Extensive exposures, mass-occurrences of various fossils, largely unmetamorphosed sediments, and uniquely preserved fossil structures such as mud mounds (WENDT 1993) account for the increasing interest of palaeontologists in the Devonian sedimentary successions of Morocco, especially of the eastern Anti-Atlas. CLARIOND (1934a, b) and ROCH (1934) are considered to be the pioneers of geological research in the eastern Anti-Atlas. In the subsequent decades, TERMIER & TERMIER (1950) and PETTER (1955, 1959, 1960) devoted their efforts to the palaeontology of the Devonian rocks of Morocco. PETTER's monographs (1959, 1960) directed the attention of numerous workers on the Devonian stratigraphy of the Tafilalt. Since then, an increasing amount of publications dealt with this topic (e.g. MASSA et al. 1965; HOLLARD 1967, 1974, 1981; ALBERTI 1980, 1981, 1982; BULTYNCK & HOLLARD 1980; BULTYNCK 1985; BECKER & HOUSE 1991, 1994, 1999, 2000a, 2000b, WALLISER et al. 1995, BELKA et al. 1997, 1999; KLUG & KORN 1999; KORN 1999; KORN et al. 2000; KLUG et al. 2000; KLUG 2001a).
Among the very many ammonoid-bearing localities in the eastern Anti-Atlas, the Ouidane Chebbi section, located 44 km east of Erfoud and 30 km east of the Derkaoua oasis (Fig. 1), is one of the most suitable sections for studying Emsian fossils within a stratigraphical context (KLUG 1998; BELKA et al. 1999). Besides Ouidane Chebbi, only few localities such as Achguig (BULTYNCK & WALLISER 1999), Bou Tchrafine (BECKER & HOUSE 1994, 1999), and Ras El Kebbar have yielded early Emsian ammonoid faunas with a comparably high diversity and abundance (Fig. 2).
Considering late Emsian to Eifelian ammonoids, the Jebel Ouaoufilal section (MASSA 1965; HOLLARD 1974; KLUG et al. 2000) yielded the best preserved ammonoid faunas of late Emsian and Eifelian age. In contrast to most other localities with time equivalent sediments age, the ammonoid associations are diverse and well preserved. Unfortunately, the Jebel Ouaoufilal sections display sedimentary features indicating condensation, hiatuses, and rare traces of cyanobacterial growth (compare WENDT et al. 1984, WENDT 1988). Additionally, several localities such as Bou Tchrafine, Hamar Laghdad (MASSA 1965; HOLLARD 1974; BULTYNCK & HOLLARD 1980; BENSAÏD et al. 1985; BECKER & HOUSE 1994, 1999), Gara Mdouara, Jebel Amelane, Jebel Mech Irdane, El Kachla, Hassi Nebech, and Ras El Kebbar have yielded Emsian and Eifelian ammonoid faunas with a comparably high diversity and abundance (Fig. 1). Many of them were not published in detail before.
Late Emsian and Eifelian ammonoids attracted the attention of numerous ammonoid workers. Almost 100 years after the pioneering investigations of BARRANDE (1865), it was particularly ERBEN (1953, 1960, 1962, 1964, 1965, 1966) who contributed important details to the knowledge of morphology, origin, and phylogeny of the earliest ammonoids from France, Germany, Turkey, Australia, and the Czech Republic. In these articles, ERBEN developed the phylogenetic framework earlier introduced by SCHINDEWOLF (1929, 1932, 1933, 1935) who was a major successor of BARRANDE concerning taxonomy and phylogeny of the earliest ammonoids. Similarily, BUCH (1832), ROEMER (1843, 1850, 1866), SANDBERGER & SANDBERGER (1850-1856), HALL (1860), KAYSER (1879, 1884), WHIDBORNE (1890), HOLZAPFEL (1895), FLIEGEL (1896), CLARKE (1899a, b), FLOWER (1936, 1943), SWEET & MILLER (1956), HOLLARD (1960), BOGOSLOVSKY (1961, 1969), WALLISER (1962, 1965, 1988), HOUSE (1962, 1965, 1978), HOUSE & PEDDER (1963), SOUGY (1969), CHLUPÁC & TUREK (1977, 1983), RUAN (1978, 1981), BULTYNCK & HOLLARD (1980), HENN (1985), GÖDDERTZ (1987), MONTESINOS (1987a, 1987b, 1988, 1990, 1991), GARCIA-ALCALDE et al. (1988, 1990), BABIN (1989), and WISSNER & NORRIS (1991) worked on Late Emsian and Eifelian ammonoid faunas from regions such as the Urals (Russia), the Tafilalt (Morocco), Nevada (USA), Bohemia (Czech Republic), and Guangxi (China).
The vast amount of stratigraphical data lead to the idea to incorporate the late Emsian to Eifelian sections from the Tafilalt into a Graphic Correlation project. The method of Graphic Correlation was introduced by SHAW (1964) and was intended to be an approach towards a quantitative stratigraphy. For the application of this method, a huge data set comprising several sections with numerous coherent stratigraphical details is needed. BELKA et al. (1997) were the first to use this method on late Emsian to early Givetian conodonts from the eastern Anti-Atlas and created a Composite Standard for the study area (the "Anti-Atlas Regional Composite"). This stratigraphical segment contains a similar amount of ammonoid taxa in a comparable abundance and hence, it appeared to be interesting to examine the stratigraphical record of this fossil group from the Tafilalt with Graphic Correlation.
The excellent preservation and abundance of Early and Midlle Devonian ammonoids in the eastern Anti-Atlas yields the possibility to study their stratigraphy and taxonomy as well as their morphology and palaeoecology. If a structure or organism is not fully understood, it is often a good idea to study it in its most original or simplest form. Consequently, early ammonoids are useful objects to learn more about functional morphology, constructional morphology, palaeoecology, and evolutionary processes in ammonoids. In the course of this study, three aspects of ammonoid palaeobiology were highlighted:

1 - Life cycles of Emsian and Eifelian ammonoids; based on conch parameters.
2 - Construction and function of the occluded umbilicus in the Pinacitinae.
3 - Habitat of the two major groups of Emsian and Eifelian ammonoids: The suborders Agoniatitina and Anarcestina.

The aims of this study are
(1) to describe and figure the most important Emsian to Eifelian sections of the Tafilalt and their ammonoid content,
(2) to depict the ammonoid succession of the late Emsian and Eifelian stages based on a Graphic Correlation of 14 sections in the Tafilalt,
(3) to revise some of the stratigraphically important taxa of Emsian and Eifelian ammonoids,
(4) to give an overview of the ammonoids of this stratigraphical interval in Morocco,
(5) to portrait changes in the conch parameters during ontogeny of Emsian and Eifelian ammonoids with their palaeoecological implications,
(6) to compare the occluded umbilicus of the Pinacitinae with similar structures of other ammonoids as approach to a functional interpretation, and
(7) to find a palaeoecological interpretation for the alternating occurrences of agoniatitid and anarcestid dominated ammonoid assemblages in the Emsian and Eifelian of the eastern Anti-Atlas based on changes in conch parameters.