Glottidia dumortieri ( Nyst, 1843 )

Glottidia dumortieri ( Nyst, 1843)

( Figs 6–14)

Material – Beugen: 3571 specimens (63–64 m: 520; 64–65 m: 2041; 65–66 m: 905; 72–73 m: 25; 73–74 m: 10; 75–76 m: 30; 76–79 m: 40).

Size (mm) –

Length 13.8 10.2 5.8 10.0 9.4 7.8 3.9 9.9 10.1 11.4

Width 6.5 5.4 3.0 4.5 4.8 3.3 1.9 4.6 4.6 5.2

Notes – G. dumortieri was originally described as Lingula from the Pliocene of Belgium by NYST (1843), and later several authors used this generic assumption (e.g. WOOD 1872; DAVIDSON 1874; VINCENT 1893; BARCZYK & POPIEL-BARCZYK 1977). However, CHUANG (1964) recognised that this species should be assigned to the genus Glottidia . Glottidia differs from Lingula mainly in the

possession of two divergent internal septa in the pedicle valve and a single centrally placed septum in the brachial valve. CHUANG (1964) illustrated only some specimens available for him with poor quality drawings. The high quality SEM photos of NBC material ( Figs 6–10) confirm that Miocene lingulides of the North Sea Basin belong to genus Glottidia . Although Lingula sp. was mentioned several times even recently in the literature, the only confirmed lingulide brachiopod is Glottidia from this area.

Although this species is abundant in some NBC samples, the taphonomic potential of lingulides is very low. Their thin and fragile shells disappear from the sediment within 2–3 weeks in recent environments ( EMIG 1990). Most of the studied specimens are also rather fragmentary, but some samples contain also well-preserved, sometimes even double valved Glottidia . This preservation refers to autochthonous fossilisation without significant transportation. In Beugen drill-hole samples these are the dominant fossils. Drilling predation is insignificant on the Glottidia specimens living burrowed in the sediment (1 out of 2041 specimens in Beugen, 64–65 m sample, and 1 out of 905 specimens in Beugen, 65–66 m sample).

Geochemical composition of Dutch Miocene Glottidia (Beugen and Delden drill holes) was discussed by KOCSIS et al. (2012). The Ε Nd data of the lindulide samples support an inflow of Atlantic Ocean water to the North Sea. The North Sea Glottidia population has average δ 18 O PO4 values that are 2–2.5% higher than those in the Paratethys, suggestive of colder and constant habitat temperatures for the Mio-Pliocene brachiopods of the North Sea Basin ( KOCSIS et al. 2012).

Glottidia ? sp.

Material – Delden (2 fragments).

Notes – Some samples from the North Sea Basin yielded indeterminable Lingulidae fragments. They are too small to show specific characters; therefore it is impossible to decide whether they belong to Lingula or Glottidia . Glottidia with question mark is used to indicate these specimens, because until now only Glottidia was surely confirmed from the Neogene of the North Sea Basin.