The authors have declared that no competing interests exist.
Conceived and designed the experiments: OWMR AMH ALA AH. Performed the experiments: OWMR ALA. Analyzed the data: OWMR ALA. Contributed reagents/materials/analysis tools: AMH AH. Wrote the paper: OWMR AMH ALA.
Rhynchocephalians, the sister group of squamates (lizards and snakes), are only represented by the single genus
A new fossil relative of
The evolution of the extraordinary dentition of
The recent genus
Rhynchocephalians were a common component of Mesozoic small vertebrate faunas
Here we report on a new taxon of rhynchocephalian from the Late Jurassic of southern Germany that further underlines the morphological and ecological diversity of rhynchocephalians and indicates high adaptive plasticity even in the dentitions of these animals. The specimen was found in the middle parts of the Moernsheim Formation exposed at Mühlheim (
Modified from
The data matrix was analysed with PAUP 4.0b10 (Swofford 2003), using a branch and bound search. The initial analyses resulted in 119 trees with a length of 187 steps (CI 0.465, RI 0.649, RC 0.302). The strict consensus tree of these trees showed poor resolution, with Oenosaurus representing a member of a polytomy of rhynchocephalians more derived than Planocephalosaurus (
The taxon Pamizinsaurus from the Early Cretaceous of Mexico (Reynoso 1997) was identified as a wildcard taxon that strongly influenced the results. This may partially be due to high amounts of missing data (64%) in this taxon; however, that several other taxa have even higher amounts of missing data (Eilenodon 68%; Cynosphenodon: 73%; Toxolophosaurus: 79%) but proved to be less problematic, indicates that the wildcard status of Pamizinsaurus might also be due to some character conflict.
In a next step, we thus removed Pamizinsaurus from the matrix and ran a second analysis with the same settings as above. The analysis resulted in only two most parsimonious trees with a length of 184 steps (CI 0.473, RI 0.654, RC 0.309). The strict consensus tree of these two trees (
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomenclature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix “
Lepidosauria Haeckel, 1866
Rhynchocephalia Günther, 1867
Sphenodontia Williston, 1925
Sphenodontidae Cope, 1871
urn:lsid:zoobank.org:act:48C1BA32-BC6D-407D-81E0-7ECFF22D77A3
urn:lsid:zoobank.org:act:6648C44F-FDC0-48B2-A6A9-399B17E07D38
Bayerische Staatssammlung für Paläontologie und Geologie, Munich, Germany, BSPG 2009 I 23; partial skull and complete mandibles (
(A)–Skull in dorsal view. (B)–Skull in ventral view. (C–D)–Right mandible in lateral (C) and medial (D) views. (E)–Left mandible in lateral view. (F)–Stereophotographs of the skull in ventral view. Abbreviations: a, angular; ar, articular; bsp, basisphenoid; bt, basal tubera; co, coronoid; cos, coronoid shelf; d, dentary; ect, ectopterygoid; eo, exoccipital/opisthotic; f, frontal; fo, foramen; j, jugal; m, maxilla; mf, mandibular foramen; mg, Meckelian groove; oc, occipital condyle; pa, parietal; pal, palatine; po, postorbital; pof, postfrontal; prf, prefrontal; pt, pterygoid; sa, surangular; sy, symphysis; tp, tooth plate. Scale bars are 10 mm.
(A)–Left maxillary tooth plate in ventral view (anterior is to the left). (B)–Enlargement of posterior part of left maxillary tooth plate, showing compound structure of the plate. (C)–Further enlargement of left maxillary tooth plate, showing closely packed, worn teeth with central pulp cavities. Scale bars are 1 mm (A, B) and 0.5 mm (C).
Posterior is to the right. Abbreviations: bc, basal cavity; f, foramen. Small arrows point to bifurcating dentine channels. Scale bar is 5 mm.
Mörnsheim Formation (Lower Tithonian)
Small rhynchocephalian with the following autapomorphic characters: maxilla with a medial process at the posterior end; ectopterygoid with a secondary lateral process that contacts the medial side of the maxilla; palatines with a midline contact in ventral view; strongly pronounced lateral longitudinal groove on the dentaries, housing several large foramina; very high coronoid process, the anterior border of which forms an angle of approximately 90° with the tooth row; coronoid with a pronounced shoulder medially; dentition composed of extensive tooth plates formed by a multitude of fused, small, pencil-like teeth.
The skull of
The skull seems to have been rather robust. As preserved, it is 24.3 mm long. Unfortunately, the exact skull length cannot be determined, since the premaxillae are missing, but these bones probably did not account for more than an additional 2–3 mm. Thus, the skull was slightly broader (28 mm) than long, as in many rhynchocephalians, but unlike the slender, elongate skull of the marine pleurosaurs
The palate is only missing most of the vomer and the posterior ends of the quadrate wings of the pterygoids (
The ectopterygoid attaches anterolaterally to the pterygoid wing. It is unusual in that it has two lateral processes, one that contacts the posterior end of the maxilla, as in other rhynchocephalians, and a more anterior one that extends anterolaterally lateral to the palatine and contacts the medial side of the maxilla (
Only the floor of the braincase and the ventral parts of the occiput are preserved. The basisphenoid is narrow at the basicranial articulation, but rapidly widens posteriorly. The basipterygoid processes seem to be stout and short, but are mostly hidden by the pterygoids. The basisphenoid has a broad, shallow depression on the ventral side between the basipterygoid processes and the low, widely separated basal tubera. The occipital condyle is broad and not separated from the basioccipital body by a constricted neck, similar to the situation in the modern
The lower jaw is 33 mm long and is especially notable for its high coronoid process, which exceeds the tooth row by approximately 8.7 mm in the right mandible and is thus almost 1.5 times higher than the body of the dentary (
The postdentary bones are entirely restricted to the posterior half of the mandible. The surangular makes up the posterior margin of the ventral part of the coronoid process and continues posteriorly to the end of the mandible. The mandibular articulation is developed as a longitudinal dorsal ridge on the articular. The ridge is sharp-edged dorsally and slightly displaced to the lateral side. Medially, it is flanked by a slightly anteroposteriorly concave medial bulge that becomes more pronounced posteriorly. This morphology is similar to the condition in derived rhynchocephalians, possibly indicating a propalinal movement of the lower jaw. The retroarticular process is short and stout. The medial side of the coronoid is thickened and forms a pronounced shelf below the tip of the coronoid process.
The most unusual character of the new taxon is the dentition. Unlike the situation in any other rhynchocephalian, broad tooth plates are present in both the maxillaries and dentaries. The maxillary tooth plates (
Under closer inspection, the surfaces of the tooth plates show small, but clearly defined, round, oval, or angular subunits, made up of concentric dentine layers with a small central cavity (
Despite its apomorphic cranial morphology and highly unusual dentition, cladistic analysis (see
Cladistic analysis of 70 osteological characters in 19 rhynchocephalian and two outgroup taxa resulted in the recovery of 2 trees with 184 steps (see
The dentition of
An interesting problem is the evolution of these tooth plates. The phylogenetic position of
One important question concerns the feeding ecology of
Despite their specialized dentition, rhynchocephalians are quite variable in their tooth morphology. Rhynchocephalian teeth can be referred to three basic functional types
The occurrence of a highly specialized rhynchocephalian close to the decline of the group in the Cretaceous
T, functional tooth type; D, interpretation of dietary preferences.
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We thank Roland Pöschl, who found the fossil, and the owners and operators of the Krautworst Naturstein quarry, Ulrich Leonhardt, Roland Pöschl and Uwe Krautworst, for donating the specimen to the BSPG. Ulrich Leonhardt, Stefan Sónyi, and Renate Liebreich are thanked for preparation of the fossil. The paper benefited from discussions with Marc Jones and Alexander Nützel. Furthermore, critical comments by Marc Jones and Nick Fraser considerably helped to improve the paper. CT scans were carried out at the Steinmann Institute of the University of Bonn with the help of Irina Ruf, which is greatly appreciated.