Author Archives: jeronen

DNA reveals Neanderthal extinction clues

Interesting! Shows that we don’t not nearly enough about this stuff yet…

Neanderthals were already on the verge of extinction in Europe by the time modern humans arrived on the scene, a study suggests.

the actual paper:

doi: 10.1093/molbev/mss074

Robust estimates of extinction time in the geological record

The rate at which a once-abundant population declines in density prior to local or global extinction can strongly influence the precision of statistical estimates of extinction time. Here we report the development of a new, robust method of inference which accounts for these potential biases and uncertainties, and test it against known simulated data and dated Pleistocene fossil remains (mammoths, horses and Neanderthals). Our method is a Gaussian-resampled, inverse-weighted McInerny et al. (GRIWM) approach which weights observations inversely according to their temporal distance from the last observation of a species’ confirmed occurrence, and for dates with associated radiometric errors, is able to sample individual dates from an underlying fossilization probability distribution. We show that this leads to less biased estimates of the ‘true’ extinction date. In general, our method provides a flexible tool for hypothesis testing, including inferring the probability that the extinctions of pairs or groups of species overlap, and for more robustly evaluating the relative likelihood of different extinction drivers such as climate perturbation and human exploitation.

Determining the natural length of the current interglacial

No glacial inception is projected to occur at the current atmospheric COconcentrations of 390 ppmv (ref. 1). Indeed, model experiments suggest that in the current orbital configuration—which is characterized by a weak minimum in summer insolation—glacial inception would require CO2 concentrations below preindustrial levels of 280 ppmv (refs 234). However, the precise CO2threshold456 as well as the timing of the hypothetical next glaciation7 remain unclear. Past interglacials can be used to draw analogies with the present, provided their duration is known. Here we propose that the minimum age of a glacial inception is constrained by the onset of bipolar-seesaw climate variability, which requires ice-sheets large enough to produce iceberg discharges that disrupt the ocean circulation. We identify the bipolar seesaw in ice-core and North Atlantic marine records by the appearance of a distinct phasing of interhemispheric climate and hydrographic changes and ice-rafted debris. The glacial inception during Marine Isotope sub-Stage 19c, a close analogue for the present interglacial, occurred near the summer insolation minimum, suggesting that the interglacial was not prolonged by subdued radiative forcing7. Assuming that ice growth mainly responds to insolation and CO2 forcing, this analogy suggests that the end of the current interglacial would occur within the next 1500 years, if atmospheric CO2 concentrations did not exceed 240±5 ppmv.

Camels in Beringia!

Last interglacial western camel (Camelops hesternus) from eastern Beringia
Grant D. Zazula, Derek G. Turner, Brent C. Ward, Jeffrey Bond

Quaternary Science Reviews
Volume 30, Issues 19-20, September 2011, Pages 2355-2360


Western camel (C. hesternus) fossils are rare from Eastern Beringia, thus there is little available information on their chronology, paleoecology, and biogeography in this region. In August of 2010, a partial proximal phalanx of a western camel was recovered from a sedimentary exposure along the White River, in the formerly glaciated terrain of southwest Yukon, northwest Canada. The fossil specimen was recovered in situ from sediments that are correlated by stratigraphic, tephra and radiocarbon data to the Marine Isotope Stage (MIS) 5 interglacial period (Sangamonian). Associated paleoenvironmental data indicates that this western camel inhabited a shrub tundra ecosystem that did not include spruce trees or boreal forest during a relatively cold interval between MIS 5e and 5a. This is the oldest reliably dated western camel fossil from Eastern Beringia and supports the model of range expansion for this species to the high latitudes of northwest North America during the last interglacial (sensu lato).

Eat Nuts.. or.. Grass? Huh?

Thure E. Cerling, Emma Mbua, Francis M. Kirera, Fredrick Kyalo Manthi, Frederick E. Grine, Meave G. Leakey, Matt Sponheimer, and Kevin T. Uno

Diet of Paranthropus boisei in the early Pleistocene of East Africa
PNAS 2011 ; published ahead of print May 2, 2011, doi:10.1073/pnas.1104627108


The East African hominin Paranthropus boisei was characterized by
a suite of craniodental features that have been widely interpreted
as adaptations to a diet that consisted of hard objects that required
powerful peak masticatory loads. These morphological adaptations
represent the culmination of an evolutionary trend that
began in earlier taxa such as Australopithecus afarensis, and presumably
facilitated utilization of open habitats in the Plio-Pleistocene.
Here, we use stable isotopes to show that P. boisei had a diet
that was dominated by C4 biomass such as grasses or sedges. Its
diet included more C4 biomass than any other hominin studied
to date, including its congener Paranthropus robustus from South
Africa. These results, coupled with recent evidence from dental
microwear, may indicate that the remarkable craniodental morphology
of this taxon represents an adaptation for processing
large quantities of low-quality vegetation rather than hard objects.

Longer in the tooth, shorter in the record?

Longer in the tooth, shorter in the record? The evolutionary correlates of hypsodonty in Neogene ruminants
P. Raia, F. Carotenuto, J. T. Eronen and M. Fortelius
Proceedings of the Royal Society B
doi: 10.1098/rspb.2011.0273
The acquisition of hypsodont molars is often regarded as a key innovation in the history of ruminant ungulates. Hypsodont ruminants diversified rapidly during the later Neogene, circa 15–2 Myr ago, and came to dominate the ruminant fossil record in terms of species diversity. Here we show that hypsodont clades had higher speciation and diversification rates than other clades. Hypsodont species had, on average, shorter stratigraphic durations, smaller range size and lower occupancy than non-hypsodont species. Within hypsodont clades, some species were very common and acquired large geographical ranges, whereas others were quite rare and geographically limited. We argue that hypsodont clades diversified in an adaptive radiation-like fashion, with species often splitting cladogenetically while still in the expansive phase of their occupancy history.

Updated chronology for the Miocene hominoid radiation in Western Eurasia

Isaac Casanovas-Vilar, David M. Alba, Miguel Garcés, Josep M. Robles, and Salvador Moyà-Solà
Published online before print March 21, 2011,
doi: 10.1073/pnas.1018562108

Extant apes (Primates: Hominoidea) are the relics of a group that was much more diverse in the past. They originated in Africa around the Oligocene/Miocene boundary, but by the beginning of the Middle Miocene they expanded their range into Eurasia, where they experienced a far-reaching evolutionary radiation. A Eurasian origin of the great ape and human clade (Hominidae) has been favored by several authors, but the assessment of this hypothesis has been hampered by the lack of accurate datings for many Western Eurasian hominoids. Here we provide an updated chronology that incorporates recently discovered Iberian taxa and further reevaluates the age of many previously known sites on the basis of local biostratigraphic scales and magnetostratigraphic data. Our results show that identifiable Eurasian kenyapithecins (Griphopithecus and Kenyapithecus) are much younger than previously thought (ca. 14 Ma instead of 16 Ma), which casts serious doubts on the attribution of the hominoid tooth from Engelswies (16.3–16.5 Ma) to cf. Griphopithecus. This evidence is further consistent with an alternative scenario, according to which the Eurasian pongines and African hominines might have independently evolved in their respective continents from similar kenyapithecin ancestors, resulting from an early Middle Miocene intercontinental range extension followed by vicariance. This hypothesis, which would imply an independent origin of orthogrady in pongines and hominines, deserves further testing by accurately inferring the phylogenetic position of European dryopithecins, which might be stem pongines rather than stem hominines.

Resources driving landscape-scale distribution patterns of grazers in an African savanna

Ecography 34: 6774, 2011
doi: 10.1111/j.1600-0587.2010.06029.x

Resources driving landscape-scale distribution patterns of grazers in
an African savanna

Izak P. J. Smit

In order to effectively manage and conserve indigenous herbivores, a good understanding is needed of how resources drive their distribution patterns. This study employed a unique dataset to test a range of ecological theories and hypotheses on free-ranging grazers. Using aerial census data collected over 14 yr across the 2 million ha Kruger National Park (South Africa), this study employs spatial autologistic regression models to explore the spatial relationships that exist between the distribution of eight indigenous grazer species and a set of resource variables. It was found that ecological theories relating to feeding guild, water-dependence, allometric scaling, gut-morphology and vulnerability to predation could explain most of the grazer distribution patterns observed in relation to surface-water, forage quality, forage quantity and habitat openness. All the grazers studied were water-dependent and occurred close to a permanent source of water in the dry season. This was ascribed to the lack of moisture in the diet of grazers during the dry season. Most ruminants’ distribution patterns were significantly associated with areas of high forage quality whereas hind-gut fermentors were neutral towards forage quality. Average forage quantity was not a significant predictor of long-term, landscape-scale distribution patterns for any of the grazer species studied. Most small- and medium-bodied grazers preferred open habitats above closed habitats, probably due to higher visibility and a lower predation risk. Large-bodied grazers did not bias their distribution patterns towards open habitats. The way in which grazers distribute themselves with respect to different resources can potentially inform management actions on appropriate scales.