Pelagic or benthic? Mode of life of the remopleuridid trilobite Hypodicranotus striatulus

Abstract

The mode of life of the remopleuridid trilobite Hypodicranotus striatulus Walcott (1875) was examined hydrodynamically with a special focus on the relationship between the autecological performances of swimming and feeding. To understand the effect of swimming height from the sea bottom on the hydrodynamic performance of the exoskeleton, we performed computational fluid dynamics simulations on four models at differing distances from the sea bottom. The results indicated that Hypodicranotus could launch itself from the sea bottom with a relatively strong hydrodynamic lift force from slow walking or swimming speeds. However, the lift force decreased as the swimming height increased at slow swimming speeds. Hence, Hypodicranotus would have had to increase its swimming speed to greater than 0.2 m/s and to obtain the most stable lift force at a swimming height equal to half of its own body height. Its exoskeletal morphology, with a forked hypostome, enabled it to launch itself at a slow velocity and swim at a modest distance, i.e., close to its own height, from the sea bottom. Feeding from the median vortex flows along the food groove between the two prongs of the hypostome may have been the best strategy near the sea bottom, where a large amount of food matter would have been available. Because arthropod musculature consists of striated muscles, which exhibit inferior endurance, Hypodicranotus most likely adapted to the near-bottom environment, where it could rest at times on the sea bottom as part of a nektobenthic mode of life.•

Computational fluid dynamics modeling of fossil ammonoid shells

“…In schemes 1 and 2, a relatively small domain size was used where the inlet is set at 3 diameters from the object, the outlet is 10 diameters from the object and each wall is 5 diameters from the object. This domain was chosen as a starting point because it has been detailed and successful in previous paleontological studies (Shiino et al, 2009(Shiino et al, , 2012(Shiino et al, , 2014. In scheme 3, a larger box was employed to reduce the influence of walls on the flow field development.…”

Late OrdovicianHolorhynchussuccession in the Siljan district, Sweden: facies, faunas and a latest Katian event

“…Vermeij 2011). The overlying succession of the Unit A (lowermost Hirnantian) includes the swimming trilobite Remopleurides (Suzuki et al 2009), which is possibly superior for feeding on suspended organic matter, as discussed for the other remopleuridid genus (Shiino et al 2012(Shiino et al , 2014. The faunal change when such nektic animals appeared was also recognised in the Prague Basin (Mergl 2011).…”

Computational fluid dynamics as a tool for testing functional and ecological hypotheses in fossil taxa

“…Shiino et al . , , ) have used a computational domain that extended three times the length of the fossil upstream, ten times the length of the fossil downstream and five times the size of the fossil in all other directions; however, in some cases it might be possible to accurately resolve the flow using a smaller domain. Sensitivity analyses can be conducted to determine the optimal domain size (see below).…”

“…; Shiino & Kuwazuru , ; Shiino & Tokuda ), trilobites (Shiino et al . , ) and echinoderms (Rahman et al . ; Dynowski et al .…”