In 1874 Sir Richard Owen gave the name Coloborhynchus clavirostrus to a small fragment of an ornithocheirid pterosaur rostrum found in rocks of the Lower Cretaceous Hastings Beds of southern England. The genus name translates to “truncated snout,” referring to the flattened front edge of the specimen.
The fragment is about 8 cm (3 inches) long, 5 cm (2 inches) tall, and 3 cm (1 inch) wide, coming from the very tip of the rostrum. The front edge is flattened rather than tapering to a point, with a triangular outline when seen from the front. The upper portion of the specimen shows the base of a sagittal crest, although its upper edge and overall shape are impossible to determine. When seen from above, the tip of the snout has a very slight lateral spooning, like many other ornithocheirids.
There are six pairs of empty tooth sockets in the specimen, showing that it had distinctive dentition. The first pair of teeth emerged from the flattened front edge of the rostrum and were directed forward. The second through fourth pairs of teeth were especially large and directed laterally, while the fifth and sixth were smaller and directed downward. A shallow depression is present on the palatal surface between and below the first pair of teeth.
Many authors in the 20th century thought that the specimen probably belonged to Ornithocheirus simus, despite coming from rocks that were 25-30 million years older than Ornithocheirus. Conversely, several other species of ornithocheirid pterosaurs from Cretaceous rocks in England, Brazil, Morocco, and the USA were assigned to Coloborhynchus, but most have been assigned to other genera.
Another English species, ‘C.’ capito, is known from several very fragmentary specimens from Upper Cretaceous rocks, and lacks the flat front edge and palatal depression of C. clavirostris, and may belong to a different genus. The Brazilian species ‘C.’ robustus, ‘C.’ piscator, ‘C.’ spielbergi, and ‘C.’ araripensis all lived several million years later and are now all considered to be species of Anhanguera or Santanadactylus. The Moroccan species Siroccopteryx moroccensis was also referred to Coloborhynchus due to a similar flattened front edge. ‘C.’ wadleighi was named from a partial snout tip found in Texas, but has since been given its own genus name, Uktenadactylus. Both Siroccopteryx and Uktenadactylus were also found in rocks formed about 25-30 million years after C. clavirostris lived.
The fragmentary nature of the only known specimen of Coloborhynchus makes its phylogenetic placement difficult to determine. In a 2018 phylogeny, Nick Longrich and colleagues found it to be an ornithocheirine ornithocheirid most closely related to Uktenadactylus and Siroccopteryx, as well as Ornithocheirus and Tropeognathus. Ornithocheirids were aerial fishers, using their very long and narrow wings to soar over the waves. They had very long snouts lined with sharp teeth which they used to pluck fish from near the surface. Many ornithocheirids had semi-circular crests near the ends of the upper and lower jaws.
Comparing Coloborhynchus to other ornithocheirids suggests that its skull was about 30-35 cm (12-14 inches) long, and it had a wingspan of about 1.5 meters (5 feet). When the Hastings Beds were deposited about 135-140 million years ago, southern England was a broad subtropical plain crossed by many large braided rivers, and ideal fishing ground for Coloborhynchus.