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Feeding behavior of Jurassic radiolarians inferred from comparison in skeletal morphology with laboratory cultured radiolarians

Matsuoka A.

Volumina Jurassica

2006

Vol. 4, no. 1

239-240

Living radiolarian research provides us with fundamental data for feeding behavior of radiolarians. Detailed observations of a variety in feeding behavior of laboratory cultured radiolarian specimens make it possible to understand the relationship between skeletal morphology and feeding behavior. This work focuses on the application of living radiolarian research to clarifying feeding behavior of Jurassic radiolarians, leading to reconstruct marine eco-system in the Jurassic oceans. Four types of feeding strategy well correspond to skeletal morphology in extant radiolarian taxa. High diversity of radiolarian skeletal morphology is partly related to having a variation in feeding strategies. The wide variation in feeding behavior means that radiolarians occupy several kinds of ecological niches in marine environments. We can infer feeding behavior of extinct radiolarian group based on their skeletal morphology. Once we recognize the role of radiolarians in food web in the modern ocean environments, we can apply it to reconstruct marine eco-system in the Jurassic time. Fluctuation in morphological diversity of radiolarian skeletons is well documented in fossil records. This fluctuation can be interpreted as change in the number of ecological niches in the marine eco-system through time. Jurassic radiolarians include most types of basic skeletal morphology of extant radiolarians except for colonial radiolarians. Extant Eucyrtidium, Pterocorys, Lipmanella and Spirocyrtis are model taxa for multi-segmented nassellarians such as Jurassic Archaeodictyomitra, Hsuum, Parahsuum, and others. Extant Lithomelissa and Pseudocubus are probably analogous to Jurassic small nassellarians like cryptocephalic and cryptothoracic taxa. Spherical and discoidal spumellarians are common in both recent and Jurassic radiolarian assemblages. Assuming that skeletal morphology indicates their feeding strategy then at least three types of feeding behavior were developed in the Jurassic time. The presence of radiolarian skeletal morphology suggests that prey of radiolarians also existed in a water column where radiolarians dwelled. The resemblance between modern and Jurassic radiolarian skeletons indicates that the marine eco-system in the present and Jurassic times is probably similar to each other in terms of the nature (size and mobility) of prey.