct graptolite zooids, but may not represent precisely the soft-body anatomy of extinct taxa. The life cycle of fossil graptolites can be interpreted from the ontogeny of the zooids of the extant Rhabdopleura and the astogeny of the fossil colonies. The planktic graptoloids (Graptoloidea) lived un-attached in the oceans and were actively moving through the water column, filtering the water column to gather food. Fossil evidence of attachment to seaweeds or other floating materials does not exist. The benthic graptolites are attached with their sicula to a firm surface either rocks, sediments or other organisms. Some of the early graptolite reconstructions are still widely distributed in the scientific literature and in palaeontology textbooks and show a considerable longevity. They are visually appealing, but in conflict with the available evidence.