Literature Review: Sabertooth Studies

by Carl Strang

Saber-toothed predators have evolved in several mammalian families. A couple interesting studies of them appeared last year in the journals I follow.

Steven C. Wallace, Richard C. Hulbert. 2013. A new machairodont from the Palmetto Fauna (Early Pliocene) of Florida, with comments on the origin of the Smilodontini (Mammalia, Carnivora, Felidae). PLoS ONE,; 8 (3): e56173 DOI: 10.1371/journal.pone.0056173  They describe Rhizosmilodon fiteae, a 5 million year old ancestor of the sabertooth cat Smilodon, from Florida, and conclude that Smilodon (which first appeared in the fossil record 2.5 million years ago) evolved in North America.

Meachen-Samuels, Julie A. 2012. Morphological convergence of the prey-killing arsenal of sabertooth predators. Paleobiology 38:1-14. She looked for correlations between saber tooth and forelimb morphology in nimravids (late Eocene-early Miocene), Barbourofelis (late Miocene), and sabertooth cats (late Miocene-Pleistocene). Felids are thought to have replaced nimravids in the “sabertooth niche.” The saber teeth have dirk-tooth forms (very elongated, laterally compressed, serrations fine or absent) and scimitar-tooth forms (less elongated, less compressed, often coarsely serrated). Dirk-toothed species have been thought to be ambush predators with more robust limbs, scimitar-tooth forms more cursorial with lighter limbs suitable for running down prey. Some, in the felid genus Xenosmilus, combined scimitar teeth with robust limbs, however. Present day large cats have strong limbs for holding prey, and kill with choke-hold bites that require round or conical, short canines for strength. Saber canines are more fragile, and unsuitable for choke holds. Saber toothed species generally proved to be more robust than the present-day conical toothed species, with larger muscle attachment points, and also had wider paws. This was especially true of nimravids, which are thought to have been tree climbers. Dirk-toothed species were somewhat more robust than scimitar species. There are several known co-occurrences of conical, dirk and scimitar species, including locations in California, Idaho and Florida. Prey apparently were subdued with the strong forelimbs, then killed with the saber teeth. Meachen-Samuels suggests that some nimravids were tree climbers, but most sabertooth species were not, an additional support being their short tails (long tails are associated with tree climbing in many present day species).

I don’t have a sabertooth photo, but the final paper applies broadly to extinct animals including mastodons.

I don’t have a sabertooth photo, but the final paper applies broadly to extinct animals including mastodons.

Sherkow, Jacob S., and Henry T. Greely. 2013. What if extinction is not forever? Science 340:32-33. In this review article the authors summarize possibilities, technical challenges and ethical considerations for bringing back extinct species through methods including back-breeding (where surviving species contain among them the genome of an extinct relative), cloning (using genetic material from museum specimens, for instance nuclei from somatic cells, to create germ egg cells), and genetic engineering (sequencing the genomes from museum specimen DNA, and editing DNA in cells from living forms to produce a match).

Lessons from Travels: Peat Soils

by Carl Strang

With November’s arrival, this blog shifts to its winter mode. I will be bringing in posts that share comments on the year’s scientific literature that are relevant to local natural history. There also will be more species dossiers. Of course, ongoing observations from the present season will continue to appear. Finally, there will be weekly episodes in the winter series. Past winter series have focused on science and spirituality (the Winter Campfire) and prehistoric life. This winter I will continue, and perhaps conclude, the Lessons from Travels series I began last year. The idea is to draw upon comparisons between northeastern Illinois and other parts of the world which cast a light on our local ecology and natural history.

A few years ago the Forest Preserve District of DuPage County collaborated with Chicago’s Field Museum of Natural History to conduct a paleontological dig at Pratts Wayne Woods Forest Preserve. Some mastodon molar teeth and bone fragments had been found at the site, and we brought in high school teachers and students to excavate parts of the site.

Here the digging began, 2007. Note the marsh in the background.

The dig went for two seasons. We mainly found fragments of the mastodon’s tusks. During the second year we uncovered some buried black spruce trees.

The stem of one of the trees runs the length of this trench.

The spruces were there when the mastodon died. That tree species no longer occurs in Illinois, though it is common in the North, where it retreated in the wake of the melting glacier. As we dug, we encountered buried soils that were familiar to me.

Buried peat soil.

This was exactly like soils we found when we dug into the permafrost in western Alaska, where I lived for several summers conducting my thesis research on glaucous gulls. Today there is much concern about the amount of carbon dioxide, and perhaps methane as well, that will be added to the atmosphere as climate change melts the permafrost. It seems that tundra fires will be major news in the future. At least then, maybe people will be able to bury their dead.

This scene, fitting with Halloween just past, is from an abandoned village site in western Alaska. The powerful churning of the surface soil as it thaws and freezes each year prevents burials.

We were not able to complete the mastodon dig. We suspect that the major bones remain beneath that marsh. The Field Museum withdrew from the project, and keeping even a small portion of the marsh pumped out for digging is more difficult and expensive than anyone wishes to pursue (though who knows, if we continue to have droughts like this past summer, it may become a practical possibility). For now the buried peat soils, the tree stems we left in place and covered, and the remainder of the mastodon, wait patiently as they have done for thousands of years.

Literature Review: Pleistocene

by Carl Strang

The following notes complete my review of last year’s scientific literature. These studies looked at the most recent epoch, the Pleistocene, and focus on the megafauna, the large mammals.

Mastodon fossil, an iconic megafaunal species

Edwards, Ceiridwen J., et al. Ancient Hybridization and an Irish Origin for the Modern Polar Bear Matriline. Current Biology, 07 July 2011 DOI: 10.1016/j.cub.2011.05.058     As described in a ScienceDaily article. This new mitochondrial DNA study places the female ancestor of all current polar bears in Ireland 50,000 years ago, at the peak of the last ice age. Brown and polar bears once were both circumpolar, or nearly so, and the ebb and flow of the glaciers brought them in and out of contact, providing hybridization opportunities. The authors mention that this continues today, with the retreat of polar ice bringing the two species more into contact, and several recent hybrid individuals are known. The researchers indicate that this process needs to be taken into consideration both in understanding the nature of these species and in conservation planning.

Long, Charles A., and Christopher J. Yahnke. 2011. End of the Pleistocene: elk-moose (Cervalces) and caribou (Rangifer) in Wisconsin. J. Mammal. 92:1127-1135. They describe the northernmost caribou fossils found to date in Wisconsin, from Marathon County. The Cervalces (also known as stag moose) from the same site is the first for the state, and northernmost for the species. The study location was at the boundary between the glacier’s Green Bay Lobe and the driftless area. The age of the caribou antler is placed at 11,260-11,170 years ago. The elk-moose was from 12,920-12,790 years ago. The caribou probably was of the more southern woodland caribou species. The older elk-moose fossil was found in a sediment layer suggesting it lived close to the edge of the glacier, in more of a tundra environment.

Eline D. Lorenzen, et al. Species-specific responses of Late Quaternary megafauna to climate and humans. Nature, 2011; DOI: 10.1038/nature10574     As described in a ScienceDaily article. They looked at a range of genetic, archeological and other evidence, and found that the megafauna that went extinct and those that survived in the northern hemisphere represent a complex picture. All had survived previous glacial cycles by finding refugia in warm periods, with populations just large enough to continue. Some were able to do so again after the most recent glacial retreat, for instance caribou and musk oxen in the far north and bison in the North American plains, and survive to this day. Others did not, and in at least most of these cases humans are implicated, either by preventing retreat to refugia or by decimating the reduced populations.

Waters, Michael R., et al. 2011. Pre-Clovis mastodon hunting 13,800 years ago at the Manis site, Washington. Science 334:351-353. (also interpreted in a news article on p. 302 of the same issue). They found a spear point made of mastodon bone, imbedded in the rib of an adult male mastodon. It is dated to several hundred years before the Clovis culture. The location near the coast in Washington State is consistent with a coastal spread of people from Beringia, where bone spear points also were used. This also supports an extended period of megafauna hunting, further pointing toward human hunting as a factor in extinctions (a long period of hunting, even if it only removes animals slightly faster than they can reproduce, increases the importance of that mortality factor).

Prehistoric Life 17

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.

Neogene Period (23.3 million years ago-present), Miocene Epoch (23.3-5.2 million years ago)

The Neogene Period (named in 1853) defines a time when a significant portion of fossil species (or at least very close relatives of them) still are in existence. The Miocene Epoch (established 1833), literally “few recent,” originally was defined by the percentage of then known fossil mollusk species still living (17%).

Life on Earth. Warming but continued dry conditions prevailed through most of the Miocene, giving way to renewed cooling in the late Miocene. This cooling was caused at least in part by the continuing growth of the Antarctic ice sheet. The resultant drop in sea level established land bridge connections from North America to South America and Asia. Continental growth, and also the rise of major mountain ranges, increased the seasonality of climate, and changed ocean circulation patterns, with upwelling zones probably setting up the conditions favoring pinniped (sea lion, etc.) evolution in the middle Miocene.

Harbor seal. Pinnipeds underwent a significant radiation in the Miocene.

Grasslands spread in the Miocene. The Perissodactyla had been the dominant ungulates, with their diversity peaking in the Eocene, but in the Miocene they declined (though rhinoceroses remained prominent throughout the epoch), while the Artiodactyla increased. The latter ungulates’ advantage may have been their ruminant digestive tract and complex high-crowned teeth, good for grazers (this was true of the larger division of artiodactyls; the pigs and hippopotami lack these specializations). Camels were very diverse in the Miocene, a remarkable example being the 12-foot-tall, giraffe-like browser Aepycamelus.

Bactrian camels, Brookfield Zoo. The camels, which had their start in North America, were very diverse on our continent in the Miocene.

The deer family appeared early in the Miocene in the Old World. By the middle Miocene, the diversification and evolution of horses was represented in part by the first one-toed species, Pliohippus of North America. Horses did not develop high-crowned molars until 4 million years after the grasses replaced trees as the dominant vegetation in the Great Plains, but their limb structure changed more quickly, so that they were able to survive by efficiently traveling longer distances between suitable habitat patches (Science 306:1467). Ungulate diversity peaked in the mid-Miocene, perhaps because frequent disturbance by the large proboscideans (gomphotheres and mastodons, which migrated into North America at that time) diversified the grassland savanna that had developed. Toward the end of the Miocene, however, much of the savanna gave way to grasslands, and there were extinctions of many of these ungulates and proboscideans.

Prairies and other grassland ecosystems spread into North America and became important here in the Miocene.

The departure of forests from much of North America is associated with the vanishing of primates from this continent.  Miocene land connections to South America and Asia resulted in significant immigrations and extinctions. Sabertooth cats and other Felidae first immigrated from Asia in the middle Miocene (ending the so-called “cat gap”).  Other new Miocene arrivals from Asia included bears, skunks, and badgers; from South America, ground sloths. There was a diversification of canids (dog family), mustelids (weasel family) and amphicyonids, though in the late Miocene the amphicyonids became extinct. The American white-footed mouse genus Peromyscus first appeared in the Miocene, and Spermophilus ground squirrels in the middle Miocene. Flying squirrels had their start in Asia in the early Miocene, with the split between Old World and North American flying squirrels happening in the late Miocene. The dominant carnivores in South America were marsupials in the Tertiary through the Miocene. The first member of the opossum genus, Didelphis solimoensis, showed up in the fossil record of Brazil in the latter part of the Miocene. Marsupials went extinct in North America in the Miocene, however.

Bears evolved in the Old World, and crossed the Bering Sea land bridge into North America in the Miocene.

Modern bird families were established in the Miocene, and the land bird orders other than the passerines underwent their great diversification. The passerine (perching birds) explosion began in the late Miocene. The first modern genera of birds began to appear in the Miocene, as well.

Local landscape. Subtropical forest of the early Miocene gave way to warm temperate to cooler temperate forests. The Texas gulf coast was swampy, so our climate very likely was at least as moist as today. We were between known areas of forests in New England that were warm temperate (hickories, chestnuts, hollies, mulberries, gums, oaks, buckthorns, elms, grapes) and shrubland-savannas on the Plains (invaded by grasses and prairie forbs as the Miocene progressed). The closest Miocene deposits are in western Nebraska, south central South Dakota, central Mississippi and SW Maryland.

Local life. Throughout the Miocene, browser-grazer pairs of rhinoceroses were found all over North America in savanna environments (the most common genera were Aphelops and Teleoceras, respectively; Teleoceras appears to have been a herding, and possibly semiaquatic species). If our area was more forested, we may have had only a browsing species. Rhinos became extinct in North America at the end of the Miocene. It seems likely that our area witnessed the transition from perissodactyl to artiodactyl dominance. Forms of rhinos (5 genera), tapirs (2 genera), horses (14 genera), dromomerycids (an extinct group of deer-like woodland browsers with horned males) and camels (5 genera, including the giraffe-like Aepycamelus) probably were here. The oreodonts were a diverse group of pig-like herbivorous artiodactyls, with at least 4 genera probably here in the Miocene. Carnivora would have been the dominant predators (diverse dogs, weasels, the large bears Indarctos and Plionarctos, “bear-dogs,” large cats, and the saber-toothed nimravid Barbourofelis), but there was also the entelodont Dinohyus. The Miocene also saw the arrival of the first proboscideans, or elephant relatives. These may have had a significant impact, killing the trees that they fed on and thus disturbing the vegetation so as to create more habitat diversity. There likely were 3 genera here, including two that were relatively elephant-like, and one that had shovel-like lower tusks that it probably used both to scoop up aquatic plants and to scrape bark from trees.

More Mayslake Fruits

by Carl Strang

Earlier I featured several plants at Mayslake Forest Preserve that produce fruits timed to coincide with the fall migration of berry-eating birds. This mutualistic interaction for the most part benefits the birds, through nutritional provisioning, while the plants get their seeds dispersed. Today I want to feature some outliers to this pattern. Let’s start with Solomon’s plume, also known as false Solomon’s seal.

Solomon's plume fruit b

Like many fall fruits, these advertise themselves to birds with a bright red color. When analyzed, however, the berries proved to be junk food, or perhaps are more accurately described as food mimics (White and Stiles 1985, Ecology 66:303-307). The plants save their energy, investing no nutritional value in these fruits. The ruse works, apparently, by exploiting the naïve instinctive response of first-time autumn migrants, the young of the year. A little different from this is the offering of the European highbush cranberry.

European highbush cranberry fruit b

Another study (Witmer 2001, Ecology 82:3120-3130) showed that the nutritional value of these berries becomes available only when they are consumed along with a significant protein source. I was impressed to learn that, like the waxwings native to the shrub’s European home, our North American cedar waxwings ignore these tempting berries until spring, when cottonwoods or other poplars are flowering. Then the birds consume the berries along with cottonwood catkins, protein in the pollen providing access to the berries’ nutritional value.

Common buckthorn fruit b

These black berries are common buckthorn fruits. They generally are ignored by birds until late winter when, apparently, the better quality foods have been depleted. Then, robins and waxwings consume them, unfortunately dispersing the seeds throughout our woodlands. Buckthorns leaf out early and lose their leaves late, casting a shade so dense that no other plants can grow beneath them. This is why these Eurasian shrubs must be removed at the beginning of woodland restoration projects. A final fruit is of no interest to birds.

Buckeye fruit 2b

Ohio buckeyes in fact are largely ignored by animals generally. This opens the possibility that, like other trees I discussed earlier, buckeyes may have been dispersed by now-extinct mastodons and other large herbivores.

Mastodons? We Don’t Need No Stinkin’ Mastodons!

by Carl Strang

In one of this spring’s earlier posts  I mentioned the difficulty Kentucky coffee trees have in getting dispersed, now that mastodons and other herbivorous megafauna no longer are around to facilitate their transport. Recently, though, I noticed that the grove of Kentucky coffee trees at Mayslake Forest Preserve has quite a few saplings coming up around its periphery.

Kentucky coffee tree leaves 2b

Most of this photo is occupied by a single, bipinnately compound leaf extending upper left to bottom right and out of the frame. Though dispersal distance clearly is more limited than it would have been in the gut of a mastodon, these trees are reproducing just fine, thank you very much.

Mastodon Trees

by Carl Strang

 

In an earlier post  I briefly described the paleontological dig that has begun in Pratts Wayne Woods Forest Preserve, centering around the find of mastodon molars and bone fragments. I mentioned that in 2008 the major discovery was of buried trees along with some black spruce cones. The Field Museum’s Scott Demel had the wood analyzed, and it proves indeed to be close to the same age as the mastodon, around 13,500 years. (In the earlier post I said the mastodon fossils were 11,500-12,000 years old; this was actually the raw carbon-14 date range, which has to be adjusted, for instance through use of tree ring records, to give the correct number of years in the past). So the mastodon died at the edge of a spruce-fringed lake.

 

On a tangentially related topic, recent wind storms have blown down some of the seed pods from a grove of Kentucky coffee trees beside the entrance drive at Mayslake Forest Preserve.

 

ky-coffee-trees-2b

 

These pods may have coevolved with mastodons and other extinct giant herbivores.

 

ky-coffee-tree-pods-b

 

The Kentucky coffee tree’s big seeds are very thick-walled and hard, just what you might expect if they need to pass through the mill of an oversized herbivore’s digestive system and survive prepared to germinate.

 

ky-coffee-tree-seed-b

 

Without such a preparation, the seedlings have a hard time breaking out, and perhaps as a consequence the Kentucky coffee tree is relatively uncommon. Certainly in DuPage County you are much more likely to find it in landscape or restoration plantings than as a wild-germinated plant.

 

Another tree in the legume family that has been tied to mastodons is the honey locust.

 

honey-locust-thorns-2b

 

This tree, also on the Mayslake grounds, shows the intimidating defensive thorns that have inspired the connection.

 

honey-locust-thorns-1b1

 

Like the Kentucky coffee tree, honey locusts have large pods. Their seeds are much smaller, however, so they have less difficulty in germinating on their own, and across its range this species is more common. It also became a popular tree for domesticated landscapes, once a thornless variety had been bred.

A third species whose seeds may have been dispersed by mastodons is the osage orange. I have not found any of these at Mayslake, but several grow beside Spring Road, less than a mile to the east.

Mastodon Camp

by Carl Strang

 

Over the past two summers I have had the opportunity to participate in a paleontological dig at Pratts Wayne Woods Forest Preserve in northwest DuPage County. This excavation, conducted by the Forest Preserve District of DuPage County and the Field Museum of Natural History, was prompted by the discovery of three mastodon molars and some bone pieces during wetland restoration work.

 

Photo courtesy Forest Preserve District of DuPage County

Photo courtesy Forest Preserve District of DuPage County

 

The dig is being structured as an education opportunity for area residents. Teachers and high school students have been the core participants in the first two years. There have been tours, presentations and half-day dig opportunities for members of the general public.

 

mc-day-8-15b

 

During the first summer, the main products were large numbers of small tusk and bone fragments.

 

mc-chunk-otusk-2b

 

In 2008 the digging revealed some small buried trees.

 

mc-day-11-9b

 

Wood samples are being analyzed, but two black spruce cones were found among the trees.

 

mc-day-9-3b

 

As I mentioned in my account of last fall’s glacier retracing trip, that tree species no longer grows this far south, but was here in this mastodon’s time 11,500 or 12,000 years ago. These paleobotanical discoveries fill in some of the picture of the local environment as local climate warmed after the glacier melted away.

 

With the major bones still waiting to be found, there is plenty of motivation to resume the dig when circumstances permit.

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