DOI: 10.5061/dryad.4mw6m90js
title: Data from: Locomotory and morphological evolution of the earliest Silurian graptolite (Demirastrites) selected by hydrodynamics

description: Interpretation of the locomotion for biostratigraphic important graptolite
 taxa is rare and rendered problematic due to their lack of close modern
 analogues and soft tissues. In this study, based on well-preserved
 specimens of the early Silurian low-helical spiral Demirastrites Eisel, we
 reconstructed three-dimensional (3D) Demirastrites models and simulated
 their locomotion by using computational fluid dynamics. Hydrodynamic
 properties (outer-wall pressure fields and velocity fields) were obtained
 and used to test the prevailing hypothesis that the Silurian low helical
 spiral graptolite Demirastrites could rotate in seawater. The
 Demirastrites models kept rotating at different velocities in the
 simulation field, which helped to counteract the impact of the water
 current and achieve stability. During rotation, higher velocity fields
 could be observed near the thecal apertures, which meant better access to
 more nutrient particles in the sea water. Our simulation thus confirmed
 the rotating locomotory pattern of the Silurian low conical graptolite
 Demirastrites for the purpose of better feeding efficiency and turbarium
 stability. Moreover, we analysed how the evolution of structural
 innovations, such as the density and width of thecae and the curvature
 angle of the rhabdosome within the recovered geological lineages of
 Demirastrites, were influenced and selected by hydrodynamics. The results
 showed that Demirastrites lineages evolved towards increased stability and
 higher rotation velocity. Our study highlights the importance of
 hydrodynamic constraints serving as hidden abiotic factors shaping the
 evolution of planktonic graptolites. 
description: # Data from: Locomotory and morphological evolution of the earliest
 Silurian graptolite (*Demirastrites*) selected by hydrodynamics
 [https://doi.org/10.5061/dryad.4mw6m90js](https://doi.org/10.5061/dryad.4mw6m90js) This data package contains FOUR files. **Data file: 3d Models** The package contains CAD files of four *Demirastrites* 3D models in STEP format (.stp). STP is a general format of a CAD 3D model. You can use most of the CAD software to open and view it, such as freeCAD ([https://www.freecadweb.org](https://www.freecadweb.org)) and OpenCascade ([https://www.opencascade.com](https://www.opencascade.com)) for free. Original Model= the reconstruction of a 3D digital model of *Demirastrites* base on *D. triangulates* Model A= a model established with more densely spaced thecae Model B = a model established with wider thecae width Model C = a model established with higher angle of tubarium curvature between th1 and th10 **Data file:** **S0_veocity_in_fixed_and_non-fixed_models** These data describe the thecal apertures flow velocity of the fixed and non-fixed models in this study. Position of the thecae = the position of each theca in the tubaria Velocity = the flow velocity of thecal apertures Fixed = original model in fixed state Non-fixed = original model in passive state **Data file: S1_veocity_in_three_different_inlet_velocities** Position of the thecae = the position of each theca in the tubaria Velocity = the flow velocity of thecal apertures 0.28m/s = the inlet velocity is set to 0.28m/s 0.014m/s = the inlet velocity is set to 0.014m/s 0.0015m/s = the inlet velocity is set to 0.0015m/s **Data file: S2_mesh_size** These data describe the method for calculating the partition mesh. Mesh element size = the size of the mesh set for each area **Data file: S3_sensitivity_analyses** In our sensitivity analysis of computational domain size, we began with computational domain measuring 130 mm long and 50 mm wide, and then repeated simulations for 5 different computational domains with progressively larger sizes. The results were considered independent of the domain size when the drag forces for a domain were less than 1% different from the next smallest domain. Based on this, we selected a domain measuring 208 mm long and 60 mm wide for use in all subsequent analyses. Length = the length of the cylinder as fluid domain Diameter = the diameter of the cylinder as fluid domain Drag forces = the drag forces of the original model Number of mesh elements = the number of mesh elements obtained by the same meshing method across various computational domains