Triamyxidae, Qvarnström & Fikáček & Vikberg Wernström & Huld & Beutel & Arriaga-Varela & Ahlberg & Niedźwiedzki, 2021

Qvarnström, Martin, Fikáček, Martin, Vikberg Wernström, Joel, Huld, Sigrid, Beutel, Rolf G., Arriaga-Varela, Emmanuel, Ahlberg, Per E. & Niedźwiedzki, Grzegorz, 2021, Exceptionally preserved beetles in a Triassic coprolite of putative dinosauriform origin, Current Biology 31, pp. 1-8 : 3

Family Triamyxidae fam. nov.

Type genus

Triamyxa gen. nov.

Differential diagnosis

Characters of the new family are put in contrast to [x] other myxophagan families: dorsal body surface without tubercles or ridges (x Lepiceridae ); eyes strongly protruding (x Sphaeriusidae , most Hydroscaphidae ); head anterior of eyes prolonged and distinctly narrowing (x Hydroscaphidae , Sphaeriusidae ); antennal bases exposed dorsally between eyes (x Hydroscaphidae , Lepiceridae ); antennal scapus and pedicel distinctly separated from each other (x Torridincolidae , Lepiceridae ), exposed in dorsal view (x Lepiceridae , modern Hydroscaphidae ); terminal maxillary palpomere long, longer than penultimate (x Hydroscaphidae , Sphaeriusidae ); mentum large, narrowing anteriad (x modern Hydroscaphidae ); prosternum long, with very short prosternal process (x Hydroscaphidae , Lepiceridae ); propleuron wide, without posterior projection (x all modern families); mesoventrite only slightly shorter than metaventrite (x Hydroscaphidae , Sphaeriusidae , Torridincolidae ); mesoventrite with wide subpentagonal elevation (x modern Hydroscaphidae , Torridincolidae ); elytra only slightly shortened, exposing 1 to 2 terminal abdominal tergites (x all modern families), truncated posteriorly (x Sphaeriusidae , Torridincolidae , Lepiceridae ); metanepisternum moderately wide anteriorly (x Sphaeriusidae , Torridincolidae , Lepiceridae ); metacoxal plates present, narrow (x Sphaeriusidae , Torridincolidae , Lepiceridae ); abdomen with 5 to 6 exposed ventrites ( Figure 4 ; x Sphaeriusidae , some Torridincolidae ); all abdominal segments with separate tergite and sternite (x Hydroscaphidae ). For more details, see Table S1. From its habitus, Triamyxidae is similar to Hydroscaphidae but differs from this family in a series of characters listed above, most notably the lack of fused tergites and sternites of abdominal segments III–VI. This abdominal configuration, a very uncommon shared derived feature and synapomorphy of extant Hydroscaphidae and the Triassic Leehermania , is clearly absent from Triamyxa , where tergites and sternites of all abdominal segments are distinctly separated ( FigureS1 ).

Figures

Figure 1. Contents of coprolite fragment ZPAL AbIII/3520 (A) The coprolite rendered semi-transparent with inclusions, such as beetle remains and fibrous networks, representing fungal colonies or algae visible. Top corner: silhouette of Silesaurus opolensis, the most probable coprolite producer. (B–D) The holotype specimen of Triamyxa coprolithica in ventral (B), lateral (C), and dorsal (D) views. (E and F) The second complete specimen in ventral (E) and anterior (F) views. Individual ventrites are indicated by roman numerals. (G) Triamyxa coprolithica preserved in various degrees of disarticulation. (H) An isolated head and two elytra that do not belong to Triamyxa coprolithica but to slightly larger beetles that were also ingested by the coprolite producer. (I) Examples of individual remains of Triamyxa coprolithica (meso- and metaventrite, head, head attached to pronotum, and three pronota). (J) Two of numerous elytra of similar size and morphology attributed to T. coprolithica. (K) Fibrous structures interpreted as fungi or algae. (L) A possible decomposed wood fragment. Color coding: blue,eyes; purple, antennae;light purple,legs. Abbreviations:abd,abdomen;ant,antenna; cox, coxa;ey, eye; fem, femur; hd, head;lgs, legs;pp, propleuron; thx, thorax; tib, tibia; troch, trochanter; trs, tarsi; ventr, ventrites. See also Figure S1.

Figure 3. Phylogenetic position and morphology of Triamyxa coprolithica (A and B) Results of Bayesian analysis of Coleoptera dataset, with fossil position in Polyphaga excluded following the prothorax morphology:(A) complete beetle tree with color-coded posterior probabilities (PPs) of Triamyxa position; (B) maximum credibility tree with Polyphaga not shown. (C–E) Reconstruction of Triamyxa morphology: (C) dorsal view; (D) ventral view of a specimen with 5-segmented abdomen; (E) specimen with exposed 6th abdominal ventrite (see Figure 4 for comparison of all specimens). (F–H) Alternative positions of Triamyxa revealed by Myxophaga analyses: (F) Bayesian, molecular topology constrained; (G) maximum parsimony, molecular topology constrained; (H) maximum parsimony, topology unconstrained. (I–Q) Comparative morphology of the prothorax in ventral view:(I) Olibrus; (J) Acrotrichis; (K) Scaphidium; (L) Nebria; (M) Beutelius; (N) Lepicerus; (O) Satonius; (P) Sphaerius; (Q) Hydroscapha. (R–T) Prothoracic morphology of Triamyxa revealed by superimposition of disarticulated remains: (R) isolated pronotum; (S) isolated pronotum with superimposed prosternum from another specimen; (T) final reconstruction with the position of propleuron. See also Figures S2 and S3.