Serracaris
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| Serracaris Temporal range: | |
|---|---|
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| The holotype of Serracaris, a fragmentary fossil | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | incertae sedis |
| Genus: | †Serracaris Briggs, 1978 |
| Species: | †S. lineata |
| Binomial name | |
| †Serracaris lineata (Resser and Howell, 1938)[1] | |
| Synonyms | |
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Serracaris is a genus of enigmatic arthropod from the Kinzers Formation of Pennsylvania. It contains one species, Serracaris lineata. This genus was formerly classed within Anomalocaris, however once it was realised Serracaris was in fact the trunk of an arthropod it was reassigned.[1]
The generic name derives from serra (“saw”) in reference to the serrated edges of its body, and caris (“shrimp”), a common suffix for prehistoric arthropod names. The specific name lineata likely derives from the straighter nature of the fossil compared to other Anomalocaris appendages.[2]
Serracaris is only known from the trunk, and even though a front margin is preserved in one specimen this is likely not a cephalon (furthermore, the region’s details are obscured by a dark stain). The exoskeleton is composed of smooth, flat sub-rectangular (rectangular with rounded edges) tergites, with gently anteriorly curved boundaries between them. The lateral margins of each extend into two long pointed backwards-curving paratergal folds, each overlapping with the other on their tergite. While exact dorsoventral (up/down) position is unclear, the backwards fold was likely under the forwards one. These folds are connected to the main tergite by a ridge, with an asymmetrical specimen suggesting they may have been able to articulate (move) along the dorsoventral axis. One much longer tergite bears especially large paratergal folds, reaching the length of around two tergites. Towards the (unpreserved) head, the segments seem to have become shorter except for this one specifically, with 12 before and at least 3 after it with a total number over around 15 segments. A specimen which is poorly preserved suggests even more, with at least 22 segments along its whole body. The telson is long, lacks an axial (middle) region and bears two long spines at its side. Unlike the folds, these spines seem to not have articulated, being separated along the midline by a small round structure with a convex tip (which may have contained the anus). The telson also seems to have had a series of small projections on its anterior edge. The exact size range of Serracaris is uncertain due to its fragmentary nature, as although the most complete specimen measures around 9 cm in its preserved portion its telson is only half the size of a different, isolated specimen.[1]