Medernach Triassic

Woutersia mirabilis (4, 10)

Sigogneau-Russell and Hahn, 1994). This unit spans the Upper Triassic, but mammalian fossils are restricted to its upper part. Thus far, specimens consist only of isolated teeth or parts thereof. Given the great antiquity of these remains, the affinities of the taxa they represent are sometimes debatable. Tricuspes, for example, occurs at several sites in the Keuper. It may be a mammal (Clemens, 1980a, 1986), but is more generally considered a cynodont (Godefroit and Sigogneau-Russell, 1995), and so we have omitted it from our listing here, but for the sake of documentation we discuss it in chapter 4. The geologically oldest site yielding an uncontested mammal from the Keuper is of Norian age and is near Halberstadt, Germany. The haramiyid Thomasia hahni is found here. Haramiyids are enigmatic mammals that may be related to multi-tuberculates, although there is not universal agreement on this point (chapter 8). They are common members of Late Triassic mammalian faunas and, if related to multituber-culates, were separated from that group by a considerable hiatus.

A cluster of sites in the upper Keuper occurs in Württemberg (Baden-Württemberg), southern Germany. These

Ocean Routes The World

figure 2.2. Late Triassic, continental Europe (all in the upper Keuper; Late Triassic). Localities or local faunas: 1, Halberstadt, Germany; 2, Württemberg, Germany; 3, Hallau, Switzerland; 4, Syren, Luxembourg; 5, Medernach, Luxembourg; 6, Attert, Belgium; 7, Hachy (Sagnette), Belgium; 8, Habay-la-Vieille (Gaume), Belgium; 9, Varangeville, France; 10, Saint Nicolas-de-Port, France.

are younger, possibly later Rhaetian in age. The fossils, which include a mixture of terrestrial and marine taxa, are commonly abraded and show signs of transportation (Sigogneau-Russell and Hahn, 1994). A mammal tooth— again belonging to the haramiyid Thomasia—was discovered near Stuttgart (in Degerloch, then a neighboring village) as early as 1847. Additional sites in the area, Olgahain and Gaisbrunnen, were worked by Friedrich von Huene and Otto Schindewolf in the first half of the twentieth century. To date, the haramiyid Thomasia (perhaps represented by two species) is the only generally accepted mammal from the Württemberg sites.

A larger, better represented assemblage of mammals is known from Hallau, Switzerland, just south of the German border. Like the Württemberg sites, it may be later Rhaetian in age (Clemens, 1986). Though Hallau was discovered in the 1870s, it was not worked extensively until Bernhard Peyer began screenwashing sediments from the site in the 1940s, work he was to continue into the 1960s. In 1956, he published a monograph on the materials collected to that date (Peyer, 1956). His collection, housed in Zürich, was restudied by William A. Clemens, who also reviewed the German collections from the Keuper (Clemens, 1980a). In addition to the haramiyid Thomasia, several "triconodonts" are known from Hallau. The mor-ganucodontid Morganucodon is represented by an endemic species, M. peyeri. Morganucodon is the best known of Late Triassic-Early Jurassic mammals, being represented elsewhere by relatively complete specimens and large series of jaws and isolated teeth (chapter 4). It is also broadly distributed, being known from the Keuper, the fissure fills of Britain, China, Greenland, and (perhaps) North America. Clemens (1980a) described two other taxa from Hallau, Helvetiodon schutzi and Hallautherium schalchi, that are also considered to be morganucodontans (Hahn et al., 1991).

In the past two decades, numerous microvertebrate sites have been worked in the Keuper ofBelgium and Luxembourg, largely owing to the efforts of Georges Wouters, Jean-Claude Lepage, and Dominique Delsate. To date five of these sites have yielded mammals. An unidentified morganucodontid has been reported from Medernach, Luxembourg (Cuny et al., 1995; Godefroit and Sigogneau-Russell, 1995). The site is probably of Norian age. The locality of Syren, Luxembourg, is assigned a Rhaetian age based on palynomorphs (Godefroit et al., 1998). The vertebrate fauna includes three mammals: a haramiyid (Thomasia antiqua), an unidentified morganucodontid, and an apparently new species of Kuehneotherium (see Godefroit et al., 1998). From the Lorraine region of Belgium, two other sites include single records of Rhaetian mammals: Attert, from which the haramiyid Thomasia woutersi is known, and Hachy (Sagnette), which has yielded a single, unidentified mammal tooth (Sigogneau-Russell and Hahn, 1994). Two species of Thomasia have also been reported from the nearby site of Habay-la-Vieille (Gaume), Belgium. The most extraordinary occurrence at this site is that of Mojo usuratus. Represented by a worn, incomplete tooth, this species has been referred to the multituberculate family Paulchoffatiidae (Hahn, 1987a; Hahn et al., 1989). This occurrence, if verified, would represent a colossal range extension for the family, which otherwise appears in the Late Jurassic. If multi-tuberculates, haramiyids, and theroteinids form a mono-phyletic group (chapter 8), this occurrence implies a remarkably early divergence of these lineages.

Other fossils from the Keuper sites in Belgium and Luxembourg further illustrate the difficulties of identifying early mammals based on tooth structure, as mentioned previously in connection with Tricuspes. Chiniquodon-toid cynodonts have a "triconodont" cusp pattern and, in some instances, divided tooth roots. Small (mouse-sized) chiniquodontoids from the Keuper include Pseudotricon-odon, Gaumia, Lepagia, and Meurthodon (see discussion in Sigogneau-Russell and Hahn, 1994). Pseudotriconodon is known from Medernach and from the Late Triassic of New Mexico (Lucas and Oakes, 1988), and may be similar to Microconodon and Dromatherium from North America (Hahn et al., 1984; Godefroit and Sigogneau-Russell, 1995; Sues, 2001). Mammalian affinities for the last two genera (both known from the Triassic Cunmock Formation of North Carolina, with Microconodon possibly present in the Dockum Group of Texas) have been variously debated (Osborn, 1887b; Simpson, 1926d; Clemens et al., 1979). Based on their probable therapsid affinities, we omit them from further discussion.

The final sites in the Keuper yielding mammalian fossils are in the Lorraine region of France. Saint-Nicolas-de-Port is the best represented of the two. The age of the site is uncertain, but it is probably at least as old as early Rhaetian (Sigogneau-Russell, 1983). An earlier, Norian age was advocated by Buffetaut and Wouters (1986) on the basis of similarity of the herpetofauna to that of Halberstadt (uppermost middle Keuper, discussed earlier), but the biostratigraphic constraints are imprecise (Hahn et al., 1989). Fossils occur in a conglomeratic layer at the base of the local section, interpreted to have been deposited in a nearshore tidal environment. The locality has been known since 1851. Large-scale fossil recovery, using underwater screenwashing techniques, was begun in 1976 by Denise Sigogneau-Russell and Donald E. Russell after the discovery of a mammal-like tooth the previous year by G. Wouters. Shortly thereafter, Clemens et al. (1979: 11) pre-sciently observed, "The locality could easily become the most prolific source of Rhaetian mammalian fossils in continental Europe." Saint-Nicolas-de-Port has fully lived up to this expectation: thus far, it has yielded more than 1,000 mammal teeth, more than three times the rest of the Keuper sites combined. The haramiyid teeth (Sigogneau-Russell, 1989b, 1990), representing two species, were later reviewed by Butler and MacIntyre (1994) in connection with a study of British haramiyids. The sample is sufficiently large (more than 200 specimens) to permit recognition of two types—those previously referred to Thomasia and Haramiya—as lower and upper teeth of the same animal (Sigogneau-Russell, 1989b), thereby solving a long-standing enigma and permitting revision of the group. Variations among teeth in the sample have tentatively been ascribed to positional differences; wear patterns also suggest a multituberculate mode of chewing (see Butler, 2000, and chapter 8).

Another notable occurrence at Saint-Nicolas-de-Port is represented by the Theroteinidae (Sigogneau-Russell et al., 1986), known by Theroteinus nikolai and Theroteinus sp. Teeth of these mammals bear some similarity to certain multituberculates (Paulchoffatiidae) and to haramiyids, but are distinct enough that Hahn et al. (1989) created a separate order for them, Theroteinida, placed with these other groups in the Allotheria (see also Butler and MacIntyre, 1994; Butler, 2000, and discussion in chapter 8).

The most abundant morganucodontan at Saint-Nicolas-de-Port is the widely distributed Morganucodon (Hahn et al., 1991). An undescribed taxon (Sigogneau-Russell and Hahn, 1994) and Brachyzostrodon, represented by two named species and perhaps as many as two others (Sigogneau-Russell, 1983b; Hahn et al., 1991), are also present. Brachyzostrodon is rather large, by morganu-codontan standards and is generally similar to South African Megazostrodon, though the two differ in occlusal pattern and presumed diet (Hahn et al., 1991).

Several "symmetrodontans" are known from Saint-Nicolas-de-Port. Kuehneotherium, first described from Late Triassic-Early Jurassic fissure fillings in Wales (see later), is represented by one or more species, based on a large and highly variable sample of isolated molars (see Sigogneau-Russell and Hahn, 1994; Godefroit and Sigogneau-Russell, 1999). Also present is the highly distinctive Woutersia with two species, W. mirabilis and W. butleri. Woutersia is broadly similar to Kuehneotherium, but is characterized by broad molars suggestive of some crushing function similar to that of the later docodontans (Sigogneau-Russell, 1983a; Sigogneau-Russell and Hahn, 1995). The final member of this diverse mammalian fauna is Delsatia rhupotopi, a possible docodontan (Sigogneau-Russell and Godefroit, 1997, see also chapter 5). Delsatia is based on molars that superficially resemble those of

Woutersia. Docodontans, which are characterized by precociously specialized molars (Jenkins, 1969b), otherwise make their first appearance in the Middle Jurassic (Wald-man and Savage, 1972; Kermack et al., 1987). Affinities of docodontans are problematic but, given that they retain many primitive features, the Docodonta may have diverged early in mammalian history (Lillegraven and Krusat, 1991; Sigogneau-Russell and Hahn, 1995). Thus, presence of some putative relatives of theirs in the Triassic may not be surprising.

The site of Varangeville is about 10 km southeast of Nancy and 4 km north of Saint-Nicolas-de-Port. Like the latter, fossils occur in a conglomerate, and the age of the horizon is not well understood. Lithostratigraphically, it corresponds to the base of the Rhaetian, which appears to be time transgressive (Godefroit, 1997). The mammalian fauna of Varangeville includes the haramiyid Thomasia antiqua, as many as three morganucodontids (including Morganucodon itself), and the "symmetrodontan" Wou-tersia mirabilis, all of which are known from Saint-Nicolas-de-Port. The most notable occurrence is that of the basal mammal group Sinoconodontidae (represented by a form similar to Sinoconodon), otherwise known from the Early Jurassic of China (Godefroit, 1997).

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