Nolfia riachuelensis, De Figueiredo, 2009

De Figueiredo, Francisco J., 2009, A new marine clupeoid fish from the Lower Cretaceous of the Sergipe-Alagoas Basin, northeastern Brazil, Zootaxa 2164 (1), pp. 21-32 : 23-28

† Nolfia riachuelensis sp. nov. ( Figs. 1–5 )

Diagnosis. Small-sized fish (reaching about 50 mm TL) differing from all clupeomorphs in the following uniquely combination of features: deep and short body ventrally armored of acute triangular scutes, all keeled; dorsal scutes lacking; deep coronoid process; smooth opercular bones; opercle narrow, about three times higher than long; deep and short subopercle with stout ascending process; 10 supraneural bones; one dorsal scaly post-cleithrum and two ventral rod-like; 18 caudal vertebrae; anteriormost abdominal vertebrae with long, thin, and cylindrical pleural ribs lying on short parapophyses; posteriormost abdominal vertebrae showing gradually long parapophyses bearing short ribs; epineural bones only in abdominal region; pelvic fin seven-rayed, originating slightly behind the origin of dorsal fin; anal fin remotely placed and short-based, with at least 10 rays; long neural spines along the body; neural spines of first, second and third preural centra long and distally convergent; three epurals, three uroneurals and the first one forming pleurostyle; second hypural fused to first ural centrum; first hypural large with proximal end close to the first preural centrum; 19 principal caudal fin-rays with 17 distally branched.

Holotype. Pz. UERJ 110 , an incomplete fish lacking most of the skull.

Etymology. From Riachuelo Formation, stratigraphic unit in which the specimen was found.

Horizon and Locality. Lower Cretaceous (Albian), Riachuelo Formation (Taquari Member), subsurface marine shale obtained at Rosário do Catete Locality , State of Sergipe .

Descriptive morphology. Form of the body — † Nolfia riachuelensis is an oblong and compressed fish, slightly deepened in the abdominal region ( Fig. 1 ). The maximum depth, taken anterior to dorsal fin, corresponds to 16 mm. Predorsal length is approximately 10 mm. The profile from the occipital region anterior to the origin of the dorsal fin is slightly convex. The dorsal fin is placed at the middle point of the body and the origin of the pelvic fin is slightly behind the vertical line passing immediately anterior to it. The anal origin is short-based and backwardly placed behind the end of dorsal fin. The caudal fin is homocercal equal-lobed. There are at least 14 pre-pelvic and five post-pelvic scutes preserved.

Skull — Most of skull is loss. The orbit region seems to be large and shows vestiges of melanic retinal pigment. Some bones of suspensorium and lower jaw are partially preserved ( Fig.2 ). The hyomandibula is deep and narrow, with a single articulatory head slightly inclined forwards and possessing a short anterior membranous process for meeting metapterygoid. A short and stocky opercular process is placed near the posterodorsal corner of the bone. The ventral process (´shaft’) of hyomandibula is slender and slightly inclined forwards.

From the metapterygoid only the rounded posterodorsal border remains but, judging by the space on the bedding plane, it was a relatively large bone.

The endopterygoid is a flimsy ovoid lamina apparently lacking teeth on oral border. Yet, the underlying ectopterygoid is boomerang-shaped and tightly joined to the antero-dorsal portion of the quadrate. The bone is strengthened by a keel along its major length and shows edentulous oral border.

The quadrate is a triangular and well-ossified bone. It shows straight dorsal margin (lacking incisure) and produces a short and prominent articular head inclined forwards. The postero-ventral process of quadrate is very short and strong. There is a shallow notch for a fistulous symplectic on its inner surface near the postero-dorsal corner.

The jaw articulation is placed slightly behind the middle point of the orbit. The metapterygoid is poorly preserved and appears to be trapezoidal and few excavated.

From the left mandible only the posterior end remains. The dentary is represented only by its acute postero-ventral process and seems to be toothless. The meeting between dentary and anguloarticular is not clearly visible. As for most of clupeoids, dentary is deep rear to produce a high coronoid process, particularly at the level of the anguloarticular. This bone shows a shallow facet for quadrate and the post-articular process is short and rounded. The retroarticular is not discernible and the trajectory of the mandibular sensory canal and associated pores are not clearly visible.

The premaxilla is not preserved. Only a fragment of a probable large and guttate posterior supramaxilla is seen lying on the posterior end of the toothless maxilla.

The opercular series is complete. The opercle is a narrow trapezoidal bone, about three times as high as long. It is totally smooth. The ventral border is larger than the dorsal one.

The preopercle is a crescent-shaped bone with the lower limb slightly convex and shorter than the upper limb. Upper and lower limbs form an obtuse angle. A preopercular sensory canal runs along anterior margin of the upper limb and curves forwardly on lower limb.

The interopercle has a convex ventral border; its dorsal portion is totally hidden by the preopercle. It seems to be as high as the subopercle. There are only two long and falcate posteriormost branchiostegals partially preserved.

Vertebral column, ribs, and intermuscular bones — The anterior end of the vertebral column is not visible so that the number of abdominal vertebrae is estimated only based on ribs and considering three anteriormost vertebrae hidden by the pectoral girdle. Thus, there are 37–38 vertebrae from which 18 are caudal. Vertebral centra are smooth and squarish along most of the vertebral column. Abdominal vertebrae ( Fig. 3 ) show long and bifid neural spines, whereas the caudal ones show medially fused spines. Each long and arched epineural bone is fused to base of the abdominal neural arch. Epineural bones not expand through caudal region and epipleural bones are not visible.

There are about 16–17 pairs of thin and long pleural ribs apparently touching firmly the border of ventral scutes. The pleural ribs are almost cylindrical (not grooved), and are attached to short parapophyses in most of abdominal region; they decrease in size towards caudal region in which the parapophyses are very long.

Ventral scutes ( Fig. 4 ) are acutely triangular with long ascending arm of about 3 mm deep (about ¼ rib length). There are, at least, 14 pre-pelvic and five post-pelvic scutes. Postero-ventrally, each scute produces a short but not pungent spine. They are deeper than those of † Nolfia kwangoensis (see restoration of Taverne, 1976, Fig. 9) and slightly decrease in size after the origin of the pelvic fin. The longest scute of ventral series reaches in size the largest anal pterygiophore.

Ten supraneural bones are counted. The two anteriormost ones are shorter and slender than other of the set. All supraneurals show dilated distal end; the slender proximal end is very inclined forwards. They are delicately ornamented with radiating striolae near distal end.

Paired girdles and fins — The main bones compounding pectoral girdle are preserved but poorly preserved ( Fig. 4 ). Thus, the post-temporal is only partially visible. It seems to be a guttate bone with moderate antero-dorsal border and scaly main body in which a sensory canal for lateral line crosses the postero-ventral border obliquely.

There is a narrow, deep, and spatulate supracleithrum lying on the upper third of cleithrum. Yet the cleithrum is very narrow, slightly curved, and deep but not sigmoid as that of † Ellimmichthyiformes .

The site of scapula is very damaged, but this bone seems to be very similar in shape and position to that of generalized living clupeids ( e.g., Harengula Gill, 1861 ; Opisthonema Gill, 1861 ). Dorsally, there is a scaly scapular (axillary) process for lodging modified trunk scales in association with the base of the pectoral fin.

The coracoid is represented by a large trapezoid lamina placed beneath scapula and contacting cleithrum anteriorly. The space between both bones is very reduced.

There is an upper scaly and triangular post-cleithrum and two aligned ventral rod-like postcleithra placed against the posterior border of middle part of cleithrum. They are very inclined backwards. Pectoral fin is short-based and placed relatively low in the flank. It bears at least 10 rays and does not reach the pelvic insertion.

The pelvic girdle is not visible because it is entirely hidden by ventral scutes. It bears seven fin-rays. The pelvic scute obeys a generalized spine-like pattern (see Whitehead, 1963) with long ascending arm.

Dorsal and anal fins —The dorsal and anal fins are very damaged. There are, at least, ten fin rays in the dorsal fin. The exact number of proximal pterygiophores is unknown. The first pterygiophore is the largest and somewhat notched anteriorly. Further pterygiophores are thin and simple rod-like bones. The anal fin is short-based and remotely positioned in the body; it origins between 11–12 caudal vertebrae. There are ten finrays and nine thin proximal pterygiophores preserved.

Caudal skeleton and fin — The caudal fin is forked and equal lobed. Unfortunately, the endoskeleton ( Fig. 5 ) is very damaged but certain details may be assessed. Hypurapophysis or parhypurapophysis are absent.

There are five preserved hypurals, but a further sixth is probable judging by the presence of space above the set. The first hypural is long and expanded. Proximally, it is placed very close to the base of the first preural and ural centra. The second hypural is slender and long. Its anterior end is dilated suggesting fusion to a reduced first ural centrum. The third hypural is almost equal in size to the first hypural. The fourth and fifth hypurals are slender and elongate.

The three posteriormost preural centra are hour-glass shaped and bear long and thin neural spines. The second ural centrum is not preserved but considering the space for that it was very reduced.

It is impossible to point out either the parhypural is fused or not to base of the first preural centrum but the spine and neural arch of this centrum are visible and form a long and slender blade. This structure is distally congruent with those spines of second and third preural centra as it does in † Nolfia kwangoensis .

There are three short and slender epurals leaving a reduced space among them and the laminate preural neural arches.

There are three uroneurals. The first one is the longest of the set but most of it is loss. Judging by imprint on rock, it is interpreted here as fused to the first preural centrum for producing a pleurostyle. The second uroneural is short and comma-like. The third one is short and elliptical; it is placed immediately above the urostyle site.

Only a short and fusiform ventral caudal scute is preserved. There are 19 principal caudal fin rays with 17 distally branched. There are at least 5–6 procurrent rays on ventral lobe.

Squamation — Faint imprints of simple and cycloid scales of moderate size and clupeoid pattern, bearing vertically arranged circuli, are preserved in certain parts along the body, but it is not possible to point out the presence or not of perforated scales of the lateral line.

Figures

FIGURE 1. †Nolfia riachuelensis sp. nov. Photograph of Pz. UERJ 110 (holotype). Scale bar = 1.0 cm.

FIGURE 2. †Nolfia riachuelensis sp. nov. Drawing of suspensorium, opercular bones, and other associated bones as preserved in Pz. UERJ 110. Scale bar = 0. 5 cm.

FIGURE 3. Drawing of anteriormost abdominal vertebrae and associated structures of †Nolfia riachuelensis sp. nov. as preserved in Pz. UERJ 110. Scale bar = 0. 2cm.

FIGURE 4. Pectoral girdle and fin and anteriormost pre-pelvic scutes of †Nolfia riachuelensis sp. nov. as preserved in Pz. UERJ 110. Scale bar = 0.5 cm.

FIGURE 5. Restoration of the caudal endoskeleton of †Nolfia riachuelensis sp. nov. based on Pz. UERJ 110. Scale bar = 0.2 cm.