Luopingcoelacanthus eurylacrimalis, Wen & Zhang & Hu & Benton & Zhou & Tao & Huang & Chen, 2013
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publication ID |
https://doi.org/ 10.4202/app.2011.0066 |
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persistent identifier |
https://treatment.plazi.org/id/03FC3C20-DF48-FFA6-FCEC-F994FF5985B5 |
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treatment provided by |
Felipe |
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scientific name |
Luopingcoelacanthus eurylacrimalis |
| status |
sp. nov. |
Luopingcoelacanthus eurylacrimalis sp. nov
Figs. 1–6 View Fig View Fig View Fig View Fig View Fig View Fig .
Etymology: The species name is derived from its unique feature, the triangular broad lachrymojugal.
Holotype: LPV−10146, a nearly complete specimen, lacking only the supplementary lobe of the caudal fin.
Type horizon: Member II, Guanling Formation, Middle Triassic ( Nicoraella kockeli Zone , late Pelsonian, middle–late Anisian).
Type locality: Daaozi Village, Luoxiong Town, Luoping County, Qujing City, Yunnan Province, China (Zhang and Zhou 2008; Zhang et al. 2008; Hu et al. 2011).
Other material.—LPV−5124, a partial specimen; LPV−10575, a head; LPV−10827, a near−complete specimen.
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Diagnosis.—Middle−sized coelacanth. Three diagnostic features are the expanded lachrymojugal, the notched dentary, the large semicircular coronoid, Skull roof has two pairs of parietals. Posterior margin of postparietals embayed. Lachrymojugal has an expanded posterior portion and a concave posteroventral margin. Squamosal has a slightly anterior expansion. Ventral surface of parasphenoid is covered by numerous granular teeth. Dentary has a deeply notched posterior border, and teeth distributed on the separated dentary plate. The first dorsal fin contains 12 robust segmented rays. The lower lobe of the caudal fin is larger than the upper lobe.
The following combination of characters, a notched dentary and an expanded lachrymojugal, is not known in any other actinistian, so the Luoping materials must represent a new taxon.
Description
Skull roof and dermal bones of snout.—The skull roof is poorly preserved in all specimens, being disarticulated in LPV−10146 ( Fig. 1 View Fig ) and LPV−10575 ( Fig. 2 View Fig ). The latter shows the parietal shield relatively well. The postparietal is large, and its posterior margin is wider than the anterior margin. There is a depressed area in the middle, and some sensory−canal pores are distributed on its surface. The postparietal is ornamented with small rounded tubercles and striae. The anterior division of the parietonasal shield is broken. However, two pairs of parietals can be identified, as in most other coelacanths. The posterior parietal is as long as the postparietal, but the anterior one is much smaller. Both of them are covered by tiny tubercles ( Fig. 2A View Fig ).
There should be several extrascapulars, but only one is preserved. It is rectangular and was not sutured to the postparietal ( Fig. 2 View Fig ). The supratemporal is triangular in shape, expanding anteriorly. It is situated at the posteroventral margin of the postparietal.
The triangular lateral rostral is seen in LPV−10575 ( Fig. 2 View Fig ), but the ventral process is not preserved. There are three pointed grasping teeth on the premaxilla.
The supraorbital series consists of six elements ( Fig. 3D View Fig ).
Cheek.—The cheek is composed of five bones: the lachrymojugal, postorbital, squamosal, and preopercle. The outline of the lachrymojugal is conspicuous in the holotype ( Fig. 1 View Fig ). It is elongated−triangular in shape, with the posterior portion greatly expanded and concave in the posteroventral corner. The infraorbital sensory canal also could not be made out. The postorbital is plate−like. The rectangular postorbital is large. It is broken into two pieces. The preopercular is triangular in shape, but not elongate as in Macropoma ( Lambers 1996) and Swenzia ( Clément 2005) . As in other coelacanths, the jugal sensory canal passes through the centre of the squamosal and into the preopercular. However, the sensory canal does not run along the posterior margin as in Macropoma ( Clément 2005) ; it crosses the preopercular along the median region, and runs toward its posteroventral corner ( Fig. 2A View Fig ). The opercular is a large subtriangular bone with rounded corners. Between the cleithrum and quadrate, a very slender symplectic is present in the holotype ( Fig. 1 View Fig ), articulating with the retroarticular. The ornamentation of the cheek region is not visible.
Parasphenoid.—The parasphenoid is well preserved in LPV−5124, in ventral view ( Fig. 3A, C View Fig ). It has the general spatulate appearance seen in most coelacanths, being constricted in its middle portion and widest in the anterior half. The ventral surface is concave medially. The whole ventral surface of the parasphenoid ( Fig. 3C View Fig ) is covered with bluntly granular teeth, as in Diplurus and Axelia (Schaeffer 1952) . The posterior portion increases in height to form a slender extension supporting the basisphenoid. The large antotic process is triangular ( Fig. 3B View Fig ) on the basisphenoid, as in Diplurus and Whiteia (Schaeffer 1967, 1976).
Palate.—The palatoquadrate on each side is visible in LPV−5124. The entopterygoid has the typical triangular shape. The angle between the ventral and posterodorsal margins is about 100 °, whereas it is roughly 50 ° in Piveteauia ( Clément 1999) and 130 ° in Diplurus (Schaeffer 1952) . The ventral border of the entopterygoid is straight, not as in Macropoma and Megalocoelacanthus where a ventral expansion is present ( Lambers 1996; Schwimmer 1994). The palatal surface is covered by numerous minute teeth, as in Diplurus (Schaeffer 1952) ( Fig. 3F View Fig ).
The rectangular metapterygoid articulates with the posterodorsal surface of the entopterygoid. The quadrate is in contact with the posteroventral margin of the entopterygoid ( Fig. 3F View Fig ).
In the holotype ( Fig. 1 View Fig ), the autopalatine has shifted from its original place. It is subtriangular in shape and its external surface is concave. Parts of the ectopterygoid− dermopalatine can be seen ( Fig. 2 View Fig ). The teeth of the ectopterygoid−dermopalatine are numerous and small, but a row of larger pointed teeth is also present, as in Swenzia latimerae ( Clément 2005, 2006).
Only the ceratohyal is visible in the hyoid arch of LPV−5124 ( Fig. 3A View Fig ). The ceratohyals are unusually powerful, and they are arched so that they are convex on the ventral side and concave on the dorsal. The truncated posterior end is about twice as broad as the anterior ( Fig. 3E View Fig ).
Lower jaw.—The middle part of the angular is very deep and shows the usual dorsal, rounded margin of most coelacanths. The surface of the angular is covered by numerous tubercles in the holotype ( Fig. 1 View Fig ), as in Sassenia and Holophagus , and not by coarse ridges as in Mawsonia and Axelrodichthys ( Cavin and Forey 2005) . The retroarticular is well preserved. The semicircular principal coronoid is situated halfway along the length of the angular. It is much larger than is usual for coelacanths, and the dorsal margin increases in height and forms a ridge. The dentary has a forked posterior margin as in Macropoma ( Clément 2005; Lambers 1996). Pointed teeth are distributed on the dental plate. The hook−shaped dentary and separate tooth plate were regarded as derived features by Forey (1991). The gulars are preserved on each side ( Fig. 1 View Fig ). They are ornamented with tiny tubercles, and the gular pit−line is in the centre of the bone.
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Shoulder girdle and pectoral fin.—The dermal pectoral girdle is composed of the cleithrum, extracleithrum, anocleithrum, and clavicle ( Fig. 2 View Fig ). The shoulder girdle is well preserved, except in the holotype ( Fig. 1 View Fig ). The cleithrum is an elongate element, the middle part is very narrow and its uppermost region is oval in shape. The extracleithrum is situated at the posteroventral corner, and the clavicle at the ventral edge. The presence of an extracleithrum is a synapomorphy of Actinistia ( Forey 1998). This element is oblong and pointed at both ends. The clavicle consists of a twisted horizontal lamina, which contacted the posterior corner of the gular plate, and of a vertical internally concave lamina that approached the cleithrum. The anocleithrum is a wedge−shaped bone with its ventral end overlapped by the uppermost margin of the cleithrum. The pectoral fin web contains 19–20 rays, all showing a transverse segmentation in their distal half ( Fig. 3A View Fig ).
Pelvic fins.—The pelvic fins are not complete in any specimen. The basal plates of the pelvic fins are situated far forward ( Table 1), near to the level of the basal plate of the first dorsal fin. The pelvic fin is lobe−like and contains about 18 segmented fin rays. The anterior rays lengthen and the posterior rays shorten backwards, while the middle rays are the longest. The longest pelvic fin is nearly 40 mm ( Fig. 3A View Fig ).
As in Diplurus , the basal plate ( Fig. 4C View Fig ) consists of a posterior division and an anterior division. The anterior division is subdivided into anterodorsal and anteroventral processes, the former being longer and extending horizontally forward, the latter being shorter and extending in an anteroventral direction to contact the anteroventral process on the other side. The posteroventral process of the posterior division is slen− der and its distal end contacts that of the other side. The posterodorsal process of the posterior division is broader than the posteroventral one.
First dorsal fin.—The first dorsal fin is supported by a triangular basal plate, with rounded corner ( Fig. 4A View Fig ). A strong ridge extended from the posterodorsal corner and branched towards the posteroventral and anterior corners. Its ventral margin is straight, not scalloped or irregular as in Caridosuctor and Polyosteorhynchus (Lund and Lund 1984) . The first dorsal fin ( Fig. 3A View Fig ) is composed of at least 12 robust rays, segmented for the distal third of their length. On the rays, there were strong longitudinal tubercles distributed both on the unsegmented and segmented portions.
Second dorsal fin.—The basal plate of the second dorsal fin ( Fig. 4B View Fig ) is a long, deeply forked bone. It has a slender Length from anterior tip of snout to base of supplementary
230 caudal fin Length of head 65 Depth of head 50 Length from anterior snout to base of first dorsal fin 95 Length from anterior snout to base of second dorsal fin 114 Length from anterior snout to posterior tip of pelvic girdle 106 Length from anterior snout to posterior tip of basal plate of
145 anal fin anteroventral process extending to the 23rd neural spine, and a longer anterodorsal process. Its posterior head is plate−like which is smaller than in Chaohuichthys (Tong et al. 2006) . About 20 segmented rays are present in the second dorsal fin of LPV−5124 ( Fig. 3A View Fig ). The fin rays have the same features as in the pectoral fin.
Anal fin.—The anal fin is lobed and it is situated slightly behind the level of the second dorsal fin ( Fig. 5A View Fig ). The outline is not clear because it is incomplete in all specimens. The basal plate ( Fig. 4D View Fig ) is similar to that of the second dorsal fin, with slender anterodorsal and anteroventral processes. The posterior division is short and broad. The two processes of the anterior division are close to the same length.
Caudal fin.—The caudal fin ( Figs. 3A View Fig , 5A View Fig ) is composed of dorsal, ventral and supplementary lobes. The supplementary lobe is missing in the holotype ( Fig. 5A View Fig ), but is well preserved in LPV−5124 ( Fig. 3A View Fig ). The ventral lobe seems to be more developed than the dorsal one, as in Sinocoelacanthus fengshanensis (Liu 1964) . The ventral lobe contains 19–20 rays, and the dorsal one contains 15–16 rays. The rays of the dorsal lobe seem to be more inclined posteriorly than those of the ventral lobe. The rays of both the dorsal and ventral lobes are segmented for about the distal half of their length, except for the first two rays. All the lepidotrichia are ornamented with longitudinal tubercles. The supplementary lobe is well developed in LPV−5124 and contains 28 segmented rays.
Axial skeleton.—The axial skeleton consists of about 50 vertebrae, as in Piveteauia from the Triassic, but not Coelacanthus from the Permo−Triassic (70 vertebrae), Coccoderma from the Jurassic (78), or extant Latimeria (91–93) ( Clément 1999). The neural arches are of the type usually found in actinistians. The neural spines are short between the head and the first dorsal fin and behind the second dorsal fin to the caudal fin, but they are long between the two dorsal fins. Haemal spine arches are absent in the most anterior part of the axis. The first one appears below the level of the posterior margin of the first dorsal fin. The first 11 arches are very short, thin and equal in size. Behind the second dorsal fin, the haemal arches increase in size. The pleural ribs are not ossified ( Fig. 5A View Fig ).
Scalation.—Scales may be seen behind the level of the first dorsal fin in the holotype ( Fig. 5A View Fig ), some of them exposed in external view. Some others are exposed showing their internal view on the left side. It is hard to identify each scale, because they overlap each other and are somewhat compacted. All scales have varying numbers of slender hollow ridges on the exposed portion, and the orientation of these ridges is highly variable: they may be parallel or arranged at slight angles to each other ( Fig. 6B View Fig ). In the extreme anteroventral region, the ridges are somewhat circular in shape and about 40 in number on the first 6–7 rows of scales ( Fig. 6C View Fig ). On the scales around the fins, the ornament also is circular tubercles. These ridges increase in length backwards. In the caudal region, the number of ridges on each scale increases to nearly 100. In the anterior portion the scales are covered with fine parallel striae.
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B2 lachrymojugal C 2 lachrymojugal second dorsal fin fin dentary anal fin lower lobe of caudal fin of caudal fin coronoid subopercle
Calcified swim bladder.—A calcified swim bladder is known in numerous actinistians, composed of superimposed bony plates. In the holotype ( Fig. 5A View Fig ), only the most external wall of the calcified bladder can be observed below the pectoral fin. The internal surface was ornamented by delicate parallel striations, as in other fossil taxa.
In living Latimeria , the bladder is not ossified and is filled with lipids, primarily wax esters ( Forey 1998), and is used for buoyancy control. In many fossil coelacanths, on the other hand, including Palaeozoic forms (e.g., Allenypterus , Caridosuctor , Coelacanthus , Hadronector , and Polyosteorhynchus ) and Mesozoic forms (e.g., Axelrodichthys , Coccoderma , Laugia , Libys , Macropoma , Mawsonia , Piveteauia , Swenzia , and Undina ), the bladder wall was covered with calcified plates ( Forey 1998; Clément 1999; Brito et al. 2010). By its position, the swim bladder appears to be homologous with the lung of air−breathing vertebrates, and it may have been filled with air or fluid, as in most modern osteichthyans, not lipids as in Latimeria . The coelacanth swim blad− der lies close behind the operculum, and is connected at the front by a single opening to the oesophagus or pharynx. The numerous overlapping bony plates linked by connective tissue seen in Axelrodichthys from the Early Cretaceous of Brazil may have functioned as an “ossified lung” ( Brito et al. 2010) in which the bony plates were a means to adapt to changes in the volume of the bladder in operating like a bellows. Other putative functions include a role in maintaining hydrostatic balance, as a resonating chamber for sound production, or for hearing ( Forey 1998).
Possible embryos.—In the ventral region of the holotype ( Fig. 5A View Fig ), beside the pelvic fin are two tiny coelacanth fossils. The first ( Fig. 5B View Fig ), near the pelvic fin, has a relatively large gular plate and trilobed coelacanth−like caudal fin. Its head length is 11 mm, and standard length is 33 mm. The second ( Fig. 5C View Fig ), near the basal plate of the pelvic fin, has its gular plate compressed on the swim bladder of the adult. Its head length is 8 mm, and the standard length is 25 mm. These two tiny coelacanths could be interpreted as embryos because the ratio of head length to standard length is 33%, which is higher than in the adult (28%; Table 1), a common feature of coelacanth (and many other) embryos (Cloutier
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2010). Further, these two embryos show the same diagnostic generic features as the adult, for example the expanded posterior margin of the lachrymojugal ( Fig. 5B View Fig 2, C 2 View Fig ) and the semicicular coronoid, confirming that the two tiny coelacanths are examples of Luopingcoelacanthus . There is no evidence of a yolk sac.
These two small coelacanths could have come to lie where they do by chance, by having been eaten, or by being unborn embryos. The first suggestion is rejected because the small specimens lie within the abdominal cavity, above some skeletal elements of the Luopingcoelacanthus adult individual, and below other skeletal elements. The second suggestion might seem to be reasonable because coelacanths are predators, and modern Latimeria is known to feed on a range of fishes, as many as 12 species ( Fricke and Hissmann 2000) that are swallowed whole; there is no evidence, however, that modern Latimeria is a cannibal. Further, we cannot argue that Luopingcoelacanthus was a cannibal because the two tiny specimens lie below the putative gut region by comparison with Latimeria , and they show no sign of disarticulation or acid damage. Evidence that they are indeed intrauterine embryos is that they most probably belong to the same genus as the enclosing adult, they show larval proportions, and they are in the correct, ventral region of the abdominal cavity just in front of the pelvic fins.
Reconstruction.—The whole−body reconstruction of Luopingcoelacanthus ( Fig. 6A View Fig ) is based primarily on the holotype, LPV−10146 ( Figs. 1 View Fig , 5A View Fig ), with confirmation of structures and measurements from the other specimens. The head shape in particular is based on the holotype and LPV−10575.
Geographic and stratigraphic range.— Type locality and horizon only.
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