Pararhincodon: a Cretaceous carpet shark revealed by CT scans

Pararhincodon is a small extinct shark genus represented mostly by tiny isolated teeth. That record changed when computed tomography revealed two three-dimensional skeletons in the English Chalk. The fossils preserve parts of the skull, jaws, gill arches, pectoral skeleton and vertebral column, letting researchers compare the animal's anatomy with living carpet sharks. A 2025 analysis placed the new species P. torquis on the stem lineage of Parascylliidae, the family of collared carpet sharks. The genus belongs in the ancient fish catalogue as a case where rare skeletons connect a long tooth record to an evolutionary hypothesis.

Quick facts

Why the old tooth record was difficult to place

The name Pararhincodon was introduced in the twentieth century for fossil shark teeth. Several forms were later assigned to the genus from tiny crowns found in Cretaceous and Paleogene deposits. The dental fossils are useful for documenting where small sharks occurred, but the teeth have few features that uniquely identify an internal branch of carpet sharks. The genus was therefore treated cautiously in evolutionary reconstructions.

Before the new English fossils, the best articulated example was P. lehmani from Cenomanian-age rocks at Haqel in Lebanon. Its single known skeleton is poorly preserved. A rod-like structure in front of the braincase and a tooth form without a labial apron suggested an orectolobiform, possibly related to Parascylliidae, but the evidence was limited. Other named species, including P. crochardi, P. germaini and P. ypresiensis, are based on teeth rather than bodies.

Two English Chalk fossils

In 2025, researchers described Pararhincodon torquis from two specimens held by the Natural History Museum in London. The holotype, NHMUK PV P 73821a, was collected at Newhaven. Its original record does not give a precise bed, so the authors considered it Santonian or Campanian and recommended a future check using associated nannofossils. That caution is important: a place name alone does not fix an exact stage.

The second fossil, NHMUK PV P 17223, was collected by H. P. Blackmore at Britford near Salisbury. Its recorded belemnite zone corresponds to the early Campanian. Both fossils occur as cartilage mineralised in chalk blocks. They are slightly compressed, yet retain three-dimensional features that would be difficult to examine in a flattened slab. An extracted tooth and dermal denticles were also studied with the main specimens.

The Newhaven block preserves most of a neurocranium, the jaws, gill arches, parts of the pectoral fin skeleton and a connected series of vertebrae. The Britford specimen preserves a second head and some vertebral and gill material. Neither is a complete shark, and no teeth are still attached to the jaws. Their association with the fossils is inferred from the teeth recovered from the same blocks and from the diagnostic anatomy.

What tomography exposed

Computed tomography allowed the researchers to inspect the internal mineralised structures without treating the surrounding chalk as if it were an empty mould. The scans clarified the braincase, jaw articulations, gill supports, pectoral girdle and vertebral centra. Across the preserved spine, the primary calcification forms short diagonal lamellae arranged in an X-like pattern. Comparable structures occur in living parascylliids and in some carcharhiniform sharks, making them useful for phylogenetic comparison.

The study compared the fossils with the skeleton of a living parascylliid and coded a broad set of anatomical characters. Both Bayesian and parsimony analyses placed P. torquis as a stem-group parascylliid: it branches outside the living pair Parascyllium and Cirrhoscyllium, rather than inside either genus. This supports a family-level relationship much more strongly than an assignment based on tooth shape alone. A stem position describes where a taxon falls relative to a later group; it does not mean the fossil was a direct ancestor of a modern species.

The anatomy also suggests mosaic evolution. Some cranial and vertebral features associated with living parascylliids were already present in Pararhincodon, while other traits appear to have developed later within the living crown group. Comparisons with described Lebanese fossils suggest that Pararhincodon may have had a less eel-like body and more forward dorsal fins than living collared carpet sharks. That body-profile inference draws on the fossil outlines and comparative anatomy, and it should not be stretched into an exact reconstruction for every species assigned to the genus.

Small teeth and a longer history

The teeth of P. torquis are very small and markedly asymmetrical. Their central cusps are triangular, and a labial protuberance contributes to the crown profile. Most other species assigned to the genus lack a pronounced apron, which helps explain why the teeth did not independently settle its family position. The new skeleton links a tooth form to a body plan, but the teeth themselves were not preserved in place along a jaw.

Isolated teeth attributed to Pararhincodon have been reported from the Albian to the Lutetian, with three named tooth species extending from the Cenomanian to the middle Eocene. The older and younger occurrences are not a single continuous population. Each assignment depends on whether the tooth characters support the genus and whether the rock layer is dated securely. Additional skeletons could show that some of the dental species need other names or reveal more variation within the genus.

What remains outside the fossil

The skeletons establish a small shark with a distinctive cranial and pectoral anatomy, but they do not preserve skin pigment, muscle, exact body mass or ordinary behaviour. There is no direct stomach content identifying what it ate. A benthic lifestyle may be plausible by comparison with living carpet sharks, but it remains an ecological inference, not a trace preserved in these blocks.

The safest reconstruction gives priority to the parts actually preserved: the head, gill supports, pectoral region and vertebral form. The overall body outline can be informed by associated impressions and family comparisons, while colour and soft fins remain artistic choices. More three-dimensional chalk fossils and better-dated isolated teeth could refine both the anatomy and the range of this early parascylliid branch.

Explore related evidence in the ancient fish catalogue.