The new material comes largely from the collection of Jürgen Sylla, a private collector who spent many years gathering marine invertebrates exclusively from the Saal quarry. His specimens, together with material from collectors Fritz Lang, Helmut Keupp, and Olaf Neubauer, were acquired by the Bavarian State Collection for Palaeontology and Geology in Munich, where nearly all of the studied material, including every type and illustrated specimen, is now housed under the repository number SNSB-BSPG 2016 XXI. The new collection alone yielded 119 species, 80 of them formally named, increasing the known species count for the quarry by more than fifty. The result is a fauna that rivals, and by most measures surpasses, every other Late Jurassic gastropod assemblage yet documented.

The rocks themselves tell part of the story. The Saal quarry exposes Upper Kimmeridgian reefal limestones, deposits formed in and around sponge and coral reefs that flourished in the warm, shallow seas covering much of southern Germany during the Late Jurassic. Such reefal settings are among the most structurally complex habitats in the ocean, offering countless microhabitats, hard substrates for attachment, crevices for shelter, and current-swept surfaces for filter feeders. The extraordinary snail diversity at Saal reflects this highly structured shallow-water environment, where bivalves, brachiopods, corals, and gastropods together built a community as rich as any modern tropical reef. The high number of species left in open nomenclature, meaning they could not be confidently assigned to a named species, reflects the fact that many specimens are fragmentary or corroded, particularly among the delicate high-spired groups.

Among the fifteen new species are several limpets that offer a glimpse of the grazing community on the Jurassic seafloor. Scurriopsis cragolis, a limpet with almost straight to slightly convex sides and densely spaced fine radial ribs, reached about 26 millimetres in length, while Pseudorhytidopilus? quadratus, a thin, cap-shaped shell with a trapezoidal outline and irregular concentric bulges, grew to 21 millimetres. Rimulopsis danuviensis, named after the river Danube, is a small limpet whose apex bends strongly backwards, overhanging the rear margin of the shell, and whose surface carries a distinctive alternation of strong and weak radial ribs with nodular intersections. These humble cap-shaped shells, often overlooked in favour of more flamboyant spiralled forms, were the lawnmowers of the reef, scraping algae and microbial films from hard surfaces.

Perhaps the most striking of the new discoveries is Kelheimia triangulata, the sole species of a brand-new genus named after the nearby town of Kelheim. This broadly conical, slightly hollow-based snail could reach nearly five centimetres across and displays a remarkable transformation during growth. Its early whorls are slender and carry intersecting spiral cords and roughly nine bulging axial ribs that form nodes along a keel, but as the shell widens, the keel and ribs vanish entirely, leaving the later whorls smooth and straight-sided, covered only by about eight wide spiral cords. This dramatic ontogenetic change, combined with a sharp angular edge between whorl face and base and a large circular aperture with a callous inner lip, sets Kelheimia apart from related Jurassic genera such as Pyrgotrochus and Conotomaria, which grow more evenly and retain a selenizone, the slit-band characteristic of many vetigastropods.

Other newcomers reveal the sheer variety of form that Jurassic snails achieved. Nododelphinula oblonga bears a strongly projecting keel and a subsutural row of nodes, with a spiral cord encircling the umbilicus whose nodes resemble hollow spines. Neritopsis? rotundatus is a rounded, low-spired neritimorph whose whorl face and base are evenly covered with more than fifteen nodose spiral cords. Cryptoptyxis? spinosus carries five sharp, narrow axial ribs per whorl, aligned in strands running across the shell, and its last whorl terminates these ribs in thorn-like extensions. Turritella lucagrita, a slender high-spired tower shell reaching 75 millimetres, changes its sculpture during growth, with the lower of three spiral cords becoming prominently protruding on the late whorls. Eustoma? gracilis, Diarthema aspera, Neuburgensia angulata, Neuburgensia rara, Oonia kimmeridgiensis, Creniturbo gibbosus, and Aphanoptyxis sinerugae, a 98-millimetre-long shell whose name means without folds because its whorls lack the internal plaits typical of its relatives, complete the roster of new species.

The study also reshuffles several existing names. Leptomaria tuberosa, described in 2017, is now considered a subjective synonym of Leptomaria goldfussi, as the new material confirmed an earlier suspicion that the two forms represent variants of a single variable species. A series of species have been reassigned to different genera: Gymnocerithium? convexoconcavum now belongs to Neuburgensia, Amphitrochus? gerberi to Serrettella, Neritopsis subvaricosa to Hayamiella, Nerinea tricincta to Aptyxiella, Nerinea staszycii to Endoplocus, and Polyptyxisella clio to Ptygmatis. Such taxonomic housekeeping may sound dry, but it matters enormously: accurate genus-level placement is the framework on which comparisons between faunas, reconstructions of evolutionary lineages, and palaeoecological analyses all depend.

One of the most intriguing findings is that collections from the same quarry, of the same age, differ considerably from one another in species composition and in the relative abundances of shared species. Fifty-nine species are known only from the earlier collections, chiefly gathered by Fritz Lang, while 54 species occur only in the Sylla collection, and 65 are shared between them. Even species present in both collections often appear in strikingly different numbers. The researchers attribute these differences to two factors: genuine facies differentiation within the quarry, where reef, fore-reef, and lagoon settings hosted different communities, and collection bias. Sylla tended to collect many more large specimens, whereas Lang preferred small ones, and the two men did not collect during the same period, meaning that quarrying operations had exposed different beds and facies at different times.

The nerineoids, an extinct group of high-spired heterobranch snails, illustrate this pattern vividly. Together, the Lang and Sylla collections document 38 nerineoid species, almost evenly split between them, yet each collection contains species entirely absent from the other. Some nerineoids grew to 20 centimetres, making them the largest gastropods and the highest-biomass members of the snail community. Nerinea moreana, a large and conspicuous species reaching 85 millimetres, is represented by 202 specimens in the Sylla collection but was completely missing from previously studied material. Conversely, the Ceritellidae are entirely absent from the Sylla collection. These complementary patterns suggest that the true diversity of the Saal fauna is even higher than the 179 species now recorded, since many specimens left in open nomenclature probably represent undescribed taxa.

The Saal quarry is currently inaccessible for safety reasons, so new fieldwork is impossible for now, but the researchers hope that other private collections from the site may surface and be studied. Each such collection, they note, adds not just new species but new information about how the reef community varied across space and through the successive beds exposed by quarrying. In an era when marine biodiversity is under unprecedented pressure, faunas like Saal offer a deep-time benchmark: a fully documented snapshot of how rich a reef-associated mollusc community could become in a warm, structurally complex shallow sea, and a reminder that even a single quarry, patiently worked over decades by dedicated collectors, can rewrite what we know about life in the Jurassic oceans.

Subject of Research: Late Jurassic gastropod taxonomy and diversity from the Saal quarry near Kelheim, Bavaria

Article Title: Late Jurassic (Upper Kimmeridgian) gastropods from Saal near Kelheim (Germany, Bavaria)

Article References: Late Jurassic (Upper Kimmeridgian) gastropods from Saal near Kelheim (Germany, Bavaria). (n.d.). https://doi.org/10.3897/zitteliana.98.138605

Image Credits: AI Generated

DOI: 10.3897/zitteliana.98.138605

Keywords: gastropods, Late Jurassic, Kimmeridgian, Saal quarry, Kelheim, Bavaria, palaeontology, reefal limestones, new species, taxonomy, nerineoids, biodiversity