A new fossil from the Eocene of Iran provides new insights regarding the evolution of the morphologically bizarre tube‐eye fish

Abstract

Stylephoriformes are a morphologically bizarre lineage of deep‐sea fishes, currently represented by a single extant species, Stylephorus chordatus , the so‐called tube‐eye fish. The phylogenetic relationships of the Stylephoriformes were extensively debated until recent genomic studies proposed a sister‐group relationship with the Gadiformes. The tube‐eye fish exhibits a suite of highly derived features, including extreme cranial kinesis, a pipette‐like oral apparatus specialized for suction feeding, and an elongate, naked ribbon‐like body lacking scales. The evolutionary origin of these unique traits is largely unknown, in part due to the complete absence of a fossil record. Here, we describe the first‐known fossil of the order Stylephoriformes, from Bartonian ( c . 40 Ma) sediments of the Pabdeh Formation, Iran. On the basis of several unique morphological features (edentulous premaxillae and dentary, moderately enlarged pterygoid elements, reduced opercle, elongate ribbon‐like body comprising more than 63 vertebrae, eight pectoral‐fin rays, absence of basipterygia, and the presence of a complete series of well‐developed lateral‐line scales) the specimen is assigned to a new genus and species: Parastylephorus anatoides . The fossil exhibits a body physiognomy, oral apparatus and cranial architecture remarkably similar to those of the extant tube‐eye, with the most derived features already present and closely comparable in morphology. This suggests that the new fossil represents a good example of long‐term morphological stasis among marine teleosts, documenting the persistence of a highly specialized body plan for more than 40 myr.