Many modern groups of marine fishes first appear in the fossil record during the early Palaeogene (66–40 million years ago), including iconic predatory lineages of spiny-rayed fishes that appear to have originated in response to ecological roles left empty after the Cretaceous/Palaeogene extinction. The hypothesis of extinction-mediated ecological release likewise predicts that other fish groups have adopted novel predatory ecologies. Here we report remarkable trophic innovation in early Palaeogene clupeiforms (herrings and allies), a group whose modern representatives are generally small-bodied planktivores. Two forms, the early Eocene (Ypresian) †Clupeopsis from Belgium and a new genus from the middle Eocene (Lutetian) of Pakistan, bear conspicuous features indicative of predatory ecology, including large size, long gapes, and caniniform dentition. Most remarkable is the presence of a single, massive vomerine fang offset from the midline in both. Numerous features of the neurocranium, suspensorium, and branchial skeleton place these taxa on the engraulid (anchovy) stem as the earliest known representatives of the clade. The identification of large-bodied, piscivorous anchovies contributes to an emerging picture of a phylogenetically diverse guild of predatory ray-finned fishes in early Palaeogene marine settings, which include completely extinct lineages alongside members of modern marine groups and taxa that are today restricted to freshwater or deep-sea environments.

The holotypes of †Clupeopsis straeleni (MRHNB IG 8630) and †Monosmilus chureloides (GSP-UM 37), as well as representative examples of extant clupeiforms, were imaged using Nixon XT H 225ST industrial μCT scanners at the University of Michigan and the Natural History Museum, London. Reconstructed datasets were visualized and segmented using Mimics v. 19.0 (Materialise, Belgium). Models of segmented skeletal elements were exported as surface files (.ply) and rendered as high-quality images in Blender v. 2.79 (blender.org). Individual scanning parameters of new tomograms generated for this study are provided in the usage notes.

3D surface models of †Clupeopsis straeleni (MRHNB IG 8630, holotype)

.ply files of cranial bony elements preserved in †Clupeopsis straeleni (MRHNB IG 8630, holotype) and segmented using Mimics v. 19.0.

Clupeopsis_straeleni_plyFiles.zip

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3D surface models of †Monosmilus chureloides gen. et sp. nov. (GSP-UM 37, holotype)

.ply files of bony elements preserved in †​​​​​​​Monosmilus chureloides gen. et sp. nov. (GSP-UM 37, holotype) and segmented using Mimics v. 19.0.

Monosmilus_chureloides_plyFiles.zip

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3D surface models of Odaxothrissa mento

.ply files of Odaxothrissa mento (UMMZ 195016) cranial bones segmented using Mimics v. 19.0.

Odaxothrissa_mento_plyFiles.zip

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3D surface models of Chirocentrus dorab

.ply files of Chirocentrus dorab (UMMZ 238306) cranial bones segmented using Mimics v. 19.0.

Chirocentrus_dorab_plyFiles.zip

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3D surface models of Setipinna [Lycothrissa] crocodilus

.ply files of Setipinna [Lycothrissa] crocodilus (UMMZ 209911) cranial bones segmented using Mimics v. 19.0.

Lycothrissa_crocodilus_plyFiles.zip

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µCT data as DICOM stack for †Clupeopsis straeleni (MRHNB IG 8630, holotype)

.7z file containing micro-computed tomography data for †​​​​​​​​​​​​​​Clupeopsis straeleni (MRHNB IG 8630, holotype) as a DICOM image stack. Voltage: 210 kV; current: 200 μA; exposure: 1000 ms; filter: 1.5 mm tin; reflection target: tungsten; effective pixel size: 65.432 μm; scanning facility: Natural History Museum, London, Imaging and Analysis Centre.

Clupeopsis_straeleni_MRHNB_IG_8630_dcm.7z

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µCT data as DICOM stack for †Monosmilus chureloides gen. et sp. nov. (GSP-UM 37, holotype)

.7z file containing micro-computed tomography data for †​​​​​​​Monosmilus chureloides gen. et sp. nov. (GSP-UM 37, holotype) as a DICOM image stack. Voltage: 190 kV; current: 205 μA; exposure: 1415 ms; filter: 1.5 mm copper; reflection target: tungsten; effective pixel size: 57.94 μm; scanning facility: University of Michigan CTEES.

Monosmilus_chureloides_GSP-UM_37_dcm.7z

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µCT data as DICOM stack for Odaxothrissa mento

.7z file containing micro-computed tomography data for the cranial region of Odaxothrissa mento (UMMZ 195016) as a DICOM image stack. Voltage: 95 kV; current: 175 μA; exposure: 1000 ms; filter: none; reflection target: tungsten; effective pixel size: 19.97 μm; scanning facility: University of Michigan CTEES.

Odaxothrissa_mento_UMMZ_195016_dcm.7z

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µCT data as DICOM stack for Chirocentrus dorab

.7z file containing micro-computed tomography data for the cranial region of Chirocentrus dorab (UMMZ 238306) as a DICOM image stack. Voltage: 105 kV; current: 160 μA; exposure: 1000 ms; filter: none; reflection target: tungsten; effective pixel size: 36.43 μm; scanning facility: University of Michigan CTEES.

Chirocentrus_dorab_UMMZ_238306_dcm.7z

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µCT data as DICOM stack for Chirocentrus nudus

.7z file containing micro-computed tomography data for the cranial region of Chirocentrus nudus (UMMZ 213502) as a DICOM image stack. Voltage: 105 kV; current: 160 μA; exposure: 1000 ms; filter: none; reflection target: tungsten; effective pixel size: 39.00 μm; scanning facility: University of Michigan CTEES.

Chirocentrus_nudus_UMMZ_213502_dcm.7z

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µCT data as DICOM stack for Setipinna [Lycothrissa] crocodilus and Lycengraulis grossidens

.7z file containing micro-computed tomography data for the cranial regions of Setipinna [Lycothrissa] crocodilus (UMMZ 209911; specimen on the left in the scan) and Lycengraulis grossidens (UMMZ 143053; specimen on the right in the scan) as a DICOM image stack. Voltage: 100 kV; current: 170 μA; exposure: 1000 ms; filter: none; reflection target: tungsten; effective pixel size: 22.55 μm; scanning facility: University of Michigan CTEES.

Lycothrissa_crocodilus_UMMZ_209911_Lycengraulis_grossidens_UMMZ_143053_dcm.7z