Laurillardia: a tiny bird near the hoopoe lineage

Laurillardia is a very small Paleogene bird known from late Eocene deposits in France and early Oligocene skeletons in Poland. Older classifications placed it among passerines, but two more complete Polish fossils helped revise its relationships. The birds are now considered possible members of the stem lineage of Upupiformes, the group containing hoopoes and woodhoopoes. Their small size, flight bones and slender bill can be assessed from fossils; exact plumage and diet cannot. The extinct bird catalogue traces how new specimens can change the picture of a fossil lineage.

Quick facts

A name with a changing classification

Laurillardia entered the fossil record through small bird remains from the Paris Basin of France. In the nineteenth century, Alphonse Milne-Edwards named the French species L. longirostris; Flot later described additional forms from Montmartre. Nineteenth-century comparisons with starlings and thrushes relied on broad similarities rather than a modern phylogenetic test. Later catalogues often placed the genus among Passeriformes. That interpretation was based on general proportions and the limited anatomical details visible in flattened or incomplete specimens.

Similarity in size or lifestyle does not by itself establish close relationship. Short legs, grasping toes and a narrow bill can evolve independently in unrelated small birds. Reliable classification depends on detailed comparisons of joints, skull structures and limb girdles, features that may be hidden or damaged in old specimens. For many decades, the French material did not allow a complete test of competing placements.

The situation improved with two skeletons from the Early Oligocene of the Polish Carpathians, described by Gerald Mayr and Zbigniew Bocheński in 2019. One was named ?Laurillardia smoleni, with the question mark deliberately expressing uncertainty about its generic assignment. The second was tentatively referred to L. munieri. These fossils supplied more anatomical detail and helped place the family Laurillardiidae near the stem of Upupiformes. This is a revised hypothesis, not proof that the genus directly gave rise to living hoopoes.

Small bodies recorded by bone measurements

The French skeletons preserve different amounts of the skull, trunk and limbs. In one species, the bony head was estimated at about 37 millimetres, with a bill around 18 millimetres. A humerus measured roughly 22 millimetres, the forearm bones around 27 millimetres, and the tarsometatarsus about 16 millimetres. The smaller L. munieri had a bony head around 34 millimetres, a humerus of about 16 millimetres and a tarsometatarsus near 12 millimetres. These are bone measurements from fossils, not total body lengths.

Some specimens were compressed during burial, so the preserved dimensions do not always reproduce the original three-dimensional shape. The shorter lower leg and separated toes are consistent with a small bird able to perch, but a posture on a fossil slab is not direct evidence of its habitual behaviour. The skeletons do include functional wing bones, supporting the conclusion that Laurillardia could fly. The fossils do not yield a measured flight speed, range or migratory route.

The bill is relatively slender and slightly curved near its base in the smaller species. That shape is compatible with taking small invertebrates from surfaces, but it does not reveal exactly how prey was captured. No gut contents or prey remains are reported in direct association. A reconstruction should distinguish the measured small bones from any inferred feather pattern, crest or colour.

From France to the Polish Carpathians

The French fossils come from late Eocene deposits of the Paris Basin, including gypsum formed in a landscape with changing lake and lagoon conditions. They document a very small bird in western Europe near the end of the Eocene. The Polish skeletons extend the record eastward and into the early Oligocene. One comes from upper layers of the Tylawa Limestones near Sanok and was preserved as a slab and counter-slab; the other came from Menilite deposits.

Those Polish beds formed in a marine basin, but the birds themselves need not have been marine. Small terrestrial animals can be transported from land into coastal water and rapidly buried in sediment. The fossils give a point of deposition, not a complete map of the animals’ living range. They also do not establish that every French and Polish specimen belongs to the same species. The second Polish skeleton is only tentatively assigned to L. munieri, and ?L. smoleni is explicitly provisional.

The early Oligocene specimens fill part of a substantial gap in the record of upupiform birds. Their presence helps connect late Eocene diversity with younger members of the broader lineage, while the long intervals between sites remain poorly sampled. A fossil gap is a gap in preserved and discovered evidence, not proof that the lineage disappeared and reappeared.

What the new placement does and does not mean

The 2019 comparison places Laurillardiidae among stem upupiforms, nearer to hoopoes and woodhoopoes than to the Eocene Messelirrisoridae. A stem placement means that a group branches outside the crown group of living representatives while sharing a deeper evolutionary relationship. It does not identify Laurillardia as the direct ancestor of the modern hoopoe. It may instead represent a side branch that retained some features of a wider ancestral group.

Small size and a narrow bill have led researchers to interpret these birds as insect-eaters. That is plausible in light of their anatomy and the ecology of living relatives, but no particular beetle, larva or other food item is preserved in the fossils. Likewise, the woodland scenes used in illustrations are informed reconstructions rather than a direct reading of the rock. The Polish fossils’ marine setting should not be confused with an aquatic lifestyle.

Questions about the disappearance of very small upupiform birds in northern regions have included changing climate and seasonal food availability. Those explanations concern broad environmental history and are not demonstrated by a single Laurillardia skeleton. The strongest evidence concerns body size, preserved anatomy and the revised family placement. Ecology and extinction remain broader interpretations that future finds may refine.

The two Polish specimens also differ in how securely they can be attached to the French genus. The question mark before ?L. smoleni is a formal signal of that uncertainty, not a typographic decoration. Researchers compare the available bones with the French species, but missing overlap can prevent a character-by-character match. The tentative referral of the second specimen to L. munieri similarly extends the known record without making every anatomical feature certain.

Geological ages sharpen the sequence but do not fill it continuously. The French material is Priabonian, the final stage of the Eocene; the Polish material is Rupelian, the first stage of the Oligocene. Their time ranges meet around the epoch boundary, yet individual fossils represent particular horizons and localities. They do not show an uninterrupted population through every intervening million years.