Giant Romanian Pterosaur Hints at Ecological Niches within the Azhdarchidae

Transylvania back in the Late Cretaceous was a very scary place.  This central part of Romania, might be associated with vampires today, thanks mainly to Bram Stoker’s Gothic horror “Dracula”, but towards the end of the Mesozoic, much of Europe was under the sea, rising above the remnants of the once mighty Tethys was an island and real monsters including giant pterosaurs lurked there.

The island is known as Hateg Island and it was a very strange place indeed.  There were dinosaurs, but the apex predator was an animal capable of flight, just like the blood-sucking protagonist from the 1897 novel.  Huge azhdarchid pterosaurs stalked Hateg Island and an international team of researchers writing in the academic journal “Lethaia”, report finding the largest pterosaur jawbone known to science.

Huge Azhdarchid Pterosaurs Stalked Hateg Island

Picture credit: Mark Witton

Niche Partitioning Amongst Giant Flying Reptiles

Pterosaurs in the family Azhdarchidae, represent the largest flying animals to have ever existed, with the longest skulls of any terrestrial tetrapod.  They were globally distributed, with azhdarchid fossils having been reported from every continent except Antarctica.  However, despite their huge size (wingspans in excess of ten metres have been estimated for several species), their fossil record is extremely poor, with most species, even giants such as Quetzalcoatlus, known from a few fragmentary, mere scraps of bone.

The mandible fossil is part of the largest pterosaur mandible (lower jaw) found to date.  The fossil was collected from Maastrichtian continental deposits near Vălioara in the Hațeg Basin, Romania.  The azhdarchid pterosaur Hatzegopteryx thambema is known from these Upper Cretaceous sandstone deposits (Red Cliffs), but this new fossil cannot be confidently referred to H. thambema due to the absence of overlapping skeletal elements.  In short, the lower jaw fossil of H. thambema which would correspond to the newly described mandible has not been found.

It has been suggested that this, as yet, unnamed Hateg pterosaur, may have been a relatively stocky, heavy-set flying reptile, with a short neck and a huge head.  It is reported that comparisons with previously described large‐sized azhdarchid mandibles indicate a certain degree of morphological and probably ecological disparity within the Azhdarchidae.  Different giants may have occupied slightly different niches in the ecosystem, in this way they could avoid direct competition.  The dividing up of resources in this way is referred to as niche partitioning.

A View of the Red Cliffs in Romania (Location of Fossil Find)

Picture credit: Mátyás Vremir

A Six to Eight Metre Wingspan for a Pterosaur

Lead author of the study, published in “Lethaia”  an international journal of palaeontology and stratigraphy, Mátyás Vremir of the Transylvanian Museum Society stated:

“It is not the largest pterosaur ever found, but it is the largest mandible recovered to date, with a reconstructed length of 110 to 130 centimetres.  This might indicate a very large size pterosaur, possibly 8 to 9 metres in wingspan.”

A trio of enormous pterosaurs are associated with the Hateg Formation.  With the discovery of this partial mandible, Transylvania can claim to be a “hot spot” for super-sized flying reptiles.  It had been thought that towards the end or the Cretaceous, the Pterosauria were in decline, however, a paper published in March this year identified a Late Cretaceous ecosystem in Morocco with at least six coeval species of pterosaur including the presence of two azhdarchid pterosaurs, one of whom could have been a giant.

To read our article about the Moroccan fossil discovery: Pterosaurs More Diverse Than Previously Thought.

Fragmentary remains of another azhdarchid pterosaur from Romania, uncovered in 2009, which have yet to be formally described, confirm that Hateg Island was home to a variety of giant flying reptiles.  The fossils associated with this pterosaur have been nicknamed “Dracula” by scientists.

A Piece of the Pterosaur Fossil Bones Nicknamed “Dracula” Eroding Out of a Cliff

Picture credit: Mátyás Vremir

Specimen Number LPB (FGGUB) R.2347

The mandible fossil, part of the back of the lower jaw exhibits anatomical traits that are present in both azhdarchid and tapejarid pterosaurs.  This suggests that the specimen (LPB (FGGUB) R.2347), comes from an animal that had a more basal position within the Azhdarchidae family.  The researchers conclude that this bone shares a number of features with the smaller azhdarchoid Bakonydraco galaczi ,which is known from much older Cretaceous deposits in Hungary.

Vremir added:

“Except for a few scraps, after more than a century of fossil collecting in Transylvania, nothing was known about Pterosaurs until the last 16 years.  In the past 10 years, the picture changed substantially and over 50 fossil specimens were collected from various sites.”

Azhdarchid Pterosaur Wrist Bone

Picture credit: Mátyás Vremir

The huge, partial mandible, the only part of the new animal found so far, was originally dug up in the Hateg region of Transylvania in 1978, but at the time it wasn’t recognised as a pterosaur fossil. Vremir and co-author of the scientific paper, Gareth Dyke, (University of Debrecen, Hungary), were visiting Bucharest’s fossil collection in 2011 and made the connection.

Flightless Giants

Using analogies such as the Elephant Bird of Madagascar and the Dodo from Mauritius, island life can lead to volant creatures evolving in very different directions.   The Dodo and the Elephant bird were descended from birds that could fly, but once established on an island, with few predators, these birds adopted a ground-dwelling existence and over many subsequent generations they lost the ability to take to the air.

Mátyás Vremir and his colleagues speculate that some of the very largest Hateg pterosaurs may have taken a similar evolutionary route.  Perhaps as young animals they could fly, a very good way to avoid terrestrial predators, but as they grew and became adults reaching a size whereby they were unlikely to be attacked by other animals, they were unable to fly.

Everything Dinosaur team members are aware that are number of papers are currently being prepared that explore this intriguing idea further.

The scientific paper: “Partial Mandible of a Giant Pterosaur from the Uppermost Cretaceous (Maastrichtian) of the Hațeg Basin, Romania” by Mátyás Vremir, Gareth Dyke, Zoltán Csiki‐Sava, Dan Grigorescu and Eric Buffetaut.

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How to Brood Your Eggs When You Weigh More Than a Tonne

The question of how dinosaurs incubated their eggs without crushing them has been a puzzle ever since the first dinosaur nesting sites were discovered nearly a hundred years ago.  A Canadian-led study has found a link between the radius of the nest of Oviraptorosauria clade members and the body size of the parent.  In research into the nesting habits of oviraptorosaurs, the scientists discovered that small species laid eggs in clusters, just like many extant birds today.  Much larger species, the giants such as Gigantoraptor, laid eggs in a stacked ring, so that they could keep their eggs close without crushing them with their bodies.

The Larger the Oviraptorosaur the Bigger the Nest Diameter

Picture credit: Masato Hattori

Dinosaurs as Dedicated Parents

Palaeontologists think that there were many different nesting strategies adopted by the diverse dinosaurs, but this study focused on the incubation of the eggs associated with oviraptorosaurs, a group of very bird-like theropods that are known from the Late Cretaceous of North America and Asia.  It is very likely that these dinosaurs were dedicated parents and that they spent many weeks, incubating their eggs by sitting on the nest.  How much parental care dinosaurs showed to their offspring remains an area of considerable controversy, but just like birds today, dinosaurs probably adopted a range of altricial, semi-precocial and precocial strategies* when it came to their young.

Lead author of the study, published in the Royal Society journal “Biology Letters”, Darla Zelinitsky, (Assistant Professor of Geoscience at the University of Calgary, Alberta, Canada), commented:

“In the largest oviraptorosaur clutches [Macroelongatoolithus], the central opening represents most of the total clutch area, likely allowing giant-sized species to rest their entire weight on this area so as not to crush the eggs.”

Forty Fossil Nests Studied

The research team, which included a former PhD student of Darla’s, Kohei Tanaka (Nagoya University, Japan), studied and measured around forty Oviraptorosauria fossil nests, most of which come from China, but fossils from North America and from elsewhere in Asia, were included in the study.  The smallest nests revealed eggs laid in clusters, but the largest nests, associated with the largest of the oviraptorosaurs, were up to 3.3 metres wide, took on a ring shape with a large, flat, central area, presumably where the adult animal sat.

A spokesperson from Everything Dinosaur commented:

“Some of the largest nests associated with the Oviraptorosauria are so wide that a smart car could be parked in the space in the middle, the metaphor is quite appropriate given that a number of giant species have been named.  Dinosaurs like the colossal caenagnathids Gigantoraptor or Beibeilong may have been much heavier than a smart car, yet it is thought that these huge animals had to sit on their nests and incubate the eggs.”

The Oogenus Macroelongatoolithus

Just like dinosaur bones, tracks and the fossilised remains of dinosaur eggs can lead to the establishment of a new genus or species.  Footprints and other trace fossils that are given a formal scientific name are characterised by the epithet “ichno”, whereas, egg fossils are characterised by the epithet “oo”, the root of which is “oolithus” from the Latin meaning “stone egg”.  Numerous dinosaur oogenera have been erected, one of the largest eggs Macroelongatoolithus, some of which measure sixty centimetres in length, are associated with the Oviraptorosauria.

To read Everything Dinosaur’s 2017 blog article about the establishment of a new species of giant Oviraptorosaur from embryos associated with Macroelongatoolithus eggs: Dinosaur Embryo Fossil Leads to New Dinosaur Species.

The researchers conclude that the smallest oviraptorosaurs probably sat directly on the eggs, whereas with increasing body size more weight was likely carried by the central opening, reducing or eliminating the load on the eggs and still potentially allowing for some contact during incubation in giant species.  This adaptation, not seen in birds, appears to remove the body size constraints of incubation behaviour in giant oviraptorosaurs.

The Cluster Layout of Eggs Associated with a Small Oviraptorosaur

Picture credit: Everything Dinosaur

Numerous species of Oviraptorosaurs have been named, most of these dinosaurs were relatively small around 2-3 metres in length, however, considerably larger taxa have been identified, giants such as Gigantoraptor erlianensis, which may have reached lengths of more than eight metres and weighed around 1.4 Tonnes.

While most nests have been found in Asia, in particular the Gobi Desert, Zelinitsky conducted research on dinosaur nests found in South Korea and Canada.

Picture credit: Everything Dinosaur

Zelinitsky added:

“It’s a unique structure, no other dinosaurs build their nests in that shape, and no living animals incubate their eggs this way.  I just think it’s really neat that we’re able to say something more about the nesting behaviours and how they changed in these oviraptorosaur dinosaurs among the various species and species sizes.”

The researchers aren’t sure why these dinosaurs sat on their eggs.  If it was to keep the eggs warm, those dinosaurs that sat in the middle of the ring probably couldn’t transfer heat as effectively as the ones that sat directly on the eggs.  However, these dinosaurs had arms covered with feathers, these “wings” could have helped to shelter the eggs and to protect them as well as providing a warmer surface area to help the eggs maintain an appropriate temperature.

The researchers describe the organisation and egg layout of the nest as a “simple and elegant” solution to the problem of large dinosaurs crushing of their own eggs.

*Altricial and Precocial Nesting Behaviours

Modern birds demonstrate a variety of behavioural responses when it comes to raising their young.  Some bird species like ducks and ostriches have highly precocial young.  The babies are able to vacate the nest and feed themselves within just a few hours of hatching.

Other bird species have a different approach, for example, most of the passerines (song birds), such as wrens, blackbirds and thrushes are helpless when they hatch and rely on their parents to provide food and to keep them warm.  In reality, the Aves (which are very closely related to the extinct oviraptorosaurs), exhibit a wide range of behaviours.  Altricial and precocial traits tend to be at opposite ends of a spectrum, given the paucity of the fossil record, it is difficult to clarify the development strategy of any extinct species.

The Altricial and Precocial Nesting Behaviour Spectrum

Picture credit: Everything Dinosaur

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