Leaf-mining insects destroyed with the dinosaurs, others quickly appeared

After the asteroid impact at the end of the Cretaceous period that triggered the dinosaurs’ extinction and ushered in the Paleocene, leaf-mining insects in the western United States completely disappeared. Only a million years later, at Mexican Hat, in southeastern Montana, fossil leaves show diverse leaf-mining traces from new insects that were not present during the Cretaceous, according to paleontologists.

“Our results indicate both that leaf-mining diversity at Mexican Hat is even higher than previously recognized, and equally importantly, that none of the Mexican Hat mines can be linked back to the local Cretaceous mining fauna,” said Michael Donovan, graduate student in geosciences, Penn State.

Insects that eat leaves produce very specific types of damage. One type is from leaf miners — insect larvae that live in the leaves and tunnel for food, leaving distinctive feeding paths and patterns of droppings.

This is a mine produced by a micromoth larva on Platanus raynoldski, a sycamore. Credit: Michael Donovan, Penn State

This is a mine produced by a micromoth larva on Platanus raynoldski, a sycamore.
Credit: Michael Donovan, Penn State

Donovan, Peter Wilf, professor of geosciences, Penn State, and colleagues looked at 1,073 leaf fossils from Mexican Hat for mines. They compared these with more than 9,000 leaves from the end of the Cretaceous, 65 million years ago, from the Hell Creek Formation in southwestern North Dakota, and with more than 9,000 Paleocene leaves from the Fort Union Formation in North Dakota, Montana and Wyoming. The researchers present their results in today’s (July 24) issue of PLOS ONE.

“We decided to focus on leaf miners because they are typically host specific, feeding on only a few plant species each,” said Donovan. “Each miner also leaves an identifiable mining pattern.”

The researchers found nine different mine-damage types at Mexican Hat attributable to the larvae of moths, wasps and flies, and six of these damage types were unique to the site.

The researchers were unsure whether the high diversity of leaf miners at Mexican Hat compared to other early Paleocene sites, where there is little or no leaf mining, was caused by insects that survived the extinction event in refugia — areas where organisms persist during adverse conditions — or were due to range expansions of insects from somewhere else during the early Paleocene.

However, with further study, the researchers found no evidence of the survival of any leaf miners over the Cretaceous-Paleocene boundary, suggesting an even more total collapse of terrestrial food webs than has been recognized previously.

“These results show that the high insect damage diversity at Mexican Hat represents an influx of novel insect herbivores during the early Paleocene and not a refugium for Cretaceous leaf miners,” said Wilf. “The new herbivores included a startling diversity for any time period, and especially for the classic post-extinction disaster interval.”

Insect extinction across the Cretaceous-Paleocene boundary may have been directly caused by catastrophic conditions after the asteroid impact and by the disappearance of host plant species. While insect herbivores constantly need leaves to survive, plants can remain dormant as seeds in the ground until more auspicious circumstances occur.

The low-diversity flora at Mexican Hat is typical for the area in the early Paleocene, so what caused the high insect damage diversity?

Insect outbreaks are associated with a rapid population increase of a single insect species, so the high diversity of mining damage seen in the Mexican Hat fossils makes the possibility of an outbreak improbable.

The researchers hypothesized that the leaf miners that are seen in the Mexican Hat fossils appeared in that area because of a transient warming event, a number of which occurred during the early Paleocene.

“Previous studies have shown a correlation between temperature and insect damage diversity in the fossil record, possibly caused by evolutionary radiations or range shifts in response to a warmer climate,” said Donovan. “Current evidence suggests that insect herbivore extinction decreased with increasing distance from the asteroid impact site in Mexico, so pools of surviving insects would have existed elsewhere that could have provided a source for the insect influx that we observed at Mexican Hat.”

Chondrophore features on fossil specimens

PRESENCE OF MIOCENE OYSTERS: RISE AND FALL OF A PALEO-ESTUARY IN THE EAST COAST OF INDIA

Living oysters of Crassostrea Sp. are abundantly found on the east coast of peninsular India. Most of the living Crassostrea sp. is reported from Athankarai estuary near mandapam. The primary object of this study is to report the occurrence of fossils of Crassostrea sp. belonging to mio-pliocene outcrops from an ephemeral stream channel of Nambiyar/Thoppuvila River up to Attankarai Pallivasal, Tirunelveli dist, Tamil Nadu, India. The present study focuses on revealing the nature of a vast paleo-estuary that had existed on the foothills of the southern end of the Western Ghats during the Mio-Pliocene age. The authors had studied the taphonomical features of Crassostrea Gigantissima Sp. and analyzed the adaptation features like heaviness and foliated nature of the shell and orientation of oyster colonies for survival. The predatory signatures on the fossil specimens indicate traces of a well flourished saline tolerable environment that resembled an ideal estuary subjected to high energy disturbances. The chalky calcareous deposits found throughout the study area could have acted as an accelerating agent for the thick, foliated and heavy calcite shells of C. Gigantissima Sp. The author proposes a vast paleo-estuary with an area of around 460 km2 during the mio-pliocene age and the remnants present today is the result of an abrupt regression due to uplift which could have taken place in this area.

Panoramic view of Thoppuvila River

Panoramic view of Thoppuvila River

outcrops containing calcareous/chalky deposits

outcrops containing calcareous/chalky deposits

Fig 6: Foliated Shell structure of C. Gigantissima

 Foliated Shell structure of C. Gigantissima

(A) Nambiyar/Thoppuvila River main channel (B) Extent of proposed paleo-estuary (C) SRTM Geospatial representation of study area (D) Possible water channels in Study area

(A) Nambiyar/Thoppuvila River main channel (B) Extent of proposed paleo-estuary (C) SRTM Geospatial representation of study area (D) Possible water channels in Study area

 

Chondrophore features on fossil specimens

Chondrophore features on fossil specimens

Citation: International Journal of Advanced Earth Science and Engineering 2014,VOLUME 3, ISSUE 1,pp.129-142,

Research Article link: http://scientific.cloud-journals.com/index.php/IJAESE/article/view/Sci-198

 

198

The bend in the Appalachian mountain chain is finally explained

The 1500 mile Appalachian mountain chain runs along a nearly straight line from Alabama to Newfoundland — except for a curious bend in Pennsylvania and New York State. Researchers from the College of New Jersey and the University of Rochester now know what caused that bend — a dense, underground block of rigid, volcanic rock forced the chain to shift eastward as it was forming millions of years ago.

According to Cindy Ebinger, a professor of earth and environmental sciences at the University of Rochester, scientists had previously known about the volcanic rock structure under the Appalachians. “What we didn’t understand was the size of the structure or its implications for mountain-building processes,” she said.

The findings have been published in the journal Earth and Planetary Science Letters.

When the North American and African continental plates collided more than 300 million years ago, the North American plate began folding and thrusting upwards as it was pushed westward into the dense underground rock structure — in what is now the northeastern United States. The dense rock created a barricade, forcing the Appalachian mountain range to spring up with its characteristic bend.

A dense, underground block of volcanic rock (shown in red) helped shape the well-known bend in the Appalachian mountain range. Credit: Graphic by Michael Osadciw/University of Rochester.

A dense, underground block of volcanic rock (shown in red) helped shape the well-known bend in the Appalachian mountain range.
Credit: Graphic by Michael Osadciw/University of Rochester.

The research team — which also included Margaret Benoit, an associate professor of physics at the College of New Jersey, and graduate student Melanie Crampton at the College of New Jersey — studied data collected by the Earthscope project, which is funded by the National Science Foundation. Earthscope makes use of 136 GPS receivers and an array of 400 portable seismometers deployed in the northeast United States to measure ground movement.

Benoit and Ebinger also made use of the North American Gravity Database, a compilation of open-source data from the U.S., Canada, and Mexico. The database, started two decades ago, contains measurements of the gravitational pull over the North American terrain. Most people assume that gravity has a constant value, but when gravity is experimentally measured, it changes from place to place due to variations in the density and thickness of Earth’s rock layers. Certain parts of Earth are denser than others, causing the gravitational pull to be slightly greater in those places.

Data on the changes in gravitational pull and seismic velocity together allowed the researchers to determine the density of the underground structure and conclude that it is volcanic in origin, with dimensions of 450 kilometers by 100 kilometers. This information, along with data from the Earthscope project ultimately helped the researchers to model how the bend was formed.

Ebinger called the research project a “foundation study” that will improve scientists’ understanding of Earth’s underlying structures. As an example, Ebinger said their findings could provide useful information in the debate over hydraulic fracturing — popularly known is hydrofracking — in New York State.

Hydrofracking is a mining technique used to extract natural gas from deep in the Earth. It involves drilling horizontally into shale formations, then injecting the rock with sand, water, and a cocktail of chemicals to free the trapped gas for removal. The region just west of the Appalachian Basin — the Marcellus Shale formation — is rich in natural gas reserves and is being considered for development by drilling companies.Note: Materials may be edited for content and length.

Jeju Island, Korea is a live volcano

In Jeju, Korea, a place emerging as a world-famous vacation spot with natural tourism resources, a recent study revealed a volcanic eruption occurred on the island. The Korea Institute of Geoscience and Mineral Resources (KIGAM) indicated that there are the traces that indicated that a recent volcanic eruption was evident 5,000 years ago. This is the first time the date of the explosion has been made clear in the region.

The research team led by Dr. Jin-Young Lee confirmed in results from radiocarbon dating for carbonized wood (charcoal) found below the basaltic layer located in Sangchang-ri, Seogwipo-si, Jeju-do it dated back to 5,000 years ago; which means the time when the basalt on the upper layer was formed took place relatively recently, i.e. 5,000 years ago, and which demonstrates that the island has experienced a volcanic eruption fairly recently.

Pictures of the sedimentary layer containing charcoal found on a stony mountain developing site in Sangchang-ri, and the carbonized wood (charcoal) sample used for the radiocarbon dating. Thick lava covers the upper gravel layer. Credit: Image courtesy of Korea Institute of Geoscience and Mineral Resources (KIGAM)

Pictures of the sedimentary layer containing charcoal found on a stony mountain developing site in Sangchang-ri, and the carbonized wood (charcoal) sample used for the radiocarbon dating. Thick lava covers the upper gravel layer.
Credit: Image courtesy of Korea Institute of Geoscience and Mineral Resources (KIGAM)

The latest volcanic eruption occurring on Jeju Island was volcanic activity known to have spewed around 7,000 years ago at Mt. Songak. The basaltic layer in Sangchang-ri is known to be formed due to the eruption in the vicinity of Byeongak Oreum 35,000 years ago; though, this study revealed that the layer is a product of the most recent volcanic activity among those known ever. Volcanic activity at Mt. Songak was limited hydro volcanic activity out of which a great deal of volcanic ash was released while it is evident that Sangchang-ri was a dynamic active volcano out of which lava was spewed and then flowed down in all directions along the inland slope.

It is also remarkable that the research team enhanced the accuracy of the findings in the radiocarbon dating technique using carbonized wood, consequently raising the reliability of the findings. Until now, previous research used the dating method for rocks covering the upper sedimentary layer, in which such dating method with the relatively longer half-life period shows limitations in determining the time the basalt was formed about 10,000 years ago.

In order to overcome the limitations of the dating method for the rocks covering the upper sedimentary layer, the research team led by Dr. Jin-Young Lee concurrently used radiocarbon dating and optically stimulated luminescence dating (OSL), using such cross-validation of which raised the accuracy of tracing the past volcanic activities.

Judging from the findings, Jeju Island is not an extinct volcano, but seems to rather be a potentially live volcano because a volcano that has erupted within 10,000 years is defined to be a live volcano on a geological basis.

Not remaining complacent for the findings, the research team plans to continuously conduct the studies on the time the volcanic rocks were formed in several regions on the island in order to identify the latest volcanic activity.

Fossil of predators brain discovered

An international team of paleontologists has identified the exquisitely preserved brain in the fossil of one of the world’s first known predators that lived in the Lower Cambrian, about 520 million years ago. The discovery revealed a brain that is surprisingly simple and less complex than those known from fossils of some of the animal’s prey.

The find for the first time identifies the fossilized brain of what are considered the top predators of their time, a group of animals known as anomalocaridids, which translates to “abnormal shrimp.” Long extinct, these fierce-looking arthropods were first discovered as fossils in the late 19th century but not properly identified until the early 1980s. They still have scientists arguing over where they belong in the tree of life.

“Our discovery helps to clarify this debate,” said Nicholas Strausfeld, director of the University of Arizona’s Center for Insect Science. “It turns out the top predator of the Cambrian had a brain that was much less complex than that of some of its possible prey and that looked surprisingly similar to a modern group of rather modest worm-like animals.”

This is a side-by-side comparison reveals the similarity between the brain of a living onychophoran (green) and that of the anomalocaridid fossil Lyrarapax unguispinus (gray). Long nerves from the frontal appendages extend to paired ganglia lying in front of the optic nerve and connect to the main brain mass in front of the mouth. Anomalocaridids had a pair of clawlike grasping appendages instead of feelers. Credit: Illustration by Nicholas Strausfeld

This is a side-by-side comparison reveals the similarity between the brain of a living onychophoran (green) and that of the anomalocaridid fossil Lyrarapax unguispinus (gray). Long nerves from the frontal appendages extend to paired ganglia lying in front of the optic nerve and connect to the main brain mass in front of the mouth. Anomalocaridids had a pair of clawlike grasping appendages instead of feelers.
Credit: Illustration by Nicholas Strausfeld

Strausfeld, a Regents’ Professor in the Department of Neuroscience in the UA College of Science is senior author on a paper about the findings recently published in the journal Nature.

The brain in the fossil, a new species given the name Lyrarapax unguispinus — Latin for “spiny-clawed lyre-shaped predator” — suggests its relationship to a branch of animals whose living descendants are known as onychophorans or velvet worms. These wormlike animals are equipped with stubby unjointed legs that end in a pair of tiny claws.

Onychophorans, which are also exclusively predators, grow to no more than a few inches in length and are mostly found in the Southern Hemisphere, where they roam the undergrowth and leaf litter in search of beetles and other small insects, their preferred prey. Two long feelers extend from the head, attached in front of a pair of small eyes.

The anomalocaridid fossil resembles the neuroanatomy of today’s onychophorans in several ways, according to Strausfeld and his collaborators. Onychophorans have a simple brain located in front of the mouth and a pair of ganglia — a collection of nerve cells — located in the front of the optic nerve and at the base of their long feelers.

“And — surprise, surprise — that is what we also found in our fossil,” Strausfeld said, pointing out that anomalocaridids had a pair of clawlike grasping appendages in front of the eyes.

“These top predators in the Cambrian are defined by just their single pair of appendages, wicked-looking graspers, extending out from the front of their head,” he said. “These are totally different from the antennae of insects and crustaceans. Such frontally disposed appendages are not found in any other living animals with the exception of velvet worms.”

The similarities of their brains and other attributes suggest that the anomalocaridid predators could have been very distant relatives of today’s velvet worms, Strausfeld said.

“This is another contribution towards the new field of research we call neuropaleontology,” said Xiaoya Ma of the Natural History Museum in London, a co-author on the paper. “These grasping appendages are a characteristic feature of this most celebrated Cambrian animal group, whose affinity with living animals has troubled evolutionary scientists for almost a century. The discovery of preserved brain in Lyrarapax resolves specific anatomical correspondences with the brains of onychophorans.”

“Being able to directly associate appendages with parts of the brain in Cambrian animals is a huge advantage,” said co-author Gregory Edgecombe, also at the Natural History Museum. “For many years now paleontologists have struggled with the question of how different kinds of appendages in Cambrian fossils line up with each other and with what we see in living arthropods. Now for the first time, we didn’t have to rely just on the external form of the appendages and their sequence in the head to try and sort out segmental identities, but we can draw on the same tool kit we use for extant arthropods — the brain.”

Strausfeld and his colleagues recently presented evidence of the oldest known fossil of a brain belonging to arthropods related to insects and crustaceans and another belonging to a creature related to horseshoe crabs and scorpions (see links below).

“With this paper and our previous reports in Nature, we have identified the three principal brain arrangements that define the three groups of arthropods that exist today,” Strausfeld said. “They appear to have already coexisted 520 million years ago.”

The Lyrarapax fossil was found in 2013 by co-author Peiyun Cong near Kunming in the Chinese province of Yunnan. Co-authors Ma and Edgecombe participated in the analysis, as did Xianguang Hou — who discovered the Chengjiang fossil beds in 1984 ¬ — at the Yunnan Key Laboratory for Paleobiology at the University of Yunnan.

“Because its detailed morphology is exquisitely preserved, Lyrarapax is amongst the most complete anomalocaridids known so far,” Cong said.

Just over five inches long, Lyrarapax was dwarfed by some of the larger anomalocaridids, which reached more than three feet in length. Paleontologists excavating lower Cambrian rocks in southern Australia found that some anomalocaridids had huge compound eyes, up to 10 times larger than the biggest dragonfly eye, befitting what must have been a highly efficient hunter, Strausfeld said.

The fact that the brain of the earliest known predator appears much simpler in shape than the previously unearthed brains of its contemporaries begs intriguing questions, according to Strausfeld, one of which is whether it is possible that predators drove the evolution of more complex brains.

“With the evolution of dedicated and highly efficient predators, the pressure was on other animals to be able to detect and recognize potential danger and rapidly coordinate escape movements. These requirements may have driven the evolution of more complex brain circuitry,” Strausfeld said.

Evidence of super-fast deep earthquake

As scientists learn more about earthquakes that rupture at fault zones near the planet’s surface — and the mechanisms that trigger them — an even more intriguing earthquake mystery lies deeper in the planet.

Scientists at Scripps Institution of Oceanography at UC San Diego have discovered the first evidence that deep earthquakes, those breaking at more than 400 kilometers (250 miles) below Earth’s surface, can rupture much faster than ordinary earthquakes. The finding gives seismologists new clues about the forces behind deep earthquakes as well as fast-breaking earthquakes that strike near the surface.

The supershear 2013 Sea of Okhotsk earthquake had similar magnitude and fault geometry as the damaging 1994 Northridge earthquake in California, but a much larger depth and faster rupture speed. The high rupture speed (approximately 8 kilometers per second, or 18,000 miles per hour) away from the hypocenter, shown as the red star, concentrates strong shaking on the "Mach front." Credit: Image courtesy of University of California - San Diego

The supershear 2013 Sea of Okhotsk earthquake had similar magnitude and fault geometry as the damaging 1994 Northridge earthquake in California, but a much larger depth and faster rupture speed. The high rupture speed (approximately 8 kilometers per second, or 18,000 miles per hour) away from the hypocenter, shown as the red star, concentrates strong shaking on the “Mach front.”
Credit: Image courtesy of University of California – San Diego

Seismologists have documented a handful of these events, in which an earthquake’s rupture travels faster than the shear waves of seismic energy that it radiates. These “supershear” earthquakes have rupture speeds of four kilometers per second (an astonishing 9,000 miles per hour) or more.

In a National Science Foundation-funded study reported in the June 11, 2014, issue of the journal Science, Scripps geophysicists Zhongwen Zhan and Peter Shearer of Scripps, along with their colleagues at Caltech, discovered the first deep supershear earthquake while examining the aftershocks of a magnitude 8.3 earthquake on May 24, 2013, in the Sea of Okhotsk off the Russian mainland.

Details of a magnitude 6.7 aftershock of the event captured Zhan’s attention. Analyzing data from the IRIS (Incorporated Research Institutions for Seismology) consortium, which coordinates a global network of seismological instruments, Zhan noted that most seismometers around the world yielded similar records, all suggesting an anomalously short duration for a magnitude 6.7 earthquake.

Data from one seismometer, however, stationed closest to the event in Russia’s Kamchatka Peninsula, told a different story with intriguing details.

After closely analyzing the data, Zhan not only found that the aftershock ruptured extremely deeply at 640 kilometers (400 miles) below Earth’s surface, but its rupture velocity was extraordinary — about eight kilometers per second (five miles per second), nearly 50 percent faster than the shear wave velocity at that depth.

“For a 6.7 earthquake you would expect a duration of seven to eight seconds, but this one lasted just two seconds,” said Shearer, a geophysics professor in the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics (IGPP) at Scripps. “This is the first definitive example of supershear rupture for a deep earthquake since previously supershear ruptures have been documented only for shallow earthquakes.”

“This finding will help us understand why deep earthquakes happen,” said Zhan. “One quarter of earthquakes occur at large depths, and some of these can be pretty big, but we still don’t understand why they happen. So this earthquake provides a new observation for deep earthquakes and high-rupture speeds.”

Zhan also believes the new information will be useful in examining ultra-fast earthquakes and their potential for impacting fault zones near Earth’s surface. Although not of supershear caliber, California’s destructive 1994 Northridge earthquake had a comparable size and geometry to that of the 6.7 Sea of Okhotsk aftershock.

“If a shallow earthquake such as Northridge goes supershear, it could cause even more shaking and possibly more damage,” said Zhan.

Changyuraptor yangi sheds light on dinosaur flight

A new raptorial dinosaur fossil with exceptionally long feathers has provided exciting insights into dinosaur flight. A paper published in Nature Communications on July 15, 2014 asserts that the fossil — discovered by an international team led by Natural History Museum of Los Angeles County (NHM) paleontologist Dr. Luis Chiappe — has a long feathered tail that Chiappe and co-authors believe was instrumental for decreasing descent speed and assuring safe landings.

The 125-million-year-old dinosaur, named Changyuraptor yangi, was found in the Liaoning Province of northeastern China. The location has seen a surge of discoveries in feathered dinosaurs over the last decade. The newly discovered, remarkably preserved dinosaur sports a full set of feathers cloaking its entire body, including the extra-long tail feathers. “At a foot in length, the amazing tail feathers of Changyuraptor are by far the longest of any feathered dinosaur,” said Chiappe.

This is an illustration of newly discovered feathered dinosaur, Changyuraptor yangi. Credit: S. Abramowicz, Dinosaur Institute, NHM

This is an illustration of newly discovered feathered dinosaur, Changyuraptor yangi.
Credit: S. Abramowicz, Dinosaur Institute, NHM

Analyses of the bone microstructure by University of Cape Town (South Africa) scientist, Dr. Anusuya Chinsamy, shows that the raptor was a fully grown adult, and tipping the scale at nine pounds, the four-foot-long Changyuraptor is the biggest of all four-winged dinosaurs. These microraptorine dinosaurs are dubbed “four-winged” because the long feathers attached to the legs have the appearance of a second set of wings. In fact, the long feathers attached to both legs and arms of these ancient predators have led researchers to conclude that the four-winged dinosaurs were capable of flying. “Numerous features that we have long associated with birds in fact evolved in dinosaurs long before the first birds arrived on the scene,” said co-author Dr. Alan Turner of Stony Brook University (New York). “This includes things such as hollow bones, nesting behavior, feathers…and possibly flight.”

How well these creatures used the sky as a thoroughfare has remained controversial. The new discovery explains the role that the tail feathers played during flight control. For larger flyers, safe landings are of particular importance. “It makes sense that the largest microraptorines had especially large tail feathers — they would have needed the additional control,” added Dr. Michael Habib, a researcher at the University of Southern California and a co-author of the paper.

The discovery of Changyuraptor consolidates the notion that flight preceded the origin of birds, being inherited by the latter from their dinosaurian forerunners. “The new fossil documents that dinosaur flight was not limited to very small animals but to dinosaurs of more substantial size,” said Chiappe. “Clearly far more evidence is needed to understand the nuances of dinosaur flight, but Changyuraptor is a major leap in the right direction.”

Gomphothere mandible uncovered

An animal once believed to have disappeared from North America before humans ever arrived there might actually have roamed the continent longer than previously thought — and it was likely on the list of prey for some of continent’s earliest humans, researchers from the University of Arizona and elsewhere have found.

Archaeologists have discovered artifacts of the prehistoric Clovis culture mingled with the bones of two gomphotheres, ancient ancestors of the elephant, at an archaeological site in northwestern Mexico.

The discovery suggests that the Clovis — the earliest widespread group of hunter-gatherers to inhabit North America — likely hunted and ate gomphotheres. The members of the Clovis culture were already well-known as hunters of the gomphotheres’ cousins, mammoths and mastodons.

Although humans were known to have hunted gomphotheres in Central America and South America, this is the first time a human-gomphothere connection has been made in North America, says archaeologist Vance Holliday, who co-authored a new paper on the findings, published this week in Proceedings of the National Academy of Sciences.

Gomphothere mandible uncovered at El Fin del Mundo. Archaeologists working in northwestern Mexico were not sure what kind of animal they had unearthed until they found this telltale jawbone, which belonged to a gomphothere. Credit: Joaquin Arroyo-Cabrales

Gomphothere mandible uncovered at El Fin del Mundo. Archaeologists working in northwestern Mexico were not sure what kind of animal they had unearthed until they found this telltale jawbone, which belonged to a gomphothere.
Credit: Joaquin Arroyo-Cabrales

“This is the first archaeological gomphothere found in North America, and it’s the only one known,” said Holliday, a professor of anthropology and geology at the UA.

Holliday and colleagues from the U.S. and Mexico began excavating the skeletal remains of two juvenile gomphotheres in 2007 after ranchers alerted them that the bones had been found in northwestern Sonora, Mexico.

They didn’t know at first what kind of animal they were dealing with.

“At first, just based on the size of the bone, we thought maybe it was a bison, because the extinct bison were a little bigger than our modern bison,” Holliday said.

Then, in 2008, they discovered a jawbone with teeth, buried upside down in the dirt.

“We finally found the mandible, and that’s what told the tale,” Holliday said.

Gomphotheres were smaller than mammoths — about the same size as modern elephants. They once were widespread in North America, but until now they seemed to have disappeared from the continent’s fossil record long before humans arrived in North America, which happened some 13,000 to 13,500 years ago, during the late Ice Age.

However, the bones that Holliday and his colleagues uncovered date back 13,400 years, making them the last known gomphotheres in North America.

The gomphothere remains weren’t all Holliday and his colleagues unearthed at the site, which they dubbed El Fin del Mundo — Spanish for The End of the World — because of its remote location.

As their excavation of the bones progressed, they also uncovered numerous Clovis artifacts, including signature Clovis projectile points, or spear tips, as well as cutting tools and flint flakes from stone tool-making. The Clovis culture is so named for its distinctive stone tools, first discovered by archaeologists near Clovis, New Mexico, in the 1930s.

Radiocarbon dating, done at the UA, puts the El Fin del Mundo site at about 13,400 years old, making it one of the two oldest known Clovis sites in North America; the other is the Aubrey Clovis site in north Texas.

The position and proximity of Clovis weapon fragments relative to the gomphothere bones at the site suggest that humans did in fact kill the two animals there. Of the seven Clovis points found at the site, four were in place among the bones, including one with bone and teeth fragments above and below. The other three points had clearly eroded away from the bone bed and were found scattered nearby.

“This is the first Clovis gomphothere, it’s the first archaeological gomphothere found in North America, it’s the first evidence that people were hunting gomphotheres in North America, and it adds another item to the Clovis menu,” Holliday said.

The dig at El Fin del Mundo, a joint effort between the U.S. and Mexico, was funded by the UA School of Anthropology’s Argonaut Archaeological Research Fund, the National Geographic Society, the Instituto Nacional de Antropología e Historia and The Center for Desert Archaeology in Tucson.

In addition to Holliday, authors of the PNAS paper include: lead author Guadalupe Sanchez, who has a doctorate in anthropology from the UA; UA alumni Edmund P. Gaines and Susan M. Mentzer; UA doctoral candidates Natalia Martínez-Tagüeña and Andrew Kowler; UA master’s student Ismael Sanchez-Morales; UA scientists Todd Lange and Gregory Hodgins; and Joaquin Arroyo-Cabrales at the Instituto Nacional de Antropología e Historia.

First Record of Eocene Bony Fishes and Crocodyliforms from Canada’s Western Arctic

Discovery of Eocene non-marine vertebrates, including crocodylians, turtles, bony fishes, and mammals in Canada’s High Arctic was a critical paleontological contribution of the last century because it indicated that this region of the Arctic had been mild, temperate, and ice-free during the early – middle Eocene (~53–50 Ma), despite being well above the Arctic Circle. To date, these discoveries have been restricted to Canada’s easternmost Arctic – Ellesmere and Axel Heiberg Islands (Nunavut). Although temporally correlative strata crop out over 1,000 km west, on Canada’s westernmost Arctic Island – Banks Island, Northwest Territories – they have been interpreted as predominantly marine. We document the first Eocene bony fish and crocodyliform fossils from Banks Island.

Principal Findings

We describe fossils of bony fishes, including lepisosteid (Atractosteus), esocid (pike), and amiid, and a crocodyliform, from lower – middle Eocene strata of the Cyclic Member, Eureka Sound Formation within Aulavik National Park (~76°N. paleolat.). Palynology suggests the sediments are late early to middle Eocene in age, and likely spanned the Early Eocene Climatic Optimum (EECO).

Conclusions/Significance

These fossils extend the geographic range of Eocene Arctic lepisosteids, esocids, amiids, and crocodyliforms west by approximately 40° of longitude or ~1100 km. The low diversity bony fish fauna, at least at the family level, is essentially identical on Ellesmere and Banks Islands, suggesting a pan-High Arctic bony fish fauna of relatively basal groups around the margin of the Eocene Arctic Ocean. From a paleoclimatic perspective, presence of a crocodyliform, gar and amiid fishes on northern Banks provides further evidence that mild, year-round temperatures extended across the Canadian Arctic during early – middle Eocene time. Additionally, the Banks Island crocodyliform is consistent with the phylogenetic hypothesis of a Paleogene divergence time between the two extant alligatorid lineages Alligator mississippiensis and A. sinensis, and high-latitude dispersal across Beringia.

Citation: Eberle JJ, Gottfried MD, Hutchison JH, Brochu CA (2014) First Record of Eocene Bony Fishes and Crocodyliforms from Canada’s Western Arctic. PLoS ONE 9(5): e96079. doi:10.1371/journal.pone.0096079

Editor: Peter Dodson, University of Pennsylvania, United States of America

CMNFV 56059, vertebral centrum of an Eocene crocodyliform from CMN Loc. BKS04-19 on northern Banks Island, NWT.  (A) Left lateral view; (B) dorsal view; (C) ventral view. h, hypapophysis; ncs, neurocentral sutural surface; pc, posterior cotyle. Scale bar equals 5 mm. doi:10.1371/journal.pone.0096079.g003

CMNFV 56059, vertebral centrum of an Eocene crocodyliform from CMN Loc. BKS04-19 on northern Banks Island, NWT.
(A) Left lateral view; (B) dorsal view; (C) ventral view. h, hypapophysis; ncs, neurocentral sutural surface; pc, posterior cotyle. Scale bar equals 5 mm.
doi:10.1371/journal.pone.0096079.g003

 

Fossils of Eocene bony fishes from northern Banks Island, NWT.  CMNFV 56070, lateral line scale of Atractosteus from CMN Loc. BKS04-16, in medial (A) and lateral (B) views. (C) CMNFV 56069, vertebral centrum of ?Amiid. (D) CMNFV 56071, Esocid scale. C and D are from CMN Loc. BKS04-19.  doi:10.1371/journal.pone.0096079.g002

Fossils of Eocene bony fishes from northern Banks Island, NWT.
CMNFV 56070, lateral line scale of Atractosteus from CMN Loc. BKS04-16, in medial (A) and lateral (B) views. (C) CMNFV 56069, vertebral centrum of ?Amiid. (D) CMNFV 56071, Esocid scale. C and D are from CMN Loc. BKS04-19.
doi:10.1371/journal.pone.0096079.g002

Earthquakes: Friction and Fracture are interrelated

Overturning conventional wisdom stretching all the way to Leonardo da Vinci, new Hebrew University of Jerusalem research shows that how things break (fracture) and how things slide (friction) are closely interrelated. The breakthrough study marks an important advance in understanding friction and fracture, with implications for describing the mechanics that drive earthquakes.

Over 500 years ago, da Vinci described how rough blocks slide over one another, providing the basis for our understanding of friction to this day. The phenomenon of fracture was always considered to be something totally different.

But new research by Prof. Jay Fineberg and his graduate student Ilya Svetlizky, at the Hebrew University’s Racah Institute of Physics, has demonstrated that these two seemingly disparate processes of fracture and friction are actually intimately intertwined.

Appearing in the journal Nature, their findings create a new paradigm that’s very different from the da Vinci version, and, according to the researchers, give us a new understanding of how earthquakes actually occur.

Fineberg and Svetlizky produced “laboratory earthquakes” showing that the friction caused by the sliding of two contacting blocks can only occur when the connections between the surfaces are first ruptured (that is, fractured or broken) in an orderly, “organized” process that takes place at nearly the speed of sound.

How does this happen? Before any motion can occur, the blocks are connected by interlocking rough contacts that define their interface. In order for motion to occur, these connections have to be broken. This physical process of breaking is called a fracture process. This process is described by the theory of crack propagation, say the researchers, meaning that the stresses (or forces) that exist at the front edge of a crack become highly magnified, even if the overall forces being applied are initially quite small.

“The insights gained from our study provide a new paradigm for understanding friction and give us a new, fundamental description of the mechanics and behavior that drive earthquakes, the sliding of two tectonic blocks within natural faults,” says Fineberg. “In this way, we can now understand important processes that are generally hidden kilometers beneath the Earth’s surface.”

The research was supported by the James S. McDonnell Fund, the European Research Council (grant no. 267256) and the Israel Science Foundation (grant 76/11).