Macrofossils: Trilobites and echinoderms Flashcards
When did the trilobite arthropods go extinct?
P-T extinction
What mode of life did trilobites have?
Mobile benthic
What are trilobites fossils useful for?
Study of evolution, dating rocks, marine deposition, zonal index fossil for lower Palaeozoic
What is the average number of thoracic segments for trilobites?
13
What is the glabella of a trilobite?
Raised median part of the cephalon, variable in size in structure. Probably had the stomach underneath it.
What habitats do echinoderms have?
Exclusively marine
Describe the evolution of symmetry in echinoderms?
Originally were bilateral, went through stages of asymmetry and briradial symmetry, now mostly have pentameral symmetry.
Give five examples of extant echinoderms
Sea lilies, starfish, brittle stars, sea cucumbers, sea urchins
How do echinoderms move and what powers it?
Move by tube feet that are powered by water being forced around the body
What is the stereom of the echinoderms?
A mesh, mostly magnesium, making up the skeleton
Are echinoderms proterostomes or deuterostomes?
Deuterstomes
What are the two categories of crinoids?
Stalked (sea lilies) and unstalked (feather stars)
How are crinoids attached to the substrate?
A segmented stalk
Define calyx, relating to crinoids
Cup-shaped plated body of crinoids that make up rows of calcite plates
Define echinoids
Free-living echinoderms with a body enclosed in a globular shell of calcareous plates (either cushion, discoidal, or heart-shaped) that bears moveable appendages.
