Researchers from Liverpool John Moores University have developed a new and innovative approach to interpreting sauropod trackways enabling them to calculate their gaits (the order in which the animal moved its four limbs to progress). Jens Lallensack and his colleague Peter Falkingham discovered that the placement of tracks relative to each other in a sauropod trackway changes in a consistent way when the animal changes its velocity (either speeding up or slowing down). Using this technique, subsequently verified by analysing the gaits of living animals such as dogs, horses, a camel and an elephant, the scientists have concluded that sauropods walked more like hippos than elephants.

A picture of the sauropod trackway (Plagne, France). Picture credit: P. Dumas/Centre National de la Recherche Scientifique.

Picture credit: P. Dumas/Centre National de la Recherche Scientifique.

Quadruped Locomotion

Four-footed animals (quadrupeds), may use different gaits such as trots, walks, and pace gaits. In a trot, one diagonal limb pair (e.g. hind right and front left) moves together, followed by the other limb pair. Many mammals use trots at faster gaits, but reptiles also use trots at slow speeds. In a pace gait, in contrast, the limbs on one side of the body (e.g. hind right and fore right) move together in a similar way as the locomotion of a camel.

In-between these extremes is the single foot gait, in which the time lag between fore and hind feet is equal – a good example of this type of locomotion is the movement of horses.

The movements of living animals can be observed, direct observation of extinct animals such as huge, long-necked, long-tailed sauropod dinosaurs is not possible, but data can be obtained by careful study of their fossilised prints and trackways.

Picture credit: Liverpool John Moores University

Examining Sauropod Tracksites

Liverpool John Moores University researchers Jens Lallensack and Peter Falkingham identified that the placement of an animal’s feet changes in a predictable and consistent way when the animal’s velocity changes. If a trackway is long enough and shows variation in stride length (indicating a change of speed), it is possible to calculate gaits and to gain an insight into how extinct animals moved.

Their predictions were confirmed in an analysis of the gaits of different types of living animal, including elephants, thanks to the help from locomotion expert Professor John Hutchinson (Royal Veterinary College, London), who provided elephant locomotion data. These new analytical methods were used to plot the limb movements along three sauropod trackways from the Lower Cretaceous De Queen Formation (Arkansas, USA). Although it is not possible to identify specific sauropod species (ichnospecies) from the De Queen Formation (Albian fauna stage) tracks, these trace fossils represent large, sauropod trackmakers (median average hind foot length 70-85 cm and maximum stride length 3.42 metres).

Commenting on the outcome of their findings, reported in the journal “Current Biology”, Dr Falkingham stated:

“Many researchers assumed that sauropods walked like elephants, with which they share many similarities, but that doesn’t appear to be the case.”

Researchers have found a way to identify the gait of sauropods by studying their tracks. Picture credit: Liverpool John Moores University.

Picture credit: Liverpool John Moores University

Sauropod Dinosaurs Compared to Elephants

As elephants are the largest living terrestrial animals alive today, it had been suggested that their locomotion was an appropriate analogy for the movement of sauropod dinosaurs. Elephants use a gait intermediate between the pace gait and the singlefoot, i.e. the two limbs on the same body side tend to swing together. The gait analysis, in the current study by contrast, revealed that sauropods instead employed a gait intermediate between the singlefoot and a trot: the opposite-side limbs tend to swing together.

Based on this data, sauropod dinosaurs had a similar gait to hippos.

To Sway or Not to Sway

If sauropods moved very differently compared to the largest land animals alive today, this suggests that these two types of animal with large body sizes evolved different solutions to locomotion. Sauropods, even the titanosaurs known for their narrower trackways when compared to other types of sauropod such as diplodocids and dicraeosaurids, have a much broader stance than elephants. Elephants place one foot almost directly in front of another producing surprisingly narrow tracks for such large animals. Sauropod trackways, in contrast, are much broader. Their particular gait allowed sauropods to have at least one foot on the ground on both the left and right sides of the body at all times, preventing swaying from side to side.

The enormous body of the titanosaur dwarfs visitors. Patagotitan mayorum skeletal reconstruction. Titanosaurs are known for their narrower tracks when compared to other types of sauropod but as many were much bigger than elephants, elephants do not make a good analogy for describing the gaits of titanosaurs or of sauropods generally. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Everything Dinosaur acknowledges the assistance of a media release from Liverpool John Moores University in the compilation of this article.

Lead author of the scientific paper Dr Jens Lallensack added:

“Sauropods chose a gait that maximised stability but still allowed for efficient walking”.

The scientific paper: “A new method to calculate limb phase from trackways reveals gaits of sauropod dinosaurs” by Jens N. Lallensack, Peter L. Falkingham published in Current Biology.

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So, the scientific paper is out and theropod feathers are about to be ruffled. The iconic Tyrannosaurus rex might not be just one species, but actually three. That is the conclusion reached by researchers Gregory S. Paul, Scott Persons and Jay Van Raalte – all highly respected scientists, but already other academics have challenged their findings.

Writing in the academic journal “Evolutionary Biology”, two new Tyrannosaurus species are proposed, a geologically older, robust form newly named Tyrannosaurus imperator that was followed by two further species the already named Tyrannosaurus rex, also a robust tyrannosaur and a contemporaneous gracile form which has been named Tyrannosaurus regina.

The spectacular Titus the T. rex exhibit at Wollaton Hall. PIcture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The Tyrannosaurus Controversy

The fearsome, apex predator Tyrannosaurus rex might be synonymous with the famous Hell Creek Formation, but Tyrannosaurus fossils have also been found in many other Upper Cretaceous deposits (Maastrichtian stage). For example, T. rex fossils or at least indeterminate Tyrannosaurus material is associated with nine other North American geological formations.

T. rex fossils have been found in exposures of the Scollard Formation of south-western Alberta the Frenchman Formation of southern Saskatchewan and south-eastern Alberta. This suggests that this large theropod roamed northern areas of Laramidia. Tyrannosaurus fossils from the Laramie Formation exposures in Colorado have been assigned to Tyrannosaurus rex. T. rex fossil material has been reported from much further south, from the Javelina Formation of Texas.

With only one species of Tyrannosaurus (T. rex), the fossil evidence as classified so far indicates that the “tyrant lizard king” had a huge geographical distribution, virtually the entire ancient landmass of Laramidia.

Furthermore, these deposits represent vast amounts of geological time. The Hell Creek Formation is believed to have been formed over two million years and as scientists have now concluded that other iconic taxa such as Triceratops evolved over this time period into new species, then surely T. rex would have been subject to the same evolutionary pressures.

A reconstruction of the skeleton of “Scotty” the T. rex. The fossils come from the Frenchman Formation of Saskatchewan (Canada) and one of the authors of the scientific paper published in the journal the Anatomical Record was Scott Persons who is a co-author of the new paper describing three Tyrannosaurus taxa. Picture credit: Amanda Kelley.

Picture credit: Amanda Kelley.

Analysis of Limb Bones (Femora)

A total of thirty-seven fossil specimens were studied by the researchers. Two-thirds of these had femora (thigh bones) associated with them and the scientists found differences in the thickness and robustness of these bones, that were unlikely a result of individual variation within a single species. In the sample studied, Gregory S. Paul and his colleagues found greater variation in femur robustness in the T. rex thigh bone material than in the whole of the other tyrannosaurid femora material known from the preceding ten million years.

The team discounted size variations based on maturity, ontogeny (growth pattern) and the age of the Tyrannosaurus when it died. Robust forms and more gracile forms of T. rex have been known for some years. Some palaeontologists have speculated that the smaller, more slender bones of some T. rex specimens compared to the more robust femora of other specimens might be explained as differences in the sexes.

If robust forms represent females, and gracile forms males, then it would be expected that the fossil record would show roughly even numbers of these bone types. However, the research team point out an uneven ratio of robust bones to gracile bones and as such they discount the differences as sexual variation.

In addition, the team report that gracile bones are only found in higher layers of sediment. These bones are geologically much younger than other more robust T. rex bones associated with lower layers.

Which Tyrannosaurus species? A cast of the T. rex specimen known as “Stan” (BHI 3033), but researchers propose that there were actually three species of Tyrannosaurus present in the Late Cretaceous of North America. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

Differences in Tooth Count

The scientists also commented on differences in tooth counts associated with Tyrannosaurus lower jaws (the dentary). Tyrannosaurus imperator (the earliest Tyrannosaurus species) had two small incisors in each dentary. Whilst the later species (T. regina and T. rex) had only one small incisor in each dentary.

The research team identified differences in the number of small incisor-like teeth in the lower jaw which they concluded was further evidence of the T. rex fossil material actually representing a trio of Tyrannosaurus species. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The researchers concede that they cannot rule out other explanations for their findings. Several palaeontologists have challenged the paper, stating that the variations seen in the fossils could be explained by factors such as individual variation amongst individuals of a single species. Like many dinosaurs, Tyrannosaurus rex changed radically as it grew and matured, this aspect of dinosaur taxonomy is going to be debated for a considerable time to come.

For fans of dinosaur models, does this mean that collectors will have to reassess their Tyrannosaurus rex models?

Which Tyrannosaurus species are you? A newly published scientific paper proposes three Tyrannosaurus species. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The scientific paper: “The Tyrant Lizard King, Queen and Emperor: Multiple Lines of Morphological and Stratigraphic Evidence Support Subtle Evolution and Probable Speciation Within the North American Genus Tyrannosaurus” by Gregory S. Paul, W. Scott Persons IV and Jay Van Raalte published in Evolutionary Biology.

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Researchers have conducted an extensive review of injured trilobites and disarticulated pieces of trilobite exoskeleton from the Emu Bay Shale Konservat-Lagerstätte on Kangaroo Island (South Australia). They conclude that the injuries caused to Redlichia trilobites were from attacks by other members of this genus. This is the oldest record of cannibalism recorded in the fossil record to date.

CollectA Redlichia rex trilobite model.

The picture (above) shows the CollectA Redlichia rex trilobite model.

To view this range of prehistoric animal figures: CollectA Prehistoric Life Models.

A Study of Redlichia Fossils from the Emu Bay Shale

The Cambrian explosion represents the rapid emergence of complex marine ecosystems and a huge burst of evolutionary activity that led to the establishment of virtually all the Animalia phyla recognised today. Whilst many palaeontologists do not like the phrase “explosion” as it implies a sudden event, opting instead to use the term “Cambrian radiation” to describe the emergence in the fossil record of abundant preserved shells and exoskeletons, the reasons for this change in the Earth’s ecosystems remains controversial.

It is thought that one of the main drivers of this evolutionary event was the development of predator/prey interactions. The proliferation of biomineralised exoskeletons and shells was a response to the evolution of the first predators capable of breaking through these defences.

Writing in the academic journal Palaeogeography, Paleoclimatology, Palaeoecology, researchers from the University of New England, (Armidale, New South Wales), Uppsala University (Sweden), the University of Adelaide (South Australia), the South Australian Museum and Cambridge University conducted an analysis of 38 injured specimens representing two large trilobite species from the 515-million-year-old Emu Bay Shale deposits (Redlichia takooensis and Redlichia rex).

Healed but scarred injuries on a fossil specimen of Redlichia rex. The red squares indicate areas of damage possibly caused by an attack by another Redlichia. Picture credit: Bicknell et al (Palaeogeography, Paleoclimatology, Palaeoecology).

Picture credit: Bicknell et al (Palaeogeography, Paleoclimatology, Palaeoecology)

Studying a Giant Trilobite

The team concluded that that the injuries they documented were caused by a durophagous (consuming hard parts of the skeleton) predator.

Specimens of both species show that most injuries are located on the posterior portion of the thorax, indicating that predators most likely attacked from behind or that intended prey presented the posterior portion of their trunk to the attacker when threatened or attempting to flee. Previous studies had indicated that Cambrian trilobites exhibit most injuries to their right side. This study refutes this, arguing there is no evidence for a preference for attacking either the right or left side of intended prey.

The injured specimens typically represent some of the largest individuals known for the Redlichia taxa. This suggests that bigger trilobites were more successful in fighting off an attack and recovering from their injuries. Smaller individuals were probably completely consumed and therefore the likelihood of finding evidence of an attack on a smaller fossil specimen was greatly reduced.

A near complete specimen of the large Cambrian trilobite Redlichia rex. Picture credit: University of Adelaide.

Picture credit: University of Adelaide

Redlichia rex

To read Everything Dinosaur’s blog post about the discovery of Redlichia rex: “King of the Trilobites” Discovered in South Australia.

The research team concludes that the scarred Emu Bay Shale trilobites represent the oldest record of cannibalism known to science.

The scientific paper: “Cambrian carnage: Trilobite predator-prey interactions in the Emu Bay Shale of South Australia” by Russell D. C. Bicknell, James D. Holmes, Stephen Pates, Diego C. García-Bellido and John R. Paterson published in Palaeogeography, Paleoclimatology, Palaeoecology.

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