New Study Suggests Dinosaurs were Warm-blooded (Endothermic)

A scientist from Stony Brook University has reassessed a study into whether dinosaurs were cold or warm-blooded.  Dr Michael D’Emic, a palaeontologist at the New York based university, has re-examined the research in a report published last summer which proposed that dinosaur metabolism was a kind of “half-way house” between a cold-blooded reptile and that of a warm-blooded mammal.  Palaeontologist Dr D’Emic suggests that dinosaurs were not mesotherms (half-way between cold and warm-blooded), but instead their growth rates suggest that the Dinosauria are indistinguishable from the Mammalia in terms of their metabolism.

The Debate Over Dinosaur Metabolism Heats Up

Where on the spectrum between endothermic and ectothermic are the Dinosauria?

Picture credit: Everything Dinosaur

Published a Technical Comment

Yesterday, (May 29th), Dr D’Emic’s study was published as a technical comment in the academic journal “Science” in response to the 2014 research.  In the absence of a living, non-avian dinosaur to study, the debate boils down to interpretation of the evidence and statistical analysis. But why the fuss over what kind of metabolism the dinosaurs had?

Ectothermic versus Endothermic – It is Rather Important

We at Everything Dinosaur doubt very much that members of the public are going to be whopping and hollering about ectotherms (cold-blooded animals) or endotherms (warm-blooded) as they leave cinemas in a few weeks time having just watched “Jurassic World”, but understanding the metabolism of the Dinosauria is essential if scientists are really going to be able to learn how these animals lived and behaved.  Let’s kick off with some simple explanations.

What does it mean to be Cold-blooded or Warm-blooded?

These terms are frequently used, but they are themselves a little misleading.  These two distinct states do not define all vertebrates, things are a little more complicated than that, but in essence a creature that is regarded as cold-blooded relies on external sources to help regulate its body temperature.  Typical examples are lizards and snakes basking in the sun to warm up in the morning, but then seeking much cooler shade to avoid over-heating in the middle of the day.

Warm-blooded animals (mammals and birds), are able to maintain a body temperature that is higher than the temperature of the environment.  In simple terms, they can generate their own body heat. This heat comes from the animal’s metabolism, the chemical reactions that take place in the body (although there are other methods of keeping cool and warming up).

Applying this to the Dinosauria

If the dinosaurs had the same body chemistry as a crocodile (a reptile, regarded as an ectotherm), then they would have been relatively inactive compared to large mammals.  Nocturnal activity could have been reduced along with geographical distribution, very cold environments would have been extremely hostile to cold-blooded dinosaurs.  This is why today, we see the majority of reptile species confined to the tropics.  If the dinosaurs had the same metabolism as birds and mammals, then they would have been much more active and not reliant on external sources to help maintain a body temperature that enabled them to function.

Body Chemistry

The type of body chemistry employed would impact on every aspect of their lives – migration, breeding, food intake, social interactions, growth rates, intra-specific and inter-specific competition and so forth.

Take food as an example.  Whether herbivore, omnivore or carnivore, an ectotherm requires a lot less food in order to survive than an equivalent sized endotherm.  Lions (warm-blooded),  have to feed every three to five days on average.  They have high metabolisms and high food demands as a result.  Nile crocodiles that live in the same environment need much less food.  One substantial meal can last a Nile crocodile several months, crocs are much less expensive to run.  Sunlight can provide their bodies with all the heat they need, they don’t need to create it themselves, so their bodies need less food.

Dinosaurs were Warm-blooded

Over the years, team members at Everything Dinosaur have posted up articles on the ectotherm versus endotherm debate.  In June 2014, we published a feature on the research carried out by student John Grady (University of New Mexico) in association with colleagues from the University of Arizona and the Sante Fe Institute.  It is the results of this research that Dr D’Emic has reassessed.

To read about the June 2014 study: Goldilocks and Dinosaurs – The Warm-blooded/Cold-blooded Debate.

Dr D’Emic proposes that further analysis of microscopic growth rings preserved in dinosaur fossil bone, suggests that dinosaurs grew as quickly as mammals.  This suggests fast metabolisms and therefore that the Dinosauria were endothermic.  The earlier study had undertaken a detailed analysis on the growth rates of a wide variety of extinct and extant organisms.  The research team led by John Grady concluded that dinosaurs were mostly like mesotherms.

Dr D’Emic stated:

“Upon re-analysis, it was apparent that dinosaurs weren’t just somewhat like living mammals in their physiology – they fit right within our understanding of what it means to be a “warm-blooded” mammal.”

Examining Bone Structure

As a Research Instructor in the Dept. of Anatomical Sciences, Dr D’Emic specialises in the study of the structure of bone.  Using microscopic slices of fossil bone that has been carefully cut and polished, the doctor read growth rings preserved in the bone just as a dendrochronologist examines tree rings.  He looked at the 2014 study from two specific view points, firstly the research had scaled down yearly growth rates to daily ones in order to standardise  the data.

Commenting on this aspect of the earlier study, he explained:

“This is problematic, because many animals do not grow continuously throughout the year, generally slowing or pausing growth during colder, drier, or otherwise more stressful seasons.”

He concluded that the 2014 study may have underestimated the growth rate of the different types of dinosaur included in the dataset, by failing to account for their uneven growth.  Like many extant animals, dinosaurs slowed or paused their growth.  This is marked by the growth rings that can be made out in micro-anatomical bone studies.  The doctor added that growth rates were especially underestimated for larger animals and animals that live in very stressful or seasonal environments – both of which characterise the Dinosauria.

Microscopic studies of Dinosaur Bone Reveal Growth Rings

The bands mark periods of arrested or stopped growth.

Picture credit: Stony Brook University

Secondly, in the paper entitled “Evidence for Mesothermy in Dinosaurs”, birds in the sample studied were treated separately from the twenty-one dinosaurs that were included,  In this reassessment, birds and dinosaur data was included as one homogeneous group.  Birds are warm-blooded and they are direct descendants of dromaeosaur dinosaurs.

The doctor explained:

“Separating what we commonly think of as “dinosaurs” from birds in a statistical analysis is generally inappropriate, because birds are dinosaurs – they’re just the dinosaurs that haven’t gone extinct.”

Were Dinosaurs Mesotherms?

Under these new conditions for examining the statistics, the birds being included in the dinosaur assessment data, lends more weight to the idea that the Dinosauria were endothermic and not the “half-way house” as mesotherms.

It seems that as with virtually all studies of this nature, the way that the data is handled and the terms of reference will influence the conclusions that can be drawn.

Microscopic Analysis of Fossilised Bones Helps Identify Growth Patterns

A microscopic image of the thigh bone (femur) of a dinosaur shows concentric rings. The rings represent unrecorded time, so an annual growth rate (dashed line in graph) is an underestimate relative to the true growth rate during the favourable growing season.

Picture credit: Scott Hartman

Comments regarding this new assessment of the earlier research have already been made.  For example, the team behind the 2014 study have responded to this analysis by commenting that the new study raises a number of important statistical and methodological questions, however, the proposals made lack biological and statistical justification.

All scientists who step bravely into this area of academic endeavour deserve our admiration, both papers are part of the rich and extremely diverse range of research that has gone into tackling this very thorny problem, it seems that the warm-blooded versus cold-blooded debate is likely to rumble on.

Australopithecus afarensis Had Neighbours!  Say Hello to Australopithecus deyiremeda 

Had you and I been able to travel back in time to the Afar region of northern Ethiopia some 3.4 million years ago in a bid to meet our ancient ancestors, we might have been spoilt for choice when it comes to trying to work out from which species we are descended from.  Lucy* the most famous example of Australopithecus afarensis had company, she had neighbours, a newly described species of Australopithecine has just been announced.

Two fragmentary upper jaws along with two fragments of lower jaws, representing fossil material from three individuals were found in March 2011 in the Woranso-Mille area of the Afar region.  These fossils have been assigned to an entirely new genus of Australopithecine, say hello to Australopithecus deyiremeda. 

Casts of the Four Fossil Jaws are Displayed

A new Australopithecus species has been described.

Picture credit: Laura Dempsey

Australopithecus deyiremeda

The fossil material assigned to Australopithecus deyiremeda (pronounced ost-tral-oh-pith-e-kus day-ihremy-dah) was described by a team of international palaeoanthropologists led by Dr Yohannes Haile-Selassie, the Curator of Physical Anthropology at the Cleveland Museum of Natural History (Cleveland, Ohio).  The fossils are estimated to between 3.3 million and 3.5 million years old, which means that this species overlapped and lived in the same region as Australopithecus afarensis, the species that the famous fossils called “Lucy” have been assigned to.

However, although A. deyiremeda and A. afarensis lived at the same time and shared the same habitat, the “Lucy” fossil material has been dated to 3.2 million years ago, meaning that the most famous representative of the Australopithecus afarensis species – “Lucy” lived more recently and could never have met the individuals whose jawbones have been preserved.

A Field Photograph Showing the First Jaw Fragment Found

The upper jaw (holotype) found on March 4th 2011.

Picture credit: Yohannes Haile-Selassie/Cleveland Museum of Natural History

The picture above shows a field photograph of the holotype (upper jaw), five teeth can be clearly seen.

A Significant Fossil Discovery

 The discovery of this new species is significant for a number of reasons.

1. This is the first irrefutable evidence of two species of Australopithecine co-existing.  These two species lived at the same time in the Middle Pliocene and in the same part of the world.
2. These fossils suggest that the Australopithecus genus was more diverse than previously thought, it had been thought that the Homo genus evolved from A. afarensis but this may not have been the case, a number of candidate species are emerging.
3. The morphology of the jaws, the size and shape of the teeth and their enamel thickness suggest characteristics not found in A. afarensis but more akin to later genera, the Paranthropus and the Homo genus, for example.  These traits go back much further in time than previously thought.

The Left Half of a Lower Jaw Found on March 4th 2011

A lower jaw fragment of A. deyiremeda.

Picture credit: Yohannes Haile-Selassie/Cleveland Museum of Natural History

Published in the Journal “Nature”

The academic paper that details this discovery has just been published in the journal “Nature”.  In recent years, the hypothesis of a relatively simple, linear progression from Australopithecus to the Homo genus and ultimately the origin of our own species has become less popular amongst researchers.  It seems the hominin family tree is much more complicated than previously thought.

To read an article written by Everything Dinosaur back in 2011, about other Australopithecus discoveries, but this time from southern Africa: The Human Family Tree Just Got More Complicated.

A Close Up of the Left Lower Jaw Prior to Cleaning

The left portion of the lower jaw, prior to cleaning.

Picture credit: Yohannes Haile-Selassie/Cleveland Museum of Natural History

A. afarensis Not the Only Potential Human Ancestor

Commenting on the importance of this fossil discovery Dr Yohannes Haile-Selassie stated:

“The new species is yet another confirmation that Lucy’s species, Australopithecus afarensis, was not the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia during the Middle Pliocene.  Current fossil evidence from the Woranso-Mille study area clearly shows that there were at least two, if not three, early human species living at the same time and in close geographic proximity.”

Dr Yohannes Haile-Selassie added:

“This new species from Ethiopia takes the ongoing debate on early hominin diversity to another level.  Some of our colleagues are going to be sceptical about this new species, which is not unusual.  However, I think it is time that we look into the earlier phases of our evolution with an open mind and carefully examine the currently available fossil evidence rather than immediately dismissing the fossils that do not fit our long-held hypotheses”.

The Very Near Complete Lower Jaw (Field Photograph)

A field photograph of a nearly complete lower jaw fossil with teeth.

Picture credit: Yohannes Haile-Selassie/Cleveland Museum of Natural History

Early Hominins Co-existing

This discovery raises the question of how multiple types of early hominins may have been able to co-exist in the same environment.  For those readers unfamiliar with the term hominin, a hominin is defined as a species more closely related to humans than to our closest extant ape relative the chimpanzee.  Clues can be found in the fossilised jaws and teeth.  The jaws of A. deyiremeda are very deep and robust, but the teeth are proportionately smaller than seen in other Australopithecines.

The canine teeth are particularly small, smaller than all known hominins that have been described previously.  The jaws and teeth may reflect adaptations to a different type of diet.

A member of the Everything Dinosaur team explained:

“Teeth are relatively common in the hominin fossil record, as the extreme hardness of the enamel means that, compared to bones for example, they have a greater fossilisation potential.  If patterns of wear can be discerned then it might be possible to hypothesis on the diet of this new species.  As the jaws and teeth are different from A. afarensis, it could be assumed that these two hominins did not compete directly with each other for food resources, in short, each species ate different types of food.”

Significant Canine Teeth

The size of the canine teeth may also be very significant.  We have four canine teeth, two in the top jaw and two in the lower  jaw. They sit between the first premolar and the last incisor and the size of the canine teeth can provide evidence about social behaviours associated with a species.

In primates, where males compete with each other over females, the canine teeth of the males are usually much larger than the canines of females.  Canine teeth can be used as weapons as the males fight each other to establish social hierarchies and dominance.

A Close Up of the Upper Jaw Fragment with the Canine Tooth Highlighted

Teeth can tell us a lot about an extinct creature.

Picture credit: Laura Dempsey, with additional annotation by Everything Dinosaur

If more teeth ascribed to A. deyiremeda can be found, then more research can be undertaken on the potential dietary differences between different hominins and some exciting inferences about social behaviours and social structures could be made.

Everything Dinosaur, acknowledges the contribution of the Cleveland Museum of Natural History in the compilation of this article.

For models and replicas of early hominins and other prehistoric creatures: Wild Safari Prehistoric World Figures and Replicas.

 Rare Discovery Provides Insight into Ancient Parasite

A team of international researchers have got up close to a prehistoric parasite, one that is perfectly preserved along with its 425-million-year-old host.  The ancient parasite, known as a “tongue worm” provides scientists with a glimpse of life and the interactions between species in a warm tropical sea that existed in Britain back in the Middle Silurian.

Fossils of tongue worms are extremely rare, examples have been recovered from Ordovician as well as older Cambrian deposits, the Silurian fossils are exceptionally well preserved, we at Everything Dinosaur believe the fossils to be part of the Wenlock Epoch biota.  The actual location of the fossil find has not been disclosed in order to protect the site from amateur fossil hunters and those keen to exploit the fossil deposits commercially.

Silurian Fossils

The fossils come from a deposit in Herefordshire, close to the border with Wales, scientists from the University of Leicester, who took part in the study stated that the tongue worm represents a new species and they range in size from 1 mm to 4 mm in length.  Tongue worms have tongue shaped bodies, a distinct head and two pairs of limbs.  At least 140 species are known to exist today, most are respiratory or gut parasites of vertebrates (usually reptiles), these fossils provide scientists with information on how these creatures evolved before they made the move onto land to become parasites of terrestrial vertebrates.

The Computer Model Showing the Ostracod Shell (grey) with the Tongue Worm attached (orange)

Looking at the micro-fauna of the Silurian.

Picture credit: Siveter, Briggs, Siveter and Sutton

The picture above shows the pentastomid Invavita piratica and its host, the ostracod Nymphatelina gravida.

Prehistoric Parasites

The newly described fossils show the tongue worm species in association with its host, in this case a species of ostracod (an arthropod).  It was professor David Siveter, (Department of Geology) at Leicester University, who  made the discovery.  An academic paper describing the new species, named as Invavita piratica, (the name translates as ancient, pirate intruder) has been published in the journal “Current Biology”.  As well as academics from the University of Leicester, the research team included scientists from Imperial College (London), Oxford University and Yale.

Tongue worms belong to the Pentastomida family, part of the subphylum Crustacea, although for many years the taxonomic relationship between this group of obligate parasites and other parts of the Arthropoda was disputed.

Tongue Worms are not Worms at all

Professor Siveter, explained that the tongue worms were not “worms” at all, they got their name because one genus resembles the tongue of an animal.  They are an unusual and widespread group of mainly obligate parasites.  An obligate parasite is an organism that cannot complete its life-cycle without finding a suitable host.

The professor stated:

“This discovery affirms that tongue worms were “external” parasites on marine invertebrates animals at least 425 million years ago.  It also suggests that tongue worms likely found their way into land-based environments and associated hosts in parallel with the movement of vertebrates onto the land by some 125 million years later.”

The Computer Model with the Ostracod Shell Removed to Reveal the Internal Parasites

Internal parasites identified by high powered scans and computer modelling.

Picture credit: Siveter, Briggs, Siveter and Sutton

Computer Generated Images

The computer image above shows the ostracod with its shell removed, showing the external pentastomids and a pentastomid near the eggs of the ostracod (parasites in orange).  The picture shows how this group of parasites got their name.  “Penta” refers to the number five and these parasites have five anterior appendages.  One is the simple mouth, the others are two pairs of hooks which they use to attach themselves to their host.  The large pentastomid  (top left) is a highly magnified image of a single parasite, not to scale with the rest of the image.

To view models and replicas of Palaeozoic creatures including many invertebrates: Prehistoric Animal Models.

Using sophisticated microscopic scanning techniques and three-dimensional computer modelling, the scientists were able to reconstruct the ostracod and its parasites.  Some of the tongue worms were found inside the ostracod’s shell , near its eggs, on which they probably fed.  Other tongue worms are attached to the external surface of the ostracod’s shell, a unique position for any fossil or living tongue worm.  These tiny fossilised creatures are helping the scientists to understand a little more about inter-relationships between parasites and potential hosts in ancient marine environments.

Back in 2012, Everything Dinosaur reported on the discovery of another ancient ostracod from the same location.  The fossil had been identified using the same techniques to discover the parasites.  Professor Siveter, named this new genus of ostracod after his wife.

To read more about this: Ostracod from Herefordshire, reconstructing the Silurian.