BULLETIN DE L’INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT VOOR NATUURWETENSCHAPPEN SCIENCES DE LA TERRE, 74: 97-103, 2004 AARDWETENSCHAPPEN, 74: 97-103, 2004 A pedunculate brachiopod population preserved in situ (Late Maastrichtian, NE Belgium) by John W.M. JAGT & Eric SIMON Jagt, J.W.M. & Simon, E., 2004. - A pedunculate brachiopod popula tion preserved in situ (Late Maastrichtian, NE Belgium). Bulletin de l'Institut royal des Sciences naturelles de Belgique, Sciences de la Terre, 74: 97-103, 2 pis., 2 figs., Bruxelles-Brussel, March 31, 2004. - ISSN 0374-6291. Abstract The in situ preservation of a population of the pedunculate micro- morphic brachiopod Aemula inusitata S teinich , 1968 is highly excep tional. The substrate is a test of a holasteroid echinoid (Echinocorys gr. conoidea) from the Lixhe 1 Member (Gulpen Formation, Upper Maas trichtian) of Haccourt (Liège, NE Belgium), on which Aemula is associated with various adnate molluscan and bryozoan species. The palaeoecology of this population of Aemula inusitata is discussed. Key-words: Aemula, brachiopod, Cretaceous, Maastrichtian, epifauna. Résumé La découverte in situ d’une population de brachiopodes pédicellés de l’espèce Aemula inusitata S teinich , 1968 est un événement exception nel. Le substrat est un test d’échinide holastéroide (Echinocorys gr. conoidea) récolté dans la Craie de Lixhe 1 (Formation de Gulpen, Maastrichtien Supérieur) sur lequel Aemula est associé à une épifaune comprenant diverses espèces de mollusques et de bryozoaires. La paléoécologie de cette population d 'Aemula inusitata est discutée. Mots-clefs: Aemula, brachiopode, Crétacé, Maastrichtien, épifaune. Introduction In situ preservation of pedunculate brachiopods is in variably rare in the fossil record. So far, only one example has been recorded from the Maastrichtian white chalk facies by S urlyk (1974), who described and illustrated four specimens of the platidiid Aemula sp. attached in living position to the test of an irregular echinoid (Echi nocorys sp.) from the Maastrichtian white chalk of Hem moor (northern Germany). Thus, the present material from Haccourt, which comprises an in situ population of eighteen individuals of Aemula inusitata, S teinich , 1968, is of particular note. The echinoid preserving the brachiopod population is housed in the collections of the Natuurhistorisch Museum Maastricht, under number NHMM GM 769 (G. Michels Colin). Description and discussion The echinoid test (PI. 1, Fig. la-d), which measures 67.9 mm in height, 80.4 mm in length and 72.0 mm in width, is a typical representative of the group of Echinocorys co noidea (G oldfuss , 1829). As pointed out by J agt (2000, p. 270, pi. 20, figs. 6, 7), there are two specimens (regis tration numbers 343a, b) in the G oldfuss type collection (Rheinische Friedrich-Wilhelms-Universität, Bonn). One is an internal flint mould; the other preserves the test and shows ‘typical’ Lixhe Member preservation. Character istic of this form is the tali profile and comparatively coarse adapical tuberculation; it is this morphology that is common in the Lixhe 1 Member (Gulpen Formation) in the Haccourt/Lixhe and Maastricht areas. It may possibly extend downwards into the Vijlen Member (Interval 6) and upwards into the Lixhe 2 Member. The test shows a rich epifauna including, in addition to the brachiopods, several specimens of the bivalve Atreta nilssoni ( von FIagenow , 1842), two of Pycnodonte vesicularis (L amarck , 1806) and a few cheilostome bryozoans. The occurrence of these adnate molluscs and bryozoans is not surprising, since almost all echinoid tests from the Lixhe 1 Member reveal such cementing species. However, the in situ pre servation of a relatively large population of Aemula re presentatives is highly unusual. This small brachiopod is often found as loose shells when bulk samples of chalk are processed (S urlyk , 1970,1972,1982; J ohansen , 1987; S imon , 1998; see also Zirr et al., 2002). A few loose specimens of A. inusitata from the white chalk facies of the Lixhe 1 Member in the Haccourt-Lixhe area are represented in the J.W.M. Jagt Collection (NHMM). The fact that the present specimens are preserved in situ on a test of Echinocorys is probably due to rapid burial, resulting from biotic or abiotic processes. Following burial, the echinoid must have remained undisturbed by burrowing animals for a prolonged period of time. The specimens of A. inusitata studied fit the diagnosis given by S teinich (1968, pp. 193, 194). The shell is