Hebertella is a common fossil in many Upper Ordovician rock units, but it is similar in appearance to several other brachiopods in Kentucky. Similarities are most striking when the brachiopods are worn or broken, or remain partly in matrix where parts of valves are concealed. Each of these brachiopods have distinctly different muscle fields on the interior of their valves, but most collected fossils are whole shells and the interiors are not exposed.The following descriptions are based on descriptions in the brachiopod treatises (Williams and Wright, 1965; Williams and Harper, 2000) and research papers by Wright and Stigall (2013, 2014).

  • Glyptorthis insculpta. This brachiopod species was historically placed back-and-forth between Glyptorthis and Hebertella (H. insculpta), so not surprisingly is similar in appearance. Glyptorthis is found in the Drakes Formation. It has a similar outline, shape, and ribbing (costae and costellae) as Hebertella. However, it has common concentric growth lines on its exterior, and has different shaped muscle scars on the interior ventral valves. The interior surface of Glyptorthis valves also commonly exhibit worm-like or vein-like impressions of the original mantle canals.
  • Plaesiomys subquaratus. Plaesiomys is found in the Drakes Formation. It has a large convex dorsal valve like Hebertella, but has a slightly more rounded outline (less subquadrate), wider costae, and a less well-developed fold and sulcus than the two species of Hebertella found in the Drakes Formation.
  • Retrorsirostra carleyi. This brachiopod was once considered a subspecies of Plaesiomys (e.g., Plaesiomys (retrosirostra) carleyi in the old brachiopod treatise, Williams and Wright, 1965), so not surprisingly is similar in appearance to Plaesiomys. A distinguishing feature is the shape of the interarea along the hingeline. In R. carleyi, the ventral interarea projects straight down from the hingeline or dips slightly anterior (forward), which is called procline, while in Plaesiomys the ventral interarea leans posteriorly (toward the rear), termed apscaline. You can see the difference in a profile view of the brachiopods.
  • Plectorthis plicatella. Small (juvenile, immature) Hebertella may be indistinguishable from Plectorthis (Walker, 1982). Plectorthis is found in the Point Pleasant tongue of the Clays Ferry Formation through Bull Fork Formation. It is most similar to H. frankfortensis, which is a smaller, rounded species of Hebertella. Both brachiopods can be found in the Clays Ferry Formation, but H. frankfortensis is rare in that unit.
  • Hebertella is also similar in appearance to the brachiopods Doleroides and Mimella, but these have not been reported in Ordovician rocks in Kentucky.
General comparison of several similar orthid brachiopods in Upper Ordovician strata of Kentucky.

 

 

 

 

 

 

Last Modified on 2019-02-25
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