The finds comprise part of an ulna, the shoulder end of an upper arm bone and a wrist bone. No further material exists. Even so, that is enough to dismiss a suspicion that small arm bones from this period immediately raise.

Lagoon, delta and an arm in the rock

Today, a cliff near Sesimbra drops to the Atlantic. During the Barremian, a stage of the Early Cretaceous, this was a landscape of lagoons and a delta. Their deposits now form the Papo-Seco Formation.

At the Areia do Mastro site, the piece of ulna and the upper-arm fragment lay close together in the rock, so both may come from the same animal. The wrist bone, by contrast, came from the rubble at the foot of the cliff, no longer in its original layer.

A bird? The bones say no

Small, delicate arm bones from the Cretaceous first make specialists think of enantiornithines. This extinct group of primitive birds was widespread at the time, and many of them could fly.

The researchers compared the shape and size of the Portuguese bones. The result: a flight-capable enantiornithine is ruled out. The ulna is slender but not specialised for any particular task, and the upper arm is only moderately robust. That fits a paravian outside the birds. Paraves is the group that contains birds and their closest relatives among the predatory dinosaurs. The exact subgroup remains open, so the researchers write ‘Paraves indet.’, meaning ‘paravian, not identified more precisely’.

Perhaps an early relative of the dromaeosaurs

The authors consider it possible that the animal belonged to an early side branch of the dromaeosaurs, the family of agile predatory dinosaurs that also includes Velociraptor. This is not certain. The researchers explicitly do not assign a new scientific name, because three fragments are not enough for one.

The find still matters. Small maniraptorans – predatory dinosaurs from the large group that also contains paravians and birds – are scarcely documented on the Iberian Peninsula. The authors therefore see two possibilities: the bones could belong to a previously unrecognised, primitive European lineage, and small predatory dinosaurs found nowhere else might have lived in Barremian Iberia.

Whether a distinct European lineage is really emerging here can only be settled with more complete skeletons.

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