Orcemys giberti Martin, Tesakov, Agustí, and Johnston, 2018

Agustí, Jordi & Piñero, Pedro, 2023, Evidence for parallel development of ever-growing molars in Early Pleistocene rodents from southern Spain and their paleoenvironmental implications, Acta Palaeontologica Polonica 68 (2), pp. 379-391 : 381-386

publication ID	https://doi.org/ 10.4202/app.01074.2023
persistent identifier	https://treatment.plazi.org/id/1A1DEB1C-423A-872E-28C7-6358FD78FBD9
treatment provided by	Felipe
scientific name	Orcemys giberti Martin, Tesakov, Agustí, and Johnston, 2018
status

Treatment

Fig. 2A–G View Fig .

Material.— Two M 2 (IPHES-BC-32, 117), two M3 (IPHES- BC-119, posterior fragment; IPHES-BC-120), and four m1 (IPHES-BC-30, holotype; IPHES-BC-31, anterior fragment; IPHES-BC-113, anterior fragment; IPHES-BC-118). All from Lower Pleistocene , Barranco de los Conejos, Guadix-Baza Basin, Spain .

Measurements.—See Table 1.

Description.—The m1 has a very simple pattern, composed of an anteroconid cap (AC2), five alternating triangles (T1, T2, T3, T4 and T5) and a posterior lobe. A thin deposit of cement can be recognized at the labial ends of the re-entrant angles. The AC2 is widely confluent with the T4 and T5, both triangles being also widely confluent. A prominent mimomyan ridge is always present, being the only mimomyan feature that can be recognized, with no evidence of enamel islet. The anterior wall of the AC2 is free-enameled as it is the case of the labial wall of the mimomyan ridge, characterized by high dentine tract. The connection between the T4 and the T3 is very straight, as it is the connection between the T3 and the T2. In contrast, the T2 and T1 are widely confluent. The connection between the T1 and the posterior lobe is again very straight.

The M2 has an occlusal pattern composed of an anterior lobe (AL1) and three alternating triangles (T2, T3, T4). The three triangles are disconnected, with no dentine connection between them.

The M3 shows a simple occlusal pattern, with an anterior lobe, two triangles (T2 and T3), and a rounded, elongated posterior cap. The anterior lobe is widely confluent with the T2, while the connection between the T2 and T1 is very straight. In contrast, the T1 is again widely confluent with the posterior cap. In the posterior cap, a very shallow BRA3 and a small LRA3 can be recognized.

Remarks.—The genus and species Orcemys giberti were established by Martin et al. (2018) on the basis of material coming from Barranco de los Conejos (type locality) and Barranco del Paso, both at the Baza Formation of the Guadix-Baza Basin. Previous papers assigned this large arvicoline to Mimomys sp. ( Agustí et al. 2013). The original sample consisted in one m1 and one M3 from Barranco de los Conejos (holotype and paratype, respectively), five m1 (four of them broken or eroded), two broken m2, two broken m3, one broken M1/2, and two M3 from Barranco del Paso. Here we add new specimens from Barranco de los Conejos, which shed new light on the variability and phylogenetic relationships of this taxon. The morphology of the m1 occlusal surface led Martin et al. (2018) to raise the question as to whether this species could be included in the lagurine genus Borsodia . However, in the same paper this assignment was discarded since the Barranco de los Conejos teeth still retained a rest of cement in the re-entrant angles. Instead, Agustí et al. (2013) suggested that the new taxon could be an in situ descendant of Mimomys medasensis ( Fig. 2J–L View Fig ), a hypothesis supported by the cladistic analysis presented in Martin et al. (2018). Described for the first time at the site of Islas Medas (NE Spain; Michaux 1971), Mimomys medasensis is a widely distributed species in the Iberian Plio-Pleistocene ( Mein et al. 1978; Esteban Aenlle and López-Martínez 1987; Sevilla et al. 1991; Agustí et al. 2011; López-García et al. 2023). An increase in size and hypsodonty has been observed in this species through time ( Chaline 1987; Sevilla et al. 1991). In contrast, the presence of this species in the Guadix-Baza Basin is scarce ( Agustí et al. 2015b), restricted to the earliest Pleistocene of the Galera section (level Galera 1G; Agustí et al. 1997). In size, Mimomys medasensis is comparable to Orcemys giberti (see Table 1) although it differs because of the development of roots. However, some levels stratigraphically close to Barranco de los Conejos (Cortijo de Don Alfonso, Orce 2, Cementerio de Orce, Fuentecica 5; Agustí et al. 1987; Oms et al. 2000) present an advanced species of arvicoline whose characters are intermediate between the two species. No formal description has been done of these specimens (see Fig. 2H, I View Fig ), which in previous faunal lists were quoted either as Mimomys ostramosensis or Mimomys cf. ostramosensis ( Agustí 1986; Agustí et al. 1987; Oms et al. 2000). This unnamed species is larger and more hypsodont than Mimomys medasensis , comparable in this way to Mimomys ostramosensis . It is characterized by the persistence of mimomyan elements, such as a prominent Mimomys -ridge (like Orcemys giberti ) and a residual enamel islet (which is already lost in Orcemys ). The persistence of this latter feature in Mimomys sp. explains the huge dentine area between the AC2, T4 and T 5 in O. giberti . However, it differs from Orcemys since it still bears roots. Therefore, a continuous lineage could be recognized in the Guadix-Baza Basin from Mimomys medasensis to Orcemys giberti throughout intermediate Mimomys sp. from Cortijo de D. Alfonso, Orce 2, Cementerio de Orce and Fuentecica 5.

Stratigraphic and geographic range.—Lower Pleistocene ( Agustí et al. 2013); Barranco de los Conejos and Barranco del Paso, both in the Guadiz-Baza Basin, Spain ( Martin et al. 2018).

Genus Manchenomys Agustí, Piñero, Lozano-Fernández, and Jiménez-Arenas, 2022

Type species: Manchenomys orcensis Agustí, Piñero, Lozano-Fernández, and Jiménez-Arenas, 2022 , Fuente Nueva 3, Lower Pleistocene. Manchenomys oswaldoreigi ( Agustí, Castillo, and Galobart, 1993)

Fig. 3 View Fig .

Material.—One M3 (IPHES-BC-146), four m1 (IPHES-BC-28, 33; IPHES-BC-38, anterior fragment; IPHES-BC-112, anterior fragment). All from Lower Pleistocene, Barranco de los Conejos, Guadix-Baza Basin, Spain.

Measurements.—See Tables 2, 3.

Description.—The occlusal pattern of the m1 is composed of an anteroconid cap ( AC 2), five alternating triangles T1, T2, T3, T4, and T5) and a posterior lobe. Cement is present in all the re-entrant angles. In all the three specimens the anteroconid is short and asymmetrical, the lingual wall being wider than the labial one. Enamel is always lacking in the anterior half of the wall of the anteroconid complex. The triangles are also asymmetrical, the lingual ones (T1, T3, T5) being wider than the labial ones (T2, T4). Specimens show undifferentiated or slightly negative enamel. LRA 4 and BRA 3 are not so deep, AC 2 and the T4–T5 dentine fields being widely confluent. The T4 and T5 are alternating, being also widely confluent. Dentine channels between the posterior lobe, T1, T2, T3 and T4 are very narrow.

The occlusal pattern of the only M3 is composed of a transverse anterior lobe, two alternating triangles (T2–T3) and a posterior cap ( PC 1). The anterior lobe, T2 and T3 are isolated, with no dentine channels. The T3 is widely confluent with the PC 1. The PC 1 is simple and rounded. A small T4 is recognized on the lingual wall of the PC 1.

Remarks.—The species Manchenomys oswaldoreigi was initially assigned to the genus Mimomys , on the basis of the extended development of roots in the m3 ( Agustí et al. 1993). Later it was included in the new genus Manchenomys , established on the basis of the species Manchenomys orcensis from different levels at the late Early Pleistocene sites of Fuente Nueva 3 (type locality, Guadix-Baza Basin) and Quibas ( Agustí et al. 2022b). The teeth from Barranco de los Conejos coincides both in size and shape with Manchenomys oswaldoreigi from its type locality, Gilena 2 ( Tables 2 and 3), being smaller than the younger Manchenomys orcensis . The values of the indexes A/L and B/W are also comparable to those of Manchenomys oswaldoreigi from Gilena 2, but also to those of Manchenomys orcensis from Fuente Nueva 3 and Quibas ( Table 4). In contrast, the values of C/W in Manchenomys oswaldoreigi from Barranco de los Conejos are remarkably low, even when compared with the type species at Gilena 2, which may be an indication of a more archaic population.

Stratigraphic and geographic range.—Lower Pleistocene; Gilena 2 (type locality), Barranco de los Conejos, Cortes de Baza 1, and Fuentecica 5, southern Spain ( Agustí et al. 1993, 2022b).

Genus Tibericola Koenigswald, Fejfar, and Tchernov, 1992

Type species: Tibericola jordanica (Haas, 1966) , Ubeidiya , Lower Pleistocene .

Tibericola vandermeuleni (Agustí, 1992)

Fig. 4 View Fig .

Studied material.— Four M 3 (IPHES-BC-121, 140–142), and 14 m 1 (IPHES-BC-26, anterior fragment; IPHES-BC-27, anterior fragment; IPHES-BC-29, 34; IPHES-BC-35, anterior fragment; IPHES-BC-36, holotype; IPHES-BC-37, anterior fragment; IPHES-BC-39, anterior fragment; IPHES-BC-40, 114–116, 135; IPHES-BC-136, anterior fragment). All from Lower Pleistocene , Barranco de los Conejos, Guadix-Baza Basin, Spain .

Measurements.—See Table 5.

Description.—In the m1, the occlusal pattern is composed of an anteroconid cap ( AC 2), five alternating triangles (T1–T5) and a posterior lobe. All the re-entrant angles are filled by abundant cement. There is a rounded, well-developed anteroconid cap. In four specimens the labial wall outlines a tiny BSA 4. In a young individual, this BSA 4 is fully developed, as it is a prominent LSA 5 ( Fig. 4 View Fig ). The LRA 3 and BRA 3 are very deep, so the dentine connection between the T4 and T5 is very straight, almost inexistent in some cases (see B/W values in Table 6). The connection between the AC 2 and T5 is relatively wide (see C/W values in Table 6), but in two specimens it is also quite straight. All the specimens show undifferentiated or slightly negative enamel.

In the M3, the occlusal pattern is composed of a transverse anterior lobe ( AL 1), three alternating triangles (T2, T3 and T4) and a posterior cap ( PC 1). The re-entrant angles are always filled by abundant cement. The T4 is widely confluent with the PC 1. The T4 and T3 can be also confluent. In contrast, the dentine connections between the T3 and T2, and between the T2 and AL 1 are very straight. In all the cases, a well-developed LRA 3 is present, which in some specimens can be very deep.

Remarks.— Tibericola vandermeuleni was originally included in Allophaiomys by Agustí (1991). Later, the affinities with Tibericola jordanica from Ubeidiya ( Israel) became evident, particularly because of the very low C/W values, which enabled to differentiate this genus from the several archaic Allophaiomys species ( Allophaiomys deucalion , Allophaiomys pliocaenicus , Allophaiomys ruffoi , Allophaiomys chalinei ). Tibericola vandermeuleni from Barranco de los Conejos is certainly less derived than Tibericola jordanica , which presents a fully developed BSA 3 and an incipient LRA 5. This is in accordance for an older age of the site of Barranco de los Conejos with respect to Ubeidiya, a site dated to 1.4 Ma. A third Tibericola species, Tibericola sakaryaensis was described by Ünay et al. (2001) from the Early Pleistocene Turkish site of Degirmendere. This species is characterized by higher B/W and C/W indexes and a lower A/L index with respect to Tibericola vandermeuleni , values which are closer to those of archaic Allophaiomys species such as Allophaiomys deucalion . In this way, based on the evolution of Tibericola , a sequence can be established for the Early Pleistocene Mediterranean sites of Degirmendere ( Tibericola sakaryaensis ), Barranco de los Conejos ( Tibericola vandermeuleni ) and Ubeidiya ( Tibericola jordanica ).