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Humble origins: Polacanthus, Hylaeosaurus, and Struthiosaurus

  • Huge Ankylosaurus has not always been THE ankylosaur. Was discovered at the beginning of the XX century, but several relatives were already known. They were simply smaller, less-armored and, above all, very fragmentary, and in the XIX were classified among the Stegosaurs. As a group, the Ankylosauria were recognized distinct only after Ankylosaurus. The thing is, one of the three inspirers of the name “dinosaur” was just an ankylosaur: Hylaeosaurus. Discovered in England in 1840, was only 4 m long and with very partial remains (as every “early” dino-discover). In famous Crystal Palace Park in London, the hylaeosaur shows up with the more-known Megalosaur and Iguanodont… but is sculpted like a giant, armor-less iguana. Some decades later, a companion was added: Polacanthus. English too, and also conviving with Iguanodon in Early Cretaceous, it was also 4 m long, and also very incomplete. In older depictions, Polacanthus had a very light armor, only made by couples of long dorsal spikes (hence the name, “many spikes”, a bony shield on its butt, and small plates on the tail. Today we know its armor was complete and Ankylosaurus-like (though even spikier) and with no club-like tails. The polacanth appears with this new look in Walking with Dinosaurs as a follower of Iguanodon’s herds. The other ankylosaurs found in Europe are usually like those cited above: small, fragmentary and clubless. To compensate, some are very coolly-named. Acanthopholis almost seems “Polacanthus” inverted. Struthiosaurus, a dwarf form living in the Late Cretaceous islets, means “Ostrich-Lizard” (making thinking it was Struthiomimus-like…). Dracopelta is the “armored dragon”. But the weirdest-named is Sarcolestes: “meat thief”.

Ankies conquer the USA: Nodosaurus, Edmontonia, and Sauropelta

  • Even in Usa the first dino-discoveries included an ankylosaur, one even more incomplete than Hylaeosaurus: “Palaeoscincus” was descibed in 1856 from isolated teeth initially believed from a lizard. Many undetermined remains were later assigned to it, making “Palaeoscincus” a Waste-Basket taxon, but now they are either regarded as dubious, or classified in other genera. The first North-American ankylosaur known from decent remains was Nodosaurus. Described during the Bone Wars, was known only from pieces of armor with no spikes: that’s why, in old portraits, Nodosaurus appears spikeless. It became the prototype of its own family, the Nodosaurids, in which every club-less ankylosaur used once to be put. More complete nodosaurids appeared in the XX century, and showed very spiky bodies: Panoplosaurus and Edmontonia (guess where it was discovered?). The latter in particular showed huge shoulder-spikes often double pointed. Nevertheless, was also narrow-headed and devoid of horns or tail-clubs, like all nodosaurs. All these nodosaurs were Late Cretaceous like Ankylosaurus. In the 1970s, Ostrom described an Early Cretaceous animal, Sauropelta: Ostrom wasn’t aware of, but started the trend to name ankylosaurs with the suffix –pelta. Also Early Cretaceous was Silvisaurus, a smaller relative. With its 7.5 long body, Sauropelta was the biggest nodosaurid known, had long lateral spikes (expecially long on the shoulders) and the back covered with small mosaic-like scutes - the typical nodosaurian armor, very different to that of Ankylosaurus made by wide rows put in line on the upper body. In 1988, famous paleontologist Bob Bakker described a shattered skull which has later revealed to be from Edmontonia. Named “Denversaurus” from the capital of Colorado (Bakker’s state), it might have given its name to the hero of a famous TV dino-cartoon broadcast just in those years.

Gimme the club: Euoplocephalus

  • Ankylosaurus was the first clubtail discovered (1908), but, again, its remains were very scanty; however, its record-size (more than 10 m long) soon made it the prototype of the whole group. But another relative has left many more remains, and still remains the most scientifically-known ankylosaur: Euoplocephalus (not “Eu-plocephalus” please). More than 40 individuals are known since the 1910s (though some of these might actually belong to species from different genera), which show a close Ankylosaurus relative two thirds its length (6-7 m), with a similar but awesomely more complex armor, which may even be described as “artistic”. A couple of flat bumps were on the neck, and two pointed spikes protruded from the shoulders. Several other spikes were placed in regular, elegant lines along its back. The head was similar to Ankylosaurus, with mosaic-like scutes on its roof, four small horns and bony eyelids. Even the elbows had three small round scutes each. Finally, the club was trefoil-shaped and almost resembled the club of French playing cards. A really cool animal to draw: in fact, Euoplocephalus appears as the actual stock ankylosaur in many dinosaur books – a fair thing, given its superior abundance in fossil record. It's also worth noting that several alleged Ankylosaurus seen in books, documentaries and maybe even films tend to have some Euoplocephalus traits, with conical horns instead of triangular, and trefoil clubs instead of oval. Despite this, “Euply” is typically non-portrayed in CGI documentaries, which will always prefer its gigantic cousin – the fact that Ankylosaurus could fight T. rex while the earlier Euoplocephalus could only battle Albertosaurs etc. doesn’t help. Together, Ankylosaurus, Euoplocephalus, Dyoplosaurus and possibly also Anodontosaurus make the only North-American members of the club-tailed family, Ankylosaurids; a fifth member, “Scolosaurus”, might have been misidentified from an Euoplocephalus skeleton that lacked the cephalic portion of the body, as well as the clubbed tip of its tail. It seemed its tail ended with two spikes (which were actually in the middle of the tail), and the scolosaur has been portrayed with this stegosaur-tail in old paleo-art and, even though few know it, even in animated cinema. If observed carefully, Rooter shows a couple of spikes on its tailtip when he goes away. According to the transitive property, he’s arguably an incorrect Euoplocephalus. On the other hand, it has been suggested that, as Euoplocephalus might be overlumped, at this point it can't be ruled out that further research will result in resurrecting Scolosaurus as valid genus.

Grumpy loners, or playful youngsters?: Pinacosaurus, Tarchia, and Saichania

  • Many more ankylosaurids are known from Asia, always from Late Cretaceous: Pinacosaurus was basically the equivalent of Euoplocephalus, smaller and with a much simpler armor, a narrower head and a hooked bill; Tarchia and Saichania were more similar to Ankylosaurus; Talarurus was hippo-shaped and short-limbed. First found in 1920s, Pinacosaurus has left in the eighties a proof of social behavior among ankylosaurs (traditionally considered loners): several youngsters found dead together in a small area, maybe buried in a sandstorm. The less-common Tarchia and Saichaniawere found in the 1970s. 8.5 m long, Tarchia is the biggest Asian ankylosaur, almost as large as Ankylosaurus; Saichania too was very large. Both ankylosaurs have rather funny names: Tarchia means “brain” and Saichania means “beautiful” (a reference to the beauty of its well-preserved skeleton). Talarurus has surprisingly appeared in Disney's Dinosaur, although only with an extremely brief cameo.

The Unfair Sex: Gastonia, Mymoorapelta, and Gargoyleosaurus

  • Since the 1990s, the classic “nodosaurid” / “ankylosaurid” bipartition has fallen down: many nodosaurids have revealed not to be related with Sauropelta or Edmontonia. Among them, the “polacanthines” (Polacanthus and Hylaeosaurus). Just in those years, new polacanthines were found in USA. The first one, following the trend to name ankylosaurs with –pelta, was called Mymoorapelta (the first North American ankylosaur from Late Jurassic, lived alongside Stegosaurus Allosaurus Diplodocus etc.) Also from the same fauna was the coolly-named Gargoyleosaurus. But the most striking discover was from Early Cretaceous, the Utahraptor age: Gastonia. Still another ankylosaur with the name ending in -a. Indeed this is the dino group with the greatest number of names ending so, giving them a bizarre “feminine” sound for these bulky “tanks”... Found in 1998, Gastonia impressed researchers because of its armor, filled with long spikes pointing to all directions. Some people have hailed it as the most armored animal ever existed on Earth: in short, a perfect opponent for the neighboring Utahraptor. Indeed, Gastonia fights the giant dromeosaurid in the Documentary of Lies Jurassic Fight Club, and ends the battle as the victor.

Naming questions: Minmi, Antarctopelta, and "Jurassosaurus"

  • Despite this example, non-stock ankylosaurs (and stegosaurs) are usually ignored in visual media. Maybe their reputation of “slow and foolish” has done its part, even though this fame is undeserved. A good example of missed opportunity was a small ankylosaur discovered in Australia, with one of the least dinosaurian name one could imagine: Minmi. [1] Discovered in 1980, this is the most complete Australian dinosaur to date, and yet it has not appeared in Spirits of the Ice Forests in which the much less-complete Leaellynasaura and even the “polar allosaur” appear (despite being their contemporary). Once considered nodosaurid, today Minmi is thought a primitive, hard-to-classify ankylosaur, perhaps with some bony plates even in its belly (a rare thing among ankylosaurs). It was also the first ankylosaur ever found in the southern emisphere, but was steadily reached by a second animal in 1986, another primitive ankylosaur, this time discovered in Antarctica. This one was the very first dinosaur ever discovered in the Ice Continent, yet has had to expect twenty years to be named: Antarctopelta. Nonetheless, the most awesome case regarding naming questions comes from Jurassic China: “Jurassosaurus nedegoapeferima”. The first term is a straight omage to Spielberg; the other is formed from the surnames of the film's main stars: Sam Neill, Laura Dern, Jeff Goldblum, Sir Richard Attenborough, Bob Peck, Martin Ferrero, Ariana Richards, and Joseph Mazzello. Even though the genus is now known as Tianchisaurus, it still keeps its bizarre species name. Well, it’s true, ankylosaurs really have some of the most awesome names within the dinosaur world.

The outsider: Scelidosaurus

  • When we think about armor-bodied dinosaurs, our minds comes to stegosaurs and ankylosaurs. But let’s not forget Scelidosaurus: a very primitive thyreophoran from Early Jurassic, discovered in Europe, North America, and perhaps in Asia. Traditionally considered in the middle between stegosaurs and ankylosaurs, some have recently suggested that it's the first true ankylosaur. Still, Scelidosaurus was more slender and far less armored than traditionally-indended ankylosaurs. Its armor was made only of small bony tubercles sparse along its body, while its small head had not a bony “cap” but just three short spikes on each rear-corner. Its limbs were more similar to bipedal ornithischians than to ankylosaurs, and some scientists have hypothesized it was at least partially bipedal. It’s a very early find among dinosaurs - its first skeleton is known since the XIX century even before Stegosaurus and Ankylosaurus have been known to science. Like most of the others earliest dino-discoveries, it was found in England. Having a not-so-impressive appearance Scelidosaurus has remained a non-stock animal. However, basal dinosaurs from Triassic and Early Jurassic often make paleontologists happier than their Late Jurassic or Cretaceous ones, because the most ancient dinosaurs help to understand a lot the affinities among the main dinosaurian groups, enhancing the reconstruction of their evolution.


  1. There is a backstory however: Minmi comes from “Minmi Crossing”, the locality in which its first skeleton has been discovered.
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