Eifelosaurus
Eifelosaurus is an extinct genus of rhynchosaurian reptile known from the Middle Triassic Röt Formation of Germany. The genus contains a single species, Eifelosaurus triadicus, known from a partial articulated skeleton including the torso, pelvis, and part of the legs and tail, preserved with the underside of the animal exposed. Eifelosaurus is a member of the family Rhynchosauridae, and indicates rhynchosaurs were already widely geographically distributed from Germany to South Africa early in their evolutionary history.
History
At some point in 1903, quarrymen in Oberbettingen, Germany, discovered the partial skeleton of a fossil reptile embedded in dark sandstone. The quarrywork locality represents outcrops of the Röt Formation, part of the Upper Buntsandstein unit, which contains rocks dating to the Early–Middle Triassic. As the exact locality was never recorded, it remains unknown. Shortly thereafter, the specimen was obtained by Stefan Dohm, a local amateur fossil collector, who contacted German palaeontologist Otto Jaekel that autumn. Dohm loaned the specimen to Jaekel for study on the condition that it was only examined superficially, and no additional preparation was performed to remove excess matrix surrounding the skeleton. Upon observing the specimen, Jaekel noted that much of the preserved bone was shattered and could have been easily removed to reveal the impression left in the sediment underneath. While he refrained from doing this, he determined that this would be beneficial in better understanding the anatomy of the preserved vertebrae and pelvis. In June 1904, Jaekel published a brief description of the specimen, for which he had an illustration of the material produced. In this publication, regarding the illustration, he commented that he could not resist adding certain clarifying details as dotted lines for some broken skeletal elements. The specimen consists of a largely articulated—albeit incomplete—skeleton, preserved in ventral view, including most of the trunk, the sacrum, five caudal vertebrae, most of the pelvis, part of both femora, and the left tibia. The skull, cervical vertebrae, pectoral girdle, forelimbs, feet, and tip of the tail are not preserved. While the skeleton is flattened and broken in several regions, most of the individual bones are not crushed or distorted.Jaekel concluded that this specimen represented a new taxon due to its lizardlike morphology and the fact that all other lizard fossils were known from younger rock layers. As such, he proposed the new binomial name Eifelosaurus triadicus based on it, stating his desire that future preparation would reveal more of the animal's anatomy, thus elucidating its relationships with other reptiles. In 1929, Friedrich von Huene argued that Eifelosaurus was not a lizard, but a member of the Rhynchosauria. At some point following its description by Jaekel, the Eifelosaurus type specimen disappeared. In 1969, French palaeontologist Bernard Krebs claimed it was still part of Dohm's fossil collection in Gerolstein, which had been destroyed in 1944 when an allied air raid on the town resulted in much of its destruction during World War II. Fortunately, the specimen had been relocated some time prior, likely after Dohm's death in 1924, and added to the collections of the Steinmann Institute for Geology, Mineralogy, and Paleontology, part of the University of Bonn. It is now accessioned at the Goldfuß Museum at the University of Bonn as specimen IGPB JAEKEL-1.
In a 1984 review of the fossils of Buntsandstein, Detlef Mader claimed that the skeleton of Eifelosaurus is strikingly similar to that of the extant tuatara. The tuatatara is part of the larger clade Rhynchocephalia, which is unrelated and only superficially similar to Rhynchosauria. Mader proposed that the presence of Eifelosaurus in the Triassic supported the existence of Sphenodon as a due to its apparent similarities. In 1994, Martin Sander and Carole T. Gee more correctly asserted the rhynchosaurian affinities of Eifelosaurus in a subsequent updated description of the region's fossils. Eifelosaurus was not discussed in depth in most research papers in the following years. Butler et al. and Ezcurra et al. mentioned the taxon in passing as an "overlooked reptile" that had been "occasionally identified as a rhynchosaur", with both acknowledging that further research was needed on the taxon to better understand its affinities.
In 2022, Hans-Dieter Sues, Martín D. Ezcurra, and Rainer R. Schoch published the first detailed analysis of Eifelosaurus triadicus since its description in 1904. Based on rigorous anatomical observations and comparisons, the researchers concluded that, like previous authors had suggested, Eifelosaurus is a member of the Rhynchosauria. They further emphasized its significance due to its older age in comparison to other members of this clade; while the oldest and basalmost rhynchosaurs are known from South Africa, Eifelosaurus is similar in age to some of them, and is the oldest European rhynchosaur. This indicates that the Rhynchosauria had already achieved a wide paleolatitudinal distribution early in the clade's evolution. Sues and colleagues recognized that the fragmentary nature of the E. triadicus holotype restricts important comparisons with other rhynchosaurs. While it does bear any autapomorphies, the specimen does show a distinct combination of traits that distinguish it from all other taxa.
Description
At around 60% complete, the holotype of Eifelosaurus measures around, and estimates have suggested a total body length in life of around. As a rhynchosaur, it likely would have been an herbivore with a distinctive protruding beak-like structure.At least 15 dorsal vertebrae are preserved, although it likely had 17 or 18, the number seen in many early archosauromorphs, including at least some rhynchosaurs. The vertebrae are, with a slight constriction in the middle, and they lack a keel on the bottom. All of the vertebral centrum lengths are effectively identical. The vertebrae bear prominent, consistent with archosauromorphs but distinct from lepidosauromorphs. No are present, more similar to rhynchosaurids than non-rhynchosaurid rhynchosaurs and rhynchocephalians. The dorsal ribs are transversely wide, giving Eifelosaurus a broad, barrel-shaped trunk. Most of the gastralia are preserved on the left side of the specimen, forming a that would have covered the trunk's entire ventral surface in life. The femur of Eifelosaurus is proportionately more robust than earlier and more basal rhynchosaurs.
Classification
To determine the relationships and affinities of Eifelosaurus, Sues and colleagues included it in an updated version of the phylogenetic matrix published by Ezcurra et al.. This analysis consistently recovered Eifelosaurus as a member of the Rhynchosauria, a clade within Archosauromorpha. More specifically, it was recovered as an early member of the family Rhynchosauridae, diverging after Rhynchosaurus articeps but before the clade comprising Stenaulorhynchinae and hyperodapedontine-line rhynchosaurids. These results are displayed in the cladogram below:Sues et al. emphasized that many phylogenetically significant characters for rhynchosaurs are focused on the skull and lower leg, regions that are not preserved in the only known Eifelosaurus specimen. Since many characters could not be scored for this taxon in their phylogenetic matrix, only one additional step was required in the analysis to shift Eifelosaurus into various other positions within Rhynchosauria, such as in a position sister to Rhynchosauridae, diverging before Eohyosaurus, any other position as a non-hyperodapedontine rhynchosaurid, or as the sister group to Rhynchosauria + all other crownward archosauromorphs. The researchers concluded that Eifelosaurus should most parsimoniously be regarded as a rhynchosaurid rhynchosaur, but cautioned that statistical support for this placement was poor due to the limited amount of observable phylogenetically significant characters.