Literature Review: Permian and Triassic

by Carl Strang

The Permian Period that ended the Paleozoic Era, and the Triassic Period that began the Mesozoic Era, continue to attract researchers’ attention. This was a time of dramatic geological activity as the continents ground together to form the supercontinent of Pangaea, a time of two mass extinctions, and a time when the first dinosaurs evolved. Today I share notes from some of last year’s literature on this time period.

Part of a mural depicting a prosauropod (sauropodomorph), one of the early dinosaurs. Field Museum of Natural History exhibit.

Stephen E. Grasby, Hamed Sanei, Benoit Beauchamp. Catastrophic dispersion of coal fly ash into oceans during the latest Permian extinction. Nature Geoscience, 2011; DOI: 10.1038/ngeo1069     Deposits of coal ash in Canada support the view that the Siberian traps volcanic eruption involved coal beds, burning huge volumes of coal and releasing significant greenhouse gases while the toxic ash itself may have been a significant ocean contaminant. The consensus now is that this massive eruption, probably connected to the collision of continents, produced atmospheric changes that led to the greatest mass extinction in the history of multicellular life.

K.M. Meyer, M. Yu, A.B. Jost, B.M. Kelley, J.L. Payne. δ13C evidence that high primary productivity delayed recovery from end-Permian mass extinction. Earth and Planetary Science Letters, 2011; 302 (3-4): 378 DOI: 10.1016/j.epsl.2010.12.033     As described in ScienceDaily article. They found evidence that high carbon dioxide concentrations from the end-Permian volcanic eruptions caused an extended period of erosion that enriched the oceans, resulting in blooms of algae and bacteria that depleted ocean oxygen levels for as long as 5 million years and delayed the recovery of marine diversity.

J. H. Whiteside, P. D. Ward. Ammonoid diversity and disparity track episodes of chaotic carbon cycling during the early Mesozoic. Geology, 2011; 39 (2): 99 DOI: 10.1130/G31401.1     They looked at the relationship between ammonoid (squid-like shelled animals) diversity and ecosystem stability as measured by carbon isotopes, in relation to the end-Permian and end-Triassic mass extinctions. They found that swimming ammonoids (regarded as top predators, along with some fish) became extinct at these times, while some more passively floating species survived. Carbon isotope ratios fluctuated chaotically in association with the mass extinctions, implying extreme food web instability, and did not regain their stability until the evolution of new groups of swimming ammonoids some 10 million years later. They mention the importance of redundancy in top predator niches, with significant overlap in ecological space occupied by diverse species groups. The authors regard these instances as cautionary tales for the current threats to top marine predators (cod, sharks, tuna, etc.).

Randall B. Irmis, Jessica H. Whiteside. Delayed recovery of non-marine tetrapods after the end-Permian mass extinction tracks global carbon cycle. Proceedings of the Royal Society B, Published online Oct. 26, 2011; DOI: 10.1098/rspb.2011.1895     As described in a ScienceDaily article. They found that on land, in parallel with their earlier marine study, there was an extended period of ecological instability apparently resulting from low species diversity and food web connectivity. Only a few species survived the end-Permian extinction, and these had practically no competition. The resulting boom and bust population cycles prevented communities from developing stabilizing checks and balances, extending the depauperate period 8 million years into the Triassic. Dominant vertebrates included the dicynodont Lystrosaurus and procolophonids, both of which had been minor players in the Permian. Pleuromeia was a lycopod or club moss, tree or bush sized, that likewise became dominant. They did a count of individual fossils to establish this pattern, finding that 78% of terrestrial vertebrate genera went extinct. The carbon cycle did not become stable until the community structure stabilized.

Martinez, Ricardo N., et al. 2011. A basal dinosaur from the dawn of the dinosaur era in southwestern Pangaea. Science 331:206-210. They describe a new fossil, Eodromaeus murphi, from NW Argentina, and classify it as a basal theropod (predatory dinosaur).  Its contemporary, Eoraptor, they move out of the theropods, reclassifying it as a basal sauropodomorph (early predecessor of the giant, 4-legged, long-necked herbivores that were to be so diverse and abundant in the Jurassic Period). They conclude that both of those groups and the ornithiscians (the remaining dinosaur group) were established by the end of the Triassic. Their analysis of contemporary fossils also supports the idea that dinosaurs rose through a process of opportunistic replacement rather than competitive displacement, filling gaps as other groups went extinct rather than pushing them aside.

Ruhl, Micha, et al. 2011. Atmospheric carbon injection linked to end-Triassic mass extinction. Science 333:430-434. They found changes in the isotopic ratios of carbon at that time that support the idea that massive volcanic eruptions released huge amount of methane, which among other things would have a climate change effect.


Literature Review: Paleozoic

by Carl Strang

This week’s assembly of papers from 2011 is a smattering of studies I encountered pertaining to the Paleozoic Era. In the Paleozoic we see the elaboration of multicellular life, first in the sea and then on land as both plants and animals solved the challenges of terrestrial life.

Peter Van Roy, Derek E. G. Briggs. A giant Ordovician anomalocaridid. Nature, 2011; 473 (7348): 510 DOI: 10.1038/nature09920     Anomalocaris is the most impressive predatory animal of the early Paleozoic, but this invertebrate previously was known only from the Cambrian Period which opened the era. This newly described species was larger than the Cambrian ones, at 3 feet long, and extends the group 30 million years beyond the Cambrian into the Ordovician Period.

G. D. Cody, et al. Molecular signature of chitin-protein complex in Paleozoic arthropods. Geology, 2011; DOI: 10.1130/G31648.1     They found surviving remnants of chitin and protein in a scorpion exoskeleton from the northern Illinois Pennsylvanian Period (310 million years ago) and in a eurypterid from Ontario’s Silurian Period (417 million years ago). The previous oldest preserved organic material was protein from dinosaur fossils. Ten years ago none of this would have been thought possible.

The next paper is about fish jaws such as this example of the extinct group known as placoderms. Field Museum of Natural History exhibit, Chicago.

Philip S. L. Anderson, Matt Friedman, Martin D. Brazeau, Emily J. Rayfield. Initial radiation of jaws demonstrated stability despite faunal and environmental change. Nature, 2011; DOI: 10.1038/nature10207     They did a comparative functional morphology study of early fish jaws across tens of millions of years, looking also at changes in fish communities. They found that jawless fish diversity was unchanged over 30 million years of overlap, calling into question the assumption that jawed fishes outcompeted them. When they did decline, there is no sign that jawed fishes expanded into abandoned ecological space. The initial diversification of jaw structure stabilized well before 400 million years ago, and subsequently remained stable in the face of significant environmental change.

Gerienne, Philippe, et al. 2011. A simple type of wood in two Early Devonian plants. Science 333:837. They describe slender fossil stems from France (407 million years ago) and from Canada (397 million years ago) that become the earliest examples of woody plants. Prior to this discovery, only herbaceous plants were known from this time, and the previous earliest woody plants were from the Middle Devonian, 397-385 million years ago. The size of the stems and details of their cellular structure support the idea that wood first evolved for fluid transport within the plant rather than for support. The timing of this development coincides with a drop in atmospheric carbon dioxide, which would have driven improvements in transport within the plant. The fossils resemble Psilophyton, a precursor of ferns and other vascular plants.

Club moss

Banks, Jo Ann, et al. 2011. The Selaginella genome identifies genetic changes associated with the evolution of vascular plants. Science 332:960-963. They sequenced the genome of a club moss, Selaginella moellendorffii, and compared the result to the genomes of angiosperm plants. Both lineages are vascular, but they diverged shortly after vascular plants appeared 410 million years ago. Club mosses are much less diverse than angiosperms, and much less important ecologically. This may be related to their lack of whole-genome duplications which happened several times in angiosperm history. Most of the genes that direct angiosperm development are present in Selaginella. Comparisons with other groups indicate that the number of genes nearly doubled, from 3800 to 6800, between aquatic green algae and early land plants represented by mosses. A smaller increase of more than 400 genes characterized the common ancestor of Selaginella and Angiosperms, then there was a further increase of 1000 genes in the Angiosperms. After that the whole-genome duplications began.

Prehistoric Life 11

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Yes, it’s a dinosaur, and yes, we’ve reached the Mesozoic Era, but this one won’t appear until later.

Mesozoic Era, Triassic Period (251-208 million years ago)

The Mesozoic Era was named in 1841 for the fossil life that characterized it, literally translated “middle life.” It is divided into three periods, the first of which is the Triassic. The Triassic Period was named for the fact that, as then understood (1834), it consisted of 3 distinct rock layers. It ended with a mass extinction.

Life on Earth. The end of the Paleozoic Era marked a major divide in marine ecosystems. The major extinctions that ended the Permian Period may have acted to remove dominant species that had held others back by niche pre-emption. After the start of the Triassic, sessile filter feeders became less dominant, and mobile species and ones living on other species became more important. In particular, the superior ability of clams to metabolize toxins, coupled to their mobility, may have allowed them to survive when the attached brachiopods and bryozoans died en masse (Paleobiology 33:397-413; Science. 322:359). Complexity of marine ecosystems in general increased (Science 314:1289). Some data indicate that oxygen climbed to levels matching today’s, but then plummeted again, hitting a minimum of just over 10% coinciding with a mass extinction at the Triassic-Jurassic boundary (Science 316:557). Other results indicate that oxygen never dropped below 15% in the Mesozoic (Science 321:1197-1200).

Clams played a significant role in the changes to marine ecosystems that followed the end-Permian extinctions.

Ammonoids diversified greatly during the Triassic, filling a broad ecological range. Most became extinct at the close of the Triassic, however, leaving a single family to diversify even more in the following Mesozoic periods. Clams also diversified in the Triassic. Rugose corals became extinct, and a new group of corals appeared. These were forming reefs by the middle Triassic, ending a long gap that began with the wiping out of reefs in the late Devonian.

Aphids first appeared in the fossil record in the Triassic.

On land, the first true flies (Diptera), thrips, aphids and possibly caddis flies and termites appeared. This period was a time of transition for plants. Plenty of Paleozoic groups such as ferns, seed ferns, cycads, club mosses and horsetails remained. Conifers and ginkgoes became increasingly important as the Triassic passed.

We have only one surviving ginkgo species today, but the group was much more diverse and important in the Triassic Period.

Among early Triassic vertebrates, therapsids, the so-called mammal-like reptiles, were important. They included large browsers, medium-sized root feeders, and large predators. Dicynodonts in large numbers but reduced diversity were among the survivors of the Permian extinctions that dominated the early Triassic. These squat, short-tailed herbivores included Lystrosaurus, mentioned in the Permian chapter. Cynodonts were another group of therapsids, consisting of a variety of herbivores and predators that were the closest relatives of the mammals. The first mammals, small and rodent-like, emerged from this group at about the same time the dinosaurs appeared, in the late Triassic.

Reptiles increasingly dominated the Triassic vertebrate fauna as time went by, both in numbers and species diversity. Most of these groups are now long extinct. Procolophonids were small chubby herbivores. Relatives of today’s lizards and turtles became more common. Reptiles known as archosaurs and their relatives were the dominant terrestrial vertebrates through most of the period. It has been speculated that a major reason for this was that the dry continental climate gave the advantage to animals that could conserve water by eliminating nitrogen waste in the form of the more solid uric acid rather than watery urea, like the therapsids and mammals. Some archosaurs, among them the aetosaurs, were on all fours. The herbivorous aetosaurs were the first heavily armored terrestrial vertebrates. Rhynchosaurs were large barrel-bodied herbivores with beaklike jaws on their round heads.

There also were a variety of predators including groups that resembled dinosaurs and gave rise to them, the first crocodiles, and the phytosaurs. The phytosaurs, which had appeared by middle Triassic times, were similar in appearance to today’s crocodiles, the most obvious difference being the location of their nostrils near their eyes rather than at the tips of their snouts. They spread around the world by the end of the Triassic. True crocodilians appeared by the late Triassic, but most of them were terrestrial predators that ran actively on all fours; today’s crocodile niche then was filled by the phytosaurs. Early ichthyosaurs (dolphin-like reptiles) appeared by the middle Triassic. Turtles appeared by the late Triassic. In the early Triassic there are fossils of nothosaurs, semi-aquatic reptiles which in post-Triassic times had plesiosaurs as descendents. The first pterosaurs appeared in the Triassic. They are not dinosaurs, though they are close relatives of them.

Alligator. Its reptile group, the crocodiles, appeared in the Triassic, but began as running terrestrial predators. A separate group, the phytosaurs (long extinct) filled the niche occupied by today’s crocodiles. The term “crocodylomorph” includes both crocodiles and phytosaurs.

The first undisputed dinosaurs appeared in the late Triassic, evolving from bipedal archosaur predators, probably in South America. Fossil footprints found in Poland and reported in 2010 suggest that the line that led to the dinosaurs had split from other archosaurs as early as 2 million years after the end-Permian extinction. The first dinosaurs were all in the order Saurischia. Saurischians were abundant in the eastern U.S., and left many footprints in New England. Many of the first dinosaurs were theropods (carnivorous, bipedal, long-necked and long-tailed). Body sizes ranged from abundant 3- to 4-footers to the largest 16-20-footers.

Freshwater ecosystems included small freshwater sharks, coelacanths, lungfishes and a variety of large and small amphibians, though these declined toward the end of the Triassic.

The Four Corners area has deposits that give a good idea of late Triassic life. Uplands had forests of araucarian “pines” well known from Petrified Forest National Monument, and true ferns in the understory. There were large amphibians, mussels, lungfish, freshwater sharks, coelacanths, aetosaurs, running crocodiles, the predatory dinosaur-like Postosuchus which was the top carnivore, phytosaurs in swamps, saurischian dinosaurs including the small predator Coelophysis, and a few primitive mammals. In many parts of the world the prosauropods, the first herbivorous dinosaurs, with their long necks and ability to reach high vegetation, became dominant in numbers or biomass. Early members of the other dinosaur order, Ornithischia, appeared by the Late Triassic. But there was a long period in the Late Triassic when dinosaurs coexisted with other archosaurs similar to their ancestors, and dinosaurs were not as common in the Late Triassic, so their rise to dominance was gradual (Science 317:358).

This mural from a 2005 temporary exhibit at the Field Museum shows a Triassic scene dominated by a prosauropod. These were the first herbivorous dinosaurs.

The end of the Triassic is marked by the extinction of all archosaurs other than dinosaurs, pterosaurs and crocodylomorphs. The possible drop in atmospheric oxygen is regarded as significant here. The dinosaurs had evolved a new air-sac system (retained in modified form in modern birds) which may have permitted their survival and also set the stage for giant body sizes in the Jurassic and Cretaceous (Science 316:557). However, a variety of possibilities remain under discussion for explaining the end-Triassic extinctions. A 2008 study finds that, just as was the case at the end of the Permian, the end-Triassic extinctions occurred at the same time as a massive volcanic eruption, this one in the central Atlantic (Science 320:434-435). Massive lava flows at that time are associated with the continental split that ultimately produced the Atlantic Ocean.

Local landscape. There are no Triassic or Jurassic rocks in Illinois. The nearest Triassic bedrock is in south central Pennsylvania. Reconstructions of North America, which still was united with the other continents, indicate that in the early Triassic, the Appalachian chain was high and mountainous, sloping down west and north into our area, with a red sandy alluvial plain beginning just west of us and extending west.

Bedrock topography suggests that throughout most of the Mesozoic a major river, the Teays, drained westward from the Appalachians, cutting across the center of Illinois, and it is likely that some local stream or streams flowed south or west as Teays tributaries.

Our area was very close to, perhaps just north of, the equator. By the late Triassic, Illinois had drifted to about 10° N latitude. New volcanoes and faulting and uplift were occurring to the East, and our area was even more elevated, with the beginning of the alluvial plain farther to the west. The warmest climate in all of the time of Earth’s life began in the middle Triassic and lasted through the Cretaceous.

Local life. Our area was dry land, in a warm equatorial climate, but the kind of vegetation is difficult to speculate about. We have to base our understanding on fossils in New England and the Four Corners area, distant but on either side of us. Likely there were a variety of insects and some therapsids and early archosaurs, as well as saurischian dinosaurs (Coelophysis, Ammosaurus) and early mammals. Both eastern (North Carolina to Nova Scotia) and southwestern U.S. formations from the late Triassic share many groups, including phytosaurs, amphibians, ornithiscian and prosauropod dinosaurs. Worldwide examinations suggest that late Triassic-early Jurassic dinosaur faunas typically included “one or two sauropodomorphs (such as prosauropods), one or two theropods (two-legged predators), and possibly one ornithischian.”

Prehistoric Life 10

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Permian Period (286-251 million years ago)

The Permian Period was named for the Perm District of Russia (1841), added because the fossils found there, though distinctive, were recognizably between those of the Carboniferous and Triassic periods. It began with a glacial period, and the fusion of the continents into the supercontinent of Pangaea. Its ending (and that of the Paleozoic Era) was a massive extinction of as many as 95% of species, now correlated with the largest known volcanic eruption in the history of the Earth, in Siberia.

Life on Earth. Trilobites became rare during the Permian, and the last of them vanished when it closed. This was the last time in which brachiopods were important, continuing to diversify during the Permian, but having many extinctions, and becoming relatively unimportant after the Permian. Snails and clams were relatively unimportant, but ammonoids (octopus relatives living in coiled shells) became widespread and diverse.

The drier climate of the Permian led to the rapid decline of the giant club moss and horsetail forests. Conifers, cycads, ginkgoes and seed ferns, which better protected their seeds from drying out, became dominant.

Ostracods and insects became more abundant. The proto-dragonflies still were around, e.g. in Kansas, and the modern Odonata, which may have evolved from them, appeared early in the Permian, as did the true bugs, scorpion flies, caddis flies and Neuroptera.

Here is part of an exhibit on Permian animals at the Field Museum of Natural History. The predator Dimetrodon is in the upper left corner.

There were two important groups of synapsids in the Permian. The pelycosaurs (e.g., carnivorous Dimetrodon and herbivorous Edaphosaurus, both known from Texas) often had long, sometimes branched spines down their backs, usually depicted as supporting a sail-like structure that they possibly used in thermoregulation. Pelycosaurs became extinct in the last half of the Permian. The other synapsids were the therapsids, often informally called mammal-like reptiles, the mammalian ancestors. The therapsids are thought by most to have descended out of the pelycosaurs; they appeared at about the time the pelycosaurs vanished. Cynodonts are the therapsid group ancestral to mammals, emerging in the late Permian.

There were reptiles other than synapsids in the Permian. This pareiasaur is an example of another group, the anapsids (again, part of the Field Museum exhibit).

Amphibians declined, though a number of large ones are known from Texas, including Eryops. There was also the bizarre, wide-skulled Diplocaulus of North America. The dry climate resulting from the formation of Pangaea boosted terrestrial vertebrates with shelled eggs; amphibians were at a disadvantage.

The Permian ended with massive extinctions, apparently the most severe the world has seen, with possibly only 5-10% of marine species and 10-35% of terrestrial vertebrates surviving. The cause is unknown, but various climatic and geological upheavals would have accompanied the collision and fusion of continents that was happening then. Two recent studies suggest that a sudden major release of methane gas may have been the direct cause of the extinctions (Science 301:1168). Other studies closely tie the extinctions to the time of the most massive volcanic eruption in Earth’s history, in Siberia (Science 305:1705, 320:434-435). Toxic hydrogen sulfide, another gas that could have been released in large amounts by volcanic eruptions, also spiked in the atmosphere at that time (Science 307: 706). The Permian was a time of stress also because atmospheric oxygen levels appear to have dropped from 30% in the early Permian to only 12% in the late Permian. This would have limited terrestrial animals to isolated pockets of habitat at low altitudes. In addition to measures of oxygen, the fact that one of the few surviving therapsids was a tunneling species (Lystrosaurus), presumably pre-adapted to low oxygen, provides support for low oxygen as a contributing factor (Science 308:398; see also Science 309: 2202). This is underlined by the fact that at least 90% of surviving terrestrial vertebrates in South Africa and Antarctica were Lystrosaurus, which also is known from South America, China, and Russia.

Local landscape. The Permian is the only Paleozoic period with no remaining deposits anywhere in Illinois (the closest areas with Permian bedrock are in the southeastern corner of Nebraska and in southeastern Ohio). Our area was land then, the seas well east and west of us. There was geological activity, though, as a magma body moved into Mississippian limestones during the Permian, creating Illinois’ fluorspar deposits and giving us our state mineral. This event probably was the result of the collision between the northern supercontinent of Laurasia with southern Gondwana to form Pangaea. Much as today’s Himalayas are building from India’s push into south Asia, a Pangaean mountain range (persisting in part as the Appalachians) extended from what is now the Gulf of Mexico to New England and Canada’s Maritime Provinces and beyond. This mountain range had an east-west orientation and was just north of the equator, with the result that our part of North America was a desert. North America was united with South America (the northern bulge of which fitted the Gulf coast) and Africa (Africa’s west coast fitted against South America and North America together).

The ice age described for the Pennsylvanian Period continued into the early Permian, but was limited to what are now the southern continents. Later in the period, atmospheric carbon dioxide rose to the point where its greenhouse function prevented glacial periods from occurring, and this inhibition continued until the Pleistocene. The warming selected for increasingly drought-tolerant plant communities as the Permian progressed, for example favoring conifers at the expense of tree ferns and seed ferns (moisture-loving plants persisted in limited low, moist refuges).

Local life. The best guess may be that we had local savannas to desert woodlands of the plant groups mentioned above, with a variety of insects, and some therapsids and pelycosaurs. Local streams would have had fishes and amphibians. But to the extent that this area was elevated, and the oxygen depletion mentioned above was a factor, there may have been a biological depletion of our central part of the supercontinent.

Prehistoric Life 9

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Pennsylvanian Period (320-286 million years ago)

The Pennsylvanian Period is named for the state of Pennsylvania (1891). This North American subdivision of the European Carboniferous Period is distinguished by many cyclic repeated advances and retreats of the sea, as indicated by alternating rock layers.

Life on Earth. This was the time of the coal forests, when the growing land area provided the home for forests of lycopsids (club mosses, the most abundant trees), sphenopsids (the group containing today’s scouring rush, horsetails and other members of genus Equisetum), ferns (including tree ferns), and seed ferns. There were early conifers as well. These were vascular but not flowering plants. Most coal was produced during this period because fungi, critical to decomposition, had not yet developed that ability to a significant extent. Dead plant tissue piled up without breaking down, ultimately was buried and fossilized into coal. As a result, oxygen built in the atmosphere to an all time high of 30% (Science 316:557).

You can see a life-sized reconstruction of a Pennsylvanian forest at the Field Museum in Chicago. Here are some model sphenopsids.

The earliest Amniota (the terrestrial egg-bearing group ultimately including reptiles, birds and mammals) appeared and diverged in the Pennsylvanian, producing the cotylosaurs (and other anapsid reptiles, a group represented by turtles and tortoises today; fossil cotylosaurs have been found as close to Illinois as Nova Scotia), synapsids (also known from N.S. and the group from which mammals ultimately evolved; the basal synapsids are referred to as pelycosaurs), and the diapsids, a reptile group that evolved into lizards, snakes, dinosaurs, birds and crocodiles.

Winged insects (including the first mayflies and enormous primitive dragonflies) first appeared in the Pennsylvanian, as did cockroaches, grasshoppers and crickets. The earliest beetle was reported from Illinois fossil material in 2009 (J. Paleont. 83:931). Some invertebrates, such as the dragonflies and certain millipedes, reached giant sizes (thanks at least in part to the elevated oxygen levels).

Local landscape. In Illinois, the sea continued its advance and retreat cycling, so that our area alternated between marine and land, often low and swampy. Our area remained just south of the equator, and the climate was warm and humid.  It is thought that alternating periods of glaciers forming and thawing on the southern Gondwana supercontinent (at that time drifting over the South Pole) caused the rises and falls of sea level that produced the local advances and retreats of the sea. Over geologic time, glacial episodes typically are associated with a continental mass at one of the poles (Antarctica in recent times).

Tree ferns still exist today. This one in Tasmania had a thick stem more than 10 feet tall.

The North American continent was beginning to collide with Europe and Africa as the sea that had begun to appear between them closed, forming the northern supercontinent of Laurasia. This event is what lifted our part of the world above the sea for good.

The nearest Pennsylvanian bedrock to Chicago is the Mazon Creek area (much of Illinois’ bedrock is Pennsylvanian), except for some bits in the Des Plaines Disturbance.

Local life. Coal forests dominated Illinois during the Pennsylvanian. Not only was coal left (itself fossil plant material), but remains of a variety of plant and animal fossils can be found just a little south of us in the world-famous Mazon Creek deposits of Middle Pennsylvanian age, just a little southwest of Joliet. Seed-fern leaves such as Medullosa, Neuropteris inflata, N. scheuchzeri, N. ovata and N. rarinerus are especially abundant (note: names of these plants are confusing, because different names are given to different parts such as leaves, stems and reproductive parts). There also were the giant sphenopsid Calamites, the smaller weedy horsetail Sphenophyllum, the tree fern Psaronius, small ferns (Pecopteris, Sphenopteris, Alloiopteris), the conifer relative Cordaites, giant club moss relatives Cyperites, Lepidodendron, Lepidophloios, and Sigillaria (up to 6 feet in diameter!), and other, smaller club mosses (Lycopodites, Bothrodendron).

Here are some giant club mosses in the Field Museum exhibit.

Most bizarre among the diverse aquatic animals was the Tully monster (Tullimonstrum gregarium), first found by amateur fossil collector Francis Tully, Illinois’ state fossil, and only known from this area. There were horseshoe crabs (Palaeolimulus, Euproops), freshwater fish (Rhabdoderma oxiguum, Conchopoma edesi, Elonichthyes peltigerus, Platysomus circularis), and mollusks, as well as a lamprey-like fish, Actinopterygian fishes (Elonichthys pettigerus, Platysomus circularis), polychaete worms (Astreptoscolex anasillosus, Escorites zelus, and others), shrimps (Belotelson sp., Kallidecthes richardsoni, Acanthotelson stimsoni, and others), a sea cucumber (Achistrum sp.), a nematode (Nemavermes mackeei), a chiton (Glaphurochiton concinnus), ribbon or priapulid worms (Archisymplectes rhothon, Priapulites konecniorum), the arrow worm Paucijaculum samamithion, the spoonworm (phylum Echiura) Coprinoscolex ellogimus, jellyfish (Essexella asherae, Octomedusa pieckorum, Anthracomedusa turnbullii), cephalopods, brachiopods (Lingula sp.), the scallop Aviculopectin mazonensis, as well as several “mystery animals” of unknown affinities. 

The Field Museum model forest includes a millipede you could put a saddle on!

Land animals included centipedes, millipedes (the giant millipede Arthropleura cristata was a flat species, 16” wide and more than 6 feet long), scorpions, cockroaches (Platymylacris paucineruis) and their relatives (Gerarus danielsi, G. vetus), and spider-like arachnids. There were amphibians (Amphibamus grandiceps, A. yelli).

The upland trees, less well known, were different from those in the swamps, and included the genera Megalopteris and Lesleya. An upland animal was the scorpion Labriscorpio alliedensis.

Prehistoric Life 8

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Mississippian Period (360-320 million years ago)

Most of the world calls the period following the Devonian the Carboniferous Period. It was named for coal deposits in Europe in 1882, marking the first massive forest terrestrial communities. Its beginning (as is that for the Mississippian Period) is defined by the first appearance of the conodont Siphonodella sulcata. In North America the Carboniferous long has been subdivided into two parts, though this distinction is vanishing as worldwide communication highlights the idiosyncratic nature of the North American pattern. The Mississippian Period is distinguished by the relative stability of the sea. It was named in 1870 for the Mississippi valley.

Walking Fern. Ferns were abundant land plants in the Mississippian.

Life on Earth. Ferns became extremely abundant in the Carboniferous, and a distinction developed between the terrestrial floras of what are now the northern hemisphere continents (characterized by club mosses, some seed ferns, and primitive conifers), and the southern hemisphere (characterized by a genus of seed ferns, Glossopteris). In North America, however, these forests were limited in the Mississippian Period by the small area of dry land.

Graptolites vanished in the Mississippian. There were no huge leaps in vertebrate evolution in the Carboniferous, but amphibians diversified and evolved better functioning legs. For example, a common ancestor of frogs and salamanders, having characteristics intermediate to those groups, lived 340 million years ago (Science 318:1237). Crinoids reached their all-time greatest abundance around the Mississippian reefs. Protozoa also diversified, with Foraminifera particularly becoming common.

Local landscape. Illinois was mainly marine during the Mississippian, but the land was not too far east and northeast, and moved closer and farther away as the sea level fell and rose, so there were episodes of limestone deposits (mainly), some of muddy bottoms (closer to shore), and even sand (very close to shore). Late in the period, the limestone-deposition areas occasionally were exposed to air, and the sea retreated as our area became land.

Indeed, much of the North American continent was raised above the sea by growing tectonic activity in that time. Our area was still south of the equator.

The nearest Mississippian bedrock is south of us, in Iroquois County (the next county south of Kankakee County), with one interesting exception. There is an odd small area called the Des Plaines Disturbance, in Cook County just northeast of DuPage, where there is a complex of faults and displacements thought to have been caused by a meteorite strike. These have placed some small areas of Mississippian rock at the bedrock surface (i.e., the meteorite drove the younger rock layers down into the older Silurian strata, so that in that place they remained while being eroded away all around).

Local life. Mississippian fossils are abundant in the southern two-thirds of Illinois. The early Mississippian was a limestone time, when brachiopods as well as crinoids and other stemmed and starfish echinoderms were abundant and diverse. Bryozoans often were important, too. Mixed in (where the rock remains in western IL) are chert nodules indicative of siliceous sponges and other marine invertebrates. A crustacean, a crayfish-like malacostracan, also was here. Geode-forming species and the spiral bryozoan Archimedes were abundant later in the Mississippian. There were some trilobites.

Fossils listed in Illinois Geological Survey monographs for the Mississippian include shark teeth, the corals Cyathaxonia arcuata and Lithostrotionella, bryozoans Evactinopora sexradiata, Prismopora serrulata, Batostomella nitidula, Worthenopora, Archimedes and Rhombopora, crinoids and blastoids Platycrinites penicillus, Pugnoides ottumwa, Talarocrinus, Pterotocrinus menardensis, Onychocrinus, Batocrinus, Schizoblastus, and Pentremites spicatus, snails Platyceras and Straparollus, the pelecypods (clams) Sulcatopinna missouriensis and Euphemia randolphensis, and brachiopods Syrigothyris, Spirifer vernonensis, S. rowleyi, S. logani, S. increbescens, Dictyoclostus crawfordsvillensis, Orthotetes keokuk,  Rotaia subtrigonia, Athyris lamellosa, Leptaena rhomboidalis, Martinia contracta, Primospora serrulata, Composita subquadrata, Skelidorygma, and Ovatia. Note that this list lumps together species from different parts of the Mississippian.

Prehistoric Life 7

by Carl Strang

This year’s winter series is a review of the prehistoric life and geologic history of northeast Illinois. Each chapter will summarize current understanding, gleaned from the literature, of what was going on with life on Earth in a particular span of time, what we know about the local landscape, and what we can say about local life. I include some references, particularly to papers published in the journal Science which commonly is available at public libraries. Contact me if you need sources for other items. The Earth is so old that every imaginable environment was here at some point, from ocean depths to mountaintops, from equatorial tropics to tundra, and from wetlands to desert.

Devonian Period (408-360 million years ago)

The Devonian Period was named in 1837 for Devonshire, where fossils were first found intermediate between those of Silurian and Carboniferous periods. Its beginning formally is defined by the first appearance of the graptolite Monograptus uniformis. For DuPage County, with a single exception, the geological deposits end with the Silurian, and do not resume until the relative eyeblink of the past 12,000 years.

Life on Earth. In some ways the Devonian period continued much as the Silurian had, with reefs and their associated life forms continuing to develop and diversify. Petoskey stone, the Michigan state rock, is a middle Devonian massive colonial tabulate coral, Hexagonaria percarinata. Brachiopods remained diverse in the Devonian, but then began their decline. Trilobites remained diverse. Crabs were a new marine arthropod group in the Devonian. A significant new group of cephalopod mollusks, the ammonites, appeared. There was a massive extinction of marine forms in the late Devonian, marking the beginning of a long period where there were no large reefs until the mid-Triassic. This mass extinction coincided with a big drop in atmospheric oxygen (Science 316:557).

Today’s bluegill are members of Osteichthyes, the first of which appeared in the Devonian.

Fishes diversified, and the Devonian has been described as the “Age of Fishes.” There were 4 groups of jawed fishes: placoderms (armored; almost entirely limited to the Devonian), acanthodians (“spiny sharks,” some of which were abundant, small school-forming fishes), Chondrichthyes, and Osteichthyes. The latter two groups, which dominate today’s fishes, both first appeared in the Devonian, including both the lobe-finned (coelacanth, lungfish) and ray-finned branches of Osteichthyes, and the first true sharks (Chondrichthyes). Lampreys likewise first showed in the Devonian fossil record. These fishes were diverse ecologically as well, with plankton feeders, bottom feeders, and mobile predators.

In 2006 paleontologists described a fossil lobe-finned fish from northern Canada, 375 million years old, that is the most clearly intermediate example to date between fish and terrestrial vertebrates. Tiktaalik roseae had “fins better engineered for standing than swimming.” Also, it had lost gill cover plates, and possessed a shoulder girdle largely separated from the skull (i.e., the fish had a neck). They probably were both poor crawlers and poor swimmers, but in their river delta environment they could escape aquatic predators (Science 312:33).

The diversification of fishes and sharks as well as shell-crushing arthropods in the “Middle Paleozoic Marine Revolution” of the Silurian and Devonian Periods had a measurable impact on some of their prey (Science 305:1453). Crinoid arm regeneration increased and antipredator morphologies became more common as this time passed. Crinoids “developed more spines, thicker calyx plates, and reduced viscera.” Regenerating crinoid arms in fossils increased from less than 5% in the Ordovician and Silurian to more than 10% in the Devonian to Pennsylvanian. Close study of another group of marine invertebrates, rugose corals, has shown that the Earth was spinning faster then, so that days were 21 hours long.

Land plants were similar all over the world, implying a uniform warm climate. Early vascular land plants were small, and mainly consisted of branching stems with spore producing structures. True leaves appeared in the Devonian. The first forests emerged by the late Devonian, the trees belonging to groups called progymnosperms and seed ferns. The seeds contain spores, and the leaves are fernlike fronds. They were the ancestors of more modern plants that appeared in the Mesozoic, the cycads and flowering plants or angiosperms. There were also giant club mosses, and the first true ferns. The Devonian also produced the first lichens.

Terrestrial invertebrates diversified, producing the first millipedes, centipedes, pseudoscorpions, spiders, harvestmen (daddy long-legs), mites, and insects (springtails being a group that has persisted to the present day).

The first, labyrinthodont, amphibians appeared in the late Devonian. At least some did come out on land, and were predators. They were sufficiently widespread that they occurred in both Greenland and Australia, which even then were well separated.

Local landscape. In the early Devonian, our area is thought to have become low land as the sea retreated, the result of crustal warping, and still was a little south of the equator. The area subsided later in the period to become a shallow sea in which limestone again was deposited. The second phase of the Appalachian mountain building occurred with the Acadian orogeny in the late Devonian, as continental plates collided to the east. Then, muds eroding from uplifted lands to the east produced the Devonian New Albany shale that forms the bed of Lake Michigan. Some of that shale was gouged out, ground up, transported and deposited by the latest continental glacier to form DuPage County’s clay soil. The nearest Devonian bedrock therefore is just east of our area. However, cracks in the upper surface of the Silurian dolomite in an Elmhurst quarry contained clay that was deposited during the Devonian (or, possibly, Mississippian).

Local life. The mud-bottomed sea was contiguous in the late Devonian from here to northern Iowa, where there were forms ranging from a lobe-finned lungfish to an ammonite along with various stromatoporoids, corals, clams, snails, brachiopods and bryozoans. Horn corals and tabulate forms were diverse and abundant.

This enormous arthrodire fossil can be seen at the Field Museum.

The fierce looking arthrodires, the most diverse placoderms, were widely distributed across North America in the middle and late Devonian. The shark-like Cladoselache, of the Chondrichthyes, is known from Ohio. Falls of the Ohio State Park at Jeffersonville, Indiana, also has middle Devonian fossiliferous limestone and shale deposits. The limestone has more than 600 species of corals, sponges, brachiopods, mollusks, echinoderms, and others.

The Devonian or Mississippian clay found in Elmhurst actually contained some fossil shark teeth. Central Illinois Devonian fossils include the branching coral Alveolites, tabulate corals Hexagonaria and Pachyphyllum, the horn coral Zaphrentis, brachiopods Schizophoria, Douvillina, Cyrtina, Atrypa, Spinocyrtia, Schuchertella, and Strophodonta, and trilobites Odontocephalus and Phacops.

Biology Along the Way

by Carl Strang


Though my trip to Canada had as its primary goal an exploration of the route of the Lake Michigan lobe of the Wisconsin glacier, an old wildlifer like me was not going to ignore the vegetative communities and wildlife along the way. I was especially interested in what I would find in the highway loop through Timmins and Hearst, Ontario, as I had never been in that area before. It’s far enough north that I passed a sign marking the watershed for rivers flowing north to the Arctic Ocean and those flowing south.




Potholes Provincial Park along Highway 101 had a little trail going to some beautiful places. The trees along the edge of this photo are black spruces, a tree of special interest because we found a couple cones of this species in the mastodon dig this summer (more on that in future posts). Black spruce was the dominant tree in many places this far north, though it no longer occurs closer to Illinois than central Wisconsin.




Kettle Lakes Provincial Park has a great trail system. Here are some photos showing a segment through paper birch,




another past savanna-spaced pines,




a closeup of lichens and a club moss.




There were edible blueberries,




beautiful bunchberries,




asters still flowering in September




but the changing colors of plants such as these honeysuckles revealing the season.




Signs of animal life included a beaver lodge in every little lake,




dew-highlighted spider webs,




and a spruce grouse.




Tomorrow I’ll conclude with wildlife at Nagagamisis Provincial Park.

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