Dal Pollo al Dinosauro

Sono noti pochissimi esperimenti che riportano la morfologia e la meccanica degli attuali uccelli indietro , fino alle modalità che erano proprie dei dinosauri.
Ecco perché quello riportato qui è un esempio prezioso per gli scienziati. I dinosauri avevano zampe con un "alluce" non opponibile, sito indietro ed in alto (come appare essere nei cani e nei gatti oggi).  Negli uccelli, invece, si trova più in basso (perché scende durante lo sviluppo embrionale, grazie all'attività muscolare locale embrionale) e permette loro di 'appollaiarsi', con l'aggrapparsi intorno ad un ramo, oppure di 'ghermire' la preda con un solo gesto. 

Bloccando tali muscoli nell'embrione, si ottengono polli con zampe 'da dinosauro'.  Un altro esperimento che dimostra attraverso quali complicate strade anche biologiche debba procedere l'informazione genetica per potere avere il proprio effetto finale.   


From chicken to dinosaur: 

Scientists experimentally reverse the evolution of the perching toe 





A unique adaptation in the foot of birds is the presence of a thumb-like opposable toe, which allows them to grasp and perch. 
However, in their dinosaur ancestors, this toe was small and non- opposable, and did not even touch the ground, resembling the dewclaws of dogs and cats. 

The perching toe from chicken to dinosaur 

 [Credit: Universidad de Chile] 

Remarkably, the embryonic development of birds provides a parallel of this evolutionary history: The toe starts out like their dinosaur ancestors, but then its base (the metatarsal) becomes twisted, making it opposable. 

Brazilian researcher Joâo Botelho, working at the lab of Alexander Vargas at the University of Chile, decided to study the underlying mechanisms. 
Botelho observed that the twisting occurred shortly after the embryonic musculature of this toe was in place. 
"This is one of the clearest examples of how indirect the morphological consequences of genetic change are mediated," Gunter Wagner, evolutionary geneticist and professor at Yale. 
Bird embryos move a lot inside the egg during development, and the onset of movement at this toe coincided with the twisting of its base.
Botelho also demonstrated that in this toe, genes of cartilage maturation were expressed at a much later stage than other digits: It retains many rapidly dividing stem cells for a much longer period. 
Such immature cartilage is highly plastic and easily transformed by muscular activity. 
These observations suggested the toe is twisted as a result of mechanical forces imposed on it by the embryonic musculature. 
Definitive proof, however, would come from experiments. 
When Botelho applied Decamethonium bromide, a pharmacological agent capable of paralyzing embryonic musculature, the result was a non-opposable toe with a straight, non-twisted base identical to that of their dinosaur ancestors. 

Only a few experiments are known to recover dinosaur traits in birds (such as a dinosaur-like shank and tooth-like structures). 
The undoing of the perching digit is thus an important new addition, and the results have now been published in Scientific Reports. 
The significance of this experiment, however, goes beyond the fact that a dinosaur-like toe is being retrieved. 
Evolutionary research often centers on mutations, but the development and evolution of the perching toe cannot be understood without the forces of embryonic muscular activity.
The study is described as "true developmental mechanics" by Gunter Wagner, an evolutionary geneticist and professor at Yale. 
"This is one of the clearest examples of how indirect the morphological consequences of genetic change are mediated. 
The experiments prove that interactions about organ systems channel the directions of organismal evolution." 

Source: Universidad de Chile [May 22, 2015]

MOA

Ancient DNA shows moa were fine 

until humans arrived

 A study by Curtin University researchers and colleagues from Denmark and New Zealand strengthens the case for human involvement in the disappearance of New Zealand's iconic megaherbivore, the moa -- a distant relative of the Australian Emu. 

D. novaezealandiae skull at the Museum für Naturkunde, Berlin 

[Credit: WikiCommons] 

All nine species of New Zealand moa, the largest weighing up to 250 kilograms, became extinct shortly after Polynesians arrived in the country in the late 13th century.

Researchers have previously suggested, from limited genetic evidence, that huge populations of moa had collapsed before people arrived and hence influences other than people were responsible for the extinction. 
Writing in the Proceedings of the National Academy of Sciences, USA, the researchers analysed the gene pools of four moa species in the 5000 years preceding their sudden extinction using ancient DNA from more than 250 radiocarbon-dated moa. 
The huge data sets provided an unprecedented level of insight into what was happening to the populations of an extinct megafauna, allowing a detailed examination of the extinction process.
 The genetic study was led by Professor Mike Bunce from Curtin University's Department of Environment and Agriculture, situated in Perth, Western Australia. 

Preserved moa (Megalapteryx) foot, Natural History Museum

 [Credit: Ryan Baumann/WikiCommons] 

"Characterising a people's interactions with the environment is a fundamental part of archaeological research -- it has been portrayed anywhere on a scale from the harmonious to the catastrophic," Professor Bunce said "Elsewhere the situation may be more complex, but in the case of New Zealand the evidence provided by ancient DNA is now clear: the megafaunal extinctions were the result of human factors. "

Lessons can certainly be learnt from the historical study of megafaunal extinctions. As a community we need to be more aware of the impacts we are having on the environment today and what we, as a species, are responsible for in the past." 

Morten Allentoft, a PhD student in Professor Bunce's laboratory and now a Post-Doctoral Fellow at the Centre for GeoGenetics in the Natural History Museum in Copenhagen, performed the genetic work. 

Restoration of an Upland Moa, Megalapteryx didinus 

[Credit: WikiCommons] 

"There is nothing in our ancient DNA data that suggests that any of the four species moa was already on the way out when humans arrived," Dr Allentoft said. "Our detailed genetic analyses, using variable nuclear markers similar to that used in forensic DNA profiling, show that moa gene pools were extremely stable throughout their last 5000 years. "If anything it looks like their populations were increasing and viable when humans arrived. Then they just disappeared." Professor Bunce and Dr Allentoft were joined in their research by Professor Richard Holdaway from the University of Canterbury in New Zealand and other co-authors. 

Author: Simon White | Source: Curtin University [March 19, 2014]

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Melanosomi, polli e dinosauri.

Un interessante studio su ciò che colorava i piumaggi di antichi animali. Forse erano già i melanosomi: organelli capaci di dare ai tegumenti ed ai loro annessi - a mezzo del pigmento melanina che essi producono - una colorazione che può andare dal bruno rossastro, al grigio, al nero. 
Dato che i melanosomi non sono facilmente distinguibili dai batteri, nei reperti antichi, una ricercatrice ha pensato di fare crescere batteri su penne di pollo (i polli son quanto di più simile oggi sia possibile trovare ai dinosauri piumati ed agli uccelli antichi) e poi di sottoporre i reperti di crescita a vari esami ottici.
Infatti, la livrea degli antichi animali - fossero essi dinosauri oppure uccelli - deve essere andata incontro ad una degradazione batterica post-mortem...
Per il momento i risultati - più che risposte - pongono altre e nuove domande.
Tanto che l'unico principio che se ne può trarre è la possibile (non sicura) distinzione tra batterio e melanoma a seconda che l'organello si trovi dentro oppure fuori del tessuto cheratinico componente la penna.
E' un inizio, ma è anche obiettivamente poco.
Ma ne sentiremo certamente parlare ancora, con ricerche su altri reperti antichi, contenenti cheratina e batteri... Chissà che un giorno non si possa dare una colorazione certa (invece che una ipotetica, come avviene fino ad oggi) a quegli antichi esseri...

Researchers re-examine the idea of 'colour’ in fossil

 feathers 

Paleontologists studying fossilized feathers have proposed that the shapes of certain microscopic structures inside the feathers can tell us the color of ancient birds. But new research from North Carolina State University demonstrates that it is not yet possible to tell if these structures -- thought to be melanosomes -- are what they seem, or if they are merely the remnants of ancient bacteria. 

Images of the fossil feather ascribed to Gansus yumenensis 

[Credit: Scientific Reports] 

Melanosomes are small, pigment-filled sacs located inside the cells of feathers and other pigmented tissues of vertebrates. They contain melanin, which can give feathers colors ranging from brownish-red to gray to solid black. Melanosomes are either oblong or round in shape, and the identification of these small bodies in preserved feathers has led to speculation about the physiology, habitats, coloration and lifestyles of the extinct animals, including dinosaurs, that once possessed them. But melanosomes are not the only round and oblong microscopic structures that might show up in fossilized feathers. In fact, the microbes that drove the decomposition of the animal prior to fossilization share the same size and shape as melanosomes, and they would also be present in feathers during decay. 
Alison Moyer, a Ph.D. candidate in paleontology at NC State, wanted to find out whether these structures could be definitively identified as either melanosome or microbe. 
Using black and brown chicken feathers -- chickens are one of the closest living relatives to both dinosaurs and ancient birds -- Moyer grew bacteria over them to replicate what we see in the fossil record. 
She used three different types of microscopy to examine the patterns of biofilm growth, and then compared those structures to melanosomes inside of chicken feathers that she had sliced open. 
Finally, she compared both microbes and actual melanosomes to structures in a fossilized feather from Gansus yumenensis, an avian dinosaur that lived about 120 million years ago, and to published images of fossil "melanosomes" by others.
 Her findings led to more questions. 
"These structures could be original to the bird, or they could be a biofilm which has grown over and degraded the feather -- if the latter, they would also produce round or elongated structures that are not melanosomes," Moyer says.
 "Melanosomes are embedded in keratin, which is a very tough protein, so they're hard to see unless there's been some degradation. But the bacteria are doing the degrading, and so that may be what we're seeing, rather than the melanosome itself. It's impossible to say with certainty what these structures are without more data, including fine scale chemical data." 
The research appears online in Scientific Reports. 

Possible next steps for Moyer include testing for the presence of keratin or bacteria within the fossils, by looking for their molecular signals. 
"The technology that we have available to us as paleontologists now is amazing, and will make it much easier to test all of the hypotheses we develop about these fossils," Moyer says. "In the meantime, perhaps we can establish some basic criteria for identifying these structures as melanosomes, such as whether they're found within the feather's interior, or externally."
 The research was funded in part by the National Science Foundation and the David and Lucille Packard foundation. 
The fossil feather was provided by the Gansu Geological Museum in Lanzhou, Gansu, China. 


Source:  North Carolina State University [March 05, 2014]
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