Dormice (Rodentia, Gliridae) from the Middle Miocene of Hambach 6C, Northwest Germany q

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Introduction
The Gliridae (dormice) are a monophyletic family of rodents that originated in Europe and began to diversify since the early Eocene (MP 10; Daams & Bruijn, 1995).Glirids continued to evolve throughout the Oligocene and reached their maximum specific diversity during the onset of the Mid-Miocene Climate Optimum (MCO; Steinthorsdottir et al., 2021) in the late Early Miocene (MN 3/4).At that time, many ecological niches were occupied by glirids, which constantly dominated European rodent faunas.Glirid diversity and specimen abundance declined significantly after the MCO in the late Middle Miocene; today living Gliridae are only represented by eight genera inhabiting Eurasia and Africa (Daams and Bruijn, 1995;Freudenthal and Martín-Suárez, 2013).
During peak diversity in the Miocene, numerous glirid faunas, as well as specimens, were discovered in Spain, France, Central Europe (mainly Germany, Austria, Switzerland), and in several localities in southeastern and eastern Europe.Fissure fillings and molasse deposits (Upper Freshwater Molasse) of southern Germany have yielded the most extensive glirid material that contributes to the understanding of their systematic evolution, biostratigraphy as well as paleoecology (Mayr, 1979;Fahlbusch and Wu, 1981;Ziegler and Fahlbusch, 1986;Wu, 1990Wu, , 1993;;Schötz, 2002).In northwestern Germany, except for the Early Miocene Echzell fauna which is dominated by small mammals and diversified glirid taxa (Jovells-Vaqué and Mörs, 2023;Vasilyan et al., 2022), Hambach 6C is a significant Middle Miocene locality not only for its rich vertebrate remains but also for its geographical uniqueness as the northwestern-most outpost of terrestrial Miocene faunas in Europe (Mörs et al., 2000;Mörs, 2002;Mörs and Kalthoff, 2004).
The Hambach opencast lignite mine is situated in northwestern Germany, ca.35 km west of Cologne.Geologically, it is located east of the Rurrand fault on the Erft tectonic block within the Lower Rhine Embayment (Fig. 1).Due to the exploitation of the lignitic brown coal, the exposed Neogene thick strata are characterized by the intercalation of coastal sands from a marine transgression (North Sea) and terrestrial sediments (Schäfer et al., 2004).Of the Miocene Ville Series, the channel filling (and floodplain) within the Frimmersdorf seam is correlated to horizon 6C in the local lithostratigraphy, and yielded a rich vertebrate fauna including marine and freshwater fish, amphibians, reptiles, and over 70 mammal species, whereas the Main Coal Seam is devoid of any bones or teeth that were dissolved by the acidic groundwater (Mörs et al., 2000;Mörs, 2002).The mammal assemblage consists of didelphids, insectivores, rodents, and large mammals such as primates, carnivores, artiodactyls, cetaceans, perissodactyls, and proboscideans; small mammals, especially rodents are predominant with 30 species represented by sciurids, petauristids, glirids, eomyids, cricetids, castorids and lagomorphs (Ziegler and Mörs, 2000;Rössner and Mörs, 2001;Nemetschek and Mörs, 2003;Mörs, 2006Mörs, , 2008;;Stefen and Mörs, 2008;Mörs and Stefen, 2010).Based on the rich association of mammalian taxa, the Hambach 6C fauna is correlated with the upper part of MN 5 (Mammalian Neogene biozone), and indicates the early Middle Miocene with a numerical age of 15.2-16 Ma (Mörs et al., 2000), fitting within the MCO expressed by warm, humid climate and high diversity of mammals (Steinthorsdottir et al., 2021).

Material and methods
The described material here includes 44 complete isolated teeth housed at the Steinmann Institute of the Rheinische Friedrich-Wil helms-Universität Bonn, Germany.All specimens were obtained by screen-washing with a sieve width of 0.5 mm.Measurements and photographs were taken using the SZX2-ILLT microscope with a 5Â magnification.Dental terminology follows Daams (1999) and Freudenthal (2004) (Fig. 2).

Systematic palaeontology
Order Rodentia Bowdich, 1821Family Gliridae Muirhead, 1819Genus Glirudinus Bruijn, 1966 Glirudinus undosus Mayr, 1979 Figs.3(A-D Description: m1.The lower molar is double-rooted; the outline of the tooth crown is subrectangular with rounded corners; the anterior part is slightly narrower than the posterior portion; the occlusal surface is slightly concave.There is a total of five main ridges and eight extra ridges; all lophids but anterolophid and posterolophid are inclined forward, making an appropriate angle with the longitudinal axis of the tooth.Main lophids are stronger than extra ridges, and thicken at labial ends; both anterolophid and posterolophid are straight, and connect with the endolophid; metalophid is long, and widens towards the labial side; both centrolophid and mesolophid are well-developed.Between the anterolophid and metalophid, there are three extra ridges of which the middle anterotropid is the longest, almost the same length as centrolophid, and links with anterolophid at the labial edge; two shorter extra ridges on each side of the anterotropid are free.The metatropid and mesotropid are present on both sides of the centrolophid, about half the width of the tooth crown.There is a labial connection between the posterolophid and posterotropid, which is isolated from the endolophid; on its both sides are two weak, tiny extra ridges in the middle part of the posterior valley.All the main ridges, except the metalophid, are connected to the endolophid lingually; at the labial side, metalophid, centrolophid and mesolophid have isolated ends.Due to the development of main and extra ridges, the valleys become extremely narrow. m2.The crown has a rounded rectangular outline and the anterior part is relatively wider for it narrows backward.The chewing surface is nearly flat; only the anterolingual edge is slightly elevated.The dental pattern of the tooth is similar to that of m1 regarding the number and distribution of ridges; the anterolophid is connected with the long anterotropid at labial ends, isolated from the metalophid.Except the metalophid, other main ridges   Daams and Bruijn, 1995;Freudenthal, 2004).A. Upper molar.B. Lower molar.Mayr (1979), Aguilar (1980), Engesser et al. (1981), Baudelot and Collier (1982), Ziegler and Fahlbusch (1986), Wu (1990Wu ( , 1993)), Kälin and Engesser (2001), Hír and Mészáros (2002), Schötz (2002), Hír (2004), Aguilar and Lazzari (2006), and García-Alix et al. (2008).
Z. Li and T. Mörs Geobios 78 (2023) 15-31 are linked to the endolophid.Different from m1, the posterolophid is curved backward, not as straight as the anterolophid.No extra ridge is developed between the posterotropid and posterolophid.M2.The outline of the upper molar is subsquare with a larger width than length; the posterior outer corner is rounded, and posterior inner side develops a right angle.The tooth has three roots: the inner one is larger and has an elongated oval shape; two smaller roots are conically shaped at the labial side.The occlusal surface is concave along the longitudinal axis, and tends to elevate at the lingual and labial edges.It has six main ridges and seven extra ridges that separate the chewing surface into long, narrow, and equally spaced valleys.Anteroloph is nearly transverse, and joins endoloph; protoloph describes an arched curvature; precentroloph and postcentroloph are straight, of the same length and run obliquely backward, without complete contact with the endoloph.The metaloph is slightly curved posteriorly, almost parallel to the posteroloph.All additional ridges are distributed alternatively with the main ridges.The isolated anterotrope is slender, and more lingual.There are three extra ridges between protoloph and precentroloph; two smaller ridges, about half the width of the tooth, are restricted to the labial part; the prototrope, as strong as the main ridge, is the longest, but is isolated from endoloph; metatrope and the extra ridge between centrolophs are equally long, but the front one is free from labial margin; the posterotrope between metaloph and posteroloph is short on the labial side.All main ridges join the labial edge; endoloph is complete, connected with anteroloph, protoloph and posteroloph.
M3.The third molar is three-rooted with a rounded triangular outline; it is slightly concave in the middle area of the occlusal surface, and there is a weak bulging at the anterior labial edge.In addition to the six main ridges, there are five extra ridges.The anteroloph is perpendicular to the long axis of the tooth; no extra ridge is present in the anterior valley; protoloph curves forward.There are three extra ridges parallel to the protoloph, and the longest prototrope joins the lingual end of precentroloph before reaching endoloph.Both centrolophs are straight; postcentroloph as well as extra ridges on each side contact with the labial margin, but remain isolated lingually; no posterotrope is developed.Except for postcentroloph, other main ridges extend to the continuous endolph, which enclose the chewing surface with anteroloph, posteroloph, and labial edge.
Remarks: The Hambach 6C material has a slightly concave or flat occlusal surface; the presence of numerous extra ridges, and well-developed endolophid on lower molars allow the attribution to Glirudinus undosus.Compared with the German MN 4 localities Petersbuch 2 and Erkersthofen, their sizes are smaller; M2 does not develop an S-curved metaloph (one of the diagnostic characters), which is also less curved or even straight on some molars from above localities (Mayr, 1979;Wu, 1993).Besides, the outline of M2 from Hambach is more quadrate, and the anteroloph is connected to the endoloph, different from teeth from Erkersthofen and Petersbuch 2.
G. undosus occurs across central Europe, France, and Spain from the early to late Middle Miocene (MN 3-MN 7+8).It has similar dental morphology with Glirudinus gracilis and Glirudinus minutus with respect of the development of extra ridges.G. minutus is characterized by a smaller size (Wu, 1993); Mayr (1979) proposed that the lingual margin of G. gracilis was more frequently interrupted than G. undosus based on a statistical analysis of material from Bissingen, Erkersthofen, and Wintershof-West; metaloph on M1-2 of G. undosus is usually (inverted) S-shaped which may tend to be straight for G. gracilis.As discussed above, however, those features are variable, and tend to be subjective to assess.Considering the wide variation in size and morphology (Mayr, 1979;Wu, 1993), informally grouped the G. undosus, G. gracilis and G. minutus into an independent category represented by complicated dental pattern in contrast to other Glirudinus species with simple dental patterns; the three species primary differ in the size of the molars.
Description: M1.The upper molar is three-rooted with two smaller ones at the labial side, and the larger one at the lingual side is elongated anteroposteriorly.It shows a rounded subsquare outline for the tooth crown slightly widens backward; the occlusal surface is flat.There are five main ridges: anteroloph, protoloph, precentroloph, and posteroloph.The extra ridges are few, and only the extremely short prototrope is present at the labial edge, which forms wide valleys between lophs.The anteroloph extends backward from anterolabial side, isolated from paracone and protocone; protoloph is the longest ridge and connects with the endoloph.Of the centrolophs, precentroloph extends backward to the metaloph at the lingual part; the shorter posteroloph is restricted to the labial part of the tooth crown.The posteroloph is transverse, thinner than other main ridges, and has the same length as metaloph; both posterior lophs are connected labially at metacone.On the lingual side, protoloph, metaloph and posteroloph are connected to the endoloph.
m1.The lower molar has two roots in anterior and posterior positions separately.Its occlusal surface is flat; the outline of tooth crown is subrectangular due to the wider anterior part being rather long.There is a total of seven ridges that are almost parallel to each other except the slightly curved anterolophid and posterolophid.The extra ridges, anterotropid and posterotropid, are of the same length.The anterolophid is isolated from paracone, but contacts with metalophid at the labial edge.Both metalophid and mesolophid are of the same width; the posterolophid is fused with the posterotropid at both sides, making a closed loop.In contrast to other main ridges, the centrolophid is short, just limited to the lingual margin of the tooth crown.Except the last two lophids, all ridges are isolated at lingual edge, therefore, the endolophid is absent; anterolophid and metalophid, posterotropid and posterolophid are connected labially whereas the mesolophid and centrolophid are separated from the connection.
Remarks: The Hambach 6C material is characterized by the subquadrate outline of M1, isolated anteroloph, flat occlusal surface, and fewer ridges, which fit well with Muscardinus thaleri.Besides, Bruijn (1966) described an extra ridge between centrolophs in the material from Manchones (MN 6) in Spain, which is present at the labial margin of the Hambach 6C specimen as well, although both are tiny crests.The difference is that the two molars from Hambach 6C are distinctly smaller than those from Aragonian and adjacent areas in Spain (Daams, 1985), and the prototrope of HaH-5997 seems shorter.M. (aff).thaleri mainly occurs in Spain; there are records from the MN 7+8 locality Castelnou 6 in southern France, Candir 2 (MN 5) and Tuglu 19 (MN 9) in Turkey (Aguilar, 1994;Joniak and Bruijn, 2015) The first record of this species is from MN 5 and existed until the late Middle Miocene (MN 7+8) (Daams, 1999).It differs from Muscardinus sansaniensis by having few ridges of the molars and a more squared outline of M1 (Bruijn, 1966), and represents an independent lineage from M. sansaniensis (García-Alix et al., 2008).
Description: M1.There are two isolated upper teeth identified as M1; of one specimen (HaH-5990) the outer corner is broken.The three-rooted molar has a subquadrate outline and a flat occlusal surface; the width of the tooth crown is larger than the length.Six of twelve are the main ridges.Anteroloph is transverse, then extends obliquely backward, but does not join the protocone.The protoloph is the longest ridge, and curves backward at the middle part; it forms an acute-angled connection with the metaloph.In both specimens the anterotrope is absent, except a tiny crest at the lingual part of the tooth crown in HaH-5278.There are 1-2 extra ridges between the protoloph and precentroloph; two extra ridges on both sides of the postcentroloph are free or connected to the labial edge.Both centrolophs run backward, almost parallel to each other; precentroloph is longer, but never joins the endoloph.The metaloph is curved, and shows an inverted S-shape; it contacts with the posteroloph at the metacone.No posterotrope is developed between the metaloph and posteroloph, which, as well as protoloph, are connected to the endoloph at the lingual border.
M2.The outline of the tooth crown is rounded rectangular, and its width is greater than its length.It has three roots and a flat occlusal surface distributed with numerous slender ridges and narrow valleys.Except that the anteroloph, metaloph, and posteroloph are transverse, other main and extra ridges run obliquely from the labial to lingual side, but with a weaker curvature backward.Extra ridges are developed on both sides of the main ridges with exception of the metaloph and posteroloph: the anterotrope at the lingual part is short and free; among the three extra ridges between protoloph and precentroloph, the middle one is as long as the main ridges and runs through the entire width of the tooth from the labial connection with the protoloph and paracone, but ends just a short distance from the lingual edge; other two weak extra ridges are shorter, about half of the middle one.That is also the case for the shorter accessory ridges between centrolophs.The metatrope is also developed with a connection to the labial edge of posterolophid.All six main ridges are connected to the continuous endoloph; the labial edge is interrupted frequently.
p4.The lower premolar is single-rooted; it has a rounded trapezoidal outline and flat occlusal surface.There are five ridges: the short anterolophid is curved anteriorly; both metalophid and mesolophid are straight, parallel to the transverse axis of the tooth crown.The posterotropid in the posterior valley is isolated; all main ridges are connected to the endolophid and the labial margin.
m1.The lower molar is double-rooted; it has a flat occlusal surface.Of the nine ridges, the anterolophid and posterolophid are transverse, almost perpendicular to the longitudinal axis of the tooth whereas other ridges are inclined backward at an angle to the axis.In the trigonid, three extra ridges are developed between the anterolophid and metalophid, the longest middle lophid is linked to the lingual edge, and the labial end is free or connected with anterolophid; of the two small ridges on each side of anterotropid, the anterior one is longer.The centrolophid is slightly shorter than mesolophid, about the same length as the anterotropid.Between the mesolophid and posterolophid is the long posterotropid, which is as strong as the main ridges, and makes a loop with posterolophid; endolophid is continuous and linked with all ridges.Both specimens have similar dental patterns either on distribution or number of ridges.The differences are that in HaH-6019 the outline of the tooth crown is subtriangular, and the paralleled centrolophid and mesolophid are linked by a spur at the middle point.
m2.This lower molar has a similar dental pattern to m1 except that the front part is wider.It has five main ridges and four extra ridges, all of which but anterolophid and posterolophid run obliquely forward and are parallel to each other.The endolophid at the lingual edge is continuous and connected by all ridges; at the labial side, the centrolophid and mesolophid are free.
m3.The double-rooted tooth has a rounded triangular outline due to the width reduction of posterior part.There is a total of eight ridges, and all main ridges and extra ridges, except the transverse anterolophid and posterolophid, are inclined backward.Three extra ridges are present between the anterolophid and metalophid, and the middle one is the longest, showing an S-shaped curvature; two others on both sides are extremely tiny, and located at the lingual border.There is a tiny ridge between metalophid and mesolophid that probably represents the centrolophid; posterotropid is connected with the arched posterolophid.
Remarks: The Hambach 6C specimens are assigned to Muscardinus sansaniensis for morphological features (flat occlusal surface, shapes, and numbers of main and extra ridges, the outline of molars), and are within the size range of M. sansaniensis, although the M2 is much wider than those from most localities, but is similar to the largest teeth from Petersbuch 2 and Sansan (MN 6, France).In general, the material described here shows a similar dental pattern with specimens from Blanquatère 1 (MN 4/5) and Sansan in France, and Eitensheim (MN 5) and Schönenberg (MN 5) in Germany, such as the acute angle between protoloph and metaloph of M1, absence of posterotrope between metaloph and posteroloph on M1-M2 (Mayr, 1979;Aguilar and Lazzari, 2006), but the metalophid of m1 is not curved as that from Blanquatère 1.The material from Anwil (MN 7+8, Switzerland), which was placed in M. sansaniensis by Daams (1999), has fewer extra ridges, a longer outline on M1, and slightly curved lophids on lower molars; these differences refer to a simpler dental pattern that is considered as derived features of the younger material (Engesser, 1972).
The type locality of M. sansaniensis is Sansan, but it occurs in several MN 5 localities, Schönenberg, Puttenhausen, Maßendorf (Germany) and Vermes 1 in Switzerland.The early record of this species is probably the Early Miocene since the two lower molars of Glirudinus modestus from Forsthart (MN 4) were moved to M. sansaniensis (Wu, 1990); Blanquatère 1 was interpreted as an MN 4/5 site (Aguilar and Lazzari, 2006), but Freudenthal and Martín-Suárez (2013) argued that the Blanquatère 1 fauna is a mixture of various ages.In the late Middle Miocene (MN 7+8), the species is mainly represented by advanced Muscardinus aff.sansaniensis with larger size, simple morphology and probably higher root numbers, which were interpreted as advanced characters (García-Alix et al., 2008;Daxner-Höck, 2010).
Genus Miodyromys Kretzoi, 1943 Miodyromys aegercii (Baudelot, 1972) Figs.3(O-U Description: DP4.The upper deciduous premolar has a rounded triangular outline with a flat occlusal surface; the width of the anterior part is greater than the length.There are three complete main ridges: protoloph, metaloph, and posteroloph; the anteroloph is less developed, just exhibiting a low and weak cingulum on the anterior wall of the crown.As the longest ridge, the straight protoloph extends obliquely backward from the paracone; metaloph is weakly curved.Between protoloph and metaloph at the labial side, there are two short ridges representing the centrolophs, and are fused into a thin crest.The arched posteroloph is much thinner than other ridges, and contacts with metaloph at protocone and metacone.The three main ridges are connected to the short lingual margin.
P4: The upper premolar has three roots, with two smaller labial roots and a single lingual one.The outline of the tooth crown is oval with a concave occlusal surface.It has four main ridges: the short anteroloph links to the paracone at the anterior outer corner, and extends to one-third of the protoloph at the lingual side; protoloph and metaloph are straight, parallel to each other; a tiny, isolated ridge situated in the middle valley.The posteroloph is much longer and higher than other ridges, and extends lingually to the connection of metaloph and protocone, but is separated from metacone; the labial edge is interrupted between posteroloph and metaloph.
M1.There are two isolated teeth identified as M1.The threerooted upper molar has a subsquare outline with a strongly rounded front inner corner; the occlusal surface of the tooth crown is concave and the labial and lingual edges stand out distinctly.It has six main ridges (anteroloph, protoloph, metaloph, posteroloph, precentroloph, and postcentroloph): the curved anteroloph extends backward at lingual side, but is separated from the endoloph.The protoloph is remarkably long; it runs obliquely backward to the endoloph, or meets the metaloph directly.Between the protoloph and precentroloph is the short prototrope, which is of the same length as postcentroloph, and is thinner and lower than the main ridge.Precentroloph is longer and higher than the postcentroloph; both ridges are separated by a narrow, deep valley, and never reach the metaloph; the labial ends may be free (HaH-5989), or contact with the edge (HaH-5262).The posteroloph runs almost parallel to the metaloph; the labial ends are isolated or connected to the metacone.The valleys between ridges are rather deep due to comparatively high-crowned molars.
M2.The two isolated M2 have an identical dental pattern on the square outline of tooth crown, the concave occlusal surface, and same number of ridges.The M2 has three roots: two smaller ones at the labial side with circular cross-section, and one lingual root that is much larger and elongated longitudinally.In addition to the six main lophs, there are two extra ridges: the prototrope that is either linked to paracone or isolated labially, and the metatrope, which is slightly thinner, and has a weak connection with centroloph.Of the main ridges, the isolated anteroloph runs parallel to protoloph, and thickens towards the lingual side.The extremely long protoloph extends posterolingually to the short endoloph; precentroloph is longer than postcentroloph, and has free labial and lingual ends, whereas the latter is labially connected with metaloph and metacone.Both centrolophs are always separated by the deep valley at the labial edge, but may be fused into a Y-shaped connection at the middle position (HaH-5272).The metaloph bends forward, and describes an S-shaped curve from the labial to the lingual side; posteroloph is isolated from metacone.On the lingual side, protoloph, metaloph and posteroloph are connected to the endoloph; there is no continuous labial edge due to the depressions between ridges.
M3.The upper third molar is three-rooted, and has a trapezoidal-rounded outline since the labial edge is strongly inclined backward; the maximal width in the anterior position is greater than the length of the tooth.The occlusal surface is slightly concave with a distinct bulge at the anterior outer corner.The crown has six main lophs and three extra ridges.Of two specimens, the transverse anteroloph may have free labial and lingual ends (HaH-5276) or is fused with protoloph at the paracone (HaH-6015).The protoloph bends anteriorly and describes an arched curvature; it always contacts the short endoloph; precentroloph is slightly shorter than postcentroloph; metaloph is mirrored Sshaped, connected with posteroloph or separated.Both anterotrope and metatrope are present but short, situated at the labial part.The two molars have similar sizes and outline, but specimen HaH-5276 has a complicated dental pattern in the middle part due to the interlaced extra ridges.
dp4.The lower milk tooth is of oval outline that widens backward; the occlusal surface is almost flat; no root is preserved.The crown has four main lophids in total, without extra ridge.The anterolophid and metalophid are labially connected, and form a semicircle; the thin mesolophid is fused with the lingual edge and extends back to the middle point of the posterolophid, which is curved posteriorly and has free labial and lingual ends.
p4.The lower premolar has a single strong root, and a slightly concave chewing surface.The tooth outline is sub-rounded with a wider posterior part.The higher trigonid consists of an anterolophid and metalophid, which are fused and form a closed circle; no centrolophid is present.In the posterior part, there is a labial connection between mesolophid, posterolophid, making a crescentic circle that opens at the posterolingual edge because of the notch between posterolophid and entoconid.
m2.The second lower molar has three roots: two smaller ones and a larger root in the anterior and posterior positions separately.It is rectangular in outline with rounded posterior corners and an elevated front inner corner; the front width is significantly larger and narrow backward.The tooth has five main lophids (anterolophid, metalophid, centrolophid, mesolophid, and posterolophid) and three additional ridges.The anterolophid is transverse, nearly perpendicular to the long axis of the tooth, and links to the metaconid; metalophid is isolated at both labial and lingual ends; centrolophid extends from the lingual edge, and ends at the middle part of the tooth.The arched posterolophid is strongly curved backward, and is fused with the mesolophid and entoconid.On each side of centrolophid are the short prototropid and mesotropid; the posterotropid is the longest, and extends to the labial part of the tooth crown; the above extra ridges are isolated.No continuous endolophid is developed for the deep valley between the centrolophid and mesolophid.All labial ends of the main lophids are free although metalophid turns forward but still remain separated from the anterolophid by a notch.
The Hambach 6C teeth are larger than Miodyromys hamadryas; it also differs from Miodyromys biradiculus, Miodyromys praecox, and Miodyromys grycivensis (Grytsiv, MN 9 in Ukraine) by the larger size and three-rooted m2 (M.grycivensis has two roots in m1) (Nesin and Kowalski, 1997); besides, the latter two species have more complicated dental pattern than M. aegercii.The mediumsized Miodyromys vagus from Hesselohe (MN 5) in Germany, has four extra ridges, a labial connection between posterolophid and posterotropid on m1-2; the metaloph of M1 is vertical to the long axis (Mayr, 1979), all features that are different from the Hambach 6C material.Description: P4.The three-rooted upper premolar has a much larger width than length; the occlusal surface is moderately concave with a rounded rectangular outline.There are four main lophs (anteroloph, protoloph, metaloph, and posteroloph), a short centroloph, and a posterior extra ridge.The anteroloph and protoloph are slightly curved forward, and labial ends are separated.The only centroloph in the middle part ends free at both sides.There is a labial connection between posteroloph and posterotrope; metaloph curves backward and is separated from posteroloph labially.This premolar has a complete and straight endoloph connected to all the main ridges, which, however, are free labially.

Genus
M1.The upper molar has a subsquare outline with rounded corners; the anterior part is slightly narrower.Its occlusal surface is strongly concave along the longitudinal trough axis in the middle part.It has nine ridges; all but the centrolophs are slightly curved.The anteroloph and protoloph link with the paracone at the anterolabial side, and extend lingually to the complete endoloph, as is the case with metaloph and posteroloph.The anterotrope is about half of the tooth width, and ends free at both labial and lingual sides; precentroloph is longer and wider than postcentroloph; both are not connected to the labial edge or the lingual endoloph.The prototrope is extremely short, situated in the middle part of the crown; posterotrope is well developed, but ends freely at the lin-gual and labial sides.There is only weak ornamentation developed at the lingual wall of the molar.
p4.There are two isolated lower premolars that have similar dental patterns except the minor differences.The double-rooted tooth is distinctly narrower in the anterior part, and shows a trapezoidal outline; the occlusal surface is slightly concave due to the comparatively higher lingual border.It has eight ridges in all; the main ridges thicken labially, and they are higher and stronger than extra ridges.In both specimens, the anterolophid joins paracone, but is free labially; the long mesolophid is connected with posterolophid and entoconid at posterolingual edge; all three extra ridges end freely at labial and lingual sides, and the posterotrope between posterolophid and mesolophid is the longest.The endolophid is continuous or interrupted due to the deep notch between mesolophid and centrolophid.
m1.The lower first molar has two roots and a concave occlusal surface.Its outline is rectangular with rounded corners; the anterior margin is just slightly narrower than the posterior part.There are nine ridges: except the centrolophid, all other main ridges are strong and noticeably thickened at the labial ends.The metalophid contacts the lingual border and turns forward to join the labial end of anterolophid, which also extends lingually to the metaconid; between both lophids is a long anterotropid, which describes a mirrored S-shaped curvature.The centrolophid and mesolophid are of similar length, but the latter is much stronger; both ridges are linked lingually and weakly connected to the discontinuous endolophid.There is also a lingual connection between the posterolophid, mesolophid and entoconid.Of the four additional ridges, metatropid and mesotropid on both sides of centrolophid are equally sized, and much lower than the main ridges.They come close to the lingual edge, but remain isolated; the posterotropid also ends freely.Due to the strong main ridges and development of additional ridges, the intercalated valleys are narrow.There is no complete endolophid at the lingual edge for the interruption between the centrolophid and mesolophid.
m2.The double-rooted tooth has a subrectangular outline with anterior margin being wider than the posterior side; the occlusal surface is moderately concave.This lower molar is characterized by nine ridges.The lingual connection of anterolophid, metaconid and centrolophid are high; metalophid is weakly connected to the lingual border; the posterolophid is curved backward and fused with mesolophid at the entoconid.The four extra ridges end freely at the lingual and labial sides; the longest anterotropid is as wide as the main ridge, and extends across the middle part of the occlusal surface.No continuous endolophid is present for there is a deep notch between the centrolophid and mesolophid.The dental pattern of the two isolated teeth is identical; the difference primarily lies in the width of ridges, which are broader and stronger in specimen HaH-5246.As a result, the valleys between ridges are much narrower in HaH-5246 whereas HaH-5268 develops a series of broader depressions and numerous slender ridges.
m3.The third lower molar has a triangular outline with a rounded posterior border, and a nearly flat occlusal surface except the slightly elevated anterolingual corner.No roots are preserved.The main ridges are comparatively slender but still stronger and higher than the additional ridges.The anterolophid is low and slender in the anterior wall of the tooth; it joins the lingual edge with metalophid as well as centrolophid separately; the arched posterolophid is fused with mesolophid lingually.The anterotropid and posterotropid are of same length, and are weakly connected to the lingual border.The endolophid is interrupted between centrolophid and mesolophid.
troloph on the upper molar, and the absence of a continuous endolophid in the double-rooted lower molar.The single M1 exhibits a lingually free precentroloph and slightly curved ridges, rather than vertical to the endoloph, which is different from the Anwil material.P. werenfelsi is considered to appear firstly in Obergänserndorf (MN 5), and existed in Richardhof-Wald (MN 10), Austria (Daxner-Höck, 1998;Daxner-Höck and Höck, 2009).It has a size similar to Paraglirulus agelakisi from Aliveri (MN 3, Greece), and is probably descended from the latter species (Meulen and Bruijn, 1982).According to Meulen and Bruijn (1982), P. agelakisi differs from P. werenfelsi mainly in the upper molars for the precentroloph is shorter and usually not connected to the endoloph; the second feature resembles the Hambach 6C upper molars but the precentroloph is clearly longer in the Hambach 6C specimen.Therefore, we assign the material to P. werenfelsi.
In addition to the type locality Anwil, P. werenfelsi is widely distributed in Miocene sites of Europe.The Hambach 6C molars are slightly larger than specimens from Schönenberg and Maßendorf (Mayr, 1979;Schötz, 2002), but smaller than those from Wiesholz (MN 6) and Anwil in Switzerland (Engesser, 1972), Las Planas 4C (MN 5/6) and Valalto 2C (MN 6) (Meulen and Bruijn 1982), Sansan (Engesser, 1972), Rudabánya (MN 9, Hungary;Daxner-Höck, 2005), Bełchatów A (MN 9, Poland; Kowalski, 1997), and several Late Miocene localities in Austria (Richardhof-Golfplatz and Götzendorf, MN 9; Richardhof-Wald, MN 10) and Germany (Kleineisenbach and Giggenhausen, MN 7+8; Marktl, MN 9; Mayr, 1979).The m1 from Hambach 6C is similar to that from Bełchatów B (MN 5/6, Poland), but the single M1 of Hambach 6C has a shorter length than that of the latter site (Kowalski, 1997).The differing tooth dimensions indicate that the size of P. werenfelsi tends to increase from older localities to younger ones.Mayr (1979) established Paraglirulus conjunctus from Erkersthofen and Paraglirulus diremptus from Marktl respectively, which were removed to Glirulus for the smaller size by (Daxner-Höck and Bruijn, 1981); the only two species of Paraglirulus, P. werenfelsi and P. agelakisi were assigned to the new subgenus Glirulus (Paraglirulus); both larger and smaller species represent long independent evolution (Meulen and Bruijn, 1982).Regarding the similar dental pattern of Paraglirulus and Glirulus, the differential diagnosis of the two genera has been in debate.The original differences were illustrated by the connection of precentroloph with the endoloph, the occurrence of continuous endolophid and root numbers on the lower molars (Engesser, 1972, Mayr, 1979), which were considered to be subjective, and difficult to assess objectively (Meulen and Bruijn, 1982).However, the diagnoses given by them are insufficient to distinguish Paraglirulus and Glirulus according to Schötz (2002), and the genus Paraglirulus is still adopted by many authors.The Glirulus characters (continuous endolophid and three roots of the lower molars; Daxner-Höck and Höck, 2009), do not completely fit well with the diagnoses of G. diremptus and G. conjunctus: G. conjunctus may have an endolophid, but both species have two roots in m1-m2 (Mayr, 1979).Therefore, we follow Mayr's opinion and retain G. diremptus and G. conjunctus in Paraglirulus.
Genus Microdyromys Bruijn, 1966Microdyromys koenigswaldi Bruijn, 1966 Figs. 5 (M-P Description: M3.The upper molar has three roots, two smaller at the labial side and one larger root at the lingual side.Its occlusal surface is slightly concave due to the elevated front outer corner; the tooth outline displays a subtrapezoidal shape for the labial border narrows backward.It develops a comparatively simple dental pattern with six main ridges and one extra ridge.The anteroloph and posteroloph are separated from the paracone and metacone; protoloph describes a long and curved shape, and connects to the prominent metacone.The precentroloph is shorter and slenderer than postcentroloph, just extending to the middle part of the tooth crown.No extra ridge is present in the anterior or posterior valley; the only one is the metatrope between postcentroloph and metaloph with isolated ends.Four main ridges (anteroloph, protoloph, metaloph and posteroloph) are connected to the complete, straight endoloph whereas the centrolophs do not reach it.The lingual border of the molar is ornamented.
m1.There are two isolated teeth identified as m1.The tworooted lower first molar has a subrectangular outline with a narrower anterior part; the occlusal surface is less concave.The main lophids (anterolophid, metalophid, mesolophid and posterolophid) extend forward with distinctly thickened labial ends.There is a labial connection between the anterolophid and metalophid, which are linked to the metaconid as well.The mesolophid, which is longest and posterolophid contact with the entoconid at posterolingual border; centrolophid is linked to lingual border (HaH-6018) or separated (HaH-5239); both anterotropid and posterotropid are free at both lingual and labial edges.No continuous endolophid is developed due to the interruption at the middle point of lingual border.Of the two specimens, the trigonid of HaH-6018 is larger than the talonid; it develops longer and stronger ridges with exposed dentine resulted from heavier wear.
m3.The lower third molar has two roots at the anterior and posterior sides separately.The outline of the tooth is subtriangular with a rounded posterior part; the occlusal surface is almost flat due to strong wear.The anterolophid is separated from the metalophid at the labial end; the centrolophid is interrupted and connected with metalophid at the lingual part.There are two additional ridges: the first one between anterolophid and metalophid is comparatively long and linked to the lingual border; the posterior extra ridges bend backward and are fused with labial part of the mesolophid.
Regarding the smaller size and comparatively simple dental pattern, the Hambach 6C material is close to both M. koenigswaldi from Valdemoros 3B (MN 4, Spain), and M. legidensis from Villafeliche 2A (MN 4, Spain).M. koenigswaldi is considered to descend from M. legidensis (Daams, 1981, Freudenthal, 2007a), the only difference between the two taxa being the larger size of the former (Daams, 1981).Therefore, it is difficult to distinguish teeth whose dimensions fall in the lower size range of M. koenigswaldi, as argued by Wu (1993) who identified Microdyromys teeth with a simple dental pattern from Petersbuch 2 as M. legidensis-koenigs-waldi, representing a transitional form between the two species due to the overlapping size ranges.M. complicatus has relatively large teeth and complicated dental pattern; M. remmerti from the Aragonian type area, Spain (MN 4-5) is larger, with a complicated and irregular dental pattern, higher numbers of ridges, both of which are significantly different from the Hambach 6C material.Description: M1.There are three isolated teeth identified as M1 that have three roots with two small ones at the labial border and one larger root situated at the lingual side.The tooth is elongated anteroposteriorly and the anterior part slightly narrows backward, displaying a subrectangular outline; the occlusal surface is moderately concave.All these molars have four main lophs (anteroloph, protoloph, metaloph, and posteroloph), and fused centrolophs.The anteroloph and posteroloph are detached from the paracone and metacone respectively; endoloph is complete, connected with the four main ridges listed above.There are some minor morphological differences among these molars, such as the position and number of extra ridges, and the concavity of occlusal surface.

Genus
M2.This three-rooted upper molar has a square occlusal outline and a moderately concave surface.It develops seven ridges that are nearly straight, perpendicular to the long axis of the tooth crown.The anteroloph is separated from the high paracone; the precentroloph, of the same length as protoloph, is connected to the endoloph, but has an isolated labial end with a distinct bulge.On the labial side there is a pronounced mesostyle.The postcentroloph is slightly shorter than the anterior one, ending at a short distance from endoloph; it is labially connected with metaloph and metacone.There is one extra ridge: the long prototrope extends from the base of paracone, and runs parallel to precentroloph, but fails to reach the endoloph, which is straight and complete, connected with four main lophs and precentroloph.
p4.The lower premolar is double-rooted with a triangular occlusal outline and rounded rear inner corner.It develops a simple dental pattern with four main lophids.All the main ridges are connected to the labial border and have free lingual ends.The centrolophid is present, but is lower and thinner than the main ridges with free labial and lingual ends.The endolophid is not continuous for the deep notch in front of the mesolophid.
m2.The three-rooted lower tooth has a subsquare outline with a broader anterior margin and longer labial border; the occlusal surface is moderately concave.It has seven lophids, two of which are extra ridges.The anterolophid and metalophid are welldeveloped, and contact with metaconid, which also occurs on the metalophid.The long centrolophid extends to the lingual border, but is not connected with the paracone.The posterolophid seems to weakly join the mesolophid and entoconid.In the anterior valley, the anterotropid is fused with the anterior wall of the anterolophid due to heavy abrasion; a short and isolated posterotropid is situated in the middle part of the posterior valley.Similar to p4, the deep valley between the centrolophid and mesolophid interrupts the endolophid at the labial side.
Remarks: Bransatoglirinae was named by Daams and Bruijn (1995) based on Bransatoglis which has been the only genus of the subfamily (ranging from late Eocene to Late Miocene) since Paraglis and Oligodyromys were synonymized with Bransatoglis (Daams, 1976;Bosma and Bruijn, 1982).In a recent study, both Paraglis and Oligodyromys were restored and the genus Microdyromys was reclassified from Dryomyinae to Bransatoglirinae (Freudenthal andMartín-Suárez, 2007b, 2013); therefore, four genera are included in the subfamily primarily on the basis of size.The revision is adopted by other researchers (Hír, 2013); but Bruijn et al. (2013) insisted the subfamily Bransatoglirinae be monogeneric regarding the stability of nomenclature.The discussion of the classification is not the focus of this paper; we follow Freudenthal and Martín-Suárez's opinion and regard Paraglis as a valid genus.According to the revised diagnosis (Freudenthal and Martín-Suárez, 2007b), Paraglis astaracensis is a medium-sized species with seven crests on the lower molars and seven or eight crests on the upper molars.The dimensions of specimens from Hambach 6C fall within the lower variation range of P. astaracensis; the number of ridges, complete endoloph, absence of developed anterotrope and posterotrope, and the precentroloph connected to endoloph, are consistent with the main features of the taxon.
Except for P. astaracensis, this genus only includes Paraglis infralactorensis during the Early/Middle Miocene.P. infralactorensis from Estrepouy (MN 3, France) has a slightly smaller size, and welldeveloped anterotrope; its precentroloph does not contact with endoloph, which is different from the Hambach 6C material.
The three isolated M1 from Hambach are characterized by strong elongation and irregular ridges, which seems different from type specimens from Sansan, as well as Anwil, but have similar dental morphology with Bransatoglis sp. from Bełchatów B except for the larger sizes (Kowalski, 1997).It should be noted that most localities produce scarce specimens but Engesser (1972), after his study of comparatively rich material from Anwil, pointed out that this taxon (Gliride X in the original description) often develops an irregular dental pattern, and cross-connections between main and extra ridges are more common than in other glirid species.

Discussion
The glirid fauna of Hambach 6C described in this paper consists of Glirudinus undosus, Muscardinus thaleri, Muscardinus sansaniensis, Miodyromys aegercii, Paraglirulus werenfelsi, Microdyromys koenigswaldi, and Paraglis astaracensis; in addition, a large-sized dormouse -Myoglis meini -was reported earlier (Nemetschek and Mörs, 2003).Therefore, eight species in seven genera were currently identified from this locality.Hambach 6C produced a comparatively diverse glirid assemblage represented by commonly known  (Bruijn, 1966;Daams, 1985;Aguilar, 1994;Joniak and Bruijn, 2015), and there is no fossil record from central Europe before.The appearance of M. thaleri in Hambach 6C extends the known biogeographic range of the species far to the northeast.Glirid diversity varies considerably in spatial and temporal domains (Table 1).Since the oldest record in the late Eocene, Gliridae became diversified during the Oligocene-Miocene, and culminated in the late Early Miocene (Daams and Bruijn, 1995).In the Miocene localities of Europe, the MN 4 locality Petersbuch 2 in southern Germany presents the highest diversity with 19 species in 11 genera, five of which are also taxa known from Hambach 6C -except Paraglis and Paraglirulus.The unusual high number of glirid taxa in Petersbuch 2 is probably the result of a temporal inhomogeneity of this fauna for the occurrence of M. aff.sansaniensis (Wu, 1993); and was partly interpreted as taphonomic bias factors (Kowalski, 1997) since the numerous taxa from layers of different ages in the fissure fillings could not be ruled out.The MN 4/5 locality Blanquatère 1 in southern France represents another highly diverse glirid assemblage (16 species; Aguilar and Lazzari, 2006), but this fauna is also considered as a mixture of various ages (Freudenthal and Suárez, 2013).Of other MN 4 localities, Echzell (8 species), Erkersthofen 1 (6 species), Erkersthofen 2 (9 species), and Forsthart (8 species) show diversities similar with the Hambach 6C fauna (Ziegler and Fahlbusch, 1986;Wu, 1993;Vasilyan et al., 2022).Some taxa -G.undosus and M. koenigswaldi -are known from most faunas above except Forsthart.Rauscheröd and Rembach (late MN 4) from the Upper Freshwater Molasse of southern Germany show a declined diversity with only 3-4 species, much lower than the contemporaneous Forsthart assemblage (Ziegler and Fahlbusch, 1986).Outside of Germany, the dormice from Oberdorf, which is earlier than Petersbuch 2, have a high diversity represented by ten taxa (Bruijn, 1998), but only Paraglis (cf).astaracensis occurs in both localities.During the Middle Miocene, the abundance of glirid taxa from numerous localities is highly variable, but the numbers of taxa in many MN 6 localities seem to decline, such as Sandelzhausen (4 species), Goldberg (2 species), Steinberg (1 species), which is also the case for Neudorf in Slovakia (4 species) and Schaffhausen (2 species) in Switzerland (Mayr, 1979;Bolliger, 2000;Sabol, 2002).However, the diversity of glirid faunas increased to some extent in the late Middle Miocene (MN 7+8): Anwil produced 11 taxa, seven of which also occur in Hambach 6C (M.(cf).koenigswaldi, P. werenfelsi, G. undosus, M. (aff).sansaniensis, M. aegercii, P. astaracensis, M. meini; Engesser, 1972;Mayr, 1979).Four taxa are shared among faunas from Hambach, Kleineisenbach (7 species), and Giggenhausen (6 species).
In terms of stratigraphic distribution, the glirids from Hambach 6C are closest to the ones from the MN 5 locality Schönenberg with similar faunal diversity and the most shared taxa.Moreover, Hambach 6C shares more taxa with Late Miocene (MN 7+8) faunas than with Early Miocene (MN 4) faunas.During the Middle Miocene (MN 5), several taxa (e.g., P. werenfelsi, M. koenigswaldi, M. aegercii, and M. sansaniensis) are very broadly known from central Europe.
Meulen and Bruijn (1982) included the majority of fossil glirid species into six groups and relevant biotopes based on the dental pattern of upper molars.Muscardinus, Myoglis, and Glirudinus belong to the ''flat molar group" which is mainly vegetarian and arboreal, preferring undergrowth thickets; Microdyromys is a member of the ''simple intermediate group" which mainly lives in forests, but also open countries; the symmetrical group that includes Paraglis has a biotope similar with the flat molar group, with the requirement of forests and open woodlands; Miodyromys belongs to the asymmetrical group preferring an open country habitat.The glirid fauna composition in Hambach 6C indicates a Middle Miocene humid forested environment with undergrowth and woodland, which is confirmed by the frequency of semiaquatic mammals (desmanine, beavers, and tragulid) and a swampy paleoenvironment in a huge estuarine delta (Mörs et al., 2000;Mörs, 2002).

Table 1
Comparison of the Hambach 6C glirid assemblage with other localities (MN 4-MN 7+8) in Europe (references are given in the text).*: According to Prieto et al. (2019); #: Microdyromys legidensis-koenigswaldi in Wu (1993).genera and species in Miocene localities of central Europe.It should be noted that the occurrences of M. thaleri are mainly from several Early/Middle Miocene sites of Zaragoza, Spain, and also in France and Turkey