Literature Review: Human Evolution

by Carl Strang

At some point, paleontological studies come back to our own ancestry. Here are my notes on some studies published last year.

Human

Human

Schmid, P., et al. 2013. Mosaic Morphology in the Thorax of Australopithecus sediba. Science 340:164-165. Irish, J. D., et al. 2013. Dental Morphology and the Phylogenetic “Place” of Australopithecus sediba. Science 340:164. These are two of a series of studies of this hominin reported in this issue. They studied skeletal portions of a single specimen from South Africa of 2 million years ago. It proves to be a mosaic of primitive and modern human features, so they conclude it is an ancestor or early form of Homo, closer to our genus and to Australopithecus africanus than is the east African Australopithecus afarensis. The structure of the arms, shoulder blades, and the narrow upper ribcage suggest this was a tree climbing species that could not run for long distances. At the same time it had the narrow waist of a human. The feet turned sharply inwards, distinguishing it from other Australopithecines. The structure of the teeth was a major line of evidence indicating the connections between sediba and Homo.

Lordkipanidze, D., et al. 2013. A complete skull from Dmanisi, Georgia, and the evolutionary biology of early Homo. Science 342:326-331. They have studied several skulls from European Georgia that provide data on individual variation of Homo erectus. It seems likely that fewer Homo species existed than had been thought, and that erectus evolved about 2 million years ago and then (alone) spread out of Africa, eventually reaching Asia 1.2 million years ago.

Meyer, Matthias, et al. A mitochondrial genome sequence of a hominin from Sima de los Huesos. Nature, 2013; DOI: 10.1038/nature12788  From a ScienceDaily article. They sequenced mitochondrial DNA from bones recovered in a cave in northern Spain. The bones, 400,000 years old, were revealed to have connections to the Denisovans, previously known only from Asia. The common ancestor between these Homo heidelbergensis bones and the Denisovans was estimated to live 700,000 years ago. The connection could reflect an ancestral split between genetic lines, or an inflow of Denisovan genes through population movements.

Rito, T, et al. 2013. The first modern human dispersals across Africa. PLoS ONE 8(11): e80031. doi:10.1371/journal.pone.0080031  Their analysis using updated technology points to the “mitochondrial Eve” in central Africa 180,000 years ago, a time of low population density. There then was a separation by 130,000 years ago between some groups that have remained in extreme southern Africa, and others in central and east Africa who became the ancestors of all modern humans. Subsequent dispersal episodes correspond to, and may have been stimulated by, a series of droughts 135,000-75,000 years ago.

Prüfer, Kay, et al. 2013. The complete genome sequence of a Neanderthal from the Altai Mountains. Nature DOI: 10.1038/nature12886  From a ScienceDaily article. They developed a complete Neanderthal genome from 50,000 years ago, and comparisons to the genomes of modern humans and Denisovans reveals a complex pattern of occasional interbreeding. Neanderthals and Denisovans prove to be very closely related, the split between them estimated at 300,000 years ago. Their common ancestor population split from the modern human line 400,000 years ago. 1.5-2.1% of non-African modern human genetics comes from later interbreeding with Neanderthals. Denisovans also contributed small portions of genes to Asian and Oceanic modern humans, the largest an estimated 6% in Australian aboriginals, New Guineans, and some Pacific islanders. Asians and Native Americans have a portion of 0.2%. The Denisovans also are found to have interbred with an unknown fourth group, possibly Homo erectus, that had split from all the others a million years ago. The genetics suggest that Neanderthal and Denisovan groups were small, and inbreeding was relatively common.

Raghavan, Maanasa, et al. 2013. Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans. Nature DOI: 10.1038/nature12736  From a ScienceDaily article. The DNA of a Siberian boy of 24,000 years ago shows elements connecting his ancestry to various parts of Asia, and also to Europe. It also has enough in common with Native American DNA to place the boy’s population as ancestral to Native Americans. Those Siberians were part of a widely wandering Eurasian people in the Ice Age, who naturally would have extended the wandering across the Bering Sea when glaciers drew it down to provide the land connection to North America.

Battaglia, V, et al. 2013. The First Peopling of South America: New Evidence from Y-Chromosome Haplogroup Q. PLoS ONE 8(8): e71390. doi:10.1371/journal.pone.0071390  They found that Central  and South American Native Americans are connected to ancestors in southern Siberia as well as to North Americans. The results support two waves of immigration from North America, one reaching Mexico and a later one rapidly populating areas farther south.

Bollongino, Ruth, et al. 2013. 2000 Years of Parallel Societies in Stone Age Central Europe. Science DOI: 10.1126/science.1245049  From ScienceDaily article. People in Europe all were hunter-gatherers until 7500 years ago (modern humans arrived there 45,000 years ago, survived the ice age, and warming began 10,000 years ago). Immigrants brought agriculture from the south around 7500 years ago, and this study found that the hunter-gatherers persisted in that culture alongside the agriculturists for 2500 years before switching to agriculture themselves. The two societies lived side by side and buried their dead in the same cave. Genetic and chemical studies indicate that hunter-gatherer women sometimes married into the agriculturists, but not the reverse.

Pugach, Irina, et al. Genome-wide data substantiates Holocene gene flow from India to Australia. PNAS, January 14, 2013 DOI: 10.1073/pnas.1211927110  They found that Australian aboriginals, who were established in that continent by 45,000 years ago, were not isolated for all of that time. Their genetics indicate that around 4000 years ago there was immigration (“substantial gene flow”) from India. That timing coincides with the arrival of the dingo, and changes in plant processing and stone tool technologies.

Literature Review: Ice Ages and Climate

by Carl Strang

Today’s literature focus is on two studies from last year that increased our understanding of ice age dynamics and how our changes to the atmosphere may alter them.

Kokechik Bay, Alaska, late winter

Kokechik Bay, Alaska, late winter

Ballantyne, Ashley P., et al. 2013. The amplification of Arctic terrestrial surface temperatures by reduced sea-ice extent during the Pliocene. Palaeogeography, Palaeoclimatology, Palaeoecology, DOI: 10.1016/j.palaeo.2013.05.002  As described in a ScienceDaily article. Recent measures of carbon dioxide in the atmosphere have brought current levels into the range of the Pliocene, which was 3.5-9 degrees F warmer than today. A modeling study indicates that the difference may have been that the Arctic Ocean then was open year-round, a condition toward which we are trending now.

Kerr, Richard A. 2013. How to make a great ice age, again and again and again. Science 341:599. News article describing a study published in Nature that reports an advance in understanding the continental glacier cycle. That cycle corresponds to the 100,000-year stretching and shrinking of the Earth’s orbit around the sun, but that’s too weak to account for ice building and declining. The group led by Ayako Abe-Ouchi modeled in the 23,000-year wobble in the Earth’s spin axis, plus global climate modeling and data on northern ice sheets, which involve changing carbon dioxide levels and the mass of the ice. Simulated ice sheets expanded and contracted in close to the actual pattern. Ice gradually builds over the 100,000-year cycle, but then the 23,000-year cycle corresponds to the warming phase of the longer one, adding summer warmth. By then, crustal depression by the ice mass means that the ice is at a lower, warmer altitude (1 km of depression), and the glacier rapidly melts.

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).

Literature Review: Mammal Evolution

by Carl Strang

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.

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.

Literature Review: Asteroid Disasters

by Carl Strang

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.

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.

Literature Review: Feathered Dinosaurs and Early Birds

by Carl Strang

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.

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.

Literature Review: The Mesozoic Era

by Carl Strang

This week’s literature notes focus on selected papers from last year on the Mesozoic Era. These papers covered assorted topics; there were enough studies of early birds and feathered dinosaurs that I will treat them separately.

Some of this fellow’s relatives had cock’s comb-like head structures. See below.

Some of this fellow’s relatives had cock’s comb-like head structures. See below.

Jones, Marc EH, et al. 2013. Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara). BMC Evolutionary Biology 13 (1): 208 DOI: 10.1186/1471-2148-13-208  From a ScienceDaily article. Fossil jaws from the Middle Triassic show that reptiles representing the common ancestor of lizards, snakes and the tuatara were among the new groups to emerge in the wake of the end-Permian mass extinction.

Peter A. Hochuli and Susanne Feist-Burkhardt. 2013. Angiosperm-like pollen and Afropollis from the Middle Triassic (Anisian) of the Germanic Basin (Northern Switzerland). Frontiers in Plant Science, DOI: 10.3389/fpls.2013.00344  From a ScienceDaily article. This pollen, which appears to belong to an insect- (probably beetle-) pollinated plant, comes from a time 100 million years before the previous accepted evolution of flowering plants. It provides a fossil anchor for the earlier end of the range of molecular clock pointers from other studies.

Varricchio, David J., Frankie D. Jackson, Robert A. Jackson, Darla K. Zelenitsky. 2013. Porosity and water vapor conductance of two Troodon formosus eggs: an assessment of incubation strategy in a maniraptoran dinosaur. Paleobiology 39 (2): 278 DOI: 10.1666/11042  They found that this small carnivorous dinosaur incubated partly buried eggs, not burying them completely like crocodiles. This conclusion is drawn in part because of egg-in-nest fossils, and largely because the fossils’ relatively few, small eggshell pores that limit moisture loss are like those of incubated eggs and unlike buried ones.

Blackburn, Terrence J., et al. 2013. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science 340:941-945.  They have dated basalt samples around the edges of the Atlantic Ocean, looked at the rock just above and below those layers, and have connected the mass extinction that marked the end of the Triassic Period with a series of massive lava flows triggered by the rift that opened the Pangaea supercontinent and began to create the Atlantic Ocean as North America, South America and Africa split apart. They date the extinction at 201,564,000 years ago. The eruptions consisted of 2.5 million cubic miles of lava, in 4 major flows. Three of the flows occurred within 13,000 years, at the same time as the extinctions, which can be dated within 20,000 years at this point.

Bonnan, MF, et al. 2013. What lies beneath: sub-articular long bone shape scaling in eutherian mammals and saurischian dinosaurs suggests different locomotor adaptations for gigantism. PLoS ONE 8(10): e75216. doi:10.1371/journal.pone.0075216  Gigantic sizes were achieved more often in dinosaurs than in mammals. This study found that dinosaurs had relatively thick cartilage pads in load-bearing joints, making gigantism more frequently workable.

Bell, Phil R., Federico Fanti, Philip J. Currie, Victoria M. Arbour. 2013. A mummified duck-billed dinosaur with a soft-tissue cock’s comb. Current Biology DOI: 10.1016/j.cub.2013.11.008  From a ScienceDaily article. They describe a mummified fossil Edmontosaurus regalis with a previously unknowable soft-tissue “cock’s comb” structure on the top of its head.

Maiorino, L, A.A. Farke, T. Kotsakis, P. Piras. 2013. Is Torosaurus Triceratops? Geometric morphometric evidence of Late Maastrichtian ceratopsid dinosaurs. PLoS ONE 8(11): e81608. doi:10.1371/journal.pone.0081608  They did a comparative developmental study of fossils originally named Torosaurus and two species of Triceratops. Their measurements indicate different developmental trajectories for the two genera, and they reject the recent suggestion that Torosaurus is simply a more mature Triceratops.

Literature Review: The Paleozoic Era

by Carl Strang

Last week I shared notes on some published papers from last year which cast light on the early Earth, when life first appeared. The Paleozoic Era was marked by the sudden appearance of abundant, diverse new fossils. What has become increasingly clear is that readily fossilized shells were the major new development, making the “Cambrian explosion” possible (the Cambrian Period is the opening chapter of that era).

Smith, M. Paul, and David A.T. Harper. 2013. Causes of the Cambrian explosion. Science 341:1355-1356. They reviewed major themes that have emerged from research in this area. Some important components are the rising sea/sinking continents which released high mineral concentrations into the oceans (providing material for constructing shells), along with the huge increase in shallow sea habitat (providing much area in which ecological interactions could take place, including predator-prey interactions which would drive the evolution of shells for prey protection and improved predator effectiveness), and growing evidence that earlier, Proterozoic organisms in fact were ancestors of Cambrian groups, which includes molecular clock estimates as well as fossil connections.

Diverse marine invertebrates appeared in the early Paleozoic.

Diverse marine invertebrates appeared in the early Paleozoic.

Jie Yang, Javier Ortega-Hernández, Nicholas J. Butterfield, Xi-guang Zhang. Specialized appendages in fuxianhuiids and the head organization of early euarthropods. Nature, 2013; 494 (7438): 468 DOI: 10.1038/nature11874  From a ScienceDaily article. They described fossils of an early-Cambrian-explosion arthropod, Chenjiangocaris kunmingensis, in which the anterior-most limbs are modified for feeding, apparently for shoveling sediment into the mouth. It was generally soft-bodied, but had a carapace. This is also the earliest known species with a central nervous system extending back from the head. It came from a new site in south China called Xiaoshiba which promises to provide many additional insights into the earliest evolution of animals.

The appearance of shells in the Cambrian, probably resulting from predator-prey interactions, made abundant fossils from that time a possibility.

The appearance of shells in the Cambrian, probably resulting from predator-prey interactions, made abundant fossils from that time a possibility.

Tanaka,Gengo, et al. 2013. Chelicerate neural ground pattern in a Cambrian great appendage arthropod. Nature 502 (7471): 364 DOI: 10.1038/nature12520  From a ScienceDaily article. They described a new species whose central nervous system is preserved well enough to show that it was a chelicerate arthropod, and thus that chelicerates split from mandibulates more than 520 million years ago. Alalcomenaeus belonged to an extinct group of large-clawed arthropods, the megacheirans, that previously had been difficult to place. It had two pairs of large eyes at the front of the head. Earlier, a similar analysis of another Chinese fossil from this deposit, Fuxianhuia, revealed a nervous system that connected it to the crustaceans, which are mandibulates (chelicerate and mandibulate arthropods are the two major groups, the former today including spiders and scorpions, the latter insects and crabs, among others).

Jean-Bernard Caron, Simon Conway Morris, Christopher B. Cameron. Tubicolous enteropneusts from the Cambrian period. Nature, 2013; DOI: 10.1038/nature12017  As reported in ScienceDaily. They described an acorn worm or hemichordate, Spartobranchus tenuis from the Burgess Shale, which is the oldest of its group by 200 million years. Its group is one of the two main groups of hemichordates, and this fossil ties the two together, as well as having connections to echinoderms and chordates. They were extremely abundant in places, and may have been important marine sediment dwellers, their function similar to terrestrial earthworms today.

Pennisi, Elizabeth. 2013. Eating was tough for early tetrapods. Science 339:390. This news article covered recent research on early terrestrial vertebrates (from much later in the Paleozoic than the species mentioned above) that looked at the challenge posed by swallowing prey on land rather than in the water. Developing that capability may have taken 80 million years, with early ones feeding in the water or carrying captured prey into the water where they could have swallowed it along with gulps of water. At some point, tongues evolved that could assist.

Linda A. Tsuji, Christian A. Sidor, J.- Sébastien Steyer, Roger M. H. Smith, Neil J. Tabor, Oumarou Ide. The vertebrate fauna of the Upper Permian of Niger—VII. Cranial anatomy and relationships of Bunostegos akokanensis (Pareiasauria). Journal of Vertebrate Paleontology, 2013; 33 (4): 747 DOI: 10.1080/02724634.2013.739537  As described in a ScienceDaily article. This pareiasaur was endemic to the center of Pangaea, which has been established geologically as a desert region (the continents fused together in the late Paleozoic, and the resulting supercontinent of Pangaea had an interior far from any sea). Apparently that region was so distinct from surrounding more moderate biomes that the boundary served as an isolating barricade for species on either side. This one was a cow-sized herbivore.

Literature Review: Early Earth

by Carl Strang

A number of studies came out last year addressing the conditions of early Earth, and how life might have gotten started. That latter subject certainly is not suffering from a lack of ideas. The opposite in fact is true, and there is a confusing array of possibilities that need to be tested and sorted out. The following notes are from studies or reports of studies that caught my eye.

Life in all its complexity had a simple start, perhaps in the sea.

Life in all its complexity had a simple start, perhaps in the sea.

Hadean Eon

Clery, Daniel. 2013. Impact theory gets whacked. Science 342:183-185. This news article reviewed the history of the giant-impact moon formation theory and its discussion at a recent meeting. The model, first proposed in 1975 by William Hartman and Donald Davis, has become the consensus understanding of how the moon formed, but there have been problems. Computer simulations have indicated that the impact as understood would leave the moon formed “almost exclusively” from material in the impactor rather than the Earth. Moon rocks have shown clearly, however, that much of the moon is made of Earth material. Several new modifications have been offered. In one the impactor is much smaller than the Mars-sized body of the original model, but the Earth is spinning much faster. In another, the impactor is closer to the Earth in size. Both require some further process to set up the system we see today. The problem could be resolved if the impactor were similar to Earth in composition, i.e. if the inner planets are not as different in composition as comparisons of Earth and Mars suggest. If rocks can be obtained from Venus, and these prove to be Earth-like, a return to the original simpler giant impact model could take place.

Archean Eon

Zaleski, Daniel P., et al. Detection of e-cyanomethanimine toward Sagittarius B2(N) in the Green Bank Telescope Primos survey. The Astrophysical Journal, 2013; 765 (1): L10 DOI: 10.1088/2041-8205/765/1/L10  They found a precursor to one of the building blocks of DNA, and another for an amino acid, in an interstellar cloud. The materials apparently assembled on ice particles.

L. M. Longo, J. Lee, M. Blaber. 2013. Simplified protein design biased for prebiotic amino acids yields a foldable, halophilic protein. Proceedings of the National Academy of Sciences 110 (6): 2135 DOI: 10.1073/pnas.1219530110  From a ScienceDaily article. As an alternative to the RNA-first idea, and to the possibility of Earth life first appearing around hydrothermic vents, they have developed evidence supporting the possibility of a protein-first idea in a salt-rich environment. The amino acids thought to have been present at the time prove capable not only of forming chains under such conditions, but also of having the critical quality of folding properly in the presence of the salts.

Wordsworth, Robin, and Raymond Pierrehumbert. 2013. Hydrogen-nitrogen greenhouse warming in Earth’s early atmosphere. Science 339:64-67. There also is an interpretive article in this issue. Collisions between the nitrogen and hydrogen atoms, common in the Archean atmosphere, would have resulted in structural changes, as the atoms in each molecule bounced back and forth, that would give them greenhouse gas properties. The authors argue that this was an important factor keeping water liquid at a time when the sun was dim. As methane-metabolizing microorganisms became abundant that gas would have increased, but the authors argue that this would have cooled the Earth, possibly resulting in ice ages in those early times.

Bryant, David E., et al. 2013. Hydrothermal modification of the Sikhote-Alin iron meteorite under low pH geothermal environments. A plausibly prebiotic route to activated phosphorus on the early Earth. Geochimica et Cosmochimica Acta 109: 90 DOI: 10.1016/j.gca.2012.12.043  Their study focuses on the importance of phosphorus and ATP in cellular energetics, and supports the possibility that phosphorus-bearing meteorites landing in hot acidic pools around volcanos could have been a step between inorganic chemistry and organic life.

University of Washington (2013, July 29). Natural affinities — unrecognized until now — may have set stage for life to ignite. ScienceDaily. Retrieved July 31, 2013, from http://www.sciencedaily.com­ /releases/2013/07/130729161514.htm  This ScienceDaily article describes findings that may shed light on the origin of life. Researchers at the University of Washington have found that certain fatty acids, in combination with the components of RNA, coalesce to form mutually protective structures, the fatty acids in a bag that brings together the nucleic acids, potentially making it easier for the latter to combine into RNA molecules. The nucleic acids reduce the disruptive effects of salt water on the fatty acid bags.

Crowe, Sean A., et al. 2013. Atmospheric oxygenation three billion years ago. Nature 501 (7468): 535 DOI: 10.1038/nature12426  From a ScienceDaily article. Study of fossil soils indicates that oxygen appeared in small amounts in the atmosphere 3 billion years ago, rather than 2.3, suggesting that photosynthesis began that much earlier.

Proterozoic Eon

Johnson, J. E., et al. 2013. Manganese-oxidizing photosynthesis before the rise of cyanobacteria. Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1305530110  From a ScienceDaily article. They studied marine deposits in South Africa from the beginning of the Proterozoic, before cyanobacteria had developed chlorophyll-based photosynthesis. They found concentrations of oxidized manganese, which apparently had been formed by earlier microorganisms acquiring electrons from dissolved manganese in a chemical process that could have been the precursor of photosynthesis by cyanobacteria.

B. A. Killingsworth, J. A. Hayles, C. Zhou, H. Bao. 2013. Sedimentary constraints on the duration of the Marinoan Oxygen-17 Depletion (MOSD) event. Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1213154110  Oxygen isotope ratios point to a large and rapid buildup of atmospheric carbon dioxide as being responsible for the end of the Snowball Earth glaciation in the Proterozoic. The ice blocked off potential sinks, especially in the oceans, so the greenhouse gas simply built (the ScienceDaily article describing the study didn’t mention the source of the gas, but volcanos would have continued to be active).

Wacey, David, et al. 2013. Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the 1.9-Ga Gunflint chert. PNAS, DOI: 10.1073/pnas.1221965110  They found evidence of preferential bacterial consumption of cyanobacteria (blue-green algae) by bacteria, the earliest evidence of one kind of organism eating another. The consumers were apparently not so interested in another bacteria species. The process would have released sulfur dioxide, adding a rotten eggs odor to the atmosphere.

Bernhard, Joan M., et al. 2013. Insights into foraminiferal influences on microfabrics of microbialites at Highborne Cay, Bahamas. PNAS, DOI: 10.1073/pnas.1221721110  They conducted experiments that supported the idea that the extinction of most stromatolites 1 billion years ago was caused by foraminifera which appeared at that time and disturbed the layered stromatolite structure (stromatolites were the abundant, layered structures formed by cyanobacteria, responsible for the early oxygenation of the atmosphere). A similar group of structures, called thrombolites, also appeared about this time with a clumped rather than layered structure. These coexist with foraminifera today.

Pennisi, Elizabeth. 2013. Nervous system may have evolved twice. Science 339:391. This news article described two genomic studies of ctenophores (comb jellies, sea animals that superficially resemble jellyfish but belong to another phylum entirely) that point to their evolving nervous systems independently of, and earlier than, all other animals. The authors of one of the studies conclude that these animals may have preceded even sponges, possibly supporting the notion that ctenophores were tied to the Ediacaran biota of the late Proterozoic.

Literature Review: Human Paleontology

by Carl Strang

This last post on the scientific literature from 2012 includes notes from studies that spanned the time range of human evolution and geographic expansion. The review begins 4 million years ago with Australopithecus anamensis in Africa, and ends a little over 10,000 years ago in Ohio.

Estebaranz, Ferran, et al. Buccal dental microwear analyses support greater specialization in consumption of hard foodstuffs for Australopithecus anamensis. Journal of Anthropological Sciences, 2012; 90: 1-24 DOI: 10.4436/jass.90006 As described in a ScienceDaily article. Microwear of molars is consistent with a diet of seeds, tubers and leaves for Australopithecus anamensis. This contrasts with the fruit-heavy diets of both the ancestor of anamensis (Ardepithecus ramidus) and its descendant Australopithecus afarensis.

Green, David J., and Zeresenay Alemseged. 2012. Australopithecus afarensis scapular ontogeny, function, and the role of climbing in human evolution. Science 338: 514-517. For the first time, shoulder blades of this species have been studied. Their similarity to those of apes (both in structure and in the fact that those of young are similar to those of adults) suggests that this upright walking species still was adapted for tree climbing as well.

Human use of fire may go back a million years.

Human use of fire may go back a million years.

Berna, Francesco, et al. Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa. Proceedings of the National Academy of Sciences, April 2, 2012 DOI: 10.1073/pnas.1117620109 They found evidence of cultural use of fire dated 1 million years ago, 300,000 years earlier than the previous evidence. This was the time of Homo erectus.

Wilkins, Jayne, Benjamin J. Schoville, Kyle S. Brown, and Michael Chazan. 2012. Evidence for early hafted hunting technology. Science 338:942-946. They found spear points in South Africa from 500,000 years ago, the time of Homo heidelbergensis, the last common ancestor of Neanderthals and modern humans. This indicates that the spears used by both had a common cultural origin. The previous known oldest spears were at 300,000 years ago.

Mathias RA, Fu W, Akey JM, Ainsworth HC, Torgerson DG, et al. (2012) Adaptive Evolution of the FADS Gene Cluster within Africa. PLoS ONE 7(9): e44926. doi:10.1371/journal.pone.0044926 They looked at genes which make possible the conversion of medium-length fatty acids from plants into longer-chain fatty acids essential for human brain function. Variation in human populations and in relation to chimpanzees points to the fixation of these gene variations around 85,000 years ago. This coincides with the time when humans began to expand through Africa away from limited coastal areas, where they had remained for the first 100,000 years of the species’ existence. The authors suggest that prior to this mutational event, humans needed fish and aquatic invertebrates to provide these fatty acids, but afterwards could live in a broader range of environments by including plants in the diet that provided the precursors for the brain chemicals. A ScienceDaily article describing this study points out that African Americans as well as Africans, who have the highest functionality of these genes, more often suffer the side effects of hypertension, coronary artery disease, and other consequences of too-efficient use of vegetable oils in cooking.

Finlayson, C., et al. (2012) Birds of a Feather: Neanderthal Exploitation of Raptors and Corvids. PLoS ONE 7(9): e45927. doi:10.1371/journal.pone.0045927 They studied remains in a number of caves and other Neanderthal sites over a long span of time, and found evidence that Neanderthals commonly and deliberately, removed corvid and raptor flight feathers, apparently for use in symbolic adornment.

Rule, Susan, et al. 2012. The aftermath of megafaunal extinction: ecosystem transformation in Pleistocene Australia. Science 335:1483-1486. They used charcoal as an indicator of human activity, a fungal dung spore for megafauna, and also looked at changes in plant communities as indicated by pollen in core samples over a time span from 130,000 to 24,000 years ago. They conclude that human hunting was responsible for Australian megafauna extinctions (at least 20 genera of marsupials, monotremes, birds and reptiles). They then argue that the timing of vegetation changes points to the loss of megafauna leading to an increase in grasses and other fine fuels, so that resulting wildfires promoted a vegetation change in the region around the cored swamp in northeast Australia, from a mixed rainforest to a desert shrub-grass ecosystem.

Human use of fire may go back a million years.

Reconstructed ground sloth

Brian G. Redmond, H Gregory McDonald, Haskel J. Greenfield, Matthew L. Burr. New evidence for Late Pleistocene human exploitation of Jefferson’s Ground Sloth (Megalonyx jeffersonii) from northern Ohio, USA. World Archaeology, 2012; 44 (1): 75 DOI: 10.1080/00438243.2012.647576 A fossil thigh bone shows saw marks from stone tools were used to filet the muscle, 13,435-13,738 years ago.

« Older entries

Follow

Get every new post delivered to your Inbox.

Join 91 other followers

%d bloggers like this: