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| Iridopristis parrisi Andrews, Schein & Friedman, 2023 |
Abstract
The record of articulated marine fish fossils during the latest Cretaceous and earliest Cenozoic is sparse. The oldest-known definitive squirrelfishes and soldierfishes, like the first examples of many extant reef-dwelling clades, are known from early Eocene deposits of Europe. Here, we describe a new genus and species of holocentroid (Teleostei: Beryciformes: Holocentroidea) based on material from three individuals from early Paleocene (Danian) deposits of New Jersey, USA using micro-computed tomography. The specimens comprise a three-dimensionally preserved skull and partial postcranium, plus two isolated neurocrania. The new taxon, †Iridopristis parrisi, possesses a unique combination of characters, including a heterosulcoid otolith morphology and an edentulous premaxillary tooth-gap, while lacking a newly proposed character for the remainder of Cenozoic holocentroids: a lamina on the lateral surface of the anguloarticular, anterior to the jaw joint. Bayesian phylogenetic analysis of morphological, stratigraphical and molecular data under the fossilized birth-death process finds that the new taxon branches from the holocentrid stem, where it is joined by two of the three squirrelfish genera from the early Eocene (Ypresian) of Bolca, Italy. We estimate a Danian divergence between Myripristinae and Holocentrinae, the two reciprocally monophyletic subfamilies of Holocentridae. Our analysis suggests that several holocentroid lineages crossed the Cretaceous–Palaeogene boundary.
Keywords: Acanthomorpha, Cretaceous–Palaeogene boundary, squirrelfishes, computed tomography, Bayesian phylogenetics, parsimony
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| Skull and abdomen of †Iridopristis parrisi in left lateral view. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. A, specimen photograph and B, rendered µCT model. Skeletal regions highlighted as follows: neurocranium (pink), suspensorium (purple), circumorbitals (coral), jaws (light blue), opercles (light orange), ventral hyoid (light green), gill skeleton (dark green), pectoral girdle (yellow), abdominal scales (dark orange), vertebral column (red). Arrow indicates anatomical anterior. Scale bar represents 5 cm. |
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| Squamation of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Photographs of the A, cheek and B, abdominal squamation. Arrows indicate anatomical anterior. Scale bars represent 1 cm. |
Infraclass Teleostei Müller, 1845
Subsection Acanthomorphata Rosen, 1973
Order Beryciformes Regan, 1911 sensu Dornburg & Near, 2021
Superfamily Holocentroidea Richardson, 1846 sensu Gayet, 1980b
Genus † Iridopristis gen. nov.
† Iridopristis parrisi sp. nov.
Diagnosis: Holocentroid with the unique combination of the following characters: orbital branch of the supraorbital sensory canal with a separate opening from the main channel of the canal; large supraoccipital crest which is triangular in lateral aspect and borders the foramen magnum; parasphenoid with ventrolateral wings; lack of a berycimorph foramen in the anterior ceratohyal; deeply notched ventral surface of the anterior ceratohyal to accommodate branchiostegals; elongate postmaxillary process of the premaxilla; maxillary shaft approximately cylindrical in cross-section and elongate; presence of an alveolar platform expanded outwardly at the symphyseal area of the dentary; distinct edentulous concavity along the mesial margin of the premaxilla; unornamented triangular facet present on the posterolateral surface of the maxilla; edentulous ectopterygoid; head of quadrate posterior to orbital margin; an unexpanded otic bulla; an otolith morphology more similar to that found in holocentrine squirrelfishes (heterosulcoid) than the specialized phenotype of myripristine soldierfishes; lack of a dorsally projecting lamina directly anterior to the anguloarticular-quadrate joint on the lateral surface of the anguloarticular; eleven abdominal centra; cycloid scales with spinoid posterior edge.
Derivation of name:
The prefix of the generic name (Irido-) from the Greek genitive declension of iridis, meaning ‘rainbow’, and serving as the etymological root for the element iridium. This refers dually to the mosaic nature of characters present in the specimen, and for its occurrence close to the Cretaceous–Palaeogene boundary, known for its famous iridium anomaly (Alvarez et al., 1980). The suffix -pristis from the Greek for ‘saw’ (entering zoological usage in this context via Cuvier, 1829), used in the extant holocentrid genera Myripristis and Pristilepis, and referring to the holocentrid affinity for bearing coarse squamation.
The specific name is in honour of David Parris, Curator Emeritus of Natural History at the New Jersey State Museum, for his discovery of the specimens described here, and in appreciation of his life-long devotion to the study of the North American fossil fauna.
Conclusions:
†Iridopristis parrisi presents as an articulated skull and abdomen from the early Danian Hornerstown Formation of New Jersey, USA. Inclusion of the specimen in a phylogenetic analysis suggests that it is a stem-member of Holocentridae, along with the Ypresian-age †Berybolcensis and †Tenuicentrum. The new species possesses multiple characters that align it more closely to Cenozoic holocentroids than to Cretaceous holocentroids, including: a separate opening of the orbital branch of the supraorbital sensory canal, ventrolateral wings of the parasphenoid, an anterior ceratohyal with no foramen, and deep notches along the ventral margin of the anterior ceratohyal to accommodate branchiostegals. Character state optimization supports character state acquisitions prior to the origin of †Iridopristis parrisi that have previously been interpreted as derived states for the subclade Myripristinae: an alveolar platform expanded near the symphysis to overhang the lateral margin of the dentary, and a concave tooth gap at the mesial margin of the premaxilla. This finding necessitates a deeper examination of phenotypic synapomorphies to support the subfamily Myripristinae. Three-dimensionally preserved fossil fishes of Danian age are rare, and further excavation of the greensand formations along the mid-Atlantic of the USA may offer greater insight into the faunal composition and evolutionary dynamics during the critical early Palaeogene history of marine spiny-rayed fishes.
James V. Andrews, Jason P. Schein and Matt Friedman. 2023. An earliest Paleocene squirrelfish (Teleostei: Beryciformes: Holocentroidea) and its bearing on the timescale of holocentroid evolution. Journal of Systematic Palaeontology. 2(1); 2168571. DOI: doi.org/10.1080/14772019.2023.2168571
