Heterodontosaurus tucki, the “different toothed lizard”


image by Dr Laura Porro

Dr Laura Porro, postdoctoral researcher, writes:

Dinosaurs capture our imaginations for many reasons: they dominated life on Earth for an extraordinary 130 million years; they evolved body shapes and lifestyles unlike those of any living animal; and some grew to immense sizes, including the largest creatures to ever walk on land.

Not all dinosaurs were enormous, however. Scurrying among the feet of such giants as Diplodocus and Stegosaurus was a cast of tiny dinosaurs. One such group was the heterodontosaurs, which form one aspect of my research.

Little known outside scientific circles, these dinosaurs were found in Africa, Asia, Europe, and North and South America. They lived from the Late Triassic until the Early Cretaceous – more than 80 million years. The largest species, Heterodontosaurus, grew only as big as a fox while the smallest species weighed less than a gray squirrel even when fully grown.

Heterodontosaurs are fascinating animals. Their name means “different toothed lizards”. Heterodontosaurs have a beak and flat, incisor-like teeth for nipping at the front of their mouths; behind these are long, sharp caniniform teeth; at the back of their jaws are large, molar-like teeth. These differently-shaped teeth are common in mammals (including humans) but unusual among lizards, crocodiles and other dinosaurs.

What did heterodontosaurs eat? Close examination of their teeth reveals heavy wear as in modern herbivores. Computer modeling of the Heterodontosaurus skull and jaw muscles have shown that it used complex jaw movements to chew food, again similar to living plant-eaters. However, the knife-like canine teeth and large, sharp claws on the hand of Heterodontosaurus resemble those of meat-eating dinosaurs. Many palaeontologists think that heterodontosaurs were omnivorous, feeding mostly on plants but occasionally eating insects or small vertebrates.

Heterodontosaurs are surprising for reasons other than their teeth. Since the mid-1990s, palaeontologists have discovered numerous dinosaurs with preserved feathers. Nearly all of these have been theropods, meat-eating dinosaurs such as Velociraptor and T. rex. Living birds evolved from theropods, and it was thought that only these carnivores possessed feathers. But the 2010 discovery of Tianyulong, a heterodontosaur from China, stunned scientists: the back, neck and tail of Tianyulong sported rows of long, primitive feathers. Tianyulong is only distantly related to birds, and the presence of feathers in this animal suggests that many plant-eating dinosaurs may have been rather ‘fuzzy’ as well!

image by Li Da Xing

Studying heterodontosaurs can be challenging. The delicate nature of such tiny bones means that specimens are often damaged during fossilization; preparing these fossils using traditional tools (such as drills, brushes or acids) risks further damage. In 2010, my colleagues and I described the heterodontosaur Fruitadens, the smallest adult dinosaur known from North America. I CT-scanned the specimen and then used computer software to ‘digitally’ prepare the specimen, producing detailed 3D models of the bones, teeth and even internal structures like blood vessels!


During our visits to museums, zoos and wild places we are awed by animal giants—looming tyrannosaurs, trumpeting elephants, and icons of conservation such as the tiger, whale and giant panda. These animals are magnificent, indeed, but it is also important to consider some of the tiny wonders of evolution—both extinct animals like Heterodontosaurus worthy of study and living creatures worthy of conservation.


The earliest known five-fingered foot

pentadactyl foot

Professor Jenny Clack, curator of Vertebrate Palaeontology at the Museum, writes about exciting fossil finds from Scotland:

This tiny fossil is either the hand or the foot (we can’t yet tell which) of a tetrapod from the Early Carboniferous of Scotland, about 350 million years old. It shows the earliest known pentadactyl – five digited – construction so far found in the fossil record. Animals from the preceding Devonian period , about 360 million years old, and for which we know their hands or feet, had more than five digits. Until this specimen was found, the earliest pentadactyl hand came from rocks about 330 million years old. It was also from Scotland, where many Carboniferous tetrapods have come from in the past.

Our ‘foot’ is part of a collection of fossils that are helping to fill in a previously conspicuous gap in the fossil record, known as Romer’s Gap, between the end-Devonian and the middle of the Early Carboniferous, a time interval of about 20 million years. During this time, tetrapods became increasingly adapted for walking on land, but how and when were more or less unknown. Our new studies have found many more fossils to help fill this gap, in the Borders Region of Scotland and in northern England.

Visit our website to find out more about this exciting project: www.tetrapodworld.com.

Morganucodon – lower jaw of an early mammal

Eo D61 Morganucodon (=Eozostrodon) watsoni 

From Pontalun quarry, near Bridgend, Glamorgan.

© Pam Gill

Photograph of specimen Eo D61 Morganucodon (=Eozostrodon) watsoni
© Dr Pam Gill

Reconstruction of the lower jaw of Morganucodon.  © Pam Gill

Reconstruction of the lower jaw of Morganucodon.
© Pam Gill

Dr Pam Gill of the School of Earth Sciences, University of Bristol, writes:

This specimen is part of the lower jaw of one of our very first mammal ancestors. It lived in the Early Jurassic, 200 million years ago, at the same time as some of the earliest dinosaurs.  Morganucodon (=Eozostrodon) was a tiny shrew sized mammal and it lived on a small limestone island in what is now Glamorgan, along with another early mammal Kuehneotherium. Hundreds of bones of these creatures accumulated in small subsurface caves, and have now been exposed by quarrying.

I have chosen this specimen of Morganucodon as it is one that was used to make a complete reconstruction of the lower jaw. Because the bones were broken when they were swept into the caves and there are no complete jaws preserved. This fossil is only a few millimeters long and is of the back end of the jaw, showing the strong jaw joint and the final molar tooth.

Eo D61 and other specimens were taken to the synchrotron in Zurich for high resolution CT scanning to make 3D reconstructions.  Three specimens were digitally “stitched together” (see the image above) to make a complete jaw, with Eo D61 as the posterior end. Biomechanical models were made from the reconstructions of Morganucodon and Kuehneotherium and showed that Morganucodon could eat hard food such as beetles, but Kuehneotherium could only slice up soft food like moths. So even the very first mammals had evolved to eat different diets so that they were not competing for food.

Balanerpeton woodi

Balanerpeton woodi specimen T1261A

©University Museum of Zoology, Cambridge

©University Museum of Zoology, Cambridge

Dr Tim Smithson, Postdoctoral Research Associate with Prof Jenny Clack, writes of a fossil from the museum’s collections:

The specimen was found by my dear friend the late Stanley Wood in a dry stone wall surrounding a field in the Bathgate Hills, Central Scotland, in 1985.  It was one of a number of important fossil amphibians Stan collected from this unusual location before he eventually tracked down the original source of the walling stones, East Kirkton Quarry. Unlike its companion, West Kirkton Quarry, East Kirkton Quarry had fortunately not been filled in and for the next five years Stan collected at the quarry. During this time he discovered a diverse fauna of Early Carboniferous terrestrial tetrapods, with Balanerpeton the most common. I spent two months with him collecting at the quarry in the summer of 1985.  I remember it well – it rained every day!  Stan wrote a short note announcing his discoveries and submitted it to Nature.  It was rejected – of insufficient general interest!  He protested, Nature relented, and it was published with a picture of Balanerpeton on the front cover. In the display case alongside the specimen is a photo collage of it prepared by Stan in the style of David Hockney.  Stan was a keen artist and photographer and this specimen inspired him to produce a work of art that to me greatly adds to the interest of the fossil.  Together, they provide an insight into a great fossil collector and examples of his many discoveries can be seen in display cases throughout the Museum.

Giant Ground Sloth

Giant Ground Sloth, Megatherium americanum, a visitor’s perspective

©University Museum of Zoology, Cambridge

©University Museum of Zoology, Cambridge

Rhys Price, visitor to the Museum of zoology, writes:

I am  HUGE “fan” of zoology and palaeontology, and have been since I was very young. At the moment I am particularly interested in the extinct megafauna of South America, 1 million years ago, especially the Giant Ground Sloth, Megatherium.

To put it briefly, to have seen a specimen of this fascinating animal was unforgettable, as well as a Smilodon (sabre-toothed cat) skull, some Glyptodon (giant armadillo) bones and a Toxodon skull.

These are just a few of many collections in the museum that have inspired me to study zoology, and palaeontology, as a hobby, and possibly a career later on.

Archaeopteryx cast

Archaeopteryx cast

© University Museum of Zoology, Cambridge 2013

© University Museum of Zoology, Cambridge 2013

Gillian Clarke, National Poet of Wales and Poet in Residence at the Museum of Zoology in Spring 2013, writes:

I am poet-in-residence in the Museum of Zoology for 10 precious days. In my first hour in the exhibition gallery I saw what is still my favourite treasure. It is the fossil of a bird, with a perfectly preserved impression made by its wing-feathers, like when you play ‘Making Angels’ in the snow, lying on your back and sweeping your arms to make wings. The Archaeopteryx is the earliest bird fossil, the size of the magpie that just left its impression in the snow on my lawn. The snow-shadow will melt. Stone has held the Archaeopteryx for millions of years, like a photograph of the Jurassic period. It makes me dizzy, just thinking about it.

Eurypterus remipes – a Sea Scorpion

© University Museum of Zoology, Cambridge 2013

© University Museum of Zoology, Cambridge 2013

Prof Michael Akam, Head of the Department of Zoology at the University of Cambridge, and former Director of the Museum of Zoology, writes:

The Eurypterids, or Sea Scorpions, were the most terrifying group of arthropods that ever lived, roaming the Paleozoic seas from about 460-255 million years ago.    The fossil specimens that we have in the Museum are quite small, 15-20cm,  but the largest specimens were truly fearsome predators – up to 2.5m long, with single claws of more than 80cm.  Our specimens come from New York State, an area famed for them.  Indeed, sea scorpions are the State Fossil of New York.

I visited one of the fossil quarries myself.  We contacted the owner, who invited us to visit his workshop.  It looks like any other small farmstead in upstate New York, nestled in the hills.  His barn, though, is full not of hay and horses, but rock saws and air drills, for preparing these most wonderful fossils, which he displays all over his house (and on the internet too, at http://langsfossils.com/eurypterids.htm)

I’m no palaeontologist, but even so, he took us up to the quarry behind the house, handed us a hammer and chisel, and invited us to split some of the blocks of shale he had excavated the previous year, and left for the frost to weaken.   The eurypterids are so abundant in this rock, that almost every split yielded a fossil or two.

Eurypterids belong to the large group of arthropods called chelicerates – a group characterised by having pincers rather than antennae as their front limbs.  Spiders and scorpions are the most familiar living chelicerates, but these land animals are only distantly related to the sea scorpions.  The closest living relatives of the sea scorpions are probably the horseshoe crabs – another ancient group of wonderful arthropods, and the only marine chelicerates to survive to the present day.

Osteolepis macrolepidotus, a fossil fish from Scotland

© University Museum of Zoology, Cambridge 2013

Osteolepis macrolepidotus. Head is to the left of the image.
© University Museum of Zoology, Cambridge 2013

Roz Wade, Education and Outreach Officer for the Museum of Zoology, writes:

I was lucky enough to study Natural Sciences here at Cambridge, specializing in Zoology. Having the museum’s collections to learn from is the most amazing resource for a student. Being able to see the animals, explore how they are put together, getting the light-bulb moment of understanding of “ahhh that’s what that structure is”… I don’t think you can get that from a text book. Nothing beats looking in detail at the animals themselves.

When I was in the third year of my degree I did a research project with Professor Jenny Clack, the Curator of Vertebrate Palaeontology here in the Museum. She showed me this fossil fish over 380 million years old, from the Middle Old Red Sandstone of Scotland, and I was hooked on palaeontology. But fossils of that age are not rare. In fact, fish fossils from the Middle Old Red Sandstone of Scotland are not particularly rare. What is special about this fossil is what is preserved.

At first glance, this fossil looks like a jumble of scales, with no clear bones in the head and not even any fins preserved. But take a close look at the head and you can see that, although there are few recognisable bones there, what is preserved is something much more astonishing. What we can see here is the natural cast of the back part of the brain cavity and inner ear. Look closely at the lump of sediment in the middle of the head and you can see nerve canals branching off it. On either side are the beautifully preserved infills of the semicircular canals of the inner ear. These are the balance organs, and are surprisingly similar to the semicircular canals inside your inner ear that are telling you which way up you are. This is a very ancient sensory system – ears evolved first for balance, not hearing, and semicircular canals are seen in all vertebrates. The physics of the inner ear means that you can tell something about the sensitivity of these organs by looking at their proportions. So not only is it amazing these structures are preserved at all, you can also say something (albeit with many assumptions to cover aspects of the system not preserved) about what these creatures, which went extinct hundreds of millions of years ago, may have sensed.

Giant Ground Sloth: Megatherium americanum

Giant Ground Sloth

© University Museum of Zoology, Cambridge 2013

© University Museum of Zoology, Cambridge 2013

Dr Chris Jiggins of the University of Cambridge Department of Zoology writes:

One of the most imposing specimens in the museum is the skeleton of the Giant Ground Sloth, Megatherium americanum. This species was part of a large megafauna in the American tropics, which until around 10,000 years ago may have reached a similar biomass to that of African mammalian herbivores in recent times. I first came across this remarkable megafauna soon after starting my PhD fieldwork in Ecuador, when I read a paper by Dan Janzen and Paul Martin entitled ‘Neotropical Anachronisms: The fruits the Gomphopheres ate’. This highly entertaining paper speculated that many of the adaptations seen in modern neotropical plants, such as giant spines on the trunks of Ceiba trees, might have arisen as a defence against these now-extinct megaherbivores. I spent many long hot days searching for butterflies in Ecuador, and in quiet moments paused to wonder what the landscape would have looked like in the presence of these massive herbivores. Incidentally, the Gomphopheres in the title of Janzen’s paper are a now-extinct group of elephant-like herbivores that would have lived alongside the ground sloths. This in itself is remarkable as the former evolved in North America, while the latter arose in South America, the two only coming together during the Great American Biotic Exchange, when the isthmus of Panama linked north and south and permitted these two great faunas to mix. Perhaps from a fieldwork health and safety perspective, it is better that these giant animals are now extinct, but this was perhaps the earliest mass extinction event caused by humans, and in my mind at least, they are sadly missed.

Aquatic Predatory Tetrapod: Crassigyrinus scoticus

A large aquatic predatory tetrapod from the Early Carboniferous of Scotland
UMZC 2011.9.1, lower jaw portion of cf. Crassigyrinus.

© University Museum of Zoology, Cambridge 2013

© J.A. Clack 2013

Professor Jenny Clack, curator of Vertebrate Palaeontology at the museum, writes about a finding fossils in Scotland:

Crassigyrinus scoticus, whose skull is illustrated at the bottom, has been known from fossils since the early 20th century. It has been found at a few localities in Scotland from rocks about 320 million years old, a time known as the late Visean and early Namurian stages of the Carboniferous period. The animal was over two metres long and its jaws were lined with many large sharp teeth adapted to produce a powerful snap-trap bite.

Last year, my husband and I went to explore some newly discovered fossil localities yielding specimens from an earlier time, about 350 million years ago. In one layer of rock we noticed a blade-like bone exposed at the edge of the rock in part of the cliff-face. The cliff formed the edge of a farmer’s field, and faced the sea, so the rocks were wet, and this particular layer was very crumbly. Very carefully, we picked out what we could of the bone (top image). In the lab, I slowly and with much frustration, consolidated the bone and tried to reassemble the pieces. They would often fall apart in new places as I stuck them together, but in the end, we could recognise the bone, in fact a series of bones. They formed the lower part of the lower jaw of an animal very like known specimens of Crassigyrinus, but 30 million years older (middle two images). Regrettably, the tooth-bearing bones were missing.

This was a very exciting find for a number of reasons. First, it showed that relatives of Crassigyrinus scoticus existed long before we thought they did. This will give us new information about the evolution of the group to which it belongs. Secondly, and more importantly, it forms part of a growing collection of fossils from the same age: the Tournaisian stage of the Carboniferous. Formerly hardly represented by fossils of vertebrates or invertebrates, this time-period has been known as ‘Romer’s Gap’. This was very unfortunate because it was during this time that terrestrial ecosystems were rebuilt following a mass extinction at the end of the Devonian period, and the time when tetrapods became more fully adapted to life on land. Thus this previously poorly known period set the stage for modern ecosystems to diversify.

We now have a large NERC-funded consortium project to study this period and these events intensively for the first time, to find out what happened at the end of the Devonian – why was there a mass extinction? – and how did terrestrial life recover from it? This fossil was one of the initial finds that helped us secure funding for the project. TW:eed project website