Paracus diepenbroeki: A new Placodont Sauropterygian From Anisian Triassic Netherlands

A new placodont sauropterygian from the Middle Triassic of the Netherlands

Authors:

Klein et al

Abstract:

A new genus and species of a non-cyamodontoid placodont is described on the basis of an incomplete and disarticulated skeleton from Winterswijk, the Netherlands, dated as early Anisian (Lower Muschelkalk). The new taxon is unique in a ventrolateral expansion of the neural arches of the posterior presacral and sacral vertebrae, in which the transverse process is incorporated. It has a round, plate-like pubis and ischium, and the only preserved long bone indicates elongated limbs. The holotype, which is relatively large (>1.35 m) for a basal sauropterygian, has still un-fused halves of neural arches and no distinct neural spine developed yet. The new taxon is assigned to non-cyamodontoid placodonts based on its round girdle elements, the morphology of dorsal-, sacral-, and caudal ribs, the straight medial and mediolateral elements of gastral ribs, and the presence of un-sutured armour plates. In spite of the large size of the holotype, there is evidence that the animal was not yet fully grown, based on the paired neural arches, and general poor ossification of the bones. The un-fused halves of neural arches are interpreted as skeletal paedomorphosis, which is typical for vertebrates with a secondary marine life style. The sacral region seems to be highly flexible.

New specimen of Placodont Psephoderma alpinum From Norian/Rhaetian Triassic Switzerland

New specimen of Psephoderma alpinum (Sauropterygia, Placodontia) from the Late Triassic of Schesaplana Mountain, Graubünden, Switzerland

Authors:

Neenan et al

Abstract:

Psephoderma alpinum is an armoured, durophagous placodont known from the alpine Late Triassic. Here we present a new, well-preserved isolated skull discovered in the Alplihorn Member (Late Norian–Early Rhaetian) of the Kössen Formation, Schesaplana Mountain, which straddles the Swiss/Austrian border. Micro-computed tomographic (µCT) scanning was used to create an accurate osteological reconstruction of the specimen, the first time this has been conducted for Psephoderma. We thus clarify disputed anatomical features from previous descriptions, such as a lack of a lacrimal and a pineal foramen that is enclosed by the parietal. We also present the first description based on µCT data of the lateral braincase wall, sphenoid region and some cranial nerve canals for Psephoderma, with the location of the hypophyseal seat, cerebral carotid foramina, dorsum sellae, prootic foramen, lacrimal foramen, as well as all dental foramina being described. This specimen represents the first skull of Psephoderma recovered in Switzerland, and features such as poorly-sutured braincase elements and its relatively small size compared to other known specimens may indicate that it was a sub-adult.

Open Water Marine Reptiles Resisted Extinction During Triassic Better

Selective extinction of Triassic marine reptiles during long-term sea-level changes illuminated by seawater strontium isotopes

Authors:

Kelley et al

Abstract:

The relationship between cycles of sea-level change and marine diversity has long been the subject of debate. Large predators may be particularly sensitive to changes in habitat availability and marine productivity driven by changes in sea-level, especially those dependent on nearshore benthic food resources. To test this relationship, we compared the proportional diversity of differing marine reptile ecotypes through the Triassic with the isotopic composition of seawater strontium (87Sr/86Sr), a geochemical index linked to tectonically controlled sea-level change. The proportional abundance of marine reptiles adapted toward a diet of shelled prey rose during times of rapid sea-level rise and fell during times of rapid sea-level fall, while open water forms were more resistant to these changes. Our results indicate that the rate of sea-level change, rather than the absolute magnitude of sea-level or flooded shelf area, played a role in shaping patterns of ecological diversification and ecologically selective extinction during the Triassic. The link between the isotopic composition of seawater strontium and the evolution of marine reptiles demonstrates that sea-level change played an important role in the structuring of marine ecosystems over geologic time.

Triassic Placodonts had a Unique Method of Teeth Replacement

Unique method of tooth replacement in durophagous placodont marine reptiles, with new data on the dentition of Chinese taxa

Authors:

Neenan et al

Abstract:

The placodonts of the Triassic period (~252–201 mya) represent one of the earliest and most extreme specialisations to a durophagous diet of any known reptile group. Exceptionally enlarged crushing tooth plates on the maxilla, dentary and palatine cooperated to form functional crushing areas in the buccal cavity. However, the extreme size of these teeth, combined with the unusual way they occluded, constrained how replacement occurred. Using an extensive micro-computed tomographic dataset of 11 specimens that span all geographic regions and placodont morphotypes, tooth replacement patterns were investigated. In addition, the previously undescribed dental morphologies and formulae of Chinese taxa are described for the first time and incorporated into the analysis. Placodonts have a unique tooth replacement pattern and results follow a phylogenetic trend. The plesiomorphic Placodus species show many replacement teeth at various stages of growth, with little or no discernible pattern. On the other hand, the more derived cyamodontoids tend to have fewer replacement teeth growing at any one time, replacing teeth unilaterally and/or in functional units, thus maintaining at least one functional crushing area at all times. The highly derived placochelyids have fewer teeth and, as a result, only have one or two replacement teeth in the upper jaw. This supports previous suggestions that these taxa had an alternative diet to other placodonts. Importantly, all specimens show at least one replacement tooth growing at the most posterior palatine tooth plates, indicating increased wear at this point and thus the most efficient functional crushing area.

246 Million Year Old Anisian Triassic Placodont Found in Europe

For around 50 million years, placodonts populated the flat coastal regions of the Tethys Ocean, in modern day Europe and China. The most distinctive feature of these [fossil marine reptiles(*)] was their teeth: The upper jaw had two rows of flattened teeth – one on the palate and one on the jawbone – while the lower jaw only had one set of teeth ideal for crushing shellfish and crustaceans.

The evolutionary origins of these placodonts remained unclear. However, a new find in a 246-million-year-old sediment layer now sheds light on the origin and phylogenetic development of the placodonts. As the Swiss and German team headed by Torsten Scheyer, a paleontologist at the University of Zurich, reveals the skull found in Winterswijk (Netherlands) is the earliest form of all known placodonts. The juvenile animal lived 246 million years ago. At around two centimeters in size, the skull is exceptionally well preserved and its characteristics set it apart from previous placodont discoveries.

The basal-most known placodonts to date have the group's trademark double row of crushing teeth in the upper jaw. The flattened teeth that give these animals their name only appear in more derived placodonts. "Unlike all the other placodonts discovered to date, the Winterswijk specimen has conical, pointed teeth instead of flattened or ball-shaped crushing ones," explains Scheyer, "which means the pointed teeth on the lower jaw slotted precisely into the gap between the palate and upper-jawbone teeth when biting."

The group's trademark double row of teeth in the upper jaw is proof that the new find is actually a placodont. According to the researchers, the teeth of Palatodonta bleekeri, the scientific name given to the Winterswijk specimen, were specialized in gripping and piercing soft prey. "The double row of teeth in the new find combined with its considerable age lead us to conclude that it is a very early placodont, from which the later forms developed," says Scheyer. The formation of crushing teeth and the specialization of a diet of shellfish and crustaceans thus developed later within placodont evolution.

The small Palatodonta bleekeri skull sheds new light on the ongoing debate on where the placodonts originated: Previous finds suggested origins in the shelf sea areas of either present-day China or Europe. Due to the considerable age of the new Dutch find and its basal form, however, the European origin of the placodonts is deemed confirmed. Scheyer and his colleagues are hoping for further exciting finds in Winterswijk to discover more about the evolution of the placodonts.

The interesting thing is that the origins of many major Triassic tetrapods seems to be in the first few million years after the PT Extinction.  

* The press release actually said dinosaur. I cannot let that pass onto my blog. Bleh.