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.
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).
There are 3 species of ground crickets that occur throughout the Chicago region (I still lack 2 county records for one of these, but expect to make up that deficit on a future Wisconsin trip). The ground crickets are the LBJ’s of singing insects (birding jargon: “little brown jobs” refers to sparrows, wrens and the like which are quick to vanish before they can be identified). Most ground crickets look identical at first glance, are tiny, and usually are brown. I’ll begin with the striped ground cricket.
The stripes are clear on this female striped ground cricket’s head.
This is the weediest of the ground crickets, first to show up in disturbed sites, and abundant in lawns. Its song consists of separate brief rough buzzes, continuously produced at 2 to 3 per second. It is low enough in pitch to hear easily, with most of the buzz’s sound range below 7 kHz. Here is a recording (complete with background bird songs and the usual traffic rumble):
The second species also occurs in open areas, but mainly where the grass is taller and vegetation better established.
Allard’s ground cricket is a close relative of the striped. The head stripes are absent, faint, or incomplete, however.
The song consists of incessant, separate quick very high-pitched notes (6 kHz) that sound like 4-6 per second but sonographs show twice that rate. There are fairly frequent, very brief pauses (again, birds and this time a train in the background):
Now I will toss in a fourth species. The tinkling ground cricket is less widely distributed than the others (so far I have found it in half of the region’s counties), but include it here to provide a comparison to the Allard’s song. Here is a recording:
The song consists of high pitched (7 kHz) individual notes, like those of Allard’s ground cricket but distinctly slower at a given temperature (1/3 to ½ as rapidly produced). It often is rendered “tink-tink-tink…” The song is uninterrupted, lacking the frequent breaks characteristic of Allard’s ground cricket (this is especially helpful late in the season, when Allard’s often slows down). The tinkling ground cricket lives in open woodlands and woods edges, and is especially abundant on sandy soils. It looks different, too.
Tinkling ground crickets have reddish tones that distinguish them from our other ground crickets.
The final, common species is the Carolina ground cricket.
The Carolina ground cricket has faint head stripes. The female is distinguished by an unusually short ovipositor.
Its song is a continuous, irregularly pulsed drone, purr or trill with periods when additional pitches are added to the song, making it more dissonant. Though the sound pulses are broad enough in pitch range to qualify as a drone, it is not far from a trill, and low enough in pitch to be heard by most, at 6 kHz. Here is a recording:
As the passing geese perhaps imply, Carolina ground crickets prefer moist habitats, from wetland edges to bottomland forests. In my residential neighborhood they are fairly common, but stick to the cooler, moister foundation shrub plantings against the houses.
We’ll have to wait a while to hear these crickets again. They winter in the egg form, and need until the very end of June or, more often, July to develop to the point where they begin singing.
Today’s collection of notes from the 2013 scientific literature focuses on mammals and their evolution. As the notes reveal, some of these topics are controversial among researchers.
This migrating bat chose a famous resting place during its journey: the Aldo Leopold shack in Wisconsin. Bats are the subject of two of the following studies.
Chang-Fu Zhou, Shaoyuan Wu, Thomas Martin, Zhe-Xi Luo. 2013. A Jurassic mammaliaform and the earliest mammalian evolutionary adaptations. Nature 500 (7461): 163 DOI: 10.1038/nature12429 They described a newly discovered Jurassic proto-mammal, Megaconus mammaliaformis, and found evidence that traits such as hair and fur originated well before the rise of the first true mammals. The squirrel-sized Megaconus had a heel spur, similar to poisonous spurs found on modern egg-laying mammals, such as male platypuses. It had mammalian dental features, and legs and feet that point to a gait similar to that of modern armadillos. At the same time it had a reptilian middle ear, ankle bones and vertebral column.
O’Leary, Maureen, et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of placentals.Science 339:662-667. Using fossil materials and an extensive character analysis, they conclude that the ancestral placental mammal from which all major surviving groups evolved lived just after the beginning of the Paleocene. This conflicts with molecular clock data that place the appearance of many groups including bats, rodents, and even-toed ungulates back in the Cretaceous. They combine the characters of the early fossils to produce a hypothetical common ancestor, an insectivorous animal resembling a shrew with a long tail.
Zhang, Guojie, et al. 2013. Comparative analysis of bat genomes provides insight into the evolution of flight and immunity.Science 339: 456-460. They did whole-genome comparisons of nuclear DNA of a Myotis and a flying fox. Significant sequences were found which may relate to the development of flight ability, and the immune systems also are different from those of other mammals. When compared to the genomes of other mammals, bats fall out most closely related to perissodactyls, then carnivores, with those groups splitting apart at an estimated time in the Cretaceous.
Ni, Xijun, et al. 2013. The oldest known primate skeleton and early haplorhine evolution. Nature 498 (7452): 60 DOI: 10.1038/nature12200 They describe a 55mya (early Eocene) Chinese fossil that is in the tarsier line but has features showing it to be close to the branch point leading to the tarsiers in one direction, anthropoids (primates including monkeys, apes and humans) on the other. It is tiny, the animal around 1 ounce in weight. Asia appears to be the likely center of early primate evolution.
Cahill JA, Green RE, Fulton TL, Stiller M, Jay F, et al. 2013. Genomic evidence for island population conversion resolves conflicting theories of polar bear evolution. PLoS Genet, 9(3): e1003345; DOI: 10.1371/journal.pgen.1003345 This most recent examination of polar bear and brown bear genetics concluded that, on the whole, polar bears have been separate from brown bears for about half the time that brown bears have been separate from black bears. The connections previously noted between the two species in southeast Alaska, and possibly in Ireland, appear to be the result of small polar bear populations being isolated during ice ages, and being swamped then by an influx of male brown bears. The polar bear is a more ancient species than that.
Zigouris J, Schaefer JA, Fortin C, Kyle CJ. 2013. Phylogeography and post-glacial recolonization in wolverines (Gulo gulo) from across their circumpolar distribution. PLoS ONE 8(12): e83837. doi:10.1371/journal.pone.0083837 Their analysis of mitochondrial and nuclear genes points to a single population of wolverines surviving the glacial maximum in a refugium somewhere in the Old World, then expanding into North America across the Bering Sea land bridge as the glaciers retreated. Subsequently, several North American populations differentiated. The fossil record likewise has them only in Eurasia prior to the late Pleistocene.
Andrew M. Minnis, Daniel L. Lindner. 2013. Phylogenetic evaluation of Geomyces and allies reveals no close relatives of Pseudogymnoascus destructans, comb. nov., in bat hibernacula of eastern North America. Fungal Biology, DOI: 10.1016/j.funbio.2013.07.001 As described in a ScienceDaily article. The closest relatives of the fungus causing white nose syndrome are species that live in European caves. This supports the idea that the fungus is an invasive species here, but one with which European bats coevolved and so have some immunity.
Today’s recording is one of a series of poems I had written about animals over the years, and set them to music for the 2002 gift CD (two of the accompaniment tracks are me playing soprano and tenor recorders). The founding image was that of dragonflies as World War I biplanes, their territorial chases calling back the aerial dogfights. Perhaps the best local example of this is the 12-spotted skimmer.
This male 12-spotted skimmer is resting, but he patrols his territory on the wing.
Winter reveals much that was hidden in the growing season. When the deciduous trees and shrubs have dropped their leaves, green walls are replaced by vistas. Smaller things now come into view as well, including a bobber-eating tree at the edge of Trinity Lake in Mayslake Forest Preserve.
How many red and white ball bobbers can you find?
I am reminded of the kite-eating tree of Charles Schultz’s Peanuts cartoons. This is right above a popular point on the lake shore for fishermen in summer. It is not entirely innocent, though, as those bobbers are attached to lengths of fishing line that are a potential entanglement hazard for birds. As I have previously documented here, orioles make use of some of the discarded line in their nest-building.
The Mesozoic Era came to an abrupt end with the arrival of an asteroid, about 6 miles in diameter, that slammed into the Earth in the vicinity of the present-day Yucatan Peninsula. The details and ramifications of that and similar events continue to attract the attention of researchers, as today’s notes from last year’s literature show.
Robertson, Douglas S., William M. Lewis, Peter M. Sheehan, Owen B. Toon. 2013. K-Pg extinction: Reevaluation of the heat-fire hypothesis. Journal of Geophysical Research: Biogeosciences, DOI: 10.1002/jgrg.20018 From a ScienceDaily article. This modeling study suggests that when the end-Mesozoic asteroid struck, it pulverized and spread a huge volume of rock material. This overheated dust spread worldwide through the atmosphere, heating the planet’s surface for a few hours to the point of setting off fires that could have killed nearly all animals and plants on or above the surface of the ground and water.
Renne, P. R., et al. 2013. Time scales of critical events around the Cretaceous-Paleogene boundary. Science 339: 684-687. Dating is becoming more precise, and this study places the Chicxulub impact event at 66,043,000 years ago, within error at precisely the time non-avian dinosaurs went extinct (the KPB, or Cretaceous-Paleogene Boundary). The authors point out, however, that stresses of climate change probably caused by the Deccan Traps volcanic eruptions had stressed the Earth’s life forms to the point where this more readily tipped the scale to mass extinction. Those massive basalt lava flows occurred within a million years prior to the Chicxulub impact, but the dating there is less precise. There were “six abrupt shifts of >2°C in continental mean annual temperatures…The most dramatic of these temperature oscillations, a drop of 6° to 8°C, occurred <100 ky [thousand years] before the KPB and was closely synchronous with notable mammalian turnover…” All these results are from studies in Montana. Sea levels also are believed to have fluctuated drastically during this time, so that brief periods of glaciation may have occurred. In Montana and adjacent Canada, mammalian faunas changed at the KPB, but that change is believed to be the result of immigration rather than the evolution of new species given the brief time interval involved.
Osprey nest, Chesapeake Bay. Somehow, life survived these calamaties.
Sanford, Ward E., et al. 2013. Evidence for high salinity of Early Cretaceous sea water from the Chesapeake Bay crater. Nature 503 (7475): 252 DOI: 10.1038/nature12714 As described in a ScienceDaily article. Chesapeake Bay was created around the Eocene-Oligocene boundary, 35 million years ago, by an impact of comet or asteroid. The result was the Bay’s 56-mile-wide basin and a disruption of aquifers, one of which is found to preserve a body of Cretaceous seawater, a kilometer below the bay’s floor. The Eocene ended with a mass extinction, but the article does not mention this.
When I mention the coneheads to people unfamiliar with singing insects, the response almost always is a smile. I have to agree: one reason why the slightly musical conehead is my favorite singing insect (at the moment) is that name. Our coneheads are all katydids in genus Neoconocephalus. I have been fortunate to spend some time in the field with Gideon Ney, a Ph.D. student at the University of Missouri who is working out of a lab led by Johannes Schul that has done a lot of work with the evolution of that group. Thanks to Gideon I am aware of two species of coneheads that are not supposed to occur as far north as the Chicago region, but turn out to be at least locally common. Today I share recordings of the 6 documented species in the region. Warning: these are not delightfully musical or even (despite the name mentioned above) slightly so. We’ll ease into it with one that is somewhat pleasant to hear: the sword-bearing conehead. Its song:
That recording was made in a grassy upland meadow, typical habitat for the species, but close enough to the edge of the woods that a few common true katydids came through loud and clear. The conehead’s song is the continuous string of rasping ticks or brief buzzes. It has been compared to the sound of a sewing machine or a distant steam locomotive.
The sword-bearing conehead is named for the very long, straight ovipositor on the female.
The next species also has a discontinuous song. The slightly musical conehead was given that name because W.T. Davis, who described it, thought it was not very loud (though he later changed his mind on that point).
The rasping sounds are easy for me to hear even with my older ears. This is a wetland species, and the males typically sing in unison.
The coneheads are named for the structure on the tip of the head, especially prominent in the slightly musical conehead.
Another species with an interrupted song is the Nebraska conehead.
The buzzes are not as rough as in the previous species, and will be heard in bushy undergrowth of woodlands, or sometimes bushes out in fields. In the southern part of the Chicago region, where the species is more common, the males sometimes sing in unison as well.
Male coneheads often sing head down. It has been speculated that the cone helps them penetrate the vegetation beneath when they are disturbed and drop to hide. Nebraska coneheads have medium sized, all black cone undersides.
The remaining 3 species all have continuous buzzes. Most common region-wide is the round-tipped conehead, a katydid of meadows and roadsides.
Listen for a crackling sound in this continuous buzz.
Here the cone is short, round, and has a small black area near the tip.
Next is the marsh conehead, which so far has turned up only in the marshes of the Indiana Dunes parks.
The sound resembles that of the round-tipped, but comes from a wetland rather than dry upland habitat.
The cone of the marsh conehead may be all green as in this female, or show variable darkness of color.
For the grand finale, here is the very loud song of the robust conehead:
This can be so loud as to be painful to the ears. It carries for long distances, as you may imagine, and is easy to hear from a car at any speed.
The robust conehead’s cone is unmarked and proportionately short. Any conehead species can come in green or brown.
The robust conehead is most abundant in areas with dry sandy soils. Its habitat range is fairly broad, from open woodlands to prairies to corn fields.
There are at least two other species which are supposed to occur in the region, but which I have not found. Perhaps next winter I will have recordings of false robust coneheads and slender coneheads to share.
Research on the Mesozoic Era has been a big focus of recent paleontological research, and much attention in particular has been paid to feathered dinosaurs and early birds. Chinese deposits, especially, have been productive. This week I share notes on selected studies in this area from last year’s literature.
It is no longer so great a stretch to refer to birds, including this great blue heron, as dinosaurs.
W. Scott Persons, IV, Philip J. Currie, and Mark A. Norell. 2013. Oviraptorosaur tail forms and functions. Acta Palaeontologica Polonica, DOI: 10.4202/app.2012.0093 From a ScienceDaily article. Unusual (for dinosaurs) fused tail vertebrae and musculature, as well as preserved tail feathers in a flightless species, suggest that oviraptorosaurs (an herbivorous group of theropods) had an active tail-feather display, presumably used in courtship.
Xing, Lida, et al. 2013. Piscivory in the feathered dinosaur Microraptor. Evolution, DOI: 10.1111/evo.12119 From a ScienceDaily article. A fossil of the hawk-sized, 4-winged dromaeosaur Microraptor proves to have been capable of short controlled flights during which it could catch smaller birds and squirrel-sized tree dwelling mammals, and now fish. This was in early Cretaceous China.
Dyke, Gareth, et al. 2013. Aerodynamic performance of the feathered dinosaur Microraptor and the evolution of feathered flight. Nature Communications, DOI: 10.1038/ncomms3489 From a ScienceDaily article. They created a life-size model of Microraptor, one of the “5-winged” feathered dinosaurs (wing-like structures on the legs, and lift-capable tail) and tested it in a wind tunnel. It could glide efficiently for long distances with slow drop in altitude, but that depended most on lift from the arm-wings. That could have set the stage for further development of those wings leading to the powered flight of birds.
Zheng, Xiaoting, et al. 2013. Hind wings in basal birds and the evolution of leg feathers.Science 339:1309-1312. They looked at 11 bird fossils from the early Cretaceous and found, despite their belonging to different groups, that they had leg wings as in the feathered dinosaur Microraptor. The authors conclude that this feature was common to all the first birds.
O’Connor, J.K., et al. 2013. A new enantiornithine from the Yixian formation with the first recognized avian enamel specialization. Journal of Vertebrate Paleontology 33: 1-12. From a ScienceDaily article. The Enantiornithes were the most diverse birds of the Mesozoic, but died out for reasons that remain unknown (modern birds were another lineage). This study describes a newly found species (Sulcavis geeorum), from the early Cretaceous Chinese Liaoning deposits, which had teeth specialized with grooves on their back faces, thought to have facilitated feeding on invertebrates with hard exoskeletons. Dental diversity in the enantiornithines presumably reflects ecological diversity and accounts for the group’s success.
Chinsamy, Anusuya, et al. 2013. Gender identification of the Mesozoic bird Confuciusornis sanctus. Nature Communications 4: 1381 DOI: 10.1038/ncomms2377 As described in ScienceDaily. They found that fossils of this species lacking ornamental tail feathers possessed medullary bone, which is used by females to store minerals for eggshell formation. Their study also found that these early birds, unlike modern ones but like dinosaurs, began reproducing before reaching maturity.
“The Great Potoo” is a song I wrote to commemorate the tropical ecology course I took as a graduate student. Tropical ecology was becoming a hot topic, and this gave me the opportunity to balance out my own subarctic research on glaucous gulls with something quite different. We spent a couple weeks at the Purdue campus in preparatory studies, then a month in Panama. The wonderful aspects of the tropics cannot be expressed well enough, and can only be suggested in the song.
Refrain: “You can look, you can look, you can look but you will never see a great potoo.
You can look, you can look, you can look but you will never see a great potoo.”
Verse 1: “The great potoo’s a strange, strange bird, both camouflaged and rare.
We’ll be a month in Panama, but you won’t see one there.
But that’s OK,” our teacher said, “the tropics they are full
Of many strange and wondrous sights all biological.”
And so we flew to Panama, in book study well versed.
In tropical ecology we were to be immersed.
But first we stayed a day or two in the City of Panama.
The sounds and sights and noise and smells unlike Indiana.
(Refrain)
Our first field camp was aptly named, all mud and mold and rust.
“The Limbo Hunt Club” it was called, what could we do but trust?
But it was set upon all sides by tropic forest rare.
And I still think in fondness of the time that we spent there.
The walking sticks were walking branches, hummingbirds galore.
One student caught a fer-de-lance upon the forest floor.
And flowers and trees, and stingless bees, leaf cutter and army ants, too.
Lizards, frogs, and butterflies; at night moths and bats flew.
In the tropics things are big and wonderful…
(Refrain)
But then one morning, perched above our open-sided shack
The tree branch sported a new stub, we looked and it looked back.
Our teacher in amazement said we couldn’t ever hope
To appreciate our luck, the great potoo was in our scope.
We climbed up high, and crawled down low, we traveled to both coasts.
I held a sea snake in my hands, chased crabs that looked like ghosts.
But of the many highlights, one that stands out is the view
From the Limbo Hunt Club clearing of that bird, the great potoo.
(Refrain).
I held a sea snake in my hands, and someone took this photo. The scales are set like little bricks, not overlapping like those of other snakes.
No, this is not a great potoo. The roll of film with my potoo pictures jammed in the camera. I thought I was extricating it in a sufficiently dark place, but I was wrong. Most of the photos were ruined. This picture of a slaty flower piercer was one of the few, albeit washed out, survivors.
You can see photos of great potoos here, and recordings of their roaring call here.
Nature Inquiries 