October 28. Bloodsucking parasites and other Jurassic insects

Something like 1,000 species of Jurassic insects have been described. Jurassic dragonflies were smaller than the giants of the Carboniferous, but still large, with wingspans on the order of 7 inches and bodies 5 inches long. They’ve been found in the Solnhofen limestone, and specimens are often offered for sale in the $1,200 to $2,000 range. The basic body plan of dragonflies hasn’t changed much over the history of the group, more than 300,000,000 years. 

Image of scorpionfly Jurassipanorpa sticta holotype. (Scale bar: 1 mm)
from He Ding, Chungkun Shih, Alexei Bashkuev, Yunyun Zhao,
and Dong Ren used under CCA-4.0-International

In 2014, researchers described a strange new insect from the Daohugou beds in northeastern China – an aquatic fly larva that is interpreted to be a salamander parasite, sucking the blood of its host to which it was attached somewhat like a remora on a shark, but only about an inch long. Those rocks in China have yielded more than 300,000 insect fossils, so that’s the source of a lot of our knowledge of Jurassic insects. Some show the color patterns in wings. And because the China locality represents just one tiny little ecosystem, it means that while we know a lot about it, there’s plenty more to know about Jurassic insects. 

One of the earliest examples of mimicry in the insect world is from a Jurassic fly from the Daohuguo beds whose wings look so much like gingko leaves that they were missed by early workers and discarded as “just another gingko leaf.” Such an adaptation would have certainly been advantageous to a bug in a world full of insectivores, from salamanders to early gliding mammals to small reptiles to, probably, early birds.

Beetles, crickets, caddis flies, moths, stoneflies, flea-like bugs, and more have been identified from Jurassic rocks around the world. Clearly, insects had diversified significantly early in their history, well before their explosive radiation that’s tied to the development of flowering plants, which we’ll get to next month.

—Richard I. Gibson

Image of scorpionfly Jurassipanorpa sticta holotype. (Scale bar: 1 mm) from He Ding, Chungkun Shih, Alexei Bashkuev, Yunyun Zhao, and Dong Ren used under CCA-4.0-International


News report:
Bloodsucking parasite

August 7. Permian insects

We talked about the giant insects in the Pennsylvanian coal swamps last month. Insects continued, of course, into the Permian, but the changing environments mean that the record is considerably less extensive because of poor preservation of insects. Coal swamps were great places to fossilize bugs, while more arid river systems and even deserts were not.  

One of the common ideas for the gigantic size of insects in the Pennsylvanian was the increased oxygen content at that time. There was a crash in oxygen levels toward the end of the Pennsylvanian and into the early Permian, perhaps related to the crash in the rainforest ecosystem – but gigantic insects are found in the Permian too, including one called Meganeuropsis, the largest insect known with a wingspan of 28 inches and a body length of 17 inches. So there is still research to do on the relationship between oxygen in the atmosphere and the evolution and size of insects.

The most common Permian insects are cockroaches and their relatives. The first true dragonflies probably evolved in the Permian from Pennsylvanian dragonfly-like ancestors. Until recently, the oldest known beetle was from the Permian, but in 2009 a fossil beetle was described in the Pennsylvanian Mazon Creek rocks. Beetles certainly did diversify during the Permian, and today there are at least 350,000 species of beetles.  

—Richard I. Gibson

Links:
Modern Beetles predate Dinosaurs 

The largest complete insect wing ever found

July 14. Insects

Based on the abundance of insects in the fossil record and analogies with modern settings, Pennsylvanian coal swamps teemed with insects and spiders. Many were delicately preserved in concretions in fine-grained sediments, like those at Mazon Creek we mentioned a few days ago. Even details such as wings and their veins are often preserved. The warm, moist climate in at least the tropical and sub-tropical Pennsylvanian world might have stimulated the evolution of insects, or it might have been more a co-evolution with the plants that dominated those swamps.  

Did the presence of insects as food promote the development of land life? Or did the pressure from evolving land predators stimulate the diversification of insects? Most likely, it was a combination of both and more. There is actually quite a gap in the fossil record between the first insects in the Devonian and the proliferation of insects in the Pennsylvanian, so their evolutionary history is not all that well known. Insects had evolved the ability to fly by Pennsylvanian time, but the details of that evolution are obscure.

Meganeura - Dragonfly photo by Hcrepin via Wikipedia under GDFL.

Pennsylvanian swamps had cockroaches four inches long, and the air buzzed with relatives of dragonflies with wingspreads of 25 inches or more. Gerarus was a bug with a wingspan of 10 centimeters – 4 inches – and a body covered with spikes.

It’s not certain why Pennsylvanian insects grew so large. A common idea is that there was more oxygen in the Pennsylvanian atmosphere, giving both more energy for growth and more lift to winged insects. There was more oxygen – possibly as much as 35% vs. today’s 21%, probably largely because of all the plants taking up carbon dioxide and giving off oxygen. But one problem with that is that gigantic insects survived and even became larger into the Permian, when oxygen levels were considerably lower than in the Pennsylvanian. It might have been that large insects were better able to manage oxygen usage than small ones.  It has also been suggested that the gigantism was a result of evolutionary pressure, an arms race, among competitors for food resources.

* * *

Florence Bascomb was born July 14, 1862, in Williamstown, Massachusetts. She was educated at the University of Wisconsin and Johns Hopkins, where she earned her PhD in geology in 1893 – the second American woman to do so. She was the first woman hired as a professional by the U.S. Geological Survey, and she also established the geology department at Bryn Mawr College. Her research focused on the igneous and metamorphic rocks of the mid-Atlantic states, including both seminal field work and state-of-the-art petrographic analysis.

Today is also Woody Guthrie’s birthday.

—Richard I. Gibson

Links:
Insect fossils in Kansas 
Gerarus
Oxygen and giant insects 
Oxygen and giant insects – another view 

Dragonfly photo by Hcrepin via Wikipedia under GDFL.

May 20. Wingless insects

Modern springtail

Given that we had forests developing by late Devonian time, you might suspect a proliferation of insects as well. You’re probably right. But insects, fragile as they are, are notoriously difficult to preserve, so the record is fairly sparse during most of the Devonian, especially the early and middle epochs of the period. The bugs in the Rhynie Chert, which we talked about on May 8, do include some primitive insects related to modern springtails. Springtails are hexapods, like insects, but technically they fall into a different group of arthropods. The first complete Devonian insect was not described until 2013 – this link is to the paper in Nature about it. That discovery helps fill in a 45-million-year gap in the fossil record of insects.  

All the few insects known from the Devonian are probably wingless – wings didn’t develop, so far as we know, until the Carboniferous, which we’ll cover in June and July. In terms of the rock record, we’ll have to wait until next month before we can really start to talk about insects. Conditions during the Devonian, including a warm climate and all those proliferating plants on land, would lead you to expect a lot of bugs, too, but the fossil evidence is poor. Either there is a preservation problem – there certainly IS a preservation problem, but we don’t know how big a problem it is – or insects were taking longer to evolve and expand into terrestrial ecologic niches than plants did. Or both.

* * *

Sometime about May 20, in the year 526 a.d., an earthquake hit Antioch, in northwestern Syria. The estimated death toll was 250,000 – maybe as many as 300,000, making it among the deadliest earthquakes in recorded history. The location is near the intersection of the tectonic boundaries between the African and Arabian Plates and the smaller Anatolian Plate that occupies most of modern Turkey. Most of the damage was actually caused by fires that followed the quake and burned for many days. The Great Church of Constantine was a victim of those fires.

—Richard I. Gibson

Modern springtail, similar to wingless insects of the Devonian. Photo by Sarefo under GNU free documentation license.