How Long is a Dinosaur’s Tail?

How long is the tail of a dinosaur?  That’s a good question, one that has quite a complicated answer, but if a definitive assessment of the morphology of caudal vertebrae (tail bones) of the Dinosauria could be carried out, then palaeontologists would be better able to piece together (literally), the tails of dinosaurs and assess their length from even fragmentary remains.

The Tail of the North African Sauropod Atlasaurus

An Atlasaurus partial tail on display in the foyer of the BBVA Bancomer Tower (Mexico City).   A new study suggests that the tails of dinosaurs were very varied in their form, shape and function.

Picture Credit: Reuters/Daniel Becerril

Research led by Dr David Hone (Queen Mary University of London), in collaboration with colleague Dr Steven Le Comber (who sadly passed away in 2019) and Dr Scott Persons of Mace Brown Museum of Natural History (Charleston, South Carolina, USA), permitted a comprehensive dataset of dinosaur tails to be built up.  The data indicates that there is considerable variation in the caudal vertebrae of members of the Dinosauria.  The number of tail bones varies, as does their morphology (shape).  In addition, overall length of the tail as a proportion of body size is inconsistent within the very diverse dinosaur clade.

With such variation, comparing tails of different genera or even dinosaurs from the same family will prove troublesome.

However, the scientists did identify some general patterns that could prove useful when it comes to learning about a genus with only a few tail bones to work with.

What’s in a Tail?  The Great Variation within the Tails of Dinosaurs

Examples of different dinosaur tails.  Note scale bar = 1 metre.

Picture Credit: Hone et al (PeerJ) with additional annotation by Everything Dinosaur

General Principles of Dinosaur Tails

Patterns of changes in centra lengths (the central part of each vertebra) along the tails of dinosaurs do vary.  However, the researchers did identify some general principles in terms of the bones that make up the tails.  For example, when viewing the tail bones from the base of the tail down to the tip, several different dinosaurs show a pattern of short centra, followed by a sequence of longer centra, with the remainder of the tail being made up of a long series of centra tapering in length.

The team suggest that this general pattern is consistent with the function of different parts of the tail, the longer centra quite near to the base of the tail help to provide support for the attachment of the large muscles associated with the top of the leg and this region of the tail.  This general pattern is not found in many early types of dinosaur, so the researchers conclude that this trait must have evolved independently in different kinds of dinosaurs over time.

A Reconstruction of the Tail of an Edmontosaurus

The reconstructed tail of the hadrosaurid Edmontosaurus.  The research team were able to identify a general pattern of bone morphology and size in a number of derived dinosaur taxa.

Picture Credit: Everything Dinosaur

Deducing Form and Function

Writing in the on-line journal “PeerJ”, the scientists state that the number of vertebrae in a given section of tail can indicate its flexibility or its stiffness.  The more vertebrae recorded over a given distance then it is likely that this section of tail was quite flexible.  Conversely, the fewer joints in any length of tail will imply reduced flexibility.

General conclusions about dinosaur tails could be made, for example:

1. The base of many dinosaur tails was flexible and allowed virtually the whole tail to be swung as a collective whole, helping to stabilise the animal as it moved and perhaps also having a defensive function in some herbivores.
2. Just passed the tail base there was a zone of relative stiffness that supported the muscles associated with the tail and rear legs (caudofemoralis musculature).
3. After the termination of the caudofemoralis and for a highly variable distance, the remaining vertebrae tapered to a reduced size.

The scientific paper: “New data on tail lengths and variation along the caudal series in the non-avialan dinosaurs” by David W. E. Hone, W. Scott Persons and Steven C. Le Comber published in PeerJ.

Horned Dinosaurs Evolved Frills to Attract Mates

The ornate and very diverse head crests and frills of horned dinosaurs (ceratopsians) probably evolved to help them attract a mate.  That is the conclusion from a study recently published in the Proceedings of the Royal Society B.  Ever since the first horned dinosaurs were discovered, palaeontologists have debated why these plant-eating dinosaurs evolved such elaborate neck shields (these features are produced by elaborate extensions to the parietal and squamosal skull bones).  It had been thought that these frills provided some protection from attack from theropod dinosaurs such as the contemporaneous tyrannosaurs, or perhaps they had a role in thermoregulation.  With so many different types of large ceratopsians known from the Late Cretaceous of North America it had also been suggested that these crests and frills played a role in species recognition.  An extensive analysis of the skulls of “first horned face” – Protoceratops (P. andrewsi), suggests that they played a role in sexual selection.

A Reconstruction of the Skeleton of Protoceratops (P. andrewsi)

A skeleton of a Protoceratops on display.  The elaborate head crest complete with fenestrae (two large holes), probably evolved as a result of sexual selection.

Picture Credit: Everything Dinosaur

Sexual Selection

Sexual selection is a method of natural selection in which members of one biological sex choose mates of the other sex to mate with.  Certain characteristics in organisms are favoured by members of the opposite sex and organisms that possess the favoured feature(s) are the ones that breed.  This leads over time to these preferred characteristics becoming more intricate and elaborate.  There are plenty of examples to be found in the natural world today, most certainly amongst the closest living relatives of the Dinosauria the birds.  The elaborate but cumbersome tails of peacocks for instance, or the ornate and very beautiful plumes of the birds of paradise.

A Male Goldie’s Bird of Paradise Displays to Attract a Mate

A Goldie’s bird of paradise displays.  The ornate feathers on this beautiful male are an example of sexual selection.

Picture Credit: Tim Laman/National Geographic Image Collection

The researchers, which included scientists from the Natural History Museum (London) and Queen Mary University of London, used computer modelling to map how the skull of Protoceratops changed as the dinosaur grew.  Protoceratops has a rich and extensive fossil record.  Hundreds of specimens have been found ranging from embryos in unhatched eggs up to large, very old adults.  This extensive fossil record made this type of horned dinosaur an ideal candidate for this study.

The Fossilised Remains of a Young Protoceratops

The fossilised remains of a young Protoceratops.  The extensive fossil record of Protoceratops made it an ideal candidate for a study into sexual selection.

Picture Credit: Gregory Erickson (Florida State University)

Sexual selection is predicted to be an important driver of evolution.  It influences adaptation and the development of new species.  There are anatomical traits and characteristics that can be identified in the fossil record that indicate sexual selection within a species is at work.   The fossilised skulls of horned dinosaurs can be studied to see if any of these traits and characteristics can be found.

Predicted characteristics of horned dinosaur skulls that indicate sexual selection having an influence include:

• Low integration with the rest of the skull.
• A significantly higher rate of change in size and shape as the dinosaur grows.
• A higher morphological variance in the parietal and squamosal when compared to other bones of the skull.

The computer modelling used to assess these traits supported the theory that sexual selection was at work within Protoceratops andrewsi.

No Evidence of Sexual Dimorphism in Protoceratops

Whilst it is notoriously difficult to identify males from females using just the fossil record, the large number of Protoceratops specimens gave the researchers the opportunity to see if they could spot evidence of male Protoceratops having different skull frills compared to the females.  Although the research involved a substantial sample set, no evidence of sexual dimorphism in skull shape was found.  This suggests that either there were no differences in frill shape between the boys and the girls or that any differences between the genders was very small.

The scientific paper supports the idea that the elaborate frills of horned dinosaurs did play a role in sexual selection.  Scientists have suspected that many of these strange anatomical features found in the Dinosauria were linked to sexual selection and display.  This evidence is extremely hard to find using the fossil record alone, however, the computer modelling and in-depth analysis used here provides evidence for the presence of signalling structures linked to sexual selection in Protoceratops andrewsi.

The scientific paper: “Three-dimensional geometric morphometric analysis of the skull of Protoceratops andrewsi supports a socio-sexual signalling role for the ceratopsian frill” by A. Knapp, R. J. Knell and D. W. E. Hone published in the Proceedings of the Royal Society B.

Single Bone Suggests Large Pterosaurs Across Both North and South Laramidia

A single bone from a large pterosaur tentatively described as an ulna found in 2016 has confirmed the presence of large flying reptiles in terrestrial ecosystems in both north and south Laramidia during the Late Cretaceous.

Writing in the on-line, academic journal “PeerJ”, Dr Andrew Farke of the Raymond M. Alf Museum of Palaeontology (Claremont, California), reports that the 36 cm long bone from a bonebed within the middle unit of the Kaiparowits Formation (Utah), extends the distribution of large pterosaurs across terrestrial environments during the Campanian of western North America.

Views of the Single Pterosaur Bone with Accompanying Line Drawings

Views of the pterosaur limb bone with accompanying line drawings.  Note scale bar = 10 cm.

Picture Credit: Farke (PeerJ)

The picture above shows various views of the single pterosaur limb bone (specimen number RAM 22574).  Dorsal (A), proximal (B) with anterior (C) and dorsal (D) views, whilst E and F represent ventral and posterior views.  Line drawing (G) shows an interpretation of the posterior view with missing parts shaded and line drawing H shows a posterior view of the complete and restored bone.  The large size of the bone has permitted Dr Farke to make an estimate of the wingspan of the pterosaur.  He estimates that this bone came from an individual with a wingspan between 4.3 and 5.9 metres.   This bone is the largest pterosaur fossil reported to date from the Kaiparowits Formation.

Based on these estimates, the Kaiparowits Formation specimen is roughly comparable in size to Cryodrakon boreas an azhdarchid pterosaur known from the Dinosaur Park Formation of southern Alberta, Canada which was formally named and described in 2019: The First Pterosaur Unique to Canada is Described Cryodrakon boreas.

Significant Pterosaur Fossil Finds Associated with Terrestrial Environments in Late Cretaceous North America

Major pterosaur fossil finds from late Campanian-aged terrestrial depositional environments in western North America.

Picture Credit: Farke (PeerJ) with additional annotation from Everything Dinosaur (silhouettes based on work from Naish and Witton)

Silhouettes are scaled to maximum estimates of wingspan for individual specimens.  The silhouette for RAM 22574 shows the minimum (black) and maximum (green) size estimates for the specimen (4.3 to 5.9 metre wingspan).

The strata in southern Alberta (Dinosaur Park Formation) from which C. boreas comes from was laid down shortly after the portion of the Kaiparowits Formation associated with this single pterosaur bone.  Thus, Dr Farke concludes that relatively large pterosaurs occurred in terrestrial ecosystems in both the northern and southern parts of Laramidia (western North America), during the late Campanian.

The scientific paper: “A large pterosaur limb bone from the Kaiparowits Formation (late Campanian) of Grand Staircase-Escalante National Monument, Utah, USA” by Andrew A. Farke published in PeerJ.