Atopodentatus unicus from Yunnan Province

The fossils of a bizarre marine reptile with a unique mouth have been discovered in south-western China.  Although its body resembles other types of marine reptile, the skull and the mouth are extremely unusual and nothing like them has been seen before in the fossil record.   A number of scientists have speculated about this strange anatomical arrangement, the upper jaw resembles a vertical slit with fine teeth arranged to form sieve-like structure.  A prehistoric animal that has a “zipper” for an upper jaw.   These adaptations indicate that this three-metre long sea creature evolved to fit a very specialist niche in the marine ecosystem of 245 million years ago.

Marine Reptile Fossils

The animal has been named Atopodentatus unicus, the name translates from the Latin to mean “peculiar teeth of unique shape” and one glance at an illustration of this particular beastie shows why the nomenclature is so appropriate.

An Illustration of A. unicus

Strange Triassic marine reptile.

Picture credit: Nobu Tamura 2014

A Bizarre Creature

This is one of those occasions when the interpretation of the fossil material and a resulting illustration needs to proceed any further discussion so that the reader can gain an impression of just how weird this animal was.

The land that makes up the border between the south-western Chinese provinces of Guizhou and Yunnan is very important to palaeontologists as they try to reconstruct how life on Earth bounced back following the End Permian mass extinction.  The rocks laid down in this region represent Early and Middle Triassic marine faunas, the fine sediments that were deposited at the bottom of a shallow, tropical sea have preserved a wealth of marine reptile fossils, along with fishes and a vast array of invertebrates.

Triassic Marine Diversity

By recording the diversity of life preserved within this series, scientists can see how life on Earth recovered from the mass extinction event that marked the end of the Permian geological period.

The Atopodentatus fossil material was found in  Luoping County (Yunnan Province), the strata in this area has been dated to around 245 million years ago (Anisian faunal stage of the Middle Triassic), a little over five million years since the extinction event that saw an estimated 95% of life on the planet wiped out.  At this time in the Triassic, a number of different types of marine reptile had evolved, all of which were descended from terrestrial ancestors.

Atopodentatus unicus

A large number of ichthyosaur specimens have been discovered, some ichthyosaurs co-existed with Atopodentatus but in younger Triassic rocks (Ladinian to Carnian faunal stages 230 to 225 million years ago), it seems that ichthyosaurs had established themselves as the largest and most important marine reptile group.  The other types of marine reptile that lived alongside Atopodentatus are almost as bizarre.

There are primitive sauropterygians, such as nothosaurs and animals that are ancestors of the much more familiar plesiosaurs and pliosaurs, protorosaurs, partially marine reptiles that were to give rise to the long-necked Tanystropheus and other peculiar archosauriforms.

It seems that this part of the world was a “melting pot” for marine reptile evolution with some groups, surviving into the Jurassic, with other types completely dying out within a few million years.

A Specimen of the Sauropterygian Nothosaur called Keichousaurus

 These rocks have been explored and mapped for more than ten years, by an international team of scientists. The report on the strange Atopodentatus has been published in the academic journal “Naturwissenschaften”, the study into A. unicus was conducted by scientists from the Canadian Museum of Nature, the Wuhan Institute of Geology and Mineral Resources as well as the Chinese Academy of Sciences.

A Newly Described Creature

Dr Xiao-Chun Wu (Canadian Museum of Nature) and his colleagues named the new prehistoric creature Atopodentatus unicus and suggest it belonged to a Superorder of reptiles called the sauropterygians.  Staff from Everything Dinosaur, having reviewed the fossil bones have suggested it might be a type of Nothosaur, but one with a very specialised feeding method.  The body of the animal was quite long, the neck short and the skull much deeper than other similar sized Triassic marine creatures.

Most nothosaurs were fish-eaters, but the dentition and the morphology of the jaws suggest that this newly discovered reptile had a weak bite and teeth unsuitable for tackling struggling prey.

Atopodentatus unicus Mouth

On each side of the mouth, A. unicus had around 35 small, pointed teeth in the front of the upper jaw.  There were around 140 similarly shaped teeth in the rest of the upper jaw, with at least 100 located in the horizontal portion with the remainder located in the vertical, zipper-like portion of the top jaw.  There were nearly 200 teeth located in the lower jaw, over half of which were in the horizontal portion with the remainder located in the shovel-headed front part.

All the teeth were covered in enamel, indicating even wear across all parts of the crown of the tooth, but the teeth do not look very worn, perhaps this hints at the sort of prey this animal specialised in catching.  Whatever it was eating, it probably had this food resource all to itself amongst the vertebrates as no other creature found to date has anything approaching the jaw anatomy of this marine reptile.

The Prepared Fossils (Atopodentatus unicus)

Bizarre Triassic marine reptile.

Picture credit: Long Cheng/Wuhan Institute of Geology and Mineral Resources

The picture shows the long, serpentine body of the reptile with the deep, shovel-shaped skull shown as an inset.  Note the well developed limbs, particularly the large humerus.  This prehistoric animal was probably only partially marine, still capable of venturing out onto land, although the broad wrist bones and elongated fingers and toes enabled the limbs to be used to help the animal swim.

The Diet of Atopodentatus?

As to what this animal actually ate, no one knows for sure, there is nothing similar living today that seems to have anything remotely like its specialised feeding apparatus, or is there?  The Bowhead Whale (Balaena mysticetus), has plates of baleen made from keratin in its mouth which it uses to sieve out planktonic organisms as it swims through Arctic waters.

The mouth of Atopodentatus may have been adapted for sieving out small creatures but not from open water like the huge-mouthed Bowhead, but from soft mud on the sea floor.  Dr Wu and his colleagues, suggest that the broad, shovel-like head of this marine reptile may have ploughed through soft sediments with its teeth sieving out soft-bodied creatures such as marine worms.

The doctor added:

“It is obvious that such delicate teeth are not strong enough to catch prey, but were probably used as a barrier to filter micro-organisms or benthic invertebrates such as sea worms.  These were collected by the specialised jaws, which may have functioned as a shovel or push-dozer and a grasper or scratcher.”

At the moment, the actual function of the jaws remain a mystery.  Perhaps a specimen will be found with stomach contents preserved or perhaps some trace fossils will be discovered the reveal a ploughed up seabed.  One of the few certainties surrounding this bizarre creature is that like a number of the strange marine reptiles that existed in the Middle Triassic seas of China, within a few million years this particular branch of the marine family tree had become extinct.

For models and replicas of prehistoric animals including Atopodentatus (whilst stocks last): PNSO Age of Dinosaurs Models and Figures.

Oldest Known Cardiovascular System Identified – Fuxianhuia protensa

The fossil of an arthropod found in rocks laid down around 520 million years ago with an exquisitely preserved cardiovascular system has been described by a team of scientists led by researchers from the Natural History Museum in London.  The specimen represents the oldest known fossil showing a rudimentary heart and blood vessels known to science.

Burgess Shale and Other Remarkable Fossil Sites

Thanks to remarkable fossil sites such as the Burgess Shale deposits in British Columbia and beautifully preserved remains of Cambrian creatures from highly fossiliferous strata from south-western China, palaeontologists have built up an astonishing amount of data on life in the seas and oceans of the world around 520 to 500 million years ago, a period in the geological history of planet Earth known as the Cambrian explosion due to the range and diversity of organisms that had evolved at that time.

The exquisitely preserved specimen represents Fuxianhuia protensa from the Middle Cambrian aged strata of the Chengjiang Formation (the Moatianshan shales of Yunnan Province, south-west China).  Fossils of this shrimp-like creature are very common in these marine shales, sixteen different phyla that have been identified from the Chengjiang Formation, a location that rivals the Burgess Shales in terms of the rich fossil record that has been preserved, although the material from the Chengjiang Formation is slightly older than the fossils from the Walcott Quarry section of the Burgess Shale deposits.  Until this particular specimen had been studied, it has been assumed that most of the internal organs of early arthropods would not survive the fossilisation process.

Fuxianhuia protensa

Some fossils had been found that indicated the presence of a digestive tract and back in October 2013, Everything Dinosaur reported the discovery of an arthropod (Alalcomenaeus spp.) from the same region of Yunnan Province that showed signs of a brain and the soft tissue preservation of a nervous system, here we report on the discovery and mapping of a complete cardiovascular system in a 520-million-year-old arthropod.

To read more about this earlier discovery: Ancient Arthropod Brain and Nervous System Studied.

Although many fossils of F. protensa are known, its taxonomic position with the Arthropoda remains unclear, it is thought to be a basal member of this phylum, which today is the largest phylum of animals and includes crustaceans, insects, spiders, mites, scorpions, centipedes, king crabs millipedes and a number of extinct Orders such as the Trilobita.

The external skeleton is most commonly preserved, either as parts shed as the animal grew or as complete specimens that represent animals that died, however, due to the exquisite degree of preservation in some specimens from the Chengjiang Formation, scientists now have a much better understanding of the internal anatomy of early arthropods.  What is remarkable, is that sophisticated cardiovascular and nervous systems seem to have evolved in the Arthropoda at an early stage in the history of life on Earth.

Fuxianhuia Fossils that have been used in the Study

Cardiovascular system in 520-million-year-old arthropod preserved.

Picture credit: Journal of Nature Communications

Fossil Examples

The photograph shows examples of the F. protensa fossil material used in the study.  Diagram (a) is a view of specimen YKLP 11336 from above (dorsal view), the location of the digestive tract running down the centre of the body is indicated by the black arrows.

Illustration (b) shows the head and the front of the animal (anterior view), specimen number YKLP 11337, the white arrows indicate the mouth of the creature.  Part (c) shows the filled gut within the abdominal segments, the gut has been preserved as carbon in this specimen (YKLP 11338).  Diagram (d) shows empty gut area marked by arrows in abdominal segments Ab9 to Ab14.

Diagram (e) shows the preserved outline of the cardiovascular system (YKLP 11335), A1 in the photograph marks the position of the left antenna and ey marks the position of the right eye.  The black triangles towards the top of the picture indicate the position of the bottom portion of the animal’s headshield.  The white outlined triangles towards the bottom of photograph (e) show the end of the thorax portion of the animal’s body.

Scale Bars

Most complete specimens of F. protensa are around 30 mm in length, the scale bars in the photographs are:

(a) = 5 mm

(b, c and d) = 1 mm

(e) = 4 mm

Commenting on the significance of this fossil discovery, palaeontologist Xiaoya Ma (Natural History Museum, London), one of the authors of the scientific paper published in the journal “Nature Communications” stated:

“It is an extremely rare and unusual case that such a delicate organ system can be preserved in one of the oldest fossils and in exquisite detail.  However, under very exceptional circumstances, soft tissue and anatomical organ systems can be preserved as fossils.”

The Internal Anatomy of an Ancient Arthropod

Scientists now have an excellent understanding of the internal organisation of the anatomy of this arthropod.  Usually, soft tissue decays rapidly after death and fossils typically only preserve the hard parts of an organism, such as the exoskeleton in the case of the Arthropoda.  With Fuxianhuia protensa the fossils show a tubular heart in the middle of the body with a complex system of blood vessels leading to the creature’s antennae, eyes, brain and limbs.

The cardiovascular system consists of the heart and the blood vessels.  It allows blood to circulate and to deliver oxygen and nutrients around the body.  Most higher forms of life in the Kingdom Animalia have such a system, although those organisms without a real body cavity such as flatworms and jellyfish do not.

The specimens studied suggest that as early as 520 million years ago, arthropods had evolved a complex internal anatomy which is very similar in structure to the internal anatomy found today in extant arthropods such as shrimps.

The Chengjiang Formation

Like the Burgess Shales, the Chengjiang Formation material has preserved much of an ecosystem that thrived in a shallow marine environment more than half a billion years ago.  It seems that these two ancient environments suffered much the same fate as each other even though just like today, in the Cambrian, these two locations were thousands of miles apart.  Both the Burgess Shale Formation and the Chengjiang Formations represent shallow marine environments which were on slopes.

From time to time mudflows, buried entire ecosystems and as a result, a wealth of organic material has been preserved.  A large number of Fuxianhuia fossil material is known from Yunnan Province, scientists believe that this Arthropod was benthic (living on the sea floor), although it is not known whether this animal was an active hunter or a scavenger.

A Schematic Diagram of the Internal Anatomy of Fuxianhuia protensa

Digestive tract and cardiovascular system of Fuxianhuia protensa.

Picture credit: Journal of Nature Communications

The Anatomy of F. protensa

The diagram above shows the internal anatomy of F. protensa.  Diagram (a) shows the cardiovascular system (red) shown in relation to the brain and central nervous system (blue).  Diagram (b) shows the whole reconstruction, with brain and segmental ganglia (blue) overlaid against the external skeleton of the animal.  Diagram (c) shows the cardiovascular system in relation to the digestive tract (green).  In all three diagrams, the tubular heart organ can be seen running down the central region of the thorax.

Thanks to highly detailed fossils from British Columbia and south-western China, scientists have been able to acquire a lot of knowledge about life in the oceans of the world during the Cambrian geological period.  Although, advanced and highly evolved cardiovascular systems were present in many organisms, the paucity of the fossil record that pre-dates the Cambrian prevents scientists from calculating when key structures such as hearts and brains first evolved.

Given the degree of sophistication seen in the Fuxianhuia material two competing theories have been put forward.  Firstly, such specialised internal structures such as hearts, brains and a cardiovascular system must have evolved gradually with incremental changes many millions of years before the Cambrian.  Secondly, the evolution of such specialised internal organs occurred relatively quickly in response to the development of predator/prey interactions and the increased availability of food resources.

The research team are able to conclude that organisms had cardiovascular systems before Fuxianhuia, but evidence of lacking in the fossil record so no further light on the subject can be cast for the time being.

The genus name Fuxianhuia is after Lake Fuxian in Yunnan Province, the specific or trivial name “protensa” means “elongated” a reference to the elongated thorax of the creature.

For replicas and models of Palaeozoic creatures including invertebrates: CollectA Prehistoric Life Models and Replicas.