Richardoestesia: a small theropod known mainly from teeth

Richardoestesia is a small theropod name founded on paired pieces of lower jaw from Alberta, not on a complete skeleton. The genus became much more familiar through isolated teeth found across western North America and elsewhere. Those teeth are harder to interpret than the jaw itself, so the type anchors a narrower and more useful story than the broad record sometimes assigned to the name.

Quick facts

The paired jaws from Alberta

The type specimen, NMC 343, comes from the Campanian Dinosaur Park Formation of southern Alberta, Canada. It preserves right and left partial dentaries with several unerupted and developing teeth. These are substantial evidence for the shape and tooth positions of the lower jaw, but they do not preserve the skull roof, limbs, pelvis, tail or skin. The jaws were first described under another name; in 1990, Philip Currie, Kevin Rigby and Robert Sloan established Richardoestesia gilmorei.

The genus honours palaeontologist Richard Estes. The type species belongs to the Late Cretaceous, despite occasional descriptions that place Richardoestesia in the Jurassic. Jurassic teeth have sometimes been referred to the genus because of their shape. That referral does not change the age of NMC 343, and it does not demonstrate that those older teeth came from the same animal or genus.

Why isolated teeth multiply the record

Small teeth are often recovered where delicate skeletons have been broken apart and dispersed. They can be distinctive: Richardoestesia-like crowns are narrow and blade-shaped, with small rounded serrations. Yet tooth shape varies along one jaw, and unrelated theropods can evolve similar cutting edges. A crown without an associated jaw is therefore a clue, not a complete identification.

Researchers have assigned many isolated crowns to R. gilmorei and to the proposed second species R. isosceles. The latter was named from a tooth whose crown is more upright in profile. Quantitative studies have shown how difficult it is to separate small theropod tooth groups using measurements alone. Some later fossils are best described as Richardoestesia-like or as a tooth morphotype, especially when they come from different ages and regions.

This is why the genus appears to span a much longer time and wider area in tooth lists than its type specimen alone warrants. An isolated crown can be compared with the type’s developing teeth, but the comparison is indirect. The broader the proposed range, the more important it becomes to ask whether one lineage is being traced or several similar-looking animals are being grouped under one convenient label.

A coelurosaur, but not a securely named family

The dentaries support a small coelurosaurian theropod. They do not securely settle whether the animal belonged with dromaeosaurids, troodontids or another branch of small feathered theropods. The isolated teeth assigned to Paronychodon pose a related problem: separate tooth names can record differences in position or shape, rather than separate animals. A comparison with Dromaeosaurus or Velociraptor is useful for discussing theropod diversity, but their skeletons cannot fill in missing Richardoestesia anatomy.

The jaws imply a small head bearing narrow, recurved teeth. They do not reveal a unique diet. Small prey, insects or pieces of larger carcasses are plausible, but no gut contents or diagnostic bite marks identify what Richardoestesia ate. Feathers are likely in many of its close relatives, yet no integument is known for this animal itself. A full-body image is necessarily a reconstruction based on broader coelurosaur evidence.

What the name reliably records

The secure starting point is the paired jaw material from the Dinosaur Park Formation. Teeth from other deposits can extend the record only when their anatomy and context justify the link. Keeping that distinction visible prevents a tooth label from being mistaken for a well-known species with a mapped range, fixed body size and certain behaviour.

Richardoestesia is included in the dinosaur catalogue as a useful example of both the value and the limits of isolated fossils. Better associated jaws, skull bones or skeletons could clarify its place among theropods. Until such material is available, the type jaws should carry more weight than the many tentative tooth referrals.