Subfamily Limoniinae Speiser, 1909 (Diptera, Limoniidae) from Baltic Amber (Eocene): The Genus Elephantomyia Osten Sacken, 1860

A revision of the genus Elephantomyia Osten Sacken (Diptera: Limoniidae) from Baltic amber (Eocene) is presented. Four species—E. baltica Alexander, E. brevipalpa Loew, E. longirostris Loew, and E. pulchella Loew—are redescribed and documented with photographs and drawings. In addition, two new species of the genus are described: Elephantomyia bozenae sp. nov., and Elephantomyia irinae sp. nov. All these fossil species are placed within the subgenus Elephantomyia. A key to the extinct species of Elephantomyia is provided, and the genus’ ecological pattern and evolutionary aspects are discussed.

Fossil representatives of the genus Elephantomyia are known from amber inclusions, mainly from Eocene Baltic amber, but none were assigned to a subgenus. Four species of Elephantomyia are known from the Baltic amber: E. baltica [8], E. brevipalpa [9], E. longirostris [9], and E. pulchella [9]. Three of these taxa-E. brevipalpa [9], E. longirostris [9], and E. pulchella [9]were originally described as species of Toxorhina by Loew [10]. Osten Sacken [3] initially placed Loew's fossils within the genus Limnobiorhynchus, but later [11] considered all of them part of his genus Elephantomyia. Although Scudder [12] claimed Toxorhina was a valid genus containing Loew's fossil species and a single recent species, thereby rejecting their placement within Elephantomyia, a later revision [13] again ascribed these species to the genus Elephantomyia (Table 1). Handlirsch [14] listed Loew's species within the genus Toxorhina, but listed the Osten Sacken [3] and Meunier [13] combinations as synonyms. Evenhuis [15] listed all Loew's species in the genus Elephantomyia. In addition to the species from Baltic amber, two species are also known from the Miocene Dominican amber: Elephantomyia grata [16], and an individual not identified to species level [17].
The discovery of a new Elephantomyia specimens from Baltic amber has allowed the description of two new extinct species within this genus. Further, this new research, which incorporates both previously known and new fossil materials, has enabled the revision of all Elephantomyia species from Baltic amber, and placement of these taxa into the subgenus Elephantomyia.

Materials and Methods Specimens
The study herein is based on material from the collections: Institute of Systematic and Evolution of Animals, Polish Academy of Sciences (ISEA PAS) (15 specimens); Museum of the Earth, Polish Academy of Sciences, Warsaw (MEPAS) (1 specimen); University of Göttingen (GMUG)

Imaging
The specimens were studied using a Nikon SMZ 1500 stereomicroscope equipped with a Nikon DS-Fi1 camera. Drawings were produced using both specimens and photographs.

Measurements
All measurements were taken with NIS-Elements D 3.0 software. The length of discal cell was measured from its basal edge to the point of connection of vein m-m with vein M 3 . The length of M 3 is given from the wing margin to the point of connection of vein m-m with vein M 3 . The relations of rostrum, wing, and abdomen length are only given in those cases where the structures are not distorted. Chresonymy is used according to open nomenclature rules proposed by Matthews [21] and Bengtson [22] for the names of fossil taxa.

Nomenclatural acts
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix "http://zoobank.org/". The LSID for this publication is: urn:lsid:zoobank.org:pub: 546335C5-B194-4221-9F68-F20A3E8E2588. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories:
Wing (Fig. 1C): 8.5 mm long; pterostigma present, not darkened, oval, pale brown; vein Sc moderate length, ending opposite two-thirds Rs length; sc-r short, twice the distance from Sc tip; vein Rs gently arcuate, only slightly longer than twice length of basal section of R 5 , shorter than the length of R 2+3+4 ; R 1 ending approximately two-fifths length of R 2+3+4 ; r-r (R 2 ) atrophied; M 3 one and half times longer than d-cell; cross-vein m-cu before d-cell mid-length, just after of fork of Mb; A 1 and A 2 almost straight.
Leg: tibial spurs not visible. Hypopygium: not clearly visible. Ovipositor: only male specimens known. Remarks. The specimen is well preserved, but the number of segments of antenna is probably 14, but the flagellomeres are very crowded and the boundaries between individual flagellomeres is not clear.

Description
Body: brown, distal part of abdomen darker than rest of body, body 3.16 mm long (without rostrum). Head: rostrum elongate, 2.14 mm long, shorter than wing, ending just after half wing length, rostrum longer than abdomen (Fig. 2C
Wing (Figs. 4F, 5A, E): 4.68 mm long, 1.18 wide (female); pterostigma present, not darkened, oval, pale brown; vein Sc moderate length, ending after half Rs length; sc-r short, twice distance from Sc tip; Rs slightly arcuate, at least three times length of R 5 basal section, almost as long as, or longer than, R 2+3+4 ; R 1 short, ending approximately one-third length of R 2+3+4 ; pterostigma base just after of Sc tip and before the bifurcation of Rs into R 1 , R 2+3+4 , and R 5 (female); r-r (R 2 ) atrophied; M 3 approximately one and half times longer than d-cell; cross-vein m-cu just before d-cell mid-length; A 1 almost straight, A 2 slightly waved.
Leg: tibial spurs presented. Hypopygium (Figs. 4E, 5D): 0.4 mm long, gonocoxite as in other species of the genus, approximately twice as long as wide, with elongate, narrow, lobe-shaped interbase; outer gonostylus narrow, not forked at the end, inner gonostylus widened in half of length, strongly narrowed in final one-third of its length; outer and inner gonostyles directed internally; aedeagus elongate.
Remarks. In contrast to other Baltic amber species of Elephantomyia, the pterostigma base in E. brevipalpa is distinctly shifted towards the base of wing, being just distal to the tip of Sc and proximal of the bifurcation of Rs into R 1 , R 2+3+4 , and R 5 (Fig. 6A-C). However, this feature is only noted in the female wing, as details of the male wing are not observable due to poor preservation.  ) irinae sp. nov., the rostrum is distinctly shorter than wing, ending just after half wing length; in E (E.) baltica, the rostrum is as long as the wing, whereas in. E. (E.) longirostris, the wing is only one-fifth longer than the rostrum, and in E. (E.) pulchella the wing is one-third longer than the rostrum. In contrast to E. bozenae sp. nov., where the rostrum is longer than the abdomen, the rostrum in E.
Ovipositor: only male specimens known.
Wing (Figs. 9E, 10B, D): 4.23-8.5 mm long, 1.04-1.41 mm wide; pterostigma present, not darkened, oval, pale brown; vein Sc moderate length, ending after half Rs length; sc-r short, at end of Sc; vein Rs arcuate, at least three times length of basal section of R 5 , shorter than length of R 2+3+4 ; R 1 ending at approximately half length of R 2+3+4 ; r-r (R 2 ) atrophied; M 3 approximately 1.5 times longer than d-cell length; cross-vein m-cu situated just after fork of Mb into M 1+2 and M 3+4 ; A 1 almost straight, A 2 slightly waved.
Ovipositor: only male specimens known. Remarks. The specimens No. K5100Z4080 (GMUG) and No. 87 (GMUG), reported as E. longirostris by Alexander [8], lack sufficient features to allow them to be clearly placed within this species. In these specimens, the rostrum is not very elongate, being about half of the wing length or shorter, and is shorter than, or as long as, the abdomen. Further study of these specimens is necessary to clarify their taxonomic status.

Diagnostic characters
E. (E.) pulchella differs from all other species of the genus Elephantomyia known from the Baltic amber in the position of cross-vein m-cu, which in this species is located at exactly half dcell length, whereas in other species of this genus, this cross-vein is situated just after the fork of Mb into M 1+2 and M 3+4 or just before the d-cell mid-length. E. (E.) pulchella also differs from the other fossil Elephantomyia species in the ratio of wing, rostrum, and abdomen length. In E. (E.) pulchella, the rostrum is one-third shorter than the wing, but is the same length, or slightly longer than, the abdomen. Moreover, in E.  The Genus Elephantomyia Osten Sacken, 1860 from Baltic Amber Head (Figs. 12C, 13B): head width 0.36-0.52 mm; rostrum elongate, 2.22-2.77 mm long, as long as or slightly longer than abdomen, one-third shorter than wing (Fig. 11C). Antenna (Figs. 11A, 12C, 13A, B) relatively short, 0.70-0.74 mm long, 15-segmented; flagellar segments crowded; scape elongate, cylindrical; pedicel wide; first flagellomere elongate, widened; second flagellomere short, widened, crowded with flagellomere 1; flagellomeres 3-6 short and widened; flagellomeres 7-15 elongate, cylindrical; final segments elongate, narrowed at apex; flagellomeres 1-5 with two elongate setae; flagellomeres 6-9 with three elongate setae; flagellomeres 10-13 with four elongate setae; elongate setae much longer than length of segments bearing them; palpus (Fig. 11B) elongate, 0.46 mm long, 4-segmented, final segment short, other segments elongate and cylindrical; system of small microtrichia clearly visible on all segments. The Genus Elephantomyia Osten Sacken, 1860 from Baltic Amber Wing (Figs. 11E, 12A, B, D): 3.8-4.50 mm long, 1.06 mm wide; pterostigma present, oval, pale brown; vein Sc moderate length, ending distal of half Rs length; sc-r short, at end of Sc; vein Rs distinctly arcuate, at least three times length of basal section of R 5 , shorter than length of R 2+3+4 ; R 1 ending at approximately half length of R 2+3+4 ; r-r (R 2 ) atrophied; M 3 approximately one and half times longer than d-cell; cross-vein m-cu at exactly half d-cell length; A 1 almost straight, A 2 slightly waved.
Leg: tibial spurs present. Hypopygium (Figs. 11D, 13C): 0.53 mm, gonocoxite as in other species, approximately twice as long as wide; interbase elongate and narrow, lobe-shaped; outer gonostylus narrow, bifid at end, distal part curved externally; inner gonostylus widened for basal half of its length, strongly narrowed for distal third of length; directed into hypopygium; aedeagus elongate.
Ovipositor: only male specimens known.

Discussion
According to recent data, the first representatives of the genus Elephantomyia appeared in the Eocene,~100 million years after the earliest representatives of the closely related genus Helius The Genus Elephantomyia Osten Sacken, 1860 from Baltic Amber (Helius lebanensis [24], and Helius ewa [25], both from the Lower Cretaceous Lebanese amber). All of species of Elephantomyia known from Baltic amber can be placed within the nominative subgenus Elephantomyia, presently the most species-rich extant subgenus which is distributed worldwide. The other three extant subgenera-Elephantomyina, Elephantomyodes, and Xenoelephantomyia-are not presently represented in the fossil record, and are also rare in the extant fauna. Of these three subgenera, Elephantomyina is particularly rare, occur only in Ecuador and Peru, whereas Xenoelephantomyia is reported solely from Peru. These two subgenera each contain a single species: Elephantomyia (Elephantomyina) supernumeraria [26] and Elephantomyia (Xenoelephantomyia) penai [6]. The final subgenus, Elephantomyodes, is distributed in the Oriental, Australian, and Oceanian regions, and is represented by 32 extant species (Fig. 14). The fossil representatives of Elephantomyia known from the Baltic amber can be clearly placed within the subgenus Elephantomyia, and differ from species of the other subgenera particularly in regards to wing venation. In Elephantomyina, a strong supernumerary cross-vein connecting R 2+3+4 and R 5 occurs shortly before the tip of the latter, and r-m connects with Rs a short distance before its fork; in addition, the tibial spurs are absent in this subgenus [4]. Elephantomyodes differs from nominative subgenus in the lack of tibial spurs and the details of wing venation, particularly in having Rs in alignment with the basal section of R 4 +5 and R 2+3 , arising almost perpendicularly from the end of the sector [5]. In contrast to Elephantomyia, subgenus Xenoelephantomyia is characterised by a reduced anal field, with a single anal vein. Differences in the wing length to rostrum ratio are clearly observable among fossil representatives of the subgenus Elephantomyia known from the Baltic amber: In E. baltica, the rostrum is equal to the wing in length, whereas the rostrum is only slightly shorter than the wing in E. longirostris (1/7 shorter than the wing) or E. pulchella (1/3 shorter than the wing). Elephantomyia differs from the closely related genus Helius [27], [28] in the development of a poorly elongated rostrum, always shorter than half body length. In both E. brevipalpa The Genus Elephantomyia Osten Sacken, 1860 from Baltic Amber and E. irinae sp. nov. we can observe that the rostrum is only slightly longer than half the wing length; these proportions can also be correlated to the length of abdomen, as in E. brevipalpa and E. irinae sp. nov. the rostrum is distinctly shorter than the abdomen, whereas in other representatives of this genus the rostrum is always longer than, or equal to, the abdomen length. The elongate rostrum is also seen in the Cretaceous species Helius ewa [25], which can be considered closely related to Elephantomyia. Therefore, it could be assumed that this feature of an elongate rostrum appeared much earlier than the earliest Elephantomyia crane-flies [25], [28]. The development of such a structure has been related to feeding behaviour, as elongate, nectar-feeding mouthparts occur among many groups of dipterans, including the Limoniidae. In modern dipterans, the exploitation of the great variety of flower types and angiosperm taxa is permitted through a unique repertoire of sensory cues, in conjunction with modified mouthparts, and the presence of frequently large to holoptic compound eyes with stereoscopic, and probably colour, vision in advanced forms [29]. Therefore, it could be hypothesized that the appearance of the elongate rostrum in Elephantomyia and related forms reflected the diversification of flowers of various floral types, including the plesiomorphic ANITA-grade [30] which began to offer various floral rewards for pollination (brood sites, starchy food bodies, nectar, pollen, and heat as a resource). The diversification of Elephantomyia would have been promoted by further diversification and specialization of floral arrangements, their scent production, size, shape, colour, thermogenesis presence, insect rewards, and overall specialization [29]. These co-evolutionary processes probably took place during the late Cretaceous and early Palaeogene, when floral structures became more variable and elaborate, nectar was anatomically deployed in various positions within the flower, and the more ingenious pollination mechanisms developed [29], [31], [32]. However, knowledge of the biology and diversity of the extant species of Elephantomyia, and of all Limoniidae, is presently insufficient to provide detailed analyses of this idea.