This is Mazon Monday post #43. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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The insects of Mazon Creek are a hugely, complex subject. We'll take the next few posts of Mazon Monday to cover this topic. There will be information from multiple sources along with some breathtaking pictures and drawings.
Insects are rare in the fossil record. It's currently thought that they evolved in the lower Silurian, with the oldest fossil, which is contested, dating from the Devonian Period, perhaps 400 million years ago. That specimen seems to be fairly derived and thus points to an earlier origin, probably along side the earliest land plants maybe in the upper Ordovician but certainly by the lower Silurian time periods. By the Carboniferous, there was an extensive radiation with fossils found throughout the coal deposits for which the period is known. More detail can be found on Wikipedia.
The most recent understanding of the evolution of insects is based on studies of the following branches of science: molecular biology, insect morphology, paleontology, insect taxonomy, evolution, embryology, bioinformatics and scientific computing. It is estimated that the class of insects originated on Earth about 480 million years ago, in the Ordovician, at about the same time terrestrial plants appeared.[1] Insects may have evolved from a group of crustaceans.[2] The first insects were land bound, but about 400 million years ago in the Devonian period one lineage of insects evolved flight, the first animals to do so.[1] The oldest insect fossil has been proposed to be Rhyniognatha hirsti, estimated to be 400 million years old, but the insect identity of the fossil has been contested.[3] Global climate conditions changed several times during the history of Earth, and along with it the diversity of insects. The Pterygotes (winged insects) underwent a major radiation in the Carboniferous (356 to 299 million years ago) while the Endopterygota (insects that go through different life stages with metamorphosis) underwent another major radiation in the Permian (299 to 252 million years ago).
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The Carboniferous (359 to 299 million years ago) is famous for its wet, warm climates and extensive swamps of mosses, ferns, horsetails, and calamites.[17] Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo-Carboniferous in age. The cooling and drying of the climate led to the Carboniferous rainforest collapse (CRC). Tropical rain forests fragmented and then were eventually devastated by climate change.[20]
Remains of insects are scattered throughout the coal deposits, particularly of wings from cockroaches (Blattodea);[21] two deposits in particular are from Mazon Creek, Illinois and Commentry, France.[22] The earliest winged insects are from this time period (Pterygota), including the aforementioned Blattodea, Caloneurodea, primitive stem-group Ephemeropterans, Orthoptera, Palaeodictyopteroidea.[17]:399 In 1940 (in Noble County, Oklahoma), a fossil of Meganeuropsis americana represented the largest complete insect wing ever found.[23] Juvenile insects are also known from the Carboniferous Period.[24]
Very early Blattopterans had a large, discoid pronotum and coriaceous forewings with a distinct CuP vein (a unbranched wing vein, lying near the claval fold and reaching the wing posterior margin). These were not true cockroaches, as they had an ovipositor, although through the Carboniferous, the ovipositor started to diminish. The orders Caloneurodea and Miomoptera are known, with Orthoptera and Blattodea to be among the earliest Neoptera; developing from the upper Carboniferous to the Permian. These insects had wings with similar form and structure: small anal lobes.[17]:399 Species of Orthoptera, or grasshoppers and related kin, is an ancient order that still exist till today extending from this time period. From which time even the distinctive synapomorphy of saltatorial, or adaptive for jumping, hind legs is preserved.
Palaeodictyopteroidea is a large and diverse group that includes 50% of all known Paleozoic insects.[12] Containing many of the primitive features of the time: very long cerci, an ovipositor, and wings with little or no anal lobe. Protodonata, as its name implies, is a primitive paraphyletic group similar to Odonata; although lacks distinct features such as a nodus, a pterostigma and an arculus. Most were only slightly larger than modern dragonflies, but the group does include the largest known insects, such as the late Carboniferous Meganeura monyi, Megatypus, and the even larger later Permian Meganeuropsis permiana, with wingspans of up to 71 cm (2 ft 4 in). They were probably the top predators for some 100 million years[17]:400 and far larger than any present-day insects. Their nymphs must also have reached a very impressive size. This gigantism may have been due to higher atmospheric oxygen-levels (up to 80% above modern levels during the Carboniferous) that allowed increased respiratory efficiency relative to today. The lack of flying vertebrates could have been another factor.
Mazon Creek has played a vital part in the understanding of insect evolution as it has produced more evidence than any of the other deposits. At one time, there were nearly 150 species belonging to 30 families and 102 genera from the concretions of the Francis Creek Shale. That number as come down a little as more fossils are found and we better understand the animals which have been found. That's a huge amount of diversity... and makes you wonder why we don't find more if them.
The "Richardson's Guide to The Fossil Fauna of Mazon Creek" is a great resource for all the fossil animals that have been found in the Mazon Creek biota. The book has two chapters on insects. One is by the legendary Frank Carpenter, who was curator of fossil insects at the Harvard Museum of Comparative Zoology for 60 years. The other chapter was written by Jarmila Kukalova-Peck, another giant in the study of insect origins.
George Langford was familiar with the insects of Mazon Creek. He devoted no less than 26 pages to them in his second book "The Wilmington Coal Fauna and Additions to the Wilmington Coal Flora", accompanied by his exquisitely detailed drawings. Here are a couple of his original handwritten pages.
Heterologus langfordorum Carpenter - Holotype; now on exhibit at the Illinois State Museum.
We'll have more to say about Heterologus langfordorum for the next Fossil Friday. Stay tuned!
