By John Barrat
New fossils found in Northeastern China have revealed a remarkable evolutionary coincidence: an extinct group of insects known as Kalligrammatid lacewings (Order Neuroptera) share an uncanny resemblance to modern day butterflies (Order Lepidoptera). Even though they vanished some 50 million years before butterflies appeared on earth, they possess the same wing shape and pigment hues, wing spots and eyespots, body scales, long proboscides, and similar feeding styles as butterflies.
In an incredible example of convergent evolution, both butterflies and kalligrammatids evolved the same physical characteristics at vastly different times and while feeding on disparate plant hosts, explains Conrad Labandeira, paleobiologist at the Smithsonian’s National Museum of Natural History. Kalligrammatids had an intricate feeding and pollinating relationship with non-flowering gymnosperms during the mid-Mesozoic; butterflies, by contrast, feed on and pollinate flowering angiosperms. Yet both major groups of seed-plants placed similar selective pressures on the two, unrelated pollinator lineages causing them to develop the same suite of physical and behavioral features.
Labandeira is lead author of a Feb. 3 paper on this discovery in the journal Proceedings of the Royal Society: B.
“Kalligrammatid lacewings are an extinct, Eurasian insect group that has been known to science for a century, but early fossils were fragmentary and not much could be learned from them,” Labandeira explains. New, well-preserved kalligrammatid fossils found between 2004 and 2012 in Middle Jurassic and Early Cretaceous lake deposits of Northeastern China revealed the features of this butterfly look-alike.
Finely deposited lake sediments preserved the insects to a remarkable degree. During their study, the scientists were able to closely examine the fossil surfaces using light microscopy, scanning electron microscopy, electron dispersion microscopy and time-of-flight–secondary ion mass spectrometry to try and characterize molecules left behind by different parts of the insect’s bodies.
“If you look at a modern butterfly wing at very high magnification, the colors that you see are actually determined by very small scales that are pigmented differently,” Labandeira says. “It looks like kalligrammatids had these same type of wing scales.” The fossils also clearly show a variety of spot and eyespot patterns—concentric circles of pigmented cells that surround a central melanin-containing disc—that produce a conspicuous display on kalligrammatid wings, This is another convergent feature shared with butterflies.
Kalligrammatid mouthparts—resembling a long flexible, straw-like proboscis—evolved from the chewing mandibles of their ancestors, the different parts of which were conjoined to form a long tube. This parallels the evolution of the proboscis from maxillary head segment in butterflies, both groups of which also originated from mandible bearing ancestors, the scientists write. Suction forces were provided by one, perhaps two, sucking pumps located in the frontal head region, mirroring those in butterflies.
“That tube is basically used to feed on surface fluids; in the case of butterflies, it is used for angiosperm nectar, to accomplish pollination,” Labandeira says. “Kalligrammatids fed upon gymnosperms which had weird reproductive structures that included elongate tubes, channels, funnels and other tubular structures.”
In one fossil the scientists were able to examine elements contained in an opaque piece of “gunk” found stuck inside the food tube of a kalligrammatid proboscis. The enriched carbon reading of the mass was consistent with a nectar-like fluid. Elemental analysis was also able to determine the likely presence of the substance melanin in kalligrammatid wing eyespots. Melanin is a common pigment in butterfly eyespots.
Pollen grains found on and next to the bodies of several kalligrammatid fossils indicate a similar feeding style with butterflies—one that promotes pollination through use of pollen and nectar as a food reward.
“What’s more,” Labandeira adds, “in butterflies things like wing coloration is under genetic control. We also believe the overall genetic developmental program of these two totally unrelated lineages is similar.”
“So … between kalligrammatids and butterflies we have the proboscis and mouthparts converging, we have the wing scales converging, we have the wing eyespots converging, we have the whole feeding biology converging and the genetic developmental program converging … This is remarkable, considering there is about a 50 million year gap between the last kalligrammatid in the mid-early Cretaceous and the earliest fossils of butterflies at the Paleocene–Eocene boundary.”
“The extinction of the kalligrammatids, we think, is probably attributable to the extinction of their host plants resulting from the expansion of the angiosperms,” Labandeira says. “Gymnosperm herbivores and pollinators bit the dust because there was a major transformation in the global flora that eliminated their hosts.”