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

O F B E A R G U L C H , M O N T A N A ( U . S . A . )

by

RICHARD LUND * & PHILIPPE JANVIER **

ABSTRACT RI~SUMI~

A second fossil lamprey is described from the Lower Carboniferous (Namurian) locality of Bear Gulch (Montana, U.S.A.), which had already yielded the type specimen of Hardistiella montanensis, the oldest and, probably, the most primitive of all known lampreys. This new specimen, which may possibly belong to the latter species, is badly preserved, but clearly shows the impressions of four to six branchial pouches which are relatively small and closely set, like those of the other Carboniferous lamprey Mayomy- zon pieckoensis. They differ thus from extant lam- preys, in which the branchial apparatus extends relati- vely far behing the eyeballs. This concentration of the branchial apparatus in early lampreys is regarded here as a primitive condition, which is also met with in many anaspids, as evidenced from their closely-set external branchial openings. The presence of an impression which recalls the loop of the trabecles in larval extant lampreys suggests that this specimen was a larval individual.

Une seconde lamproie fossile est d6crite dans le gise- ment carbonif~re inf6rieur (Namurien) de Bear Gulch (Montana, U.S.A.), qui avait d6j~t livr6 le sp6cimen type de Hardistiella montanensis, la plus ancienne, et probablement la plus primitive, de toutes les lam- proies connues. Ce nouveau sp6cimen, qui ne peut ~tre rapport6 qu'avec doute ~ cette esp~ce, est relati- vement mal conserv6, mais montre nettement la trace de quatre ~ six poches branchiales &roitement acco- 16es, comme celles de Mayomyzon pieckoensis, l'autre lamproie fossile du Carbonif~re moyen. Elles diff~- rent en cela des lamproies actuelles chez qui l'appareil branchial s'6tend relativement loin en arri~re de l'oeil. Cette concentration de l'appareil branchial chez les lamproies carbonif&es est ici consid6r6e comme un caract~re primitif pour le groupe, que l'on retrouve 6galement chez les Anaspides, autant que l'on puisse en juger par leurs orifices branchiaux externes 6troite- ment contigus. La pr6sence, sur ce nouveau sp6cimen, de traces 6voquant les trab6cules sugg~re aussi qu'il pourrait s'agir d'un individu larvaire.

KEY-WORDS : VERTEBRATA, PETROMYZONTIDA, LOWER CARBONIFEROUS, U.S.A., ANATOMY, BRANCHIAL APPA- RATUS, LARVAL STAGE.

MOTS-CL]~S : VERTEBRATA, PETROMYZONTIDA, CARBONIFI~RE INF]~RIEUR, U.S.A., APPAREIL BRANCHIAL, STADE LARVAIRE.

INTRODUCTION

A few years ago, the now famous Lower Carbonife- rous fish locality at Bear Gulch (Montana, U.S.A.) yielded a relatively well preserved lamprey, Hardis- tiellct montanensis JANVIER & LUND (1983). In being

slightly older (Namurian) than the previously descri- bed fossil lamprey Mayomyzon pieckoensis BAR- DARCK & ZANGERL (1968, 1971) from the Pennsylva- nian of Illinois, Hardistiella is now the earliest

* Department of Biology, Adelphi University, Garden City, Long Island, New York 11530, U.S.A. ** LA 12 du CNRS, Institut de Pal6ontologie, 8 rue Buffon, 75005 Paris, France.

Geobios, n ° 19, fasc. 5 p. 647-652, 2 fig., 1 pl Lyon, octobre 1986

- - 648 - -

lamprey hitherto recorded. It has been regarded as the most primitive member of the Petromyzontida, since it seems to have retained a true anal fin. It differs also from all other known lampreys in having relatively large otoliths (Janvier & L u n d 1983, fig. 3).

A second lamprey has been discovered in Bear Gulch during the summer 1985, and despite its

comparatively poor state of preservation, it provides some complementary data to the knowledge of the structure of these early representatives of the Petromyzontida. This specimen, described herein belongs to the collection of Carnegie Museum of Natural History (C.M.N.H.), n ° 4105.

DESCRIPTION

Like all the Bear Gulch specimens this lamprey is preserved as a slightly tarry impression in a calcareous flagstone (pl. 1, figs. 1, 2). It has been photographed dry (pl. 1, figs. la, 2a) and immersed in water (pl. 1, figs. lb, 2b) in order to reveal various details of the head. Contrary to the holotype of Hardistiella monta- nensis JANVIER & LUND 1983 (fig. 1), which had been pressed laterally during fossilization and, thus, shows quite accurately the actual body shape of the living animal [this applies also to the holotype of Mayomyzon pieckoensis (BARDACK & Z A R G E R L ,

1968, fig. 1)], the new Bear Gulch specimen seems to have received a rather dorsolateral thrust during fossi- lization, hence its comparatively higher body shape. The tail and median fins are almost invisible, but the head structures are somewhat better preserved than in the first specimen. Whether or not this specimen also belongs to the species H. montanensis is difficult to say, however, the fact that it comes from exactly the same locality may support this attribution.

The head shows an enlarged anterior lobe, which may correspond to the << snout >> or the oral hood. It contains a few tarry dots (te., fig. 1B), which may be traces of some tectal cartilages. Behind this lobe, there is a dumbell-shaped black spot (e., fig. 1), which is almost certainly the trace of the two eyeballs. Dor- sally to it, there is a lozenge-shaped impression (?tr., fig. 1B), which may be either a trace of the braincase or, more likely, that of the trabecles only. In fact, a comparison with the skeleton of an extant larval lam- prey shows a striking similarity between this impres- sion and the loop which is formed by the trabecles and the trabecular commissure. Moreover, this impression is produced anteriorly into a small bifurcated process (o1., fig. 1B), which may be the trace of the olfactory capsule, as also suggested by a comparison to an extant larval lamprey (pl. 1, fig. 3). If this interpreta- tion is correct, we have to assume that this specimen is a larval individual, a condition which would be in agreement with its very small size.

A

-'~" ~ ~ " - ' ~ " .~:, "

I I ?c.

B ~ _ _ ~ ?tr.

• " ~ ol.

d.t. " ~ t(.

?b.6 71o.5 b.4 b.3 b2 b.1

Fig. 1 - - Petromyzontida gen. et sp. indet., Lower Carbonife- rous, Namurian , Bear Gulch, Montana (U.S.A.). Cameralucida drawing of specimen n ° C M N H n ° 4505, head region. A counterpart o f B. Scale : 1 mm . b.1-4, impressions of branchial pouches ; ?b.5-6, possi- ble impressions o f branchial pouches ; ?c., possible trace of the notochord ; d.t . , trace of the digestive tract ; e., trace of the eyeballs ; o1., trace of the olfac- tory capsule ; te., trace of possibly tectal cartilages of the snout ; ? tr., possible traces of the trabecles.

Carbonif~re inf6rieur, Namurien, Bear Gulch, Montana (U.S.A.). Dessin/ t la chambre claire de la t&e du sp6ci- men n ° C M N H n ° 4105. A est la contre-empreinte de B. ]~chelle : 1 mm. b. l -4, traces de poches branchiales ; ?b.5-6, traces pos- sibles de poches branchiales ; ?c., trace possible de la chorde ; d.t . , trace du tube digestif ; e., trace des yeux ; o1., trace de la capsule olfactive ; te., trace possible des cartilages tectaux du museaux ; ?tr., trace possible des trab6cules.

-- 649 - -

The most interesting detail displayed by this speci- men is the branchial apparatus. Contrary to the holotype of H. montanensis, which showed only a few branching impressions (Janvier &Lund 1983, fig. 2A, << b.a. >>), interpreted as traces of the branchial arches, this specimen shows distinctly at least four dark impressions (bl-4, fig. 1B), situated posteroven- trally to the eye trace, and which are certainly the tra- ces of individual branchial pouches. A careful exami- nation of the specimen in immersion reveals the faint trace of two more branchial pouch impressions (? b.5- 6, fig. 1B). One may thus assume that there are pos- sibly six branchial pouches.

Behind this series of branchial pouches, there is an elongated black impression which is most probably that of the digestive tract (d.t., fig. 1), preserved in the same position as in the holotype of Mayomyzon pieckoensis (BARDACK & ZANGERL, 1968, fig. 1). In the posterior part of the specimen, there is a ventral dark area which may be due to the accumulation of organic matter in the posterior part of the digestive tract, in particular in the cloaca, as it is often obser- ved in larval extant lampreys.

No trace of the notochord is preserved, except perhaps a thin black line behind the head (?c., fig. 1B). Further, no traces are preserved of the large seg- mental structures labelled X in the holotype of H. montanensis (JANVIER & LUND, 1983).

COMPARISON AND DISCUSSION

The arrangement of the branchial pouches in this specimen shows a striking similarity to that in Mayomyzon pieckoensis, and differs markedly from that in extant lampreys. In fact, the branchial pouches in both carboniferous lampreys appear as very short, closely set, and gathered immediately behind the braincase (fig. 2B). This arrangement is particularly clear in a specimen of M. pieckoensis preserved in dorsal aspect (Bardack & Zangerl 1971, fig. 2). By contrast, in all extant lampreys, the branchial appara- tus is much more elongated in shape, and extends over a length which is up to three times that of the preorbi- tal region of the head (fig. 2A), whereas the length of the branchial apparatus in both Mayomyzon and the specimen described here is approximately equal to the preorbital part of the head.

As noted earlier by Bardack & Zangerl (1971), this shorter branchial apparatus is virtually the only diffe- rence which can be noticed between Mayomyzon and extant lampreys. Whether it is derived or primitive is difficult to decide. However, there are some argu- ments in favor of the latter solution. First, a compari- son with Silurian and Devonian jawless craniates, in particular the Anaspida, shows that most of these forms possessed numerous, but small and closely-set, branchial pouches. The closely-set external branchial openings of anaspids had been interpreted by Stensi6 (1964, fig. 28C) as indicating the presence of elonga- ted external branchial duct gathered into a bundle, in the same way as in some myxinoids. It may also indi- cate that the branchial pouches were very short, high and closely set. If, as generally assumed on various

grounds (Janvier 1981 ; Janvier & Lund 1983), the Petromyzontida are << rooted >> among anaspids sensu lato or are the sister-group of the Anaspida (sensu stricto), the presence of such a concentrated branchial apparatus in the early representatives of the group may not be surprising.

A

B

Fig. 2 - - Comparative representation of the branchial apparatus in the Recent (A) and Carboniferous (B) Petromyzon- tida. Outline of the branchial pouches. A, based on Marinelli & Strenger 1954 ; B, based on Bardack & Zan- gerl 1968.

Comparaison des proportions de l'appareil branchial chez un Petromyzontida actuel (A) et carbonif6re (B). Contour des poches branchiales en gris6. A, d'apr~s Marinelli & Strenger 1954 ; B, d'apr~s Bardack & Zan- gerl 1968.

Secondly, Hardistiella is regarded as the primitive sister-group of Mayomyzon + extant lampreys

P L A T E 1

Fig. 1 - - Petromyzontida gen, e t sp. indet., Lower Carboniferous, Namurlan, Bear Gulch, Montana. Specimen 4105, Carne. gie Museum of Natural History. Part (a) and counterpart (b) photographed dry. x 3.

Carbonif~re inf6rieur, Namurian, Bear Gulch, Montana. Sp6cimen n ° 4105, Carnegie Museum of Natural History. Empreinte (a) et contre-empreinte (b), photographi6es A sec.

Fig. 2 - - The same specimen. Part (a) and counterpart (b) photographed in water, x 3.

MSme sp6cimen. Empreinte (a) et contre-empreinte (b), photographi6es en immersion dans l'eau.

Fig. 3 - - Petromyzon marinus L., 100 mm larva, cleared and stained specimen, x 3. ol., olfactory capsule ; tr., trabecles.

Larve de 100 mm 6claircie et color6e. ol., capsule olfactive ; tr., trab6cules.

G e o b i o s

n ° 19, fasc. 5

P1.1

R. L u n d & Ph. Janvier

la

lb

2a

2b

3

~i ̧ i~i

I t r .

ol.

- - 652 - -

(Janvier & Lund 1983). I f this specimen belongs to the genus Hardistiella, this would mean that both Carbo- niferous lampreys have this type of branchial appara- tus and, thus, that it is a plesiomorphous condition for extant lampreys.

The exact number of branchial pouches in these early lampreys is difficult to decide. Bardack & Zan- gerl (1968, 1971) claimed that Mayomyzon possessed seven branchial pouches like extant forms, but the discovery of new material (Bardack & Zangerl 1971) seems to support a lesser number, perhaps only five. In the bear Gulch specimen, there are surely four pouch traces, and possible one or two more.

I f this second specimen is a larval individual, as sug- gested by the possible traces of the trabecles, then this concentrated branchial apparatus was already present in the ammocoetes stage in Carboniferous times. In extant larval lampreys, the branchial apparatus is, as in adults, very elongated in shape (pl. 1, fig. 3). Moroever, the absence of the large postbranchial seg- mented structures seen in the holotype of H. monta- nensis (Janvier & Lund 1983, ~t X ~) may support the possibility that these were traces of gonads, as the quality Of preservation of this part of the two speci- mens in equal.

CONCLUSIONS

The discovery of this new fossil lamprey -possibly a larval individual- confirms that the branchial appara- tus was considerably more concentrated and shorter in Carboniferous forms than in extant ones. Although

no fossil lamprey is known between the Carbonife- rous and Recent times, one may infer that the evolu- tion of the group since that time is marked chiefly by an increase of the volume of the branchial apparatus.

REFERENCES

BARDACK D. & ZANGERL R. (1968) - First fossil lamprey : A record from the Pennsylvanian of Illinois. Science, Washington, 1962, 1265-1267.

BARDACK D. & ZANGERL R. (1971) - Lampreys in the fossil record. In The Biology of Lampreys (M.W. HAR- DISTY & I.C. POTTER eds), Academic Press, London, 1, 67-84.

JANVIER P. (1981) - The phylogeny of the Craniata, with particular reference to the significance of fossil ~ agna- thans )). J. Vert. Paleont., Norman, 1(2), 121-159.

JANVIER P. & LUND R. (1983) - Hardistiella montanensis n. gen. et sp. (Petromyzontida) from the Lower Carboni- ferous of Montana, with remarks on the affinities of the Lampreys. J. Vert. Paleont., Norman, 2(4), 407-413.

STENSIO E. (1964) - Les Cyclostomes fossiles ou Ostraco- dermes. In Trait6 de Pal6ontologie (J. PIVETEAU 6d.), Masson, Paris, 4(1), 96-382.

M anuscrit d6finitif regu le 04.09.1986