Melissiodon sp.

Crespo, Vicente D., Ríos, María, Marquina-Blasco, Rafael & Montoya, Plini, 2025, The Early Miocene muroids (Muroidea, Rodentia) of the Ribesalbes-Alcora Basin (Spain): A thriving haven during a time of migration, Fossil Record 28 (1), pp. 187-218 : 187-218

Melissiodon sp.

Figs 8 U – Y , 10

Localities.

BC 1 and MAB 3.

Material (number of remains).

Suppl. material 1; BC 1 (2): 1 M 1, 1 M 3; MAB 3 (3): 1 m 1, 1 m 3, 1 M 3.

Measurements.

Suppl. material 2.

Description.

m 1 ( MAB 3; Fig. 8 U ): The tooth is elongated, with a subtriangular outline, and high, sharp cusps. The anteroconid has a lingual cusp, and the labial ridge is short. The lingual cusp has an anterior spur. The metaconid complex connects to the lingual anteroconid and is slightly connected to the posterior metalophulid. The anterior metalophulid connects with both anteroconids, developing a small ridge between the two. The protoconid has a short ectostylid. The posterior metalophulid is long and contacts the anterior ridge of the entoconid on the lingual side of the tooth. The posterior metalophulid has a posterior cusp and does not connect with the mesoconid. The mesolophid is medium in size and isolated. The mesoconid is well-developed. The entoconid complex connects with a well-developed posterolophid.

m 3 ( MAB 3; Fig. 8 V ): fragmented molar, with high, sharp cusps. The anterolophid connects the lingual side of the tooth with the metaconid, enclosing a small lingual anterosinusid. The metaconid has a small posterior spur. The anterior metalophulid is connected to the anterolophid and encloses a small, deep labial anterosinusid. The tooth has a small mesolophid and an incipient ectomesolophid. The hypolophid is medium-sized and isolated. The posterolophid does not connect with the entoconid.

M 1 (BC 1; Fig. 8 W ): tooth fragment, with both anterocones. The labial anterocone has an anterior ridge. A posterior ridge connects both anterocones. The lingual anterocone contacts the protocone complex. The anterior protolophule reaches the metacone complex.

M 3 (BC 1; Fig. 8 X ): The molar is subquadrangular, with high, sharp cusps, and a complex morphology. The tooth has a short anteroloph connected to the paracone complex. The anterosinus is short and deep. The anterior protoloph is connected to the paracone complex, and in addition, it has a posterior spur. The posterior protoloph is connected to the posterior part of the paracone complex, where two posterior ridges begin, connecting the lingual ridge with the anterior metaloph. A small entoloph starts at the protocone, but without reaching the hypocone. Both metalophs are connected, and the posterior one reaches the hypocone.

Variability in other sites: In MAB 3 (Fig. 8 Y ), variability is evident in the configuration of the anteroloph, which does not connect with the paracone. The protolophs are separated and connect forming a V-shape. The posterior protoloph is short and does not connect to the hypocone, and the latter does not connect to the metacone, with the anterior crest of the hypocone being isolated. The posterior crest of the hypocone ends at the posterior part of the tooth. The specimen of BC 1 is slightly narrower than that of MAB 3 (Fig. 10 B ).

Remarks.

The Melissiodontinae family is thought to have a primitive origin, as it probably first appeared in the early-middle Eocene of Asia ( Wessels et al. 2018). The genus includes eight species: Melissiodon chatticus Freudenberg, 1941 , Melissiodon emmerichi Schaub, 1925 , Melissiodon schalki Hrubesch, 1957 , Melissiodon schroderi Hrubesch, 1957 , Melissiodon quercyi Schaub, 1920 , Melissiodon dominans Dehm, 1950 , Melissiodon schlosseri Schaub, 1925 , and Melissiodon schaubi Dehm, 1935 . The genus Edirnella was proposed by de Bruijn et al. (2013) as the ancestor of this genus. The earliest known record of Melissiodon dates back to the early Oligocene, most likely from Ehingen in the MP 23 ( Hrubesch 1957), and the most recent one in the Early Miocene, probably from Forsthart in the upper MN 4 ( Mödden 1999). The number of records from this period is limited, with only a few examples from Central Europe, France, Germany, Turkey, and the Iberian Peninsula. In these areas, the presence of only the M. dominans and M. schlosseri species has been documented ( Antunes and Mein 1986; Mödden 1999; Ünay et al. 2003; Jovells-Vaquè and Casanovas-Vilar 2018 b; Jovells-Vaquè and Mörs 2023). Another species of the genus Melissiodon was discovered in the Miocene area of El Fallol, situated in the Vallès-Penedès Basin. Crusafont et al. (1955) originally named it Melissiodon arambourgi . However, subsequent research by Mein and Freudenthal (1981) and Jovells-Vaquè and Casanovas-Vilar (2018 b) posited that it should be regarded as a synonym of M. dominans . Utilising the MN 4 material from Beon 2 ( France), Bulot et al. (2009) proposed the designation of a new species, basing this assertion on the comparatively diminutive size of the MN 4 material in relation to the MN 3 populations. Nevertheless, no formal description has been provided due to the limited quantity of available material.

The fossil record of Melissiodon in the Early Miocene of the Iberian Peninsula is mainly limited to a few isolated teeth or tooth fragments recovered from several sites in the eastern part of the Iberian Peninsula. These sites include Level Q of Barranco del Candel (Magro Basin; Adrover et al. 1987), Ramblar 1, 3 B and 7, Bañon 2 and 11 A (Calatayud-Montalbán Basin; Sesé 1987), and Sant Andreu de la Barca, Molí de Can Calopa, Sant Andreu de la Barca 1, San Mamet, Turó de les Forques 1, El Fallol (Vallès-Penedès Basin, Jovells-Vaquè and Casanovas-Vilar 2018 b), and Montalvos 2 (Teruel Basin; Hordijk et al. 2015).

The material from the Ribesalbes-Alcora Basin (Fig. 10 ) exhibits a smaller size than that of the populations of this genus from MN 1-3, and falls within the variability presented in MN 4, as observed in Beón 2. Conversely, Montalvos 2 exhibits a greater quantity of material than that of the other MN 4 sites, and a larger size ( Bulot et al. 2009; Hordijk et al. 2015). In comparison to the material from Central European and Vallés-Penedés Basin sites, the size of the material studied here is typically smaller ( Jovells-Vaquè and Casanovas-Vilar 2018 b; Jovells-Vaquè and Mörs 2023).

The m 1 of MAB 3 is notably intricate, exhibiting a distinctive set of characters that are not observed in any population of the genus Melissiodon . The mesolophid is isolated, making contact exclusively with the mesoconid. Additionally, there is direct contact between the posterior metalophulid and the entoconid, and no contact between the metaconid and the posterior metalophulid. This differs from the descriptions provided by Ziegler and Fahlbusch (1986) and Fejfar (1989) for other Central European MN 4 populations. The Montalvos 2 population exhibits a markedly elongated labial part ( Hordijk et al. 2015). The anteroconid complex closely resembles that observed in the Wintershof West population of M. dominans ( Hrubesch 1957) , except for the labial part, which is slightly less extended. The high variability in M 3 morphology falls within the range observed in the Wintershof West population ( Hrubesch 1957).

The primary concerns regarding the lower Aragonian collections of this genus pertain to the scarcity of remains (less than 1 % of all mammals), the substantial degree of fragmentation of the remains, and the challenge in discerning the morphology of the small tooth fragments belonging to this genus. Consequently, the classification of these specimens is often uncertain ( Mödden 1999). Notwithstanding the aforementioned challenges, two species of the genus have been formally described from the European Early Miocene. One of the species, M. schlosseri , is known only from its type locality, Haslach ( Mödden 1999). In other localities, such as Mokrá-Quarry La Chaux 7 or Ulm Uniklinik, taxa that are related (aff.) to the former species have been recorded ( Werner 1994; Engesser and Mödden 1997; Bonilla-Salomón et al. 2022). The second species is M. dominans (or its related forms (aff. )), regarded as a problematic taxon, given that most of the remains discovered in Europe are attributed to this species, despite the lack of definitive evidence or the scarcity of the remains. A third species, a descendant of M. dominans , has been identified in the lower Aragonian, distinguished by its smaller size relative to its ancestor. However, the scarcity of remains has precluded its formal description ( Bulot et al. 2009).

The distinguishing characteristics between M. schlosseri and M. dominans are as follows: the former exhibits greater cusp thickness, while the latter possesses a squarer m 1 with a labial anteroconid that is slightly extended in the latter. The labial anteroconid of M. dominans from Wintershof West ( Hrubesch 1957) and the new species from Beón ( Bulot et al. 2009) exhibit a ridge-form, which is even more elongated in the lower Aragonian species. In contrast, M. schlosseri is characterised by a labial anteroconid with a cusp-form. A further noteworthy distinction emerges in the diagnosis of M. schlosseri , where an elevation in the posterolophid is documented ( Schaub, 1925). As Werner (1994) observes, this feature is likely attributable to intraspecific variation. It is noteworthy that the morphology of the m 1 from the Ribesalbes-Alcora Basin is similar to that described by Bonilla-Salomón et al. (2022; Fig. 3 Q ), although in the present case, it is considerably smaller in size.

Consequently, upon thorough review of extant literature from multiple European localities, it was determined that specific populations of M. aff. dominans could be re-assigned to M. schlosseri , as evidenced by the findings in Vieux Collonges (Mein and Freudenthal 1981). This underscores the imperative for a comprehensive re-evaluation of the genus and its potential re-classification. Furthermore, the m 1 from the Ribesalbes-Alcora Basin exhibits a smaller size compared to those previously described by Mein and Freudenthal (1981). The m 1 from Ribesalbes-Alcora Basin is distinguished by an isolated mesolophid with an isolated on the anterior part and a slightly elongated labial anteroconid. These characteristics differentiate it from M. dominans from Central Europe and the Vallès-Penedès Basin. It is a closer alignment with M. aff. dominans ( Jovells-Vaquè and Casanovas-Vilar 2018 b; Jovells-Vaquè and Mörs 2023) is also noteworthy.

In consideration of the aforementioned morphological characteristics, the specimen exhibits primitive traits analogous to those observed in the Wintershof West population. It is comparable in size to the recently discovered but as yet unnamed species from Beon. Furthermore, the characteristics of the genus Melissiodon exhibit a high degree of variability, and the available comparative material is exceedingly scarce ( Mödden 1999). Consequently, the Melissiodon material from the Ribesalbes-Alcora Basin will be assigned open nomenclature until a more substantial collection of remains becomes available for formal description.

Figures

Figure 3. Comparison of length and width measurements (in mm) of Megacricetodon primitivus from Ribesalbes-Alcora Basin. M. primitivus from Valtorres (type locality (t. l. )); M. vandermeuleni from Fuente Sierra 4 (t. l.); M. hellenicus from Aliveri NQ (t. l.); M. collongensis from Vieux Collonges (l. t.); M. bezianensis from Bézian; M. bavaricus from Langenmoosen (t. l.); and the material from Ribesalbes-Alcora Basin (Fahlbusch 1964, Bulot 1972, Maridet 2003, Oliver and Peláez-Campomanes 2013, 2014, 2016; this publication).

Figure 8. Teeth of Eumyarion weinfurteri, Melissiodon sp., and Muroidea indet. From the Ribersalbes-Alcora-Basin. Eumyarion weinfurteri: A. Left m 1 (MAB 3-161); B. Left m 1 (MAB 3-162); C. Right m 1 (MAB 5-75); D. Left m 1 (MAB 5-76); E. Right m 2 (FS 1-29); F. Left m 2 (MAB 3-203); G. Right m 2 (MAB 3-206); H. Left m 2 (MAB 5-53); I. Right m 2 (MAB 5-54); J. Left m 3 (MAB 3-241); K. Right m 3 (MAB 3-242); L. Left m 3 (MAB 5-56); M. Right m 3 (MAB 5-57); N. Right M 1 (MAB 3-82); O. Left M 1 (MAB 3-83); P. Right M 1 (MAB 5-515); Q. Left M 2 (MAB 3-111); R. Right M 3 (MAB 3-133); S. Left M 3 (MAB 3-134); T. Left M 3 (MAB 3-135). Melissiodon sp.: U. Right m 1 (MAB 3-168); V. Left m 3 (MAB 3-169); W. Left M 1 (BC 1-32); X. Left M 3 (BC 1-31); Y. Left M 3 (MAB 3-727). Muroidea indet.: Z. Right M 2 (MAB 0 A- 43). Scale bar: 1 mm.

Figure 10. Comparison of length and width measurements (in mm) of Melissiodon sp. from Ribesalbes-Alcora Basin. M. dominans from Erkertshofen 1, Dolnice 1, Montalvos 2, Petersbuch 2, Sant Andreu de la Barca, and Wintershof West (type locality (t. l.); M. aff. dominans from Beaulieu 2 B, and Vieux Collonges; Melissiodon sp. from Beón 2; and the material from Ribesalbes-Alcora Basin (Hrubesch 1957, Mein and Freudenthal 1981, Mein 1989, Ziegler and Fahlbusch 1986, Fejfar 1989, Bolliger 1992; Bulot et al. 2009, Hordijk et al. 2015, Jovells-Vaqué and Casanovas-Vilar 2018 b, this publication).