Literature Review: Cenozoic Prior to Pleistocene

by Carl Strang

The Cenozoic Era extends from the catastrophe that ended the Mesozoic Era up to the present day. Today’s literature review includes some research published last year pertaining to the bulk of the Cenozoic. Next week I will finish with some Pleistocene studies.

Leaf mine

Winkler, Isaac S., Conrad C. Labandeira, Torsten Wappler, and Peter Wilf. 2010. Distinguishing Agromyzidae (Diptera) leaf mines in the fossil record: new taxa from the Paleogene of North America and Germany and their evolutionary implications. J. Paleont. 84:935-954. Leaf-mining flies’ “mines often can be distinguished from those of other insects by the presence of an intermittent, fluidized frass trail that may alternate between the sides of the mine.” These researchers found an example of this pattern in an early Paleocene fossil sycamore leaf, Platanus raynoldsii, from Montana. They also see in those leaves “associated stereotypical marks identical to damage caused by feeding punctures of extant adult female Agromyzidae prior to oviposition.” This is the earliest fossil agromyzid (the family of these leaf-mining flies), named Phytomyzites biliapchaensis. Sycamores today do not have leaf mining agromyzids. The researchers speculate that this was “an evolutionary, possibly opportunistic colonization in the midst of the ecological chaos following the end-Cretaceous event in North America.”

Antoine, P.-O., et al. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B: Biological Sciences, 2011; DOI: 10.1098/rspb.2011.1732     Caviomorph rodents are the group that today characterizes the South American fauna and includes such species as guinea pigs and capybaras. These researchers found fossils of 3 species from 40 million years ago, much older than the previously known earliest South American rodents. The fossils indicate that the origin of that continent’s rodents was a rafting colonization from Africa.

Clarke, Julia A., et al. 2010. Fossil evidence for evolution of the shape and color of penguin feathers. Science 330:954-7. They describe a fossil giant penguin (Inkayacu paracasensis) from Peru, 36 million years ago in the late Eocene Epoch. The penguin’s primary wing feathers were difficult to distinguish from the coverts. Body contour feather shafts were broad like those of today’s penguins, and of similar proportionate length. Melanosomes suggest the colors were gray and reddish-brown.

Mihlbachler, Matthew C., et al. 2011. Dietary change and evolution of horses in North America. Science 331:1178-1181. They measured crown height and microwear of horse molars from the early Eocene on. There was considerable variation in the amount of wear for a given crown height, but in general wear increased with height. They interpret this to mean that selective pressure for increasing crown height generally was weak. There were times, however, when wear was greater, “including the early Miocene shortly before the first appearance of Equinae, the horse subfamily in which high-crowned dentitions evolved.” This supports the connection between the spread of grasslands in the Miocene (grasses are a relatively abrasive food) and the evolution of high-crowned teeth.

Cycad, King’s Canyon, central Australia.

Nagalingum, N.S., et al. 2011. Recent synchronous radiation of a living fossil. Science 334:796-799. They looked at cycad relationships based on molecular comparisons with fossil calibrations. The earlier assumption was that today’s 300 species are a holdover that survived the large drop in diversity in the Jurassic and Cretaceous that occurred with the rise in flowering plants, and thus are “living fossils.” Surprisingly this research group found that today’s species are the result of a diversification that began in the late Miocene, so that they “are not much older than ~12 million years.”

Lessons from Travels: Migrants Elsewhere

by Carl Strang

When we are at home in Illinois, we categorize our birds with respect to their status when we see them here. They may be year-round residents, breeders that migrate south for the winter, winter residents, or migrants that breed north of us and pass through in the spring and fall. Those categories do not define the birds from their own perspective, however, and we can get some sense of this when we see them perfectly at home in other places. When we think of yellow-throated warblers, for instance, we typically associate them with sycamores, not with palm trees.

Yellow-throated warbler in Belize.

Still, there is a consistency in the open canopies of sycamores and palms that makes sense from the bird’s perspective. Though we commonly think of our breeding birds as being northern animals that head south to escape the winter, it might be better to regard them instead as tropical birds that travel north to take advantage of high summer productivity and fewer predators.

Travel also allows us to broaden our perspective on migrants, when we see them on their breeding grounds. This was one of the side benefits of the summers I spent in western Alaska. On the rare occasions when we see long-tailed ducks in northeast Illinois they are quiet, placid, unobtrusive. They are quite the opposite on their breeding grounds.

Male long-tailed duck, Kokechik Bay study area.

When courtship commences they become very noisy with un-duck-like tenor voices, chasing each other at rocket speeds and coming very close, apparently using people as picks. The females incubate large clutches of eggs, producing tiny dark ducklings.

In those days we called them oldsquaws. Here a mother and ducklings share a pond with red-necked phalaropes, which then were known as northern phalaropes.

Tundra swans have extraordinary courtship and territorial displays, and make huge nest mounds. Biologists can count eggs from the air. The young are placid.

Nonbreeders gather into flocks of 30 or more.

In the treeless tundra, dunlins advertise by hovering 10 feet above the ground, trilling a song that is almost identical to that of American toads. They have well camouflaged ground nests with 4 eggs.

When we see them as migrants in Illinois, dunlins are traveling in small flocks and behaving as shorebirds.

Jaegers are rarely encountered seabirds in Illinois, sought along the edge of Lake Michigan especially during the fall migration. On the breeding grounds they are predators.

Long-tailed jaegers are beautiful and graceful, hovering like kestrels in their hunt for tundra voles and bird eggs.

Two species nested there, the other being the parasitic jaeger.

Parasitic jaegers are larger than long-taileds. Once I saw one chase down and swallow whole an adult red-necked phalarope.

Such experiences sit in my mind, reminding me to think of these animals in terms of their entire lives rather than the more limited glimpses we see in Illinois.

Great Blue Heron Dossier

by Carl Strang

It has been a while since I posted one of my species dossiers. The idea is to make a record of what I know of a species from my own experience rather than what I have learned from others. This is a valuable exercise. When I got the idea and started it, I was embarrassed by how little I could write even for common species. It has forced me to pay more attention, to observe more, to be more discriminating in what I can claim to know about natural history. Even books and, yes, Internet sources like this blog need to be read skeptically. Today I choose the great blue heron, a species that played an important role in inspiring my interest in natural history studies. Records are dated with my code that begins with the day of the month, followed by a two-letter month code (usually the first two letters of the month’s name) and a two-numeral year. The code 16JE99 would indicate June 16, 1999.

Great Blue Heron

First observed at Hawk Lake, where several fished along the east side each evening in summer during my childhood. These were an early inspiration for my bird watching interest. Also observed in PA, along the Tippecanoe River in IN, in DuPage County, in Florida. Seek food usually in relatively deep water, sit-and-wait foraging. They quickly extend the neck to seize or spear fish or other prey. On rare occasions I have seen them briefly swimming on the surface of water too deep to wade. One in FL waited for fishermen to catch fish, then ran up in hope of getting the catch.

They have loud raucous squawking calls, a brief one in flight (often when disturbed) and a longer more rattling one when handled (i.e. at Willowbrook’s wildlife hospital).

Rookery established around 1967 south of Culver, Indiana, near the Tippecanoe River, in several large sycamores at the edge of a small woodlot near S.R. 17. That site still was used through 1986. Birds appear standing in nests in mid-March, radiate out in many directions to feed. Great blue herons then also reached all parts of DuPage County, IL, despite no rookeries there (a large rookery south of the county at Plainfield).

24JA89. A great blue heron flying east of Lake Maxinkuckee, IN.

10MR00. Several herons have returned to the new, small (10-nest) colony at Danada Forest Preserve.

7MY00. Great blue herons croaking in flight, traveling above West DuPage Woods Forest Preserve. An extended string of them, so the calls may be communication between flying birds.

13NO01. I count 25 nests, now, in the Danada rookery. The trees are at the edge of a pond. They are not sycamores, but I didn’t get close enough to ID. Elm shape.

21FE02. A single heron was standing on a nest in the Danada rookery at 4p.m. The winter has been mild, and it’s not inconceivable that a GBH could have survived the winter locally.

1SE02. At 10:30 p.m., a great blue heron in Geneva, standing in shallow water in the Fox River, apparently fishing in the street lights.

16JE03. This year I know of 2 large nesting colonies in DuPage County, both established in recent years. One is at Danada Forest Preserve, the other at Pratts Wayne Woods, near the intersection of Rt. 59 and Stearns Road and visible from both.

8AU03. I kayaked between Willow Springs Road in Cook County and Route 83 in DuPage on the Des Plaines River. There is a strung-out colony of great blue herons nesting over a 2-mile stretch of river that spans the county line. The nests are in scattered dead trees close to the riverbank, taller than the surrounding trees, 2-5 nests in half a dozen trees total. Though separated sometimes by more than a hundred yards, the trees each seem to have one of the others in view.

28MR06. At Tri-County State Park, the 2 nests from last year (a new satellite of the Pratts Wayne colony) gradually had lost most of their sticks. On the 23rd, herons returned (later than in the larger colonies), and now are building the nests back up. One seen carrying a long thin stick in its beak, flying up to a perch beside the nest and giving it to its mate standing in the nest, who then added it. Two additional pairs perching in those trees, but no new nest starts yet.

18JA09. Danada. Checked great blue heron rookery. Most of the 15-20 nest trees were living cottonwoods, and 90% of the nests were in these. Two were dead trees, and three were willows. One cottonwood had 16 nests, a couple had 13, one had 11. Total nests counted 142. The rookery is in a swampy area around a large pond. Last summer I also learned of a rookery at Churchill Forest Preserve, on the islands in the East Branch of the DuPage River.

11OC10. During a dragonfly monitoring run on the Des Plaines River I noticed that, in addition to the scattered great blue heron nests in tree tops along the shore, there is at least one group of trees with a number of nests in a more concentrated colony. There are more than a dozen nests in at least 3 adjacent trees. This cluster is on the river’s south bank, east of Route 83.

Rookery Trees

by Carl Strang


The great blue heron was the bird that first inspired my interest in learning about nature when I was a 7-year-old, watching several of them in a small lake one calm summer evening. A few years later a number of great blue herons established a new nesting colony near my hometown of Culver, Indiana, among the large branches of a grove of sycamore trees  in a swampy woodland.




An interesting development over the past decade has been the proliferation of great blue heron rookeries in DuPage County. One on Danada Forest Preserve near the center of the county had 25 nests or so by 2001. Another large colony has been growing for several years at Pratts Wayne Woods. Close to there, at James Pate Phillips (Tri-County) State Park, an offshoot of the Pratts Wayne rookery existed for a few years in a group of dead trees, but this experiment is on the verge of ending as the trees lose branches. There is another small rookery at Churchill Forest Preserve, and a final one strung out along the Des Plaines River in and adjacent to southeast DuPage County.


Remembering the Indiana rookery, I was curious about what species of trees were supporting the Danada colony. On a recent frigid weekend morning I went there to find out. It had to be done in mid-winter, both to avoid disturbing the birds (which could begin to return by the end of February), and to take advantage of frozen ground and water for easy travel.




I found the colony to be situated in swampy woodland surrounding a large pond. Most of the 15-20 nest trees were living cottonwoods, and 90% of the nests were in these.




Two of the nest trees were dead, and three were willows. One cottonwood had 16 nests, a couple had 13, and one had 11.




I counted a total of 142 nests. There may have been more; we have had some strong wind storms since the nesting season which could have dismantled some nests. Like sycamores, cottonwoods have open canopies and thick branches capable of supporting the relatively large stick nests herons construct. Most of the trees in the colony woods were cottonwoods, so a statistical examination limited to that bit of woodland would not reveal much about heron preferences. It appeared likely that the other trees there simply lacked the necessary support structure. A few willows were used, but each had the capacity for fewer nests. The better question is how the birds choose the rookery site in the first place. Trying to answer that would require a longer-term examination of many colonies.

Sycamore anthracnose

by Carl Strang

The sycamores were magnificent this fall, demonstrating their rebound from a challenge that was thrown at them in the spring. We had a relatively cool wet spring this year, which supported the growth of the sycamore anthracnose fungus. The fungus is a disease that interferes with fluid transport in sycamore twigs to the point where leaves are cut off and must be dropped. It also attacks the leaves directly. The result is a sickly looking canopy (first photo).



In time the summer temperatures rose and the fungus declined. The trees invested in new sets of leaves and got through the rest of the season in good shape, as their green and golden brown leaves in mid-October testify (second photo). Both photos were from Fullersburg Woods Forest Preserve, in June and October respectively.



Way back in my undergraduate dendrology class, we learned that the anthracnose is not a serious problem. Current web accounts are a little more alarmist, but the trees are not in real danger unless the fungal expression is prolonged or repeated. I don’t think that happens often enough, at least in northeastern Illinois, to be a concern.

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