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Unnamed Enspel Formation Fossil Ants
Jessen (2020) examined ant fossils from the Enspel Formation, Rhineland-Palatinate, Germany (Oligocene) (see the Antwiki Enspel page for a general overview of the material she studied). The specimens were collected as part of yearly excavation campaigns between 1995 and 2013 conducted by the Directorate General for Cultural Heritage Rhineland-Palatinate, Directorate Archaeology, Department of Earth History.
Introduction
The majority of the fossil ant species described here belong to the tribe Stenammini. This tribe is well represented in the fossil record, especially by the genera Aphaenogaster with 19 species, and Paraphaenogaster with 4 species (referring to Antwiki, August, 2019). According to Branstetter et al. (2016, p. 8) “... this richness belies the fact that the placement of many of these fossil taxa within the tribe, or within genera in the tribe, is dubious, largely due to uncertainty in both diagnostic characters and generic boundaries”. This statement also applies to some extent to the species of the genera Aphaenogaster and Paraphaenogaster described here. Gyne of the two genera Aphaenogaster and morphogenus Paraphaenogaster are very similar in the following essential morphologic features: size, more or less elongate head, triangular mandibles, 12-segmented antenna without distinct club, high and arched mesonotum, pedunculate petiole, features for distinguishing between the two genera are poor. In Aphaenogaster, the cell rm is developed, in Paraphaenogaster it is not. The morphogenus Paraphaenogaster was established by Dlussky (1981), basically based on males showing a specific wing venation pattern.
Specimen Depository
The material was studied and stored in the Directorate General for Cultural Heritage Rhineland-Palatinate, Directorate Archaeology, Department Earth History, Mainz, Germany. In the long term, they will be deposited in the “Typothek” of the State Collection of Natural History Rhineland-Palatinate/Museum of Natural History Mainz, Mainz, Germany (NHMM).
Specimen Numbers and Codes
Abbreviation of specimen numbers:NHMM= Naturhistorisches Museum Mainz; PE = Palaeontology Entomology; 2009 = found in 2009; 6281 = running inventory number of the year; LS = Landessammlung (State Collection). Information on the layer is given. They refer to the standard profile in Felder et al. (1998).
Paraphaenogaster
Paraphaenogaster cf. loosi Specimen: NHMM-PE2013/5037-LS, winged gyne Position: Head dorsal, alitrunk, petiole, postpetiole (partly), first gastral tergite dorsolateral.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S14.
Remarks: This specimen has not been classified as the paratype of Paraphaenogaster loosi, because the morphology of its petiole and postpetiole is not clear. It differs from P. loosi in its colour. As mentioned above, the colour has no taxonomic value, see Chapter: Material and Methods.
Paraphaenogaster cf. loosi
Specimen: NHMM-PE1995/7896-LS a+b, winged gyne. Position: Head from ventral, alitrunk from ventrolateral, petiole, postpetiole, and gaster from lateral.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S12.
Paraphaenogaster cf. schindleri
Specimen: NHMM-PE2010/5462-LS, winged gyne. Position: Head, alitrunk, and petiole dorsal, postpetiole and first gastral segment dorsolateral.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S6-10.
Remarks: Unfortunately, central parts of the head, like posteriorly extending area of the clypeus and the frontal triangle, are not preserved. Also, it is not clear if this species has two almost parallel running long carinae like Paraphaenogaster schindleri. As this specimen has some characteristics, like body size, shapes of head, mandibles, petiole and postpetiole in common with P. schindleri, it is specified as Paraphaenogaster cf. schindleri. It is not allocated to the genus Messor because CI in extant Messor gyne is in most species distinctly above 100. Also, outer lines of mandibles are not strongly bend. An assignment to the genus Aphaenogaster is not strongly supported. Neither by the relatively high CI nor by its petiole shape, nor by its wing venation pattern. Vein rs-m is very weak.
Paraphaenogaster cf. schindleri
Specimen: NHMM-PE2002/5019-LS, winged gyne. Position: Head, alitrunk petioli, and gaster from lateroventral.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S14.
Remarks: This specimen resembles Paraphaenogaster schindleri in body length, head size and head shape, the latter especially with regard to the occipital corners. Although dorsal side of head cannot be seen, an assignment as Paraphaenogaster cf. schindleri appears to be appropriate.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE1995/5175-LS, winged gyne. Formicidae indet. Wedmann 2000: 68, Fig. 23 (wing).
Position: Parts of alitrunk, petiole, postpetiole, and parts of gaster from lateral, one forewing. Head and legs are missing.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Remarks: This specimen most probably has a BL > 11. Based on the combination of an arched mesonotum, protruding scutellum, its petiole and postpetiole shape and its wing venation pattern; this specimen is allocated to the genus Paraphaenogaster. As the head is completely missing, specimen cannot be assigned more precisely.
Ten males were examined more closely. All show the typical Paraphaenogaster wing venation pattern. Males show slight differences in shape and sculpture of head, pronotal neck, alitrunk, petiole and postpetiole. However, these differences are considered too small to exist as an independent species under consideration of possible taphonomic influences. Only one new species is described from this variety of conservation images.
Paraphaenogaster cf. wuttkei
Specimen: NHMM-PE1995/6227-LS, winged male.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Position: Head, alitrunk dorsal, petiole lateroventral; postpetiole dorsolateral, parts of alitrunk and complete gaster missing.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE2001/5194-LS, male.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56-24.79 Ma, Mertz et al. 2007), layer S12.
Position: Head ventral, alitrunk lateral, petiole dorsolateral, postpetiole dorsal, disarticulated, gaster partly missing.
Remarks: This specimen is characterised by its indication of a pronotal neck. It differs from P. wuttkei in BLw/oG (5.5 vs. 6.2 in P. wuttkei) and FWL (6.1 vs. 9.1 in P. wuttkei). The strong parallel striation on the petiole has this specimen in common with the sample NHMM-PE2001/5160-LS. The latter, however, does not show any indication of a neck.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE2010/5697-LS, male.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Position: Head ventral, alitrunk lateroventral, petiole lateral, gaster dorsal.
Remarks: The specimen NHMM-PE2010/5697-LS is characterised by its comparably nodiform postpetiole with a narrowed helcium. Postpetiole constricted towards gaster. Both petioles with fine dense striae. Postpetiole without dorsal notch. In addition, size and forewing length is comparably small (BLw/oG: 5.05, FWL: 5.7).
Paraphaenogaster incertae sedis
Specimen: NHMM-PE2010/5576-LS, male (photograph, see Supplementary Data 2: Fig. 1)
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S14 u.
Position: Head dorsal, alitrunk lateral, petiole lateroventral, only remnants of the postpetiole are preserved, only first gastral segment and the second gaster sternite are preserved. Remarks: In this specimen, the pronotum seems to be stretched forward so that it gets a neck-shaped impression, but no distinct pronotal neck seems to be developed. The head is also not extended to the back.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE2001/5160-LS, male.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S12.
Position: Head dorsal, alitrunk lateral, petiole and postpetiole dorsolateral, gaster strongly damaged, wings only partly preserved.
Remarks: This specimen differs from all other Paraphaenogaster males by a combination of its slender petiole, which ends posteriorly in a flat node, the barely constricted helcium, the strong regular striation and the thickened posterior margins of both petioles.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE1995/7286-LS, male.
Position: Body parts are preserved in different positions: head lateroventral, alitrunk lateral (deformed), petiole and postpetiole lateroventral, gaster dorsal.
Remarks: Petiole and postpetiole of this specimen are similar to those of the sample NHMM-PE1995/6227-LS. Clypeus and frontal triangle unfortunately cannot be seen.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE1997/6133-LS, winged male.
Position: Head missing, alitrunk lateral, petiole and postpetiole dorsolateral, gaster lateral.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Paraphaenogaster incertae sedis
Specimen: NHMM-PE2001/5139-LS, male.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S12.
Position: Head ventral, alitrunk dorsolateral, petiole and postpetiole missing, gaster partly missing.
Stenammini
Stenammini incertae sedis Specimen: NHMM-PE2010/5496-LS, winged gyne.
Position: Head, alitrunk, petiole, postpetiole (partly), gaster (partly) dorsolateral.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S12.
Remarks: The wing venation pattern is not preserved. The head in slightly deformed, so its head shape and CI are not clear. It is similar to Paraphaenogaster bizeri in size and general habitus, but there is no clear evidence to distinguish it clearly between the two genera: Paraphaenogaster or Aphaenogaster. This specimen is characterised by its well developed, rounded propodeal lobes. This definitely makes it different from Paraphaenogaster loosi; in P. bizeri, the potential propodeal lobes cannot be assessed. It is not assigned to Messor, because shapes of head and mandibles do not support this. It is not assigned to Stenamma, because antennal sockets are not close and there is no indication for the existence of neither two distinct ridges nor for a long finger-like projection of the median part of the clypeus that extends backwards between the antennal sockets.
Stenammini incertae sedis
Specimen: NHMM-PE1995/9611-LS, gyne.
This specimen is lacking information on taxonomically important body parts, like clypeus, antenna, spines and forewings. Based on some characteristic features, like pedunculate petiole, highly arched mesonotum, triangular-shaped mandibles, it could be allocated to the genus Aphaenogaster or Paraphaenogaster.
Position: Head from ventrolateral, alitrunk, petiole, postpetiole, and parts of gaster lateral.
Type locality and horizon: Enspel Oilshale, Rhineland- Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S6-8.
Remarks: This specimen is characterised by its combination of BL > 12; its big head in relation to the length of the alitrunk, a remarkably high and short alitrunk, its dorsally rounded, dome-shaped petiolar node and its thick transverse stripes at the posterior face of the propodeum. Further specimens are needed to give a valid species diagnosis.
Myrmica
Myrmica cf. schaefersi
Specimen: NHMM-PE2010/5676-LS, winged gyne.
Position: Head, alitrunk, petiole, postpetiole and parts of gaster from dorsolateral.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Remarks: The colour of the clypeus is not darkened as with Myrmica schaefersi. This may reflect a natural diversity of colouration, or it may have been caused by various taphonomic processes. The clypeus is clearly striated in this specimen, but the two strong ridges running in M. schaefersi from the frontal lobe to the front edge of the clypeus are not visible here. The absence of the two ridges and the larger CI do not provide sufficient evidence for the creation of a separate species, as both characteristics may be different due to conservation. Apical funicular segment shows an additional suture. This is not valued as a separate segment, as it most likely may be caused by taphonomic processes.
Myrmicinae
Myrmicinae incertae sedis
Specimen: NHMM-PE2011/5020-LS, worker.
Position: Head dorsal, alitrunk dorsolateral, petiole, postpetiole and gaster most likely from dorsolateral.
Type locality and horizon: Enspel Oilshale, Rhineland-Palatinate, Germany. Enspel Formation, Upper Oligocene, MP 28; (24.56–24.79 Ma, Mertz et al. 2007), layer S16.
Remarks: This specimen differs from all known fossil worker of the genera Paraphaenogaster or Aphaenogaster by its almost rectangular head shape and its comparable large eyes. Because this worker specimen is lacking antenna and the complete petiole, an allocation on genus level is not appropriate. Even the assignment to the subfamily Myrmicinae is based on an assumption.