Changing Views on Sauropods – Long-necked Dinosaurs

The huge, long-necked sauropods such as Diplodocus and Brachiosaurus are extremely well known in popular culture but although many museums exhibit specimens of these enormous creatures, our level of scientific knowledge particularly the phylogeny of these creatures remains relatively poor.  Thanks to recent discoveries of some seemingly transitional forms from prosauropods to the true sauropods, dinosaurs such as Lessemsaurus from Argentina and Chinshakiangosaurus from China for example, our understanding of the evolution of these animals is more complete.

The sauropods were a truly remarkable group of dinosaurs, with some of the oldest sauropod fossils dating from the beginning of the Jurassic and with the last titanosaurs surviving in the Americas and other parts of the Southern Hemisphere right up to the end of the Cretaceous, approximately 66 million years ago.  Although these animals had their hey day in the Jurassic, no other type of herbivore has dominated terrestrial ecosystems quite like the sauropods.  With their massive bulk, animals like Apatosaurus for instance could weigh in excess of 30 tonnes; they decimated the vegetation within an environment before moving on in vast herds to find fresh feeding areas.

Sauropods represent a truly unique group of animals, there is nothing alive today to compare with them and their size, power and myriad of forms are truly amazing.  Most sauropods are classified into two distinct types, the Macronaria (big nostrils), nasal openings in skulls are bigger than the orbit (eye).  Sauropods typical of the Macronaria group are animals such as Brachiosaurus and Camarasaurus.

To see a scale model of Brachiosaurus and other sauropod figures: Dinosaur Models and Toys.

The other main type of sauropod are the Diplodocoidea, animals such as Diplodocus and Seismosaurus.  Some very bizarre forms of sauropod are known.  For example, scientists know that a number of later sauropods (titanosaurs) were armoured, but also many of the lesser known sauropods also possessed body armour, scutes and even clubs on the ends of the tail.

Shunosaurus from the mid Jurassic of China had a club on the end of its tail.  When the first fossils of this dinosaur were found in 1979, the tail was thought to have become damaged and the bones had not healed properly and had become infected, producing this abnormal growth in the single specimen discovered.  Several fully articulated fossil Shunosaurus are now known and all possess this club-like feature on the end of their tails.  Scientists were able to conclude that the swollen tail of this dinosaur was not the result of an injury or disease (pathology), but this dinosaur possessed the equivalent of a medieval mace on the end of its tail.

An Illustration of Shunosaurus

Picture credit: Everything Dinosaur

To view a model of Shunosaurus and other figures in the Safari Ltd model collection: Wild Safari Prehistoric World.

This particular sauropod is estimated to have reached lengths in excess of 9 metres and it was one of the most common type of long-necked dinosaur found in what was a vast, Jurassic floodplain now being excavated at the Dashanpu quarry site.

Othniel Charles Marsh 1831 – 1899

On the 29th October 1831, Othniel Charles Marsh was born.  He was destined to become one of the most influential and important palaeontologists of the 19th century.

Othniel Charles Marsh

Born in New York, Charles was educated at Yale and went onto study geology and mineralogy.  Following this he travelled to Germany to study palaeontology.  Returning to America, he was appointed professor of vertebrate palaeontology at Yale University (the first professor of palaeontology ever appointed in the United States), he went onto persuade his uncle, the wealthy entrepreneur and philanthropist, George Peabody, to establish a museum of natural history (Peabody Museum at Yale).

Marsh was one of the great pioneers of American palaeontology, leading a number of successful exhibitions to the west of the United States as the geology of this territory began to be opened up and fully explored.  He described 19 different genera of dinosaur and competed fiercely with his rival Edward Drinker Cope to find the best specimens for the museums back in the east of the USA.  Their rivalry became known as the “Bone Wars”.  Marsh’s expeditions made a number of important discoveries, they unearthed the first American pterosaur fossils and Marsh went onto name and describe some of the most famous of all the dinosaurs Allosaurus, Apatosaurus and Diplodocus.

A Model of an Allosaurus

New for 2020 the Mojo Fun Allosaurus dinosaur model. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Mojo Fun range of models and figures includes replicas of several prehistoric animals that were named and described by Othniel Charles Marsh: Mojo Fun Prehistoric and Extinct Animal Models.

A number of extinct species have been named in honour of this professor, for example the hypsilophodontid Othnielia (fossils found in Colorado, USA), was named after Othniel Charles Marsh.

Writing Scientific Papers

Marsh also devoted a great deal of his time to writing papers and attempting to find order amongst vertebrate evolution, describing a number of toothed birds and flying reptiles.   One of his greatest contributions to science was his study of the evolution of horses, published as the Darwinian debate raged.  Marsh’s paper outlining how horses evolved from small, many-toed browsers to fleet footed, large single-toed grazers was seen by many scientists of the day of evidence in support of Darwin’s theory of natural selection.

While travelling to the western USA in 1868, Marsh was told of a strange discovery of what was believed to be human bones in Nebraska.  He was curious but doubted that the bones belonged to an ancient race of humans, however, he did ask to view them and quickly identified them (correctly), as ancient horse fossils.  Marsh insisted on having the remains sent to him for further analysis.  He determined that they had come from an animal from Pliocene times that was barely three feet tall  and had long slender legs which ended with three toes on each foot. He dubbed the small horse Equus parvulus (now known as Protohippus).

In subsequent expeditions to the the western USA more fossils of horses were found, a mystery in itself as horses were not known in America until they were introduced by the Spanish.

Using the many different types of horse fossil found and relating each discovery to the age of the rocks from which the fossil was extracted, Marsh was able to build up a picture of the evolution of equines.  In a paper published in 1874 in the scientific journal “American Naturalist”, Marsh describes some of the horse fossils he found on an expedition in Wyoming and Utah. One of these skeletons, he named Eohippus, or “the dawn horse.”

By studying the numbers of toes and different degrees of variation, especially the variations in the leg bones Marsh was able to set out a chronological order of horse development from the small browser Eohippus to the modern horse.  Marsh determined the line of descent by examining the metacarpal bones (toe bones) of the different horses.  He compared what he found to the legs of modern horses, and found remnants of digits IV and II along the cannon bones (this is more evident in the forefeet that hind).

The time scale shows the Palaeogene on the left right up to modern times with the domestic horse.  Over millions of years the primitive horses gradually evolved into the larger, faster running animals we know today.

Darwin’s theory of natural selection operates on very small differences that exist between living things in a population.  Any slight mutation or modification that an animal has may give it an advantage over its contemporaries.  This animal is more likely to survive and pass on this trait to its offspring.  As a result of heredity it is likely that these descendants will have the features of the parent and will therefore pass this feature on when they breed too.  In this way, a mutation can become inherent in an entire population over time.

Support for Darwin’s theory was difficult to obtain as central to his argument was that these differences altered organisms over vast amounts of time.  Marsh’s study of the evolution of the horse from a four-toed small browser into the single-toed animal we know today was evidence supporting Darwin’s theory.

Charles Darwin himself, although quite elderly, expressed a desire to travel to America to see Marsh and his collection at Yale.  It was this work that helped popularise the theory of natural selection amongst New World scientists and it is for this ground-breaking study, as well as his work on the dinosaurs that Othniel Charles Marsh is best remembered.

Jellyfish – An example of a “Living Fossil”

Most of us are familiar with jellyfish and have occasionally encountered them as washed up animals as we walk along a shoreline.  Others may have had the unfortunate experience of bumping into one whilst swimming and getting stung.  Depending on the species these stings can be very painful, but apart from the occasional thought about how curious these animals look, few of us rarely consider these animals or indeed recognise them as living fossils, unchanged for over 600 million years.

Jellyfish

Jellyfish belong to a phylum called Cnidaria (pronounced nigh-dare-ee-a).  This phylum consists of a huge range of animals, almost all of them associated with marine environments.  Cnidarians have a central mouth, surrounded by tentacles which possess stinging cells (called nematocysts).  The tentacles are used to catch and disable prey which is then drawn into the central mouth and consumed.  Within the fossil record, by far the most important type of Cnidarians represented are the corals.  These animals may live in colonies or have a solitary habit.  All corals secrete a hard, exoskeleton made up of calcium carbonate and the extant species today are known as scleratinian corals.  These scleratinian corals (solitary or can be linked together sharing a colonial skeleton), evolved relatively recently appearing at around the beginning of the Mesozoic, after the great Permian extinction event.  Older coral fossils found in the Palaeozoic fossil record are either rugose corals (solitary or colonial) or tabulate corals (always found in colonies).  These types of corals both went extinct at the end of the Permian but fossil corals are known to date right back to Ordovician aged sediments.

The Phylum Cnidaria

The phylum Cnidaria also has soft-bodied representatives, these are the sea anemones and jellyfish, scientists believe that these type of animals are even older than the first corals.  Being soft-bodied, jellyfish and sea anemones are very poorly represented in the fossil record, in fact these fossils are extremely rare and the number of fossil specimens found to date does not represent the diversity or indeed the abundance of these animals throughout the Phanerozoic eon (or indeed the Cryptozoic eon).

Jellyfish Fossils

There are some strange, preserved ripples and hollowed out round depressions found in very finely grained, sandstone, Cambrian sediments from around the world.  These are believed to be the fossilised remains of jellyfish.  It is thought that many of the fossils of these animals that we have were formed when mass strandings of jellyfish occurred after a storm.  Having been washed up onto a Cambrian or Ordovician shoreline, the carcases of these animals would not have been eaten by scavengers as there was no significant life on the land during these geological periods.  Some of them may have  been quickly buried and under exceptional conditions, preserved as impressions in the rocks.

It is thought that primitive life such as bacteria and cyanobacteria first evolved as far back as 3.5 billion years ago, but complex multi-celled animals appeared much later, sometime between 700 and 620 million years ago.  Multi-celled animals are termed metazoans (pronounced met-ah-zo-ans) and their appearance in the fossil record marks the ending of the Cryptozoic (hidden life also known as the Precambrian) and the start of the Phanerozoic eon (visible life).

Studying Early Life

Certainly, the fossil evidence for the first metazoans is extremely poor.  All the first complex creatures were entirely soft-bodied but their fossils are evidence of complex multi-celled organisms living in late Precambrian times.  The Ediacaran Hills in the Flinders range of mountains in South Australia was one of the first places studied.  This is why the fossils of such organisms are often referred to as “Ediacarans”.  This was a world dominated by jelly and from fossils found in places as diverse as Siberia and Namibia, scientists are able to calculate that even 620 million years ago, primitive life was abundant and diverse.  The jelly structures of the Ediacarans may have been more robust than those found in jellyfish, after all, jellyfish consist of 95% water, this may explain why Ediacaran animals may have been more readily fossilised than jellyfish.  However, certainly by the Cambrian, jellyfish were very much established and as carnivores would have been perhaps one of the most feared predators around during the early Palaeozoic.

An Illustration of a Jellyfish

Picture credit: Everything Dinosaur

The picture above is of a typical jellyfish with a bell-like structure and trailing tentacles.  Jellyfish are often termed Medusa, a reference to Greek mythology and the Gorgon Medousa who had snakes instead of hair.

To view replicas of fossil animals: Fossil Replica, Dinosaur Models, Prehistoric Animal Models.

Animals as diverse as jellyfish and corals are grouped in the Cnidaria phylum as all these organisms share a central mouth surrounded by stinging tentacles (termed nematocysts).  Scientists believe that corals, sea anemones and jellyfish are all descended from a common ancestor, that had these features.  There are many thousands of species of jellyfish found today.  They live in polar seas as well as the tropics and can be found right through the water column with nektonic forms (animals that live above the sea floor), being found in shallow seas and at extreme depths.  It is thought that there have been hundreds of thousands of species of jellyfish, but only a few specimens have been preserved in the fossil record.  Jellyfish have no definite head structure, no internal organs as such and most have only the most primitive senses.  Jellyfish are very much dependent on sea currents to move them, most species drift with the prevailing current, although a number of Classes can pulse their bells to help them move vertically through the water column.

Cambrian Animals

Although regarded as extremely simple animals when compared to the Chordates for example, during the Late Precambrian and into the Cambrian these types of animals may have been amongst the top predators around at the time.  Jellyfish predating on other organisms may have been a causal factor in the speeding up of evolution (known as the Cambrian explosion), as predator/prey relationships developed.  Our ancestors, those simple animals with a notochord would have fallen victim to the stinging tentacles of the jellyfish.  Perhaps they began to evolve improved senses, a significant head end to house these new senses and stronger groups of paired muscles around a central nervous strip to help them escape from their jellyfish foes.

The next time you see a jellyfish washed up on a beach as you walk along a shoreline, you might well give it a second glance.  It represents a type of animal that has been around for something like 600 million years and its evolution may well have contributed to the evolution of the earliest Chordates and the speeding up of evolution as predator/prey relationships developed.  Jellyfish can certainly be described as “living fossils”.