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2 12, 2019

New Toothy Pterosaur Identified from the Afro-Arabian Continent

By | December 2nd, 2019|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Photos/Pictures of Fossils|0 Comments

Mimodactylus libanensis Newly Described Lebanese Pterosaur

The Pterosauria were very probably ubiquitous over much of our planet during the Mesozoic.  Once these flying reptiles had begun to diversify during the Late Triassic and into the Jurassic, these winged-wonders, the first vertebrates to master powered flight, would have spread far and wide.  Trouble is, although palaeontologists have described more than 120 genera, our knowledge of the Pterosauria is limited and scientists rely on a few key deposits to provide them with the majority of specimens to study.  Pterosaurs are now known from every continent, but surprisingly, very little material has been collected from Africa and the Arabian peninsula.

Writing in the academic journal “Scientific Reports”, a team of international scientists have announced the discovery of a Late Cretaceous pterosaur from Lebanon.  Mimodactylus libanensis is the most complete pterosaur specimen to have been discovered from the Afro-Arabian continent.  Intriguingly, the fossil material shows a strong taxonomic affinity with a genus known from China (Haopterus gracilis), together the pair form a new clade of toothy pterosaurs – the Mimodactylidae.

A Life Reconstruction of the Newly Described Pterosaur Mimodactylus libanensis

A life reconstruction of the pterosaur Mimodactylus.

A life reconstruction of Mimodactylus.  This flying reptile lived on the western side of the Tethys Seaway, which divided Europe from North Africa.  The sea was shallow with many reefs and lagoons, it was a spur of the mighty Tethys Ocean that stretched eastwards to south-eastern Asia.

Picture Credit: Julius Csotonyi

Long, Narrow Wings

The fossil specimen comes from the famous Hjoûla Lagerstätte of Lebanon, a deposit famous for its beautifully preserved fossil fish, but tetrapod fossils are exceptionally rare.  The nearly complete and articulated skeleton indicates that Mimodactylus had long, narrow wings and that it would have been well-adapted to soaring over the sea, in a similar way to extant frigate birds.  As to what this pterosaur ate, that is open to speculation, but the robust, conical teeth located at the front of the jaws suggest a durophagus diet.  Perhaps this pterosaur fed on molluscs and other shelled creatures.

A View of the Fossilised Remains of Mimodactylus libanensis

Mimodactylus fossil material and line drawings.

Mimodactylus views of the fossil material and accompanying line drawings.  Photo (a) and drawing of the complete specimen.  Close up (b) of scapula and coracoid whilst (c) shows detail of the wrist, showing the relation of the pteroid and the carpus.  Detail (d) of the humerus.  Note scale-bars, a: 50 mm; b-d: 10 mm.

Picture Credit: Kellner et al/Scientific Reports

The Mimodactylidae

The single specimen represents a sub-adult, the wingspan is estimated to be around 1.3 metres, but in the absence of any fossil material representing an adult animal, the actual size of a fully grown Mimodactylus is not known.  A phylogenetic analysis of the 95 million-year-old specimen suggests that Mimodactylus libanensis is closely related to pterosaurs from Asia and that with the taxon Haopterus gracilis, which is known from the Yixian Formation of Liaoning Province (north-eastern China), it forms a new clade of derived toothy pterosaurs, the Mimodactylidae.

One of the co-authors of the scientific paper, Michael Caldwell (University of Alberta), commented:

“This means that this Lebanese pterodactyloid was part of a radiation of flying reptiles living in and around and across the ancient Tethys Seaway, from China to a great reef system in what is today Lebanon.”

What’s in a Name?

The genus name is from the acronym (MIM), the Mineral Museum of Beirut in Lebanon, where the specimen is housed and the Greek “dactylos” meaning digit.  The trivial epithet honours Lebanon where this rare specimen was found.  An honourable mention to the anonymous philanthropist who acquired the fossil and ensured this important pterosaur was kept in Lebanon.

A Closer View of the Skull and Jaws of Mimodactylus libanensis

Mimodactylus skull and jaws.

A close up view of the skull and the jaws of Mimodactylus (inset – close view of the conical teeth). Scale bars (a) 10 mm and (b) 1 mm.

Picture Credit: Kellner et al/Scientific Reports

The scientific paper: “First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity” by Alexander W. A. Kellner, Michael W. Caldwell, Borja Holgado, Fabio M. Dalla Vecchia, Roy Nohra, Juliana M. Sayão and Philip J. Currie published in Scientific Reports.

1 12, 2019

The Theropod Majungasaurus Replaced Teeth as Fast as Herbivorous Dinosaurs

By | December 1st, 2019|Dinosaur and Prehistoric Animal News Stories, Dinosaur Fans, Main Page, Photos/Pictures of Fossils|0 Comments

Majungasaurus – Elevated Tooth Replacement Rate

Scientists writing in the academic journal “PLOS One”, have really got their teeth into an aspect of dinosaur anatomy, that surprisingly has not attracted that much research to date.  Dinosaurs replaced their teeth, as teeth were shed, perhaps when feeding or fighting, then replacements would erupt from the gumline permitting these reptiles to retain their toothy grins.  The speed of tooth replacement can provide palaeontologists with important information about feeding ecology.  The fastest tooth replacement rates had been associated with herbivorous dinosaurs, the likes of the Ceratopsia and the hadrosaurids.  After all, these plant-eaters fed on very coarse plant material so their teeth were subjected to plenty of wear and tear.  In this new study, undertaken by researchers at Ohio University and Adelphi University (New York), tooth replacement rates for three carnivorous dinosaurs were calculated.

Surprisingly, Majungasaurus (M. crenatissimus), from the Late Cretaceous of Madagascar, had a much faster tooth replacement than the other theropods studied.  Its tooth replacement rate puts it on a par with the rates associated with the horned dinosaurs and the duck-bills.

Computer Generated Images of the Skull of Majungasaurus

Majungasaurus skull diagram.

A diagram showing the details of the skull of Majungasaurus.  Views (A) left lateral, (B) buccal view, (C) dorsal view, (D) ventral view, (E) posterior view, (F) anterior view.

Picture Credit: Memoirs of the Society of Vertebrate Paleontology/Ohio University/from Sampson, S. D. and L. M. Witmer (2007)

Rapid Replacement of Majungasaurus Teeth

CT scans and detailed cross-sectional analysis were carried out on individual teeth and jaw elements associated with three theropod dinosaurs.  These dinosaurs were the blunt-snouted, deep-skulled Majungasaurus along with Allosaurus and Ceratosaurus.  High tooth replacement rates were identified in three genera, but the researchers concluded that Majungasaurus replaced its teeth much faster than either Allosaurus or Ceratosaurus.  Majungasaurus would form a new tooth in each socket every fifty-six days or so, whilst Allosaurus and Ceratosaurus took in excess of a hundred days.

Lead author of the research, Michael D. D’Emic, (Adelphi University), explained the significance of this finding by commenting:

“This meant they [Majungasaurus] were wearing down their teeth quickly, possibly because they were gnawing on bones.  There is independent evidence for this in the form of scratches and gouges that match the spacing and size of their teeth on a variety of bones — bones from animals that would have been their prey.”

Assistant professor D’Emic went onto add that extant animals too, gnaw on bones, this is a way for them to get certain nutrients, but to feed like this requires exceptionally tough and strong teeth, Majungasaurus did not have teeth like that, so they evolved an accelerated replacement strategy to compensate.

Examining Tooth Replacement in Theropod Dinosaurs

Theropod dinosaurs in the study - Allosaurus, Ceratosaurus and Majungasaurus.

Studying tooth replacement in theropod dinosaurs.  Three theropod genera were studied – Allosaurus, Ceratosaurus, Majungasaurus.  Scale bar for (a), (b) and (c) equals 10 cm, the scale bar for (d), (e) and (f) equals 100 μm.

Picture Credit: M. D. D’Emic et al/PLOS One with additional annotation by Everything Dinosaur

The picture (above), shows computer generated images of jaw elements of each dinosaur associated with the study (a) Allosaurus, (b) Ceratosaurus and (c) Majungasaurus.  The images (d-f) show histological tooth sections which reveal incremental growth lines that can help to determine the individual age of teeth (d) Majungasaurus, (e) Ceratosaurus and (f) Allosaurus.

Using a statistical model to predict tooth age from tooth length measured in CT slices, replacement rates for these three genera are estimated at:

  • Majungasaurus 56 days
  • Allosaurus 104 days
  • Ceratosaurus 107 days

The rapid replacement rate recorded in Majungasaurus puts it on a par with living sharks and herbivorous dinosaurs.

This research builds on an earlier paper published twenty years ago, the authors of this new study suggest that with so many new dinosaurs being named and described over the last two decades or so, there is a lot of scope to build on the data collected so far and to provide further insights into dinosaur feeding ecology.

Michael D’Emic stated:

“I’m hoping this latest project spurs more people to study other species.  I bet that it will reveal further surprises and hopefully that will lead to a better understanding of how dinosaurs evolved to be successful for so long.”

Now that less destructive forms of study are available to scientists, the analysis of tooth wear and the internal structures of dinosaur teeth will help to provide a clearer picture regarding dinosaur feeding behaviour and dietary preferences – now that’s something to smile about.

An Illustration of the Late Cretaceous Abelisaurid Majungasaurus (M. crenatissimus)

A drawing of Majungasaurus.

An illustration of the abelisaurid Majungasaurus.

Picture Credit: Everything Dinosaur

The scientific paper: “Evolution of high tooth replacement rates in theropod dinosaurs” by Michael D. D’Emic , Patrick M. O’Connor, Thomas R. Pascucci, Joanna N. Gavras, Elizabeth Mardakhayav and Eric K. Lund published in PLOS One.

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