Santanaraptor placidus and Mirischia asymmetrica resided in what is now Brazil throughout the Early Cretaceous date, some 112 million years back.

The holotypes of these coelurosaur types were found in the Romualdo Formation in 1996 and 2000, respectively.

“The Romualdo Formation is a world-famous Early Cretaceous fossil Konservat Lagerstätte that crops out along the margins of the Araripe Plateau, in northwestern Brazil,” stated Dr. Rafael Delcourt from the Universidade de São Paulo and coworkers.

“Its macrofossil record consists of among the most varied and unspoiled ichthyofaunas of the Mesozoic, along with plants, invertebrates, turtles, crocodilians, pterosaurs, and theropod dinosaurs.”

“Spinosaurs are probably the best-known Romualdo theropods, with numerous referred specimens, consisting of the unspoiled skull of Irritator opposition and the snout of Angaturama limai“

“Among coelurosaurs, Santanaraptor placidus and Mirischia asymmetrica originated from the exact same deposits that yielded the spinosaurs, that is, the better-known upper carbonate concretion levels of the Romualdo Formation.”

In the brand-new research study, Dr. Delcourt and his co-authors from Brazil, Argentina and Germany modified and compared the anatomy of Santanaraptor placidus and Mirischia asymmetricawith the objective of examining their phylogenetic affinities and possible synonymy.

Their analysis puts both types in a group of early branching maniraptoromorph dinosaurs, together with Juratyrant langhami and Tanycolagreus topwilsoni from the Late Jurassic of Laurasia, recommending an early diversity of coelurosaurs in the location.

Regardless of the small overlapping of skeletal components, they have physiological distinctions that support their acknowledgment as unique types.

“The clade consisting of Juratyrant langhami Mirischia asymmetrica Tanycolagreus topwilsoniand Santanaraptor placidus appears to trace back a minimum of to the Late Jurassic of Laurasia, prior to the opening of the Apulian path, which permitted faunal exchange throughout the Early Cretaceous,” the paleontologists stated.

“In truth, a number of coelurosaur groups happen in both Laurasia and Gondwana at the time, consisting of Megaraptora, in addition to branches of Ornithomimosauria, Alvarezsauridae, and Dromaeosauridae.”

“Our phylogenetic proposition much better matches the readily available biogeographical information than those nesting the Romualdo coelurosaurs to the primarily Laurasian Compsognathidae and Tyrannosauroidea.”

“Yet, additional research study, consisting of more comprehensive field work, is required to untangle the early radiation of coelurosaurs, consisting of the affinity of the Romualdo kinds.”

A paper on the findings was released November 18, 2025 in The Anatomical Record

_____

Rafael Delcourt et alThe coelurosaur theropods of the Romualdo Formation, Early Cretaceous (Aptian) of Brazil: Santanaraptor placidus satisfies Mirischia asymmetrica The Anatomical Recordreleased online November 18, 2025; doi: 10.1002/ ar.70085