Comprehensive Review of Dinosaur/Bird Relationship Published

The evolution of the Aves (birds), can be regarded as one of the most significant moments in tetrapod evolution.   From their Mesozoic origins, the birds have thrived and today they have a global distribution and still outnumber the Mammalia in terms of extant species.  Spectacular fossils, particularly those from northern China, demonstrate that birds are members of the Theropoda.

Numerous palaeontologists and other scientists have got together to publish a comprehensive overview of that part of the Theropoda most closely related to living birds.  The volume entitled “Pennaraptoran Theropod Dinosaurs – Past Present and New Frontiers” has been edited by Research Assistant Professor Dr. Michael Pittman of Hong Kong University and Professor Xing Xu (Chinese Academy of Sciences).

Pennaraptoran Theropod Dinosaurs – Past Progress and New Frontiers

Picture credit: Bulletin of the American Museum of Natural History and Julius T Csotonyi

The Origin of Birds

The Pennaraptora are a clade that consists of the Aves, as well as the pennaceous feathered dromaeosaurids, troodontids, oviraptorosaurians and the scansoriopterygids.  It was erected relatively recently (2014), it is defined as the most recent common ancestor of Oviraptor philoceratops, the “raptor” Deinonychus antirrhopus, and Passer domesticus (the house sparrow), and all descendants.  To improve understanding about this clade the International Pennaraptoran Dinosaur Symposium (IPDS), was held at the University of Hong Kong in the spring of 2018 and as a follow-up to this event, a special volume detailing the scientific papers and research has been published in the journal “Bulletin of the American Museum of Natural History”.

The symposium permitted the drafting of a comprehensive cladogram demonstrating evolutionary relationships within the Pennaraptora.

Evolutionary Tree of Pennaraptoran Theropods

Picture credit: Pittman et al

Commenting on the significance of this volume, co-editor Dr Pittman stated:

“The volume documents past progress, works toward consensus on key unresolved issues, breaks new ground in the field and identifies priority areas for future research.”

Split into Three Sections

The publication has been divided into three main sections and consists of fourteen chapters:

1).  The Fossil Record, Systematics and Biogeography – how fossils have shaped the definition of the clade.

2).  Anatomical Frontiers – with a focus on recent fossil discoveries particularly related to the manus (hand) and the skull.

3).  Early Flight Study – research into the origin and evolution of powered flight.

Incisivosaurus – A Primitive Member of the Oviraptorosauria

Picture credit: Xing Xu and Waisum Ma

Examining the Relationship Between Extant Aves and Theropod Dinosaurs

The third part of the volume, looking at the evolution of flight examines recent efforts to identify the small pennaraptorans that first took to the skies, what their flight capabilities were and how their flight might have been acquired.  A new broader context is postulated for flight behaviour as part of a functional landscape.  Wing-assisted incline running (WAIR), a behaviour seen in modern birds that is proposed as an early stage of flight development, is argued as a later innovation based on a study of modern ostriches.

Co-editor Professor Xu commented:

“The volume involved 49 experts from more than 10 countries whose views cover much of the current discussion on pennaraptoran palaeobiology and evolution.”

One of the contributors, Dr Daniel Field (Cambridge University), added:

“This is a landmark volume that advances our understanding of pennaraptoran dinosaurs and identifies key areas to address in the years ahead.”

Sapeornis chaoyangensis – An Early Cretaceous Avialan

Picture credit: Serrano et al

Everything Dinosaur acknowledges the assistance of a media release from Hong Kong University in the compilation of this article.

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Bristol Channel Could Provide Oldest Evidence of Insular Dwarfism

The flamboyant Baron Franz Nopcsa did much to establish the concept of island dwarfism, that is animals on islands with limited resources often evolve into much smaller forms.  Baron Nopcsa was the first person to suggest dwarf dinosaurs based on specimens associated with the Late Cretaceous Hateg Island, but a team of researchers including scientists from Bristol University, have uncovered evidence of island dwarfism in strata laid down in the Upper Triassic millions of years before the Hateg biota evolved.

Late Triassic Island Dwarfs

Writing in the “Proceedings of the Geologists’ Association”, the researchers report on an analysis of fossil remains from strata laid down around 205 million years ago that suggests ancient North American reptiles lived on an island archipelago in the area that now forms South Wales and the Bristol Channel.

Student Matthew Skinner, (School of Earth Sciences at Bristol University), studied a treasure trove of fossil material that had been collected from Ruthin Quarry back in the 1950s and housed as part of the fossil collection at the National Museum of Wales (Cardiff).  The fragmentary and very fragile material documented life on a small tropical island during a time in Earth’s history when the Atlantic Ocean did not exist and Europe and North America were only partly separated and what division there was consisted of narrow, shallow seaways dotted with small islands.

World Map (Late Triassic) The Black Square Shows the Approximate Location of the Island Archipelago

Eleven Different Taxa

In total eleven different taxa were identified, many of the vertebrates identified from the Ruthin Quarry fossils were reminiscent of fossils associated with much older strata in North America.  The researchers describe the Ruthin Quarry biota as “relictual”, they are the remnants of a population that was once much more widely distributed.  The Ruthin Quarry specimens are some 25 million years younger than the similar fossils known from North America.

Matthew Skinner commented:

“We were amazed to discover that most of the Ruthin beasts showed greatest similarity to relatives from North America.  Of course, at that time, one could just hop across from South Wales to New York.  The islands provided little space and food and so regular-sized animals couldn’t survive on them; the Ruthin animals were all dwarf versions of their closest mainland relatives, maybe half the size on average.”

Professor Mike Benton (Bristol University), who supervised the research study, explained:

“Our other questions were about the effects of island life.  We know today that animals on remote islands can evolve in different ways from on the mainland.  Often they become smaller, as there is less food, and they might be anachronistic – meaning they are throw-backs to much more ancient animals from the mainland.”

As most of the taxa identified from the site possess closest relatives that are found in much older strata and their body size is small, the scientists have concluded that these fossils record evidence of island dwarfism, also referred to as insular dwarfism.  This is the oldest known record of this biological phenomenon.

A New Species – Smilodonterpeton ruthinensis

The team identified cartilaginous fish including the primitive shark Rhomphaiodon minor from a single tooth which helped to date the material.  Numerous reptiles were described including parareptiles from the Procolophonidae family, one procolophonid is a new species and has been named Smilodonterpeton ruthinensis (chisel-toothed reptile from Ruthin).

Other reptiles identified include three species of rhynchocephalians (beak lizards, distantly related to the living Tuatara of New Zealand), the herbivore Tricuspisaurus thomasi and archosaurs including a small, predatory crocodylomorph similar to Terrestrisuchus.  Although less than a metre in length, this crocodylomorph may have been the top predator on the island.  From this inventory, a simple food chain for the Ruthin Quarry fossil site could be constructed.

Location of the Fossil Finds and the Ruthin Quarry Food Chain

Picture credit: Bristol University

CT Scans and Three-Dimensional Computer Models

A number of the delicate fossil specimens were subjected to non-destructive CT scans to help reveal their anatomical details.  Tricuspisaurus had been named and scientifically described in 1957, but its taxonomic relationship with other reptiles was unclear.  This research has enabled the scientists to challenge the view that Tricuspisaurus was a procolophonid.

Co-author of the paper, Dr David Whiteside (Bristol University and the Palaeontology Department of the London Natural History Museum), stated:

“It has been questioned for many years how Tricuspisaurus is related to the other reptiles.  I was keen we found out what it really was, and Matthew was able to CT scan the specimens and this showed that its teeth were located in tooth sockets and it had a beak at the front of its jaws.  This confirms it was not a procolophonid, as had been thought, but a distant relative of birds, crocodiles and dinosaurs.”

CT Scan and Digital Image of the Lower Jaw of Tricuspisaurus

Picture credit: Bristol University

For a related article on the Bristol Channel/South Wales archipelago: Getting to Grips with the Jaws of Clevosaurus.

The scientific paper: “Late Triassic island dwarfs?  Terrestrial tetrapods of the Ruthin fissure (South Wales, UK) including a new genus of procolophonid” by M. Skinner, D. Whiteside, and M. Benton published in the Proceedings of the Geologists’ Association.

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