Tag: Trilobites

Paleontology News for October 2019.

There have been some important fossil discoveries lately that span nearly the entire time period of multi-cellular life on Earth. I think I’ll start with the earliest and work my way forward in time.

We usually think of complex social behavior as being a recent development in the history of life. After all we have the most complex societies of any species and we’re one of the youngest of Earth’s creatures, right?

Humans have been social as long as we’ve been Human. (Credit: History.com)

Well it is worth remembering that some insects like ants have been living together in complex hives for around 200 million years and we now know that many species of dinosaurs traveled in herds for protection. So obviously some forms of social behavior predate human beings by quite a long time.

However some animals have been social a lot longer than we have. (Credit: Phys.org)

Now a new series of fossils from Morocco is providing evidence that social behavior existed as far back as the lower Ordovician period, about 480 million years ago. The fossils shown a large number of individuals of the trilobite species Ampyx priscus arranged in a line with the front end of their bodies all pointing in the same direction. The clear indication is that these creatures were moving together in a very orderly line, a behavior requiring considerable neural and sensory ability.

Trilobites of the species A pricus moving together in a line 480 MYA. (Credit: The New York Times)

The reason why these trilobites were moving together in a line will probably never be known for certain but the fact is that arthropod species like spiny lobsters, ants and even caterpillars are known to behave in a very similar fashion today. These trilobites provide another example of how old doesn’t necessarily imply simple or primitive. 

One of the critical events in the history of life on this planet has to be the moment when the first vertebrate animal, a fish, climbed out of the water and gingerly set foot on the land. All land dwelling bony animals, all amphibians, reptiles, including the dinosaurs, birds and mammals, including you and I are beholden to that ancient creature.

An artists illustration of what the first vertebrate to step onto land may have looked like. (Credit: Phys.org)

So it’s not surprising that paleontologists are keenly interested in learning as much as they can about those early land vertebrates. The recent discovery of a new species of tetrapod, that is a four-limbed animal, gives an insight into what kind of creature may have been the first to make that historic step. Discovered in the Sosnogorsk formation along the banks of the Izhma River in the former Soviet Republic of Komi the animal has been dated to about 372 million years ago during the Devonian Period.

Artists impression of the recently discovered Terapod from the Komi Republic. (Credit: Daily Mail)

Named Parmastega aelidae the animal is a strange mixture of both fish and land animal characteristics. For example the placement of its eyes on the top of a flat skull clearly indicates an animal that is watching what is going on above the waterline. At the same time however the animal’s shoulder girdle is made of partially cartilaginous bones, making those bones too weak to be able to support a land animal. So P aelidae may have been a water animal whose prey lived out of the water. A modern example would be a crocodile and indeed the long snout filled with sharp teeth of P aelidae strongly resembles that of a crocodile.

A comparison of the skull of the terapod (r) to that of a modern crocodile (l). (Credit: Daily Mail)
A fossil jawbone of the terapod showing numerous sharp teeth. (Credit: Phys.org)

The discovery of such fossils as P aelidae gives us further knowledge in our quest to understand how our ancestors evolved to become the dominant kind of life on land.

Another critical moment in the history of life on Earth surely came after the asteroid collision that led to the extinction of the dinosaurs along with 75% of all species of life. The questions of how quickly did life recover from that disaster, and what kind of animals became dominant now that the dinosaurs were gone are key to our understanding the natural world today? Paleontologists know that in order to answer these questions they need to find fossil sites from the time immediately after the asteroid strike.

The asteroid that killed the dinosaurs landed in the Yucatan peninsula of Mexico forming a crater 300 km wide. (Credit: Research.utexas.edu)

Just such a fossil site was recently discovered by paleontologists Tyler Lyson and Ian Miller of the Denver Museum of Nature and Science just outside the nearby city of Colorado Springs. The location, known as Corral Bluff is yielding a treasure trove of fossils from a time less than a million years after the asteroid strike. The finds include over 1,000 mammal fossils from 16 different species along with reptiles, birds and 6,000 plant fossils. The most important finds discovered by the researchers consisted of dozens of delicate mammalian skulls.

Doctors Lyson (r) and Miller (l) searching for mammal fossils at Corral Bluff. (Credit: KPBS)

While the fossils are still being studied a few conclusions can be reached. During the reign of the dinosaurs mammals remained small, rare and nocturnal creatures no larger than a squirrel, about one kilogram maximum. The fossils obtained from Corral Bluff however show that is less than a million after the dinosaurs were gone mammals had already greatly increased in both size and number with one of the species discovered estimated as having a mass more than 50 kg.

Artists impression of one of the little mammals that repopulated the world after the extinction of the dinosaurs. (Credit: USA Today)
Some of the mammal fossils found at Corral Bluff. (Credit: Reuters)

The fossils from Corral Bluffs give witness to how quickly the mammals were evolving to fill up the ecological niches left vacant by the extinction of the dinosaurs. At the same time the paleontologists are making other discoveries as well, among them the remains of the earliest known legume, a pea plant that might very well have provided high protein food for some of the growing population of mammals.

The history of life on Earth is both long and complex but paleontologists don’t mind that at all. It just mean that there are many more fascinating discoveries waiting to be made.

Paleontology News for August 2019: Special Trilobite edition

A couple of new discoveries have recently been published about the ancient and extinct sea creatures known as trilobites so I thought that this would be a good opportunity to discuss these fascinating creatures in some detail. I’ll begin with a few general facts about trilobites.

The Trilobite Phacops rana, the state fossil of Pennsylvania (Credit: Flickr)

First of all trilobites are members of the phylum arthropoda, the jointed limbed animals that include crustaceans, insects and spiders. In fact trilobites are generally recognized as the earliest members of that group of animals with fossils going back as far as 540 Million years ago. Trilobites not only evolved a long time ago they also went extinct a long time ago. The last trilobites died in the Permian extinction event about 250 million years ago, see my posts of 16 February 2019 and 2 June 2018. That’s several million years before the first dinosaur ever evolved!

Because trilobites lasted so long, and their exoskeleton fossilized so easily paleontologists have been able to identify more than 50,000 different species. During their almost 300 million year existence trilobites evolved to occupy nearly all of the ecological niches occupied by modern marine arthropods including that of scavenger, predator, filter feeder and even a swimming species that fed off of the plankton near the surface.

Looking at the figure below, you can see that Anatomically trilobites are defined by their broadly oval shape and the three main sections of their body going side to side, right pleural lobe, axial lobe, which is often raised, and left pleural lobe. Many people incorrectly think that the three lobes of the name trilobite refer to the three sections going front to back with the cephalon (head), thorax and pygidium (tail). (I did when I was young!)

The main anatomic parts of a Trilobite (Credit: Wikipedia)

Early trilobites, such as Olenellus from the Cambrian period seen below, had a cephalon that was much larger than their pygidium. As trilobites evolved however their tails grew to almost the same size and shape as their head as seen below in Phacops from the Devonian period. This adaptation allowed later trilobites to roll up into a protective ball in much the same way as a modern armadillo does. Fossils of such rolled trilobites are often found in Devonian, Mississippian and Pennsylvanian rocks.

The Cambrian Trilobite Olenellus fremonti (Credit: American Museum of Natural History)
An enrolled specimen of Phacops rana (Credit: Fine Art America)

With a history of 300 million years and at least 50,000 species trilobites varied considerably in their particulars, especially size and ornamentation, see images below. The largest known trilobites are from the genus Isotelus of the Ordovician period some 450 million years ago specimens of which are as long as a meter. There are a number of candidates for the smallest member of the group but many small trilobites were no larger than a pea.

A beautiful specimen of Isotelus maximum (Credit: Geoclassics)
A species of Trilobite ornamented with spines, presumably for protection (Credit: Tack Raccoons)
Another spiny trilobite (Credit: Catawiki)

For the most part however trilobites remained rather conservative in their basic body plan. This may have contributed to their eventual extinction as competitors such as crustaceans and fish evolved structures like jaws and manipulating pincers that allowed them to outperform the trilobites.

As fossils a complete trilobite is fairly rare, one or two can represent a good day’s hunting. On the other hand recognizable pieces of trilobites are very common. The reason for this is that like all arthropods trilobites had to molt in order to grow. So a single live trilobite could in the course of its life produce many empty shells that would quickly break up to produce a lot of trilobite pieces.

Fragments of many fossils including a Trilobite tail right in the middle (Credit: The fissil forum)

A couple of recent studies have further increased our knowledge of these ancient creatures. The first concerns the discovery of a new species of trilobite from Australia that has been named Redlichia rex. The name is a reference to the well known dinosaur Tyrannosaurus rex because of R rex’s large size, 30cm, and leg spines that could be used to crush the trilobites food. The fossils of R rex come from the Emu bay shale of Australia’s Kangaroo island and are exceptionally well preserved revealing details of even the animal’s delicate antenna, see image below.

Artists impression of Redlichia rex along with a fossil specimen (Credit: Species new to Science)

Because of R rex’s large size and crushing legs it is believed that the trilobite was a predator, and perhaps even a cannibal. Specimens of R rex have been found with healed injuries so the question is, what could have preyed on these large, for the Cambrian period, animals. While there are several possibilities it has also been suggested that R rex may have preyed on its own kind!

The second discovery also comes from a fossil site that is well known for exceptionally well-preserved specimens, the Guanshan location in eastern Yunnan province China. In this study it’s not a new species of trilobite that’s been announced, it’s the discovery of the earliest known evidence for a stomach and digestive system!

Using some of the best specimens of the trilobite Palaeolenus lanteroisi, see image below, researchers from the American Museum of Natural History in New York and the Early Life Institute at Northwest University in Xi’an China actually succeeded in ‘dissecting’ the fossils. That is, they have managed to carefully remove a portion of the upper layers of the fossil in order to examine the petrified remains of the animal’s internal organs.

Examples of dissections performed on fossils of long dead Trilobites (Credit: Hopkins, Chen, Hu and Zhang)

What they found was a well-developed digestive system with a large stomach or ‘crop’ in its cephalon. That’s right trilobites appear to have had their stomach’s in their heads not far from their mouths!  A long alimentary canal then went through the length of the rest of the trilobite’s body to an anus at the animal’s posterior. Trilobites have a special place in the history of life, as one of the first complex, multi-cellular forms of animal they dominated the ancient Cambrian and Ordovician seas. Thereafter they gradually declined, finally becoming extinct during the Permian catastrophe. Nowadays for any fossil hunter a good trilobite specimen will always be a small prize to be treasured.