The Ancient Arrowhead Pokémon – Diplocaulus

Do you like Pokémon? Recently, packs of the Pokémon Trading Card Game (PTCG) have been appearing in convenience stores everywhere. This collectible card game has brought many Pokémon back into the spotlight. Among them, one that left a particularly strong impression on me is the Generation VIII pseudo-legendary Pokémon Dragapult. What makes this Pokémon so memorable is that its design is inspired by a mysterious prehistoric animal—Diplocaulus.

Official artwork of Dragapult (ドラパルト)（圖片來源：神奇寶貝百科，採用 CC BY-SA 4.0 授權）

The genus Diplocaulus lived from the Carboniferous to the Permian and belonged to the lepospondyl amphibians. Its type species is Diplocaulus salamandroides. These animals grew to about one meter in length, with five digits on both the forelimbs and hindlimbs. Their most striking feature was the enormous head shaped like an isosceles triangle, giving the impression that the animal was wearing a giant boomerang on its head. Few prehistoric vertebrates possess such an unusual appearance.

Map showing the fossil localities of the genus Diplocaulus

Timeline illustrating the geological range of the genus Diplocaulus（白稜製作）

Why did Diplocaulus evolve such a strange skull shape? The honest answer is that no one knows for certain. Even paleontologists remain unsure why the skull evolved into two sharply projecting lateral horns. At present, two main hypotheses have been proposed.

One group of researchers suggests that the distinctive skull may have functioned as a defense against predators, making it difficult for them to swallow the animal whole. However, fossil evidence raises serious questions about this idea. Bite marks found on Diplocaulus fossils indicate that predators often attacked from behind the neck rather than attempting to swallow the animal from the front. In some cases, predators such as the synapsid Dimetrodon appear to have crushed the skull directly, dismembering the prey rather than being hindered by its shape.

Size comparison diagram of Diplocaulus（圖片來源：Nobu Tamura，採用 CC BY-SA 4.0 授權）

Another hypothesis proposes that the boomerang-shaped skull improved hydrodynamic performance. According to this idea, the wide skull could have acted like a hydrofoil, allowing the animal to move through swift currents more efficiently and enabling it to rise or sink in the water with reduced resistance. Yet this explanation also has its weaknesses. Modern amphibians that inhabit fast-flowing streams have not evolved comparable structures, suggesting that such a skull shape may not provide a clear advantage. As a result, the true function of the skull remains unresolved, and numerous additional hypotheses have been proposed without reaching a definitive conclusion.

Skeletal reconstruction of Diplocaulus（圖片來源：Herman Douthitt，CC0 1.0 公共領域）

The mysteries surrounding Diplocaulus extend beyond its skull. Its evolutionary relationships are also complex and controversial. As mentioned earlier, it belongs to Lepospondyli, a group traditionally classified among amphibians. However, phylogenetically these animals appear to be closer to amniotes than to the so-called “true amphibians,” the temnospondyls. Lepospondyls are often regarded as the sister group of early amniotes, largely because of their distinctive vertebral structure. Their vertebrae consist of solid bone forming a cylindrical element that surrounds the notochord—an anatomical arrangement that gave rise to the name “lepospondyl.” This vertebral structure resembles that of amniotes, leading some researchers to suggest placing them within the broader lineage of early amniotes.

In recent years, however, this interpretation has been challenged. Some paleontologists have proposed that Lepospondyli may actually represent a polyphyletic grouping—a broad assemblage that includes species from multiple evolutionary lineages rather than a single natural clade. According to this view, many animals currently classified within Lepospondyli may not share a single common ancestry. Nevertheless, this hypothesis still requires further evidence and remains under debate.

Fossil specimen of Diplocaulus, housed at the Whiteside Museum of Natural History（圖片來源：Neil Pezzoni，採用 CC BY 4.0 授權）

Replica fossil and modern reconstruction model of Diplocaulus（圖片來源：Camelops，採用 CC BY-SA 4.0 授權）

Perhaps reflecting these taxonomic uncertainties, the Pokémon inspired by Diplocaulus, Dragapult, was given the Dragon and Ghost types—somewhat reminiscent of a reptilian creature—rather than Water and Ground types like Pokémon such as Quagsire or Swampert.

Beyond Pokémon, Diplocaulus also appears frequently in games and other media. In Monster Hunter: World, for example, it appears as an environmental creature known as the Wiggler-like “Arrowhead Gecko.” In Ark: Survival Evolved, the animal is portrayed as a companion that can provide players with an oxygen buff.

Alternative artistic reconstruction of Diplocaulus（圖片來源：Nihil scimus分，採用 CC BY-SA 4.0 授權）

This concludes a brief introduction to Diplocaulus. Many aspects of this remarkable animal remain unresolved, and paleontologists continue to investigate its biology and evolutionary history. Perhaps one day future discoveries will finally reveal why this ancient amphibian carried such an extraordinary boomerang-shaped head.

This is Rodrigo—see you next time.

Author: Rodrigo

References:

1. Beerbower, J.R. (November 1963). "Morphology, paleoecology, and phylogeny of the Permo-Pennsylvania amphibian Diploceraspis". Bulletin of the Museum of Comparative Zoology. 130 (2): 31–108.

2. Zoehfeld, Weidner K.; Bakker, Robert T.; Flis, Chris J.; Pettersson, Carl B.; Bell, Troy H. (2013). "Abstract: BURROWS AND BREAK-INS ON THE TEXAS PERMIAN DELTA: STACKED AESTIVATING AMPHIBIANS AND ATTACKS BY DIMETRODON (2013 GSA Annual Meeting in Denver: 125th Anniversary of GSA.