New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana...

N E W G E N E R A A N D S P E C I E S O F C O E L A C A N T H S F R O M T H E B E A R G U L C H

L I M E S T O N E ( L O W E R C A R B O N I F E R O U S ) O F M O N T A N A ( U . S . A . )

by

RICHARD LUND * & WENDY LUND *

ABSTRACT RI~SUM]~

Four new spegies of coelacanths (Actinistia) from the Namurian E2b marine Bear Gulch Limestone of Montana are described, and a fifth species, originally described as an actinopterygian, is redescribed. Two new suborders are diagnosed. The taxonomy is : Suborder Coelacanthocdei, family Rhabdoderma- tidae, Caridosuctor populosum nov. sp., suborder Hadronectoroidei nov., family Hadronectoridae nov., Hadronector donbairdi nov. sp., Polyos- teorhynchus simplex nov. sp. and Allenypterus montanus MELTON. Lochmocercus aciculiodontus nov. sp. is incertae sedis.

Quatre nouvelles esl~ces de Coelacanthes (Actinis- tia) sont d6crites dans le calcaire namurien marin E2b de Bear Gulch (Montana, U.S.A.), et une cinqui~me, d~crite auparavant comme Actinopt&ygien, est red& trite. La taxonomie suivie dans cet article est : Sous- ordre Coelacanthoidei, famille Rhabdodermatidae, Caridosuctorpopulosum nov. sp., sous-ordre Hadro- nectoroidei nov., famille Hadronectoridae nov., Hadronector donbairdi nov. sp., Polyosteorhynchus simplex nov. sp. et Allenypterus montanus MELTON. Lochmocercus aciculiodontus nov. sp. est incertae sedis.

KEY-WORDS : ACTIN1STIA (COELACANTHIFORMES), CARBONIFEROUS, NAMURIAN, MONTANA, NEW TAXA.

MOTS-CLI~.S : ACTINISTIA (COELACANTHIFORMES), CARBONIFt~RE, NAMURIEN, MONTANA, NOUVEAUX TAXONS.

INTRODUCTION

The osteichthyan order Coelacanthiformes (Actinis- tia) includes fishes ranging from Late Devonian to the recent. Known fossil coelacanths differ from each other only in proportions or in relatively small details of osteology. The morphology of the Palaeozo~'c coelacanths, however is known only for Diplocercides ( = Nesides) (Stensi0, 1922, 1937), Rhabdoderma (Moy- Thomas, 1937 ; Forey, 1981), and Coelacanthus (Schaumberg, 1978), from the Late Devonian, Late

Carboniferous and Early Permian respectively. Of these three genera, moreover, the description and diagnosis of Rhabdoderma were not based upon the type species of the genus and are seriously in error (Moy- Thomas, 1937 ; Lurid & Lurid, in press). The osteology of the Palaeozoic coelacanths, therefore, is so poorly known that plausible hypotheses of relationships are not presently possible.

* Department of Biology, Adelphi University, Garden City, N.Y. 11530 U.S.A.

Geobios, n ~ 17, fasc. 2 p. 237-244, 5 fig. Lyon, avril 1984

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The Namurian E2b marine Bear Gulch Limestone of Montana presently contains 5 species of coelacanths. One of these is the most abundant fish in the fauna, and the 5 species account for approximately 15% of the fish specimens collected. One of the five species, Allenypterus montanus MELTON (1969) has quite an atypical shape for a coelacanth and has pre- viously been described as an actinopterygian. The other species are more typical in body form. The five species constitute a significant addition to the know- ledge of the order. Details of the morphology are dis- cussed elsewhere (Lund& Lurid, in press).

A b b r e v i a t i o n s : Specimens axe deposited either at the University of Montana Geological Museum (MV), Missoula, Montana, or the Section of Vertebrate Fos- sils, Carnegie Museum of Natural History (CM), Pittsburgh, Pennsylvania.

H o r i z o n a n d Locality : All specimens were collected from the Namurian E2b (Chesterian) Lower Carboni- ferous Bear Gulch Limestone member of the Heath Formation, Big Snowy Group, South of Becket, Fer- gus County, Montana.

SYSTEMATICS

Order COELACANTHIFORMES (ACTINISTIA)

Suborder C o e l a c a n t h o i d e i

Type-family : Coelaeanthidae AGASSIZ, 1839

DIAGNOSIS : T h e nasal-frontal-parietal series of bones is flanked by a single supraorbital series, the supraorbital lateral line canal lying under the lateral margins of the nasal to parietal bones. A supratemporal is either greatly reduced or absent. There may be 5 or fewer bones in the cheek, that may be loosely associated. A subopercular is present. Postcranially, the second dorsal fin axis articulates with the posterodor- sal margin of its basal plate, the anal fin plate is located in the ventral body wall anterior to the first hae- mal spines and the peritoneal cavity extends posterior to the anus.

]_NCLUDED FAMILIES : Coelacanthidae, Rhabdoder- matidae, Laugiidae, Diplocercididae.

Family Rhabdodermatidae BERG, 1958

Type-genus : Rhabdoderma REIS, 1888

DIAGNOSIS : Paired premaxillae unornamented, the ascending lamina of each perforated by a large pore for the rostral organ. Bones of the ethmoid commis- sure and rostral area are small, loosely associated and bordering large lateral-line canal pores. An antorbital bone is present and is perforated by two pores for the rostral organ. The anterior margin of the postorbital

is set posteriorly to the intracranial joint. Cheek bones 5 in number, thin, completely covering cheek. Supratemporal is reduced to a thin bone surrounding the otic lateral line canal. 5 extrascapulars. Pelvic plates suture across midline and have anterolateral exten- sions ; anal fin support may not ossify. Caudal fin rays each have one endoskeletal support.

COMMENTS �9 The genus Rhabdoderma was erected by O.M. Reiss (1888) with Coelacanthus elegans New- berry designated as the type-species. J.A. Moy- Thomas (1937) placed several north American and British Carboniferous coelacanths into synonymy with R. elegans on the basis of scale ornamentation and fin plates. He presented a revised description and restoration of this species that is devoid of reference to the horizon, localities and specimen numbers used in its description. Over 135 acid cleaned and prepared specimens of R. elegans from Linton, Ohio, the type locality, have been prepared, deposited at Carnegie Museum and have been analysed (Lund & Lund, in press). It is clear that Rhabdoderma elegans is not the species of fish illustrated by Moy-Thomas.

Genus Caridosuctor nov. gen.

Type-species : Caridosuctor populosum nov. sp.

DIAGNOSIS : Provisionally, the same as for the type species.

ETYMOLOGY �9 Car ido, a schrimp, and suctor, to suck, alluding to its probable food preference as

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judged by stomach contents and to its feeding mecha- nism.

Carldosuctor populosum nov. gen., nov. sp.

fig. 1

DIAGNOSIS : Marine rhabdodermatids having large dentary, precoronoid and ectopterygoid teeth. The preorbital region is higher and more rounded than in other rhabdodermatids, the cheek bones deeply overlap each other and the operculum. The operculum articulates with the tabular and the posterior margin of the tabular is level with the posterior margin of the skull. Tubercular ornamentation is sparse on the

anterior skull-roof and preorbital region, dense on the very thin cheek bones of large individuals. Dense ver- miform ornamentation is found on operculum and angular behind the angular pit line ; sparse linear ridges on skull-roof posterior to intracranial joint. The first dorsal fin plate has ventral processes indicating fusion from supraneural elements. The second dorsal fin is anteroposteriorly elongated and bears a posterior articulation for the fin axis, and the anal plate, which rarely ossifies, is a simple rod in the ventral body wall, anterior to the first hemal spine. Pelvic plates are very broad anteriorly, with 3 major and one minor anterior lateral process. The size ranges from 79mm to 217 mm in standard length. Elliptical caudal fin and cylindrical body form.

Fig. 1 - - Cartdosuetorpopulosum nov. gen., nov. sp. , res torat ion based on CM 25590, MV 6021. Bear Gulch Limestone. Scale : 10 mm.

M E R I S T I C CHARACTERS : vertebral segments : 9-11 cervicals, 23-26 abdominals, 20-25 caudals ; pectoral rays :13-15 ; pelvic rays : 3-4 + 10-13 ; first dorsal rays : 3-4 + 7-9 ; second dorsal rays : 4-5 + 10-14 ; anal rays : 2-3 + 10-13 ; epicaudal rays : 3-4 + 14-16 ; hypocaudal rays ; 3-4 + 11-13.

TYPE SPECIMEN : MV 6021 (fig. 1).

REFERRED SPECIMENS ' MV 2557, 2804, 2917, 2924, 2928, 2997, 3092, 3567, 3570-3572, 3576, 3626, 3632, 3633, 3759-3761, 3820, 3861, 5547, 5548, 6022-6040, 6208-6214, 6939-6944. CM 25590 (fig. 1), 27299- 27306, 27309 (counterpart 27311), 27312 (counterpart 27313), 27310, 27314-27322, 30671-30710, 30717- 30723, 35203, 35528-35536, 35675-35678, 37513- 37519.

T Y P E L O C A L I T Y : Becket, Montana, U . S . A .

T Y P E LEVEL : Namurian E2b.

ETYMOLOGY:populosum, populous, as this is the most abundant fish in the Bear Gulch Fauna.

Suborder Hadronectoroldel nov.

Type-family : Hadronectoridae, new family

DEFINITION:The nasal-frontal-parietal series of bones is anamestic in early ontogeny, and is flanked by mesial and lateral supraorbital canal bone series. The mesial supraorbital series may fuse with the nasal- parietal series during ontogeny. An unreduced supratemporal bone is present. The cheek is compo- sed of five tightly fitted or overlapping bones. Both opercular and subopercular bones are present. Post- cranially the second dorsal fin axis articulates directly

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above its basal plate and the anal fin, directly below its plate, is supported by the first hemal spine. There is no extension of the peritoneal cavity posterior to the anus.

COMMENT:There is only one family presently known. The smallest known young of this group is approximately half the length of that of the smallest known members of the Coelacanthoidei.

Family Hadronectoridae nov.

Type-genus : Hadronector, nov. gen.

DIAGNOSIS : The same as for the suborder.

Genus Hadroneetor nov. gen.

Type-species : Hadronector donbairdi n o v . g e n . , n o v . sp .

DIAGNOSIS : Provisionnally, the same as for the type- species.

ETYMOLOGY:Hadronector, meaning stocky swim- mer.

Hadronector donbairdi nov. gen., nov. sp.

fig. 2

DIAGNOSIS " The premaxilla bears a narrow dorsal lamina emarginated for one or more pores. The rostral- postrostral series is large, contains 6 bones and extends posteriorly to the level of the orbit. Late- ral suborbital bones tend to fure into 3 or 4 elements ; medial supraorhital bones are very narrow over orbits. The supratemporal contains the anterior end of the otic lateral line canal and pores. The posttemporal is located posterior to the lateral extrascapular. The pelvic plates are anteriorly forked and broad, are located midabdominally and bear a posteromedian articular process. The body is short, stocky, ranging in size from 28 mm to 108 mm. All external skull bones are heavily ornamented, but the ornamentation is not necessarily in concordance with the underlying bone pattern. The ornamentation on the premaxillae grades into fine teeth along the oral margin. A small extracleithrum is present. Caudal fin outline is almost squared off in larger specimens.

Fig. 2 -- Hadroneetor donbairdi nov. gen., nov. sp., restoration based on MV 3635, CM 30723. Bear Gulch Limestone. Scale : 10 mm.

M_ERISTIC CHARACTERS : Vertebral segments : 9 cervicals, 13 abdominals, 19-24 caudals ; pectoral rays II ;pelvic r a y s : 3 + 8 ; first dorsal r a y s : 3 + I I ; second dorsal rays 2-3 + 7-II ; anal rays : 3 + 7-9 ; epicaudal rays : 3-4 + 18-21 ; hypocaudal rays : 3-4 + 17-21.

TYPE SPECIMEN : MV 3635 (fig. 2). REFERRED SPECIMENS : M V 3574 (counterpar t , 3605), 3863 (counterpart, 3865), 5098, 6041, 6215. CM 27307, 27308, 30711-30713, 30723 (fig. 2), 35537. ETYMOLOGY : named in grateful appreciation for the many years of help and encouragement provided by Donald Baird, Princeton University.

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Genus Polyosteorhynchus nov. gen.

Type-species : Polyosteorhynchus simplex nov. sp.

DIAGNOSIS : Provisionally, the same as for the type. species.

ETYMOLOGY:Polyosteorhynchus, meaning many snout bones.

Polyosteorhynchus simplex nov. sp.

fig. 3

DIAGNOSIS " The dorsal margin of the premaxilla is emarginated for one or more pores and bears few, large teeth. The rostral bone is small and postrostrals are either very small or absent. The nasal-frontal parietal series is not bilaterally symmetrical and there are no enlarged, clearly defined parietal bones.

Neither supraorbital series modified by fusion. The anterior end of the otic canal passes between postparietal and supratemporal. The anterior end of the postorbital abuts against the skull somewhat posterior to the intracranial joint, and there may be one or two squamosals. Pelvic plates are long, narrow, do not bear a posteromedian articular process and are posi- tioned midabdominaUy. The size ranges from 35 mm to an estimated 186 mm in standard length, with maximum height of the body midway between the posterior margin of the head and the origin of the first dorsal fin. Bones of the skull are relatively thin and ornamented withocoarse, low, flat-topped tubercles or ridges, although the premaxilla is ornamented and the anterior bones of the ethmosphenoid are sparsely ornamented. The premaxiUa bears 3-4 large teeth Bones of the cheek are deeply overlapping. The extracleithrum is large. Caudal fin outline is almost square in larger individuals.

3

Fig. 3 - - Polyosteorhynchus simplex nov . g e n . , nov . sp . , r e s t o r a t i o n b a s e d o n M V 2946, 6042, 6043. Bea r G u l c h L i m e s t o n e . Scale : 10 m m .

MERISTIC CHARACTERS : vertebral segments : 8-9 cervicals, 23-24 abdominals, 25-26 caudals ; pectoral rays : 8-9 ; pelvic rays : 12 ; first dorsal rays : 7 ; second dorsal rays : 14 ; anal rays : 12-16 ; epicaudal rays : 3-4 + 4-15 ; hypocaudal rays : 3-4 + 4- 16.


REFERRED SPECIMENS : MV 2946 (fig. 3), 3584, 6042 (fig. 3), CM 27283, 30597, 30714, 35540.

ETYMOLOOY : simplex, refers to the evolutionarily and morphologically basic pattern of the anterior bones of the head.

Genus Allenypterus MELTON, 1969

Type-species : Allenypterus montanus MELTON.

REVISED DIAGNOSIS " Provisionally, the same as for the type-species.

Allenypterus montanus MELTON, 1969

fig. 4

1969 - - Allenypterus montanus nov. gen., nov. sp., Melton, 1969.

1977 - - Allenypterus montanus MELTON, Glickman, 1977.

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REVISED DIAGNOSIS �9 Moderate sized coelacanth with high, strongly compressed dacriform body, extended epicaudal fin and vestigial hypocaudal fin. Premaxilla is narrow, apparently unperforated and unemargina- ted, and bears a row of fine teeth. There are a small median rostral and postrostral, and the rostral may be a product of the fusion of paired elements. The mesial supraorlfital series overlies the lateral line canal and fuses relatively late in ontogeny with the most mesial skull roofing bone resulting in a pore and canal bea- ring naso-frontal-parietal series and an unmodified lateral supraorbital series. There are several supple- mentary canal bones between the anterior supraorbital canal series dorsally and the lateral rostral bones ventrally. The anterior end of the otic canal passes beneath the supratemporal-postparietal suture. The posttemporal is in contact with the posterolaterally expanded tabular. Postcranially, there is a median ventral row of thick scales between clavicles and pelvic girdle. Pelvis plates are high triangles that do not

articulate in the ventral midline and are located near the rear of the peritoneal cavity. The dorsal lobe of the caudal fin originates anterior to the level of the first caudal segment, is low and elongate and has an endoskeletal support-fin ray ratio grater than 1/1. Fin rays and length of the hypocaudal lobe are greatly reduced and have a 2/1 ratio to endoskeletal skp- ports. The terminal lobe bears no fin rays. The body reaches maximum height at the level of the first dorsal fin and gradually slopes downward from the second dorsal fin to the terminal lobe. The first dorsal fin rays are short, well articulated and of uniform height. Individuals range in size from 32 mm to 152 mm in standard length. All external bones of the head except the premaxilla are heavily ornamented with broad, flat topped ridges. Seven lateral supraorbitals border the orbit, the last two of which fuse, and five in the series anterior to the orbit. Bones of the cheek are thin and broadly overlap each other, the operculars and the posterior end of the lower jaw.

4 t t

Fig. 4 - - Allenypterus montanus MELTON, restoration based on MV5381, CM 37509. Bear Gulch Limestone. Scale : 10 ram.

MERISTIC CHARACTERS : Vertebral segments : 8 cervicals, 20-21 abdominals, 36-44 caudals ; pectoral rays : 6-7 ; pelvic rays : 6-7 ; first dorsal rays : 2-3 + 11-4 ; second dorsal rays : 6-9 ; anal rays : 6-7 ; epicaudal rays : 3-4 + 55-69 ; hypocaudal rays : 15 ; 6- 9 scales in median ventral scale shield.

TYPE SPECIMEN : M V 2 5 5 5 .

REFERRED SPECIMENS " MV 2771, 2920, 2949, 3640, 4736, 5381 (fig. 4), 5382, 5549, 5550, 6216, 6217,

6937, 6938, 7033-7035. CM 27284-27288, 30627, 30628, 30716, 35200, 35202, 35363, 35538, 35539, 37509(fig. 4).

COMMENTS :Allenypterus montanus was originally described as an actinopterygian of the family Doryp- teridae (Melton, 1969). In all characteristics of cranial and postcranial morphology, except for the body form, it is clearly a coelacanth. Its body form is uni- que among known coelacanths.

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Ineertae sedis

Genus Lochmocercus nov. gen.

Type-species : Lochmocercus aciculodontus nov. sp.

DIAGNOSIS -" Provisionally, the same as for the type species.

ETYMOLOGY : Lochme, a brush, and cercos, tail, referring to the appearance given by the high fin ray- endoskeletal support ratio.

anocleithrum is stout and may have contacted the posterior margin of the skull. The extracleithrum is large but unusually firmly fixed to the shoulder girdle. Pelvic plate is quadrangular and lacks significant peri- chondral bone, its axial element are ossified. Fins rays have a 2/1 ratio to endoskeletal supports. Bones of the skull roof sparsely ornamented with coarse tubercles, lateral bones more densely ornamented. There are 31-33 vertebral elements in the trunk, 3 + 8 first dorsal fin rays, 2 + 9 rays in the second dorsal fin and 4 + 23-28 in both epicaudal and hypocaudal lobes of the caudal fin. Caudal fin outline is elliptical in known specimens.

Lochmoeercus acleulodontus nov. sp.

fig. 5

DIAGNOSIS : A moderate sized supratemporal bears pores and the canal for the anterior end of the otic canal. The antorbital bears two pores, the lacrimoju- gal several large pores, and the cheek bones are tightly abutted against each other. The anterior margin of the postorbital is close to the intracranial joint. The lower jaw lacks an anterior angular diastema, the oral margin of the dentary is continuous with that of the precoronoid to the base of the coronoid bone. Den- tary and precoronoid bear a row of large teeth. Both opercular and subopercular bones are present. The

Fig. 5 - -


REFERRED SPECIMENS : MV 6218. CM 27406, 30715, 35210.

ETYMOLOGY : Aciculos, needle, and odontos, tooth.

COMMENTS : L. acicuiodontus is the rarest and most poorly preserved of the Bear Gulch coelacanths. Nei- ther the rostral region nor the axial skeleton are completely preserved on any specimen. It is, however, the only coelacanth in the fauna with a 2/1 ratio of caudal fin rays to endoskeletal supports.

s 'x,, ' -

Lochmocercu$ aciculodontus nov . g e n . , nov . sp . , h o l o t y p e , M V 6044. Bea r G u l c h L i m e s t o n e . S c a l e : 10 m m .

DISCUSSION

The Bear Gulch Hadronectoroidei are collectively more primitive in all useful character states than all other known coelacanths (Lund &Lund , in press).

They are also better preserved than any other Paleo- zoic coelacanths, which renders accurate phyletic analysis more difficult than customarily. The resul-

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tant scheme of relationships thus is a series of grades of evolution in which there are virtually no conclusive connecting links between grades. Even within the Hadronectoroidei it is not possible to demonstrate any ordering of relationships in a single most parsi- monious scheme.

Among the Devonian and Carboniferous coelacanths for which even a modicum of useful informa- tion is available, it is only possible to say that two

concurrent major groups. The Coelacanthoidei, represented by the Devonian Diplocercididae (Sten- siO, 1922, 1937; Bjerring, 1973) and possibly by Lochmocercus, were more derived in most known characters than the Hadronectoroidei . The Devonian Euporosteus (Stensi0, 1937) is known f rom one isola- ted ethmosphenoid that may best be assigned provisionally to the Hadronectoroidei on the basis of mul- tiple series of bones.

Acknowledgements

We gratefully appreciate the aid of William G. Melton Jr. through the years of field quarrying, and the many volun- teers that have helped. The ranchers of the Grassrange- Forest Grove area have graciously extended their hospitality and permission to work on their land. Financial support for

this project has been provided by grants from Carnegie Museum of Natural History, and National Science Fonda- tion grants BMS 75-02720, DEB 77-02348 and DEB 79-19492.

REFERENCES

BJERRING H. (1973) - Relationships of coelaeanthiforrns. Zool. J. Linn. Soc., London, Suppl. n ~ l,ovol. 53, p. 179-205.

FOREY P. (1981) - The coelacanth Rhabdoderma in the Bri- tish Isles. Palaeontology, London, vol. 24, p. 203-229.

GLICKMAN W.L. (1977) - Allenypterus montanus (Cros- sopterygii, Cor from the Bear Gulch Limestone of Montana. Ms. Thesis Adelphi University, Garden City, 29 p.

LUND R. & LUND W.L. (in press) - The coelacanths from the Bear Gulch Limestone (Namurian) of Montana and the evolution of the Coelacanthiformes. Bull. Carnegie Mus. nat. Hist., Pittsburgh.

MELTON W.G. Jr. (1969) - A new dorypterid fish from Central Montana. Northwest Science, Missoula, vol. 43, p. 196-206.

MOY-THOMAS J.A. (1937) - The Carboniferous coelacanth fishes of Great Britain and Ireland. Proc. Zool. Soc., London, ser. B, vol. 3, p. 383-415.

REIS O.M. (1888) - Die Coelacanthiden, mit besonderer Bertlcksichtigung der im weissen Jura Bayerns vorkom- menden Gattungen. Palaeontographica, vol. 35, p. 1-96.

SCHAUMBERG G. (1978) - Neubeschreibung yon Coelacan- thus granulatus AGASSIZ (Actinistia, Pisces) aus dem Kupferschiefer von Richeldorf (Perm, W.-Deutschland). Palaeont. Z., Stuttgart, vol. 52, p. 167-197.

STENSIO E.A. (1922) - Uber zwei Coelacanthiden aus dem Oberdevon yon Wildungen. Palaeont. Z., Stuttgart, vol. 4, p. 167-210.

STENSIO E.A. (1937) - On the Devonian coelacanthids of Germany, with special reference to the dermal skeleton. K. svenska VetenskAkad. Handl., Stockholm, ser. 3, vol 16, p. 1-56.

Manuscrit d6finitif requ le 01.02.1984

New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana...

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