Arxiu d'etiquetes: migration

Dinosaurs from the North Pole: Live at Prince Creek

When we think about dinosaurs, we probably imagine them walking through a dense, tropical jungle or wandering in a warm, foggy swamp. But as a matter of fact, some dinosaur species lived in very high latitudes, as the ones found in the Prince Creek formation. This Alaskan geologic formation is one of the most important sources of arctic dinosaurs, as many fossils have been found in it. In this entry, we’ll describe some of these dinosaurs from the North Pole, and we’ll explain some of the difficulties they had to endure in order to survive in the northernmost point of the planet.

ALASKA 75 MILLION YEARS AGO

The Prince Creek formation is situated in the north of Alaska and dates from around 80-60 million years ago, at the end of the Cretaceous, the last period of the Mesozoic. At that time, North America was divided by the Western Interior Seaway; the eastern continent or Appalachia, and the western continent or Laramidia, north of which the Prince Creek formation was deposited.

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Map of North America at the end of the Cretaceous period, with the Prince Creek formation marked in red, from the article New Horned Dinosaurs from Utah Provide Evidence for Intracontinental Dinosaur Endemism.

At the end of the Cretaceous period, the Prince Creek formation was further north than it is today. Yet, at that time the Earth was going through a greenhouse effect phase, so the climate was a little warmer than it is today. It is thought that the mean annual temperature at Prince Creek was about 5°C, with summer maximums at about 18-20°C. Still, the difference in temperature between summer and winter would have been quite remarkable (currently, at the same latitude, it’s about 56°C).

Even if temperatures were not as low as the ones of present-day Alaska, the dinosaurs of Prince Creek had to endure long, dark winter months. Yet, the slightly higher temperatures and the proximity to the sea, produced a higher diversity of plant species. Observing the fossilized flora, we know that the landscape was that of a polar woodland, with angiosperm-dominated forests and a large number of fern, moss and fungus species, with some areas of seasonally-flooded grasslands.

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Drawing by Julio Lacerda of Prince Creek’s landscape and wildlife.

As for the fauna, palaeontologists were surprised at the great number of big animals found. The fact that dinosaurs were found in such high latitudes is what makes us think that these were endotherm animals that generated their own body heat. Also in Prince Creek, there aren’t any fossils of other ectotherm reptiles like turtles, crocodiles or snakes, which are usually found in other United States deposits of the same period. Currently, dinosaurs are thought to be neither endotherm nor ectotherm, but mesotherm animals, which generated body heat metabolically, but were unable to control its temperature or keep it stable.

TOUGH HERBIVORES

The relatively abundant vegetation, allowed the presence of a great diversity of plant-eating dinosaurs in such high latitudes. While the smaller herbivores had little trouble because of their low energetic requirements, the larger herbivores probably had more difficulties in order to find enough food, especially during the harsh winter months. The dinosaur fossil found at the highest latitude is Ugrunaaluk (literally “ancient grazer” in Inupiaq language from northern Alaska) a hadrosaurid or “duck-billed dinosaur”. This ornithopod measured up to 10 metres long and weighed around 3 tonnes, making it one of the largest animals in Prince Creek.

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Reconstruction by James Havens of a herd of Ugrunaaluk kuukpikensis, moving under the polar lights.

Ugrunaaluk were herbivorous animals that lived in groups. Even if many author think that these animals performed long migrations like today’s birds and mammals in order to avoid the lack of food during the winter, some others argue that young Ugrunaaluk (which had a less active metabolism than current endotherms) would had been unable to endure such long journeys. Ugrunaaluk probably moved to areas were the vegetation better tolerated the severity of winter, even if it’s thought that these great herbivores survived during the dark winters feeding on bark, ferns and probably aquatic vegetation during the coldest months.

The other great Prince Creek plant-eater was Pachyrhinosaurus (literally “thick-nosed lizard”) a ceratopsid widely-distributed through the United States, with a large protuberance on its nose which may have been used as a weapon during intraspecific combats, and a pair of laterally-facing horns on the top of its frill. Pachyrhinosaurus was the largest animal of Prince Creek, measuring up to 8 metres long and weighing up to 4 tonnes. It is possible that it used its nasal protuberance to shovel through the snow to reach the plants buried under it, similar to today’s bisons.

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Reconstruction of a pair of Pachyrhinosaurus perotorum by James Havens.

All the animals of Prince Creek had arduous lives. Almost all the fossils of both Ugrunaaluk and Pachyrhinosaurus, indicate that these species matured quickly and died young. Observing the growth of the different bones that have been found, it is thought that these dinosaurs rarely lived for over 20 years of age, probably due to the harsh conditions of their habitat but also to the presence of predators.

PREDATORS LARGE AND SMALL

The largest predator of the region was Nanuqsaurus (“polar bear lizard”, from Inupiaq language), a tyrannosaurid. This animal had a highly developed sense of smell which allowed it to detect their prey or animal carcasses in low light during the polar winter. Also, although there is no evidence, it was probably covered in feathers which would have protected it from the cold, as many closely-related theropods presented feathers to some extent.

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Reconstruction of Nanuqsaurus hoglundi by Tom Parker.

What’s more surprising about Nanuqsaurus is its size, much smaller than that of its relatives. While other tyrannosaurids from the same time measured between 10 or 12 metres long and weighed up to 9 tonnes, Nanuqsaurus was more of a pygmy tyrannosaur, with an estimated length of 6 metres and a weight of 800 kg. This diminutive size was probably caused by the fact that it lived in an environment where food availability varied through the seasons. Apart from the fact that their prey’s population densities probably weren’t very high, during winter months many herbivores would migrate to other areas.

By contrast, there was another theropod that presented the opposite adaptation. Troodon (“wounding tooth”) was a relatively small dinosaur, about 2.9 metres long and 50 kg of weight. This is a pretty abundant dinosaur in many North American deposits. Troodon was a highly active carnivorous animal, with a good binocular vision and it’s also believed to be one of the most intelligent Mesozoic dinosaurs.

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Reconstruction of two Troodon inequalis playing in the snow by Midiaou.

While Nanuqsaurus was smaller by the lack of abundant prey, Troodon specimens found at Prince Creek were characterized by their bigger size, compared with the ones from other deposits. This is what is called the Bergmann’s Rule, according to which the populations of a species that live in colder climates tend to be larger than the populations living in warmer climates, as this way they lose less body heat. Also, the larger eyes of Prince Creek’s Troodon, would give them advantage hunting during the long winter nights.

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Image from the article A Diminutive New Tyrannosaur from the Top of the World, in which we can see the size of Nanuqsaurus (A) compared with some other tyrannosaurids (B, C, D and E) and two Troodon specimens (F and G) from different latitudes.

As you can see, dinosaurs not only thrived in warm and tropical environments. Even if their populations weren’t very large and their living conditions were harsher, these dinosaurs were able to adapt and survive in the polar forests of Prince Creek, and many of them surely gazed at the spectacular northern lights of 75 million years ago.

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Assembly of the different dinosaur species from the Prince Creek formation by James Kuether.

REFERENCES

The following sources have been consulted during the elaboration of this entry:

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Migratory birds: tireless traveler

Do you realize that some birds appear for certain time and place but suddenly, one day, dissapear again until the next year? Where do they go and why do they decide to fly though thousands of kilometres? Certainly, migration of birds is a phenomenon that has fascinated the human being from the beginning. In this post you will have an overview of the migration and discover fun and interesting facts of these wonderful birds. 

WHAT IS THE MIGRATION?

Migration is a natural phenomenon that happens in different species, but is particularly striking in birds. Requirements of essential resources (food, breeding areas,…), in several phases of their life cycle, is the main reason to start the journey to look for more favourable terms. The migration is a regular seasonal  movement that are performed by birds and coincide with the amount of a resource or different seasons, between breeding and wintering grounds.

Migration of short distance, for example when animals are moving from mountain areas at lower altitudes because of the temperature. On the other hand, migration of long distance when birds are traveling thousands of kilometres  through physical, meteorological and ecological barriers.

From Ice Age, migratory birds have evolved to fly long distances because in this way they are able to occupy different habitats and benefit from season resources in other climates. The migratory behaviour originating from an evolution because of climate changes on the Earth, and it is necessary an animal adaptation to the conditions in the new area. This behaviour was developed in species from more Northern latitudes in the Northern Hemisphere and in southern regions in the Southern Hemisphere.

WHAT TYPES OF MIGRATORY MOVEMENTS ARE THERE?

Migratory birds travel twice per year, in different seasons and times in their annual cycle. In the prenupcial (or spring) migration period birds fly from wintering to breeding areas. In the breeding areas there are enough resources to feed their offspring and safe breeding places. In the postnupcial (or winter) migration period adults and young birds fly to the wintering areas because of the weather and the high resource availability.

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Group of grus in the wintering area where weather and conditions are better than en North of Europe – Photo: Manuel Gómez Calzado

These movements have concrete patterns in each species and develop the different migratory routes, but researches have discovered the routes can be variables.

So, according to the migratory pattern there are longitudinal, altitudinal or latitudinal migrations. It could be variances in migratory behaviour between individuals, including in the same species, according to several factors us age, sex or population.

MIGRATORY ROUTES

Birds use these migratory movements through specific routes, with important features (catchment of a river, mountain ranges, coast,…) and ensure favourable conditions for the journey. Also, the rest areas are used to rest and feed in long routes.

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Migratory routes on the world – Photo: SEO-BirdLife

In the majority of birds from Europe and Asia, such us storks and vultures, spend the winter in the tropical Africa area, crossing their route the Arabian Peninsula and the Suez Canal. Migratory birds from the United States and Canada have their wintering areas in Mexico and Central America, and their routes depend of their area of origin: birds from east cross through the Gulf of Mexico or the Mississippi river basin; birds from west through the Rocky Mountains and Mexico Mountains, and finally, birds from Pacific used the cost or the open sea.

However, the routes can be different and depend of the distribution of birds; for example a bird species from Eurasia that pervaded North America. Their relatives used to spend the winter in Africa, so the population from North America cross Canada, the North Atlantic and Europe to spend the winter in Africa.

Researches show the routes are not so fixed us we though, and they can change according to the requirements of the species and environmental conditions over time. Also, there are fluctuations between different groups in the same species.

HOW DOES MIGRATION HAPPEN?

Human beings have always tried to answer the question ‘how is it possible birds fly so far?’. Several researches shows birds use a mix of mechanisms to migrate: the
Earth’s magnetic field, positions of the Sun, Moon and stars, polarized and ultraviolet light, recognising geographical features, reflected sound waves, taste and smell.

A research showed the migratory birds have proteins on their retina that is like a light-sensitive compass. When it is lightened with sunset light, the CPF molecule reacts and forms other compound that is sensitive to the magnitude and direction of a weak magnetic field. Two electrons rotate in opposite direction because of this chemical reaction, and the bird finds the north and south direction.

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A group of proteins that birds use during the migration – Photo: http://concienciangela.blogspot.com.es/

For some birds, such us the mayority of passerine birds, migration is an innate and individual process and they have special mechanisms to find the right way. In other cases, when birds fly in group, the migratory behaviour is developed through social learning because young birds travel with adults. Birds born of parents with different migratory routes used to choose a middle migratory route.

DISCOVERING SOME CURIOUS FACTS

The bird that travel father is the Arctic tern (Sterna paradisaea) from the Arctic, its breeding area in summer, to Antarctic to find food in winter. This distance is about 80000 km per year, and this species has developed the ability to sleep with a hemisphere off and another on flying directly.

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Arctic stern (Sterna parasidaea) and its migration – Photo: Birdlife

 

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In a research about Alpine swift (Tachymarptis melba), it was showed that this species can stand on the air for 6 months in their migration to Africa. The most interesting is that all vital processes are being on the air.

The migratory bird that flies higher is the common crane (Grus grus) and they can fly over the Himalaya mountain each year carried by the thermal currents. Breeding areas of this species are in the north of Europe and Centre and Northwest of Asia, also there are some groups in southeastern Europe and close to the Caspian and Black Seas. The wintering areas are in Spain, Portugal, north and east of Africa, south of France and south Asia.

REFERENCES

  • “Birds Migratory flyways influence the phylogeography of the invasive brine shrimp Artemia frasciscana in its native American range” – Joaquín Muñoz, Franciasco Amat, Andy J. Green, Jordi Figuerola and Africa Gómez
  • Effect of climate on the migration behavior of the common buzzard Buteo buteo – Martin, Beatriz; Onrubia, Alejandro; Ferrer, Miguel – 2014, Climate Research 60: 187 – 197 (2014)
  • Regional Forest Fragmentation and the Nesting Success of Migratory Birds – Robinson, Scott K.; Thompson III, Frank R.; Donovan, Therese M.; Whitehead, Donald R.; Faaborg, John; – Scientific Journal (JRNL) – 1995