Ramphoprionidae Kielan-Jaworowska, 1966

Tonarová, Petra, Suttner, Thomas J., Hints, Olle, Liang, Yan, Zemek, Marek, Kubajko, Michal, Zikmund, Tomáš, Kaiser, Jozef & Kido, Erika, 2024, Late Ordovician scolecodonts and chitinozoans from the Pin Valley in Spiti, Himachal Pradesh, northern India, Acta Palaeontologica Polonica 69 (2), pp. 199-215 : 206-207

Family Ramphoprionidae Kielan-Jaworowska, 1966 Genus Spitiprion Tonarová, Suttner, & Hints nov.

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Etymology: After Pin River section Spiti in the Trans-Himalayan region of northern India.

Type species: Spitiprion khannai Tonarová, Suttner, & Hints sp. nov., see below. By monotypy.

Diagnosis.—As for the type species.

Remarks.—The closest known ramphoprionid to Spitiprion is Megaraphoprion Eriksson, 2001. The biggest difference is fully denticulated dentary of the first maxillae of the latter genus and the ramus of right first maxilla (MI) is more slender in Spitiprion . Spitiprion has also much more prominent and slender hooks on the first maxillae than the type species M. magnus . The second maxillae of S. khannai Tonarová, Suttner, & Hints gen. et sp. nov. also differ considerably from the type species of Megaraphoprion. The second maxillae (MII) of M. magnus are sturdy, with wide ramus and blunt teeth whereas the MIIs of S. khannai Tonarová, Suttner, & Hints gen. et sp. nov. are rather slen- der, with pointed denticles and pointed ramus, reminding the second maxillae of Ramphoprion Kielan-Jaworowska, 1962 .

Stratigraphic and geographic range.—Katian, Upper Ordovician of Pin Member ( Amorphognathus ordovicicus Conodont Biozone ), Takche Formation, Pin Valley, Spiti, India.

Spitiprion khannai Tonarová, Suttner, & Hints sp. nov. Figs. 3A–G, 4; SOM 1–6.

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Etymology: In honour of the Indian palaeontologist Ashok K. Khanna (1951–1984), who first described scolecodonts from India.

Holotype: CGS PT _159_4, left first maxilla, from sample P/8/69. Type locality: Pin River section, Spiti, India.

Type horizon: Amorphognathus ordovicicus Conodont Biozone, Katian , Upper Ordovician.

Material.— Five isolated left MI ( CGS PT _159_3, 159_4, 169_1, 169_16, 170_2), 5 isolated right MI ( CGS PT _159_5, 168_8, 169_2, 159_17, 170_ 1), 1 MII ( CGS PT _159_2), 1 partly preserved apparatus (including left and right MI, MIV) ( CGS PT _159_1). All from the type locality and horizon .

Diagnosis.—MI elongated, widest in the posterior third. The dentary spread along the posterior half of the jaw length, terminating with a prominent and bent anterior hook. The right MI with a conspicuous slender ramus of rectangular shape, with a prominent inner wing occupying approximately posterior third of jaw, the wing is ending with a pointed extension. The left MI with a prominent inner wing extending approx. posterior 40% of the jaw, ending by a prominent pointed extension. In the outer margin, slightly below the centre protrudes a prominent extension, symmetrically to the inner wing extension. The dentary of both first maxillae is occupied by 8 to 12 relatively small but sharp denticles. The un-denticulated hook starts at approx. mid-length of the jaw, and it has an almost whip-like ending. The myocoele opening occupies about one-third of the jaw length. The MIIs are expected to be near mirror images of each other, with a slender ramus placed in the anterior-most part, pointed denticles, with the most prominent first denticle. MIV (right confirmed) is slightly longer than wide, occupied with relatively large and sturdy denticles. The basal plate was not found, but most likely it is sub-rectangular, with small denticles and a tapering antero-dextral process.

Description.— Right MI: Length 480–540 µm, width 120– 126 µm, width is approx. four times shorter than length (width 0.2–0.3 of jaw length), dorsal view: the 9–12 pointed denticles are bent outwards, with the tip often broken off. The undenticulated hook extends for approx. half of the maxilla length (compared with other ramphoprionids that have denticulated also the anterior part of the dentary), the bend pointed tip is very slender and long. Typical for the species is a prominent extension of the maxilla on the centre of both outer and inner face.

Ventral view: the myocoele opening represents approx. 1/3 of the maxilla. In the ventral view, all denticles are visible through the myocoele opening (i.e., the length of the denticulated dentary approximately matches the length of the myocoele opening).

In the right MI (Fig. 3E) remained attached also an attachment lamella (AL). The ALs are attached to the bases of MI, and when the jaws are retracted, the AL extend anteriorly-posteriorly on either side of the maxillae to near MIII and MIV, therefore they may increase resistance to hyperextension of the primary maxillae that may result from contact of the open jaws with struggling prey or surrounding substrate—this potential function of the AL is consistent with the motile carnivorous lifestyle of Lumbrinereis latreilli Audouin & Milne Edwards, 1834 ( Clemo and Dorgan 2017). However, it is supposed that ramphoprionids do not have descendants in the recent oceans ( Kielan-Jaworowska 1966), therefore the lifestyle and diet remain speculative.

Left MI: Length 430–580 µm, width 126–138 µm, width is approx. 4 times shorter than length (width 0.2–0.3 of jaw length), dorsal view: the shape of the maxilla is rectangular in the posterior area and tapers anteriorly to the un-denticulated anterior part that extends for half of the maxilla length and ends with a prominent hook-like slender fang. The dentary consists of ten pointed denticles that are situated only in the posterior half of the dentary, the denticles are bent outwards, and decrease in size toward the posterior end, with the smallest first two and last two denticles. Posteriormost denticles are tightly packed and continue into the un-denticulated short ridge. The posterior margin is rather short, it extends 14% of the jaw length. Among other ramphoprionids the posterior margin represents 20 to 30% of the jaw length in Protarabellites species, 15 to 20% of the jaw length in Ramphoprion species, and 19 to 25% in Megaramphoprion magnus Eriksson, 2001 . In ventral view, the myocoele opening extends a little more than 1/3 of the maxilla (approx. 35–40% of the jaw length), which is more closed than in other ramphoprionid species—where it is usually representing from 0.4 ( Ramphoprion bialatus Hints, 1998 ) to 0.8 ( Protarabellites triangularis ) of the maxilla length.

Left MII: Length 300 µm, width 180 µm (0.6 of the jaw length). The dentary is prominent, strongly elevated, gently curved, occupying the entire jaw length, and equipped with ten denticles of similar size as in the first maxillae. The first two biggest teeth are followed by two smaller denticles and then a row of teeth of similar size. The ramus is prominent but very narrow, triangular in shape. In the ventral view, the myocoele is almost gaping.

Right MIV: Jaw is about as high as long, it is quite flat, with an almost square outline. The left side is occupied by seven to eight sturdy denticles of more or less similar size, except for the first bigger denticle. The preservation (flattening) of MIV may have influenced the appearance of the maxilla and may be modified when more material is at hand.

Other jaws presently unknown.

Remarks.—The ramphoprionids, known solely by their jaws ( Eriksson 2002), emerged in the Middle Ordovician ( Kielan-Jaworowska 1962, 1966; Szaniawski 1996) and their youngest known record is late Ludfordian (Ludlow, Silurian) in age ( Eriksson 2001). Up to now, there were four genera included in the family, the type genus Ramphoprion Kielan-Jaworowska, 1962 , Protarabellites Stauffer, 1933 , Pararamphoprion Männil & Zaslavskaya, 1985 , and Megaramphoprion Eriksson, 2001 . Eriksson (2002) suggested that the Silurian ramphoprionids were inhabiting only regions close to the equator, but Tonarová et al. (2012) confirmed their presence in the Ludfordian of the Prague Basin, which was located between 25 and 30 degrees south during the Ludfordian (Tasáryová et al. 2014).

The family Ramphoprionidae was considered basal and fairly primitive among labidognath families ( Eriksson 2001). However, their jaw apparatuses exhibit characters considered both primitive, such as denticulation in first maxillae and advanced, such as enclosed to sometimes near strongly enclosed myocoeles. Therefore, ramphoprionids were presumably more advanced than the polychaetaspids, а group with similar jaw apparatus architecture, although the latter apparently have а longer (documented) stratigraphic range (cf. Kielan-Jaworowska 1966; Szaniawski 1996).

However, the first maxillae of Spitiprion khannai Tonarová, Suttner, & Hints gen. et sp. nov. differ from other ramphoprionids by the reduced denticulation to only half of the maxillae. Eriksson (2001: figs. 9.28, 9.31–44, and 45, and 46, respectively) reported from Gorstian and Ludfordian (Ludlow, Silurian) of Gotland a decrease in denticulation of the species Ramphoprion gotlandensis in the anterior part of the first maxillae dentaries, but that was reflected by a paucidate dentary, i.e., usually blunt denticles with longer gaps in between. The loss of denticulation in the first maxillae is observed in several extant polychaete groups, e.g., in the families Eunicidae or Onuphidae ( Beesley et al. 2000; Paxton 2009). However, the denticulation can be variable, e.g., in the labidognath family Paulinitidae Lange, 1947 ( Langeites lublinensis Szaniawski and Wrona, 1973 ) and in the extant prionognath family Oenonidae ( Drilonereis Claparède, 1870 ). Palaeozoic paulinitids were considered directly ancestral to modern labidognaths by Kielan-Jaworowska (1966).

Stratigraphic and geographic range.—Katian, Upper Ordovician, Pin Member ( Amorphognathus ordovicicus Conodont Biozone ), Takche Formation, Pin Valley, Spiti, India.