The revision, led by researchers examining dozens of newly recovered teeth from Upper Jurassic marine deposits near the village of Mahlstetten in southwestern Germany, demonstrates that this animal was not a synechodontiform at all. Instead, the evidence points to it being a galeomorph, the superorder that contains most familiar modern sharks, including hammerheads, tiger sharks and catsharks. The finding reshapes how palaeontologists view the diversity of Jurassic shark faunas and highlights just how much evolutionary experimentation was underway in the seas of that era.

Elasmobranchs, the group that includes sharks, rays and skates, are among the most successful lineages of cartilaginous fishes. They first appeared at the end of the Palaeozoic and underwent a major diversification during the Jurassic, when nearly all of their major clades show up in the fossil record. Yet reconstructing that history is notoriously difficult. Because shark skeletons are made of cartilage, they rarely fossilise intact. The overwhelming majority of what palaeontologists know about ancient sharks comes from isolated teeth and dermal denticles, the tiny tooth-like scales that covered their skin.

Teeth are abundant because sharks are polyphyodont, meaning they continuously shed and replace their teeth throughout their lives. This constant turnover produces enormous quantities of dental remains, which are highly valuable for taxonomy. But it also creates problems. Shark dentitions are heterodont, meaning that teeth vary considerably in shape depending on their position along the jaw, with differences running from the front of the mouth to the back and sometimes between upper and lower jaws. Distinguishing between features that are genuinely diagnostic of a species and those that simply reflect where a tooth sat in the mouth requires careful analysis, and many fossil species described in past centuries were based on material far too incomplete to capture this variation.

The genus Synechodus itself illustrates the problem. Its type species, Synechodus dubrisiensis, was described from an associated tooth set found in Late Cretaceous deposits in England. Over twenty additional species were subsequently assigned to the genus, spanning an extraordinary range from the Permian to the Palaeocene. But researchers have increasingly noticed that many of these species differ from the type in significant ways, including crown ornamentation and the pattern of vascularisation inside the roots. The Permian species Synechodus antiquus and several Triassic forms already show clear differences, and it is likely that many of them belong to genera that have yet to be identified. Synechodus, in other words, may be functioning as a waste-basket taxon, a convenient label for anything that looks vaguely similar but resists precise classification.

Curvorudentis prorogatus was caught in exactly this trap. Kriwet described it in 2003 from Callovian deposits at Kłęby in northwestern Poland, assigning it to Synechodus primarily on the basis of root characters such as short root grooves and several margino-lingual foramina. When four additional teeth were later discovered at Ogrodzieniec Quarry in southern Poland, from Middle Callovian and lower Oxfordian layers, questions began to mount. Those teeth showed significant differences from Synechodus dubrisiensis, particularly in root structure and crown ornamentation, casting doubt on the original assignment.

The new material from Mahlstetten changes the picture entirely. The fossiliferous layers there are greyish marls of the Mutabilis zone, dating to the early Kimmeridgian stage of the Late Jurassic, deposited under outer-shelf and open-water conditions. This contrasts with the restricted environments of the contemporaneous Solnhofen Archipelago and Nusplingen Lagerstätten. A private collector, E. Unger of Ravensburg, spent many years recovering palaeontological material from the site, and the specimens used in the study were subsequently donated to the State Museum of Natural History Stuttgart. Researchers photographed the teeth using scanning electron microscopy after sputter-coating them at the Museum of Natural History in Berlin, allowing extremely detailed examination of their surface features.

What those images revealed is a dental architecture unlike anything else in the Jurassic. The teeth are wide, with up to three pairs of lateral cusplets flanking a triangular main cusp. The basal labial margin, the front edge of the tooth near its base, is distinctly sinuous and curves into a pronounced concave arch beneath the main cusp. The labial crown face carries folds that run parallel to the cutting edges, with additional short vertical ridges on the cusps and cusplets, and a prominent labial crown extension that covers the root. Inside the root, the vascularisation follows a hemiaulacorhize pattern, with foramina and parallel nutritive grooves opening onto the lingual protuberance. None of these features match Synechodus, whose teeth lack the basal labial curvature and the parallel labial folds, and whose roots show a pseudopolyaulacorhize vascularisation pattern with a basally flat root and a typical labial depression.

The comparison with other Jurassic sharks was equally revealing. Teeth of Paraorthacodus, another synechodontiform genus, have a straight labial margin ornamented with sub-vertical ridges and delicate, well-separated cusplets, quite unlike the curved, fold-bearing teeth of Curvorudentis. The monotypic genus Bavariscyllium, from the Tithonian of the Solnhofen Archipelago, has shorter anterior teeth with lower, more acute cusplets and asymmetric root lobes. Palaeocarcharias, traditionally considered an early lamniform, has mesiodistally compressed teeth with no ornamentation and no lateral cusplets at all. Palaeoscyllium, another Solnhofen genus, shows strongly marked apico-basally directed ridges and a compressed lingual protuberance. Curvorudentis stands apart from all of them, and the researchers concluded that it required not just a new species assignment but a new genus, named from the Latin words for curvatures and tooth, in reference to the distinctive curved basal labial margin.

The reassignment to galeomorphs rests on several characters of high taxonomic value: the centrally developed concavity of the basal labial crown face, the well-developed crown shoulders, the presence of numerous open foramina in the lingual face of the root, and the hemiaulacorhize vascularisation pattern with divergent and basally oriented root branches. These traits are widely observed in both modern galeomorphs, such as the catshark Halaelurus bürgeri and the proscylliid Proscyllium habereri, and in fossil galeomorphs like Palaeoscyllium and Bavariscyllium. Interestingly, the teeth also show what appears to be a minor dignathic heterodonty, the kind of difference between upper and lower jaw teeth seen in living galeomorph sharks, where upper jaw teeth have cusps inclined toward the commissure while lower jaw teeth stand upright. More material will be needed to confirm this, but the pattern is suggestive.

Where exactly Curvorudentis sits within the galeomorphs remains unresolved. The researchers note that it shares some features with modern carcharhiniform taxa but differs in others, including the lateral extension of the enameloid, the labial crown folds parallel to the cutting edges, and the almost squared, mesiodistally elongated root with oblique and divergent branches. The systematic positions of Palaeoscyllium and Bavariscyllium within galeomorphs have also recently been challenged and remain uncertain, and Curvorudentis appears to be in a similar position, a galeomorph whose precise affinities cannot yet be pinned down.

The Mahlstetten discovery also extends the geographic and temporal range of the species considerably. Previously known only from Middle Jurassic deposits in Poland, Curvorudentis prorogatus is now documented from the early Kimmeridgian of Germany, its stratigraphically youngest occurrence to date. Its environmental distribution spans from nearshore settings in Poland to the offshore conditions of Mahlstetten, suggesting that this was a small, unspecialised mesopredator, comfortable in a range of marine habitats. As palaeontologists continue to re-examine old collections with modern imaging techniques and larger comparative datasets, it seems likely that more waste-basket taxa will be unpacked, and more unexpected branches of the shark family tree will come into focus.

Subject of Research: Taxonomic revision of a Jurassic shark species based on fossil teeth

Article Title: Revision of the extinct shark Synechodus prorogatus Kriwet, 2003 ( Chondrichthyes , Elasmobranchii ) and its galeomorph affiliation

Article References: Begat, A., Villalobos-Segura, E., Amadori, M., Klug, S., & Kriwet, J. (2026). Revision of the extinct shark Synechodus prorogatus Kriwet, 2003 (Chondrichthyes, Elasmobranchii) and its galeomorph affiliation. Swiss Journal of Palaeontology, 145, 303-311. https://doi.org/10.3897/sjp.145.187852

Image Credits: AI Generated

DOI: 10.3897/sjp.145.187852

Keywords: Jurassic, sharks, paleontology, elasmobranchs, teeth, taxonomy, galeomorphs, Synechodus, Germany, Poland, fossil, heterodonty