The Oldest Plesiosaur in Town – Rhaeticosaurus mertensi

The fossilised remains of the world’s oldest plesiosaur described to date are reported in the journal “Science Advances”. The animal has been named Rhaeticosaurus mertensi.

Following the end-Permian mass extinction event, the world’s ecosystems took several million years to recover.  In marine environments, just as on land, the mass extinction event led to devastating losses, it has been estimated that 57% of marine families died out.  However, as the Triassic progressed, a number of terrestrial reptiles adapted to marine habitats and new, diverse ecosystems evolved.

It had long been suspected that the Plesiosauria (the long-necked plesiosaurs and the big-headed pliosaurs), the most diverse and longest-lived of all the extinct marine reptile groups, had their origins in the Triassic, but the fossil evidence for basal plesiosaurs was somewhat lacking.  However, the discovery of a partially articulated fossil in a clay pit, close to the village of Bonenburg in North Rhine-Westphalia (Germany), has helped to plug a gap in the fossil record.

The Fossilised Remains of the World’s Oldest Plesiosaur

Picture credit: Georg Oleschinski

Rhaeticosaurus mertensi

The fossil discovery marks the first plesiosaur specimen to be recovered from Triassic-aged rocks.  It is the oldest plesiosaur to be found to date, the only one which dates from the Triassic Period.

Intriguingly, a study of cross-sections of some of the larger fossilised bones in the 2.37-metre-long skeleton, support previous research that suggests these marine reptiles grew rapidly and were (most likely), warm-blooded.  The new species has been named Rhaeticosaurus mertensi, (ree-ti-co-sore-us mur-ten-see), the genus name comes from the last faunal stage of the Triassic (the Rhaetian), the trivial name honours  private collector Michael Mertens, who made the initial fossil discovery.

201-million-year-old Fossil

Michael Mertens discovered the specimen in 2013, some of the neck bones had been lost but the majority of the skeleton was in situ.  The resulting excavation, study and publication in the academic journal “Science Advances”, is a credit to the parties involved, namely Herr Mertens, the natural heritage protection agency, the Münster museum, and scientists from various institutes including Bonn University, the Osaka Museum of Natural History, the University of Tokyo and the Natural History Museum of Los Angeles County, amongst others.

Co-author of the Scientific Paper Tanja Wintrich with the Fossil Finder Michael Mertens

Picture credit: Professor Martin Sander (University of Bonn)

The Long-lived and Diverse Plesiosauria

In a press release from Bonn University, plesiosaurs are described as especially effective swimmers.  They evolved a unique, four-limbed propulsion using broad flippers, in essence, “flying underwater”.

One of the authors of the scientific paper Professor Martin Sander explained:

“Instead of laboriously pushing the water out of the way with their paddles, plesiosaurs were gliding elegantly along with limbs modified to underwater wings.  Their small head was placed on a long, streamlined neck.  The stout body contained strong muscles keeping those wings in motion.  Compared to the other marine reptiles, the tail was short because it was only used for steering.  This evolutionary design was very successful, but curiously it did not evolve again after the extinction of the plesiosaurs.”

An Illustration of a Typical Long-necked Plesiosaur

Picture credit: Everything Dinosaur

Bone Histology Suggests Rapid Growth and Potential Endothermy

The Triassic plesiosaur already has the typical long-necked plesiosaur bauplan and it was, like most of its descendants, a pelagic piscivore (an active swimmer, hunting fish).  Analysis of the bone structure indicates that the specimen represents a juvenile, one that was growing rapidly.  Thin cross-sections of fossil bone were compared to Jurassic and Cretaceous specimens and the team’s findings support the hypothesis that to grow this quickly, these reptiles needed to be warm-blooded.

Professor Sander stated:

“Plesiosaurs apparently grew extremely fast before reaching maturity.  Since plesiosaurs spread quickly all over the world, they must have been able to regulate their body temperature to be able to invade cooler parts of the ocean.”

The Hind Leg Bones of Rhaeticosaurus mertensi

Picture credit: Science Advances

In the photograph (above), the part of the femur (f) is a cast as this bone was cross-sectioned as part of the bone study.

Rhaeticosaurus mertensi – Filling a Gap in the Fossil Record

The evolution of the Plesiosauria is poorly understood.  They are probably descended from a group of long-necked, marine reptiles known as pistosaurs, fossils of which are associated with Middle to Late Triassic deposits.

An example of a pistosaur is Bobosaurus (B. forojuliensis) from the Rio del Lago Formation of Italy (Carnian faunal stage of the Triassic).  However, Bobosaurus lived some thirty million years before Rhaeticosaurus evolved.  This German fossil discovery helps to fill in a little of the temporal gap in the fossil record of this successful lineage.

Rhaeticosaurus has been assigned to a basal position within the Pliosauridae family and its discovery reveals that the diversification of the Plesiosauria was a Triassic event and a number of genera survived the end Triassic extinction into the Jurassic.  The researchers conclude that the bone histology of this Late Triassic marine reptile suggests that the evolution of fast growth and an elevated metabolic rate were adaptations to an active, pelagic life-style foraging in open water.

Articulated Cervical Vertebrae (C) and Elements from the Left Front Limb (D)

Picture credit: Science Advances

The new specimen corroborates the hypothesis that the open ocean life of plesiosaurians facilitated their survival of the end-Triassic extinction.

The scientific paper: “A Triassic Plesiosaurian Skeleton and Bone Histology Inform on Evolution of a Unique Body Plan” by Tanja Wintrich, Shoji Hayashi, Alexandra Houssaye, Yasuhisa Nakajima and P. Martin Sander published in the journal “Science Advances”.

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Triceratops Skeleton Turns Out to be Torosaurus

A partial, horned dinosaur skeleton, initially thought to represent a young adult Triceratops has been reassessed following a month of preparation and cleaning and identified as a Torosaurus (T. latus).  It was back in September that Everything Dinosaur first reported on the dinosaur fossil discovery in Thornton, Colorado (USA).  Sadly, the highly respected Denver Museum of Nature and Science palaeontologist, Mike Getty was taken ill at the dig site and passed away shortly afterwards.

Turns out, what was initially identified as a Triceratops has proved incorrect.  As the Denver Museum of Nature and Science preparators have worked on the fossil bones, they have uncovered enough material to confidently ascribe the fossils to the closely related, but much rarer Torosaurus latus.

An Illustration of the Horned Dinosaur Torosaurus latus

Picture credit: Everything Dinosaur

The picture (above) shows a PNSO Torosaurus dinosaur model.

To view the range of PNSO models and figures: PNSO Age of Dinosaurs Models.

Triceratops and Torosaurus

Analysis of the large head shield that projects backwards from the skull has shown the frill of bone to be quite thin, with two distinct large holes (fenestrae), anatomical traits that are associated with Torosaurus and not Triceratops.  The new diagnosis was made after a careful comparative study using Triceratops specimens already within the Museum’s vertebrate fossil collection.  Torosaurus fossils are exceptionally scarce.  There are several thousand Triceratops (T. horridus and T. prorsus) fossils, representing something like 2,000 individuals.  In contrast, there are approximately 7 partial skulls of Torosaurus known.

A Skeletal Drawing Showing the Extent of the Fossil Material Found at the Thornton Site

Picture credit: Denver Museum of Nature and Science

A spokesperson for Everything Dinosaur commented:

“The fossil find at Thornton is highly significant.  The majority of the front-end of the individual has been excavated including an almost complete skull.  This specimen may provide palaeontologists with valuable information on how Torosaurus changed as it grew up.  In addition, these fossils could help to identify other Torosaurus specimens in museums that have been misidentified and labelled as Triceratops.”

Is Torosaurus Just a Very Old Triceratops?

The lack of Torosaurus fossil material compared to other horned dinosaurs from North America, led to speculation that Torosaurus was not a valid genus, that the fossil material ascribed to Torosaurus actually represented very old, very mature examples of Triceratops.  The Thornton specimen seems to represent a young adult animal, this may help to clarify the Torosaurus versus Triceratops debate.

To read an article published in 2010, that details an American study that suggested that Torosaurus fossils were actually Triceratops: The Extinction of Torosaurus – Second Time Around.

Fossilised Bones Being Exposed at the Thornton Dig Site

Picture credit: Denver Museum of Nature and Science

An Extremely Rare Fossil

Joe Sertich (Curator of Dinosaurs at the Denver Museum of Nature and Science), stated:

“Not only is the fossil more complete and better preserved than I imagined, but it has also revealed itself to be something extremely rare.  The Thornton beast is by far the most complete, and best preserved, ever found.”

Nicknamed “Tiny”

The specimen has been nicknamed “Tiny”, but the work of preparing and studying these fossils is no small task.  The material was unearthed at a Saunders Construction site for a new Public Safety Facility.  Cleaning efforts have also revealed several more skull bones and a complete tibia (lower leg bone).  An estimated 95 percent of the skull and at least 20 percent of the skeleton have now been identified, making this the most complete Cretaceous-aged fossil discovered in Colorado.

Visitors to the Museum can observe the fossil preparation process in the Fossil Prep Laboratory, cleaning and preparing is estimated to take several more months.

Joe Sertich at the Dig Site Working on “Tiny” the Torosaurus

Picture credit: Denver Museum of Nature and Science

We wonder what Mike Getty would have made of it all?

To read more about the sad death of renowned scientist Mike Getty: Highly Respected Palaeontologist Dies at Dig Site.

Everything Dinosaur acknowledges the assistance of the press team at the Denver Museum of Nature and Science in the compilation of this article.

Ostromia crassipes – The First European Member of the Anchiornithidae

The first fossil of Archaeopteryx to have been discovered, turns out not to represent the “Urvogel” at all.  In a reassessment of the fossil, known as the Haarlem specimen, as it is part of the vertebrate collection housed at the Teylers Museum in Haarlem (Holland), it has been re-described as a small predatory dinosaur belonging to the anchiornithid family.  The dinosaur has been named Ostromia crassipes, the genus name honours the late John Ostrom, who identified the Haarlem specimen as a theropod and was instrumental in the work that led to the definition of dinosaurs as dynamic, active reptiles.

The Haarlem Specimen – the Holotype of Ostromia crassipes

Picture credit: Oliver Rauhut/Ludwig-Maximilians-University (Munich, Germany)

The fossil studied, actually consists of two parts, the counterslab TM 6929 (left) and the main slab (right) TM 6928.

Ostromia crassipes

Archaeopteryx was named in 1861, however, the Haarlem specimen was found four years earlier.  To date, around a dozen specimens have been assigned to the Archaeopteryx genus, including a single, fossilised feather.  The discovery of Archaeopteryx supported the theory of natural selection proposed by Darwin and Wallace as it represented a transitional form between reptiles and birds.  Archaeopteryx fossils support the idea that modern birds are descendants of carnivorous dinosaurs.

Writing in the academic journal “BMC Evolutionary Biology”, palaeontologists Oliver Rauhut and Christian Foth from the Staatliches Museum für Naturkunde in Stuttgart have re-examined the Haarlem specimen.  They conclude that this fossil differs in several important respects from the other known representatives of the genus Archaeopteryx.  The researchers conclude that the fossil is not an Archaeopteryx at all, but a representative of the very bird-like maniraptoran dinosaurs known as anchiornithids.

These crow-sized, predatory dinosaurs possessed feathers on all four limbs, and they predate the appearance of Archaeopteryx by several million years.

Commenting on their study, Dr Oliver Rauhut stated:

“The Haarlem fossil is the first member of this group found outside China and together with Archaeopteryx, it is only the second species of bird-like dinosaur from the Jurassic discovered outside eastern Asia.  This makes it [the Haarlem specimen] even more of a rarity than the true specimens of Archaeopteryx.”

Subtle Anatomical Differences and Bone Osteology

The scientists looked at the relative proportions of limb, toe and finger bones and noted that the Haarlem material (TM 6929 and TM 6928), was different from other Archaeopteryx specimens.  In addition, it had affinities with the fossilised remains of Anchiornis from China.  Furthermore, differences in bone osteology were observed.  For example, the Haarlem fossil specimen has a regular, well-developed longitudinal furrow on the exposed medial side of the preserved manual phalanx, this furrow is not present on any of the finger bones ascribed to Archaeopteryx.

Comparing the Finger Bones (Manual Phalanges) of Various Theropods

Picture credit: BMC Evolutionary Biology

The photograph (above) shows close-up views of the finger bones (manual phalanges) of several theropods, analysis of the shape of the bones, their features and their proportions led the researchers to conclude that the Haarlem specimen was not Archaeopteryx.

(a). a right manus (hand) of the Thermopolis specimen of Archaeopteryx

(b). the right manus of the Solnhofen specimen of Archaeopteryx

(c). the left manus of the juvenile theropod from Germany Sciurumimus albersdoerferi (image resolved under UV light)

(d). second finger of the small Late Jurassic Theropod Compsognathus longipes

(e).  the impression from the first finger of the anchiornithid Anchiornis huxleyi

(f). the first finger of Caudipteryx, a feathered theropod from the Early Cretaceous of China

Learning About Fauna of the Solnhofen Archipelago

Discovered in 1857, the Haarlem fossil specimen was found about 6 miles (10 kilometres), to the north-east of the closest Archaeopteryx locality known (Schamhaupten) which is near the town of Altmannstein in southern Bavaria.

The Jurassic-aged rocks in this area were laid down in a shallow sea, in which were scattered numerous small islands, an archipelago, that provided an environment, superficially similar to that of the Caribbean today.  These islands that once covered southern Bavaria, are known as the Solnhofen archipelago, the region from which all known specimens of the genus Archaeopteryx come from.

The taxonomic reassignment of the Haarlem specimen to the feathered Anchiornithidae has provided a fresh insight into the evolution of the Avialae and indicates that the first bird-like dinosaurs originated in Asia.  During the Middle to the Late Jurassic these creatures migrated westwards, reaching the Solnhofen archipelago of Western Europe some 150 million years ago.

The Haarlem fossil was originally recovered from what was then the eastern end of the archipelago, quite close to the mainland.  Unlike Archaeopteryx, anchiornithids were (most likely), unable to fly, and might not have been able to reach the more remote islands offshore.   All true fossils of Archaeopteryx found to date were recovered from the lithographic limestone strata further to the west, closer to the open sea.  This implies that dinosaurs like Ostromia may have been limited in their distribution, compared to the volant Archaeopteryx.

Faunal Distribution in the Solnhofen Archipelago (Late Jurassic)

Picture credit: Everything Dinosaur

In the diagram above, Ostromia may have been unable to reach the more remote parts of the island chain whilst Archaeopteryx, which was capable of powered flight (its aerial abilities are still debated), would have been more able to “island hop”.

Based on these new findings, the researchers postulate that other known Archaeopteryx fossils may need reassessment.

Dr Rauhut suggests:

“Not every bird-like fossil that turns up in the fine-grained limestones around Solnhofen need necessarily be a specimen of Archaeopteryx,”

The scientific paper: “Re-evaluation of the Haarlem Archaeopteryx and the Radiation of Maniraptoran Theropod Dinosaurs” by Christian Foth and Oliver W. M. Rauhut published in BMC Evolutionary Biology.

An article on Archaeopteryx research: Archaeopteryx Had Feathered “Trousers”.

The oldest Archaeopteryx fossil: The Oldest Archaeopteryx in Town?

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Pterosaurs Even More Like Birds

Pterosaurs like birds, were capable of powered flight.  It seems that command of the skies is not the only thing that these two types of vertebrate had in common.  Thanks to a remarkable series of discoveries from the remote Turpan-Hami Basin located in the Xinjiang Uygur Autonomous Region (north-western China), palaeontologists have learned that pterosaurs, like many living birds nested in colonies, that they had preferred nesting sites and when young, pterosaurs needed a degree of parental care, just like many species of birds today.

Pterosaur Nesting Colony (Hamipterus tianshanensis)

Picture credit: Zhao Chuang

Hundreds of Pterosaur Eggs Discovered

Writing in the journal “Science”, researchers from the Chinese Academy of Sciences along with collaborators from a number of research institutions in Brazil have published a paper describing the discovery of 215 pterosaur eggs, 16 of which contain the remains of embryos.  The eggs and the numerous fossil bones associated with the site have been attributed to Hamipterus tianshanensis, a flying reptile first named and described in 2014 whose exact taxonomic position in the pterosaur family tree remains open to debate.

That point notwithstanding, H. tianshanensis has been propelled to super-stardom, like a Pteranodon taking to the air, representing one of the most significant Pterosauria discoveries made to date.

An Assemblage of Pterosaur Fossils

Picture credit: Xinhua/Wang Xiaolin

Pterosaur Nesting Grounds

Significantly, the number of eggs discovered are far too many to have been laid by a single female.  This suggests that these flying reptiles nested in colonies and furthermore, the overlaying of multiple clutches of eggs indicates that pterosaurs, like many birds today, returned to the same nesting sites each year.  As the authors conclude, “the similarity between these groups goes beyond wings”.

The Remains of Numerous Individuals at the Site

Picture credit: Xinhua/Alexander Kellner

Three-Dimensional Fossil Egg Preservation

The eggs were not laid at the location where they were discovered.  This exceptional Lagerstätte preserves a series of tragic events, it seems that periodically, the nesting area was subjected to flooding as a result of seasonal storms.  Many of the eggs have been preserved in three dimensions, caused by the encroachment of sediment.

Computed tomography scans have revealed minute details of some of the embryos preserved within the eggs.  For example, an almost complete skeleton of a hatchling shows that bones related to flight were less developed than bones of the hind limb, indicating that new-borns might have been able to walk but not fly.

The front limb bones lack ossification and had yet to fully form, whilst the leg bones such as the femora are well developed.  This suggests that the young pterosaurs were unable to fly, but not completely helpless, their strong legs would have meant that they would not have been stuck in the nest but quite capable of locomotion.  However, these new insights have led the palaeontologists to conclude that, in the case of Hamipterus at least, the offspring were less precocious than previously assumed.

In short, mum and dad (coming to that bit next), had to take care of their young, bring food to them and protect them from predators.

Evidence Suggests that Pterosaurs Cared for their Young

Picture credit: Zhao Chuang

The Significance of Dad

Hamipterus tianshanensis was named and described three years ago.  This fossil location had been discovered several years before, but the pterosaur body fossils and the associated pterosaur egg material (forty specimens and five eggs), were not scientifically described until 2014.

In the 2014 paper (Wang et al), which was written by many of the scientists involved in this latest study, it was postulated that differences in head crest shape or size helped to distinguish males from females.

It was proposed that specimens with larger skull crests were males.  This suggests sexual dimorphism in this species and, if this idea is taken a little further, it implies that the males may have played a role in helping to bring up the next generation. After all, fossilised remains of what might represent adult males have been swept together with the nest site fossils.  Many male birds share parental responsibilities and lots of extant Aves such as the Wandering Albatross (Diomedea exulans) for instance, pair for life.  Perhaps, adult pterosaurs also had monogamous behaviour.

A Close-up View of the Preserved Leathery Egg of Hamipterus

Picture credit: Xinhua/Wang Xiaolin

Inferring Behaviours

To what degree the Pterosauria and Aves share behaviours remains a controversial area.  Further research into the remarkable Hamipterus Lagerstätte has greatly increased our knowledge about flying reptiles but we must be careful not to infer or imply too much from the fossil evidence.  The scientists conclude that the discovery of all these bones and fossilised eggs supports the idea that these pterosaurs nested in colonies and that they returned to a favoured nesting site to breed.

Two of the Authors of the Scientific Paper Inspect Part of the Remote Dig Site

Picture credit: Xinhua

The scientific paper: “Egg Accumulation with 3D Embryos Provides Insight into the Life History of a Pterosaur” by Xiaolin Wang, Alexander W. A. Kellner, Shunxing Jiang, Xin Cheng, Qiang Wang, Yingxia Ma, Yahefujiang Paidoula, Taissa Rodrigues, He Chen, Juliana M. Sayão, Ning Li, Jialiang Zhang, Renan A. M. Bantim, Xi Meng, Xinjun Zhang, Rui Qiu and Zhonghe Zhou published in the journal “Science”.

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Sauropod Print from South Korea Reveals Polygonal Scales

A team of scientists based in South Korea have published a paper in the academic journal “Nature” that reports on the discovery of a sauropod dinosaur footprint that has preserved the impression of the underside of the foot. The polygon-shaped scales on the underside of the long-necked dinosaur’s feet (plantar surface), would have provided grip and traction, helping these large creatures to traverse soft mud and slippery ground.

Sauropod Foot Impression Fossil (South Korea)

Picture credit: Nature

Largest Sauropod Print with Underside Surface Preserved

The very distinctive foot impression and its cast, reported upon in this study, represent the largest known sauropod footprint with skin details found to date.  The single print measures more than fifty centimetres across.  The footprint impression was left in silty mudstone as a large sauropod crossed a mudflat in the late Early Cretaceous (Albian faunal stage of the Early Cretaceous).

The researchers from Pukyong National University, Busan (South Korea) and Seoul National University (Seoul), describe a single footprint from the Lower Cretaceous Haman Formation discovered in south-eastern South Korea, they suggest that the floodplain sediments were formed by sheetflood processes, where shallow water moves relatively slowly across slightly sloping ground.  The palaeoenvironment is interpreted as being a semi-arid area with lakes and ponds which was occasionally subjected to wetter weather, resulting in some flooding.

Microbial mats formed across the low-lying ground, adjacent to the water sources and the presence of these microbial mats may have helped with the preservation of the foot details.

A Reconstruction of the Sauropod Foot (Underside)

Picture credit: Hyun Jeong Yoo

The researchers conclude that some sauropods by the late Early Cretaceous had a well-developed polygonal skin texture covering nearly the whole of their foot pads.  This foot pattern is reminiscent to that found on the pads of extant elephants.  These scales would have helped increase stability when these large and heavy animals crossed wet ground.

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