1. Introduction

Burmese amber has supplied scientists with a wealth of invertebrate, vertebrate and plant fossils, showing examples of the range of life that existed in this mid-Cretaceous forest. The Reduvoidea is one of the hemipteran lineages that has been previously reported in these deposits (Poinar 2018). Based on a cladistic analysis, the present fossil also has features of the Reduvoidea, such as a length greater than 5 mm, ocelli positioned on an elevated disc just behind the eyes, non-raptorial forelegs, 3-segmented tarsi and “fossula spongiosa” on the fore tarsi (Lent & Wygodzinsky 1979). However, other features, such as the long labium that surpasses the sulcus, the venation of the forewing, the bulging eyes and shape of the head and antennomeres are unique characters of this specimen. Since the fossil cannot be placed in any modern family of the Reduvoidea, it is described in a new extinct family, the Palaeotanyrhinidae nov.

2. Material and methods

The specimen originated from the Noije Bum 2001 Summit Site mine excavated in the Hukawng Valley and located southwest of Maingkhwan in Kachin State (26°20′N, 96°36′E) in Myanmar. Based on paleontological evidence, this site was dated to the late Albian of the Early Cretaceous (Cruickshank & Ko 2003), placing the age at 97 to 110 Ma. A more recent study using U-Pb zircon dating determined the age to be 98.79 ± 0.62 Ma or at the Albian/Cenomanian boundary (Shi et al. 2012). Nuclear magnetic resonance (NMR) spectra and the presence of araucaroid wood fibers in amber samples from the Noije Bum 2001 Summit Site indicate an araucarian tree source for the amber (Poinar et al. 2007). Observations and photographs were made with a Nikon SMZ-10 R stereoscopic microscope and Nikon Optiphot compound microscope with magnifications up to 800 X. Helicon Focus Pro X64 was used to stack photos for better depth of field. Characters and terms presented by Schuh & Slater (1995) and Schuh et al. (2009) were used in the present study. Measurements were performed on scaled photos using ImageJ software.

The characters observed suggest that this aberrant new true bug belongs to infraorder Cimicomorpha. To discuss its placement within the infraorder, a cladistic analysis was performed based on the morphological dataset by Schuh et al. (2009). From among the 73 characters included in the character matrix 33 were observable in Palaeotanyrhina. Missing characters are mostly internal structures or obscure features, and thus cannot be studied in an amber inclusion. However, it must be noted that even fragmentary morphological data acquired from fossils improves morphological phylogenies and provide the basis to form and test hypotheses on relationships among taxa or evolutionary scenarios (Edgecombe 2010; Koch et al. 2021).

Parsimony analysis was performed using TNT 1.1 software (Goloboff et al. 2008) under equal weights. Analysis was composed using traditional search strategy. All characters were treated as non-additive. Characters were optimized on a strict consensus of 60 equally parsimonious trees using “fast optimization” in WinClada (Nixon 2002).

LSID Zoobank for publication: urn:lsid:zoobank.org:pub:D7EBE43B-3F8B-4486-B423-3A715C7CD69B

Fig. 1.

Holotype of Palaeotanyrhina exophthalma gen. et sp. nov. in Burmese amber. A – Dorsal view. Bar = 1.5 mm. B – Lateral view. Arrow shows tip of labium. Bar = 1.2 mm. C – Ventral view. Arrow shows tip of labium. Bar = 1.3 mm.

3. Systematic paleontology

Fig. 2.

Holotype of Palaeotanyrhina exophthalma gen. et sp. nov. in Burmese amber. A – Dorsal view of head. A = Antenniferous tubercle; AC = anterior clypeus; AL = anterior lobe of pronotum; B = synthlipsic bridge; N = neck or collar; O = ocellar tubercle; S= scape; PC= posterior clypeus and frons; PL = posterior lobe of pronotum. Bar = 0.5 mm. B – Lateral view of head. C = pronotal callus; N = neck or collar; O = ocellus (ocellar tubercle distorted to lower left side); S = scutellum. Bar = 1.1 mm. C – Lateral view of eye. Arrow shows basal stalk. Bar = 0.2 mm.

4. Discussion

Palaeotanyrhina exophthalma gen. et sp. nov. displays an amalgamation of exoskeletal structures which are characteristic of various heteropteran groups. One of the most notable of these character states, the bilobate head, is characteristic to the infraorder Enicocephalomorpha (Wygodzinsky & Schmidt 1991; Grimaldi 1993, Spangenberg et al. 2013). In this case it is coupled with a conspicuous head extension similar to the genus Proboscidopirates Villiers, 1958 (e.g., BAňAř et al. 2015, figs. 1–3, 5). The simplified venation of the mesothoracic wing, is also to be observed in an enicocephalomorphan genus, Alienates Barber, 1953 (Wygodzinsky & Schmidt 1991). However, the mesothoracic wing is homogeneous in Enicocephalomorpha [hemelytron is bipartite (clavus+corium and membrane) in Palaeotanyrhina] and tarsal formula 1-1-1 in Enicocephalomorpha (tarsal formula 3-3-3 in Palaeotanyrhina). This suggests that Palaeotanyrhina has a closer relationship with “modern” heteropteran groups. In the extensive phylogenetic analysis of Schuh et al. (2009), the monophyly of Cimicomorpha was supported by the anteriorly inserted labium, this character state can also be observed in Palaeotanyrhina gen. nov. Furthermore, fossula spongiosa occurs in several predaceous cimicomorphan taxa, an elongate head is observed in e.g., the triatomine genera Eratyrus and Rhodnius (Reduviidae: Triatominae) and an example of a elongate labiomere III coupled with shortened labiomeres I–II and IV is present in the enigmatic reduviid family Velocipedidae (Van Doesburg 2004). Considering the above, we regard Palaeotanyrhina to be an aberrant extinct lineage of Cimicomorpha. To test this hypothesis, we performed a phylogenetic reconstruction based on the morphological characters included in the matrix of Schuh et al. (2009). An exhaustive search under equal weights resulted in 60 equally parsimonious trees (L = 295, CI = 37, RI = 82), from which a strict consensus was estimated (Fig. 6). The resulted topology corresponds to the morphology-only analysis of Schuh et al. (2009, fig. 4), with terminal branches of the Miridae clade. The clade Reduvioidea (Pachynomindae + Reduviidae) was considered monophyletic, supported by three non-homoplasious transformations: one antennal pedicellar trichobothria present (9: 1), abdominal spiracles on sternum adjacent to discrete laterotergite (44: 1) and paired pseudospermathecae situated on ectodermal portion of median oviduct (66: 1). Contrastingly, on the tree of Schuh et al. (2009) Reduvioidea was supported by a single non-homoplasious character (9: 1). Including a single fossil record has improved the support of the clade, which agrees with the conclusions of Edgecombe (2009) and KOCH et al. (2021).

Fig. 3.

Holotype of Palaeotanyrhina exophthalma gen. et sp. nov. in Burmese amber. A – Antennae. Arrowhead shows insertion point. Numbers refer to segments. Bar = 0.3 mm. B – Extended head (Eh); L= labrum; La1= first labial segment. La2= second labial segment. Bar = 0.4 mm. C – Dorsal view of extended head and antennomeres. CF= clypeal flanges; PF = protruding flanges. Bar = 180 µm.

Palaeotanyrhina was nested within the Reduvioidea clade as a basal taxon in all resulting trees. Palaeotanyrhina was also diagnosed by two homoplasious transformations: labial groove present on thoracic sternum (13: 1) and costal/ M-R veins extending to apex of corium on anterior wing margin (36: 1). In addition, Palaeotanyrhina displays a set of characters which are to be considered unique in terms of the superfamily Reduvioidea, e.g., extremely elongate head, stylate eyes, ocelli situated on protruding synthlipsic disc and triblobate pronotum with well-developed collar.

Considering the above, Palaeotanyrhinidae fam. nov. was erected to accommodate this new monotypic genus that represents an extinct, aberrant lineage of Reduvioidea. Further elucidation on its relationship within the superfamily and the evolutionary significance of Palaeotanyrhina awaits further phylogenetic analysis involving other known fossil reduvioid true bugs and an improved character matrix.

Fig. 4.

A–C – Holotype of Palaeotanyrhina exophthalma gen. et sp. nov. in Burmese amber. A – Tip of labium. Note two extended maxillary stylets and short mandibular stylet. Arrow shows joint between segments. Bar = 148 µm. B – Mesotarsus. Arrowhead shows short first tarsomere. Bar = 0.2 mm. Insert shows pygophor. Bar = 0.1 mm. C – Strap-like cover (arrows) enclosing fossula spongiosa on protarsus. Right arrowhead shows short first tarsomere. Left arrowhead shows released secretion from fossula spongiosa. Bar = 0.2 mm. D – A reduviid (specimen HE-4-21 deposited in the Poinar amber collection maintained at Oregon State University) in Dominican amber that has applied resin to its fore tibia (arrowhead). Bar = 1 mm.

Fig. 5.

Features of holotype of Palaeotanyrhina exophthalma gen. et sp. nov. in Burmese amber. A – Fossula spongiosa on protarsus. Arrows show borders of sheath than encloses protarsus. Bar = 56 µm. B – Forewing. Note two large closed cells on corium, a cloudy area on the embolium possibly representing a greatly reduced pterostigma and the absence of a claval commissure. Bar = 1.4 mm. C – Anterior portion of head; ac = elongated anterior portion of head; p = sensory papilla on labrum; pc = posterior portion of head; s = first segment of labium; Bar = 0.4 mm. D – Metatarsus. Bar = 300 µm.

Fig. 6.

The placement of Palaeotanyrhina gen. nov. within the infraorder Cimicomorpha. Strict consensus of 60 equally parsimonious trees resulted by traditional search under equal weights in TNT 1.1 software.

In Figs. 4C and 5A, a sheath enclosing the fore tarsus can be observed. Considering its position and contents, it may contain a gluey substance associated with sticky trap predation (STP), a predation method which can be observed in extant reduviid subfamilies Harpactorinae and Bactrodinae (Avila-NÚnez et al. 2017). Adhesive fluid used to trap prey can be of endogenous or exogenous origin (Zhang & Weirauch 2013). The former can be observed in the tribe Harpactorini where the bugs possess a specialized dermal gland that secrets the fluid, while in the latter case the insect harvests the sticky substance from plants and purposely coats its legs and other body parts as occurs in “resin bugs” (Reduviidae: Harpactorinae: Apiomerini) (Fig. 4D). While on Palaeotanyrhina, this phenomenon is clearly endogenous and shows the ancient nature of this predation method, suggesting that Palaeotanyrhina was a predaceous true bug most likely feeding on smaller arthropods.

5. Conclusions

Here, we report an aberrant new true bug, Palaeotanyrhina exophthalma gen. et sp. nov. from mid-Cretaceous Burmese amber. This monotypic new genus displays an amalgamation of characters attributed to various heteropteran groups. A careful study of the exoskeletal features suggests that Palaeotanyrhina is a representative of infraorder Cimicomorpha. To determine its placement, a phylogenetic analysis was performed which concluded that this new aberrant true bug should be assigned to the superfamily Reduvioidea, and since its characters are unique in terms of the superfamily, a new family, Palaeotanyrhinidae nov., should be erected to accommodate it. The observation of traces suspected to be an adhesive substance combined with the presence of fossula spongiosa suggest that Palaeotanyrhina was a predator feeding on smaller arthropods.