Tyrannobunus, BARTEL & DUNLOP, 2023

BARTEL, CHRISTIAN & DUNLOP, JASON A., 2023, First eupnoid harvestmen (Arachnida: Opiliones: Eupnoi) from mid-Cretaceous Kachin amber, with notes on sexual dimorphism in Halitherses grimaldii (Arachnida: Opiliones: Dyspnoi), Palaeoentomology 6 (3), pp. 278-291 : 280-281

Genus Tyrannobunus gen. nov.

urn:lsid:zoobank.org:act:62A6E27F-F467-4A96-AB1F-455F0D7A8074

Type species. Tyrannobunus aculeus gen. et sp. nov.

Etymology. Named from the Latin word tyrannus (ruler) combined with the frequently used harvestmen suffix ‘bunus’. Gender masculine.

Diagnosis. Body small, oval and dorsally covered with setiferous tubercles. Ocular tubercle with relatively large laterally directed eyes, located at the anterior border. Pedipalps long and heavily armed with spines and setiferous tubercles, except pedipalp tarsus. Legs also long and completely covered with spines and setiferous tubercles from coxa to tibia. Male penis elongate, slender and without complex structures.

Remarks. GPIH05127 ( Figs 1 , 2 ) is interpreted as an adult male eupnoid, due to the well-developed armature on the body and legs, the high number of leg tarsomeres and, significantly, the presence of the male genitalia (penis). A single claw on all four legs and a claw on the pedipalp tarsus support the placement of the fossil within the suborder Eupnoi . Its habitus does not match any of the previously known Eupnoi fossils. There are some similarities with Lacinius bizleyi Mitov, Dunlop & Penney, 2015 from the much younger Bitterfeld and Baltic ambers. Both L. bizleyi and the new Burmese amber fossil show well developed leg spination ( Fig. 1A, C ) and apophyses on the pedipalp patella ( Fig. 2B ). The ocular tubercle of our new fossil is, however, completely different from that of L. bizleyi as it is located at the anterior border of the carapace and has much larger eye lenses ( Figs 1B , 2A ). The pedipalps of the new specimen are also more heavily spined. The latter condition is very rare among modern eupnoids, but is reminiscent of the habitus of many laniatoreans where heavily spined pedipalps are quite common across several different families. As noted above, the tarsal claw pattern excludes Laniatores and among the living eupnoids an apparently heavily sclerotized body with its large dorsal tubercles may indicate affinities to the family Sclerosomatidae and its subfamily Sclerosomatinae , where such features can be quite common. A smooth pedipalp claw on the other hand might argue against this family, as most sclerosomatids have a pectinate pedipalp claw. Within Sclerosomatidae , relatively large dorsal tubercles / spines and well developed leg spination can be observed in, e.g., the genera Astrobunus Thorell, 1876 and Homalenotus Koch, 1839 . Nevertheless, the pedipalps and the ocularium do not match those of the fossil. Another interesting character of the fossil is the penis, which is documented here for only the second time in an amber harvestman ( Fig. 2C, D ). Compared to many of the living harvestmen, the penis of the new fossil is relatively simple.

However, especially within Palpatores a simple penis is still widely distributed. One example of a living species with a comparable penis morphology for sclerosomatids would be Leiobunum tohokuense Suzuki, 1976 . Having said this, members of the subfamilies Leiobuninae and Gagrellinae feature typical winglets on the penis, which are not present in our amber specimen. Those penial winglets can e. g., be observed in the Jurassic sclerosomatid Mesobunus dunlopi Giribet, Tourinho, Shih & Ren, 2012 . A similar rather simple penis morphology can also be observed in the recently described genus Martensopsalis Giribet, Baker & Brouste, 2021 ( Eupnoi : Neopilionidae ) from New Caledonia. Nevertheless, most of the other morphological characters in the fossil are completely different from these modern genera.

The eupnoid family Phalangiidae includes a few additional genera (other than Lacinius ) where spiny legs frequently occur, for example Homolophus Banks, 1893 , Scleropilio Roewer, 1911 or Acanthomegabunus Tsurusaki, Tchemeris & Logunov, 2000 . However, all of these genera again bear much smaller eye lenses, which are in a more central position, removed from the anterior carapace border. Large eyes with a similar form can be observed in the Eupnoi family Caddidae , but here they are usually even larger compared to those observed in the fossil. The spination of the appendages is additionally restricted to the pedipalps in Caddidae . Furthermore, the penis morphology is rather complex in most genera of this family, except Caddo Banks, 1892 ( Groh & Giribet, 2015; Pinto-da-Rocha & Giribet, 2007). Given that the character combination preserved in the new fossil does not conform to any living eupnoid genus, we propose a new genus and species.

Figures

FIGURE 1. Tyrannobunus aculeus gen. et sp. nov., holotype: GPIH05127. A, Camera lucida drawing of the complete specimen in ventral view. B, Close up of the dorsal body and ocularium, eye lenses arrowed. C, Close-up of the ventral body. Abbreviations: ey, eye lens; fe, femur; mt, metatarsus; oc, ocular tubercle; pa, patella; pe, penis; pp, pedipalp; ta, tarsus; legs numbered from I–IV. Scale bars = 1.0 mm (A) and 0.5 mm (B, C).

FIGURE 2. Tyrannobunus aculeus gen. et sp. nov., holotype: GPIH05127. A, Close-up of the ocularium (camera lucida drawing). B, Close-up of the chelicerae and pedipalps in ventral view (pedipalp patella apophysis arrowed). C, Camera lucida drawing of the penis. D, Close-up of the penis in ventral view. Abbreviations: ap, apophysis; bo, body; ch, chelicerae; ey, eye lens; gl, glans; oc, ocularium; pe, penis; pp, pedipalp; st, stylus; tc, truncus; legs numbered from I–IV. Scale bars = 0.5 mm (A, C) and 0.25 mm (B, D).