Fifty-six million years ago, just before earth's carbon dioxide levels and average temperatures soared, many species of primitive primates went extinct in North America for reasons unclear to scientists. Now, a study of fossilized molars appears to exonerate one potential culprit in the animals' demise: competition with primitive rodents for food.
In a study described in an advance online article in the American Journal of Physical Anthropology and conducted primarily by Kristen Prufrock, now a graduate student at the Johns Hopkins University School of Medicine, a team of paleontologists examined dental clues to the diets of so-called stem primates and rodents who plied North America at the end of the Paleocene epoch.
Other paleontologists had suggested many of the stem primates—which superficially resembled rodents but had some primate characteristics, such as long, grasping fingers—died off because rodents outcompeted them for their preferred foods. But when Prufrock, then studying at the University of Toronto Scarborough, and her colleagues took CT scans of 13 rodent and 181 stem primate jaws held in multiple museums, the shapes of their molars revealed that most of the primates ate different types of food than the rodents. The results, says Prufrock, call into doubt the idea that food competition with rodents killed off the primates.
Most of the jaw specimens were collected in Wyoming and Montana and were scanned with a micro CT scanner. Second mandibular molars used for grinding food were isolated using imaging software.
"We found that one genus of stem primates, Chiromyoides, lived at about the same time and had adapted to eat the same foods as primitive rodents, but the others either were adapted to eating different foods or lived at different times," Prufrock says. "So competition from rodents was unlikely to have been the main reason for the decline of most of the stem primates. Something else must have been the driving force."
The head of Air Force acquisition, just back from the Dubai Air Show, said the United States must act fast to make it easier and quicker for allies to buy US weapons through the Foreign Military Sales (FMS) system.
If we don’t, Bill LaPLante said at an event put by on the Lexington Institute, a Washington thinktank, then we have to accept that our allies will buy Chinese weapons, even if they are copies of US gear and don’t work nearly as well as US weapons.
“US stuff is in incredibly high demand. Overseas people are desperate, they are desperate for our stuff,” Bill LaPLante told an event put on the Lexington Institute, a Washington thinktank. “We need to do something about it. It’s urgent.”
LaPlante made his case bluntly and with force: “Guess who’s over there selling stuff? I don’t know. China???” Their reconnaissance drone looked just like the Reaper. Their new fighter looks just like the F-35. Are they are as good, he asked rhetorically? Probably not. But LaPlante pointed to the intricate US system of approving Foreign Military Sales. It requires inputs and reviews by the State, Defense and Commerce departments. It requires congressional notification and review. It takes time, often years.
The European saber-toothed cat (Homotherium latidens) found in the “Spear Horizon” at Schöningen (Germany)
Authors:
Serangeli et al
Abstract:
The 300,000 year old Lower Paleolithic site Schöningen 13 II-4 became world famous with the discovery of the oldest well-preserved and complete wooden spears. Through ongoing excavations, new archaeological discoveries of scientific importance are still being made from the same archaeological layer where the spears were found. In this context, remains of a rare carnivore species, the European saber-toothed cat (Homotherium latidens), were recovered. Here we present five teeth and one humerus fragment that are unambiguously from two individual saber-toothed cats. The humerus is a unique specimen; it shows evidence of hominin impacts and use as a percussor.
The Homotherium remains from Schöningen are the best documented finds of this species in an archaeological setting and they are amongst the youngest specimens of Homotherium in Europe. The presence of this species as a carnivore competitor would certainly have impacted the lives of late Middle Pleistocene hominins. The discovery illustrates the possible day-to-day challenges that the Schöningen hominins would have faced and suggests that the wooden spears were not necessarily only used for hunting, but possibly also as a weapon for self-defense.
Biotic replacement and mass extinction of the Ediacara biota
Authors:
Darroch et al
Abstract:
The latest Neoproterozoic extinction of the Ediacara biota has been variously attributed to catastrophic removal by perturbations to global geochemical cycles, ‘biotic replacement’ by Cambrian-type ecosystem engineers, and a taphonomic artefact. We perform the first critical test of the ‘biotic replacement’ hypothesis using combined palaeoecological and geochemical data collected from the youngest Ediacaran strata in southern Namibia. We find that, even after accounting for a variety of potential sampling and taphonomic biases, the Ediacaran assemblage preserved at Farm Swartpunt has significantly lower genus richness than older assemblages. Geochemical and sedimentological analyses confirm an oxygenated and non-restricted palaeoenvironment for fossil-bearing sediments, thus suggesting that oxygen stress and/or hypersalinity are unlikely to be responsible for the low diversity of communities preserved at Swartpunt. These combined analyses suggest depauperate communities characterized the latest Ediacaran and provide the first quantitative support for the biotic replacement model for the end of the Ediacara biota. Although more sites (especially those recording different palaeoenvironments) are undoubtedly needed, this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.
PR pop sci version.
The role of clade competition in the diversification of North American canids
Authors:
Silvestro et al
Abstract:
The history of biodiversity is characterized by a continual replacement of branches in the tree of life. The rise and demise of these branches (clades) are ultimately determined by changes in speciation and extinction rates, often interpreted as a response to varying abiotic and biotic factors. However, understanding the relative importance of these factors remains a major challenge in evolutionary biology. Here we analyze the rich North American fossil record of the dog family Canidae and of other carnivores to tease apart the roles of competition, body size evolution, and climate change on the sequential replacement of three canid subfamilies (two of which have gone extinct). We develop a novel Bayesian analytic framework to show that competition from multiple carnivore clades successively drove the demise and replacement of the two extinct canid subfamilies by increasing their extinction rates and suppressing their speciation. Competitive effects have likely come from ecologically similar species from both canid and felid clades. These results imply that competition among entire clades, generally considered a rare process, can play a more substantial role than climate change and body size evolution in determining the sequential rise and decline of clades.
Closely related groups can differ dramatically in their diversity, but why this happens is a fundamental question in evolutionary biology, dating back to Darwin's observation that a few hyper-diverse groups dominate the modern biota. One of the most extreme examples of this observation is found in the comparison of rodents (Rodentia) and rabbits (Lagomorpha). These two mammalian orders are sister groups, but while rodents have diversified to over 2000 living species and an enormous range of body sizes, lagomorphs (rabbits, hares, and pikas) are limited to fewer than 100 relatively small species. A new study presented at the Society of Vertebrate Paleontology Annual Meeting shows, surprisingly, that competition with ungulates (hoofed mammals), intensified by climate change, are to blame for the lagomorphs' limited diversity.
Susumu Tomiya of the Field Museum of Natural History and Lauren Miller of the University of California at Berkeley were intrigued by the observation that lagomorphs have spread to all continents except Antarctica and inhabit a variety of environments, but the group contains only about 80 living species of small herbivores, compared to roughly 2,000 species of rodents. According to Dr. Tomiya, "Mammalian groups that are ubiquitous at the global scale--rodents and bats, for example--tend to be species-rich and show many different ways of living. Lagomorphs are a paradox in this sense." Lagomorphs also show a much more limited range of body size and forms relative to rodents: the average weight of the largest living species (Alaskan hare) is approximately 5 kg (11 lb), whereas the largest living rodent (capybara) is twelve times larger at about 60 kg (133 lb). Given that the two groups are each other's closest evolutionary relatives, and they have been evolving for roughly the same amount of time (~55 million years, give or take a few million years), the difference in their diversity is striking.
Importantly, fossils from Mediterranean islands show that lagomorphs are capable of becoming much larger than seen today. Nuralagus rex from the Pliocene of Minorca is estimated to have weighed about 12 kg. Ecologists and evolutionary biologists have suggested that such gigantism can take place only in absence of competitors, as is sometimes the case with island faunas. They reasoned that, if competition were an important factor in determining body size evolution, the conspicuous absence of giant lagomorphs (by today's standards) on continents could be explained by long-standing presence of potential competitors, such as ungulates (e.g., horses, deer, cows, pigs, and their extinct relatives).
Tomiya and Miller tested this hypothesis by examining the rich North American fossil record. They compared the trajectories of maximum lagomorph body size and minimum ungulate body size over the last 30 million years, revealing two phases of body size evolution in lagomorphs. In the late Oligocene, the largest lagomorphs (comparable in body mass to medium-sized hares living today) coexisted with similar-sized and even smaller ungulates (some of which were as small as modern-day cottontails). This body-size relationship was fundamentally altered following a major climatic transition that prompted opening-up of forests and establishment of grasslands in the early Miocene. For the next 20 million years or so, the maximum lagomorph size shifted in parallel with the minimum ungulate size, suggesting a dynamic body-size boundary between the two groups maintained by competitive interactions.
This study suggests that competitive interactions (and resulting division of resources that minimizes such interactions) may be a key factor determining diversification of mammals over millions of years.
Patterns of Evolution of the Ediacaran Soft-Bodied Biota
Author:
Grazhdankin
Abstract:
When each of the Avalon-, Ediacara-, and Nama-type fossil assemblages are tracked through geological time, there appear to be changes in species composition and diversity, almost synchronized between different sedimentary environments, allowing a subdivision of the late Ediacaran into the Redkinian, Belomorian and Kotlinian geological time intervals. The Redkinian (580–559 Ma) is characterized by first appearance of both eumetazoan traces and macroscopic organisms (frondomorphs and vendobionts) in a form of Avalon-type communities in the inner shelf environment, whereas coeval Ediacara-type communities remained depauperate. The Belomorian (559–550 Ma) is marked by the advent of eumetazoan burrowing activity in the inner shelf, diversification of frondomorphs, migration of vendobionts from the inner shelf into higher energy environments, and appearance of tribrachiomorphs and bilateralomorphs. Ediacaran organisms formed distinctive ecological associations that coexisted in the low-energy inner shelf (Avalon-type communities), in the wave- and current-agitated shoreface (Ediacara-type communities), and in the high-energy distributary systems (Nama-type communities). The Kotlinian (550–540 Ma) witnessed an expansion of the burrowing activity into wave- and current-agitated shoreface, disappearance of vendobionts, tribrachiomorphs and bilateralomorphs in wave- and current-agitated shoreface, together with a drop in frondomorph diversity. High-energy distributary channel systems of prodeltas served as refugia for Nama-type communities that survived until the end of the Ediacaran and disappeared when the burrowing activity reached high-energy environments. This pattern is interpreted as an expression of ecosystem engineering by eumetazoans, with the Ediacaran organisms being progressively outcompeted by bilaterians.
Competition and constraint drove Cope's rule in the evolution of giant flying reptiles
Authors:
Benson et al
Abstract:
The pterosaurs, Mesozoic flying reptiles, attained wingspans of more than 10 m that greatly exceed the largest birds and challenge our understanding of size limits in flying animals. Pterosaurs have been used to illustrate Cope’s rule, the influential generalization that evolutionary lineages trend to increasingly large body sizes. However, unambiguous examples of Cope’s rule operating on extended timescales in large clades remain elusive, and the phylogenetic pattern and possible drivers of pterosaur gigantism are uncertain. Here we show 70 million years of highly constrained early evolution, followed by almost 80 million years of sustained, multi-lineage body size increases in pterosaurs. These results are supported by maximum-likelihood modelling of a comprehensive new pterosaur data set. The transition between these macroevolutionary regimes is coincident with the Early Cretaceous adaptive radiation of birds, supporting controversial hypotheses of bird–pterosaur competition, and suggesting that evolutionary competition can act as a macroevolutionary driver on extended geological timescales.
