Dilambdogale gheerbranti, Seiffert, 2010

Seiffert, Erik R., 2010, The oldest and youngest records of afrosoricid placentals from the Fayum Depression of northern Egypt, Acta Palaeontologica Polonica 55 (4), pp. 599-616 : 601-607

Dilambdogale gheerbranti sp. nov.

Figs. 3–7 .

Etymology: In honor of the French paleontologist Emmanuel Gheerbrant, for his numerous contributions to the study of Paleogene Afro−Arabian placental mammals, including “insectivoran−grade” placentals.

Holotype: CGM 66005 , a maxillary fragment preserving the distal alveolus for P3, the crowns of P4 and M1, the mesiobuccal root of M2, and the infraorbital foramen ( Fig. 3 ).

Type locality: Birket Qarun locality 2 (BQ−2), northern Egypt.

Type horizon: Earliest Priabonian (earliest late Eocene), Umm Rigl Member of Birket Qarun Formation.

Material.— The type specimen; DPC 23306 E, left M2; DPC 23307 A, right M3; DPC 23007 H, left m2; DPC 23736 A, right mandibular fragment with m1 and talonid of p4; DPC

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P4

23780C, left m2; DPC 23784D, right M1; DPC 23983C, right mandibular fragment with p4–m1; DPC 24001A, left P4; DPC 24081B, right mandibular fragment with p2–4; DPC 24103A, right mandibular fragment with m1–3; uncatalogued specimens at the CGM.

Diagnosis.—Differs from Miocene−to−Recent tenrecoids primarily in retaining a well−developed metacone and protocone on M1–3, small conules on M1–2, a cuspate (rather than crestiform) stylocone on M1–3, and well−developed talonid and hypoconulid cusps on the lower molars. Further differs from tenrecoids other than Protenrec in having the distal root of P3 placed lingual to the mesiobuccal root of P4. Differs from Widanelfarasia in having a relatively well−developed P4 ectostyle; a shorter postmetacrista on M1; well−developed and cuspate (rather than crestiform) metacone, stylocone, and parastyle on M3; a cuspate, rather than crestiform, stylocone on M2; and in having an m1 with a relatively broad talonid and more buccally placed cristid obliqua, delimiting a relatively poorly−developed hypoflexid. Differs from late Paleocene Todralestes in having a “w”−shaped arrangement of the buccal crests on M1–2, relatively broad stylar shelves, no pre− or postcingula on M1–3, and a P4 ectostyle, −crista, and −fossa. Differs from late Paleocene Afrodon chleuhi in having a dilambdodont M2, relatively broad stylar shelves, and slightly taller molar trigonids. Differs from? Garatherium todrae (known only from upper molars) in lacking distinct upper molar premetaconule cristae and postpara− and premetacristae that contact the mesostyle buccally.

Description.—The dental morphology of D. gheerbranti is known from four upper tooth loci (P4, M1, M2, M3) and six lower tooth loci (p2, p3, p4, m1, m2, m3) ( Figs. 3–6 ). Measurements for upper and lower teeth are provided in Table 1 and Table 2, respectively. The holotype partial maxilla (CGM 66005, Fig. 3 ) contains P4–M1 and preserves the infraorbital foramen, the alveolus for the distal root of P3, and the mesial halves of the lingual and mesiobuccal alveoli for M2; P4, M1, M2, and M3 are also known from isolated teeth ( Fig. 6 ). Partial mandibles together preserve p2–m 3 in place ( Figs. 4 , 5 ), and most of these loci are also known from isolated teeth ( Table 1). Though found in isolation, the M2–3 are assigned to this species because (i) they are of similar size to, and occlude well with, the m 2–3 in the hypodigm, and (ii) they bear a strong resemblance to the upper teeth of younger Widanelfarasia , P2–M3 of which are preserved in place in a single maxilla (Seiffert et al. 2007).

A partial alveolus that is preserved mesial to the double−rooted p2 ( Fig. 4A ) is relatively large, and, as in Widanelfarasia , was presumably for the lower canine. If this interpretation is correct, then (d)p1 was absent in Dilambdogale , as in Widanelfarasia and all extant afrosoricids (Seiffert and Simons 2000). The p3 and p4 both bear tall protoconids; that of p3 is mesially inclined, and has a long postprotocristid on its gradually sloping distal face. There is a tiny paraconid at the base of the p3 protoconid which is slightly lingual to the mesiodistal long axis of the tooth, and a larger hypoconid that is present at the distal terminus of the postprotocristid. There is a very faint and short lingual cingulum just distal to the paraconid, but it does not continue across the rest of the crown. The base of the crown is somewhat staggered with respect to the alveolar plane; the distal aspect of the crown base, above the distal root, extends closer to the alveolar plane than the mesial part of the crown base.

The p4 also has a small paraconid at the base of the protoconid ( Fig. 4A, C ); this cusp is relatively large and robust when compared with the p3 paraconid, but is nevertheless still very small in comparison to the tall p4 protoconid ( Fig. 4C 2 ). The metaconid is approximately half the height of the protoconid ( Fig. 4C 2 ), and is placed lingual, and slightly distal, to that cusp ( Fig. 4C ). A faint protocristid extends from the protoconid to the metaconid. Distinct and closely situated entoconid and hypoconid cusps are present on the lingual aspect of the talonid, with the hypoconid being slightly larger than the entoconid. There are very faint entocristid and hypocristid crests, but no cristid obliqua, and the p4 hypoflexid is deep. There are no lingual or buccal cingulids.

On m1 ( Fig. 4B, C, E ), the paraconid is large, mesially oriented, and is placed slightly buccal and far mesial to the metaconid. There is no premetacristid descending mesially from the metaconid, leaving the trigonid broadly open lingually. The paraconid is connected to the protoconid by an elongate paracristid that bears a distinct notch along its midpoint. The protocristid connecting the metaconid and protoconid varies from being perpendicular to the long axis of the tooth, to being slightly oblique. The metaconid is slightly doi:10.4202/app.2010.0023

lower than the protoconid. The talonid is preserved on DPC 23736A ( Fig. 4E ); the basin is subequal in width to the trigonid, has a relatively shallow hypoflexid, and distinct entoconid, hypoconid, and hypoconulid cusps, the latter of which projects distally. The cristid obliqua meets the posterior wall of the trigonid slightly buccal to its midpoint. The m2–3 ( Fig. 4B, D ) differ from m 1 in having oblique cristids that terminate midway between the protoconid and metaconid cusps, protocristids that are consistently transversely oriented, and relatively deep hypoflexids. All lower molars have talonids that are slightly longer than trigonids, oblique cristids and hypocristids that meet at a sharp angle, and distinct precingulids.

The mesiobuccal aspect of P4 is missing on all of the specimens that have been recovered thus far, but the alveolus for the mesiobuccal root is placed mesial to the preserved part of the crown, suggesting that Dilambdogale probably had a prominent parastyle on P4, as has been documented for Todralestes ( Gheerbrant 1991b) and Widanelfarasia (Seiffert et al. 2007) . The P4 bears a tall paracone cusp and a very small and mesially placed protocone. Like many crown tenrecoids, Dilambdogale also has a distinct ectostyle cusp distal and buccal to the apex of the paracone. DPC 24001A has a very faint ectocrista descending from the buccal face of the paracone to meet the ectostyle. Together with the elongate postparacrista, these structures delimit a shallow distolabial ectofossa. The P4 has no conules and no pre− and postcingula, but a tiny crestiform hypocone is present, and is connected to the protocone by a weak postprotocrista. Though the parastylar region is missing, it is clear that it would have protruded from a very low point on the mesial face of the paracone.

A relatively unworn M1 is present in the holotype specimen ( Fig. 3 ). This locus is also represented by an isolated tooth with a more worn stylar region ( DPC 23784 D; Fig. 6D ). The M 1 resembles Widanelfarasia in having a “W”−shaped arrangement of the pre− and postparacristae and pre− and postmetacristae. In mesial and distal view, the paracone, metacone, and protocone are approximately equal in height. The paracone and metacone show some “fusion” of their bases. The stylar region of the M 1 in the holotype specimen exhibits some wear, but it is clear that the stylocone would have been the largest and tallest cusp on the buccal aspect of the tooth, followed by the parastyle. It appears that there was also a very small mesostyle at the trough of the ectoflexus, and a similarly small cusp “D” on the periphery of the metastylar lobe. This interpretation is supported by the clear presence of these cusps on M2 (see below). The trigon is restricted due to encroachment of the centrally placed para− and metacone and is bordered lingually by distinct pre− and postprotocristae. A small, lingually−placed paraconule is present and bears a postparaconule crista on DPC 23784 D but not on CGM 66005 ; the preprotocrista bypasses the lingual aspect of the paracone and is continuous with the parastylar area. There is a short but distinct hypoparacrista that connects the paraconule and the lingual face of the paracone on DPC 23784 D, but this is absent on the holotype specimen. A small metaconule is present but is more buccally placed than the paraconule. A distolabially oriented postmetaconule crista leaves the trigon open distally on DPC 23784 D, but this crest is not present on CGM 66005 . There is no premetaconule crista, and no pre− or postcingula, on either specimen .

M2 is represented by two isolated specimens ( DPC 23306 E, Fig. 6B ; DPC 23780 C, Fig. 6C ). The M 2 is much broader (buccolingually) than M1. Of the two primary buccal cusps, the paracone is closest to the protocone (and is placed farther from the buccal margin than is the metacone). In lingual and buccal view, the paracone is taller than the metacone ( Fig. 6C 2 ). When compared with M1, the protocone is relatively prominent, but the trigon is more constricted mesiodistally. The stylar shelf bears a tall and distinct stylocone and a much smaller mesostyle and cusp “D” ( Fig. 6C 2 ). The parastyle is prominent, and the parastylar lobe forms a prominent mesial “hook” which, based on the placement of the mesiobuccal root of M2 implanted in the holotype partial maxilla, would have curved around the buccal aspect of the metastylar lobe of M1, as in Widanelfarasia (Seiffert et al. 2007) . A paraconule is not evident on DPC 23780 C, but is present, though minute, on DPC 23306 E; on the latter specimen the paraconule is connected to the base of the paracone by a short postparaconule crista. As on M1, the paraconule is situated closer to the protocone than is the metaconule, there is no premetaconule crista, and there are no pre− or postcingula .

M3 (represented solely by DPC 23307A, Fig. 6A ) has well−developed paracone and metacone cusps, the postpara− and premetacristae of which are slightly buccally oriented in a weakly “W”−shaped arrangement. The metacone is smaller than the paracone, both in height and in volume. The postmetacrista is buccally (rather than distally) oriented and is continuous with the buccal aspect of a very broad stylar shelf. The stylocone and parastyle are distinct and well−developed, and, at least on DPC 23307A, an accessory cuspule is present on the buccal face of the tooth just distal and labial to the parastyle. A crestiform metaconule is present but no paraconule is evident, perhaps due to wear. It is clear that there is no postparaconule crista and no pre− or postcingula.

Various fragments of the mandibular corpus are preserved (see, e.g., Figs. 4A, B , 5 ). The corpus is fairly shallow, being only slightly taller than trigonid height, and bears a mental foramen below m1 ( Fig. 5 ) and p2. Little is preserved of the distal part of the mandible but the anterior part of the masseteric fossa appears to have been well−developed.

Humerus.—A small distal humerus ( Fig. 7 ) from locality BQ−2 (DPC 24108A) is attributed to Dilambdogale gheerbranti on the basis of size, morphology, and relative abundance. The only other small mammals known from BQ−2 that the humerus could be attributable to (on the basis of size alone) is the chiropteran Qarunycteris ( Gunnell et al. 2008) and the anomaluroid rodent Shazurus (Sallam et al. 2010a) . DPC 24108A exhibits none of the distinctive derived features of chiropteran distal humeri (see, e.g., Simmons and Geisler 1998), excluding the possibility that the specimen is attributable to Qarunycteris . The morphology of a distal humerus of the large anomaluroid Kabirmys from BQ−2 (Sallam et al. 2010b, c) is radically different from that of DPC 24108A, suggesting that its smaller relative Shazurus is unlikely to exhibit the morphology observable on DPC 24108A.

DPC 24108A does bear clear morphological resemblance to the distal humeri of some extant tenrecoids, particularly species of Microgale , which lends additional support for its attribution to Dilambdogale . Features shared with many species of Microgale , such as the presence of an entepicondylar foramen, a moderately developed brachioradialis flange, a deep radial fossa, a shallow olecranon fossa, and an ovoid capitulum with a proximodistally tall but laterally tapering capitular tail, are, however, presumably primitive within Afrosoricida , and possibly within Afrotheria . Perforation of the bony lamina separating the olecranon and radial fossae, as occurs in DPC 24108A, also occurs variably in species of Microgale (Salton and Sargis 2008) . The medial aspect of the trochlea is missing, but in distal view there is a distinct notch separating the capitulum from the lateral aspect of the tro−

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Widanelfarasia Dilambdogale Chambilestes ? Garatherium Afrodon Todralestes chlea, as in species such as Microgale talazaci . DPC 24108A also preserves the distal part of a sharp deltopectoral crest, the more proximal part of which trends laterally. DPC 24108A bears no special resemblance to the humeri of Malagasy Geogale and African potamogalids, which are likely to be autapomorphic in lacking entepicondylar foramina and having relatively reduced brachioradialis flanges. The humeri of golden moles reflect their highly fossorial existence in having features such as elongate medial epicondyles, globular capitula, mediolaterally long trochleae, and humeral shafts that are strongly laterally canted relative to the long axis of the distal articulation (e.g., Asher and Avery 2010). None of these features are seen in DPC 24108A.

The morphology of DPC 24108A is consistent with Dilambdogale having been a very generalized terrestrial quadruped. The combination of a shallow olecranon fossa and a deep radial fossa suggest that Dilambdogale habitually maintained postures in which the forearms were typically held in acute flexion. DPC 24108A bears none of the structural features of the distal humerus that are typically correlated with saltatory locomotion, habitual fossoriality, arboreality, or dedicated aquatic behavior in extant mammals.

Comparisons.—As already noted, the fossil record of small mammals is relatively poor in Afro−Arabia (Seiffert 2010), and as such it is rare for “insectivoran−grade” placentals (sensu Asher 2005) to be documented by more than a few tooth loci. Therefore Dilambdogale , despite being represented solely by P4–M3 and p2–m3 and a distal humerus, actually allows for more extensive comparisons than many other important taxa from Afro−Arabian Paleogene, some of which are only documented by upper teeth (e.g., Garatherium , Chambilestes ).

The genus that is best−documented from older horizons in Africa is latest Paleocene Todralestes variabilis ( Gheerbrant 1991b, 1994). Todralestes differs from Dilambdogale in retaining upper molar features which, based on their occurrence in other afrotherians (e.g., Seiffert 2007), may be primitive within that clade—e.g., relatively narrow stylar shelves, short prepara− and postmetacristae, linear centrocristae, absence of deep ectoflexi, presence of pre− and postcingula, and, in some individuals, small hypocones on M1–2 ( Fig. 8F ). Stylar cusps are also poorly−developed and crestiform in Todralestes , but are much more prominent in Dilambdogale , and Todralestes lacks an ectostyle on P4, whereas this cusp is very prominent in Dilambdogale . The morphology of P 4 in Todralestes is otherwise also very similar to that of Dilambdogale in having a long postparacrista and a very low, small, and mesially positioned protocone. Dilambdogale is more similar to Todralestes in the lower dentition, differing primarily in having larger para− and hypoconid cusps on p3, an entoconid on p4, relatively broad lower molars with more distinct talonid cusps, and molar protocristids that tend to be less obliquely oriented with respect to the long axis of the molar crown.

Seiffert et al. (2007) noted that Todralestes , Widanelfarasia , and Protenrec all have an odd configuration of the maxilla and P3–4 complex, in which the distal root of P3 is lingually placed, being mesial to the lingual root of P4, rather than being mesial to the mesiobuccal root as in other afrotherians. This feature is also seen in Dilambdogale ( Fig. 3 ). This morphology appears to be related to the placement of the rostral aperture of the infraorbital foramen; in all of the aforementioned taxa, the rostral aperture is placed just dorsal to the mesiobuccal root of P4, and the alveolar process of the maxilla lateral to the P3 is similarly offset medially, leading to a distinctive constriction of the palate at the junction between P3 and P4. This morphology is also seen in the extant Malagasy tenrec Geogale ( Butler 1984) , and, interestingly, the early Eocene hyaenodontid Koholia from Algeria ( Crochet 1988). These taxa also all have a greatly enlarged paracone on P4, a mesiobuccal root of P4 that is widely exposed in lateral view, and, in those taxa that preserve a P 3 in place ( Widanelfarasia , Protenrec , and Geogale ) there is a distinctly “stepped” transition from the apex of the P4 to that of P3 ( Fig. 3 ) This surely would have also been the case in Dilambdogale and Todralestes , given the small size of the occluding p3, and the position of the distal P3 alveolus far dorsal to the base of the P4 crown. As strange as this overall pattern may be, its presence in a variety of early Paleogene African mammals with very different dental morphology suggests that this condition may be plesiomorphic at a high taxonomic level within Afrotheria .

The upper dentition of the alleged adapisoriculid Afrodon chleuhi , from the same latest Paleocene deposits that yielded remains of Todralestes variabilis ( Gheerbrant 1988, 1995; Gheerbrant et al. 1998), is more similar to Dilambdogale than is Todralestes in having relatively broad stylar shelves, longer and more buccally oriented prepara− and postmetacristae, more pronounced ectoflexi, a relatively lingually placed paraconule, and absence of pre− and postcingula. However A. chleuhi is not as derived as Dilambdogale in that it retains a linear centrocrista and a stylar shelf that is not as broad ( Fig. 8E ); the stylar cusps are also more crestiform in A. chleuhi . The lower molars and p4 of A. chleuhi are also relatively broad, with deep hypoflexids (as in Dilambdogale ), and its p4 talonid is more complex than that of Todralestes . Afrodon tagourtensis , from the earliest Eocene of Morocco ( Gheerbrant 1993; Gheerbrant et al. 1998), is even more similar to Dilambdogale than is A. chleuhi in having a relatively elongate buccal margin on M1, and, on p4, a distinct entoconid.

Of all other older Afro−Arabian mammals, Dilambdogale is most similar in its occlusal morphology to Garatherium mahboubii from the early Eocene of Algeria ( Crochet 1984; Mahboubi et al. 1986). A similar species that has been referred to as? Garatherium todrae is also known from the latest Paleocene localities that preserve remains of Afrodon chleuhi and Todralestes variabilis ( Gheerbrant et al. 1998) . Unlike Afrodon and Todralestes , but as in Dilambdogale , Garatherium exhibits well−developed dilambdomorphy, with a “W”−shaped arrangement of crests connecting the paracone and metacone ( Fig. 8D ). Like Dilambdogale , Garatherium has distinct parastyle, stylocone, mesostyle, and “D” cusps along the buccal margin, but in Garatherium the mesostyle and cusp “D” are even more prominent, and the mesostyle is met by the postpara− and premetacristae.Further resemblances include the lack of pre− and postcingula. At present no lower teeth or upper premolars have been attributed to Garatherium , limiting comparisons with Dilambdogale , however the distinctive upper molar features shared by the two taxa increase the likelihood that the two species may be closely related, and that G. mahboubii is indeed a placental as argued by Gheerbrant (1991a), and not a peradectine marsupial as was initially suggested ( Crochet 1984; Mahboubi et al. 1986).

The enigmatic genus Chambilestes from the early or early middle Eocene of Tunisia ( Gheerbrant and Hartenberger 1999; Fig. 8C ) differs from Dilambdogale in having distinct pre− and postcingula, small hypocones on M1–2, well−developed postpara− and premetaconule cristae, and a relatively narrow stylar shelf. On the basis of predicted occlusal relationships, Seiffert and Simons (2000) suggested that Chambilestes might have affinities with Widanelfarasia , but now that the upper dentition of Widanelfarasia is known (Seiffert et al. 2007), this possibility appears remote. Chambilestes might be more closely related to Todralestes (Seiffert 2010) , specifically early Eocene Todralestes butleri ( Gheerbrant 1993) .

Of all Paleogene Afro−Arabian taxa, Dilambdogale is most similar to latest Eocene Widanelfarasia (Seiffert and Simons 2000; Seiffert et al. 2007). The upper and lower teeth of these genera exhibit a series of striking resemblances, but Dilambdogale appears to be more primitive in having relatively broad lower molar talonids ( Fig. 9), a larger metacone on M2, and a distinct and cuspate metacone on M3. In each of these features, Dilambdogale is similar to early African “adapisoriculids” such as Afrodon , while Widanelfarasia exhibits derived features that arguably align the genus with later tenrecoids (Seiffert et al. 2007).

Stratigraphic and geographic range.—Earliest Priabonian, northern Egypt.

Figures

Fig. 3. Holotype maxilla of the afrosoricid placental Dilambdogale gheerbranti gen. et sp. nov., from the earliest late Eocene (earliest Priabonian) locality BQ−2, Birket Qarun Formation, Fayum Depression, northern Egypt. A. Occlusal view of CGM 66005, left maxillary fragment preserving the alveolus for the distal root of P3, crowns of P4–M1, and partial alveoli for the mesiobuccal and lingual roots of M2. B. Line drawing of CGM 66005 in lateral view, showing the position of the infraorbital foramen and the orbital rim.

Fig. 4. Lower dentition of the afrosoricid placental Dilambdogale gheerbranti gen. et sp. nov. from the earliest late Eocene (earliest Priabonian) locality BQ−2, Birket Qarun Formation, Fayum Depression, northern Egypt. A. Oblique lingual view of DPC 24081B, a right mandibular fragment preserving the alveolus for the lower canine and the crowns of p2–4. B. DPC 24103A, right mandibular fragment preserving the worn crowns of m1–3 in oblique lingual (B1) and occlusal (B2) views. C. DPC 23983C, a right mandibular fragment preserving p4–m1 in occlusal (C1) and lingual (C2) views. D. DPC 23783B, a left mandibular fragment preserving m2–3 in occlusal (D1) and lingual (D2) views. E. Occlusal view of DPC 23736A, a right mandibular fragment preserving the talonid of p4 and the complete crown of m1. F. DPC 23307H, a left m2 in occlusal view.

Fig. 5. Buccal view of DPC 23783B, a left mandibular fragment of the afrosoricid placental Dilambdogale gheerbranti gen. et sp. nov., from the earliest late Eocene (earliest Priabonian) locality BQ−2, Birket Qarun Formation, Fayum Depression, northern Egypt, preserving m2–3.

Fig. 6. Upper dentition of the afrosoricid placental Dilambdogale gheerbranti gen. et sp. nov. from the earliest late Eocene (earliest Priabonian) locality BQ−2, Birket Qarun Formation, Fayum Depression, northern Egypt. A. DPC 23307A, right M3, in occlusal (A1) and distal (A2) views. B. DPC 23306E, left M2, in occlusal view. C. DPC 23780C, left M2, in occlusal (C1) and buccal (C2) views. D. DPC 23784D, right M1, in occlusal (D1) and mesial (D2) views. E. DPC 24001A, left P4, in distal (E1) and occlusal (E2) views.

Fig. 7. DPC 24108A, right distal humerus attributed to the afrosoricid placental Dilambdogale gheerbranti gen. et sp. nov., from the earliest late Eocene (earliest Priabonian) locality BQ−2, Birket Qarun Formation, Fayum Depression, northern Egypt.

Fig. 2. Stratigraphic placement of afrosoricid−bearing localities in the later Paleogene rocks exposed in the Fayum area, and proposed correlation of local polarity zones to the Geomagnetic Polarity Timescale (GPTS), following Seiffert (2006) and Seiffert et al. (2008). Locality BQ−2, which yielded the remains of Dilambdogale gheerbranti described here, is estimated to be ~37 Ma; Quarry I, which produced remains of Qatranilestes oligocaenus, is estimated to be ~29.5–30 Ma.

Fig. 8. Comparison of occlusal morphology of the upper second molar (scaled to the same approximate buccolingual width) in a series of Paleogene African mammals with possible afrosoricid affinities. A. Widanelfarasia bowni (latest Eocene, Jebel Qatrani Formation, Egypt), based on Seiffert et al. (2007). B. Dilambdogale gheerbranti (earliest late Eocene, Birket Qarun Formation, Egypt). C. Chambilestes foussanensis (late early or early middle Eocene, Chambi, Tunisia), based on Gheerbrant and Hartenberger (1999). D.?Garatherium todrae (late Paleocene, Jebel Guersif Formation, Morocco), based on Gheerbrant et al. (1998). E. Afrodon chleuhi (late Paleocene, Jbel Guersif Formation, Morocco), based on Gheerbrant (1988). F. Todralestes variabilis (late Paleocene, Jbel Guersif Formation, Morocco), based on Gheerbrant (1991b).