Literature Review: Mesozoic Era

by Carl Strang

As always, fascination with dinosaurs in particular produced plenty of interesting new Mesozoic Era studies published in 2014. Those focused on the evolution of birds will follow next week.

Dinosaurs weren’t the only Mesozoic life forms, but they certainly are the first to come to mind.

Dinosaurs weren’t the only Mesozoic life forms, but they certainly are the first to come to mind.

Grady, John M., et al. 2014. Evidence for mesothermy in dinosaurs. Science 344:1268-1272. They looked at growth rates as indicated by bone rings, comparing such data to present-day ectotherms, endotherms and mesotherms such as certain sharks, tuna, sea turtles and echidnas. They found that the dinosaurs fit with that last group. Given the climatic warmth of the Mesozoic, this is a feasible result, giving them an advantage over slower ectotherms without the higher energy demands of endotherms.

Motani, Ryosuke, et al. 2014. A basal ichthyosauriform with a short snout from the Lower Triassic of China. Nature, DOI: 10.1038/nature13866 This fossil, Cartorhynchus lenticarpus, from 4 million years post-Permian mass extinction, fills the gap between terrestrial reptiles and marine ichthyosaurs. The 16-inch-long animal had flippers but strong wrists, a short snout, and heavy bone structure. It is regarded as an amphibious reptile that lived in coastal China, the heavy bones having been predicted as necessary for withstanding wave forces.

Koschowitz, Marie-Claire, Christian Fischer, and Martin Sander. 2014. Beyond the rainbow. Science 346:416-419. They review recent literature and paint a picture of dinosaurs first evolving proto-feathers as insulation, facilitating their new capacity for greater metabolism. This was especially important in the theropod lineage that ultimately led to birds, as body size decreased over time. Such a covering would have hidden the skin’s structural color, however, taking away any prismatic or reflective production of iridescence, blues, greens, and ultraviolets, and losing them as a signal. That loss provided a selective advantage to vaned feathers, which recovered the structural color capability. The vaned feather in turn provided the foundation, eventually, for flight. These steps are dependent upon the dinosaurs’ color vision, which they share with a broad range of reptiles.

Godefroit, P., et al. 2014. A Jurassic ornithischian dinosaur from Siberia with both feathers and scales. Science 345:451-455. Kulindadromeus zabaikalicus was found in a new site in Siberia. It is a basal ornithiscian that had filamented feathers, for the first time proving these were not limited to the theropods (earlier, fossil ornithiscians have been found with bristle-like feathers). Filamented ones were found on the limbs, and the rest of the body was largely covered in bristle-like feathers. The tail and lower legs were scaled. This dinosaur was around 1m long.

Button, D. J., E. J. Rayfield, and P. M. Barrett. 2014. Cranial biomechanics underpins high sauropod diversity in resource-poor environments. Proceedings of the Royal Society B: Biological Sciences 281 (1795): 20142114. DOI: 10.1098/rspb.2014.2114 They reconstructed the anatomy of coexisting sauropods, Camarasaurus and Diplodocus, to get an idea of how two such enormous animals could coexist in an arid, relatively plant-poor, environment. Camarasaurus had a strong bite, and could handle tougher vegetation such as woody plants. Diplodocus had a weaker bite but stronger neck, so it would have had an easier time pulling out and handling softer plants like ferns.

Geological Society of America. 2014. “Kung fu stegosaur: Lethal fighters when necessary.” ScienceDaily, <>. Robert Bakker and colleagues described an allosaur pubis bone which developed an infection following a wound from a stegosaur tail spike. The infection probably killed the predator. The wound is an indication of an accurate defensive tail swing by the stegosaur.

Grossi, B., et al. 2014. Walking like dinosaurs: chickens with artificial tails provide clues about non-avian theropod locomotion. PLoS ONE 9(2): e88458. doi:10.1371/journal.pone.0088458 They raised chickens with artificial tails attached, to see if this change in center of mass would change their locomotion to match that theorized for theropods. The experiment was successful, producing birds that moved more through use of femoral movement rather than the more crouched, knee focused gait of birds.

Andrew A. Farke, W. Desmond Maxwell, Richard L. Cifelli, Mathew J. Wedel. 2014. A ceratopsian dinosaur from the Lower Cretaceous of western North America, and the biogeography of Neoceratopsia. PLoS ONE 9(12): e112055. doi:10.1371/journal.pone.0112055  They describe the earliest known North American ceratopsian, a crow-sized dinosaur similar to contemporary similar Asian species, providing evidence for a connection between the continents around that time. Montana is the location of the find.

Ibrahim, Nizar, et al. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345:1613-1616. They describe a partial skeleton of Spinosaurus aegyptiacus from Morocco. It shows several adaptations for a semiaquatic lifestyle, including nostrils brought back to the midpoint of the skull; an elongate neck and trunk that shift the center of mass forward; a downsized pelvic girdle; short limbs; solid limb bones (helpful to counter buoyancy when swimming); and muscle attachment indicators and flat-bottomed claws on the hind feet “consistent with aquatic foot-propelled locomotion.” The long rays on the dorsal spine “may have been enveloped in skin that functioned primarily for display on land and in water.” Its age is estimated at 97 million years. The elongate toothy snout may indicate this was largely a fish predator. It was found in river sediments, in a river system where there were common sharks, sawfish, coelacanths, lungfish and others.

Krause, David W., et al. 2014. First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism. Nature, DOI: 10.1038/nature13922 As described in a ScienceDaily article. This describes the unprecedented find of a complete skull from Madagascar, a 20-pound mammal contemporary with the latest dinosaurs, and by far the largest southern continent mammal from the Mesozoic (this is only the third Cretaceous mammal skull from the entire southern hemisphere). Vintana sertichi was a gondwanatherian, a southern hemisphere group previously known only from a few teeth. It appears to have been a nocturnal herbivore, with very large eye sockets and anchors for strong chewing muscles. The details of the skull show that this group is close to the multituberculates and another odd group, the Haramiyida.

Literature Review: Paleozoic Era

by Carl Strang

The first animals which unambiguously connect to present day forms appear in the fossil record early in the Paleozoic Era, which began 542 million years ago, billions of years after the planet first formed. Here are some notes from studies of this era published in 2014.

American alligator. One of the following studies places the split between the reptilian crocodile-dinosaur-bird group and the lizard-snake group at the very end of the Paleozoic Era.

American alligator. One of the following studies places the split between the reptilian crocodile-dinosaur-bird group and the lizard-snake group at the very end of the Paleozoic Era.

Cong, Peiyun, et al. 2014. Brain structure resolves the segmental affinity of anomalocaridid appendages. Nature, DOI: 10.1038/nature13486 They studied the brain structure of Lyrarapax unguispinus, a fossilized relative of Anomalocaris, and found it was both simpler than those of its contemporary prey, and very similar to those of today’s onychophorans, or velvet worms, terrestrial southern hemisphere forest floor predators with unusual antennae that connect to the brain in the same way that the pair of grasping appendages connected to the brain of Lyrarapax. The similarities suggest a common ancestry.

Jourdan, F., et al. 2014. High-precision dating of the Kalkarindji large igneous province, Australia, and synchrony with the Early-Middle Cambrian (Stage 4-5) extinction. Geology 42 (6): 543. DOI: 10.1130/G35434.1 From a ScienceDaily article. The first major extinction event, which took out 50% of species in the Middle Cambrian, was caused by a mass volcanic eruption in Australia according to this study.

Morris, Simon Conway, and Jean-Bernard Caron. 2014. A primitive fish from the Cambrian of North America. Nature, DOI: 10.1038/nature13414 New Burgess shale fossils from the Cambrian of 505mya (million years ago) show detail in one of the earliest fishes, Metaspriggina, in which branchial arches are revealed as paired, with the first pair slightly thicker than the others (a step toward the first jaw). They had large eyes, and probably were good swimmers.

Shubin, Neil H., Edward B. Daeschler, and Farish A. Jenkins, Jr. 2014. Pelvic girdle and fin of Tiktaalik roseae. PNAS, DOI: 10.1073/pnas.1322559111 From a ScienceDaily article. They describe the anatomy of the rear part of this fish, previously known only from anterior portions. This animal was transitional toward terrestrial life, living in a delta environment where the ability to cross over land from stream to stream was advantageous. It was large, as much as 9 feet long, with large teeth making it somewhat reminiscent of a crocodile. It was lobe-finned, had a flexible neck, and rudimentary lungs. Its well-developed shoulder girdle previously was known, but it had been assumed that it crawled with only its front fins. The surprise was that the pelvic girdle also is developed, with a ball and socket joint and strong hind fins, so these fish had rudiments of four, rather than just two legs.

Ezcurra, M.D., T.M. Scheyer, and R.J. Butler. 2014. The origin and early evolution of Sauria: reassessing the Permian saurian fossil record and the timing of the crocodile-lizard divergence. PLoS ONE 9(2): e89165. doi:10.1371/journal.pone.0089165 They took a close look at Permian fossils in an attempt to resolve debate on when the split happened between the reptilian line leading to crocodiles, dinosaurs and birds on the one hand (archosauromorphs) and lizards and snakes on the other (lepidosauromorphs). They concluded that only the former have been found in the Permian, and place the earliest possible time for the split at 254.7 million years ago (very late Permian).

Literature Review: Proterozoic Eon

by Carl Strang

The Proterozoic Eon spanned the immense period of time from 2.5 billion to 542 million years ago. It has captured the imaginations of many researchers, because its rocks have teased them with clues that hint at amazing stories, such as the first eukaryotic life forms, a billion-year stall-out of life’s evolution, a globe-covering ice age (“snowball Earth”), and the first appearance of multicellular organisms, which may or may not be connected to those we have today. Here are my notes from last year on some studies of that eon.

There was no terrestrial life in the Proterozoic, but this was the time when the Chicago region’s crust joined the North American continent, appending itself to the southern boundary of the Canadian Shield.

There was no terrestrial life in the Proterozoic, but this was the time when the Chicago region’s crust joined the North American continent, appending itself to the southern boundary of the Canadian Shield.

Northwestern University. 2014. “Mysterious Midcontinent Rift is a geological hybrid.” ScienceDaily, <>. This article described a collaborative project, still unpublished, focusing on the mid-continent rift that left Lake Superior as its most visible feature. The rift was underway in the mid-Proterozoic when it filled with magma and stopped opening. More magma subsequently poured out on top of it, pushing the original body down and thickening the crust there. The feature thus combines rift characteristics with those of a large igneous province, and contains more volcanic rock than any other mid-continent rift on the planet. Incidentally the pieces of volcanic rock we find in local glacial drift came from that source.

Sánchez-Baracaldo, Patricia, Andy Ridgwell, and John A. Raven. 2014. A Neoproterozoic transition in the marine nitrogen cycle. Current Biology, DOI: 10.1016/j.cub.2014.01.041  From a ScienceDaily article. They used molecular clock estimation to place the appearance of nitrogen fixing by cyanobacteria at 800 million years ago. This may have removed the nutrient limitation that was holding life back, setting the stage for proliferation both of biomass and of evolutionary potential. However, this timing also is just before the Snowball Earth glaciation event, and the authors suspect that the algal bloom might have sequestered enough carbon to be a trigger for that event.

Hoyal Cuthill, Jennifer F., and Simon Conway Morris. 2014. Fractal branching organizations of Ediacaran rangeomorph fronds reveal a lost Proterozoic body plan. PNAS, DOI: 10.1073/pnas.1408542111  From a ScienceDaily article. They looked at the 3-dimensional structure of Ediacaran life forms (referred to as rangeomorphs), and found that their fractal designs efficiently filled the space around them. They argue that these were animals, living too deep in the sea for photosynthesis, which absorbed dissolved nutrients directly from the water. This was possible until predators, filter feeders and more mobile life forms rendered this subsistence style unsupportable.

Liu, Alex, et al. 2014. Haootia quadriformis n. gen., n. sp., interpreted as muscular Cnidarian impression from the Late Ediacaran period (approx. 560 Ma). Proceedings of the Royal Society B, DOI: 10.1098/rspb.2014.1202  From a ScienceDaily article. They described an Ediacaran fossil from Newfoundland, 560 million years old, concluding that it was a cnidarian with muscle tissue, the earliest animal with muscle.

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.



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.

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