A fossil brain from the Cretaceous of European Russia and avian sensory evolution

Abstract

Fossils preserving traces of soft anatomy are rare in the fossil record; even rarer is evidence bearing on the size and shape of sense organs that provide us with insights into mode of life. Here, we describe unique fossil preservation of an avian brain from the Volgograd region of European Russia. The brain of this Melovatka bird is similar in shape and morphology to those of known fossil ornithurines (the lineage that includes living birds), such as the marine diving birds Hesperornis and Enaliornis, but documents a new stage in avian sensory evolution: acute nocturnal vision coupled with well-developed hearing and smell, developed by the Late Cretaceous (ca 90Myr ago). This fossil also provides insights into previous 'bird-like' brain reconstructions for the most basal avian Archaeopteryx--reduction of olfactory lobes (sense of smell) and enlargement of the hindbrain (cerebellum) occurred subsequent to Archaeopteryx in avian evolution, closer to the ornithurine lineage that comprises living birds. The Melovatka bird also suggests that brain enlargement in early avians was not correlated with the evolution of powered flight.

A Review of the Mongolian Cretaceous Dinosaur Saurornithoides (Troodontidae: Theropoda)

“…There also is no apparent folding of the cerebellum as in avialans (Kurochkin et al, 2005) and oviraptorosaurs (Kundrá t, 2007;Balanoff et al, 2007). Lateral to the cerebellum are the paired floccular lobes (fig.…”

“…The cerebellum is compressed mediolaterally and lacks the lateral expansion present in avialans (Dominguez-Alonso et al, 2004;Kurochkin et al, 2005). There also is no apparent folding of the cerebellum as in avialans (Kurochkin et al, 2005) and oviraptorosaurs (Kundrá t, 2007;Balanoff et al, 2007).…”

Cranial Osteology of the Theropod Dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria)

“…Although it does not account for evolutionary relationships (see Felsenstein, 1985), the encephalization index is still the most widely used metric to discern whether the volume of an endocast is more typical of ''avians'' or ''paraphyletic reptiles'' (i.e., Reptilia in the noncladistic sense, lacking Aves) (Jerison, 1969;Hopson, 1977Hopson, , 1979Alonso et al, 2004;Kurochkin et al, 2007). The encephalization index of the oviraptorid Conchoraptor gracilis falls within the range of avians (Kundrá t, 2007); thus, ostensibly showing another avian similarity.…”

Olfactory acuity in theropods: palaeobiological and evolutionary implications

“…enlarged cerebellum and reduced olfactory bulbs) relative to the brain of non-avian theropods to meet flight requirements. Indeed, many studies have suggested that the brain architecture of extant birds may not have evolved until the advent of more derived, and presumably more agile, ornithurine birds (Larsson et al 2000;Kurochkin et al 2007). …”