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THE name “tyrannosaur” conjures up images of towering predators with enormous heads and ridiculously small arms. But Moros intrepidus wasn’t like that. This 96-million-year-old tyrannosaur was the size of a deer, a lanky pipsqueak of a predator.

It is far from the only dinosaur to strut onto the stage this year – 31 new species have been named so far. There’s , discovered in Patagonia, which hit the headlines for the forward-facing spines jutting from its neck, and little unearthed in China, which confirmed that some feathery dinosaurs flapped around using bat-like wings.

These add to a tally of more than a thousand species of dinosaur known to have roamed Earth in the Triassic, Jurassic and Cretaceous periods – everything from tiny omnivores no bigger than a pigeon to long-necked dinosaurs that stretched over 30 metres long.

“The pace of dinosaur discovery is so fast these days, one could label it frantic,” says palaeontologist Lindsay Zanno of North Carolina State University. And it shows no sign of letting up just yet. It seems we are entering the golden era of dinosaur discovery.

The very first dinosaurs evolved about 245 million years ago, during the early part of the Triassic period (see “Diagram”). Most stayed small until a mass extinction of their reptilian rivals cleared the way for dinosaur domination during the Jurassic period. This is when dinosaur evolution kicked into high gear, and the trend continued through the Cretaceous until another mass extinction wiped out most dinosaurs 66 million years ago. Birds are the only dinosaurs that survived, which is why researchers often distinguish between avian and non-avian dinosaurs.

Humans have long endeavoured to understand dinosaurs. At Flag Point in southern Utah, for example, by Native Americans unmistakably document Jurassic dinosaur tracks found nearby. Dinosaurs as we know them today got their name in 1842, when English anatomist Richard Owen first used the word in a report on Britain’s fossil reptiles, dinosaur meaning “terrible lizard”. At the time, only three had been uncovered: the carnivorous Megalosaurus, the herbivorous Iguanodon and the armoured Hylaeosaurus.

The Great Bone Rush of the late 19th century quickly increased that number, with classics such as Triceratops and Ceratosaurus bringing the ancient reptiles fame. Museums raced to source showstopper specimens to draw in the crowds. Yet while these might have impressed the public, dinosaurs weren’t especially inspiring to those who studied fossils and the evolution of life on Earth. For much of the 20th century, many palaeontologists viewed these creatures as anomalies that deserved their extinction for being too big and strange to survive. It took a renaissance in the late 20th century – a total rethink of dinosaurs as hot-blooded, successful animals – to spark the ongoing search for ever more of them.

Explorations in Asia, South America and elsewhere soon delivered a stunning array of new species. Entire groups never seen before were introduced, such as the bulldog-snouted, carnivorous abelisaurs from the southern hemisphere and the famous feathered-dinosaurs from China. “When I compare what we knew about dinosaurs when I was a student and what we know now, I’m astounded,” says palaeontologist Catherine Forster of George Washington University.

Finding every single species of dinosaur that ever lived is an impossibility because the fossil record is an incomplete transcript of life on Earth. The best we have are small snapshots from places where sediment was deposited, such as floodplains and dune-covered deserts, that were then thrust to the surface where palaeontologists can find them. We will know little, if anything, about those dinosaurs that lived in environments that eroded away, like mountains.

“Dinosaurs were viewed as anomalies that deserved their extinction”

But there are ways to predict what may be out there. One is to look at what has already been found in a group to estimate what undiscovered species might still be awaiting discovery. This is where discoveries like the tyrannosaur – whose name is derived from the Greek term for impending doom – help. The earliest members of the tyrannosaur family show up in North America’s fossil record about 150 million years ago. Yet they are then virtually absent until about the 80-million-year mark, when they re-emerge as giant, big-headed, tiny-armed apex predators. “Tyrannosaurs just pop up in North America during the last 15 million years of the Cretaceous as large-bodied predators sitting atop the food chain,” says Zanno.

M. intrepidus changes that story. Its bones were first spotted jutting out of a site in Utah back in 2013, and it was described as a new species by Zanno and her colleagues earlier this year. At 96 million years old, it sits right in that gap and indicates that tyrannosaurs in the region must have had their growth spurt sometime between that 96 and 80-million-year time slice. “Moros opens a window on what the ecology of tyrannosaurs was like before they rose to power,” she says.

M. intrepidus does something else, too. There are now two fossil gaps on either side of the dinosaur – its ancestors and its later relatives – that are waiting to be filled. Each new find bring up questions about how that discovery connects to others, and where to look to fill the remaining gaps.

Another way to predict the missing dinosaurs is to turn to maths. In biology, organisms are categorised by their species and the genus that the species belongs to, and researchers have devised models to estimate the numbers of dinosaur genera and species that once existed. In 2006, for example, statistician Steve Wang of Swarthmore College, Pennsylvania, and Peter Dodson, a palaeontologist at the University of Pennsylvania, that palaeontologists had some hope of discovering, based on published records of dinosaur discoveries and a mathematical formula that links observed data to unseen types. At that time, about 500 had been named, indicating that more than 70 per cent were yet to be found.

More recently, , ecologists Jostein Starrfelt and Lee Hsiang Liow at the University of Oslo, Norway, accounted for both the incompleteness of the fossil record and biases in how the fossil record is studied – for example, by the different research interests of academics – to come up with an estimate of 1536 discoverable dinosaur genera. At that time, 974 had been identified, meaning that 37 per cent were yet to be found.

This illustrates just how much progress has been made in uncovering lost dinosaurs in recent years. Even so, the dinosaur record may be richer than the predictions say. “I think the estimate of total richness for the dinosauria we made is an underestimate,” says Starrfelt. Not only are there likely to be updates to the models used to estimate dinosaur diversity, but new discoveries in familiar formations will alter dinosaur counts and bump up the numbers of those yet to be found.

In 2010, for example, Richard Butler at the University of Birmingham, UK, and his colleagues described one of the smallest dinosaurs yet found. Named , this omnivorous biped with prominent teeth was found in the Morrison Formation, a rich and well-studied source of dinosaur fossils dating from near the end of the Jurassic. And last month another small dinosaur, an early raptor named Hesperornithoides miessleri was described from the same formation.

It is the search for small dinosaurs like these that is filling in our understanding of even well-examined places. “New research has shown that small dinosaurs are strongly underrepresented in the fossil record because their delicate bones are more susceptible to destruction by scavengers and the elements before they can become fossils,” says David Evans at the University of Toronto, Canada. But they are out there. “Over the past two decades, many of the new dinosaur species being recognised from classic localities like Dinosaur Provincial Park in Alberta and in the Hell Creek Formation of the western US are on the small end of the dinosaur size range, below the size of an average person,” he says.

“We are just scratching the surface in terms of dinosaur diversity,” says Evans. “The potential to fill in our knowledge of dinosaur diversity on the small end of their size range is huge.” This includes unusual forms of dinosaurs as well as species similar to those we have already found. In June this year, for instance, Max Langer at the University of São Paulo in Brazil, and his colleagues, described an unusual dinosaur they named in the Cretaceous rock of southern Brazil. The dinosaur belonged to an enigmatic group called noasaurs, and stands out by having feet that balanced the dinosaur’s weight on a single toe of each foot, which seem to match strange tracks found nearby. But similar tracks are also seen in older Jurassic rocks – indicating that another one-toed dinosaur is still awaiting discovery in those older strata.

So where can we look to find all these missing species? There is still a great deal of dinosaur-bearing rock that has yet to be searched even once, much less dug into for detail. “Some of the future hotspots for dinosaur palaeontology are in south-eastern and central Asia, much of Africa, and some northern countries of South America,” says Zanno. Remote, difficult-to-work sites could yield important finds, too. “The Arctic and Antarctic have huge potential for new dinosaur discoveries,” says Evans. The Cretaceous strata of Africa is also little-explored compared with that in other parts of the world, he says, and could yield important finds. That is still a lot of ground to cover.

Some time periods are hazy in the palaeontological imagination. “Targeting poorly known time periods, like the Middle Jurassic, is critical,” says Forster. This was the time period during which dinosaurs truly became globally dominant and increased the range of sizes they were capable of reaching.

The novelty of these finds will undoubtedly continue to make headlines. But there is more to this than raw numbers. “Dinosaurs, or any fossils, are part of our collective past,” says Forster. Finding new species is the first step in visualising and understanding evolution and extinction. As Forster says, “dinosaurs and ourselves are all part of the same ever-changing system”.