Under cover at pre-angiosperm times: a cloaked phasmatodean insect from the Early Cretaceous Jehol biota

Abstract

Background: Fossil species that can be conclusively identified as stem-relatives of stick- and leaf-insects (Phasmatodea) are extremely rare, especially for the Mesozoic era. This dearth in the paleontological record makes assessments on the origin and age of the group problematic and impedes investigations of evolutionary key aspects, such as wing development, sexual size dimorphism and plant mimicry.

Methodology/principal findings: A new fossil insect species, Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov., is described on the basis of one female and two male specimens recovered from the Yixian Formation (Early Cretaceous, ca. 126±4 mya; Inner Mongolia, NE China; known as 'Jehol biota'). The occurrence of a female abdominal operculum and of a characteristic 'shoulder pad' in the forewing allows for the interpretation of a true stem-Phasmatodea. In contrast to the situation in extant forms, sexual size dimorphism is only weakly female-biased in this species. The peculiar wing coloration, viz. dark longitudinal veins, suggests that the leaf-shaped plant organ from the contemporaneous 'gymnosperm' Membranifolia admirabilis was used as model for crypsis.

Conclusions/significance: As early as in the Early Cretaceous, some stem-Phasmatodea achieved effective leaf mimicry, although additional refinements characteristic of recent forms, such as curved fore femora, were still lacking. The diversification of small-sized arboreal insectivore birds and mammals might have triggered the acquisition of such primary defenses.

Figure 1. Renphasma sinica Nel and Delfosse, 2011.

Holotype specimen MNHN A31857, ♂ (negative imprint). A. Habitus. B. Detail of terminalia (as located on A); arrow indicates the vomer terminal hook.

Figure 2. Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov., habitus drawings (* indicate intercalary veins; see text for abbreviations; all at the same scale).

A. Specimen CNU-PHA-NN2012003, ♂. B. Holotype specimen CNU-PHA-NN2012002, ♂. C. Specimen CNU-PHA-NN2012001, ♀.

Figure 3. Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov., habitus photographs.

A. Specimen CNU-PHA-NN2012003, ♂. B. Holotype specimen CNU-PHA-NN2012002, ♂. C. Specimen CNU-PHA-NN2012001, ♀.

Figure 4. Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov.

A–B. Specimen CNU-PHA-NN2012002, ♂, head morphology (see text for abbreviations), as located in Figure 3B. A. Drawing. B photograph. C–F. Terminalia morphology (see text for abbreviations). C–E. Specimen CNU-PHA-NN2012002, ♀, photographs, as located in Figure 3C. C. Photograph with interpretation, to be compared to D and E. F. Specimen CNU-PHA-NN2012002, ♂, as located in Figure 4A.

Figure 5. Heteropteryx dilatata (Parkinson, 1798), details of the ‘shoulder pad’ (all at the same scale).

Shoulder pad of the right forewing and left forewing indicated by a blue and green arrow, respectively. Base of the right hind wing indicated by a red arrow. A. Dorsal view. B. Left lateral view, slightly tilted laterally.

Figure 6. Exemplars of Membranifolia admirabilis Sun and Zheng, 2001 in Sun, Zheng, Dilcher, Wang and Mei, 2001 (all at the same scale, and same scale as Figure 2 ).

A. Holotype specimen PB19184. B. Specimen PB19196. C. Specimen PB19185.

Figure 7. Live reconstruction of Cretophasmomima melanogramma Wang, Béthoux and Ren sp. nov. (several exemplars) among Membranifolia admirabilis Sun and Zheng, 2001 in Sun, Zheng, Dilcher, Wang and Mei, 2001 (interpreted as Gingkophyte leaf organ).

A less camouflaged early orthopteran, Parahagla sibirica Sharov, 1968, is captured by the insectivorous Eomaia scansoria Ji, Luo, Yuan, Wible, Zhang and Georgi, 2002, one of the earliest eutherian mammals. Reprinted under a CC BY license, with permission from S. Fernandez.