''Sarotrocercus'' is a small

Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ag ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

known from

Burgess shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

, reaching a centimetre or two in length (). ''Sarotrocercus'' is only known from 7 specimens. It may lie in the arthropod crown group, and a recent study has revised some points of its original description.

Morphology

''Sarotrocercus'' had a head shield followed by a trunk of 10 or 11 segments and a

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

featuring a series of spines on the end. A pair of big eyes at the end of stalks ventrally emerged from the front of the head. The head bore two pairs of sturdy appendages that are armed with rows of inner spines. At least the anterior 9 trunk segments each possess a pair of appendages, which are only known by lobe-like exopods that are fringed with setae.

Ecology

In the original description, ''Sarotrocercus'' had been interpreted as a

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

nektonic Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms t ...

animal that swam freely on its back, moving perhaps through movements of the trunk appendages and the action of its long tail tuft. This was mainly based on the rarity of the specimens, as the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

contains few swimming organisms; the submarine landslides that buried organisms mainly smothered benthic and nektobenthic organisms. However, based on the redescription by Haug et al. 2011, ''Sarotrocercus'' may had been

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

or at least swimming close to the seafloor, as the robust head appendages rather suggest a grasping or raking function.

External links

References

{{Taxonbar, from=Q3017283 Cambrian arthropods Burgess Shale fossils Monotypic arthropod genera