Chilesaurus diegosuarezi Transitional Fossil – Root and Branch Reform of the Dinosaur Family Tree

A bizarre Late Jurassic dinosaur called Chilesaurus diegosuarezi had been described as a member of the Theropoda group, but this strange little dinosaur that seemed to possess anatomical characteristics reminiscent of Sauropods, Ornithischian dinosaurs as well as meat-eating Theropods, has been re-described, this time as a “missing link” between the Theropods and the bird-hipped, Ornithischians.  The re-think has to do with the use of datasets to assess the taxonomic relationships between different types of dinosaur.  Chilesaurus may be the first dinosaur to be reassessed in the light of a new way of looking at the dinosaur family tree, chances are, it won’t be the last.

An Illustration of the Bizarre Late Jurassic Dinosaur from Southern Chile C. diegosuarezi

An illustration of Chilesaurus, once classified as a Theropod now regarded as a transitional fossil towards the Ornithischia.

Picture Credit: Nobumichi Tamura

Chilesaurus diegosuarezi Discovery and Description

The first fossils of this three-metre long dinosaur were found by a pair of geologists who were hiking in the remote Aysén region of southern Chile.  Scientists have mapped and explored these deposits (the Toqui Formation – Upper Jurassic) and a description of this dinosaur was published in the journal “Nature” in 2015.

To read Everything Dinosaur’s article written in 2015 reporting the discovery of Chilesaurus: Chilesaurus – a Dinosaur Designed by a Committee

The dinosaur had some strange features that set it apart from other dinosaurs.  Some of these features, such as the over-sized claw which could be extended outwards, on the first digit on the hands of Chilesaurus were reminiscent of the large claws found on the first digits of the front limbs of primitive Sauropods.  However, it had a skull similar to that seen in Theropods, but the jaws were lined with spoon-shaped teeth that pointed outwards at a slight angle.  These teeth were unique in the Theropoda and suggested a plant-eating diet.  In addition, the pubic bone in the pelvis was pointing backwards not forwards as in the Theropods, this pelvic arrangement was typical of a bird-hipped dinosaur, an Ornithischian.  These and other anatomical features made Chilesaurus into a bit of a conundrum for the palaeontologists studying it.  This dinosaur was difficult to place on the Dinosauria family tree, because of its combination of characteristics.  In the original 2015 paper, Chilesaurus was described as a Tetanuran Theropod, a member of the “stiff-tailed” group of bipedal, mainly carnivorous dinosaurs, meaning that it was distantly related to Megalosaurus, the ornithomimids and the Tyrannosaurs.

The Teeth in the Lower Jaw of Chilesaurus were Unlike Any Other Teeth of a Theropod

Teeth adapted for cropping plants.

Picture Credit: Dr Fernando Novas (Museo Argentino de Ciencias Naturales (Buenos Aires, Argentina)

New Dataset – New Classification

Researchers Matthew Baron (Cambridge University) and Paul Barrett (Natural History Museum), writing in the Royal Society journal “Biology Letters” describe how they applied a different dataset to assess the phylogenetic relationship between Chilesaurus and other dinosaurs.  When C. diegosuarezi was first described, back in 2015 the researchers used several datasets to test the interrelationships within the Dinosauria, but crucially, the focus of this analysis was on looking at the relationships within the Saurischia.  In March of this year, Matthew and his co-researchers proposed re-drawing the dinosaur family tree, in essence, resurrecting work undertaken by Thomas Huxley in the late 19th Century, that unites the Saurischia and the Ornithischia together into a new clade called the Ornithoscelida.

Theropods Grouped with Ornithopods

Under this revision, the Theropoda, which are closely related to extant birds and classified as Saurischian dinosaurs (lizard-hipped), were united with the bird-hipped dinosaurs, the Ornithopods, Thyreophora, Ceratopsian, Hadrosaurs etc.

When Chilesaurus was examined again, using the taxonomic relationships proposed by the newly drawn dinosaur cladogram, Chilesaurus was placed in a new position.  The idea that it was a Tetanuran Theropod based on this dataset could be discounted.  Instead, Chilesaurus is placed at a point in the dinosaur family tree where the Ornithischia diverged from their close relatives.  The basal position of Chilesaurus within the clade and its suite of anatomical characters suggest that it might represent a “transitional taxon”, bridging the morphological gap between the Theropoda and the Ornithischia.

Chilesaurus “Missing Link” on the Road to the Ornithischia

In this new Chilesaurus study, the consensus tree formed via the phylogenetic analysis indicates this dinosaur was a basal Ornithischian.

Picture Credit: Royal Society Biology Letters

In the diagram above, the Chilesaurus (red star) is seen as a potential link between the Saurischian Theropoda and the Ornithischian dinosaurs.  Chilesaurus may therefore provide an insight into the evolutionary origins of the bird-hipped dinosaurs.  It may also have an extensive ghost lineage (thin black line), going back to the Middle Triassic.

To read the Everything Dinosaur article, published in March 2017, about the redefinition of the Dinosauria: Root and Branch Reform in the Dinosaur Family Tree

Co-author of the research, Professor Paul Barrett (Natural History Museum) explained the significance of this new paper:

“Chilesaurus is one of the most puzzling and intriguing dinosaurs ever discovered.  Its weird mix of features places it in a key position in dinosaur evolution and helps to show how some of the really big splits between the major groups might have come about.”

Finding a Better Fit within the Dinosauria – Chilesaurus diegosuarezi 

An illustration of Chilesaurus that shows a suite of dinosaur traits.

Picture Credit: Gabriel Lio

Patagotitan mayorum – 69 Tonnes of Titanosaur

This week has seen the long-awaited publication of a scientific paper on the super-sized Titanosaur fossils that Everything Dinosaur blogged about in May 2014.  Writing in the “Proceedings of the Royal Society B (Biology)”, the researchers, which included José L. Carballido and Diego Pol (Museo Paleontológico Egidio Feruglio, Trelew, Argentina), have described this new dinosaur and given it a formal scientific name.  Patagotitan mayorum translates as “the Mayo family Patagonian Titan”.  It may already be familiar to readers, as this fossil discovery was documented in a BBC television programme narrated by Sir David Attenborough back in 2016.  Indeed, a life-size cast of this dinosaur has been on display at the American Museum of Natural History (New York) for nearly eighteen months.

The Life-size Mounted Exhibit of the Newly Named Titanosaur (Patagotitan mayorum)

A cast of the giant Titanosaur Patagotitan mayorum.

Picture Credit: BBC TV

Size Isn’t Everything

Most of the media sources that have covered this announcement have focused on the estimated weight of Patagotitan.  When first studied, the body weight estimate of this beast, (represented by the fossilised remains of at least seven individuals) was put at 77 tonnes.  The researchers have down-sized Patagotitan somewhat in the scientific paper, but at a reported 69 tonnes, this is still an immensely heavy beast, potentially close to the theoretical limit for a body weight of a terrestrial animal.

Patagotitan mayorum – A Size Comparison

Patagotitan mayorum size comparison with an adult African elephant and a human for scale.

Picture Credit: G. Lio/Everything Dinosaur

With an estimated body length of 37 metres and a weight of 69 tonnes, Patagotitan can lay claim to the title of the largest land living animal to be described to date based on substantially complete fossil remains.

To read an article on the initial excavation of the Titanosaur fossil bones: Biggest Dinosaur of all – a New South American Contender

For an article providing information on the BBC documentary: Attenborough and the Giant Dinosaur

An Unprecedented Quantity of Titanosaur Fossil Material

The species’ scientific name was inspired by the region where this new species was discovered, Argentina’s Patagonia (Patago); by its strength and huge size (titan), and by the Mayo family, on whose ranch the fossils of this new Sauropod species were discovered.  The substantial amount of fossil material including a celebrated 2.4-metre-long femur was discovered in three distinct layers, representing flood plain deposits.  The researchers have concluded that these large herbivores must have been regular visitors to this area, perhaps this was on a migration route.  The water flow was unable to dislodge most of the fossil bones, their sheer bulk allowing the remains to be preserved relatively “in situ”, although in a disarticulated state.

The Life-size Cast of Patagotitan mayorum at the American Museum of Natural History (New York)

Titanosaur exhibit (Patagotitan mayorum).

Picture Credit: The American Museum of Natural History/D. Finnin

Estimating the Body Weight of Giant Titanosaurs

The Titanosauria clade represents the most disparate group, in terms of body size of all known Sauropods.  Some of the smallest members of the Sauropodmorpha are represented by Titanosaurs such as the five-metre long Magyarosaurus from Romania, whilst this clade also contains giant animals like Argentinosaurus, Alamosaurus, Dreadnoughtus and the newly described Patagotitan.  Calculating the body weight of an extinct animal, even one with numerous fossil bones to study, is a challenging task, body weight has to be inferred using a variety of methods.

Dr José Luis Carballido (Museum of Paleontology Egidio Feruglio) explained:

“We compared the remains of Patagotitan mayorum with all the species that could be related to it, not only in terms of size, but also those that lived at the same time or had certain features in common.  Among them we included species such as Argentinosaurus, Puertasaurus and Futalognkosaurus, which are other giant species of dinosaurs from Argentina.”

The researchers undertook a phylogenetic study and concluded that the majority of the giant Titanosaurs of Patagonia belong to a single lineage.  This suggests that gigantism within the Titanosauria evolved only once and not multiple times.  The scientists conclude that all the truly huge dinosaurs were related to each other and form a natural group – the Lognkosauria.

Dr Diego Pol added:

“This group of giants probably emerged by the end of the Lower Cretaceous (Patagotitan mayorum would be the oldest) and had survived until the middle Late Cretaceous between 100 and 85 million years ago.”

Patagonia – A Titanosaur Paradise

Titanosaurs diversified and radiated around Gondwana during the middle Early Cretaceous and as a group they survived right up to the end of the Cretaceous, but in Patagonia during the early Cenomanian faunal stage some species obtained enormous sizes the reasons for an evolutionary pressure to grow so big are unclear.

Dr Pol commented:

“About 100 million years ago, a subgroup of Titanosaurs really went crazy in body size.  There must be something in the environment, in how much resources and food was available, in the climate, something must have allowed this fantastic size.  All these contenders for the heavyweight championship of dinosaurs, they all lived in same place, in the same time…understanding why and how these animals evolved into such a fantastic size is the million-dollar question.”

When Excavating Giant Titanosaurs Limb Bones Make Excellent Seats

Filming the documentary “Attenborough and the Giant Dinosaur”.

Picture Credit: Museo Paleontológico Egidio Feruglio

Links to the Rinconsauria

In addition, the scientists consider this super-sized lineage of Titanosaurs a sister group to the Rinconsauria, a clade of Titanosaurs also known from Argentina which are regarded as basal to the group, or at least retaining primitive traits.  The Rinconsauria, which includes Rinconsaurus caudamirus and Aeolosaurus were not giants themselves, in fact, this clade includes some of the smallest South American Titanosaurs described to date.

For the time being the moniker used to describe this huge dinosaur when it was being excavated – “enormosaurus” is redundant, that is until the next huge Sauropod fossil find!

The scientific paper: “A New Giant Titanosaur Sheds Light on Body Mass Evolution Among Sauropod Dinosaurs” by José L. Carballido, Diego Pol, Alejandro Otero, Ignacio A. Cerda, Leonardo Salgado, Alberto C. Garrido, Jahandar Ramezani, Néstor R. Cúneo, Javier M. Krause published in “The Proceedings of the Royal Society B”.

Lemmysuchus obtusidens – Named after Lemmy from Motorhead

On December 28th 2015, the English heavy-metal musician, Lemmy, the founder of Motörhead and doyen of the metal-music genre passed away.  Since that day, many scientists who were fans of Lemmy’s music have sought out ways to honour him*.  It seems that tracks such as “Bomber”, “Overkill”, “Louie Louie” and the iconic “Ace of Spades” are very popular with academics and scientists from a number of disciplines and this week, hard-drinking, hard-living Lemmy, was honoured by having a particularly nasty Jurassic teleosaurid crocodile named after him.  Say hello to Lemmysuchus obtusidens, the newest member of the Teleosauridae, the name means “Lemmy’s blunt-toothed crocodile”.

Dorsal View of the Skull of Lemmysuchus obtusidens

Skull fossil and accompanying line drawing of Lemmysuchus.  Scale bar = 10 cm.

Picture Credit: Trustees of the Natural History Museum, London

From a Clay Pit Near Peterborough

The fossil material now assigned to this new genus was excavated in 1909 from a clay pit near the town of Peterborough (Cambridgeshire), several specimens were collected from the Middle Jurassic strata (Callovian faunal stage).  It was incorrectly catalogued and assigned to a different species, several cladistic and anatomical reviews later and the blunt-snouted, blunt-toothed teleosaurids have undergone a significant revision and fossil material formerly assigned to Steneosaurus obtusidens has ended up in need of a new taxa hence the establishment of Lemmysuchus within the academic literature.

One of the authors of the scientific paper, which has just been published in the Zoological Journal of the Linnean Society, Michela Johnson (University of Edinburgh), described Lemmysuchus:

“With a metre-long skull and a total length of 5.8 metres, it would have been one of the biggest coastal predators of its time.”

A Close View of the Jaw Showing the Robust Teeth

Part of the jaw of Lemmysuchus showing the robust teeth.

Picture Credit: Trustees of the Natural History Museum, London

Durophagous or Macrophagous Diet

In contrast to several other Middle Jurassic teleosaurids, Lemmysuchus had a broad snout and large, robust teeth, this suggests that this substantial crocodylomorph had a different diet to its relatives.  Most teleosaurids were fish-eaters and their jaws, teeth and skulls show adaptations to a piscivorous diet.  The jaws of Lemmysuchus indicate that this reptile might have dined on turtles or other hard-shelled creatures such as ammonites.  It could have made short work of any small marine reptile carcass that it found, it could even have been an active predator of other marine reptiles.

A Nasty Crocodile from the Middle Jurassic of England

Lemmysuchus obtusidens illustration.

Picture Credit: Mark Witton

Paleoartist Dr Mark Witton has recreated the terrifying world of Lemmysuchus obtusidens.  The beautiful reconstruction shows a large Lemmysuchus feeding on a plesiosaur, whilst Rhamphorhynchoid pterosaurs scavenge the remains of an Ichthyosaur that has been washed ashore.

Subtle Nods to Lemmy and to John Martin

The atmospheric image created by Mark Witton, includes a subtle hint towards one of the pieces of artwork associated with Motörhead.  The pattern on top of the crocodylomorph’s skull is a homage to the “snaggletooth” logo that adorned a number of album covers.  In addition, this stunning artwork, depicting a European shoreline some 164 million years ago, pays tribute to one of the earliest depictions of ancient marine reptiles, an illustration by John Martin for the seminal publication “Great Sea Dragons”, by Thomas Hawkins, which was first printed back in 1840.

John Martin depicted a savage, violent seascape dominated by great serpent-like creatures.  Having noted the serpentine archway in Dr Witton’s illustration, Everything Dinosaur contacted Mark and enquired how this archway came to be included.

Mark explained:

“The archway in the background is a nod to the serpentine creature in the background of John Martin’s classic 1840 illustration “The Sea-Dragons as They Lived”.  Much of the right side of the image is a tribute to this work, as is the fact that virtually all the animals in my painting are savage and predatory.  We know that the Jurassic didn’t have any serpentine creatures like those imagined by Martin, so I had to improvise a little by changing his animal to a rock feature and landmass (the adjacent island is where the second ‘hump’ of his creature would be).  I decided to homage his work because, in a lot of ways, 19th century palaeoart is not dissimilar to iconography associated with the harder side of rock music, to which Lemmysuchus has an obvious connection.  Both are a bit silly in how dark and aggressive they are so, though stemming from very different cultures, they’re actually artistic bedfellows.”

“Great Sea Dragons” Illustration by John Martin circa 1840

The 1840 illustration of marine reptiles and pterosaurs by John Martin.

Talented paleoartist Mark has recently published a new work, highlighting his illustrations and providing an insight into the process or imagining and then recreating prehistoric scenes.  The book is entitled “Recreating an Age of Reptiles”, it is highly recommended.

To read a review of “Recreating an Age of Reptiles”: “Recreating An Age of Reptiles” by Dr Mark Witton

Dr Witton added:

“It was quite fun bringing three very different influences together for this painting: the science of the animal itself; the aggressive, dark imagery associated with Motörhead and the influence of old school palaeoart.”

Lemmy from Motörhead (Ian Fraser Kilmister)

Lemmy (birth name Ian Fraser Kilmister).

Co-author Lorna Steel, (Dept. of Earth Sciences, Natural History Museum), proposed that the fearsome crocodylomorph should be named after her late musical hero.

Dr Steel stated:

“Although Lemmy passed away at the end of 2015, we’d like to think that he would have raised a glass to Lemmysuchus, one of the nastiest sea creatures to have ever inhabited the Earth.”

*In early 2016, a petition was organised to get the discoverers of the recently named, super-heavy element 115 Ununpentium, to change its name to Lemmium.  Despite attracting a reported 100,000 signatures the bid to place the heavy metal music pioneer onto the Periodic Table failed.  Still it’s not every day that you get a bone-crushing, Jurassic marine crocodile named after you.