Colorful illustrations can bring even the most lifeless structures to live. Sometimes it is important that a reader or player has a good idea of how something or someone looks. That’s when illustrations are useful. They are a great way to help people get an idea of what a scene,…

by Angus Konstam The background When the Romans came to Scotland in AD 80, they knew little or nothing about the Celtic tribes who lived in the region. Faced with invasion, the tribesmen of the lowlands either submitted to Roman occupation or withdrew to what they thought was the safety of their hilltop forts. This proved a costly mistake, as the two largest forts in the area fell to the might of the Roman army and its siege artillery. The tribes who resisted (known by the Romans as the Selgovae and the Novantae) were brought to their knees by the end of the year, and the Roman Governor Agricola consolidated his northern frontier along the line of the Forth and Clyde rivers. The area was completely pacified by the start of AD 82. So much for the defensive protection of the lowland hillforts. Further north a fresh challenge awaited Agricola, as he planned to lead his armies into eastern and north-eastern Scotland, beyond the Firth of Forth. These Celtic tribesmen had used their fortified bases in what is now Stirlingshire to harry the Romans, and Agricola had had enough. In AD 83 he launched his legions in an expedition of conquest, cornering the local ‘Caledonian’ tribesmen in battle at Mons Graupius (84) and inflicting a decisive defeat on his opponents. During the advance his flanks were secured by a series of Roman auxiliary forts designed to prevent Caledonian movement out of the Highlands. His fleet sailed north as far as Orkney, forcing the submission of the coastal communities they encountered. Although the Roman tide receded due to commitments elsewhere, the threat of punitive attacks against the Caledonian tribes continued, forcing the local Celts to maintain strong defensive positions and to ensure their near-constant readiness for war. The Roman defensive line along the Forth–Clyde line was abandoned around AD 100, and the frontier was re-established between the River Tyne and the Solway Firth, a position which was defended during the reign of the Emperor Hadrian (AD 117–138). The Romans returned north for a time during the reign of the Emperor Antonius Pius (AD 138–161), and the Antonine Wall was built along the old Forth–Clyde line, before it too was abandoned after the death of the Emperor. From that point on Hadrian’s Wall marked the northernmost frontier of the Roman empire. Although the tribes immediately to the north of the wall were relatively peaceful, those further north were more hostile. At the start of the 3rd century AD the Emperor Septimus Severus (AD 193–211) led punitive expeditions against the Caledonians, as did the Emperor Constantius I Chlorus (AD 305–306) a century later. It was during this last expedition that we first hear of the Caledonians being referred to as the ‘Picts’, or painted people. Historians generally take this date as the mark that divides the era of the Picts from that of their Caledonian forebears, and provides a convenient finishing point for our study. In early Celtic Scotland, there were three main types of fortifications in use during this period: the brochs, the duns and the hillforts. Towers in the north: the brochs The Broch of Gurness stands on the shore of a stunningly beautiful bay and sound in Orkney. It was built at some point between 500 and 200 BC, and the broch itself formed part of a defensive site that included a village and a series of encircling ramparts and ditches. The brochs of Iron Age Scotland were a virtually unique solution to the defensive requirements of their builders. Spectacular even in ruin, these structures often combined the functions of a defensive retreat with that of a communal focal point. They protected the local people from petty bandits, raiding war parties and on occasion, from full-scale invasions. As such they often formed the nucleus of small communities, or were located close to existing settlements. This means that any true study of them as fortifications needs to be combined with a look at the communities they served, and the people who built them. From there we can look at the fortifications which succeeded them, and which provided defensive strongpoints for the Picts, who inherited the land from the Iron Age broch-builders. A broch was an imposing circular fortification built using drystone walling. This meant that no mortar was used, but the irregularly shaped stones were chosen so that they fitted roughly together. They were tall, grim, windowless structures, containing a passage within the walls which eventually led to an upper rampart. The only entrance was a small, easily-defensible doorway at ground level. Two walls were separated by passageways, stairs and galleries, which eventually led up through the walls to the circular upper parapet, where the defenders could rain missiles down on the heads of their attackers. While the Broch of Gurness is considered an early example of the genre, the Broch of Mousa in Shetland is probably the most intact example of a later (and more classical) broch structure. Precursors of the earliest brochs were probably the strong circular houses whose ruins are located in the same geographical area as the brochs. Almost all brochs are located in the north and west of Scotland in Caithness, Orkney, Shetland and Skye, while a few others were built further south. The majority of them are concentrated in Orkney, Shetland and Caithness. Dating evidence suggests that most were built between the start of the 1st century BC, and the late 1st century AD, although this has been questioned due to the equivocal dating material so far discovered. Further evidence suggests that ‘proto-brochs’ or precursors to the classical broch structure could have been built as early as the 6th century BC, while we know that some remained in use until at least the early 3rd century AD, if not later. Although we know a lot about the structures themselves, and we can analyse their defensive qualities, we know very little about who exactly built them, and why. Obviously numerous theories have been proposed, and it was only recently that archaeologists reached a general consensus on what may have happened. Clearly, they were designed for defence. The Broch of Mousa alone stands to a height of some 13 metres (40 feet), and would have been a proof against all but the most determined assault, unless the attacker had Roman-style siege artillery. The low narrow entranceway made it difficult to batter down the door, and the walls of Mousa were too high for ladders. The hollow interior was probably roofed over, and was large enough to house livestock, provisions and people until the threat had passed. We know little about who the threatening attackers might be, but Celtic, Roman or German raiding parties might have come to these areas in search of slaves. Although not impregnable, smaller brochs would have guaranteed that an attack against them would have been costly, and thus they acted as a form of deterrent against any potential aggressor. Until comparatively recently, brochs were sometimes referred to as ‘Pictish towers’, or even associated with the Norsemen (vikings). While these links have been disproved, the terms indicate a general lack of understanding of the brochs and the broch builders. We know a certain amount about the late prehistoric people who lived in what is now Scotland from their archaeological legacy. They were not Scots, as that political entity post-dated the broch builders by a millennium, but we have no alternative name to identify them by, as no written records survive from this culture and period. The term ‘Celtic’ has been widely used to describe all the iron age people of this period who inhabited most of Europe, including Scotland, but some archaeologists baulk at using such a widely applied appellation. As for the term ‘Pictish’, their time came later, and the Picts have usually been identified with the inhabitants of north-east and east central Scotland from the early 4th century, when the name first appeared in Roman written records. The broch builders had been long gone by then, and while the Picts may well have been the descendants of these broch builders, archaeological information is unable to prove a clear descent from one group to the other. Various theories have been proposed, including ones where the Picts reached Scotland from overseas, and similarly that the broch people were somehow different from the pre-Celtic people who inhabited the rest of Scotland. It is probably true that the pre-Celtic people of Scotland intermingled with later waves of Celtic migrants, but there is no direct Celtic broch building tradition. It has been suggested that while the rest of Scotland was overrun by the Celts, the broch builders retained their independence, and fortified their settlements. Whoever built them, their appearance coincided with the arrival of the Celts, and their disuse began following the arrival of the Romans in Scotland. Some archaeologists have given the broch builders the clumsy appellation of proto-Picts, but this does the earlier people a disservice. The broch builders displayed certain qualities which were absent elsewhere in the Pictish homeland (which included Orkney and Shetland), so although there are many theories, there are few answers to the mystery of who these enigmatic people were. It is possible that by the time the Pictish era, the local population had effectively become as Celtic as the rest of Scotland. Certainly we know that most brochs were abandoned at some point during the 3rd century AD, which is close enough to the appearance of the Picts as a distinctive people to suggest some link between the two dates. Blockhouses in the west: the duns The term ‘dun’ is used to identify a particular type of small fort which was built extensively all across south-western and western Scotland, with the greatest concentration found in Argyll. These circular or oval dry-stone structures were similar to brochs, but were much smaller. While some were built on flat ground, most were constructed on rocky outcrops or natural defensive positions to enhance their defensive properties. Their walls were usually built using two thick dry-stone walls, with a solid core of rubble used as infill between them. Some used timber to lace the structures together (as was the case with the first hillforts), but most had a smooth outer face, devoid of timber reinforcements. In some examples the wall was reinforced at the base to allow the construction of higher or heavier structures. Like the brochs, the entrance was small and protected by chambers to discourage battering attempts. A particularly impressive example (the Dun of Leccamore, on Luig) even boasts an internal stairway, and other design features suggest some form of correlation between the broch builders and the defensive properties of these smaller dun structures. While some earlier timber-laced duns have been dated to the 6th or 5th century BC, the majority appear to have been built during the period after the Romans came to Scotland, during the 2nd and 3rd centuries AD. Some show evidence of occupation, abandonment and re-occupation, suggesting they were used when the situation warranted it, and in more peaceful times they may have been abandoned for more spacious and convenient settlements nearby. They also show signs of a far longer occupation than the brochs to the north or the hillforts to the south and east. Dun Cuier on Barra was occupied until around AD 500, while Kildalloig in Argyll appears to have remained in use as late as the 8th century. Unlike the brochs or hillforts, most duns appear to have been little more than fortified homesteads or farms, but they remained a feature of the Scottish landscape for over a thousand years, and outlived both other forms of early Celtic fortification. Strongholds in the south: the hillforts Nobody knows how or exactly when the Celts reached Scotland. Towards the end of the Bronze Age (around 700 BC), these newcomers began to arrive, bringing the new technology of the Iron Age with them. These Celts also introduced a new feature to the Scottish landscape. Over the next eight centuries, hillforts would appear in various sizes, from small fortified farms to full-scale fortified hilltop townships. They provided refuge for the local Celtic communities who faced attacks and raids from their neighbours. While well-designed to protect the Celtic tribespeople from their own kind, they proved less effective against the Romans. Although the early Bronze Age defensive ring at Meldon Bridge in Lothian is probably the earliest fortified site in Scotland, the first hilltop fortifications appeared around 600 BC or slightly earlier. These took the form of timber-laced fortified circles. In some cases the ramparts were fire damaged during their period of use, which allowed the sites to be carbon dated. While the dating range is wide most appear to have been actively built or expanded during the 6th century BC or later. These timber-laced structures continued to be built in Scotland until the coming of the Romans in the late 1st century AD, although the style of the fortifications became more elaborate with time. Timber-lacing was a technique used to stabilise both earthen ramparts, stone walls or rubble infill by laying horizontal wooden beams across the structure, binding it together. In other words, the timber provided a massive framework which was filled with stones and rubble, then faced with solid stone. A wooden walkway and palisade were then built on top of this defensive perimeter. Thick wooden gates protected the entrances to these hilltop enclosures. Surviving examples such as the stone and earthen wall of the fortification at Abernethy in Perthshire (occupied during the 1st century BC) show the surviving slots in the walls where these beams were placed, and had rotted away. In cases where the forts were destroyed by fire (probably during an assault), fire damage caused by the burning timber has left its mark on the surviving stonework, which has sometimes been fused together. In rare instances, the remains of timber-lacing survives, such as at Kaimes Hill in Midlothian. Timber-laced forts were built throughout central and eastern Scotland and around the Moray Firth to the north, and this distribution matches that of early Celtic finds such as axe heads dating from the 7th century BC and later. This proves that the early Celtic people who occupied central and eastern Scotland relied on these types of fortifications for their protection. The nature of these hillforts changed over time. In some cases, the original timber-laced structures were replaced or rebuilt in later periods. At Kaimes Hill a series of stone-faced ramparts replaced these earlier defences, and a series of ditches were dug around the perimeter to strengthen the position. One additional refinement was the setting of a ring of pointed stones around the outside of the wall, creating a disruptive obstacle which would hinder any attackers. The trouble with timber-lacing was that the timbers were difficult to replace once they rotted, or they could be destroyed by fire with relative ease. Archaeological evidence suggests that while timber-lacing continued to be used in Scotland during the early Celtic period, the weakness of the design was apparent to the builders. Consequently when the local Celtic tribes of lowland Scotland were faced with the prospect of Roman invasion in the late 1st century AD, many forts were strengthened and improved by the addition of all-stone walls and the digging of ditches outside the walls. In addition to their walls or earthen ramparts, most of these defensive positions were topped by wooden palisades. These forts were almost exclusively built on hilltops to impove their defensive capabilities, and in many cases the walls enclosed some form of interior settlement. Of some 1,500 fortified sites in Scotland, the majority of these forts were located in lowland Scotland, below the Forth–Clyde line. This surprisingly high figure includes small fortified farmsteads and isolated stone structures from the same early Celtic period. As some of these were built over 700 years before the Romans appeared, it comes as no surprise that many had been abandoned for centuries by the 1st century AD, although a handful remained in continuous use throughout their history. Unlike the sprawling hillforts such as Maiden Castle in England, these Scottish fortifications were small, and probably only served small local communities. The two exceptions were Traprain Law and Eildon Hill, both of which were substantial defensive positions, and the latter containing over 300 roundhouses. This meant that in times of danger, an entire tribe could seek refuge within its walls. One of the problems with Scottish hillforts is the lack of available information about their history. We rarely know how long they were occupied or when, and what function they served apart from a defensive one. It does seem that at least at certain periods, the hillforts which enclosed settlements tended to be under continuous occupation when the Romans appeared. Another variant of the hillfort was the promontory fort, which was found at various points along the east coast of Scotland, such as St. Abb’s Head, Dunnotar and Urquhart (the last was actually on the shores of Loch Ness, not the North Sea). All but the last were most probably established as fortified sites well before 300 AD, but all three were developed into major fortifications during the Pictish period, and the last two were actual Pictish fortifications. Similarly, the promontory at Burghead on the Moray Firth was developed as a Pictish stronghold. In all three sites, elements of the old hilltop fort designs were used, as the headland was cut off from the mainland by a series of defensive walls and ditches. Again, the Burghead fortification may have predated the start of the historic Pictish period, but the lack of hard dating evidence makes it impossible to say so with any certainty. Certainly the system of three lines of earth and rubble defences and intervening ditches is similar to that found in hilltop forts from 300 BC on, and we know the Picts added an inner citadel to the fortified point at Burghead. The spot was also a good anchorage, and it has been suggested that Burghead was used as a Pictish base from which maritime raids were launched down the coast into Roman Britain. Certainly there seems to be a legacy of construction methods which linked the known Pictish fortifications (Inverness, Dunadd, Dundurn, Dunottar, Dunkeld, Clunie, Scone, Inveralmond and Forteviot) to the earlier hilltop forts in the same area (Tayside, Moray and Grampian). Summary To sum up, although the Iron Age landscape of Scotland is littered with fortifications, these can be divided into three groups. The brochs of the northern and western isles are virtually unique, and their design displays a high level of architectural and military appreciation. To the south-west the duns were smaller counterparts, and less likely to be situated in coastal locations. These remained in use until well after the arrival of the Scots from Ireland, and outlasted all but a handful of coastal fortifications which were probably used by both the Celts and their Pictish descendants in eastern Scotland. As for the rash of hillforts in southern Scotland, the majority fell from use following the Roman invasion of the late 1st century AD. Despite this, their methods of construction were adapted for use by the Picts as well as the Scottish peoples who inhabited the southern lowlands when the Romans withdrew. Scotland is unique in that so many of its monuments are still extant, and have been saved from centuries of development. Although the region produced methods of early Celtic fortification that were unique, any study of these defensive sites helps us understand both the people who built them, and their Pictish or Scottish descendants. Further Reading Armit, Ian, Celtic Scotland, Historic Scotland Publication – Batsford Press, London, 1997 Breeze, David J., Roman Scotland, Historic Scotland Publication – Batsford Press, 1996 Ritchie, Anna, and Breeze, David, Invaders of Scotland, Historic Scotland Publication – HMSO, 1990 Ritchie, Graham and Anna, Scotland: Archaeology and Early History, Edinburgh University Press, 1991 Ritchie. J. N. G., Brochs of Scotland, Shire Publications, 1988 Sutherland, Elizabeth, In Search of the Picts, Constable and Co., 1994 Wagner, Paul, Warrior 50: PictishWarrior AD 297–849, Osprey, 2002

The Bedford Hours is a French late medieval book of hours. It dates to the early fifteenth century ; some of its miniatures, including the portraits of the Duke and Duchess of Bedford, have been attributed to the Bedford Master and his workshop in Paris. The Duke and Duchess of Bedford gave the book to their nephew Henry VI in 1430.[1] It is in the British Library, catalogued as Add MS 18850.

The story of how dinosaurs were resurrected for cinema in the early 20th century tends to focus on the visual components of these technical feats: the 2D animation and stop-motion technology that made long-extinct reptiles move again. But alongside making dinosaurs walk and run, cinematic dinosaurs also gave them a voice, imagining their snarls, barks, screeches and roars. Perhaps the first film to do this (or certainly the first mainstream, widely-seen film, at any rate) was 1933’s King Kong, where a charging Stegosaurus might take the title of first vocalising dinosaur in cinematic history: The crew of the Venture encounter a Stegosaurus: a famous scene from 1933's King Kong and, potentially, the first dinosaur cinema audiences ever heard vocalise. From Youtube's Prehistoric Classics. The same film would give us plenty of other prehistoric animal action and noise, but by far the most famous is surely the snarling, screeching Tyrannosaurus: Tyrannosaurus takes on King Kong in er, King Kong (1933). We've all seen it a million times, but go on, watch it again: you know you want to. Note the screechy tyrannosaur noises, presumably to contrast with Kong's throaty roars. From Youtube's Movieclips. Over the last century, cinematic dinosaur appearance and the technologies used to depict them have changed dramatically but one thing has remained the same: dinosaurs are as loud and noisy as ever. We’ve even seen the development of conventions and tropes around what dinosaurs sounded like. Sauropods are often given haunting, humpback whale-like songs and dromaeosaurs are frequently assigned aggressive, high-pitched snorts, snarls and crackles. And, of course, big theropods — especially Tyrannosaurus — invariably have deep, bellowing roars. It’s no exaggeration to say that the Jurassic Park Tyrannosaurus roar is as iconic and recognisable as its now-famous (maybe infamous?) design. The desire to depict talkative, raucous dinosaurs has long transcended media capable of conveying sound. Even movie dinosaurs were noisy and boisterous before we had the technology to make them truly roar on screen. The 1925 silent film The Lost World features plenty of roaring, snarling and bellowing stop-motion dinosaurs framed by director Harry O. Hoyt in dramatic close-up. Even in silence, the intent of these shots is obvious, and we simply have to imagine their vocalisations ourselves. Fantasia’s famous 1940 Rite of Spring sequence performed a similar trick for artistic reasons, juxtaposing a roaring Tyrannosaurus against booming segments of Igor Stravinsky’s famous composition. Static, traditional palaeoart also has a strong emphasis on animal vocalisations. Peruse any gallery of prehistoric animal restorations (such as this, at my new website!) and we inevitably find heaps of artworks showing grunting, chirping, screaming dinosaurs. Viewed objectively, it is a little strange that we focus so much on this behaviour in our artwork. Why don’t we render more non-acoustic behaviours that are arguably better suited to a totally visual medium? And furthermore, why draw so much attention to an aspect of dinosaur behaviour we don't know much about? Subconsciously, we just can’t get away from the call — pun not intended — of depicting extinct animals vocalising. An Archaeopteryx siemensii perches on driftwood, opens its mouth and calls out... what, exactly? We palaeoartists can't resist drawing animals posed mid-vocalisation, despite our lack of knowledge about extinct animal sound production. Clearly, we've collectively decided that prehistoric reptiles were vocal, noisy species, and this is understandable. It is, after all, what we experience around us today. Our world is full of singing, calling birds and barking, bellowing mammals. Whales sing, lions roar, and frogs croak. It stands to reason, then, that dinosaurs would be just as vociferous, and that a Jurassic or Cretaceous dawn would be full of strange, wondrous hoots, bellows, chirrups and songs that we can only imagine. I am, of course, leading up to a weighty “however”. What if our assumption of noisy, vociferous dinosaurs is simply... wrong? This is, of course, a very strong accusation, especially because we can say very little definitively about dinosaur vocalisation owing to our lack of fossilised dinosaur throat tissues and vocal organs. The preservation of such anatomies among Mesozoic dinosaurs is not impossible, these having been found in Vegavis iaai, a Mesozoic bird that lived in Antarctica 69-66 million years ago (Clarke et al. 2016); but this remains an exceptional occurrence: Vegavis is the only Mesozoic dinosaur known with preserved vocalisation anatomy. We can, however, use fossils and data from extant reptiles and birds to make predictions about dinosaur vocal ability, and several researchers have attempted this (e.g. Weishampel 1981; Senter 2008; Brazaitis and Watanabe 2011; Clarke et al. 2016; Reide et al. 2016). Among the more famous examples of such works is Phil Senter’s 2008 Voices of the past: a review of Paleozoic and Mesozoic animal sounds, a synthesis of what we know of sound production among ancient animals. In his section on birds and their ancestors, Senter makes the bold suggestion that non-avian dinosaurs may have been — yikes — entirely non-vocal (Senter 2008). In other words, this posits that dinosaurs may have not only been much quieter than their pop culture counterparts, but actually reliant on non-vocal acoustics when they wanted to communicate audibly. This notion — which I’m calling the "silent dinosaur hypothesis” — gained a fair bit of discussion online when first published and still crops up in modern conversations about dinosaur behaviour. But how does it hold up over a decade on, and did it ever have a sound basis to begin with? Non-vocal (or, at least, closed-mouth) interaction between male and female Ceratosaurus nasicornis. Were dinosaurs limited to posturing and other means of display for their communication with one another? Some hypotheses suggest so. To explore this further, it will help to outline what non-vocal animal acoustics are. We animals make noise all the time simply by existing and going about our lives. These ‘passive’ noises are classed as non-vocal acoustics. They include sounds that come from acts like breathing, forcing air around your throat tissues, and hitting or rubbing body parts against each other or external objects. Many animal species exploit these phenomena to make deliberate, structured sounds for communication. A hiss, for example, is little more than forcefully expelling air through our throats and mouths. A snort is much the same, except using our noses. We can also purposefully slap or rub body parts together or against the ground, water or vegetation to create loud noises. Some species have developed special anatomy purely to create non-vocal sounds, with the most obvious example being rattlesnake tails. Non-vocal acoustics are everywhere once we start noticing them, and Senter (2008) argued that they may have been the only sounds made by dinosaurs. It's incontrovertible that these are the only noises we can be confident that dinosaurs made because they can be generated regardless of vocal capability. Whatever other noises dinosaurs created, we know that they could hiss, snort, stamp their feet and so on, and living diapsids show that such behaviours are used as communication strategies among extant dinosaur relatives. Non-vocal acoustics are also perfectly compatible with the large noses and crests that may have acted as resonating chambers in certain dinosaurs, too (e.g. Weishempel 1981; Witmer and Ridgely 2009). We know, for instance, that some non-vocal snake species use resonating cavities in their throats to turn hisses into growls (Young 1991; see an example here of the slightly terrifying noises from of a king cobra). So, yes, non-vocal acoustics make a lot of sense for dinosaurs — documentary makers, take note. But Senter's (2008) accusation is that dinosaurs could only make non-vocal sounds, and that requires us to consider 'true' vocalisations: the sounds animals make by forcing air through their vocal organs. Mammals, amphibians and non-avian reptiles use a larynx for this purpose, while birds have their own, unique voice organ: the syrinx. It’s the evolution of this structure that prompted Senter’s suggestion of non-vocal dinosaurs. Unlike the larynx, which is situated at the top of the throat, the syrinx is located at the base of the trachea where the airway forks into the lungs. It also works in a different way to a larynx. Rather than passing air over vocal folds, the syrinx generates sound from the airway walls themselves. Rushing air from the lungs flutters these membranes and associated cartilages in a manner that produces sound, and the location of the syrinx at the fork where the trachea becomes a pair of bronchial tubes allows for especially complex vocalisations: each bronchial component can vibrate asymmetrically, making two sounds at once. To keep their airways open, avian syrinxes are reinforced with well-mineralised cartilaginous rings. In modern birds, it seems that syrinxes can also only function with assistance from a clavicular air sac (Senter 2008), although experiments indicate vocalisation without this structure may be possible (Clarke et al. 2016). Thanks to fossils of Vegavis, we can be confident that extinct duck and goose relatives like Conflicto antarcticus — a Palaeogene species from Antarctica shown here — were capable of making honking, goose-like sounds. But we have very little direct evidence for the sort of noises more rootward dinosaurs were able to make. The reinforced structure of the syrinx and its possible association with an air sac means that, unlike larynxes, they have some geologically detectable elements. In theory, this allows us to gauge roughly when, and in which lineages, they evolved even if fossil syrinxes themselves are rare. We can search for evidence of the clavicular air sac pneumatising the bones of the pectoral girdle and forelimb, as well as fossils of those reinforcing, mineralised rings holding the syrinx open. Although soft-tissue in nature, these structures are found in Cenozoic bird fossils (Clarke et al. 2016), so they evidently have decent enough fossilisation potential in the right circumstances. The results of such searches have come back without much to report, however. Even in well-preserved Mesozoic dinosaurs, we find no consistent evidence for clavicular air sacs outside of the ornithothoracines (the group of avialans that includes enantiornithines and crown birds, but see Senter 2008; Wedel 2009 for a few exceptions) and not a single mineralised airway has been discovered in a non-avian dinosaur (Senter 2008; Clarke et al. 2016). This suggests that the syrinx was developed very late in dinosaur evolution, perhaps not even being present in feathered, otherwise extremely-bird-like dinosaurs (Clarke et al. 2016; Kingsley et al. 2018). We should not assume, of course, that the avian syrinx sprang into existence fully-formed — surely it had to develop via intermediary ‘proto-syrinx’ structures first (Kingsley et al. 2018) — but we don’t know what that structure was nor what features might evidence its existence. With our present dataset, all we can say is that the avian syrinx as we know it probably wasn’t present in most non-bird dinosaurs. It follows that if dinosaurs did not have a syrinx, they were probably incapable of making the rich, complex noises of modern birds. And this is where things get especially interesting. OK, so dinosaurs weren't singing like passerines, but most reptiles have a larynx, and we can be pretty certain that dinosaurs did too. So Senter must be wrong, right? Dinosaurs merely vocalised like modern reptiles: case closed. Well, not necessarily, because we don't know if the dinosaur larynx was functional. Many lizard larynxes lack vocal folds and thus cannot vocalise, and opinions differ on whether their vocal abilities were independently lost from a vocal reptilian ancestor (e.g. Kingsley et al. 2018) or convergently gained from a historically silent one (e.g. Russel and Bauer 2021). Furthermore, birds also have a larynx, but it's also non-functional. This leaves dinosaurs evolutionarily bracketed by crocodylians (with a functioning larynx) and birds (with a non-functioning larynx), creating ambiguity about the ancestral state of dinosaur vocal organs. The ancestral acoustic capabilities of other reptiles is thus very important to determining what the original state of archosaur vocalisation was. There are two possible models (Kingsley et al. 2018): perhaps archosaurs were ancestrally silent, with crocodylians and birds to developing functional vocal organs independently of one another; or they were vocal, with birds augmenting and/or replacing the larynx for an unknown reason late in dinosaur evolution. And this touches on another key question with bearing on dinosaur vocalisation: why did birds develop the syrinx at all? One possibility is that the syrinx evolved in response to having lost, or having never developed, a vocal organ in the first place (Kingsley et al. 2018), a scenario implying that at least some theropods, if not all dinosaurs, went through a silent phase in their evolutionary history. The bottom line is that there's still a lot to learn about the evolution of reptile vocalisation, and there are reasonable, entirely plausible models that align with Senter’s (2008) proposal that dinosaurs were non-vocal (below). A handy graphic showing two competing models of syrinx evolution, from Kingsley et al. 2018. This assumes that reptiles were ancestrally vocal, but this doesn't change considerations of syrinx evolution too much. Essentially, we have two options: birds evolved a syrinx alongside a functioning larynx, or the dinosaur larynx wasn't functional, and the syrinx evolved as a novel structure to exploit vocal communication. The latter model, of course, implies at least some non-vocal dinosaurs. These ideas are, of course, very difficult to test without appropriate fossil data. Senter (2008) noted some support from non-vocal lizards using visual communication instead of aural, thus placing extra significance on the often extravagant display structures of dinosaurs. Might all those crests, horns, frills, fancy scales and elaborate feathers have evolved because dinosaurs were essentially mute, primarily visual communicators (Senter 2008)? A counterargument to this is that lizards communicate visually without such crests, horns and so on, but the concept of some dinosaurs using display structures to compensate for a lack of vocal capability is still an interesting idea. But before we get carried away with all this, we should note that the silent dinosaur hypothesis is not the only model of archosaur acoustic evolution on the table. A case can be made that, whatever weirdness was going on with syrinx evolution, dinosaurs were still capable of making laryngeal sounds. It has been noted that birds and crocodylians share several similar vocal behaviours that implies inheritance from a shared, vocal ancestor (e.g. Brazaitis and Watanabe 2011; Clarke et al. 2016) and some models of reptile evolution posit that all reptiles were ancestrally vocal, implying a functioning larynx in Dinosauria (Kingsley et al. 2018). Such concepts predict that dinosaurs vocalised at least in relation to matters of territory and courting, as well as to communicate between parents and offspring (Clarke et al. 2016). It’s difficult, of course, to know what specific sounds were made, and this isn't just because larynxes rarely fossilise: it's also because reptilian vocal anatomy is just not as well studied as that of birds and mammals (e.g. Rittenhouse et al. 1998; Reide et al. 2015; Russel and Bauer 2021). Recent work has shown that, although most reptile vocalisations are relatively simple compared to those of frogs, mammals and birds, there is a lot of variation in larynx structure across reptile species, and that their vocal tissues and acoustic capabilities can be very sophisticated, sometimes competing with mammals and birds in complexity (Brazaitis and Watanabe 2011; Reide et al. 2015; Russel and Bauer 2021). Among the most developed reptile vocal capabilities are those of crocodylians, which include a repertoire of behaviourally-specific hisses, grunts, bellows, snorts and chirps (Garrick et al. 1978), and those of geckoes, which use a range of single and repetitive chirps for advertising and alarm purposes (Russel and Bauer 2021). Perhaps, assuming dinosaurs did have functional larynxes, they made similar sounds. I'll take any excuse to link to videos of bellowing alligators. American alligators typically bellow in water, but — as this video shows — they perform a similar behaviour on land, too. Note the closed mouth and inflating neck tissues here, and read on. From Youtuber JadeAtema. We should clarify that the comparisons made by some researchers between reptilian and mammalian larynxes does not necessarily imply that dinosaurs vocalised like mammals. The throat tissues of reptiles and mammals are quite different in that reptiles can inflate their neck tissues with air from their lungs, whereas mammalian throat cartilage and muscles prohibit this action (Reide et al. 2016). This equips diapsids with a distinct mechanism for loud, deep sound production: closed-mouth vocalisation. By closing their mouths to prevent air escape and pumping air into their necks, reptiles and birds can create resonating chambers which allow for much deeper, lower-frequency vocalisations than could be achieved with a 'standard' open mouth call. We might intuitively think of crocodylians employing this behaviour to create loud, awesome bellows (especially the American alligator, which is the champion of crocodylian bellowing - see Garrick et al. 1978 and video above) but this tactic is not just used by big, exotic species: the cooing of pigeons and the ‘a-woo’ of eider ducks are also closed-mouth vocalisations. These acoustics have developed repeatedly throughout archosaur evolution and may have been practised by the dinosaur-crocodylian ancestor (Reide et al. 2016), so it seems reasonable to imagine this behaviour being used by dinosaurs making especially loud, deep and far-reaching noises. This may have been especially so among large species as, in birds at least, closed-mouth vocalisations have mostly evolved among bigger-bodied lineages (Reide et al. 2016). Predictions of archosaur voice evolution do not suggest that all dinosaur vocalisation would be closed-mouth (Reide et al. 2016), but those of us interested in depicting dinosaurs making their loudest, most intimidating noises should consider closed-mouth behaviours more likely than the usual stereotype of cat-like roaring (indeed, the roaring ability of Panthera species is associated with an unusual throat and laryngeal configuration (see Weissengruber et al. 2002), so we shouldn’t regard it as a ‘typical’ noise for any extinct animal to make, especially a reptile). But we're getting a little off-topic now: we're here to talk about silent dinosaurs, not booming ones. So let's wrap things up. To summarise, there are a few take-homes here. The first is that the general assertion that we know nothing about dinosaur vocalisation isn’t really true: we certainly don’t know much, but we’re not entirely devoid of intelligent comment, either. A lot of the papers cited in this post are available online and are well-worth reading if you want to know more about the topics discussed above. The second is that the silent dinosaur hypothesis is far from a done-deal, but it has a more legitimacy than we might first expect. It's not, despite its unorthodoxy, a crazy idea and actually fits some interpretations of dinosaur vocal evolution, even if we can't really tell how right or wrong it is at the moment. There are huge caveats around any model of dinosaur vocal evolution, of course, the most important being that our models are so poorly informed by fossil data that one new discovery could turn everything we’ve predicted on its head. And that leads to a third main point: whatever ideas of dinosaur vocalisation we think are correct, we should appreciate that they’re not much more than personal preferences at the moment. But that’s fine, and it's even liberating for artists and filmmakers. This uncertainty gives us a huge playground for depicting dinosaur behaviour in ways we haven’t considered before. What does a non-vocal Tyrannosaurus do instead of roaring when it wants to look impressive? How do sauropods communicate without singing? What noises did Mesozoic birds make before they developed the syrinx? We don’t know, but it’s sure a heck of a lot of fun to think about. Enjoyed this post? Support this blog for $1 a month and get free stuff! This blog is sponsored through Patreon, the site where you can help artists and authors make a living. If you enjoy my content, please consider donating as little as $1 a month to help fund my work and, in return, you'll get access to my exclusive Patreon content: regular updates on upcoming books, papers, paintings and exhibitions. Plus, you get free stuff - prints, high-quality images for printing, books, competitions - as my way of thanking you for your support. As always, huge thanks to everyone who already sponsors my work! References Brazaitis, P., & Watanabe, M. E. (2011). Crocodilian behaviour: a window to dinosaur behaviour?. Historical Biology, 23(01), 73-90. Clarke, J. A., Chatterjee, S., Li, Z., Riede, T., Agnolin, F., Goller, F., ... & Novas, F. E. (2016). Fossil evidence of the avian vocal organ from the Mesozoic. Nature, 538(7626), 502-505. Garrick, L. D., Lang, J. W., & Herzog, H. A. (1978). Social signals of adult American alligators. Bulletin of the AMNH; v. 160, article 3. Kingsley, E. P., Eliason, C. M., Riede, T., Li, Z., Hiscock, T. W., Farnsworth, M., ... & Clarke, J. A. (2018). Identity and novelty in the avian syrinx. Proceedings of the National Academy of Sciences, 115(41), 10209-10217. Riede, T., Li, Z., Tokuda, I. T., & Farmer, C. G. (2015). Functional morphology of the Alligator mississippiensis larynx with implications for vocal production. The Journal of experimental biology, 218(7), 991-998. Riede, T., Eliason, C. M., Miller, E. H., Goller, F., & Clarke, J. A. (2016). Coos, booms, and hoots: The evolution of closed‐mouth vocal behavior in birds. Evolution, 70(8), 1734-1746. Russell, A. P., & Bauer, A. M. (2021). Vocalization by extant nonavian reptiles: a synthetic overview of phonation and the vocal apparatus. The Anatomical Record, 304(7), 1478-1528. Senter, P. (2008). Voices of the past: a review of Paleozoic and Mesozoic animal sounds. Historical Biology, 20(4), 255-287. Weishampel, D. B. (1981). Acoustic analyses of potential vocalization in lambeosaurine dinosaurs (Reptilia: Ornithischia). Paleobiology, 7(2), 252-261. Weissengruber, G. E., Forstenpointner, G., Peters, G., Kübber‐Heiss, A., & Fitch, W. T. (2002). Hyoid apparatus and pharynx in the lion (Panthera leo), jaguar (Panthera onca), tiger (Panthera tigris), cheetah (Acinonyx jubatus) and domestic cat (Felis silvestris f. catus). Journal of anatomy, 201(3), 195-209. Witmer, L. M., & Ridgely, R. C. (2009). New insights into the brain, braincase, and ear region of tyrannosaurs (Dinosauria, Theropoda), with implications for sensory organization and behavior. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 292(9), 1266-1296.

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