Copper and Jin—Ordovidian–Silurian brachiopod evolution, extinction, and recovery


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Figure 9. Serial sections and reconstruction of Koigia sp. Specimen GSC 131800 from a coastal bluff section on the east side of the cove at Ruisseau aux Algues (loc. A314), Fox Point Member (basal 3 m), Becscie Formation. Note the lack of skeletal connection between the crura and jugal blades. Number below each serial section denotes distance (mm) from shell apex.


Occurrence.—Aeronian to Telychian, ?Wenlock.


Remarks.—When proposing the genus Hyattella, Hall and Clarke (1893) compared Athyris junia Billings, 1866 with the type species H. congesta. Schuchert (1913, p. 415) renamed the genus Hyattidina because the name Hyattella was pre-occupied. The shells of Hyattidina show considerable variability,


ranging from almost smooth and round to those with an angular fold and sulcus. The brachidia, however, are quite consistently developed, with a simple jugum and laterally directed spiralia. The reconstruction of the jugum and spiralium by Hall and Clarke (1894, pl. 40, fig. 26), based on a silicified shell from “Reynale’s Basin, New York”, is essentially correct, but missed the sharp angle and juxtaposition of the crura and umbonal blades (which are shown as a straight connection). Our material, presented herein, is very similar in shape and size to the type Hyattidina congesta from the “Clinton... Lockport, New York” as figured by Hall and Clarke (pl. 40, fig. 26). Alvarez and Rong (2002, p. H1556) selected a neotype from the Hall collection, which has a more prominent fold-sulcus


than seen commonly in the Anticosti specimens, which are flatter, with a weaker fold. Hall and Clarke (1893, p. 61; 1894, p. 767) illustrated the type species H. congesta with a simple jugum (referred to as a “loop top”), similar to that of the Anticosti species. Alvarez and Rong (2002) described Hyattidina, and its


subfamily, as lacking a median septum and a jugal saddle, and having a shell with numerous growth lines and thin dental


plates. Based on the new data from this study, these criteria should be emended to describe a smooth shell (without prominent growth lines), a distinct septum, relatively thick dental plates, and a jugal saddle. The information on the shape and configuration of umbonal blades, crura, jugum and spiralia, as presented in this study, is also new. Alvarez and Rong (2002, p. H1556) used the “numerous growth lines” to assign the genus to the superfamily Athyridoidea. Our data makes such assign- ment doubtful. Alvarez and Rong (2002) also allocated a Ludlow age to the genus, but the type and most other species of the genus are Telychian in age, thus much older. On Anticosti, the lowermost occurrence of the genus, which is often abundant, and shell-bed forming, or packed in large nests, is in the Macgilvray Member of the upper Gun River Formation (mid- Aeronian; Copper et al., 2013). It retains this abundance into to the Ferrum Member of the Jupiter Fornation (early middle Telychian; for example, see Hyattidina cf. junia, below), becoming rare in the Pavillon Member (mid-Telychian). In the richly fossiliferous Anticosti succession with abundant athyr- ides, Hyattidina is absent from the upper Katian through lower Aeronian strata. Internally, the brachidia of Anticosti Hyattidina are


quite similar to those of Hindella in the jugum and short crura, but differ from Koigia, which has a simpler, rounded jugum, and fewer spiral whorls. Thus there is little to distinguish the brachidia in the hyattidines and hindellines, and we thus place them in the same family Hindellidae. Hyattidina and Koigia have much less ventral apical prismatic callus than either Hindella or Cryptothyrella,


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