Hesperornithoides miessleri – Helping to Map Out the Bird Family Tree

A joint team of British and American palaeontologists have announced the discovery of a new species of dinosaur that roamed the Late Jurassic of Wyoming.  The specimen consisting of both cranial and postcranial material lived around 150 million years ago and it has been tentatively placed within the troodontid branch of the Paraves part of the Theropoda.  It could help scientists to better understand the evolutionary relationships between feathered dinosaurs and true birds and it raises intriguing questions as to when powered flight evolved within the Dinosauria.

The little dinosaur, estimated to have measured less than a metre in length (single known specimen is either an adult or a sub-adult), has been named Hesperornithoides miessleri.

A Life Reconstruction of the Newly Described Dinosaur H. miessleri

A life reconstruction of Hesperornithoides miessleri.

Picture Credit: Gabriel Ugueto

An Inhabitant of Wetlands

Writing in the academic journal PeerJ, the authors which include scientists from the University of Manchester, report the taphonomy of the fossil material suggests that this dinosaur was an inhabitant of wetland environments for at least a portion of its life history.  The fossil material was actually discovered back in 2001, whilst excavation work was being carried out on the fossil material associated with Supersaurus.  The fossil comes from Converse County (Wyoming), from strata making up the middle portion of the famous Morrison Formation.  The fossil-bearing strata from the “Jimbo Quarry” has been variously dated to the Oxfordian and Tithonian ages of the Jurassic.

Full Skeleton of Hesperornithoides miessleri

Hesperornithoides fossil material “left” (A) and “right” (B) sides of the blocks after final preparation (B).  Scale bar = one cm.

Picture Credit: Levi Shinkle

A Resident of the Famous Morrison Formation

The Morrison Formation is famous for its vertebrate fossils, including many examples of dinosaurs, such as Allosaurus, Ceratosaurus, Diplodocus, Brontosaurus and Camarasaurus.  The carnivorous Hesperornithoides is the smallest dinosaur described to date from Wyoming.

Palaeontologist Bill Wahl  (Wyoming Dinosaur Centre), a co-author of the scientific paper, recalled how excited the field team were when they uncovered the block containing the partially articulated bones.

He stated:

“We were removing a ledge of overburden rock and found, unfortunately with a shovel, some tiny, delicate bones poking out.  We immediately stopped, collected as much of the bones as possible and spent the next few days frantically searching for more.  Only after some of the bones were cleaned did we realise that we had found something spectacular.”

In 2005, the fossil specimen was donated to the Big Horn Basin Foundation, a research and education-based not-for-profit organisation that was merged with the Wyoming Dinosaur Centre back in 2016.  This is how Hesperornithoides miessleri came into the Wyoming Dinosaur Centre’s fossil collection.  The fossil, now known as WYDICE-DML-001, was nicknamed “Lori”  and was examined by Dean Lomax (University of Manchester) and co-author of the study back in 2008, a successful crowdfunding campaign permitted extensive research to be undertaken.

Dean commented:

“I remember the first time I laid my eyes on this little dinosaur.  Even back then, I knew it was a significant discovery.  But, it wasn’t until 2015 when our dino team formed and we began to study ‘Lori’ in much more detail than ever before.”

Reconstructed Quarry Map of “Lori” (Hesperornithoides miessleri)

Association of skeletal elements assembled from 3-D scans of specimen blocks prior to final mechanical preparation.

Picture Credit: PeerJ

Found on Private Land

The specimen was found on private land owned by the Miessler family.  The trivial name honours their help, support and assistance in bringing this little theropod to the attention of the scientific community.  The genus name is a combination of “Hesper”, referring to its discovery in the American West and “ornis” a nod to its very bird-like anatomy.

A Reconstruction of the Skeleton of Hesperornithoides miessleri

Skeletal Reconstruction Hesperornithoides miessleri (scale bar = 25 cm).

Picture Credit: Scott Hartmann

A Key Conclusion of the Study

A key conclusion of the scientific paper relates to the origin of powered flight within the Dinosauria.  Hesperornithoides was very probably entirely terrestrial.  It could not fly, but it has a very bird-like body, suggesting that many features associated with an avian anatomy evolved in dinosaurs that lived out their lives on the ground.  It is the oldest dinosaur of this type, known from more than just teeth fossils from North America.  The terrestrial and flightless lifestyle is consistent with the base of Paraves, and with the base of paravian subclades, suggesting that avian flight evolved within the Avialae, most likely in the Late Jurassic or Early Cretaceous.

Lead author of the paper and PhD student at the University of Wisconsin-Madison, Scott Hartman stated:

“We wanted to expand the dataset used to test dinosaur-bird relationships, so we added hundreds of new species and tens of thousands of new characters.  We found that Lori is a primitive member of a group of dinosaurs that includes Troodon, but perhaps more importantly we discovered that the smaller details of the family tree of bird-like dinosaurs isn’t quite as resolved as some researchers would claim.”

Scott Hartman continued:

“For example, it only takes a few changes in the dataset for Hesperornithoides to be found as a closer relative of Velociraptor than of Troodon.  One robust finding we did come up with is that even as the interrelationships changed, the primitive members of all these groups were non-flying ground dwelling dinosaurs.  That means that some small relatives of Velociraptor such as Microraptor that looks like it could have glided evolved this separately from the modern bird family.”

Hesperornithoides Cranial Material

Hesperornithoides cranial material and interpretative line drawings.

Picture Credit: Levi Shinkle

The scientific paper: “A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight” by Hartman, S., Mortimer, M., Wahl, W. R., Lomax, D. R., Lippincott, J. and Lovelace, D. M and published in PeerJ.

Everything Dinosaur acknowledges the help of a media release from the University of Manchester in the compilation of this article.

Vespersaurus paranaensis – A Desert Dwelling Dinosaur

Roaming the Late Cretaceous of Brazil some 90 to 85 million years ago, was a little, fast-running, carnivorous dinosaur with a unique way of getting about.  The dinosaur has been named Vespersaurus paranaensis and at an estimated length of just over a metre (maximum length 1.6 metres), this was no giant, but its discovery will help scientists to work out the taxonomic relationships amongst an obscure group of theropods known mainly from Gondwana and provide new insight into theropod locomotion.

Writing in the academic journal “Scientific Reports”, the researchers suggest that Vespersaurus supported its weight on just one digit (metatarsal III and toe III), it may have been essentially monodactyl i.e. it had one main, central weight-bearing toe.  The other toes associated with support and weight bearing in the Theropoda (digits II and IV), were very much smaller and may even have been held off the ground.

A Life Reconstruction of the Newly Described Brazilian Theropod Vespersaurus paranaensis

A life reconstruction of the Brazilian dinosaur Vespersaurus.

Picture Credit: Rodolfo Nogueira

Affinities with the Abelisauroidea

Analysis of the fossil material, which includes vertebrae, elements from the pelvis and limbs along with fragmentary skull bones suggests that this little dinosaur is a member of the Abelisauroidea, specifically the Noasaurinae, an enigmatic subfamily collectively known from sparse fossil material mostly from southern latitudes.  For example, Vespersaurus has the reduced forelimbs which are characteristic of the abelisaurids and it is hoped that these fossils will help palaeontologists to better understand the phylogeny of these Late Cretaceous predators.  Although only about 40% of the skeleton is known, these fossils represent one of the best examples of a member of the Noasauridae family found to date and the most complete dinosaur specimen from the whole of the Bauru Sub-basin.  It is also the first dinosaur to be described from rocks that constitute part of this basin, the Caiuá Group.

Frontal (Skull Bone) and Views of an Isolated Tooth (Vespersaurus paranaensis)

Cranial and dental remains of Vespersaurus paranaensis, an isolated frontal and an isolated broken tooth.

Picture Credit: Scientific Reports (Langer et al)

A Late Cretaceous Desert Environment

The majority of the strata making up the Caiuá Group represent sandstones that were deposited by the action of wind (aeolian deposits).  During the Late Cretaceous, this region of Gondwana was an extensive desert.  The fossil record is particularly sparse with only a handful of animals recorded from what probably would have been oases.  Arguably, the most famous fossils from this part of the world represent a pterosaur monodominant bonebed (Caiuajara dobruskii).  Other than Caiuajara and this new dinosaur, the only other vertebrate fossils known from this area represent a lizard and a turtle.

Pectoral Elements and Limb Bones (V. paranaensis)

Pectoral girdle and limb elements of Vespersaurus paranaensis.

Picture Credit: Scientific Reports (Langer et al)

To read about Caiuajara: New Species of Flying Reptile Identified from Pterosaur Graveyard

Strange Footprints

Examination of the foot bones and toes suggests that this dinosaur supported its weight on just a single, central digit.  Such an anatomical adaptation (a monodactyl stance), has not been recorded in the Archosauria before, but such a form of locomotion had been inferred by palaeontologists as numerous footprints indicating an enlarged weight-bearing toe in a theropod dinosaur have been found in rocks of the same age as the sediments that yielded the fossils of Vespersaurus.

A Close Up of the Foot Showing the Weight-bearing Toe

A close-up view of the foot of Vespersaurus showing the weight-bearing central toe.  Footprints suggesting a monodactyl stance have been found in the same stratigraphic unit that yielded the new dinosaur.

Video image credit: Universidade de Sáo Paulo et al

Helping to Classify the Noasaurinae

The Noasaurinae are a branch of the Abelisauroidea consisting of small, predatory theropods known from Upper Cretaceous strata mostly associated with Gondwana (southern latitudes).  Perhaps the best known noasaurid is Masiakasaurus knopfleri, from the latest Cretaceous (Maastrichtian) of Madagascar, but two other taxa from Argentina described from relatively fragmentary fossil material have been assigned to the Noasaurinae (Noasaurus leali and Velocisaurus unicus).  Other dinosaurs from outside South America have also been tentatively assigned such as an as yet, unnamed specimen from India, Deltadromeus agilis from Morocco and Genusaurus sisteronis from France.  It is hoped that this more complete fossil specimen will permit palaeontologists to better understand taxonomic relationships within the Noasaurinae and their wider placement within the Abelisauroidea.

Building a Family Tree of the Abelisauroidea

Vespersaurus is assigned to the Noasaurinae, a sub-family of the Abelisauroidea clade of theropods.  The suggested position of Vespersaurus is shown by the red dinosaur silhouette.

Picture Credit: Scientific Reports (Langer et al)

Etymology of Vespersaurus

The generic name derives from the words “vesper” (Latin for evening/west) and “sauros” (Greek for lizard/saurian), in reference to the name of the town Cruzeiro do Oeste (Western Cross), where the fossils were found.  The specific epithet refers to the Paraná state, the authors report that V. paranaensis represents the first non-avian dinosaur from that area of Brazil.

The scientific paper: “A new desert-dwelling dinosaur (Theropoda, Noasaurinae) from the Cretaceous of south Brazil” by Max Cardoso Langer, Neurides de Oliveira Martins, Paulo César Manzig, Gabriel de Souza Ferreira, Júlio César de Almeida Marsola, Edison Fortes, Rosana Lima, Lucas Cesar Frediani Sant’ana, Luciano da Silva Vidal, Rosangela Honório da Silva Lorençato and Martín Daniel Ezcurra published in the journal Scientific Reports.