Fossil Record
The earliest trilobites known from the fossil record are fallotaspids (order Redlichiida, suborder Olenellina, superfamily Fallotaspidoidea) and bigotinids (order Ptychopariida, superfamily Ellipsocephaloidea) dated to some 540 to 520 million years ago. Contenders for the earliest trilobites include Profallotaspis jakutensis (Siberia), Fritzaspis sp. (western USA), Hupetina antiqua (Morocco) and Serrania gordaensis (Spain). All trilobites are thought to have originated in present day Siberia, with subsequent distribution and radiation from this location.
Fallotaspids lack facial sutures, that is to say fallotaspids are thought to pre-date facial sutures (as opposed to a group that secondarily lost facial sutures). Fallotaspids are strongly suggested to be the ancestral trilobite stock: absence of facial sutures; apparently un-calcified protaspid stages and fallotaspids underlying (pre-dating) or co-existing with all other trilobite occurrences. However, recent developments suggest the picture is more complicated, and likely to change as more information comes to light.
Read more about this topic: Trilobite
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