Psacodromeus recta, Lee & Nam & Park, 2024

Psacodromeus recta sp. nov.

Material. Holotype KNUL-1114-106, Paratype KNUL-1114-109

Etymology. The species name recta is derived from the Latin word recta , meaning straight.

Locality and horizon. Sacheon-si, Sanam-myeon, Gyeongsangnam-do, Republic of Korea; Jinju Formation, Early Cretaceous, Albian

Diagnosis. Lateral margin of the pronotum straight; the anterior margin of the pronotum is extremely narrower than the posterior margin.

Description. Body lengths ranging from 6.3 mm (KNUL-1114-109) to 9 mm (KNUL-1114-106) and widths from 3.5 mm (KNUL-1114-106) to 5 mm (KNUL-1114-109). Head narrowed anteriorly, with a rounded basal edge; anterior edge of labrum rounded; maxillary palp with three segments, third one slightly wider than others; antennae long, with 11 antennomeres.

Pronotum wider posteriorly, with lateral outer margins straight; posterior margin concave, but the middle partly protruding, pronotum with an overall tetragonal shape; prosternum almost straight posteriorly and contiguous with procoxae; prosternal process short and contiguous with mesoventrite, mesoventrite large, resembling an inverted triangle, with anterior margin pulled posteriorly in middle and posterior margin slightly pulled anteriorly in middle; metepisternum anteriorly large and extremely narrowed posteriorly; metepimeron roughly square-shaped, with posterior part slightly wider than anterior one; epipleuron thick; elytra oval and narrowed posteriorly; no striae or punctures on elytra; prolegs preserved with procoxae and profemora in KNUL-1114-106; profemora poorly preserved in KNUL-1114-109; procoxa polygonal, profemur slightly narrower distally, but with a straight overall outer margin; midleg preserved in KNUL-1114-106, including mesocoxa, mesofemur, and a part of mesotibia; mesocoxa rounded to polygonal and larger than procoxa; mesofemur wide distally, with widest part at middle; mesofemora poorly preserved in KNUL-1114-109; hindlegs preserved in both KNUL-1114-106 and KNUL-1114- 109; metacoxal plate elongated laterally and meeting epipleuron; metacoxae large and polygonal; metafemur widest anteriorly and slightly narrowed distally; metatibia almost straight, widest at distal end; metatarsus with five segments.

Remarks. The overall morphology of KNUL-1114-106 and KNUL-1114-109 are showing the features of the family Trachypachidae including: 1) head narrower than prothorax; 2) Antennae inserted between eyes and base of mandibles; 3) antenna filiform and formed with 11 antennomeres; metacoxae extended laterally, meeting with lateral margins of body ( Ball, 2000).

The overall body shape of KNUL-1114-106 and KNUL-1114-109 is teardrop-shaped. The head is narrowed anteriorly, with a triangular shape. The anterior edge of the pronotum is rounded and sharp. These features are diagnostic for the genus Psacodromeus ( Ponomarenko, 1977) . Most species of Psacodromeus ( P. crassus , P. gutta , P. ovalis , and P. rugosus ) have been discovered from the Jurassic of Kazakhstan ( Ponomarenko, 1977). Only P. minor has been discovered from the Gurvaneren Formation in Mongolia, which is dated as Early Cretaceous, Aptian ( Ponomarenko, 1986). P. recta sp. nov. is differ from the P. minor that 1) lateral margin of the pronotum is straight (rounded in P. minor ) and 2) width of anterior margin of pronotum noticeably narrower than the posterior margin (slightly narrower in P. minor ).