Archive for ‘fossil’

November 17, 2009

Cold-blooded Goats?

The fossil remains of a prehistoric goat-like artiodactyl that once lived on Mediteranean islands over 1.5 million years ago provides evidence of how some large mammals may have survived in resource-poor ecosystems. Myotragus, a Plio-Pleistocene bovid from the Balearic Islands off the eastern coast of Spain have a particular bone structure that is shared with cold-blooded reptiles. Not cold blooded, but having a variable growth rate according to changing environmental conditions:

The Press Release from Institut Català de Paleontologia:

Mammal or reptile? Researchers from the ICP discovered that the bovidae Myotragus balearicus‘ metabolism was more similar to a reptile metabolism than a mammal one.

Researchers Meike Köhler and Salvador Moyà, from the Institut Català de Paleontologia (ICP-UAB) have released the results of a highly innovative research in the field of paleontology. Using paleohistological techniques, they were able to infer the physiology of extinct species. The study, based on the goat-like bovidae Myotragus from the Balearic Islands, has been published in the prestigious scientific journal Proceedings of the National Academy of Science USA (PNAS).

The Myotragus balearicus, is an extinct mammal, similar to a goat, that belongs to the family Bovidae. All the Myotragus fossil data has been found in Mallorca, Menorca, Cabrera and Dragonera. The first Myotragus balearicus was discovered in the beginning of S. XX.(sic) and since those early days, it has been center of many paleontological studies. All thanks to its remarkable characteristics, fruit of an evolution in terms of insularity.

The islands and their fossil legacy are authentic laboratories of evolution for paleontologists. In fact, we can say that they are experiments in evolution, due to the islands have many environmental factors determined: small geographic area, limited resources, and trophic (ecosystem) limited by the absence of large mammals predators. The fossil islands also give us a proper time perspective to study the evolution, thanks to the scale of geological time. A variable that the study of the actual islands can not provide us, today.

Myotragus lived more than 5 million years in an island. A very long time for a species survival, especially in an area as small as an island, which means limited resources and fluctuating. Therefore, researchers were asked how this species had been able to survive more than double the time than their mainland relatives.

The results of histological thin section of a large sample of Myotragus’ bones, with which we study the bone tissue and its growth pattern, show that Myotragus were closer to a physiological crocodile (reptile) that to a mammal. The histology showed that Myotragus’ bone grew unlike any other mammal, at a slow pace and flexible, stopping periodically growing, reaching maturity at very advanced ages which meant a significant increase in longevity; similar to existing crocodiles. The explanation of why this happened is simple. Mammals are endotherms (warm-blooded) and, unlike cold-blooded (cold blood) spend a lot of energy to maintain body temperature constant. When resources are scarce, some individuals chose burning less energy, ie, individuals with a lower metabolism. This implies, however, grewing at a much slower pace, reaching maturity later and living longer.

The results of the study published in the article “Physiological and life history strategies of large mammal fossils in a resource-limited environment” in the renowned scientific journal Proceedings of the National Academy of Science (PNAS) suggest that although Myotragus were an endothermic mammal, they could experience lethargic seasons when weather conditions brought a lack of resources and made life difficult for them. The abundance of Myotragus’ fossil found in caves suggests the possibility of these mammals using the caves to pass the difficult seasons, lowering metabolism and reducing vital functions.

Currently, some deer or goat-like bovidae can leave the expensive maintenance of a constant body temperature (endothermy) in a very critical period, generating a temporary fluctuation of body temperature (heterotèrmia). However, the only large mammal that hibernates is the bear. Bears are dangerous animals that suffer little or no predation. In addition, during their hibernation, they can wake up at any time and their temperature never falls below 20 º C. Bears and Myotragus balearicus shared the absence of threats from predators, because Myotragus lived in an island. This enabled them, not only to reduce their metabolism in difficult moments, but also to get to stop their growth, delayed age reproduction, extend their longevity (life years) or cease feeding at critical moments.

Today, scientific experiments are conducted to study the rhythms of life and longevity. Researchers study the reactions of invertebrates and small mammals (mice) under conditions of stress and lack of resources. Observations conducted with by this type of research point to the increased longevity or duration of the life of these animals. The results presented by the ICP provide an example which supports this hypothesis and explain the evolutionary reasons for this increase in longevity. Reducing the pace of life and increased longevity are favored under conditions of stress and lack of resources. Thus, research in paleontology supports research in other fields such as medicine. Thanks to this inter-disciplinary, the study of a goat-like bovidae that evolved into a natural laboratory conditions (islands) could reveal the mechanisms that influence the physiology of humans and causes of longevity.

This scientific study is free online:
Physiological and life history strategies of large mammal fossils in a resource-limited environment. Meike Köhler and Salvador Moyà-Solà. Proceedings of the National Academy of Science (PNAS)

October 15, 2009

Darwinopterus – a (Little) Link Fest

Another distinct transitional fossil making is in the news – Darwinopterus modularis, a small flying reptile that has features from both the basal long-tailed pterosaurs (the ‘rhamphorhynchoids’) and the short tailed pterodactyloids that show up later in the fossil record.

Below are some of the blog responses to the new discovery announced at Proceedings of the Royal Society B on the 14 October:

The complete paper is avalable free online:

Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull
Junchang Lü1, David M. Unwin, Xingsheng Jin, Yongqing Liu1 and Qiang Ji1

The Abstract:

The fossil record is a unique source of evidence for important evolutionary phenomena such as transitions between major clades. Frustratingly, relevant fossils are still comparatively rare, most transitions have yet to be documented in detail and the mechanisms that underpin such events, typified by rapid large scale changes and for which microevolutionary processes seem insufficient, are still unclear. A new pterosaur (Mesozoic flying reptile) from the Middle Jurassic of China, Darwinopterus modularis gen. et sp. nov., provides the first insights into a prominent, but poorly understood transition between basal, predominantly long-tailed pterosaurs and the more derived, exclusively short-tailed pterodactyloids. Darwinopterus exhibits a remarkable ‘modular’ combination of characters: the skull and neck are typically pterodactyloid, exhibiting numerous derived character states, while the remainder of the skeleton is almost completely plesiomorphic and identical to that of basal pterosaurs. This pattern supports the idea that modules, tightly integrated complexes of characters with discrete, semi-independent and temporally persistent histories, were the principal focus of natural selection and played a leading role in evolutionary transitions.

The University of Leister press release can be found here.

October 6, 2009

The Link – Full video on CBC

The Canadian Broadcasting Corporation has the full Darwinius documentary The Link available on The Passionate Eye. A “CSI style investigation of the controversial evolutionary “missing link” between early primates and humans.

Go here to see the The Link.

See the Open Access article at PLoS One,

Franzen JL, Gingerich PD, Habersetzer J, Hurum JH, von Koenigswald W, et al. 2009 Complete Primate Skeleton from the Middle Eocene of Messel in Germany: Morphology and Paleobiology. PLoS ONE 4(5): e5723. doi:10.1371/journal.pone.0005723 (pdf)
October 1, 2009

Ardipithecus Round-up – 1 October, 2009

A ‘new’ homonid is revealed. 15 years after the discovery of the fossils, Science has released the Ardipithecus ramidus papers and the media is astir. Here is a collection of the initial reactions to the Science Magazine Special. (Registration required)

And the list will go on and on…

October 1, 2009

Now Online – A New Kind of Ancestor: Ardipithecus Unveiled

Science Online has released the Ardipithecus ramidus Special Issue:

July 8, 2009

Toofless Avian Ancestor

A new fossil bird from the Lower Cretaceous lacustrine deposits of the Jiufotang Formation in Liaoning, northeast China is described. Zhongjianornis yangi is the earliest bird yet found that completely lacks teeth.

From the abstract:

Phylogenetic analysis indicates that Zhongjianornis is phylogenetically basal to Confuciusornis and the dominant Mesozoic avian groups, Enantiornithes and Ornithurae, and therefore provides significant new information regarding the diversification of birds in the Early Cretaceous. It also represents the most basal bird that completely lacks teeth, suggesting that tooth loss was more common than expected in early avian evolution and that the avian beak appeared independently in several avian lineages, most probably as a response to selective pressure for weight reduction.

A new Lower Cretaceous bird from China and tooth reduction in early avian evolution. Zhonghe Zhou and Fucheng Zhang Zhiheng Li. Proc. R. Soc. B doi:10.1098/rspb.2009.0885

June 17, 2009

Fossil Clues for Digital Evolution

A new fossil discovery in China is providing interesting clues into the evolution of fingers:

Limusaurus inextricabilis (“mire lizard who could not escape”) was found in 159 million-year-old deposits located in the Junggar Basin of Xinjiang, northwestern China. The dinosaur earned its name from the way its skeletons were preserved, stacked on top of each other in fossilized mire pits.
A close examination of the fossil shows that its upper and lower jaws were toothless, demonstrating that the dinosaur possessed a fully developed beak. Its lack of teeth, short arms without sharp claws and possession of gizzard stones suggest that it was a plant-eater, though it is related to carnivorous dinosaurs.
The newly discovered dinosaur’s hand is unusual and provides surprising new insights into a long-standing controversy over which fingers are present in living birds, which are theropod dinosaur descendants. The hands of theropod dinosaurs suggest that the outer two fingers were lost during the course of evolution and the inner three remained.

Read the complete press release at the National Science Foundation.
See Carl Zimmer’s interpretation of the discovery at The Loom

(The Limusaurus skeleton was found preserved with a small crocodile skeleton. Photo Credit: Xu Xing. The image shows a reconstruction of Limusaurus; there is no evidence of feather structures. Credit: Portia Sloan)


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