Prehistoric Life 18

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.

Pliocene Epoch (5.2-1.64 million years ago)

The Pliocene Epoch, literally “more recent,” originally was defined (1833) by the percentage of then known fossil mollusk species still living (35-95%). Its end is marked by the beginning of the glacial times.

Life on Earth. In the Pliocene, grazers became largely supplanted by more generalist herbivores as savannas became widespread in Eurasia and North America. The dominant groups were camels, antilocaprids (e.g., pronghorn “antelope”), and Equus horses (which, like most horses, originated in North America). Opossums diversified in South America, mammoths appeared in Africa (early Pliocene), the North American rhinoceroses vanished (middle Pliocene), and Sorex shrews appeared in the late Pliocene.

Sorex shrews like our short-tailed shrew of today made their evolutionary appearance in the Pliocene Epoch.

Land bridges finally allowed camels to spread into South America and Asia in the Pliocene (a camel survived in North America into late Pleistocene times). In the middle Pliocene, continued connection to Asia brought immigration of more carnivores, deer, and the elephant Stegomastodon. From North America to Eurasia went a rabbit, a squirrel, the beaver, and Equus.

The world’s lynx and cheetahs first appeared in North America, crossing to the Old World via the Bering Sea land connection.

In the late Pliocene, new appearances were pocket gophers, the white-tailed deer genus Odocoileus, raccoons, the giant beaver, bobcat (Old World lynxes, and also cheetahs, trace their ancestry to the New World where their groups first appeared), the New World porcupine family, eastern mole, and masked shrew.

Modern deer made their appearance in the Pliocene.

In the meantime, the first hominids were beginning to walk upright in Africa 3.8-4 mya (million years ago; Science 307:1545). Upright walking may have begun in the trees, as a hand-assisted way of negotiating thin, flexible branches (Science 316:1328 ). “Lucy,” Australopithecus afarensis (3-3.6my ago), regarded as a human ancestor or close to it, has been tied to the older A. anamensis (4mya), which in turn may have come from the still older Ardipithecus ramidus (4.4mya). Fossils of all three species were found in the same African river valley (Science 312:178). Ardipithecus significantly was a woodland dweller; apparently upright walking was not a product of a grassland habitat (Science 326: 64). Genus Homo had evolved by the late Pliocene, with species from Africa to Asia. Homo habilis and H. erectus are two earlier species which apparently overlapped considerably in time, so that it is uncertain whether the latter descended from the former (Science 317:733). Examination of limb structure points to habilis being arboreal while erectus was terrestrial, so a connection by descent is unlikely (Science 320:609).

The New World chickadees evolved from a single species that emigrated from Eurasia in the Pliocene.

Birds also were dispersing, and our modern species began to emerge. At least some modern songbirds had evolved by the early Pliocene (Auk 124:85). The chickadees and titmice, which had appeared in Eurasia originally, came over to North America in the Pliocene. The first crested species (titmouse) came over around 4 mya, and a single non-crested (chickadee) founder species around 3.5 mya. Subsequent evolution led to the 3 modern titmouse species and about 7 chickadees in the Americas. One terror bird species, in genus Titanis, reached North America from South America 2-3 million years ago, but was extinct by the end of the Pliocene.

Local landscape. Cooling and increased seasonality continued in the Pliocene (the middle Pliocene was the last time that Earth temperatures were warmer than at present).  Climate in the early Pliocene was significantly warmer than today; the major difference apparently was that the El Niño pattern of Pacific Ocean currents was permanent rather than episodic as it is today. The re-establishment of such a pattern is a possible outcome of global warming (Science 312:1485). Woodlands were more open in the Pliocene, perhaps savanna-like in places in our area. Elsewhere in North America, the continent developed its first near-modern boreal forest, as well as the first deserts, tundra and permafrost areas.

The Pliocene brought increasing seasonality, and extensive savannas replaced much of the Miocene grasslands.

The nearest Pliocene deposits are tiny areas in southern Indiana, and extensive areas in eastern Nebraska. By the Pliocene, much of northeast Illinois was draining eastward into the river that ultimately was enlarged by Pleistocene glaciation to become Lake Michigan. This happened when the relatively erosion-resistant and eastward-sloping Niagaran dolomite beneath us was brought close to the surface. Today, surface waters are directed by much more recent glacial deposits on top of that bedrock, and all ultimately flow into the Des Plaines-Illinois River system, ending up in the Gulf of Mexico rather than the North Atlantic.

Local life.  There is a likelihood that the camels, antilocaprids and horses (including Equus, the genus that includes modern horses) were represented locally. Deer, rabbits, beavers, raccoons, sabertooth cats (including Meganteron, an ancestor of the famous Smilodon), bears, the scavenging “hyaenoid dog” Borophagus, otters, and skunks are other likely species at that time.

Words of Tracking: Common Walking Gaits

by Carl Strang

 

In an earlier set of posts (find under Methods category in sidebar to left) I introduced the alphabet of tracking, i.e., identification of the kind of animal that made the track. Today I want to take the next step toward reading the stories that footprints have to tell us. That is, to look at the basic gaits. A gait is a pattern of footprint placement, the building block from which an animal’s trail is built, and it also is the order in which the feet step as the animal moves. You will find the same gaits given different names in different references. I follow the terminology of my teachers at the Tom Brown school (link in left margin of the frame).

 

The pace gait is the usual traveling gait of certain animals, such as raccoons and bears, whose wide-bodied proportions favor swinging their weight from side to side, stepping with both left feet at once, then both right feet. If you try this, in a comfortable rather than lunging effort, you will find that your feet produce side by side pairs of footprints, left front foot beside right hind foot, right front foot beside left hind foot. Here is the pattern in a set of raccoon tracks.

 

Pace gait, raccoon

Pace gait, raccoon

 

 

The opposite of a wide body is a long skinny body, which we find in weasels. If your body is, to exaggerate, something like a rope with two little feet at each end, the easiest way for you to proceed will be to move both your front feet together, then both your hind feet, with the hind feet landing behind the front feet. This gait is called the bound. Often the feet are somewhat offset, an indication that the animal oriented its body axis at an angle rather than in line with its direction of travel.

 

Bound gait, mink

Bound gait, mink

 

 

Another gait in which the front feet move together and the hind feet move together is the gallop. This is common in rodents and rabbits, animals whose hind legs are more powerful than the front, so that the hind feet land in front of the front feet. Cottontails typically place one front foot in front of the other, while rodents such as mice and squirrels, as well as masked shrews, place their front feet side by side (in the photo the shrew is moving left to right).

 

Gallop gait, cottontail

Gallop gait, cottontail

 

Gallop gait, masked shrew

Gallop gait, masked shrew

 

 

There is one circumstance in which cottontails place their front feet side by side, however. I will leave this one for you to puzzle over. Look for examples this winter, see if you can figure it out. Here’s a photo so you know what to look for.

 

Cottontail gait puzzle

Cottontail gait puzzle

 

 

The final common walking gait is typical of hoofed animals (white-tailed deer in NE Illinois), the dog family and the cat family, as well as us (when do we walk on all fours?). This one is called the diagonal walk, and unlike the others the feet move separately in a sequence: left front, right hind, right front, left hind. In this case the left feet come down in close to the same place, and so do the right feet. The overall impression is a zigzag between right foot pairs and left foot pairs, hence the name for this gait.

 

Diagonal walk gait, wolf (Isle Royale)

Diagonal walk gait, wolf (Isle Royale)

 

 

There are other gaits, but they are less common or are special cases and will be reserved for later. Also, the connections I have made between animals and gaits are limited to routine travel. When circumstances require, animals shift out of their normal walking gait. For instance, a raccoon in an extreme hurry does not, cartoon like, do a real fast pace gait. Instead, it shifts into a gallop. Tracks outside the normal pattern are a clue that something unusual, therefore interesting, was happening.

Sketching Mayslake’s Trophic Structure

by Carl Strang

 

 

As I familiarize myself with an area, there are several big conceptual nets with which I try to comprehend that place. These lack fine detail, but provide first approximations that can be filled in as I learn more. One conceptual frame for an area is its general topography and drainage pattern. Another is the general human history and influence on the land. A third is the mosaic of vegetation communities. A fourth is the geology. Today I want to focus on yet another frame, the trophic structure. This is a broad-brush first stage in constructing a food web. The trophic levels of an ecosystem are the steps through which energy “flows” (the quotes are a field ecologist’s recognition that abstract food pyramid diagrams, and the arrows that connect food web elements on the page, cover up a certain amount of desperate flight-and-chase, crunching, and screaming. All our lives continue at a cost, but I digress).

 

In earlier posts I have documented some of Mayslake’s animal life. The top predators mentioned already include coyotes and mink. A day seldom goes by without me seeing a red-tailed hawk or two. I also have seen tracks of great horned owls, and the Mayslake staff have observed these birds at that preserve for years.

 

Great horned owl tracks, Mayslake

Great horned owl tracks, Mayslake

 

 

Note that in this photo, the great horned owl tracks are farther apart than in the photo I took on the Christmas bird count. This is the more typical spacing, but again there is that odd asymmetry in the toes.

 

 

Mayslake’s part-time predators include raccoons and skunks, among others.

 

Skunk tracks (far right), Mayslake

Skunk tracks (far right), Mayslake

 

On a smaller scale, I have seen tracks of short-tailed and masked shrews, which are predators of small animals including invertebrates but also mice.

 

Common plant-eating animals at Mayslake include deer, mice, voles, squirrels, chipmunks and cottontail rabbits. There are also the wandering winter birds eating seeds (as in the paper birch account).

 

Rabbit trail, Mayslake

Rabbit trail, Mayslake

 

 

Over 50 kinds of trees, shrubs and vines, along with uncounted herbaceous plants, are the preserve’s primary producers, solar energy harvesters that form the foundation for the whole trophic shebang. In the warm months, each kind of plant hosts several insect consumers that in turn are food for predators including an influx of migrant nesting birds.

 

And let’s not forget the scavengers. Some of the animals listed already, the coyote and skunk for instance, along with opossums such as the young one whose tracks I saw in the southern part of the preserve recently, are happy to clean up the odd dead carcass they encounter.

 

Mayslake is not a huge property as forest preserves go, but it’s big enough and diverse enough in vegetative structure to support a complex community for which I have here provided only the broadest of introductory sketches. More detail to come.

Alphabet of Tracking: 5 Toes Front and Hind Feet

by Carl Strang

 

Today I continue my tracking primer with a focus on mammals whose feet typically show 5 toes on the front and hind feet of complete tracks (but remember that in the field you often have only partial footprints; this is where dirt time comes in, as mentioned in the last post). Local animals in today’s category are raccoons, opossums, members of the weasel family, and shrews. Bears also are in this category, though they are even less likely than mountain lions to show up in northeast Illinois.

 

Black bear track

Black bear track

 

 

Raccoon tracks have long, round-tipped toes and are among the most frequent footprints we notice, because these are common animals, they often are passing through muddy areas, and they are heavy enough in body to sink into the surface.

 

Raccoon track

Raccoon track

 

 

Opossum tracks are, like the animals themselves, amazing and odd. Typically the hind foot is rotated so that it is oriented sideways, wrapping around the heel of the front foot with the big toe pointing in and the other four pointing out. The toes on the front foot are spread so widely that the overall effect reminds me of a star.

 

Opossum tracks

Opossum tracks

 

 

Our most common local weasel family representatives are the mink and the striped skunk, but I remain alert for otters as well. Mink tracks have a round appearance overall. Though primarily aquatic animals, their footprints often turn up away from water (in DuPage County it is not possible for them ever to be truly distant from water, however).

 

Mink tracks

Mink tracks

 

 

Otters likewise are aquatic. Their tracks are bigger, and they likewise can travel distances over land between water bodies. (I am deliberately not including size measurements. I have to leave something for your own inquiry!). I have not encountered an otter in DuPage County yet, but given the success of the program re-introducing them to the state I regard this as simply a matter of time.

 

Otter track

Otter track

 

 

Striped skunk tracks at first glance often remind me of domestic cat tracks, except that five smaller toes are crowded into the space of the cat’s four. Skunk tracks have toenail marks, with the longer toenails of this digging animal’s front feet prominently in front of the ends of the toes.

 

Striped Skunk tracks

Striped Skunk tracks

 

 

Shrews are tiny animals. Most of their tracks you encounter will be in snow, and so will not show the individual toes. Masked shrews are much smaller than mice, and so their sets of tracks will be smaller (quarter coin provides scale; the photo includes an entire set of four footprints to the left, and another to the right of the coin).

 

Masked Shrew tracks

Masked Shrew tracks

 

 

Least shrews likewise are tiny, but these are much rarer than masked shrews. Short-tailed shrews often show a diagonal walk gait pattern (to be explained once we reach the “word” level of this introduction).

 

(probable) Short-tailed Shrew tracks

(probable) Short-tailed Shrew tracks

 

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