Were feathered dinosaurs the ancestors of birds?

There is some evidence that there were species of dinosaur that had feathers, but these were not necessarily the ancestors of modern birds.

Sinosauropteryx was a carnivorous dinosaur that lived around 125-120 million years ago in what is now China. It was about one metre long. The fossils that have been discovered show that, instead of reptilian scales, parts of its body were covered by feathers.

Avimimus was a much later dinosaur (75-70 million years ago), also from China but slightly larger than Sinosauropteryx at 1.5 metres long, that also shows evidence that it bore feathers. This is due to the fact that its arm bones bore ridges of the same size and shape as those found on modern birds. It also had a mouth that was a similar shape to that of a bird’s beak.

So can these dinosaurs be seen as the direct ancestors of birds? The answer is “almost certainly not”, because the fossil record indicates that birds evolved from a completely different ancestry.

In that case, what was the function of the feathered arms if they were not the precursors of wings?

The suggestion has been made that these dinosaurs were warm-blooded and they evolved feathers as a means of keeping warm in winter. Other dinosaur species appear to have evolved fur for the same reason. It might also be that coloured feathers could have been useful as camouflage for small dinosaurs seeking to hide in vegetation.

It is a frequently made mistake to assume that the process of evolution implies some sort of purpose, in that each change between species of different time periods denotes a continuous progress from primitive to advanced. However, that is not the way that evolution works. There are many “dead ends” in the story of evolution, so it should not surprise us to find common features in more than one evolutionary sequence of creatures, but also to find that these features performed different functions.  

There was never any certainty that feathers would lead inevitably to flight. It just so happened that down one evolutionary path this was the end result, but that was not the case with the two species mentioned above.

© John Welford

Ostrich dinosaurs

The name “ostrich dinosaur” has been given to a group of creatures that lived during the late Cretaceous period (110-66 million years ago), in what is now North America and Asia. The proper name for the group is Ornithomimosaurs. They acquired their popular name because of their resemblance to modern ostriches in their size and overall shape.

They were tall and slim with powerful hind legs that would have allowed them to run fast. The front limbs worked like arms with fingers and sharp claws that could grasp their food. They had beak-like toothless mouths that would also have made them look like modern flightless birds.

One ostrich dinosaur was Struthiomimus which would have been four metres long and two metres tall. Fossils have been found in Alberta, Canada. Others were Gallimimus (8 metres long), Dromiceiomimus (3-4 metres) and Ornithomimus (4-5 metres, see picture) which could probably run at up to fifty miles an hour.

This class of dinosaurs would have eaten seeds and fruits, plus worms, lizards and other small animals.

© John Welford

Ornitholestes

Ornitholestes was a meat-eating coelurosaur dinosaur that lived around 155 million years ago which is towards the end of the Jurassic period. This was about the time that the first birds were appearing, having evolved from reptiles, and the name Ornitholestes means “bird robber” because it was originally supposed that the animal preyed on early birds and their nests. However, this is unlikely given that birds were evolving in what is now Europe and the very rare fossils of Ornitholoestes have only been found in what is now the state of Wyoming.

Ornitholestes was no great size, being only about two metres (six feet) from nose to tip of tail. It would therefore have relied on its speed for catching its prey and escaping from larger predators. It may also have developed keen senses of sight and smell for the same purposes.

Ornitholestes had small sharp teeth and strong arms that ended in long claws. These suggest that the animal might have preyed on the young of other dinosaur species, possibly grabbing them as they hatched from their eggs and making off at speed when the parents realised what was happening. The “robber” part of the name was therefore quite likely to have been appropriate, although the eggs and young being attacked were not those of birds!

© John Welford 

Massospondylus: a dinosaur from the Jurassic era

Massospondylus was a prosauropod dinosaur that lived around 200 to 185 million years ago, which places it in the early Jurassic period when reptiles were the dominant life form on planet Earth.

Massospondylus lived mainly in what is now Africa. More than 80 fossils of Massospondylus (in various states of completion) have been found, which has enabled it to be one of the best-studied dinosaurs.

It was about 4.5 metres long with half of this being its tail. It had strong hind legs, which would have been useful both for escaping from predators and for reaching the high-growing vegetation that was almost certainly its food source.

Given the small size of its head (and therefore jaw), as compared to its body, Massospondylus would have had to spend a large proportion of its waking hours eating. The animal’s front teeth were large and strong – ideal for biting the tough stems of fern-like plants – but its other teeth were not adapted to chewing. This suggests that the food was gulped straight down and then mashed up in the stomach, possibly aided by stones that Massospondylus would have swallowed.

© John Welford

Prosauropod dinosaurs

The Prosauropods, also known as Plateosaurids, were the first large dinosaurs. They lived during the late Triassic and early Jurassic eras (230-180 million years ago).

They were plant-eating dinosaurs with long necks and tails, small heads, wide bodies and four strong legs. Although they walked on all fours, some of them, such as Plateosaurus, may have reared up on their hind legs to reach leaves on tall plants. This was an animal that was up to nine metres long and may have weighed as much as three tonnes.

Riojasaurus lived about 220-215 million years ago in what is now Argentina. It was ten metres long and probably weighed about two tonnes.

Fossils of Sellosaurus, which lived 215-210 million years ago, have been found in Europe.

Lufengosaurus, from the early Jurassic, lived in what is now China and was up to nine metres long. A skeleton of Lufengosaurus was the first complete dinosaur fossil to be found in that country.

The Prosauropods were followed by the Sauropods that were even bigger but with the same basic shape having long necks and tails.

© John Welford

Baryonyx

Baryonyx was a carnivorous dinosaur that lived in the early Cretaceous era about 130 million years ago. The first discovery of a Baryonyx fossil was made in Surrey, England, in 1983.

Baryonyx was about 10 metres long, of slim shape, with a long narrow tail and a crocodile-like mouth and snout. An unusual feature was the strong thumb claw on the front legs. This claw measured 35 centimetres in length and may well have been related to Baronyx’s feeding habits.

Specimens of Baronyx have been found alongside fossilised fish scales, which give another clue as to this animal’s probable way of life.

It very much looks as though Baryonyx was a fish-eating dinosaur that behaved in a similar fashion to the modern crocodile. The signs point to Baryonyx having lived in swamps or alongside rivers. It would dart its long neck forward to snatch fish out of the water, and it would use its massive thumb claws to hook fish and other water-dwelling creatures.

Modern fresh-water crocodiles had not evolved during the era when Baryonyx was around, so it is entirely possible that Baryonyx was unchallenged in its role as a fish-eating predator at this time.

© John Welford

Eustreptospondylus

Eustreptospondylus was a large meat-eating dinosaur that lived during the Jurassic era about 165-160 million years ago. Its fossils have been found in an area that comprises the present-day counties of Oxfordshire and Buckinghamshire in England.

The first fairly complete specimen was found in 1870 and it was mistakenly categorised as “Megalosaurus”, which was the only genus of meat-eating dinosaurs known at the time to have existed in that region. It was not until 1964 that Eustreptospondylus was identified as a separate species and given its own name.

The name means “well-curved backbone”, which refers to the arrangement of the bones of the spine.

Eustreptospondylus measured about six metres from nose to tip of tail and probably weighed about 400 kilograms (900 pounds). It was equipped with a mouthful of very sharp teeth and would have been a fearsome hunter. It probably preyed on sauropod plant-eating dinosaurs such as Cetiosaurus.

© John Welford

Dilophosaurus

Dilophosaurus was a meat-eating therapod dinosaur that lived about 195-190 million years ago, which was in the early Jurassic period. It was one of the earliest large predatory dinosaurs that is known about from the fossil evidence.

Dilophosaurus was about six or seven metres in length, including its long tail. It probably weighed in excess of 500 kilograms (1100 pounds) which places it in the same weight category as the polar bear.

The name means “two ridged reptile”, which refers to the parallel plate-like ridges on the animal’s head. Given that these do not look to have been strong enough to be used as weapons, it is possible that they were covered in brightly coloured skin and used to warn off rivals or enemies, or as part of a mating ritual.

Fossils of dilophosaurus were found in 1942 in Arizona, USA, but the creatures may well have lived in other places. The species was only designated and named in 1970, due to difficulties posed by the fragmented nature of the fossils.

© John Welford

Coelophysis

Coelophysis was a small, agile dinosaur that lived during the Triassic era about 210 million years ago. It was about three metres long and it would have stood about waist-high to the average human, had any been around at the time. Being of light build, with hollow bones, it would only have weighed about 20 kilograms (44 pounds).

It had long, powerful back legs, so it would have been able to run quickly, and its smaller front legs would have been used like arms. It had “hands” with three clawed fingers that would have been used to catch and hold its prey. Its mouth was full of small sharp teeth.

The “arms” feature contrasts sharply with meat-eaters that appeared much later in the Dinosaur Age, such as Tyrannosaurus, that had forelimbs with no discernible purpose. More than 140 million years elapsed between Coelophysis and Tyrannosaurus, which is many millions of years longer than the gap between Tyrannosaurus and us! There was therefore plenty of time in which evolution could make substantial changes between dinosaurs similar to Coelophysis and those resembling Tyrannosaurus.

Coelophysis belonged to the therapod group of meat-eating dinosaurs. Its food probably consisted mainly of lizards, worms and insects.

A large number of Coelophysis fossils were found at Ghost Ranch, New Mexico, USA, in 1940. They may have been a herd of animals that drowned during a sudden flash flood.

© John Welford

Allosaurus

Ask just about anyone to name a meat-eating dinosaur and they are quite likely to say “Tyrannosaurus”. This was a fearsome hunter that lived at the end of the Age of the Dinosaurs about 65 million years ago. However, there was a very similar animal that filled the same niche in the natural world 90 million years earlier; this was Allosaurus.

Allosaurus lived during the late Jurassic about 155-150 million years ago. Fossils have found in the American midwest, notably Utah, Wyoming and Colorado. However, close relatives of Allosaurus may have lived in what is now Europe and Africa.

Allosaurus was 11-12 metres in length (36-39 feet) and could have weighed up to four tons. It had a massive head (up to a metre long) and jaws that could be flexed to allow huge bites to be taken.

The late Jurassic was also populated by massive sauropod dinosaurs including Diplodocus and Brachiosaurus. These may well have formed a major part of the diet of Allosaurus.

© John Welford

Carnotaurus

Carnotaurus was a therapod dinosaur that lived during the Cretaceous era about 75 to 70 million years ago. Fossils have been found in Argentina, the first discovery being made in 1985.

Carnotaurus was a medium-sized dinosaur at 8 to 9 metres in length, weighing around one ton.

The skull was relatively tall from top to bottom but short from front to back, which accounts for its name which translates as ‘meat-eating bull’ in reference to the appearance of its head.

Carnotaurus had two small horn-like projections above the eyes, and a row of scales along the spine that produced a series of regularly placed lumps.

Carnotaurus was similar to Tyrannosaurus in that it had tiny ‘arms’ for which the use is difficult to envisage – they would have been too short to reach the animal’s mouth.

Although Carnotaurus was clearly a meat-eater, its teeth and jaws were not particularly large or powerful. This suggests that it would have preyed on smaller plant-eating dinosaurs.

© John Welford

The evolution of birds

It is generally believed that birds evolved from reptiles and are the nearest living creatures to the dinosaurs, the last of which suffered extinction some 65 million years ago. However, the exact evolutionary route from Tyrannosaurus Rex to house sparrow is not so easy to work out.

Dinosaurs to birds

It is known that the skies 150 million years ago were patrolled by massive winged reptiles called pterosaurs, but these were not the ancestors of modern birds. For one thing, they did not have feathers and, for another, they belong to a different branch of the evolutionary tree.

Dinosaurs, by which is meant land-dwelling reptiles of the Triassic, Jurassic and Cretaceous eras (251 to 65 million years ago) can be divided into two main branches, the Saurischians and the Ornithischians, based on their hip structure. Confusingly enough, birds evolved from the first-named group, not the second. They are therefore more closely related to carnivorous reptiles such as Tyrannosaurus and Velociraptor than herbivores such as Iguanodon and Stegosaurus.

Archaeopteryx

The idea that birds evolved from dinosaurs was first proposed after the discovery in Germany in 1861 of the fossilised impression of a creature from 150 million years that was clearly a reptile but which also had feathers. This was named Archaeopteryx (meaning “ancient feather”) and was widely hailed as being an intermediary between dinosaurs and birds, given that the structure of its bones and the arrangement of the feathers made it entirely possible for Archaeopteryx to fly. It would have been about the size of a modern raven. The discovery came only two years after the publication of Darwin’s “The Origin of Species” and was seen as confirmation of Darwin’s conjecture that species could evolve into new ones.

However, there are doubts over whether Archaeopteryx was the direct ancestor of modern birds, or whether that honour belongs to a creature related to Archaeopteryx that has not, as yet, turned up in the fossil record. Another complication has been the discovery of fossils (in China in 1998) of dinosaurs that had feathers but clearly were not suited for flight.

The suggestion is therefore that feathers evolved for a purpose other than enabling a creature to fly. It is quite possible that the original function of feathers was to provide insulation or to attract mates, and that Archaeopteryx and its relatives and descendants adapted them as a means of achieving flight.

One theory is that an ancestor of Archaeopteryx might have hopped along the ground and grabbed insects out of the air. Those that jumped higher would get the most insects and the ability to flap the wings and take off altogether evolved from that activity.

So where might birds have come from?

The fossil record includes later specimens that show how early bird species might have developed. These include Ichthyornis and Hesperornis from the Upper Cretaceous (100 million years ago).

The virtual disappearance of the dinosaurs 65 million years leaves open the question of how the bird ancestors managed to survive, especially if the reason for the disappearance was a strike on Earth by a large meteor or small asteroid, resulting in worldwide destruction of plant life due to vast dust clouds preventing proper sunlight from reaching the surface for a number of years. It has been suggested that the small size of proto-birds might have been a factor, coupled with the insulation provided by feathers and their ability to fly to whatever food sources were available.

In the post-dinosaur world the evolution of birds took off in many directions, aided by the fact that winged flight enabled birds to reach locations that presented many different ecological challenges that in turn led to further evolutionary development. By 60 million years ago the ancestors of modern herons, vultures and kingfishers are known to have been living, and most of the bird families in existence today are known to have evolved by the end of the Miocene (11 million years ago).

Continuing evolution

Evolutionary changes are still taking place in bird populations. Charles Darwin noted how the finches of the Galapagos Islands had evolved different feeding strategies to cope with the variety of food available between different islands within the same group, and those changes would have taken place relatively recently in the geological timescale, given that the islands themselves had only emerged from the ocean within the past four million years.

An even more recent example of bird adaptability leading to species evolution is that of the feral or urban pigeon which has developed characteristics that are quite distinct from its rural cousin the woodpigeon, due to having abandoned the cliffs of coast and mountain for the manmade cliffs of city buildings.

What all this shows is that evolution is a process that affects all living creatures, as it has done ever since the only life forms on the planet were viruses and bacteria.

© John Welford