The phyllocarid crustacean Montecaris from the ...

The phyllocarid crustacean Montecaris from the Devonian of northwestern Canada BRIANR. PRATT Department of Geology, University of Toronto, Toronto, Ont., Canada M5S IAl

Received September 30, 1986 Revision accepted October 3 1, 1986 The presence of Montecaris in North America is confirmed by a fragment of this phyllocarid crustacean from the Headless Formation (Middle Devonian) of the Mackenzie Mountains.

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La prisence de Montecaris en AmCrique du Nord est confinnee par un fragment de ce crustacC phyllocaride de la formation d'Headless (DCvonien moyen) des monts Mackenzie. Can. J. Ealth Sci. 24, 1267- 1269 (1987)

Introduction Fossil phyllocarid crustaceans are uncommon and rarely well preserved. Previously documented occurrences of the genus Montecaris are from the earliest Frasnian of Germany (Jux 1959, 1960) and Australia (Rolfe 1966; Brunton et al. 1969) and the Gedinnian and Famennian of Czechoslovakia (Chlupae 1960, 1963). This paper documents the first record of this genus in North America, apart from a specimen from the subsurface of northeastern British Columbia originally described as Spathiocaris? sp. (telson) by Copeland (1960) and redescribed here. All examples of this genus are from deeper water sediments deposited seaward of shallow-water carbonate banks. Biogeographically, Montecaris belongs to the equatorial Old World Faunal Realm (see, e.g., Oliver 1976; Heckel and Witzke 1979), and its presence in Canada corroborates the similar biogeographic affinity of other fossils in the cordilleran Devonian. Stratigraphy Paleozoic strata of northwestern Canada record several phases of development of extensive tropical carbonate shelves rimming an ocean that lay to the present-day west (Lenz 1972). Massive, shallow-water limestones of the Nahanni Formation in the southeastern Mackenzie Mountains, Northwest Territories, and its approximate correlative in the Rocky Mountains of northeastern British Columbia, the Dunedin Formation, represent one of these episodes (Lenz 1982). The new specimen of Montecaris described here was collected from the Headless Formation, which underlies and is the deeper water equivalent to the Nahanni (Noble and Ferguson 1971); it has been shown on the basis of conodont biostratigraphy to be Eifelian in age (Chatterton 1976, 1978). The Dunedin Formation is overlain by deep-water shales of the Besa River Formation, which represent rapid drowning of the carbonate platform (Morrow 1978), an event that took place in the Frasnian, as suggested also by conodonts (Taylor and Mackenzie 1970). The specimen described as Spathiocaris? sp. (telson) by Copeland (1960) was recovered about 30 m above the base of the Besa River. The new specimen was collected from recessive, poorly fossiliferous, thin-bedded argillaceous limestones in the upper part of the Headless Formation, an unknown covered distance, but probably not exceeding a few tens of metres, below the gradational contact with massive limestones of the Nahanni Formation. Below the sample horizon are laminated, noncalcareous silty shales. (The surface geology was described by Douglas and Nonis (1960, 1977).) Montecaris sp. A thus Printed in Canada 1 lmprimd au Canada

inhabited relatively deep water below wave base, on a carbonate ramp seaward of shallow-water coral and stromatoporoid biostromes.

Systematic paleontology CLASS Malacostraca Latreille, 1806 SUBCLASS Phyllocarida Packard, 1879 ORDER Archaeostraca Claus, 1888 SUBORDER Ceratiocarina Clarke, 1900 FAMILY Echinocarididae Clarke, 1900 SUBFAMILY Montecaridinae Rolfe, 1966 Remarks This taxon embraces the two genera Montecaris Jux, 1959 and Eleutherocaris Clark in Zittel, 1900. The diagnosis states that the lateral bristles of the telson are movable (Rolfe 1969). Those in Montecaris sp. A appear not to be, and this character should not be considered diagnostic. GENUS

Montecaris Jux, 1959

Type species Montecaris strunensis Jux, 1959 from the Upper Plattenkalk (Frasnian) of Bergisch Gladbach in the Rhineland, Federal Republic of Germany (by original designation).

Diagnosis Carapace bivalved, each oval, connected by a straight median dorsal border extending to a short posterolateral spine; four deep anterodorsal grooves, the first and fourth uniting ventrally; lateral ridge long, extending to a posteroventral spine; telson wide, equal in length or shorter than furca, with strong lateral bristles. Age range Devonian (Gedinnian- Famennian) (Rolfe and Edwards 1979). Other species Montecaris lehmanni Jux, 1960; M. brunnensis ChlupBE, 1960; and M. antecedens ChlupBZ, 1960. Remarks According to ChlupBE (1963), Baituganocaris Krestovnikov, 1961 (type species B. tatarica) from the southern Urals is a junior synonym of Montecaris. ChlupAE (1963) recognized only the type species as valid; the remaining four were considered inadequately described. Rolfe (1969) provisionally regarded Baituganocaris as a separate genus, based on differences in the carapace, but noted that if it should prove to be synonymous with Montecaris, the subfamily Baituganocari-

CAN. J. EARTH SCI. VOL. 24, 1987


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FIG. 2. Upper is a reconstruction of the ventral side of the caudal parts of Montecaris sp. A from the Headless Formation. Part enclosed in the circle shows the ridges and grooves on the dorsal side. Lower is a transverse view of the anterior portion of the caudal parts. Areas deduced are shown with dotted lines. Scale bar is 5 mm.

the Ram River (61 "47'45"N, 123"57'15"W). Telson and left furcal ramus are molds; right furcal ramus is pyritized.

FIG. 1. Montecaris from western Canada. (A) Montecaris sp. A. Telson and furca, ventral view, latex cast, GSC 69150, x 3. Headless Formation, Eifelian, District of Mackenzie. Cone-shaped impression on furcal ramus is a tentaculitid. (B) Montecaris sp. B. Last abdominal segment, telson, and furca, ventral view, GSC 13791, x 5. Frasnian, northeastern British Columbia.

dinae would have priority over Montecaridinae. Eleutherocaris (type species Echinocaris whitjieldi Clarke, 1885) from New York State is similar to Montecaris, differing in the carapace and in the narrower telson. Spathiocaris? sp. (telson) from northeastern British Columbia (Copeland 1960) was regarded as Montecaris by ChlupiE (1963) and, tentatively, by Rolfe (1969). All specimens of Montecaris are in the range of 15 cm or less in length, except for those reported from Australia, which reach approximately 60 cm (Brunton et al. 1969). Montecaris sp. A (Figs. lA, 2) Material One uncompressed specimen (GSC 69150) showing mainly the ventral aspect of the caudal appendages, from the Headless Formation (Middle Devonian), Ram Plateau, Mackenzie Mountains, Northwest Territories, along a creek 3 krn south of

Description Telson is dagger shaped, more than 16 mm long, 6 mm wide anteriorly and tapering posteriorly, and 2 mm thick. The anterior portion is roughly elliptical in cross section; the ventral surface has a broad central depression; the posterior portion is rounded and circular in cross section. The telson bears at least six nonarticulated pairs of lateral bristles directed obliquely backward; the terminal pair of bristles is 2 mm from the posterior tip of the telson. Bristles are circular in cross section, straight, and with swollen basal regions that merge into the telson, where they are separated by oblique furrows. They are evenly spaced about 1 &I apart; the most anterior bristle is 5 mm long, whereas the most posterior is 1.5 mrn long. Furcal ramus is flame-like, more than 18 mm long, 1 mm thick, and 6 mm wide anteriorly and tapering posteriorly to a level even with the telson; cross section is flattened elliptical. Dorsal surface possesses a narrow, inner submarginal keel and a broader keel displaced laterally inward from the axis; ventral surface is gently depressed from the lateral margins. Remarks Lack of the carapace precludes a specific assignment. The four species of Montecaris do exhibit some differences in the caudal appendages. In both M. strunensis and M. brunnensis, the furca is longer than the telson. The telson and furca are of equal length in M. lehmanni, M. antecedens, and B. tatarica (ChlupaiE 1963), and therefore M. sp. A resembles them in this character. The lateral bristles of M. antecedens are curved, somewhat irregular in length, and longest toward the posterior, whereas those of M. strunensis, M. brunnensis, M. lehmanni, and M. sp. A are straighter and more regular in length and distribution on either side of the telson. The bristles of M. sp. A merge into the telson, where their bases are separated by furrows directed obliquely backward; this configuration would not have allowed the bristles to be bent around like those of M. antecedens, which were probably simply attached to the

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telson and were likely articulating. It is uncertain whether the bristles are integral parts of the telson o r not in the other species of Montecaris, because they are preserved as carbonaceous films without primary relief. The telson tip may be blunt in M. sp. A and M. strunensis, whereas in other species it terminates in a spine.


Montecaris sp. B (Fig. 1B) Synonomy Spathiocaris? sp. (telson), Copeland, 1960, p. 9, P1. 1, fig. 14. Montecaris sp., Chlupie, 1963, p. 114. Material One compressed specimen (GSC 13791) showing the ventral aspect of the caudal appendages and last abdominal segment, preserved as a carbonaceous film, from the Besa River Formation (Upper Devonian), Central Leduc Toad River (Joint Venture) No. 1 C-10-e/94-N-7 well (5 165 -5 170 feet (1574 - 1576 m) ), northeastern British Columbia (59O21 'N, 124'59'W). Description Last abdominal segment is squarish in outline, 3.5 mm wide, and probably with a convex posterior margin. Telson is dagger shaped, 12 mm long, and 3.5 mm wide anteriorly and tapering posteriorly to a point. The ventral side appears to have a broad central depression. Telson bears three or more pairs of now-contorted, hollow lateral bristles directed obliquely backward; the terminal pair is 4 mm from the posterior tip of the telson; each bristle is about 2.5 mm long. Furcal ramus is flame-like, 13 rnrn long, and 2 mm wide anteriorly and tapering posteriorly to a level even with the telson. The ventral surface appears to have a central depression. -Remarks .- .... .. ..-

~~~k of a precludes a specific assignment. Copeland (1960) referred this specimen questionably to Spathiocaris because it occurs in strata containing Spathiocaris "shields" and suggested it might represent the caudal parts of these objects. Spathiocaris shields are now known to be ammonoid aptychi (Rolfe 1969, p. 329; Rolfe and Edwards 1979). ChlupiE (1963) regarded it as Montecaris, as did Rolfe (1969), tentatively. Although preservation is poor, this specimen resembles M. lehrnanni, M. antecedens, and M. sp. A in that the telson and furca are equal in length. The telson is pointed, as opposed to blunt apparently in M. sp. A and possibly in M. strunensis. The lateral bristles are fewer than in other species of Montecaris; it is not certain whether they are articulated and movable, as Copeland (1960) proposed, but they have been contorted during compaction and diagenesis such that their original nature is uncertain. The furcal rarni are proportionately narrower with respect to the telson than those of other species of Montecaris.

Acknowledgments I thank A. Jackson and D. C. Ford (McMaster University) for the opportunity to collect the specimen in 1974 during geomorphological research supported by Parks Canada; A. R. Ormiston (Amoco Production Co.) and W. D . I. Rolfe (Royal Museum of Scotland), who provided advice on its affinity; W. D. Boyce (Newfoundland Department of Mines and

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Energy) for photographic help; R. Ludvigsen (University of Toronto) for encouragement; and R. Ludvigsen, M. J. Copeland and W. D. I. Rolfe for criticizing the manuscript. BRUNTON, C. H. C., MILES,R. S., and ROLFE,W. D. I. 1969. Gogo Expedition 1967. Proceedings of the Geological Society of London, No. 1655, pp. 79-83. CHATTERTON, B. D. E. 1976. Distribution and paleoecology of Eifelian and early Givetian conodonts from western and northwestern Canada. In Conodont paleoecology. Edited by C. R. Barnes. Geological Association of Canada, Special Paper 15, pp. 143 - 157. 1978. Aspects of late Early and Middle Devonian conodont biostratigraphy of western and northwestern Canada. In Western and Arctic Canadian biostratigraphy. Edited by C. R. Stelck and B. D. E. Chatterton. Geological Association of Canada, Special Paper 18, pp. 161-231. CHLUPAE,I. 1960. Die Gattung Montecaris Jux (Crustacea Phyllocarida) im alteren Palaozoikum der Tschechoslowakei. Geologie, 9: 638-649. 1963. Phyllocarid crustaceans from the Silurian and Devonian of Czechoslovakia. Palaeontology, 6: 97 - 118. COPELAND, M. J. 1960. The occurrence of Echinocaris and Spathiocaris (Phyllocarida) in western Canada. Geological Survey of Canada, Bulletin 60, pp. 1 - 11. DOUGLAS, R. J. W., and NORRIS,D. K. 1960. Virginia Falls and Sibbeston Lake map-areas, Northwest Territories. Geological Survey of Canada, Paper 60-19. , compilers. 1977. Geology of Sibbeston Lake, District of Mackenzie. Geological Survey of Canada, Map 1377A, scale 1 : 250 000. HECKEL,P. H., and WITZKE,B. J. 1979. Devonian world palaeogeography determined from distribution of carbonates and related lithic palaeoclimatic indicators. In The Devonian System. Edited by M. R. House, C. T. Scrutton, and M. G. Bassett. Special Papers in Palaeontology , 23: 99 - 123. Jux, U. 1959. Phyllocariden-Reste aus dem oberen Mitteldevon der Bergisch Gladbach-Paffrather Mulde. Palaontologische Zeitschrift, 33: 166-171. 1960. Montecaris lehmanni, a new crustacean from the Rhenish Devonian and the problem of its systematic position. Journal PaleOntolog~~ 34: 152. LENZ, A. C. 1972. Ordovician to Devonian history of northern Yukon and adjacent District of Mackenzie. Bulletin of Canadian Geology, 20: 321 -361. 1982. Ordovician to Devonian sea-level changes in western and northern Canada. Canadian Journal of Earth Sciences, 19: 1919 - 1932. MORROW, D. W. 1978. The Dunedin Formation: a transgressive shelf carbonate sequence. Geological Survey of Canada, Paper 76-12. NOBLE,J. P. A., and FERGUSON, R. D. 1971. Facies and faunal relations at edge of early Mid-Devonian carbonate shelf, South Nahanni River area, N.W.T. Bulletin of Canadian Petroleum Geology, 19: 570-588. OLIVER, W. A. 1976. Biogeography of Devonian rugose corals. Journal of Paleontology, 50: 365 -373. ROLFE,W. D. 1966. Phyllocarid crustacean fauna of European aspect from the Devonian of Western Australia. Nature (London), 209: 192. 1969. Phyllocarida. In Treatise on invertebrate paleontology. Part R. Arthropoda 4(1). Edited by R. C. Moore. Geological Society of America and the University of Kansas Press, Lawrence, KS, pp. R296-R331. ROLFE,W. D. I., and EDWARDS, V. A. 1979. Devonian Arthropoda (Trilobita and Ostracoda excluded). In The Devonian System. Edited by M. R. House, C. T. Scrutton, and M. G. Bassett. Special Papers in Palaeontology, 23: 325 -329. TAYLOR, G. C., and MACKENZIE, W. S. 1970. Devonian stratigraphy of northeastern British Columbia. Geological Survey of Canada, Bulletin 186.