Temporal Range: Late Triassic (235-208 Mya)
Length: 1.8 metres
- Discovery: Psephoderma is the only other genus in the placochelyid family of placodonts, alongside Placochelys. Christian Erich Hermann von Meyer, who also named Cyamodus, coined the name Psephoderma in 1858.
- Description: Psephoderma looked fairly similar to Cyamodus, although it was slightly larger in size. Like Cyamodus, Psephoderma had a shell carapace which was divided into two separate pieces; one which covered the shoulders and back and another which covered the hind legs. This carapace was made up of a number of interlocking hexagonal osteoderms.
Psephoderma was one of the largest shelled placodonts and many researchers believe this is most likely due to the fact that it lived towards the end of the Triassic era; when marine predators were also growing larger. Like all placodonts, Psephoderma was well adapted to eating shellfish. However, rather than having forward facing teeth, like most other placodonts, Psephoderma had a beak shaped mouth. This beak was used to pluck shellfish from between rocks and other marine debris, after which the grinding teeth further back in the mouth would be able to crush the shell.
Psephoderma was one of the last placodonts to have ever lived before the group became extinct at the end of the Triassic period.
Temporal Range: Late Triassic (235-223.4 Mya)
Length: 1 metre
- Discovery: Henodus is the only known member of the henodontid family of placodonts. Fossils of Henodus have been discovered in Germany and the species was named by Friedrich von Huene in 1936.
- Description: Henodus is the placodont which most resembles a modern day turtle in terms of looks. It had a single piece carapace which covered the entire body and stretched out almost covering the limbs entirely. This carapace was extremely tough; made up of a fusion of a large number of interlocking bony scutes, which were then covered by a layer of horn. The carapace of Henodus was fused to its spine, and was almost as wide as it was long. This oversized shell would have acted as the ultimate form of protection from marine predators, and it is likely that most Triassic predators would not have been able to fit the shell of a fully grown Henodus between their jaws. This shell however would have been a great hindrance when Henoduswas on land, and coupled with its extremely weak limbs, it is thought that Henodus would have spent very little time on land.
Henodus differed from other placodonts in that the mouth was broad and squared off instead of pointed. Researchers believed Henodus would have used its broad mouth to shovel through sediment to find buried shellfish, whilst other placodonts with pointed mouths were better suited to plucking shellfish from between rocks. Henodus is the only placodont thus far to be found in non-marine deposits, suggesting it may have lived in brackish or freshwater lagoons and this unique lifestyle may explain its different feeding style.
Temporal Range: Middle Triassic (239.5-223.4 Mya)
Length: 0.9 metres
- Discovery: Placochelys is a member of the placochelyid family of placodonts. The first fossil specimen was recovered from Hungary in Europe.
- Description: Placochelys was one of the smallest placodonts to have ever lived, with the largest recovered specimen measuring less than one metre in length. Of all the placodonts, Placochelys looked the most similar to the modern day sea turtle. It had a flat shell, smaller in size than the one found on Cyamodus. The shell itself was covered with a number of bony osteoderms and would have acted as a defence mechanism from predators.
The skull of Placochelys was incredibly compact and robust. It is likely that the mouth was a predominantly toothless horny beak, lined with just a handful of specialised broad teeth. The animals jaw muscles were extremely strong, meaning Placochelys was extremely efficient at crushing shellfish.
The limbs of Placochelys were paddled-shaped and would have been used to propel the animal through the water. However, unlike the modern sea turtle, Placochelys still had distinct toes. It also had a fairly short, stocky tail.
Temporal Range: Middle Triassic (241.1-235 Mya)
Length: 1.3 metres
- Discovery: Cyamodus was a placodont known from fossil remains found in Germany. It was named by Christian Erich Hermann von Meyer in 1863. It is the type genus for the group of placodonts known as the cyamodontids; the group of heavily armoured placodonts.
- Description: Cyamodus was a fairly small placodont, growing to around 1.3 metres in length. Its most characteristic feature is the two-part shell carapace found on the upper surface of the body. The larger half of the shell covered Cyamodus from the neck to the hips and spread out so that it almost encompassed the entire limbs. The second, smaller part of the shell covered the hips and the base of the tail. The shells themselves were covered in a mixture of hexagonal and circular plates of armour. The tail was stout and covered in a number of osteoderms, as were the proximal portions of the limbs.
It is thought that Cyamodus would have dragged its broad, flat body along the shallow sea bed, searching for shellfish, in a similar manner to that of modern day stingrays. Some researchers have suggested that, because of its strongly developed dentition, strong limbs and deeper body, Cyamodus was less bottom-dependent and possible more mobile than most placodonts, perhaps living in rougher waters or a more rocky environment.
It has also been noted that juvenile specimens of Cyamodus have an extra tooth on the roof of the mouth, compared to adult specimens. This suggests that Cyamodus reduced the number of teeth as they grew to maturity.
Temporal Range: Middle Triassic (241.1-235 Mya)
Length: 3 metres
- Discovery: Placodus is one of the best known and most commonly found of all the placodonts. It was named in 1833 by Swiss palaeontologist Louis Agassiz, who indecently thought the teeth he had first discovered belonged to a fish. It was not until 1858 when Richard Owen recognised that the teeth were in fact reptilian that Placodus was identified as a reptile. Since then, numerous fossils have been found in Germany, France, Poland and also China.
- Description: Like Paraplacodus, Placodus had a stocky body with a lengthy tail. It was also the largest of the known placondonts, growing to lengths of around three metres. Also like Paraplacodus, it had three forward-pointing teeth in each premaxilla but, unlike its close relative, these teeth were incredibly robust and the ends of each one were broad and rounded. The skull was particularly strong, developed so as to be able to cope with the stresses of crushing seashells.
The vertebral processes of Placodus dove-tailed into each other and were firmly connected, creating an extremely rigid trunk. It also possessed a row of bony scutes along the top of its neural spines which likely would have given Placodus some form of defence from predators. Like Paraplacodus, Placodus was a negatively buoyant creature; its large body and heavy bones mean it would have had no trouble staying on the seafloor to feed.
Temporal Range: Middle Triassic (241.1-235 Mya)
Length: 1.5 metres
- Discovery: A complete, disarticulated skeleton of Paraplacodus was discovered in Northern Italy and the species was subsequently named in 1931 by Bernard Peyer. The skeleton has not been worked on since 1942.
- Description: Paraplacodus belongs to the unarmoured group of placodonts, the placodontiods. Measuring 1.5 metres in length, it was medium sized and built like an oversized modern day newt. Its most distinctive feature were its teeth. It had three lengthened, forward-pointing teeth in each premaxilla and two corresponding elongated teeth in each dentary. These were then complimented by a number of rounded crushing teeth. These jaws were ideally designed for crushing shellfish and other marine crustaceans.
Paraplacodus had thick ribs and each vertebrae included a long transverse process, creating an almost box-shaped torso. This square cross-section allowed Paraplacodus to remain close to the seabed whilst hunting for food. In addition, the forelimbs were notably short, yet fairly robust, and the hand was fairly small.
Placodonts (Temporal Range: 245-200 Mya)
To begin this Triassic series, I wanted to cover some of the other creatures which lived alongside the dinosaurs during this particular time era. The first of these creature groups are the placodonts.
The placodonts were an intriguing group of marine reptiles (measuring between 1-3 metres in length) that first appeared during the Middle Triassic period, but became extinct at the Triassic/Jurassic boundary. The first specimen was discovered in 1830, but the order Placodontia was not developed until 1871, when Edward Drinker Cope classified the placodonts within the Sauropterygia (the group which includes the plesiosaurs) . The earliest forms, like Placodus, were characterised by their heavy, barrel-shaped bodies, similar in appearance to that of the modern day iguana. However, as the number of marine predators began to increase as the Triassic period progressed, the placodonts developed bony plates on their backs. By the end of the Triassic era, these bony plates had grown to cover the animal’s entire body; meaning the final placodonts resembled creatures similar to the modern day sea turtle. It is widely thought that this armour plating served a predominantly defensive purpose, protecting the animal’s fleshy body, although it has also been suggested that the armour may have helped to improve hydrodynamic efficiency.
It is believed that due to their dense bone structure and heavy armour plating, that the placodonts would have been far too weighty to have floated in the ocean and would have had to expend a great deal of energy to swim to the water surface. This had led researchers to suggest that the placodonts would have lived in shallow waters and not in deep oceans. In addition, it is thought that the placodonts would not have been confined to water and would have had the ability to travel on land, possibly to breed or nest.
The placodont diet consisted mainly of marine molluscs and brachipodods, so their teeth were tough and extremely thick, specifically designed to crush the shells of small, aquatic invertebrates.
Check back over the next few days to see individual fact-files based on the different members of the placodont family.
Picture: Placodus, one of the first placodonts
The Triassic is a period of time which extends from 252.2 to 208 Mya (million years ago). The name Triassic was coined by German geologist Friedrich Von Alberti in 1834, and relates to the three distinct rock layers that formed during the era. These rock layers can be seen throughout Germany and northwestern Europe and are formed of a layer of red beds, capped by a layer of chalk, followed by black shales.
The Triassic follows a period of time known as the Permian, and began in the wake of the Permian-Triassic extinction event; an event which left the Earth’s biosphere impoverished. Terrestrial life did not fully recover and diversify until midway through the Triassic era. The shelled, marine-dwelling, ammonites recovered, expanding from a single line which survived the Permian extinction. The fish fauna for the period remained very uniform, highlighting the fact that very few fish families survived through to the Triassic. Despite this, there were a large number of marine reptiles present throughout the Triassic. These included pachypleurosaurs, nothosaurus, placodonts, the first plesiosaurs and the highly successful ichthyosaurs.
On land, the early Triassic period was dominated by basal amphibians and a handful of therapsids (the ancestors of mammals), which had managed to survive the extinction event. However as the Triassic period progressed the therapsids were slowly displaced by archosaur reptiles (the ancestors of dinosaurs). The increase in archosaur numbers likely forced the surviving therapsids and their mammalian succesors to live as small, mainly nocturnal insectivores. The archosaurs on the other hand, evolved at a rapid pace, with different clades of archosaur evolving into different things. By the mid-Triassic the first pterosaurs and dinosaurs were present; but shared land space with a number of other reptile groups, including the aetosaurs, the rhynchosaurs, the first turtles, and the first crocodilians (the sphenosuchians).
Geography & Climate:
During the Triassic, almost all the Earth’s land mass was concentrated into a single supercontinent, known as Pangea. The mid-Traissic saw Pangea begin to gradually rift into two separate landmasses, Laurasia to the north and Gondwana to the south. The global climate during the Triassic was mostly hot and dry, with deserts spanning much of Pangaea’s interior. However, the climate shifted and became more humid as Pangaea began to drift apart. There is no evidence of glaciation at or near either pole; in fact the polar regions were moist and temperate, a climate ideally suited for the reptilian creatures which dominated the Triassic time era.
A year or so ago I started up a blog, called DinoFiles, with the intention of writing daily fact-files about the numerous different dinosaur species. The blog itself was fairly successful and I had a great deal of fun running it. However, with final year university exams and then subsequently trying to organise the rest of my life, DinoFiles sort of fell by the wayside. Now though, with summer fast approaching and my free time increasingly substantially, I hope to again start up and maintain a dinosaur-related blog.
I felt a fresh start was needed, rather than just continuing with my previous blog. The plan is to theme the blog around the three main dinosaur-related time eras (Triassic, Jurassic and Cretaceous) and different land locations. The reason for doing this is because quite often information on dinosaurs fails to demonstrate the temporal and geographical range of different species. Often dinosaurs get lumped together in a single collective, leaving many people unaware of just how long, and how dominantly, dinosaurs roamed the Earth.
Hope everyone enjoys DinoFiles II, and if anyone is interested in helping out with the writing of any dinosaur fact-files, please do get in touch!