Earliest Ancestor of Terrestrial Herbivores Discovered

When watching a wildlife documentary it is easy to overlook some fundamental truths about today’s complex ecosystems with their multi-layered food chains.  Lions attacking zebras on the Serengeti, caribou grazing on Arctic lichens and mosses, foxes chasing after rabbits for instance.  We have predators which prey on primary consumers of plant materials, the predator/prey relationship.  However, such complex ecosystems have not been present throughout the history of land vertebrates, back in the days of the very first land animals with backbones ecosystems were populated by carnivores, it seems the ability to digest tough plant materials such as cellulose had to evolve and that herbivory has its roots amongst the meat-eaters.

Fossil Find

Newly published research into the fossil of a reptile discovered in Kansas, by scientists from the University of Toronto Mississauga in collaboration with researchers from Museum für Naturkunde and Humboldt-University (Berlin), had shed light on the evolutionary processes that led to the transition of carnivores into land herbivores.  The specimen which consists of some cranial material from the back of the skull, the backbone, ribs, elements from the pelvic girdle and the right rear limb was collected by Dr Larry Martin, the curator of the Dyke Museum of Natural History, University of Kansas.  Dr Martin was exploring a highly fossiliferous location known as Hamilton Quarry in south-eastern Kansas.  Strata laid down at this site were formed in a tidal environment with changing sea levels.

A diverse variety of fauna and flora has been preserved including many fish species, some amphibians and a few, rare reptiles.   The twenty centimetre long specimen was poorly preserved with those bones exposed in the matrix showing signs of erosion.  To preserve the fossil and to allow it to be properly studied, the fossil was loaned to the Biology Department at the University of Toronto. It was encased in epoxy resin to stabilise it and to permit further cleaning and preparation.  Unfortunately, the acidic solution used to clean the fossil and to reveal important anatomical details dissolved the fine, conical teeth that had been preserved in the jaw.

Photograph and Illustration of the Fossil Material (KUVP 9616b)

Scale bar = 1 cm

Picture credit: PLOS One/Reisz RR, Fröbisch J.

The skull material is located in the top right of the image, with the hind limb and the pelvic bones located top left.  The fossil material is believed to represent a juvenile.

Eocasea martini

The little reptile has been named Eocasea martini.  The genus name means “dawn or first Caseidae”, the clade of synapsids that this animal belonged to.  The specific or trivial name honours Dr Larry Martin.  Caseids are an ancient group of terrestrial vertebrates that form part of a larger group known as synapsids.  Synapsids represent a diverse and unusual group of vertebrates, that include the ancestors of modern reptiles and all mammals, plus those reptiles that have closer affinities to Mammalia than they do to extant reptiles, the so-called mammal-like reptiles.  The fearsome Dimetrodon is an example of a synapsid along with the tusked dicynodonts such as Placerias and the ancestors of today’s mammals.

An Illustration of Eocasea martini

Ancient fossil shed light on the earliest ancestors of land herbivores.

Picture credit: Danielle Dufault

A “Ghost Lineage”

The fossil has been dated to around 300 million years ago, (Upper Pennsylvanian of the Carboniferous).  The discovery helps to close a twenty million year gap between E. martini and the next oldest caseid known from the fossil record.  When scientists map the evolution of closely related organisms and find large gaps in the known fossil material, leading back to a very early ancestral form, as in this case, it is referred to as a “ghost lineage”.

Commenting on the significance of the research, Professor Robert Reisz of the Department of Biology at the University of Toronto stated:

“The evolution of herbivory was revolutionary to life on land because it meant terrestrial vertebrates could directly access the vast resources provided by terrestrial plants.  These herbivores in turn became a major food resource for large land predators.”

One of the authors of the paper published in the on line scientific journal PLOS One, Jörg Fröbisch (Museum für Naturkunde and Humboldt-University in Berlin), added:

“Eocasea is one of the oldest relatives of modern mammals and closes a gap of about twenty million years to the next youngest members of the caseid family.  This shows that caseid synapsids were much more ancient than previously documented in the fossil record.”

Analysis of the fossil material indicates that Eocasea martini was a basal member of the caseids, a carnivore feeding on small animals and insects but fossils of caseids dating from the Permian provide clear evidence that terrestrial herbivores evolved from this group’s small, carnivorous members, animals such as Eocasea.

Evidence for Herbivory

The evolution of the ability to consume, process and digest tough plant material is regarded by many scientists as one of the most important developments in the evolution of land living animals with backbones.  Adapting to a diet largely consisting of vegetation requires some modifications to the body plan of an animal, these adaptations can be observed by studying the fossil bones of long extinct creatures.  For example, in order to cope with hard to digest cellulose, the digestive tract tends to get much bigger and a larger, wider body is required to support a bigger gut.  A longer or broader trunk region can be seen in preserved fossils when their skeletons are compared to those of similar sized carnivores.

The body cavity becomes modified to house a bigger digestive tract, which in turn has to house a huge number of symbiotic bacteria to permit the fermentation and and breakdown of plant cells.  Palaeontologists, can therefore identify Palaeozoic herbivores because their rib cages are typically much wider with a bigger capacity than closely related insectivores and carnivores.

 The Wide Body of Edaphosaurus (Herbivorous Pelycosaur)

Wide-bodied Edaphosaurus a herbivorous sail-backed reptile.

Picture credit: Everything Dinosaur

The image (above) shows a Bullyland Edaphosaurus figure.  To view the range of Bullyland “Prehistoric World” figures including the Edaphosaurus (whilst stocks last): Bullyland “Prehistoric World” Models.

The researchers conclude that Eocasea is one of the first animals to have started the process that would result in the establishment of modern ecosystems, with many plant-eaters supporting fewer types of predator – the start of more complex food chains.

Intriguingly, the research team went onto identify that the ability to digest and process vegetation was not just established in the lineage that includes the caseids, it arose independently at least five times more, including twice in the Reptilia.

Professor Reisz added:

“When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed.  Multiple groups kept re-evolving the same herbivorous traits.”

The five groups developed the novel ability to live off plants in staggered bursts with synapsids such as Eocasea preceding reptiles by nearly 30 million years.  This shows that herbivory as a feeding strategy evolved first amongst those synapsids that are the ancestors of the Mammalia.  Our ancestors evolved a taste for plants long before that branch of the terrestrial vertebrates that includes extant reptiles, the dinosaurs and Aves (birds).

Moving onto a plant-eating diet, resulted in a dramatic change in the size of early herbivores over the duration of the Permian geological period.  Four of the five groups showed that as the Permian progressed so herbivores got bigger and bigger.  The age of the super-sized grazer had dawned.  Professor Reisz observed that the caseids showed the most extreme examples of size increase.  The earliest member of the group, the diminutive Eocasea martini probably weighed less than two kilogrammes when fully grown.  Later caseids weighed more than two tonnes, one of the largest known being the enormous, fat bellied Cotylorhynchus whose fossils have been found in the United States.

The research team have stated that the study of Eocasea has led to more questions being asked then answers found.  For example, why didn’t the ability to digest plant material evolve earlier on?  Why did herbivory evolve independently in at least five lineages of vertebrates?

Perhaps there are fossils out there which will shed further light on these mysteries.

Parahupehsuchus longus – Armoured Marine Reptile with a “Corset”

As life on Earth recovered from the devastating End Permian mass extinction event which took place some 250 million years ago, it seems that a myriad of strange and bizarre vertebrates evolved to take advantage of vacant niches in ecosystems that had arisen due to the extinction of so many different types of organism.  One of the strangest marine creatures known to science has just been described in the on line scientific journal PLOS One.  It seems that as environments and ecosystems recovered in the Early Triassic, so marine tetrapods evolving the capability to eat other marine tetrapods came about in earnest and the first tetrapod apex predators of the sea appeared.

Marine Tetrapods

This led to the evolution of body armour and other forms of protection in smaller marine tetrapods that were now the potential prey.  Step forward the bizarre Parahupehsuchus longus, around a metre long, marine reptile that evolved a bony tube that completely surrounded its body wall, like a sort of armoured corset.  Just like a corset, breathing movements and body movements may have been restricted, but the primary role for this unusual pseudo carapace was probably protection against attacks from a much larger predatory marine reptile that shared P. longus’s watery world.

Parahupehsuchus longus

Back in 2011, scientists from the Wuhan Centre of China Geological Survey undertook a field excavation in Yuan’an County, Hubei Province, (east central China), to find Early Triassic marine reptile fossils.  The strata in this part of China represents exposures of marine sediments laid down in a shallow tropical sea around 248 million years ago (Jialingjiang Formation).  The area had been mapped and studied since the late 1950’s and a number of marine reptile genera unique to this part of the world had already been named and described.  However, when Chinese scientists first studied these fossil rich deposits, the strata was believed to be younger, dated to the Anisian faunal stage of the Middle Triassic.

Triassic Marine Strata

The rocks at this location were thought to be roughly the same age as Triassic marine strata found in the provinces of Yunnan and Guizhou (south-western China).  More recent studies have assigned the sediments exposed around Yuan’an County to be up to three million years older than most of the sedimentary rocks bearing marine reptile fossils in Yunnan and Guizhou.  The rocks which entombed Parahupehsuchus longus date to around 248 million years ago (Olenikian faunal stage of the Lower Triassic).

This is significant because the vertebrate fossils found in Yuan’an County are much closer to the End Permian extinction event than those from south-western China, the ecosystem represented is one that is at an earlier stage of recovery from the most devastating extinction event known.

Parahupehsuchus longus (Holotype Material WGSC 26005)

Scale bar = 10cm.

Picture credit: PLOS One

In the diagram above the strange bony carapace-like structure surrounding the body of this new species of marine reptile can be clearly made out.  The labels in red have been added by Everything Dinosaur to help readers gain a better understanding as to the layout of the fossil as the skull and much of the tail is missing.

Ten Marine Reptile Specimens

The research team identified more than ten marine reptile specimens, one partially complete fossil represents this new genus.  Most of the marine reptile specimens discovered represented animals of around a metre in length, but one fossil suggests a marine reptile of around 4 metres in length.  Although not formally described yet, the skull is robust and the teeth that of a meat-eater.  It has been suggested that this reptile was the apex predator.  Parahupehsuchus evolved its corset-like body to resist attacks from this much larger marine reptile.

Surprisingly, very few fish fossils have been found in the strata that contains the marine reptile fossils.  This might be a reflection of fossil preservation bias, but if there were few fish species present and this may not be that surprising as something like 57% of all marine families died out at the end of the Permian, it seems that marine reptiles evolved to attack and hunt other marine reptiles.  The corset of Parahupehsuchus may have evolved as a response to the predatory pressure.

The Order Hupehsuchia

Parahupehsuchus has been assigned to the Hupehsuchia Order of marine reptiles.  This Order currently consists of just three genera, all of which are found in the Lower Triassic sediments of Hubei Province.  The first named and described was Nanchangosaurus, then in 1972 a near complete specimen of a new type of marine reptile that had been discovered was named this was Hupehsuchus.  Palaeontologists consider that Parahupehsuchus was closely related to Hupehsuchus.

Parahupehsuchus pronounced “par-rah-hoop-pay-sook-cus” means beside Hupehsuchus which refers to the taxonomic relationship between these two genera.  The term Hupehsuchus is derived from Hupeh, an alternative spelling for Hubei Province and the Greek word for crocodile.

Hupehsuchus nanchangensis  Fossil Material (specimen number WGSC 26004)

Scale bar = 10cm.

 Picture credit: PLOS One

The more complete specimen (diagram B) above, provides scientists with clues to how Parahupehsuchus might have looked.  It may have had a long narrow, toothless snout like its close relative Hupehsuchus.  It was probably capable of moving around on land as well as being adapted to a marine environment and although the tail is missing in the holotype specimen it is likely that the tail was quite powerful and Parahupehsuchus propelled itself through the water with sideways movements of its tail, in a similar to modern crocodilians today.

Toothless Jaw

If indeed Parahupehsuchus had a toothless jaw, then it may have eaten soft-bodied creatures such as squid.  This bizarre marine reptile remains unique amongst vertebrates for the strange configuration of its trunk.

Its body is completely surrounded by a bony tube, around fifty centimetres long and nearly seven centimetres deep.  The tube is made up of overlapping ribs and gastralia (belly ribs).  This tube and the presence of dermal armour on the dorsal surface of the skeleton (back) have been interpreted as defensive features to withstand the bites of larger marine reptiles.  This is evidence that by the Early Triassic, ecosystems had recovered enough from the End Permian extinction event to permit the establishment of complex marine tetrapod food chains dominated by large apex vertebrate predators.

The Front Dorsal Region of Parahupehsuchus longus

White scale bar shown on actual fossil material = 1cm.

Picture credit: PLOS One

The unique corset-like body protection is made up of a combination of fused true ribs, belly ribs (gastralia) and neural spines.

Key

red = dermal armour, scales and ossicles (da)

dark brown = first segment of neural spine (ns1)

dark green = second segment of neural spine (ns2)

grey = ribs (ri)

orange = lateral gastralia (lg)

white = median gastralia (mg)

green = bones of the left forelimb

arf (pink) = anterior rib facet extending from the parapophysis, dia (light brown) = diapophysis of the neural arch, para (yellow) = parapophysis main facet.

Note that ribs and gastralia overlap in a complex manner and the double rib articulation prevents rib motion.  This would have made chest movements difficult for breathing and restricted the body movements to aid swimming and locomotion on land.

Although, the ribs are expanded in a similar way to that of a turtle’s shell, Parahupehsuchus is not closely related to the Chelonia (turtles, tortoises and terrapins).  This might be an example of convergent evolution.

Scientists hope to find more fossils of this strange marine reptile in rocks that make up the Jialingjiang Formation and with further research they intend to build up a more detailed picture of the food chain that is represented by this Lower Triassic fossil material.

For models and replicas of marine reptiles and other creatures: PNSO Age of Dinosaurs Figures and Models.