North and South American Pleistocene Quaternary Bears Evolved Giantism Independently

The work of University of Adelaide researchers is shedding new light on the evolution of what are believed to be the largest bears that ever walked the Earth.

Dr Kieren Mitchell, from the University's Australian Centre for Ancient DNA, School of Biological Sciences, has a new paper just published in Biology Letters.

He writes: "During the Pleistocene (2.5 million years ago - 11 thousand years ago) giant bears weighing over 1,000kg roamed both North and South America. These giants belonged to a now practically extinct subfamily of bears - Tremarctinae - which is today only represented by the small, herbivorous Andean spectacled bear (Tremarctos ornatus).

"The giant North American bears (Arctodus) and South American bears (Arctotherium) have long been believed to be each others' closest relative. However, by comparing ancient DNA data obtained from representatives of the two extinct genera and comparing them with the living species, we were able to show that Arctotherium is most closely related to Tremarctos and not Arctodus.

"The implication of this result is that these bears represent a remarkable instance of convergent evolution, as giant bears appear to have evolved independently in both North and South America.

link.

Kolponomos: The Miocene Neogene "Otter Bear" had a Smilodon-like Bite

New research suggests that the feeding strategy of Kolponomos, an enigmatic shell-crushing marine predator that lived about 20 million years ago, was strangely similar to a very different kind of carnivore: the saber-toothed cat Smilodon. Scientists at the American Museum of Natural History used high-resolution x-ray imaging and computerized biting simulations to show that even though the two extinct predators likely contrasted greatly in food preference and environment, they shared similar engineering in jaw structure, suitable for anchoring against prey with the lower jaw and forcefully throwing the skull forward to pry loose its food. The study is published today in the journal Proceedings of the Royal Society B.

The only known specimens of Kolponomos--primarily skulls and teeth of two species--were recovered from ancient marine deposits along the Pacific coast of Oregon, Washington, and possibly Alaska. Because of its peculiar morphology and the small number of fossils, the animal's place in the evolutionary tree remains a mystery.

"When Kolponomos was first described in the 1960s, it was thought to be a raccoon relative," said Camille Grohé, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History's Division of Paleontology and a co-author on the new paper. "But later research on the skull base led some to think it might be a seal or a bear relative instead, and studies of its teeth show that they are very similar in both shape and wear to the teeth in sea otters."

Sea otters pry their prey--hard-shelled marine invertebrates like clams and mussels--off of surfaces using their hands and rock tools, then crush the shells with their teeth or against their chests, again using tools. By studying Kolponomos fossil material from the National Museum of Natural History in Washington, D.C., and comparative specimens from the American Museum of Natural History, the research team originally set out to test if the extinct predator used otter-like shell-crushing to eat. But the scope of the research expanded after Grohé's collaborator Z. Jack Tseng noticed something curious in parallel to work he was conducting on the saber-toothed cat Smilodon.

"I started seeing a great deal of similarity between the jaws of Kolponomos and Smilodon," said Tseng, a National Science Foundation and Frick Postdoctoral Fellow in the American Museum of Natural History's Division of Paleontology and the lead author on the new paper. "Both of them have a distinctive profile with a deep jaw bone that tapers off toward the back, and both have an expansion of the mastoid processes and the skull's back surface, suggesting large attachment sites for muscles that let the animal move its head powerfully but with control. We definitely didn't expect to bring Smilodon into this study of feeding in a clam-eating marine carnivore, but that's what we ended up doing."

link.

South American Giant Short-faced Bear's Diet Evolved Through the Pleistocene Quaternary

South American giant short-faced bear (Arctotherium angustidens) diet: evidence from pathology, morphology, stable isotopes, and biomechanics.

Authors:

Soibelzon et al

Abstract:

Arctotherium angustidens Gervais and Ameghino, 1880 (the South American giant short-faced bear) is known for being the earliest (Ensenadan Age, early to middle Pleistocene) and largest (body mass over 1 ton) of five described Arctotherium species endemic to South America. Here we assess the diet of this bear from multiple proxies: morphology, biomechanics, dental pathology, stable isotopes and a previous study using geometric morphometric methodology. Results favor the idea of animal matter consumption, probably from large vertebrates in addition to vegetable matter consumption. Most probably, active hunting was not the unique strategy of this bear for feeding, since its large size and great power may have allowed him to fight for the prey hunted by other Pleistocene carnivores. However, scavenging over mega mammal carcasses was probably another frequent way of feeding. South American short-faced bears adjusted their size and modified their diet through Pleistocene times, probably as a response to the diversification of the carnivore guild (from the few precursory taxa that crossed the Panamanian Isthmus during the Great American Biotic Interchange).

The Social and Sex Lives Of Extinct Miocene Neogene Bear Relative Indarctos arctoides

On the Socio-Sexual Behaviour of the Extinct Ursid Indarctos arctoides: An Approach Based on Its Baculum Size and Morphology

Authors:

1. Juan Abella (a,b)
2. Alberto Valenciano (c,d)
3. Alejandro Pérez-Ramos (d,e)
4. Plinio Montoya (f)
5. Jorge Morales (b)

Affiliations:

a. Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona. Edifici ICP, Campus de la UAB s/n, Barcelona, Spain

b. Museo Nacional de Ciencias Naturales-CSIC, Madrid, Spain

c. Departamento de Geología Sedimentaria y Cambio Medioambiental. Instituto de Geociencias (CSIC, UCM), Madrid, Spain

d. Departamento de Paleontología, Facultad de Ciencias Geológicas UCM, Madrid, Spain

e. Institut Cavanilles de Biodiversitat i Biologia Evolutiva, Universitat de València, Paterna, Spain

f. Departament de Geologia, Àrea de Paleontologia, Universitat de València, Burjassot, Spain

Abstract:

The fossil bacula, or os penis, constitutes a rare subject of study due to its scarcity in the fossil record. In the present paper we describe five bacula attributed to the bear Indarctos arctoides Depéret, 1895 from the Batallones-3 site (Madrid Basin, Spain). Both the length and morphology of this fossil bacula enabled us to make interpretative approaches to a series of ecological and ethological characters of this bear. Thus, we suggest that I. arctoides could have had prolonged periods of intromission and/or maintenance of intromission during the post-ejaculatory intervals, a multi-male mating system and large home range sizes and/or lower population density. Its size might also have helped females to choose from among the available males.

Query: Was the Cave Bear's Genome Mapped?

Polar Bears Speciated From Brown Bears 150kya?

A rare, ancient polar bear fossil discovered in Norway in 2004 is yielding a treasure trove of essential information about the age and evolutionary origins of the species whose future is now seen as synonymous with the devastation wrought by climate change.

A paper published in the current issue of the Proceedings of the National Academy of Sciences U.S.A. by researchers at the University at Buffalo, Penn State University, the University of Oslo and other institutions is filling in key pieces of the evolutionary history of polar bears and brown bears, including their response to past climate changes.

"Our results confirm that the polar bear is an evolutionarily young species that split off from brown bears some 150,000 years ago and evolved extremely rapidly during the late Pleistocene, perhaps adapting to the opening of new habitats and food sources in response to climate changes just before the last interglacial period," says Charlotte Lindqvist, PhD, research assistant professor in the UB Department of Biological Sciences and lead author on the paper with Stephan C. Schuster at Penn State's Center for Comparative Genomics and Bioinformatics.

"Very few polar bear fossils have been found, leading to widely varying estimates of exactly when and how polar bears evolved," explains Øystein Wiig, polar bear expert and co-author at the University of Oslo's Natural History Museum. "Because polar bears live on the ice, their dead remains fall to the bottom of the ocean or get scavenged. They don't get deposited in the sediments like other mammals."

But in 2004, an Icelandic geologist found a rare, well-preserved, 110,000- to 130,000-year-old jawbone and canine tooth fossil in the Svalbard archipelago of Norway. This specimen was subsequently sent to Wiig for analysis.

UB's Lindqvist, who was working at Oslo's Natural History Museum as a postdoctoral researcher, extracted DNA from the sample after drilling into the bone and tooth to obtain the powder to analyze.

When she arrived at UB in 2008, she obtained tissue samples from modern polar bears and brown bears and began analyzing them at UB's New York State Center of Excellence in Bioinformatics and Life Sciences after starting the collaboration with Schuster at Penn State.

This work resulted in the sequencing of the complete mitochondrial genome of the fossil; they then used that information to develop mitochondrial sequencing of the other bears and to construct phylogenies showing that the ancient polar bear evolved within the lineage of brown bears.

"Since the brown bears from Alaska's Admiralty, Baranof and Chichagof Islands are the polar bears' closest relatives, it was crucial to include them in our study in order to more precisely date when polar bears appeared as a distinct species," Lindqvist explains. "The fact that our ancient polar bear lies almost directly at the splitting point between this unique group of brown bears and polar bears, that is, close to their most recent common ancestor of the two species, was very intriguing. It provided an ideal opportunity to ultimately settle the time of polar bear origin."

fascinating. No time to comment though.

Miocene Marine Ursoid? Huh?

First sloths. Now bears?! Doesn't Mother Nature have any sort of sense of decency?! She corrupts all these nice, beautiful, innocent terrestrials through evolution into filthy, marine critters.

Bad Mama Nature! Bad! No cookie!

Go read about this in a brief post on Dots in Deep Time written by our Suomic addition to the paleo blogosphere, Ville Sinkkonen (welcome!).