Ptychotrygon: a Cretaceous ray with a smooth enlarged rostrum

Ptychotrygon was an extinct Cretaceous rajiform ray, not a modern sawfish. Its enlarged rostrum lacked the rows of lateral denticles often shown in older illustrations, while its small oral teeth have a distinctive pyramidal crown and transverse ridges. Most species are known from teeth under two millimetres long. The genus is one of the more unusual batoids in the ancient fish catalogue.

Quick facts

A ray that should not be drawn as a toothed saw

Otto Jaekel established Ptychotrygon in 1894. Its type species is P. triangularis, first named by Reuss in 1845 as Ptychodus triangularis. The genus belongs to Ptychotrygonidae, an extinct ray family within Rajiformes. The informal label “sawskate” refers to the broader extinct group Sclerorhynchoidei, but it can mislead if it is taken to mean that every member carried a row of spikes along the snout.

The revised diagnosis describes an enlarged rostrum without lateral rostral denticles. Two parallel canals run along its underside. This distinguishes Ptychotrygon from better-known toothed forms such as Ischyrhiza and Onchopristis. The rostrum may have helped the ray sense or disturb prey near the seabed, but its exact movements are not preserved. Electroreception is plausible by comparison with living rays, not a directly measurable trait of the fossil genus.

Small oral teeth with a strong crown

Most species are identified from oral teeth typically less than two millimetres long. The crown rises as a sharp central pyramid above an oval base and carries transverse crests. A labial apron can extend over the root; the lingual face is less developed, and a short broad uvula can interlock with neighbouring teeth. The root has two lobes and a distinctive arrangement of foramina.

Teeth form rows in the upper and lower jaws, and their shapes change from the centre toward the sides. A loose tooth therefore has to be compared with others of similar position. The number of species assigned to the genus has exceeded twenty, but many names were founded on small samples. Modern revisions compare the whole crown, apron, root and tooth position rather than naming a species from a single ridge.

The 2022 review considered P. ellae and P. boothi, found together in the Campanian of Wyoming, as possible synonyms. A difference in the central cusp could reflect position or sexual dimorphism rather than separate species. That is a proposed interpretation, not a preserved observation of sex. The same review described a new Patagonian species, P. ameghinorum, from abundant isolated teeth and dermal denticles in the Mata Amarilla Formation of Santa Cruz Province, Argentina.

A Southern Hemisphere occurrence, not a complete body

The holotype of P. ameghinorum, MPM-PV 1160.1.1, is a tooth. Paratypes add further teeth and skin denticles, but not a complete skeleton. The material records the first confirmed occurrence of the genus in the Southern Hemisphere and extends its known distribution into Patagonia. It does not reveal the width of the ray's disc, the precise tail shape or the length of the rostrum.

The Mata Amarilla Formation represents a coastal system influenced by marine and continental water. Different layers record shifting conditions, so the habitat of the ray should be tied to its specific fossil bed. Teeth assigned to other species of Ptychotrygon occur across Europe, North America and Africa, but that broad map combines many taxa with unequal levels of support.

Feeding and the limits of inference

The small oral teeth are unlike the broad, closely packed crushing pavement of Pseudohypolophus. Their shape is compatible with grasping or processing small fish and invertebrates. No direct stomach contents or prey remains attached to an individual Ptychotrygon establish a specific diet.

An enlarged smooth rostrum could have aided the animal as it searched above or within soft sediment. That is a functional possibility; the fossils do not show a particular digging motion or hunting behaviour. The body was presumably flattened like other rays, but a tooth alone cannot determine disc proportions, fin edges, colour or skin pattern. The best reconstruction keeps the smooth rostrum and labels the rest as comparative anatomy rather than presenting a familiar sawfish as fact.

For that reason the genus is most informative as a dental and partial-anatomical record. The crowns provide repeatable characters for classification, the rostral diagnosis corrects a persistent visual error, and the Patagonian material broadens its geography. Its complete appearance and daily ecology remain much less certain than its fossil teeth.

Explore related evidence in the ancient fish catalogue.