Dakotaeschnidium spedeni, NEL, 2021

NEL, ANDRÉ, 2021, Maastrichtian representatives of the dragonfly family Aeschnidiidae question the entomofaunal turnover of the early Late Cretaceous, Palaeoentomology 4 (3), pp. 209-212 : 210

Dakotaeschnidium spedeni sp. nov.

( Fig. 1 ) urn:lsid:zoobank.org:pub:C625EE39-050C-49CC-9182-220F212BCFB4

Material. HolotypeYPM IP 028154 (collector Ian G. Speden, 1962, IP number 28154; lot count 1; part/counterpart). Invertebrate Paleontology, Yale Peabody Museum, New Haven, USA.

Etymology. Named after Ian G. Speden who collected the type specimen.

Diagnosis. As for the genus. Wing membrane darkened.

Description. A fragment of hind wing showing the discoidal triangle, hypertriangle, a fragment of the postdiscoidal area, the submedian space and basal part of anal area, 11.7 mm long, 21.0 mm wide; whole membrane very dark with yellow veins; part of wing basal to hypertriangle missing; hypertriangle subdivided into ca. 40 small irregular cells, 1.9 mm wide, 11.6 mm long; discoidal triangle clearly transverse, subdivided into more than 27 irregular cells, with vein MAb more than 7.0 mm long, curved, vein separating discoidal triangle from hypertriangle 3.1 mm long, and vein MP+CuA 6.6 mm long; postdiscoidal area very broad at base, with more than 13 rows of cells between MAa and MP; anal area very broad, 16.2 mm wide; only three posterior branches of AA in anal area; no infrasubdiscoidal space basal to basal subdiscoidal space; basal subdiscoidal space transverse, posteriorly opened because vein AA1a poorly defined, distal subdiscoidal space transverse, with a shape of acute triangle, very broad and long, subdivided into ca. 70 irregular cells, no angle between AAspl and AA1a veins; PsA vein clearly visible vanishing one cell basal to antero-basal angle of discoidal triangle; submedian space subdivided into more than 11 irregular cells; area between RP and MA subdivided into numerous cells disposed in three rows.

Type locality and horizon. Fox Hills Formation, Trail City Member. USA; South Dakota; Dewey County; float, conc. 5, face on SW side of SSE-trending spur, 1.25 miles W of E end of Long’s Ridge , Long’s Ridge , and 6 miles W of Whitehorse. Maastrichtian, Late Cretaceous.

Remarks. The very broad anal of this fossil is typical of that of a hind wing of an Aeschnidiidae , with a basal subdiscoidal space and a distal subdiscoidal space. The transverse discoidal triangle is also only found in this family ( Fleck & Nel, 2003). The particular shape of the distal subdiscoidal space of YPM IP 028154 is also found in Gigantoaeschnidium ibericus Nel & Martinez-Delclòs, 1993 , but the basal subdiscoidal space of Gigantoaeschnidium is much smaller than that of YPM IP 028154, and it has an angle between AAspl and AA1a veins (Fleck & Nel, 1993: fig. 63a). Angloaeschnidium toyei Fleck & Nel, 1993 and Cooperaeschnidium durandi Fleck & Nel, 1993 have their distal subdiscoidal spaces similar to those of YPM IP 028154 but their distal subdiscoidal spaces are much smaller than that of YPM IP 028154. They also have only one row of cells in their hypertriangles.

Even if Santanoptera gabbotti Martill & Nel, 1996 (Aptian, Crato Formation, Brazil) is based on a forewing, its distal subdiscoidal space is similar to that of YPM IP 028154, and it has no angle between AAspl and AA1a veins (Fleck & Nel, 1993: fig. 89). They also share the presence of two rows of cells in the hypertriangle, two in the submedian space, and two-three in the basal part of area between RP and MA. Nevertheless, Santanoptera has a smaller basal subdiscoidal space that is posteriorly closed by a well-defined vein AA1a.

Despite the fact that the specimen YPM IP 028154 is reduced to the basal third of a hind wing, it has a series of characters allowing to consider that it corresponds to a new genus and species, possibly related to the South American genus Santanoptera , as they share the very particular absence of an angle between AAspl and AA1a veins, and presence of several rows of cells in hypertriangle, submedian space, etc.

Figures

FIGURE 1. Dakotaeschnidium spedeni gen. et sp. nov., holotype YPM IP 028154. A, Part. B, Counterpart. Scale bars = 5 mm.