Iridopristis parrisi, Andrews & Schein & Friedman, 2023

Andrews, James V., Schein, Jason P. & Friedman, Matt, 2023, An earliest Paleocene squirrelfish (Teleostei: Beryciformes: Holocentroidea) and its bearing on the timescale of holocentroid evolution, Journal of Systematic Palaeontology (2168571) 21 (1), pp. 1-36 : 5-21

† Iridopristis parrisi sp. nov.

( Figs 2–15 )

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 .

Material. Holotype: NJSM GP12145 ( Figs 2–4 ), an articulated skull preserved in three dimensions plus incomplete postcranium. Referred specimens: NJSM GP12381 , two isolated neurocrania with associated opercular elements and vertebrae ( Fig. 5 ). Photogrammetric models of the incomplete postcranium and two referred neurocrania can be accessed via Figshare (10.6084/m9. figshare.21754541).

Occurrence. ‘Main Fossiliferous Layer’ of the Hornerstown Formation in Sewell, New Jersey, USA.

Remarks. NJSM GP 12145 is mentioned, but not described, by Stewart (1996), who considered it an intermediate between Cretaceous and Cenozoic taxa. The void space of the saccular otoliths of NJSM GP 12145 are figured and described by Schwarzhans et al. (2018), who aligned the specimen with holocentrine squirrelfishes due to an absence of the specialized myripristine otolith morphology described by Schwarzhans (2010).

Description

Neurocranium. The neurocranium of the holotype of † Iridopristis parrisi is broken in two, but remains in association. The anterior portion preserves the mesethmoid, lateral ethmoids, vomer, and part of the parasphenoid, and the posterior portion preserves the frontals, pterosphenoid, parietals, sphenotics, pterotics, epioccipitals, prootics, exoccipitals, basioccipitals, and the remainder of the parasphenoid ( Figs 6 , 7 ). The supraoccipital crest, nasals, basisphenoid, and the most lateral portions of the left pterotic are not preserved.

The bones making up the ethmoid region are largely disarticulated, and the nasals are not preserved with the specimen. The mesethmoid is shattered dorsally and is disarticulated from the vomer, while the articulations with the lateral ethmoids are broken but remain in close physical association. The parasphenoid and vomer are articulated, although the vomer is displaced left-laterally. Anterior portions of the frontals that would contribute to the dorsal margin of the orbit are entirely absent. The left frontal is broken anterolaterally where it would contact the supraorbital shelf in life. The left pterosphenoid is broken and displaced mesially. A break separates the anterior and posterior half of the parasphenoid at the level of the myodome. The posterior portion of the parasphenoid remains tightly bound to the prootic and basioccipital, while the anterior section of the element has been shifted dorsally and to the right. There is no definitive supraoccipital crest preserved in life position on the holotype neurocranium. The midline between the epioccipitals bears a jagged surface and suggests that a laminar, bony extension was broken away at this site. Fragments have been reattached in this area during preparation, but they are incomplete. Instead, description of the supraoccipital crest is based on two referred neurocrania designated NJSM GP12381 .

The mesethmoid is best-preserved ventrally, though dorsal pieces are still preserved near the margins of the lateral ethmoids. The mesethmoid is more posterior relative to the vomer than would be expected in life, suggesting taphonomical displacement. The ventral process of the mesethmoid is triangular in ventral view, and would have articulated with the vomer ventrally.

The lateral ethmoids have a broadly triangular aspect in anterior view, and are best-preserved along their lateral margins. The lateral ethmoids are smooth along the orbital margin, with the foramen of the olfactory nerve visible in posterior view, but obscured in anterior view by the shattered mesethmoid.

The vomer is firmly attached to the anteroventral surface of the parasphenoid. A triangular knob emerges from its ventral surface. The dorsal surface of the vomer bears a large lateral flange on either side. Each curves mesially towards its counterpart and the anterior margin of the vomer, forming the notch into which the mesethmoid would have articulated.

The frontals dominate the dorsal surface of the neurocranium. They are ornamented by protuberances arranged in linear series that extend the length of the frontal. These show a radiating pattern, diverging from one another as they approach the posterior margin of the bone. Comparable ornamentation is visible on the referred specimens ( Fig. 5 ; 10.6084 /m9.figshare. 21754541), representing key evidence supporting their attribution to † Iridopristis . The frontals are triangular in dorsal view, with a deep canal separating them along the midline. The right frontal bears a supraorbital shelf laterally which is ornamented with the same protuberances as the remainder of the frontal. A deep supraorbital canal divides this shelf from the main body of the frontal. Each frontal is divided medially by a canal. The posterior margin of the frontals comprises a ledge that overhangs the most anterior portion of the parietal. The parietals are triangular in dorsal view, and their posterior extremities overhang the epioccipitals.

The sphenotic is anterodorsal to the prootic, posteroventral to the frontal, lateral to the pterosphenoid, and anteroventral to the pterotic. It is bounded dorsally by a large lateral flange extending posterolaterally from the margin of the supraorbital shelf towards the exoccipitals. This extension obscures the anterior facet of the hyomandibular head in lateral view. The hyomandibular facet extends across portions of the sphenotic, prootic and pterotic. The pterosphenoid forms the dorsomesial border of the orbit, is bounded dorsomesially by the frontal, dorsolaterally by the sphenotic, the prootic ventrally, and the other pterosphenoid mesially. The left pterosphenoid appears to be broken away from the remainder of the braincase, but remains in close association.

The pterotic articulates with the epioccipitals posteromesially, the frontal anteromesially, the sphenotic anteromesially, and the prootic ventrally. The posterior margin of the pterotic comprises the prominent dorsolateral crests on the lateral margins of the skull. The ventrolateral surface of the pterotic bears an articular surface accommodating the posterior head of the hyomandibula, with the dilatator fossa present on the dorsal surface.

The prootic is bounded by the pterosphenoid anteromesially, the sphenotic anterodorsally, the pterotic dorsally, the exoccipital posterodorsally, the basioccipital posteroventrally, and the parasphenoid ventrally. The prootic carries a dorsoventrally oriented flange lateral to the pars jugularis and posteroventral to the facet for the anterior head of the hyomandibula. The mesial margin of the prootic is flanged anterolaterally, and forms the dorsolateral margin of the myodome.

The epioccipitals articulate with the pterotic anterolaterally, the parietals and frontals anterodorsally, and the exoccipitals posteroventrally. A buttress along each of the lateral margins of the epioccipital continues ventrally onto the exoccipital. A trough bearing a raised midline extends between these buttresses, marking the presumptive position of the supraoccipital crest.

The referred neurocrania preserve the supraoccipital crest to varying degrees ( Fig. 5 ; 10.6084 /m9.figshare. 21754541). Together, they suggest that the crest was large and triangular in lateral aspect, being overall more similar to the condition found in myripristines than holocentrines. The supraoccipital is continuous with the dorsal margin of the braincase, extending posteriorly and curving ventrally to form a perpendicular angle with the dorsal margin of the foramen magnum. The dorsal margin of the supraoccipital crest is laterally expanded where it meets the posterior of the braincase; it is not clear if this is a remnant of a transverse crest or if it represents the shape of the supraoccipital itself. The ventral margin of the supraoccipital appears to be in contact with the foramen magnum – a state that has been referred to by other authors as a spina occipitalis ( Davesne et al., 2016; Johnson & Patterson, 1993).

The exoccipital is bounded ventrally by the basioccipital, anteriorly by the prootic and pterotic, dorsally by the epioccipital, and mesially by its counterpart. The dorsal portion of the exoccipital bears the ventral continuation of the buttress and trough present on the epioccipital. The lateral margin of the exoccipital forms a prominent shelf that meets the pterotic anteriorly. The most posterior portion of the exoccipital bears a large condyle bounding its counterpart mesially and the basioccipital condyle ventromesially; collectively these form the occipital condyle. Each exoccipital bears three foramina dorsal to the exoccipital condyle, presumably for passage of the occipital nerves (see Patterson, 1964, fig. 48 for homologous foramina in the Cretaceous acanthomorph † Hoplopteryx lewesiensis [ Mantell, 1822]). The semicircular foramen magnum lies dorsal to the exoccipital condyles.

The basioccipital is bounded dorsally by both exoccipitals, anteriorly by both prootics, and ventrally by the parasphenoid. The basioccipital condyle spans nearly the entire width of both exoccipital condyles. The basioccipital condyle is convex, the margins gently curving dorsally. Along the ventral midline of the occipital condyle is a shallow fossa. Anterior to this fossa is a shallow trough that continues to the boundary of the parasphenoid. These features likely accommodated the soft tissue anatomy of the dorsal aorta in life (see Grande & Bemis, 1998 for examples in fossil amiids).

The lateral wall of the otic chamber is flat, presenting no lateral expansion. Portions of the prootic, exoccipital and basioccipital make roughly equal contributions to this lateral wall. No clear openings in the otic wall are present in the holotype specimen, but the referred neurocrania appear to bear an opening more reminiscent of that piercing the otic bullae of living holocentrids.

The parasphenoid is elongate and contacts the basioccipital posteriorly, the prootic posterodorsally, and the vomer anteriorly. The parasphenoid is approximately triangular in axial cross-section, bearing laterally expanded flanges along the ventral margin posteriorly. There is no mesial ascending process at the level of the myodome that would articulate with the descending process of a basisphenoid. This is interpreted as taphonomical loss rather than genuine absence. The posterior margin of the parasphenoid interdigitates with the ventral surface of the basioccipital, forming small ridges along the posteroventral portion of the neurocranium.

Infraorbitals and sclerotic ossicles. The infraorbitals comprise the paired lachrymals ( IO 1), preserved on both sides of the fossil, and fragments of subocular shelf that are broken away from more posterior infraorbital fragments. No definitive sclerotic ossicles are evident in tomograms. Overall, the infraorbital series is poorly preserved and disarticulated ( Figs 2–4 ).

The left lachrymal is approximately rhomboidal in lateral view, and bears numerous protuberances on the lateral face. Two grooves extend anteroventrally along the lateral surface and are connected to one another beneath a bony bridge. The anteroventral groove spans approximately one-fourth of the total length of the lachrymal, and curves dorsally to meet the more posterior groove. The posterior groove becomes enclosed within the lachrymal at three-fourths the total length of the element, and then re-emerges at the posterodorsal margin. The mesial surface of the lachrymal possesses a posteromesially directed shelf anteriorly emarginated by a dorsoventrally flattened flange. The lachrymal is considerably longer anteroposteriorly than it is tall dorsoventrally.

The more posterior fragments of the infraorbitals are large, approximately square in shape and bear rugose ornamentation on their lateral surfaces. The more mesial fragments of subocular shelf associated with the laterally facing infraorbitals are relatively thick and concave on the orbital margin. Individual bones cannot be identified.

Jaws. The upper and lower jaws are preserved in tight association, but are described and figured separately for clarity. The upper jaws consist of the maxillae and premaxillae ( Fig. 8A, B ). With the exception of the anterior-most quarter of the left example, the supramaxillae are not preserved with the specimen. The ascending process of the premaxillae are not preserved. The shaft of the left maxilla is shattered at multiple points but remains articulated. The descriptions are based on the right upper jaw.

The premaxilla is anteroposteriorly elongate, approximately three-fourths the total length of the maxilla, and tightly associated with the maxilla dorsally. The premaxilla comprises an anterior, dorsally projecting articular process closely associated with the head of the maxilla and a more posterior alveolar process that contributes to the oral margin and bears small, rounded teeth. The premaxillary articular process is rounded and oblong in lateral view. What remains of the ascending process is a mesially protruding flange capped dorsally by an irregular surface. As such, the articular process spuriously appears as the dominant feature at the anterior end of the premaxilla. The ventral margin of the ascending process lacks teeth and curves dorsomesially away from the alveolar process, forming an edentulous concavity along the ventromesial margin of the premaxilla. The most anterolateral portion of the alveolar process of the premaxilla is laterally expanded to form a tooth-bearing shelf. The anterior teeth along this shelf are larger and more rounded than those located posteriorly. The alveolar process is deeply grooved dorsally and accommodates the maxilla. The postmaxillary process is approximately twice the height of the underlying alveolar process and elliptical in mesial view, the posterior margin gently sloping down to the rest of the posterior arm. The remainder of the premaxilla is slender and terminates at a point posteriorly.

The maxilla is oar-shaped in lateral view. It lies dorsal to the premaxilla and lateral to the dentary and angular. The slender anterior portion of the maxilla bears a broad, omega-shaped head. This head covers the posterodorsal margin of the articular process of the premaxilla. A notch posterior to the maxillary head accommodates the anterior process of the palatine. A small rectangular process extends ventrolateral to this groove. The body of the bone posterior to the maxillary head consists of an elongate shaft with an approximately cylindrical cross-section. Small, unorganized protuberances ornament the lateral surface of this shaft. Posterior to the shaft the maxilla becomes laterally compressed and dorsoventrally expanded. This posterior portion is approximately circular in lateral view and bears ornamentation arranged in anteroposteriorly directed rows. A wedge-like facet at the dorsal interface between the maxillary shaft and the posterior expansion marks the articulation area for the supramaxilla(e) ( Fig. 8A ). The posterior portion of the maxilla bears a triangular, anteriorly directed facet ( Fig. 8A , labelled ‘mpf’) on the ventrolateral margin. This facet aligns with the ventral lamina of the maxilla that articulates with the alveolar process of the premaxilla.

The mandible comprises the dentary, anguloarticular, and retroarticular ( Fig. 8C, D ). The left anguloarticular is shattered approximately midway along the length, in line with the breaks on the maxillary shaft. Likewise, the posteroventral portions of the left dentary have been broken and disrupted. Approximately one-quarter of the alveolar platform has broken away midway along the length of the right dentary. Descriptions below are based primarily on the right lower jaw.

In lateral view, the anterior portion of the dentary is rectangular. It bifurcates posteriorly into two tapering processes. The dentary bears larger, more blunt, conical teeth anteriorly than along the remainder of the alveolar platform. These anterior teeth sit on a bulbous region overhanging the most anterolateral margin of the dentary, and align with the mesial edentulous concavity of the premaxilla. Posteriorly, smaller teeth continue along approximately half the length of the dentary. The alveolar platform is broken, but remains articulated in both dentaries. The midlength section of the dentary alveolar platform is bounded ventrally by a deep fossa. A posterodorsally oriented coronoid process lies behind the alveolar platform. This process slopes upwards at approximately 140 Ǫ and constitutes half the total length of the dentary. The coronoid process rises above the premaxillary alveolar arm, and is mesial to the posterior portion of the maxillary arm. The complementary ventral arm of the dentary and the coronoid process together form a deep posterior socket that accommodates the anterior point of the anguloarticular. The entirety of the ventrolateral surface of the dentary is ornamented by small, anteroposteriorly aligned protuberances reminiscent of those found on the frontals. Two oblong pores for the mandibular canal are present along this surface, one closer to the anterior margin of the dentary, and another more elongate one at approximately the mid-length of the element.

The anguloarticular inserts into the posterior socket of the dentary, coming to a point anteriorly. The angular bears well-developed condylar and coronoid processes. The latter is laminar and is sinusoidal in transverse cross-section, presumably having accommodated the adductor mandibulae pars rictalis in life ( Datovo & Vari, 2013). The ventrolateral surface of the angular is ornamented by the same small, anteroposteriorly directed protuberances found on the dentary and frontals. This ornamentation does not continue onto the retroarticular. The right retroarticular is loosely bound to the right anguloarticular, directly beneath the condylar process. It is approximately triangular in lateral view and, while it is difficult to discern ornamentation on the right retroarticular, the left retroarticular exhibits a reticulated, maze-like pattern not evident on other bones.

Suspensorium. The suspensorium comprises the hyomandibula, symplectic, metapterygoid, quadrate, endopterygoid, ectopterygoid, and palatine ( Fig. 9A, B ).

Descriptions below are based on the better-preserved left side of the specimen.

The left hyomandibula is broken at approximately mid-height but remains in life position. The hyomandibula is approximately trapezial in lateral view. It is broader dorsally and tapers to a ventral shaft that articulates with the metapterygoid anteriorly and the symplectic and interhyal ventrally. The mesial surface is smooth, but the lateral surface bears a pronounced ridge. This ridge begins one-quarter of the length from the symplectic and interhyal articulation and continues to the height of the opercular process, where it turns anteriorly to meet the rounded dorsal head that joins the suspensorium with the neurocranium. The opercular process of the hyomandibula lies along the same anteroposterior axis as the anterior dorsal head. A dorsally projecting, triangular lamina extends between the dorsal head and the opercular process of the hyomandibula, and is interpreted as a secondary dorsal head. This presumably articulated with the ventral surface of the pterotic in life. Another lamina is present along the ventral margin of the dorsal head of the hyomandibula, bounded dorsally and posteriorly by the pronounced ridge along the dorsoventral midline. The hyomandibular arm terminates ventrally at a head. This ventral head bears an articular surface, two-thirds of which is occupied by the interhyal, with the remainder joining the symplectic.

The left metapterygoid is approximately square in lateral view, with the posterior boundary tightly linked with the ventral arm of the hyomandibula and the symplectic. Ventrally, it joins the dorsal lamina of the quadrate. The most posterodorsal portion of the metapterygoid obscures the hyomandibular shaft in lateral view. The anterodorsal margin of the metapterygoid is bifurcated, bearing a mesially protruding flange anteriorly that is approximately half the total height of the bone.

The quadrate is triangular in lateral view. The posterior margin bears flanges directed posteromesially and posterolaterally, forming a notch on the mesial surface that accommodates the symplectic. A two-headed condyle at the ventral corner of the quadrate articulates with the condylar process of the anguloarticular of the lower jaw.

The symplectic is rod-like and lies in a notch on the inner face of the quadrate. Nearly half the total length of the symplectic extends beyond the dorsal margin of the quadrate, where the bones curves at an angle of approximately 120 Ǫ to follow the posterior margin of the metapterygoid. The dorsal end of the symplectic articulates with the ventral arm of the hyomandibula. The more ventral portion of the symplectic is thin and tapers to a point, while the dorsal portion is robust with a blunt termination.

The ectopterygoid includes two arms: one that extends anteroposteriorly and one that extends dorsoventrally. The two arms meet at a gentle angle of approximately 100 Ǫ. The posterodorsal margin comes to a point where the margins of the endopterygoid, quadrate, and metapterygoid meet. The dorsal arm is fractured anteriorly and near the ventral arm, but remains in place. Tomograms show no obvious signs of dentition along the mesial margin of the entopterygoid.

The left endopterygoid is shattered and ventrally displaced. However, it remains in close association with the metapterygoid posteriorly, the palatine anteriorly, and the ectopterygoid ventrally. The lateral surface of the endopterygoid contacts the dorsal surface of the ectopterygoid, and curves mesially to form the thin lamina that defines the floor of the orbital cavity. Dentition is not apparent in tomograms.

The palatine is approximately triangular in coronal cross-section. Its ventral margin bears a laterally protruding, dorsoventrally compressed shelf that extends the length of the bone. The ventrolateral margin of this shelf bears a field of small teeth. A dorsoventrally compressed anterior palatine process attaches to the main body of the palatine at the anterior midline of the bone. The anterior palatine process is strongly turned 45 Ǫ anterolaterally, wrapping around the dorsal surface of the maxilla and fitting into the groove posterior to the omega-shaped maxillary head. The anterior palatine process is broken from the body of each palatine, but remains in close association.

Opercular series. The opercular series comprises the preopercle, interopercle ( Fig. 10A, B ), and a dissociated operculum separate from the skull portion of the specimen ( Fig. 10C, D ). No subopercles are associated with the specimen. The right preopercle is not preserved with the specimen, while the left preopercle is broken anteroventrally and shattered posterodorsally, with fragments out of life position. The opercle is only partially intact, with one large fragment, a smaller fragment glued onto the primary fragment, and another small loose piece that is not affixed to the remainder of the element. Descriptions of the opercular series are based on the left side of the skull.

The preopercle is boomerang-shaped in lateral view, with its two arms joining at approximately a 50 Ǫ angle. The mesial surface bears no notching or ornamentation. The anterior margin of the lateral surface of the preopercle bears a smooth, deep groove that accommodates the ventral arm of the hyomandibula. A ridge located posterior to this smooth surface bears ornament consisting of small protuberances. A broad groove, spanning approximately half the width of the preopercle and floored with smooth bone, lies posterior to this ridge. Ornamentation posterior to this groove matches the pattern at the anterior margin of the preopercle.

The interopercle is rhomboidal in lateral view. The mesial surface is smooth. The anterior and dorsal margins bear a smooth surface marking the area of overlap for the preopercle. The ventral portion of the anterior margin, in close association with the anguloarticular, is deeply indented. The remainder of the lateral surface is ornamented in small protuberances.

The operculum bears the opercular facet anteriorly, where it would have met the hyomandibula. The lateral surface bears a lineated rugose ornamentation that is more comparable to the surface texture on the jaws than on other bones of the opercular series ( Fig. 10C ). A prominent ridge lies along the mesial surface, along the same anteroposterior axis as the opercular facet ( Fig. 10D ).

Ventral hyoid arch. The ventral hyoid arch comprises the dorsal and ventral hypohyals, the anterior and posterior ceratohyals, the branchiostegals, the interhyal, and the urohyal ( Fig. 11 ); it is intact and mostly preserved in articulation on both sides of the specimen. The urohyal has been displaced away from the basihyal, and the right interhyal is not preserved with the specimen. Many branchiostegals are broken posteriorly, although they remain in association with the ceratohyals anteriorly. Descriptions of the ventral hyoid arch are based on the left side of the skull.

The dorsal hypohyal is approximately rectangular in lateral view, apart from a notch-like canal at the middle of its ventral margin. The ventral hypohyal has a rounded anterior margin and bears a posteroventral facet that articulates with the anterior head of the anterior ceratohyal. The remainder of the posterior margin of the ventral hypohyal curves posterodorsally with the articular surface of the anterior ceratohyal.

The anterior ceratohyal is laterally compressed and approximately trapezial in lateral dimension. Its anterior margin slopes down to an anterior head that meets the ventral hypohyal. The ventral margin bears four notches marking articulations for branchiostegals. The posteroventral corner of the anterior ceratohyal is broken and displaced mesially. The posterior margin of the anterior ceratohyal is flush with the posterior ceratohyal, and bears no evidence of fusion to the latter. The anterior ceratohyal is imperforate, instead bearing a deep groove on the lateral surface extending two-thirds the length of the bone and continuing onto the posterior ceratohyal.

The posterior ceratohyal is triangular in lateral view and laterally compressed. The anterior margin is straight and meets the anterior ceratohyal. A thickened knob at the posterior tip of the posterior ceratohyal marks the articular surface for the interhyal. The interhyal is an oblong rectangle in lateral view. Its ventral tip contacts the posterior ceratohyal. The interhyal bears a deep fossa along the ventrolateral margin that is directed anterodorsally from the articulation with the ventral facet.

Four branchiostegals articulate with the ventral margin of the anterior ceratohyal, while an additional three branchiostegals lie lateral to the anterior ceratohyal and another two lie lateral to the posterior ceratohyal. The four branchiostegals that articulate with the ventral margin of anterior ceratohyal bear pronounced hook-like processes at their proximal ends. More posterior branchiostegals bear weaker hooks. The branchiostegals protrude laterally along the midline of the anteroposterior axis, a feature mirrored by a shallow groove along the mesial surface, defining a chevron-like shape in transverse cross-section. The ventral margin of the branchiostegals do not bear any visible spination.

The urohyal is shattered posteriorly. It is approximately triangular in lateral view ( Fig. 11C ) and bears an anteriorly directed dorsal ramus. Lateral flanges extend from the ventral margin of the urohyal, and taper posteriorly. These flanges form a ventrally directed midline pocket, the inside of which bears four visible notches ( Fig. 11D ).

Ventral gill skeleton. The ventral gill skeleton comprises basibranchials 1–3, hypobranchials 1–3 and ceratobranchials 1–5 ( Fig. 12A, B ). The ventral gill skeleton is articulated anteriorly and laterally, while the more posterior and mesial portions are more disrupted. There is no evidence of the basihyal in tomogram slices; similarly, basibranchial 4 and hypobranchial 4 cannot be seen or are not readily identifiable in the specimen. Descriptions of the ventral gill skeleton are based on whichever branchial bones are most identifiable rather than those from one side of the specimen.

Basibranchial 1 is short and knob-like, rounded and thicker anteriorly, tapering posteriorly where it meets basibranchial 2 and hypobranchial 1. Basibranchial 2 is more elongate than basibranchial 1, and bears an anteroventral arm that is associated with the posterior margin of basibranchial 1. Basibranchial 3 is taphonomically shifted ventrally and to the right, and is thickened anteriorly where it meets basibranchial 2. Posteriorly it tapers to a point.

Hypobranchial 1 is elongate and linear, with an anterior head thinner in transverse cross-section than the remainder of hypobranchial 1 and curving ventromedially to meet the basibranchials. Hypobranchial 2 is shorter than hypobranchial 1 and similarly possesses an enlarged anterior head that curves mesially towards the interface of basibranchial 2 and basibranchial 3. The ventral surface of hypobranchial 2 is hollowed.

Ceratobranchial 1 is rod-like. Its dorsal surface is smooth, while its ventral surface is hollowed out, bearing lateral laminae that enclose a longitudinal trough which would have accommodated the gill filaments in life. Ceratobranchials 2–4 are broadly similar to CB 1. The right ceratobranchial 5 is rod-like, bearing a diamond-shaped platform on the dorsal surface that spans three fourths the total length.

Tomograms do not reveal any visible pharyngeal teeth.

Dorsal gill skeleton. The dorsal gill skeleton comprises epibranchials 1–4 and pharyngobranchial 3 as a toothplate ( Fig. 12A, C ). The dorsal gill skeleton is greatly disrupted from life position on the right side of the skull. The left side is more intact, remaining in partial association with the ventral gill skeleton. All descriptions of the dorsal gill skeleton are based on the left side members.

Epibranchial 1 is elongate and bears a dorsal groove beginning at the posterior margin and spanning half of the total length. This groove terminates at an anterodorsally facing uncinate process approximately one-third the total length of epibranchial 1. Epibranchial 2 is approximately the same length of epibranchial 1 and bears a dorsal groove that terminates posteriorly, extending approximately three-fourths the total length of the element. The mesial margin of this groove bears a lamina that forms part of a broad anterior head that would articulate with the pharyngobranchials in life. Epibranchial 3 is approximately two-thirds the lengths of epibranchials 1 and 2. Epibranchial 3 is elongate and bears a dorsal groove extending two-thirds the length of the surface. A large uncinate process approximately one-third the overall length of the bone projects dorsally from the middle of the mesial face of epibranchial 3. The posterior margin of the uncinate process of epibranchial 3 bears a thin lamina that extends half the length to the posterior margin. Epibranchial 4 is more expanded at its proximal and distal ends than at its midlength, where it bears a large uncinate process.

Pharyngobranchial 3 is roughly triangular in ventral view, and forms a continuous pharyngeal tooth plate ventrally, though a small taphonomical break separates the anterior and posterior portions of the element. There is a posterodorsally directed process on the dorsal surface approximately midlength along the lateral margin of pharyngobranchial 3. As in extant holocentrids, there does not appear to be a pharyngobranchial 4.

Gill rakers. Approximately six gill rakers are preserved in association with the first gill arch ( Fig. 12A ). These are elongate, roughly one-third of the total length of ceratobranchial 1. They are cruciform, with a small head proximally, two points branching perpendicular to the main axis, and converging to a point distally.

Pectoral girdle. Preserved portions of the pectoral girdle include the most dorsal portions of the left supracleithrum and cleithrum, the ventral portion of postcleithrum 1, the dorsal portion of postcleithrum 2, fragmentary portions of the right cleithrum, and the most ventral portions of the cleithrum on both sides of the specimen ( Fig. 13 ). The entirety of the pectoral girdle is fragmentary. Descriptions of the supracleithrum, cleithrum and postcleithrum are based on the left-side members.

The fragment of the supracleithrum is lateral to the most dorsal piece of the cleithrum, and is approximately triangular in shape. The anterior margin of the cleithrum is nearly vertical, while the posterior margin is approximately semicircular. The postcleithrum lies mesial and ventral to the cleithrum. Postcleithrum 1 is broken dorsally, appearing almost rectangular in lateral aspect. The anterior margin is roughly straight, while the posterior margin is rounded off. The fragmentary piece of postcleithrum 2 is approximately triangular.

The ventral portion of the cleithrum is shattered but individual fragments remain in close association. It is weakly sinusoidal in dorsoventral cross-section, and follows the posterior margin of the skull from the edge of the opercles to the midline. Mesially, the ventral portion of the cleithrum is curved posteriorly to associate with its counterpart.

Pelvic girdle. There are no fragments of pelvic girdle preserved in the holotype or referred material.

Squamation. Cycloid scales with a spinoid posterior margin are present along the entirety of the holotype specimen ( Fig. 14 ). These scales are ovoid, with a height greater than their width. On the skull, scales can be found lateral to the quadrate and metapterygoid, between the posterior margin of the maxilla and the anterior margin of the preopercle, and along the ventral surface between the angular and subopercle ( Fig. 14A ). The scales on the cheek have approximately 20 pronounced, anteroposteriorly-aligned ridges. Anteriorly, the ridges of the cheek scales coalesce to form a reticulated pattern. The scales on the ventral surface of the skull specimen bear fewer spines at the posterior margin than those on the cheek. The abdomen is covered in scales larger than those on the head ( Fig. 14B ). Spination is numerous, with greater than 25 ridges along the posterior margins of each scale, though these ridges are less well developed than those of the cheek scales. Each scale along the lateral line bears a large anteroposteriorly aligned crest, with a pore at the posterior margin of the anterior overlapping scale. The lateral line aligns approximately with the height of the vertebral column for the length of the preserved abdomen.

Axial skeleton. The articulated postcranium of the holotype preserves 13 vertebrae in total: a complete series of 11 abdominal vertebrae plus the two anterior-most caudal vertebrae ( Fig. 15 ). The first centrum lacks a preserved neural arch or evidence of a broken neural arch, and it is interpreted as being autogenous as in extant holocentrids. The remaining neural arches are broken and not diagnostic. Two small, rod-like epineurals are present anteriorly. The first three centra bear strongly developed transverse processes, while the transverse processes of centra 4 and 5 are weakly developed. The remaining centra do not appear to bear transverse processes. Ribs begin on the third centrum, and appear to be taphonomically absent from centra 8–10. The 11th centrum bears a fragment of the final rib that may be antero-posteriorly expanded as in extant berycids and holocentrids. Centra 7–11 bear ventrally directed parapophyses to which ribs would have articulated; these processes increase conspicuously in length along the series. A bridge between parapophyses on centrum 9 encloses an aortic canal, and subsequent centra bear the canal. Haemal spines begin on the 12th centrum, and are inclined posteriorly.

Figures

Figure 2. Photogrammetric model of the skull of †Iridopristis parrisi, gen. et sp. nov., holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA.

Figure 3. 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 MCT 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.

Figure 4. Skull and abdomen of †Iridopristis parrisi in right lateral view. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. A, specimen photograph and B, rendered MCT 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), scales (dark orange), vertebral column (red). Arrow indicates anatomical anterior. Scale bar represents 5 cm.

Figure 5. Referred specimens of †Iridopristis parrisi. NJSM GP12381, Hornerstown Formation, early Paleocene (Danian), New Jersey, USA, comprising remains of two individuals preserving portions of neurocrania, pectoral girdle, opercular series and vertebral column. Upper row depicts the left side of specimens, lower row depicts the right side of specimens. A, individual preserving neurocranium including intact supraoccipital crest, fragments of left hyomandibula, right operculum, both posttemporals, and the first three vertebral centra; and B, specimen preserving neurocranium including fragmentary supraoccipital crest, right operculum, both posttemporals, and the first three vertebral centra. Abbreviations: c, centra; fr, frontal; n, neurocranium; op, opercular; pas, parasphenoid; pt, posttemporal; soc, supraoccipital. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 6. Neurocranium of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT model in A, right lateral, B, posterior, C, dorsal and D, ventral views. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 7. Neurocranium of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Line drawings of rendered MCT models in A, right lateral, B, posterior, C, dorsal and D, ventral views. Abbreviations: boc, basioccipital; epo, epioccipital; exo, exoccipital; fr, frontal; hyfa, anterior facet for hyomandibula; hyfd, dorsal facet for hyomandibula; let, lateral ethmoid; met, mesethmoid; pa, parietal; pas, parasphenoid; pro, prootic; pto, pterotic; pts, pterosphenoid; soc, supraoccipital; v, vomer. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 8. Right upper and lower jaws of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT models of A, upper jaw in lateral view (maxilla in light blue, premaxilla in dark blue), B, upper jaw in mesial view, C, lower jaw in lateral view, and D, lower jaw in mesial view. Abbreviations: a, anguloarticular; d, dentary; m, maxilla; mpf, posterior facet of maxilla; pm, premaxilla; ra, retroarticular; smf, facet for supramaxillae. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 9. Suspensorium of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT model in A, lateral and B, mesial views. Abbreviations: ecp, ectopterygoid; enp, endopterygoid; h, hyomandibula; mpt, metapterygoid; pal, palatine; q, quadrate; sym, symplectic. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 10. Left preopercle and interopercle of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT model in A, lateral and B, mesial views. Photographs of operculum in C, lateral and D, mesial views. Abbreviations: iop, interopercle; pop, preopercle. Arrows indicate anatomical anterior. Scale bar represents 5 cm for panels A and B, and 1 cm for panels C and D.

Figure 11. Left ventral hyoid apparatus of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT models showing the A, lateral and B, mesial views of the hypohyals, ceratohyals, interhyal, and branchiostegals, and the C, urohyal in lateral and D, ventral view. Abbreviations: br, branchiostegals; cha, anterior ceratohyal; chp, posterior ceratohyal; hhd, dorsal hypohyal; hhv, ventral hypohyal; ih, interhyal; uh, urohyal. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 12. Gill skeleton of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT models of A, complete gill skeleton in lateral view, including the dorsal and ventral gill skeleton and associated gill rakers, B, ventral gill skeleton in dorsal view, C, dorsal gill skeleton in ventral view. Ventral gill skeleton in green, dorsal gill skeleton in olive, gill rakers in lime. Abbreviations: bb, basibranchials; cb, ceratobranchials; eb, epibranchials; hb, hypobranchials; pb, pharyngobranchials; rk, gill rakers. Arrows indicate anatomical anterior. Scale bar represents 5cm.

Figure 13. Pectoral girdle of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Rendered MCT model in A, left lateral and B, right lateral views. Abbreviations: cl, cleithrum; co, coracoid; pcl, postcleithrum; scl, supracleithrum. Arrows indicate anatomical anterior. Scale bar represents 5 cm.

Figure 14. 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 1cm.

Figure 15. Axial skeleton of †Iridopristis parrisi. Holotype (NJSM GP12145), Hornerstown Formation, early Paleocene (Danian), New Jersey, USA. Shown in left lateral view. Abbreviations: c, centra; en, epineural; hs, haemal spines; r, ribs. Arrow indicates anatomical anterior. Scale bar represents 5 cm.