Scientists Explore the Miniature Ecosystem Created by an Ichthyosaur Carcase

It has been known for some time that when cetaceans (whales and dolphins) die and their corpses settle on the seabed, the carcase can sustain a diverse ecosystem for many years, even decades with the largest individuals.  Palaeontologists had long suspected that the corpses of marine reptiles that patrolled the seas of the world long before the whales evolved, would have played a similar role, but until now this area of marine reptile research had not been that thoroughly investigated.

Studying Decay

Stepping up to this challenge, scientists from the Natural History Museum (London) and the Centre for Research in Earth Sciences (Plymouth University) set about mapping the evidence preserved on the fossilised bones and surrounding matrix of an ichthyosaur skeleton found in southern England.

The team concluded that although there was evidence for a succession of community feeding phases, phases which are very similar to those found in association with cetacean remains deposited in shallow water, the fossilised communities differed from those associated with whale carcases deposited in deep water environments.  One phase, consisting of the establishment of a community feeding on inorganic compounds such as methane and sulphides (known as the “sulphophilic phase”) seemed to be absent according to this fossil study.

Exploring the “After Life” of an Ichthyosaur

Ichthyosaurus model (Carnegie Collectibles).

Picture credit: Everything Dinosaur/Safari Ltd

Ichthyosaur

Ichthyosaurs were a very diverse group of marine reptiles that evolved in the Early Triassic and survived up until the Late Cretaceous (Olenikian faunal stage of the Early Triassic to Turonian faunal stage of the Late Cretaceous).  Although, ichthyosaurs had the same basic, streamlined body plan, a number of families are now recognised and these reptiles, only distantly related to the Dinosauria are regarded by many palaeontologists as amongst the best adapted of all the reptiles to a marine existence.

The specimen studied was a highly disarticulated Ophthalmosaurus fossil, from Dorset.  The fossil represents a three-metre-long individual from the upper part of the Ringstead Clay Member of the Sandsfoot Formation, Late Oxfordian faunal stage.  We estimate that this specimen is approximately 157-156 million years old (Jurassic).  The carcase came to rest on a shallow sea bed, the bones became scattered over an area of several square metres before final burial.  The break-up of the skeleton was probably caused by a combination of scavenging and the action of currents, possibly high energy water flows as a result of storm activity.

Trace Fossil Evidence

The researchers identified a wealth of trace fossil evidence indicating feeding on the carcase by scavengers as well as evidence of organisms grazing on the bones themselves.  Marks made by the teeth of fish were identified and the “star-shaped” feeding scratches from the ichnospecies Gnathichnus pentax were found.

An ichnospecies is an organism only known from trace fossil evidence. The strange five-pointed, star shapes etched over many of the fossilised reptile bones are very similar to the patterns made by living sea urchins with their five-toothed feeding apparatus.  Scientists have interpreted these star-shaped patterns on the bones as evidence of grazing by a prehistoric sea-urchin (echinoid), G. pentax. It would have been feeding on mats of algae that had formed.

Trace Fossil Evidence on the Ophthalmosaurus Bones

Rib showing sharp, narrow grooves (white arrows) probably left by the scavenging action of small fishes.

Picture credit: Nature Communications

The picture above shows a close up of an Ophthalmosaurus rib bone showing signs of having been scavenged by small fish. The arrows indicate potential bite mark evidence (scale bar = 0.5cm).

Evidence of Grazing on the Fossilised Bones by Echinoids (Sea Urchins)

G. pentax ichnospecies on a fragment of fossil rib.

Picture credit: Nature Communications

The photograph above (b) shows the tell-tale grazing pattern of the ichnospecies Gnathichnus pentax on one of the fossilised bones (scale bar = 1cm).

A Close up of the Star-Shaped Feeding Pattern

Scale bar = 0.2cm.

Picture credit: Nature Communications

The Mesozoic Equivalent of a Whale Fall Incident

Commenting on the study, Richard Twitchett (Natural History Museum), one of the research paper’s co-authors stated:

“This is the first time anybody has described the ecological succession in the Mesozoic equivalent of a whale fall in detail.”

When an extant whale dies and its body sinks to the seabed,  scientists have identified a number of distinct and sometimes overlapping ecological phases.  First, scavengers remove the flesh and other soft tissues from the carcase.  Then snails and the charmingly named bone-eating, snot-flower worms (Osedax genus) feast on the blood and the fluids from the decomposing remains.

The last phase sees the hard parts such as the bones themselves being digested by microbes which feed on the fats (lipids) stored in the bones.  Tube worms live off the microbes and the likes of the bone-eating snot-flower worms persist.

Feeding by Scavengers

When the insides of the Ophthalmosaurus’s bones were examined under powerful microscopes further evidence of feeding by scavengers was found.  A number of tiny, fossilised molluscs were discovered.  These are associated with the same ecological community phase now associated with the bone-eating, snot-flower worms.  However, there was no sign of the “sulphophilic stage”, in which oxidised inorganic compounds such as sulphides and methane, derived from microbial activity as the fats inside the bones are broken down are consumed by a chemosynthetic community.  The chemosynthetic community found on the carcases of whales in deep water (greater than two hundred metres) consists of free-living bacteria and bivalves (for example, the genus Beggiatoa).

Evidence of Microscopic Scavenging Activity within the Fossilised Bone

Close-up of the bioeroded area where microborings are perpendicular to the external bone surface

Picture credit: Nature Communications

The picture above (e) shows a highly magnified section of ichthyosaur bone (ib) and the adjacent micrite rim represents a fine-grained calcite layer formed by the action of microbes boring into the substrate.

Mats of Microbes

Instead, the ichthyosaur’s bones were colonised by mats of microbes which attracted sea urchins and other grazing invertebrates.  The bones also became the home for a number suspension feeders, such as oysters that cemented themselves to the remains of the skeleton, forming a miniature “reef phase” as described by the scientists.  The remains were eventually buried entombing the remnants of the ecosystem that had been established to exploit the last resources from the dead animal.

When large cetaceans perish, a reef phase is less likely to occur as most carcases settle in deeper water and the ubiquitous bone-eating snot-flowers rapidly destroy the skeleton.  The researchers conclude that shallow-water ichthyosaur falls do provide a range of ecosystem opportunities to other organisms similar to the ones seen in studies of dead whales and dolphins.  However, it seems such shallow water corpses do not support any specialised chemosynthetic communities.

Rukwatitan bisepultus – A Rare African Giant

Titanosaurs are a bit like buses, you wait for ages and then two of them come along together.  No sooner did we complete our synopsis on the research on the colossal Dreadnoughtus schrani, a newly described titanosaur from south-western Patagonia, then we have the opportunity to discuss another new species, this time from Africa.  This new titanosaur, named Rukwatitan bisepultus may not be quite as big as the newly described Dreadnoughtus but we at Everything Dinosaur estimate that fossils excavated from a hazardous cliff face in a steep quarry represent a dinosaur that was around ten metres long, or possibly much bigger.

Comparisons with the fossil bones from the Malawisaurus indicate that this titanosaur could have exceeded sixteen metres in length.  This herbivore would have been able to survey its floodplain home from a height of approximately four metres.

Rukwatitan bisepultus

An Artist’s Impression of the New Titanosaur (Rukwatitan bisepultus)

New genus of titanosaur described from Tanzania.

Picture credit: Mark Witton

Studying Titanosaurs

But with titanosaurs, size isn’t everything.  Rukwatitan may not be a record breaker in terms of its body mass but its discovery is perhaps more significant than the fossils of the South American giants.  This is only the fourth genus of titanosaur discovered in Africa* and the palaeontologists at the University of Ohio, who excavated the fossils out of the cliff over two field seasons, are confident that their find will help scientists to understand more about the global distribution and the diversity of the titanosaurids as well as helping to piece together more data on the evolution of sub-Saharan dinosaurs.

A Silhouette of Rukwatitan bisepulutus Showing Fossils Found

Scale bar = 1 metre

Picture credit: Eric Gorscak (Ohio University)

The picture above shows a bauplan of the new titanosaur and the position of the fossil bones that were found in relation to the body plan.

Titanosaurs are wide-bodied sauropods that probably evolved sometime in the Late Jurassic and survived until the Cretaceous mass extinction event.  They are the only sauropods known to have survived into the Late Cretaceous, but only in South America did these animals make up a significant proportion of the herbivorous megafauna, elsewhere, the ornithopods dominated.  When compared to other types of Sauropoda, titanosaurs tended to have wider bodies, due to the more robust and larger pectoral area (chest).  The limbs were strong and stocky, often the front limbs were longer than the hind limbs.

The spinal column was more flexible than in diplodocids, perhaps helping them to rear up more easily.  The heads were small, proportionately smaller than other types of sauropod.  Titanosaurs were geologically widespread and their fossils have been found on all the continents including Antarctica.  A number of sub-families have been identified and some of the titanosaurids are amongst the largest, terrestrial vertebrates known to science.

To read about the Antarctica fossil find (2011): Titanosaurs of the Antarctic.

The fossils were found in the Rukwa Rift Basin area of south-western Tanzania (hence the genus name).  Scientists from Ohio University in collaboration with several other universities have carried out a number of excavations from the Red Sandstone Group deposits, that form part of the Galula Formation.  Fossils of turtles, crocodilians and primitive mammals have also been found in the formation, as well as dinosaur remains.  The fossil bearing strata is believed to have been laid down approximately 100 million years ago (Late Albian faunal stage of the Cretaceous).

The Fossils were Excavated from a Steep Cliff Face

The fossils were excavated from a steep cliff.

Picture credit: Patrick O’Connor (Ohio University)

The vertebrates associated with the Galula Formation have shown some unique anatomical features indicating that the floodplain environment which is represented by these sandstone deposits may have been separated from other parts of Gondwana, permitting a unique fauna to evolve.  Last year, scientists from Ohio University reported the discovery of a new type of crocodilian (Rukwasuchus yajabalijekundu) that was different from other crocodilians found in deposits of the same geological age but from further north.

Some of the Fossils Exposed after Excavation

Fossil material exposed.

Picture credit: Ohio University

One of the authors of the scientific paper, published in the “Journal of Vertebrate Palaeontology”, Patrick O’Connor (Professor of Anatomy at Ohio University) stated:

“There may have been certain environmental features, such as deserts, large waterways and/or mountain ranges that would have limited the movement of animals and promoted the evolution of regionally distinct faunas.  Only additional data on the faunas and the palaeo-environments from around the continent will let us further test such hypotheses.”

Two Caudal Vertebrae (Tail bones) from the Site

A number of caudal vertebrae including several articulated vertebrae have been found.

Picture credit: Ohio University

* Team members have had a go at naming the four genera of African titanosaurs currently described, here we go:

1. The basal titanosaur from Tanzania (Upper Tendaguru Formation) – Janenschia robusta (Late Jurassic)
2. The Lithostrotian titanosaur from Malawi (unknown formation) Malawisaurus dixeyi (Cretaceous)
3. The basal Lithostorian titanosaur? Rukwatitan bisepulutus (described above)
4. The Lithostrotian titanosaur from Egypt (Bahariya Formation) Paralititan stromeri (Late Cretaceous)

To read the acclaimed article written by Everything Dinosaur on the newly discovered titanosaur Dreadnoughtus: New Titanosaur from South-Western Patagonia.