dinosaur – Nix Illustration

Diamantinasaurus

Diamantinasaurus matildae was a sauropod dinosaur that lived in what is now northeastern Australia during the Late Cretaceous, about 94 million years ago.

It was either part of an early evolutionary branch of the titanosaurs, or at least very closely related to them.

Growing up to around 15m long (~50′), it’s represented by multiple specimens of varying ages, including one of the most complete individual necks of any sauropod. Unlike later-diverging titanosaurs it still had thumb claws on its hands, and it’s unclear if it had any osteoderm armor.

A patch of preserved skin shows polygonal scales with a rough bumpy surface texture — but based on what’s now known from other types of sauropod it probably had a variety of other scale shapes and sizes across different regions of its body.

Recent discoveries of titanosaurian footprints in Mongolia also suggest that the large claws on these sauropods’ hind feet were mostly buried in soft tissue, with only the tips visible in life.

Fossilized gut contents in one specimen indicate Diamantinasaurus was a generalist herbivore eating a wide range of plant species, browsing from low to high foliage heights, and swallowing its bites without chewing. This particular individual wasn’t fully grown, however, and so it may have been in the process of transitioning from a low-level “juvenile” diet to a higher-level “adult” one.

Spectember/Spectober 2025 #07: Kelp Yourself

An anonymous submission asked for a “live bearing bird”:

A digital sketch of a speculative aquatic descendant of moa birds, shown swimming in a kelp forest. It has a small head with a turtle-like beak, a long neck, no wings at all, a streamlined body, and large flipper-like webbed feet. Clumps of long ribbon-like feathers run down its back, vaguely mimicking the appearing of kelp fronds.

Rimurimuornis ovovivipara is a future descendant of the broad-billed moa, in a timeline where these Aotearoan birds weren’t hunted to extinction.

About 2m long (~6’6″), this fully aquatic bird grazes in kelp forests and seagrass meadows. It’s a rather slow swimmer, propelled solely by its large flipper-like feet – because like all moa it completely lacks wings.

Its ancestors’ laid incredibly thin-shelled eggs, and a combination of reducing the hard shell away even further to a more leathery state, then increasing egg retention time inside females’ bodies, has led to this lineage evolving an ovoviviparous form of live birth at sea.

It also has long ribbon-like feathers along its back that mimic the appearance of seaweed fronds. While terrestrial moa have few large predators to worry about, Rimurimuornis has to contend with sharks, orca-like whales, and leopard seal-like pinnipeds, and if its camouflage fails its primary tactic to discourage attacks is defensive defecation.

Spectember 2025 #04: Kerguelen Kingdom

A couple of anonymous submissions asked for “Kerguelen fauna before it sank 20 million years ago” and “a predator which prowled Cenozoic Kerguelen before it sank”:

[Context: The Kerguelen Plateau is today almost entirely underwater, but during the Cretaceous Period much larger parts were above water as island landmasses. Initially forming during the Gondwanan breakup of what would become Australia, India, and Antarctica, it was eventually left isolated in the forming southern Indian Ocean, and due to long-term volcanic hotspot activity it may have gone through as many as three different periods of rising and sinking before finally almost completely submerging about 20 million years ago.]

In the early Cenozoic, around the time of the Paleocene-Eocene Thermal Maximum, there’s less of Kerguelen’s land above water than there was in the Cretaceous, but the climate is warm-temperate and conifer forests cover the plateau’s islands.

A digital sketch of a speculative descendant of enantiornitheans. It's a large chunky shaggy-feathered flightless bird with a small head, toothed jaws instead of a beak, a long neck, vestigial wings with small claws, thick legs, and a pair of ribbon-like tail feathers that end in wider spaded plumes.

Enantiochen reliquia is a flightless bird standing around 1.5m tall (~5′), and its toothy jaws, wing claws, and ornamental ribbon-like tail plumes on males identify this species as an enantiornithean, descended from a small flighted form that just barely survived through the K-Pg extinction here.

It’s the largest current inhabitant of the Kerguelen plateau, a browsing herbivore filling a similar ecological role to the later moa of Aotearoa.

A digital sketch of a speculative descendant of gondwanatherian mammals. It vaguely resembles a rabbit with small pointed ears, with a deep snout, long digging claws on its digits, a short thin tail, and long hind feet.

Cuniculitherium kerguelensis is another Mesozoic holdover, a gondwanatherian mammal — although a little less unique than Enantiochen since other gondwanatheres still also survive in early Cenozoic South America and Antarctica.

About 40cm long (~1’4″), it’s a rather rabbit-like burrowing herbivore with long hind feet and a fast bounding gait, traits its lineage originally evolved to evade unenlagiine theropods and small terrestrial crocodylomorphs prior to the end-Cretaceous extinction. Those predators are gone from Kerguelen now, but…

A digital sketch of a speculative descendant of australobatrachian frogs. It has a large head, short chunky limbs, and an elongated body with a row of bony amor plates along its spine.

Daptobatrachus archaeotropus is a descendant of australobatrachian frogs. In a case of island gigantism it’s close to the size of a cat, around 50cm long (~1’8″), and with its elongated body, stubby hind legs, and a row of osteoderms down its back, it almost looks like a throwback to the Permian.

Although unable to hop, it’s an ambush predator capable of raising itself up for very brief bursts of crocodile-like galloping, preying on pretty much anything it can potentially fit into its mouth.

Gigantspinosaurus

Gigantspinosaurus sichuanensis was an early stegosaur that lived during the mid-Jurassic, about 166 million years ago, in what is now southwestern China.

Around 4.5m long (~14’9″), it had relatively small back plates and a pair of enormous shoulder spikes. It’s unclear exactly how the shoulder spines were positioned in life, but based on how they were found articulated in a fairly complete skeleton they seem to have swept sideways and backwards, protecting Gigantspinosaurus’ flanks.

Skin impressions show a mosaic of polygonal scales with scattered “rosettes” made up of larger scales surrounded by a ring of smaller scales, with a rough ridged surface texture that may have reduced light glare – suggesting an overall more matte appearance rather than glossy.

The thigh bones of one specimen are pathological, showing evidence that these dinosaurs sometimes suffered from bone tumors.

Duonychus

Duonychus tsogtbaatari was a therizinosaurid dinosaur living in what is now the Gobi Desert in southern Mongolia during the Late Cretaceous, around 96-90 million years ago.

Like other therizinosaurids it would have been a chunky-bodied herbivore with a small beaked head atop a long neck, long rake-like claws on its hands, stout legs, and a rather short tail. But it was rather small compared to most of its close relatives, estimated at about 3m long (~9’10”), with its known fossil remains including several vertebrae, partial ribs and pelvis, and a set of nearly-complete arms and hands.

Its hands had only two well-developed fingers, with a small splint-like vestigial third finger, an anatomical condition convergently seen in some other theropod groups but previously unknown in therizinosaurids. One of its long curved claws also preserved a rare example of a thick keratinous sheath, showing that in life the claw was over 40% longer than its bony core.

Duonychus’ elbow and finger joints had a fairly limited range of motion – more similar to the forearms of Tyrannosaurus than other therizinosaurids – but its claws were able to flex almost 90° at the tips of its fingers, which may have given it the ability to reach out and grab onto foliage with a very strong and precise grip.

Mexidracon

Mexidracon longimanus was an ornithomimid dinosaur that lived during the late Cretaceous, about 72 million years ago, in what is now northern Mexico.

It was a fairly small ornithomimid at around 2.5-3m long (~8-10′), and its leg proportions suggest it was less specialized for fast running than some of its other relatives. But its most unique feature was its hands, with extremely elongated metacarpal bones – giving it palms that were longer than its upper arm!

It’s unclear what the function of these unusual limbs was. Possibly they gave Mexidracon extra reach to hook its claws onto foliage and pull it within reach of its head, in a similar manner to ground sloths, chalicotheres, and therizinosaurs.

Isisaurus

Isisaurus colberti was a sauropod dinosaur that lived in what is now India and Pakistan at the end of the Cretaceous Period, about 70-66 million years ago.

It was part of the titanosaur group of sauropods and had some unusual proportions* compared to its close relatives, with elongated forelimbs and a relatively short chunky neck. Since it’s only known from a partial skeleton its full size is unknown – estimates have been made as large as 18m long (~60′) but it was probably somewhat smaller, closer to around 11m in length (36′).

(*Measurement errors in the original paper resulted in some very weird proportions, but more recent and rigorous reconstructions have made Isisaurus not quite so cursed-looking.)

Like most other titanosaurs it probably lacked the thumb claws seen in other sauropods, and it may also have had some bony osteoderm armor studding its skin.

Coprolites that may represent Isisaurus’ poop show evidence of several different fungi that grow on tree leaves in humid tropical and subtropical climates, suggesting that this sauropod was a selective browser somewhat like modern giraffes.

Avisaurus

Avisaurus darwini here lived at the very end of the Cretaceous, about 66 million years ago, in what is now the Hell Creek fossil beds in Montana, USA.

It was a member of a diverse group of Mesozoic birds known as enantiornitheans, which retained claws on their wings and often still had toothed snouts instead of beaks – and being part of the avisaurid family it was also one of the larger known examples of these birds, similar in size to a modern hawk at around 60cm long (~2′).

Although this species is only known from isolated foot bones, the remains have distinct enough anatomical features to show that Avisaurus had powerful gripping talons similar to those of modern hawks and owls, suggesting it had a similar lifestyle hunting small vertebrate prey in the ancient swampy Hell Creek ecosystem.

Spectember/Spectober 2024 #07: Mole Dino

Today’s spec creature is a combination of a couple of submissions – James P. Quick asked for “a post-K/Pg relict dinosaur from pre-glaciation Antarctica”, and an anonymous asked for “a subterranean (like, say, Talpa or Spalax) burrowing dinosaur”:

At the time of the K/Pg mass extinction some of the small ornithopods that inhabited Late Cretaceous Antarctica had been developing increasingly complex burrowing behavior and a more generalist omnivorous diet than most other ornithischians – and, along with their ability to endure the long dark cold polar winters, this was juuust about enough for them to survive while the rest of their non-avian cohorts vanished.

They were very briefly a fairly successful disaster taxon in the devastated polar forests, but they were quickly displaced by other diversifying survivors and never really got another ecological foothold to regain anything close to the non-avian dinosaurs former glory.

Instead the little ornithopods specialized even further for burrowing, spending more and more of their lives underground to avoid the increasing competition and predation from mammals and birds.

A shaded sketch of a speculative descendant of small ornithopod dinosaurs in Antarctica. It's a fuzzy little mole-like animal with a hoked beak at the tip of its toothy snout, no eyes, a keratinous shield on its head, large shovel-clawed forelimbs, a chunky body, stocky legs, and a fat bristly tail.

Now, well into the Cenozoic at the dawning of the Miocene, Cthonireliqua quicki is the very last representative of the non-avian dinosaurs. Small and stocky and mole-like, just 15cm long (~8″), it has muscular forelimbs with large shovel-like claws, a keratinous shield on its head, and a thick bristly tail where large fat reserves are stored.

Its eyes are almost completely absent, only vestigial remnants present under the skin of its face, and it navigates its extensive burrows using sensitive whisker-like filaments and its keen senses of hearing and smell. Still omnivorous like its ancestors, it feeds on whatever it comes across while tunneling – mainly worms, insects, smaller vertebrates, roots, and tubers.

Unfortunately for Cthonireliqua, and the rest of its Antarctic ecosystem, time is running out. Over the last few million years Antarctica’s climate has been steadily cooling and drying, the continent has become fully isolated, and the Antarctic Circumpolar Current has formed. Glaciation is well underway in the continental interior, and the once-lush forests are shrinking away and being replaced with tundra.

Soon all evidence of these dinosaurs’ existence will be buried under the ice.

Spectember 2024 #03: Terrible Toucan

This concept comes from thecomiccreator, who suggested a “carnivorous/omnivorous toucan”:

A shaded sketch of a speculative descendant of toucans, shown both standing on one leg and in flight. Its a stork-like bird with a massive long serrated beak, a bald vulture-like head and ruffed neck, large broad wings with slotted flight feathers, and long legs with two forward-facing toes and two backwards-facing toes.

Descended from toco toucans inhabiting savanna grasslands, Deinotukan auctorcomicus is a large stork-like bird standing about 1.2m tall (~4′).

Unlike its mostly-frugivorous ancestors it’s primarily a scavenger, soaring on thermals with its long broad wings and following vultures towards sources of carrion. Its massive serrated beak allows it to efficiently open up tough-skinned carcasses, and with its nostrils positioned up near its eyes it can probe around inside much deeper than other scavengers while still being able to breathe.

It also opportunistically hunts live prey, especially during the breeding season while raising chicks, slowly stalking around on foot snatching up anything small enough to fit in its mouth and be swallowed whole.

Its beak contains an extensive network of blood vessels, which along with the large surface area make it an effective way of shedding excess heat in its hot tropical habitat – but when soaring at high altitudes where temperatures are near-freezing it’s also able to shunt blood flow away from its beak to conserve body heat instead.