- Email: [email protected]
Middle Devonian Thelodonti (Agnatha) from the Khush-Yeilagh Formation, North-East Iran
-- 889 --
M I D D L E D E V O N I A N T H E L O D O N T I (A GNA THA ) FROM THE KHUSH-YEILAGH FORMATION, NORTH-EAST IRAN.
by Suzan TURNER* and Philippe JANVIER**
Abstract New thelodont scales from the type section of the Khush-Yeilagh Formation, between Shahrud and Shahpasand (Iran), are described. They are provisionally referred to as Skamolepis sp. and Turinia cf. hutkensis. Together with T. hutkensis from South-East Iran and some undescfibed scales from the Givetian of Australia, these specimens are some of the youngest thelodont scales known to date, since they are of Lower Eifelian age.
R6sum6 Des 6cailles de Th61odontes d'un type nouveau et provenant de la coupe type de la Formation de Khush-Yeilagh, entre Shahpasand et Shahrud (Iran), sont d6crites. Elles sont provisoirement attribu6es ~ Skamolepis sp. et Turinia cf. hutkensis. Ces pi6ces repr6sentent, avec T. hutkensis du Sud-Est de l'Iran et quelques 6cailles in6dites du Giv6tien d'Australie, les 6cailles de th61odontes les plus r6centes connues ~ ce jour et sont dat6es de 1Eif61ien inf6rieur.
Introduction The thelodont scales described herein were discovered in 1975 by Dr. B. Hamdi (G.S.I., Tehran), in the basal part of the type section of the Khush-Yeilagh Formation, 2 km West of Khush-Yeilagh village (southern Mazenderan, Iran). They have been found in a carbonaceous sandstone layer which overlies the arkosic sandstone layer containing the "Khush-Yei!a~Main Fish Horizon (Khl)" (1). They were associated with actinopterygian scales resembling Orvikuina, oogones of charophytes and some conodonts suggestive of an Upper Emsian or Lower Eifelian age (Hamdi, pets. com., 1976). G.-M. Stampfli (2) and D. Brice et alii (3) recently published detailed accounts on the stratigraphy of the KhushYeilagh Formation, and suggested, following F. Bozorgnia (4), that the base of this formation is of Lower Eifelian age.
* The Hancock Museum, Newcastle upon Tyne NE2 4PT, England. ** Laboratoire de Pal6ontologie des Vert6br6s, Universit6 Paris VI, 4, place J ussieu,75230 PARIS Cedex 05, France.
G~obios n ° 12 - fasc. 6
p. 889 - 892, 1 fig.
Lyon, d~cembre 1979
- 890 The preliminary study of the "Main Fish Horizon" (1), which lies at the very base of this formation, leads to approximately the same conclusion [ it should be pointed out here that G.-M. Stampfli (2) and D. Brice et alii (3) referred erroneously this fish horizon to the base of the Padeha Formation ]. Consequently, it can be assumed that the age of these thelodont scales is Eifelian, and most probably Lower Eifelian. The thelodont-bearing layer is indicated "BS 89" on G.-M. Stampflrs log [(3), fig. 3]. The scales have been recovered by acetic acid preparation. They are mineralised and dark brown in colour. The histological structure has been studied with the aid of anise oil.
I.
Description
Three main scale forms are present : - scale A (fig. 1, A); - scales B and C (fig. 1, B and C) ; - scales D and E (fig. 1, D and E). Scale A is small, with a broken crown, neck and base. The crown outline is lozenge-shapedwithaplain rim, tapering to a posterior mid point which does not extend beyond the base. The neck is smooth, shallow anteriorly, deepening posteriorly as the crown rises to an angle of about 10°. The neck curves into a shallow base which forms a torus around a large pulp cavity. This is young thelodontidid scale, the dentine tubules rising from the single pulp canal. It may be a head scale or a pectoral flap scale. It is most similar to simple scales of Turinia which V.-N. Talimaa (5) has referred to T. polita. This species is only known from the Lower Devonian, but this simple scale form may not be restricted to any particular genus but may be typical of young scales in several thelodontidid genera, such as Apalolepis,
Nikolivia, Gampsolepis. Scale B is broken about midway across the base. There is a long crown rising from the mid-dorsal base at an angle of about 25 ° and extending beyond it. The crown is flattened and expands posteriorly. There is a raised central bifurcated ridge which curves down anteriorly into a shallow furrowed neck. Laterally, there are two dorsal side spurs, each with subsidiary ridges. Posteriorly and laterally the crown sweeps down at a steep angle into a broad moat-like neck. The posterior ventral surface of the crown has a central keel with at least four side ridges. The pulp cavity is large, widening anteriorly. Immersing the scale in anise oil, the central single pulp canal can be seen passing into the centre of the crown tapering posteriorly. Dentine tubules branch of this at right angles passing into the lateral lappets. This scale appears to be thelodontidid and most resembles those of Skamolepis (5). Scale C is similar to scale B. The base is not so wide and the anterior rim is more rounded. The crown is longer and the base forms a torus around the large ventral pulp opening. In anise oil there appear to be two lateral dentine canals branching and leading posteriorly from the main pulp canal, with dentine tubules coming off all three canals. This scale also resembles those of Skamolepis [(5), pl. 51, fig. 3, pl. 53, fig. 1 - 4 and pl. 54, fig. 3], but is more robust. Scale D is a large scale with a broken base. The crown is larger and, like scales B and C, extends posteriorly well beyond the base. Unlike these two scales, the crown tapers to a posterior point and the lateral spurs or lappets are absent. However, the ventral posterior crown has a mid keel and four paired lateral ridges as in scales B and C. Histologically, this is another young scale. In the crown form, it does resemble some scales of Turinia.
--
891
--
A2
C1
C
C3
D1
D2 .~:..":
n"
[,
.....
Fig. 1 -
Thelodonti
I
,,
.~:-::.... !..:::~..
I
gen. and sp. indet.
Base of the Khush-Yeilagh Formation (Lower Eifelian), Khush-Yeilagh, North-East lran. - A : possible thelodontidid head scale in external (A1) and lateral (A2) view ; - B and C : Skamolepis- like scales, in external (B 1 and C1), internal (B2 and C2) and lateral (B3 and C3) view; - D and E : scales resembling those of Turinia hutkensis, in external (D 1 and E 1), internal (E2) and lateral (D2 and E3) view. Specimens collectively numbered MGSI 50, and deposited at the Museum of the Geological Survey of Iran, Teliran.
Thelodonti gen. et sp. indet. Base de la Formation de Khush-Yeilagh (Eif61ien inf~rieur), Khush-Yeilagh, Nord-Est de l'Iran. - A : ~caille c6phalique pr6sum6e de Th61odontidide en vue externe (A 1) et lat6rale (A2) ; - B e t C : 6cailles de type Skamolepis, en vue externe (B1 et C1), interne (B 2 et C2) et lat6rale (B3 et C3); - D et E : ~cailles ressemblant fi celles de Turinia hutkensis, en vue externe (D 1 et E l), interne (E 2) et lat~rale (D 2 et E3). Sp6cimens num6rot6s collectivement MGSI 50, et d6pos~s au Mus6e du Service G6ologique d'Iran (T6h6ran).
-- 892 -Scale E is similar to scale D. This is the only complete scale. Its crown rises steeply from the posterior half of the base. There is a central raised platform on the crown tapering to a posterior mid point. The platform is curved anteriorly, bifurcated with a shallow central groove. There are two pairs of lateral lappets. The pair nearer the mid point taper into the posterior point and are widest mid way along the crown length, where they taper anteriorly into the wide moat-like neck. The outer pair of lappets expand from the posterior neck under the first set,but does not reach the mid point. The base is fiat, rounded posteriorly but elongated anteriorly into a long down-pointed spur. The pulp cavity is small and positioned on the postero-ventral side of the base. There appears to be a single pulp canal leading into the centre of the crown with branching dentine tubules radiating from this into the crown. This scale is mature histologically and also resembles some scales of Turinia, particularly in the presence of an anterior spur to the base. Scales D and E are most similar to Turinia hutkensis GOUJET & BLIECK (6).
II. Discussion These scales are thelodontidid all but one being young scales. They appear to represent two taxons but with such a small sample it is by no means certain that there may not be scales which grade between the two main forms. Scales B and C may belong to the genus Skamolepis and represent a new species. Scales D and E may belong to the same animal or represent a scale form of Turinia cf. hutkensis. Scamolepis has previously been described from the Emsian/Eifelian boundary in the U.S.S.R. and Spitsbergen (5). There are scales present in the Middle Devonian limestones of New South Wales, Australia, which also appear to belong to this genus. Turinia hutkensis has been found just below Givetian layers in the Kerman region (Iran) and may be Middle Devonian.
Thelodont scales have been found by Roger Dring in the Givetian Gnuedna Formation of Western Australia and are presently under study (S.T.).
Acknowledgements We are greatly endebted to Dr. B. Hamdi (Tehran) for the loan of the material belonging to the Museum of the Geological Survey of Iran.
References (1) (2) (3) (4) (5) (6)
BLIECK A. et alii. - Palaeovertebrata, Montpellier, (in press). STAMPFL1 G.-M. - Th~se Univ. Genbve, 1978, 329 p. BR1CE D. et alii - Riv. Ital. Paleont.,Milano, 84, 1978, p. 1 - 56. BOZORGNIA F. - N a t . Iranian Oil Co., Tehran, 1973, 158 p. KARATAYUTE-TALIMAA V.-N. -Mokslas, Vilnius, 1978, 334 p. BLIECK A. & GOUJET D. - A n n . Soc. geol. Nord, Lille, 1978, p. 363 - 372.
M I D D L E D E V O N I A N T H E L O D O N T I (A GNA THA ) FROM THE KHUSH-YEILAGH FORMATION, NORTH-EAST IRAN.
by Suzan TURNER* and Philippe JANVIER**
Abstract New thelodont scales from the type section of the Khush-Yeilagh Formation, between Shahrud and Shahpasand (Iran), are described. They are provisionally referred to as Skamolepis sp. and Turinia cf. hutkensis. Together with T. hutkensis from South-East Iran and some undescfibed scales from the Givetian of Australia, these specimens are some of the youngest thelodont scales known to date, since they are of Lower Eifelian age.
R6sum6 Des 6cailles de Th61odontes d'un type nouveau et provenant de la coupe type de la Formation de Khush-Yeilagh, entre Shahpasand et Shahrud (Iran), sont d6crites. Elles sont provisoirement attribu6es ~ Skamolepis sp. et Turinia cf. hutkensis. Ces pi6ces repr6sentent, avec T. hutkensis du Sud-Est de l'Iran et quelques 6cailles in6dites du Giv6tien d'Australie, les 6cailles de th61odontes les plus r6centes connues ~ ce jour et sont dat6es de 1Eif61ien inf6rieur.
Introduction The thelodont scales described herein were discovered in 1975 by Dr. B. Hamdi (G.S.I., Tehran), in the basal part of the type section of the Khush-Yeilagh Formation, 2 km West of Khush-Yeilagh village (southern Mazenderan, Iran). They have been found in a carbonaceous sandstone layer which overlies the arkosic sandstone layer containing the "Khush-Yei!a~Main Fish Horizon (Khl)" (1). They were associated with actinopterygian scales resembling Orvikuina, oogones of charophytes and some conodonts suggestive of an Upper Emsian or Lower Eifelian age (Hamdi, pets. com., 1976). G.-M. Stampfli (2) and D. Brice et alii (3) recently published detailed accounts on the stratigraphy of the KhushYeilagh Formation, and suggested, following F. Bozorgnia (4), that the base of this formation is of Lower Eifelian age.
* The Hancock Museum, Newcastle upon Tyne NE2 4PT, England. ** Laboratoire de Pal6ontologie des Vert6br6s, Universit6 Paris VI, 4, place J ussieu,75230 PARIS Cedex 05, France.
G~obios n ° 12 - fasc. 6
p. 889 - 892, 1 fig.
Lyon, d~cembre 1979
- 890 The preliminary study of the "Main Fish Horizon" (1), which lies at the very base of this formation, leads to approximately the same conclusion [ it should be pointed out here that G.-M. Stampfli (2) and D. Brice et alii (3) referred erroneously this fish horizon to the base of the Padeha Formation ]. Consequently, it can be assumed that the age of these thelodont scales is Eifelian, and most probably Lower Eifelian. The thelodont-bearing layer is indicated "BS 89" on G.-M. Stampflrs log [(3), fig. 3]. The scales have been recovered by acetic acid preparation. They are mineralised and dark brown in colour. The histological structure has been studied with the aid of anise oil.
I.
Description
Three main scale forms are present : - scale A (fig. 1, A); - scales B and C (fig. 1, B and C) ; - scales D and E (fig. 1, D and E). Scale A is small, with a broken crown, neck and base. The crown outline is lozenge-shapedwithaplain rim, tapering to a posterior mid point which does not extend beyond the base. The neck is smooth, shallow anteriorly, deepening posteriorly as the crown rises to an angle of about 10°. The neck curves into a shallow base which forms a torus around a large pulp cavity. This is young thelodontidid scale, the dentine tubules rising from the single pulp canal. It may be a head scale or a pectoral flap scale. It is most similar to simple scales of Turinia which V.-N. Talimaa (5) has referred to T. polita. This species is only known from the Lower Devonian, but this simple scale form may not be restricted to any particular genus but may be typical of young scales in several thelodontidid genera, such as Apalolepis,
Nikolivia, Gampsolepis. Scale B is broken about midway across the base. There is a long crown rising from the mid-dorsal base at an angle of about 25 ° and extending beyond it. The crown is flattened and expands posteriorly. There is a raised central bifurcated ridge which curves down anteriorly into a shallow furrowed neck. Laterally, there are two dorsal side spurs, each with subsidiary ridges. Posteriorly and laterally the crown sweeps down at a steep angle into a broad moat-like neck. The posterior ventral surface of the crown has a central keel with at least four side ridges. The pulp cavity is large, widening anteriorly. Immersing the scale in anise oil, the central single pulp canal can be seen passing into the centre of the crown tapering posteriorly. Dentine tubules branch of this at right angles passing into the lateral lappets. This scale appears to be thelodontidid and most resembles those of Skamolepis (5). Scale C is similar to scale B. The base is not so wide and the anterior rim is more rounded. The crown is longer and the base forms a torus around the large ventral pulp opening. In anise oil there appear to be two lateral dentine canals branching and leading posteriorly from the main pulp canal, with dentine tubules coming off all three canals. This scale also resembles those of Skamolepis [(5), pl. 51, fig. 3, pl. 53, fig. 1 - 4 and pl. 54, fig. 3], but is more robust. Scale D is a large scale with a broken base. The crown is larger and, like scales B and C, extends posteriorly well beyond the base. Unlike these two scales, the crown tapers to a posterior point and the lateral spurs or lappets are absent. However, the ventral posterior crown has a mid keel and four paired lateral ridges as in scales B and C. Histologically, this is another young scale. In the crown form, it does resemble some scales of Turinia.
--
891
--
A2
C1
C
C3
D1
D2 .~:..":
n"
[,
.....
Fig. 1 -
Thelodonti
I
,,
.~:-::.... !..:::~..
I
gen. and sp. indet.
Base of the Khush-Yeilagh Formation (Lower Eifelian), Khush-Yeilagh, North-East lran. - A : possible thelodontidid head scale in external (A1) and lateral (A2) view ; - B and C : Skamolepis- like scales, in external (B 1 and C1), internal (B2 and C2) and lateral (B3 and C3) view; - D and E : scales resembling those of Turinia hutkensis, in external (D 1 and E 1), internal (E2) and lateral (D2 and E3) view. Specimens collectively numbered MGSI 50, and deposited at the Museum of the Geological Survey of Iran, Teliran.
Thelodonti gen. et sp. indet. Base de la Formation de Khush-Yeilagh (Eif61ien inf~rieur), Khush-Yeilagh, Nord-Est de l'Iran. - A : ~caille c6phalique pr6sum6e de Th61odontidide en vue externe (A 1) et lat6rale (A2) ; - B e t C : 6cailles de type Skamolepis, en vue externe (B1 et C1), interne (B 2 et C2) et lat6rale (B3 et C3); - D et E : ~cailles ressemblant fi celles de Turinia hutkensis, en vue externe (D 1 et E l), interne (E 2) et lat~rale (D 2 et E3). Sp6cimens num6rot6s collectivement MGSI 50, et d6pos~s au Mus6e du Service G6ologique d'Iran (T6h6ran).
-- 892 -Scale E is similar to scale D. This is the only complete scale. Its crown rises steeply from the posterior half of the base. There is a central raised platform on the crown tapering to a posterior mid point. The platform is curved anteriorly, bifurcated with a shallow central groove. There are two pairs of lateral lappets. The pair nearer the mid point taper into the posterior point and are widest mid way along the crown length, where they taper anteriorly into the wide moat-like neck. The outer pair of lappets expand from the posterior neck under the first set,but does not reach the mid point. The base is fiat, rounded posteriorly but elongated anteriorly into a long down-pointed spur. The pulp cavity is small and positioned on the postero-ventral side of the base. There appears to be a single pulp canal leading into the centre of the crown with branching dentine tubules radiating from this into the crown. This scale is mature histologically and also resembles some scales of Turinia, particularly in the presence of an anterior spur to the base. Scales D and E are most similar to Turinia hutkensis GOUJET & BLIECK (6).
II. Discussion These scales are thelodontidid all but one being young scales. They appear to represent two taxons but with such a small sample it is by no means certain that there may not be scales which grade between the two main forms. Scales B and C may belong to the genus Skamolepis and represent a new species. Scales D and E may belong to the same animal or represent a scale form of Turinia cf. hutkensis. Scamolepis has previously been described from the Emsian/Eifelian boundary in the U.S.S.R. and Spitsbergen (5). There are scales present in the Middle Devonian limestones of New South Wales, Australia, which also appear to belong to this genus. Turinia hutkensis has been found just below Givetian layers in the Kerman region (Iran) and may be Middle Devonian.
Thelodont scales have been found by Roger Dring in the Givetian Gnuedna Formation of Western Australia and are presently under study (S.T.).
Acknowledgements We are greatly endebted to Dr. B. Hamdi (Tehran) for the loan of the material belonging to the Museum of the Geological Survey of Iran.
References (1) (2) (3) (4) (5) (6)
BLIECK A. et alii. - Palaeovertebrata, Montpellier, (in press). STAMPFL1 G.-M. - Th~se Univ. Genbve, 1978, 329 p. BR1CE D. et alii - Riv. Ital. Paleont.,Milano, 84, 1978, p. 1 - 56. BOZORGNIA F. - N a t . Iranian Oil Co., Tehran, 1973, 158 p. KARATAYUTE-TALIMAA V.-N. -Mokslas, Vilnius, 1978, 334 p. BLIECK A. & GOUJET D. - A n n . Soc. geol. Nord, Lille, 1978, p. 363 - 372.