Monday, May 28, 2012

Change in developmental timing was crucial in the evolutionary shift from dinosaurs to birds: study

Tyrannosaurus rex. Image: Nobu Tamura, via Wikipedia.

May 27 2012

At first glance, it's hard to see how a common house sparrow and a Tyrannosaurus Rex might have anything in common. After all, one is a bird that weighs less than an ounce, and the other is a dinosaur that was the size of a school bus and tipped the scales at more than eight tons.
For all their differences, though, scientists now say that two are more closely related than many believed. A new study, led by Harvard scientists, has shown that modern birds are, essentially, living dinosaurs, with skulls that are remarkably similar to those of their juvenile ancestors.

As reported in a May 27 paper in Nature, Arkhat Abzhanov, Associate Professor of Organismic and Evolutionary Biology and Bhart-Anjan Bhullar, a PhD student in Abzhanov laboratory and the first author of the study, found evidence that the evolution of birds is the result of a drastic change in how dinosaurs developed. Rather than take years to reach sexual maturity, as many dinosaurs did, birds sped up the clock – some species take as little as 12 weeks to mature – allowing them to retain the physical characteristics of baby dinosaurs.

"What is interesting about this research is the way it illustrates evolution as a developmental phenomenon," Abzhanov said. "By changing the developmental biology in early species, nature has produced the modern bird – an entirely new creature – and one that, with approximately 10,000 species, is today the most successful group of land vertebrates on the planet."

"The evolution of the many characteristics of birds – things like feathers, flight, and wishbones – has traditionally been a difficult problem for biologists," Mark Norell, chair of the Division of Paleontology at the American Museum of Natural History and one of the paper's co-authors, said. "By analyzing fossil evidence from skeletons, eggs, and soft tissue of bird-like dinosaurs and primitive birds, we've learned that birds are living theropod dinosaurs, a group of carnivorous animals that include Velociraptor. This new work advances our knowledge by providing a powerful example of how developmental changes played a major role in the origin and evolution of birds."

While it's clear simply from looking at the skulls of dinosaurs and modern birds that the two creatures are vastly different – dinosaurs have distinctively long snouts and mouths bristling with teeth, while birds have proportionally larger eyes and brains – it was the realization that skulls of modern birds and juvenile dinosaurs show a surprising degree of similarity that sparked the study.
"No one had told the big story of the evolution of the bird head before," Bhullar said. "There had been a number of smaller studies that focused on particular points of the anatomy, but no one had looked at the entire picture. What's interesting is that when you do that, you see the origins of the features that make the bird head special lie deep in the history of the evolution of Archosaurs, a group of animals that were the dominant, meat-eating animals for millions of years."

To tackle the problem, the researchers turned to an unusual methodology. Using CT scanners, they scanned dozens of skulls, ranging from modern birds to theropods – the dinosaurs most closely related to birds – to early dinosaur species. By marking various "landmarks" – such as the orbits, cranial cavity and other bones in the skull – on each scan, researchers were able to track how the skull changed shape over millions of years.

"We examined skulls from the entire lineage that gave rise to modern birds," Abzhanov said. "We looked back approximately 250 million years, to the Archosaurs, the group which gave rise to crocodiles and alligators as well as modern birds. Our goal was to look at these skulls to see how they changed, and try to understand what actually happened during the evolution of the bird skull."
What Abzhanov and colleagues found was surprising – while early dinosaurs, even those closely related to modern birds, undergo vast morphological changes as they mature, the skulls of juvenile and adult birds remain remarkably similar.

"This phenomenon, where a change in the developmental timing of a creature produces morphological changes is called heterochrony, and paedomorphosis is one example of it," Abzhanov explained. "In the case of birds, we can see that the adults of a species look increasingly like the juveniles of their ancestors."

In the case of modern birds, he said, the change is the result of a process known as progenesis, which causes an animal to reach sexual maturity earlier. Unlike their dinosaurian ancestors, modern birds take dramatically less time – just 12 weeks in some species – to reach maturity, allowing birds to retain the characteristics of their juvenile ancestors into adulthood.

"This study is a prime example of the heuristic power in multidisciplinary, specimen-based, anatomical research," said Gabe Bever of NYIT's New York College of Osteopathic Medicine and a co-author of the paper. "That the mechanisms of evolutionary events millions of years old can be circumscribed with this combination of modern and fossil specimens is remarkable."

Ultimately, Abzhanov said, the way the bird skull evolved – through changes in the developmental timeline – highlights the diversity of evolutionary strategies that have been used over millions of years.
"That you can have such dramatic success simply by changing the relative timing of events in a creature's development is remarkable," he said. "We now understand the relationship between birds and dinosaurs that much better, and we can say that, when we look at birds, we are actually looking at juvenile dinosaurs."

"It shows that there's so much for evolution to act upon," Bhullar agreed. "When we think of an organism, especially a complex organism, we often think of it as a static entity, but to really study something you have to look at its whole existence, and understand that one portion of its life can be parceled out and made into the entire lifespan of a new, and in this case, radically successful organism."

Journal reference: Nature search and more info website
Provided by Harvard University search and more info website 


Thursday, May 17, 2012

The Rockhopper Penguin

Eudyptes chrysocome
rockhopper penguin

By Devon Phelan

  • Classification
Kingdom Animalia (animals)
Eumetazoa (metazoans)
Bilateria (bilaterally symmetrical animals)
Deuterostomia (deuterostomes)
Phylum Chordata (chordates)
Craniata (craniates)
Subphylum Vertebrata (vertebrates)
Superclass Gnathostomata (jawed vertebrates)
Euteleostomi (bony vertebrates)
Class Sarcopterygii (lobe-finned fishes and terrestrial vertebrates)
Tetrapoda (tetrapods)
Amniota (amniotes)
Class Reptilia
Class Aves (birds)
Subclass Neognathae (neognath birds)
Infraclass Neoaves (modern birds)
Order Sphenisciformes (penguins)
Family Spheniscidae (penguins)
Genus Eudyptes (rockhopper, macaroni, and related penguins)
Species Eudyptes chrysocome (rockhopper penguin)
Subspecies Eudyptes chrysocome chrysocome
Subspecies Eudyptes chrysocome filholi
Subspecies Eudyptes chrysocome moseleyi

Geographic Range

Rockhopper penguins are found on islands in the southern ocean, such as the Falkland Islands. They occur farther north than many other penguin species.
Biogeographic Regions
neotropical (Native ); atlantic ocean (Native )


Rockhopper penguins are found in high grasses called tussocks, where they make burrows and nest. As their name implies, they live on rocky shorelines.

Habitat Regions
temperate ; terrestrial ; saltwater or marine

Terrestrial Biomes
savanna or grassland

Aquatic Biomes

Physical Description

Range mass
2000 to 3000 g
(70.48 to 105.73 oz)

Average length
55 cm
(21.65 in)

Rockhopper penguins measure about 55 centimeters in length and weigh around 2.5 kilograms. These birds stand upright on two short feet. Their legs are set far back on the body. The waterproof coat, composed of feathers that average 2.9 centimeters in length, is white on the underside and bluish-black on the top. The head has bright yellow plumage on the brow; the yellow feathers extend along the sides. The top of the head has spiked black feathers. The wings are strong, stiff, narrow and flipper-like. Rockhopper penguins have tiny eyes.

Other Physical Features
endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism
sexes alike


Mating calls, which are species specific, are called "ecstatic vocalization." This draws attention to the bird and announces its intentions. Penguins mate with the same partners from previous years. (Williams, 1981)

Mating System
Breeding interval
Rockhopper penguins breed once yearly.

Range eggs per season
1 to 2

Rockhopper penguins typically mate in the early spring or late summer, enabling the young to go to the sea in the mid-summer. They mate in vast colonies and lay up to two eggs, although sometimes pairs "adopt" a third egg. The first egg is usually 20-50% smaller than second one. The small egg is usually lost, although it is capable of maturing into a normal bird. Adopted eggs are also typically lost. After each egg is laid, it is turned over to the male who sits on it and keeps it in his brood pouch for the next four months until it hatches. (Williams, 1981)
Key Reproductive Features
seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate)
While the male penguin sits on the incubating egg, he is nourished by the female, or else he fasts for the entire period. If the female does not return with food for the chick once it has hatched, the male produces "penguin's milk" from his digestive system and regurgitates it for the baby.
Parental Investment
precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Male); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male)


Average lifespan
Status: wild

10 years

The average lifespan of a rockhopper penguin is 10 years.


Penguins are very sociable animals. It is very rare to see one alone. Rockhopper penguins are the most aggressive, as well as the most numerous, penguins. They hide their heads under their wing while they rest. Rockhopper penguins leave the breeding colony in late summer or fall and spend 3-5 months at sea, where they find food. Penguin wings are used exclusively for swimming, these sea birds do not fly.
Key Behaviors
natatorial ; diurnal ; territorial ; social ; colonial 

Communication and Perception

Their loud cry, "ecstatic vocalization", is used to announce their presence, attract a mate, or announce the boundaries of their territory. As well as vocalizing, these birds shake their heads and cause their yellow eyebrows to fly into a "halo" in order to attract a mate.
Communication Channels
visual ; acoustic

Food Habits

Rockhopper penguins eat primarily krill (Euphausiacea). They also eat squid and other crustaceans. They make daily trips to the sea to forage.
Primary Diet
carnivore (Eats non-insect arthropods)
Animal Foods
fish; aquatic crustaceans

Economic Importance for Humans: Positive

Penguins are a tourist attraction, and they are one of the main reasons people travel to the Falkland Islands and other habitats of these penguins.

Conservation Status

IUCN Red List of Threatened Species [Link]

More Information
CITES [Link]

No special status
It is estimated that rockhopper penguins have undergone a decline of more than 30% in their total population size over the past 30 years. For this reason, they are classified as vulnerable by the IUCN. If the decline continues, they may be uplisted to endangered in the near future. Threats to rockhopper penguin populations include commercial fishing, which reduces the amount of available prey, and oil spills. (Bingham, 2002; BirdLife International, 2004; Ryan and Cooper, 1991)

Other Comments

Rockhopper penguins keep warm by their well-developed fat layer and system for maintaining heat.


Tanya Dewey (editor), Animal Diversity Web, University of Michigan Museum of Zoology.
Devon Phelan (author), University of Michigan.


Gorman, James. 1990. The Total Penguin. Prentice Hall Press, NY.

Grzimek, Dr.Dr.h.c. Bernhard. 1972. Grzimek's Animal Life Encyclopedia. p.133-134. Van Norstrand Reinhold Co. NY.

New Scientist. "Did Warm Water Kill Falkland Penguins?" IPC Magazine Ltd. Vol. 114. May 28, 1987. p.22.

Bingham, M. 2002. The decline of Falkland Islands penguins in the presence of a commercial fishing industry. Revista Chilena de Historia Natural, 75(4): 805-818.

BirdLife International, 2004. "Eudyptes chrysocome" (On-line). 2004 IUCN Red List of Threatened Species. Accessed November 14, 2005 at

Ryan, P., J. Cooper. 1991. Rockhopper penguins and other marine life threatened by drift net fisheries at Tristan da Cunha, South Atlantic Ocean. Oryx, 25(2): 76-79.

Williams, A. 1981. The clutch size of macaroni penguins Eudyptes chrysolophus and rockhopper penguins Eudyptes chrysocome. Emu, 81(2): 87. 

To cite this page: Phelan, D. 1999. "Eudyptes chrysocome" (On-line), Animal Diversity Web. Accessed May 16, 2012 at

Friday, May 11, 2012

Bird Color Variations Speed Up Evolution

 Left: Grey morph of the Eastern Screech Owl (Megascops asio). Right: Rufous morph of the Eastern Screech Owl. (Credit: Left: Wolfgang Wander via Wikipedia, Creative Commons license; Right: Greg Hume via Wikipedia, Creative Commons license)

Bird Color Variations Speed Up Evolution

ScienceDaily (May 9, 2012) — Researchers have found that bird species with multiple plumage colour forms within in the same population, evolve into new species faster than those with only one colour form, confirming a 60-year-old evolution theory.

The global study used information from birdwatchers and geneticists accumulated over decades and was conducted by University of Melbourne scientists Dr Devi Stuart-Fox and Dr Andrew Hugall (now based at the Melbourne Museum) and is published in the journal Nature.

The link between having more than one colour variation (colour polymorphism) like the iconic red, black or yellow headed Gouldian finches, and the faster evolution of new species was predicted in the 1950s by famous scientists such as Julian Huxley, but this is the first study to confirm the theory.
By confirming a major theory in evolutionary biology, we are able to understand a lot more about the processes that create biodiversity said Dr Devi Stuart-Fox from the University's Zoology Department.

"We found that in three families of birds of prey, the hawks and eagles, the owls and the nightjars, the presence of multiple colour forms leads to rapid generation of new species," Dr Stuart-Fox said.
"Well known examples of colour polymorphic species in these families include the Australian grey goshawk which has a grey and pure white form, the North American eastern screech owl and the Antillean nighthawk, each with grey and red forms."

The team focused on birds because although colour polymorphism occurs in many animals (such as fish, lizards, butterflies and snails), there is a wealth of information on colour variation in birds, as well as on species classification (taxonomy), partly thanks to birdwatchers or 'twitchers'.
"We looked at five bird families with a high proportion of colour polymorphism and compared their rates of evolution with those with only one colour form," Dr Stuart-Fox said.

By modeling evolutionary rates using publicly available genetic information accumulated over a quarter of a century, the study found that colour polymorphism speeds up the generation of new species. Colour polymorphic species tend to evolve into species with only one colour form (monomorphic), explaining why existing species with different colour forms are relatively young and also rare.

The study found that colour polymorphic species were younger not only in the birds of prey but in the songbirds, which account for more than half of the world's bird species.

Study co-author Dr Andrew Hugall noted that when scientists like Julian Huxley proposed that colour polymorphism speeds up the generation of new species over half a century ago, they did not have the huge amounts of data needed to support it.

"Using many decades of natural history information and 25 years of genetic sequence information we were able to generate the massive family trees, such as a tree of more than four thousand songbirds, needed to model rates of bird evolution in this study," he said.

"Now that we've identified this pattern for the first time, our next step is to test some of the explanations proposed for why colour polymorphism leads to accelerated evolution."

Story Source:
The above story is reprinted from materials provided by University of Melbourne.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:
  1. Andrew F. Hugall, Devi Stuart-Fox. Accelerated speciation in colour-polymorphic birds. Nature, 2012; DOI: 10.1038/nature11050

University of Melbourne (2012, May 9). Bird color variations speed up evolution. ScienceDaily. Retrieved May 11, 2012, from ­source
 **My Note: So does this mean that this explains the lack of speciation in penguins over the millenia?**