Jurassic Angiopteris (marattiales) from north yorkshire

Rewew of Palaeobotany and Palynology, 51 (1987) 65 93

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Elsevier Science Publishers B V. Ams_terdam - - Printed In The Netherlands

JURASSIC ANGIOPTERIS (MARATTIALES) FROM NORTH YORKSHIRE C.R. H I L L

Department of Palaeontology, Br~t~sh Museum (Natural H~story), Cromwell Road, London SW7 5BD (U K) (Revised manuscript accepted February 26, 1986)

Abstract Hfl], C R, 1987 Jurassic Angtopter~s (Marattmles) from North Yorkshire Rev Palaeobot_ Palynol, 51 65 93

Angmpterm blacku Van Konunenburg-van Clttert from the Middle Jurassic of North Yorkshire is redescrlbed, based mainly on recently collected maternal It is similar to extant specms of Angmpter~s but differs in its more elongate and relatively pointed sporangm which give the sorus as a whole a distractive stellate appearance, the sporangm have a greater spore product]vity per sporangium and the pinnules lack the acuminate apex of the hvlng specms The taphonomy, palaeoecology and phylogenetms of the fossil are discussed PrehmInary expemments on rotting of extant ferns in neutral to acid cond~tmns, relevant to the interpretatmn of taphonomIc changes, are descmbed The shape of the sporangia and the pattern of cells on the]r walls in extant Angmpter~s are also descmbed, whmh provides a background of knowledge against which to interpret the relatmnships of the fossil objectively

Introduction Of the six extant genera of Marattiales only S w a r t z a n d Angwpter~s H o f f m a n n have been recorded as fossils. Mesozoic occurrences of Marattta are particularly numerous a n d w e l l d o c u m e n t e d (e.g H a r r i s , 1961) b u t f o s m l s o f Angmpter~s f r o m a n y s t r a t i g r a p h m horizon are few and poorly known. The only s u b s t a n t i a l r e c o r d a t p r e s e n t is t h e Y o r k s h i r e J u r a s s m s p e c i e s A n g i o p t e r i s blacki~ f i r s t des c m b e d by V a n C i t t e r t (1966) f r o m a s i n g l e f r a g m e n t o f f e r t i l e p i n n u l e . S i n c e 1970, a d d i tional specimens have been collected, which have provided additional reformation on ;ts morphology and have facihtated study of s p o r e s m s l t u A blacki~ p r o v e s o n d e t a i l e d c o m p a r i s o n ( A p p e n d i x II) t o be v e r y s i m i l a r t o extant species of Angmpteris but has some differences In particular, no other marattmlean fern has sorl of such a spreading, stellate

Marattla

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appearance Some of the differences are of taxonomic significance but others represent effects of preservation or reflect on the incomplete study of related extant species. The object o f t h i s p a p e r IS to a t t e m p t to d i s c m m m a t e w h i c h o f t h e d i f f e r e n c e s a r e t a x o n o m ; c a l l y s o u n d , to provide a revised description on this basis, and to e v a l u a t e t h e r e l a t i o n s h i p s a n d p a l a e o e c o l o g y o f A. blackn. S i m p l e r o t t i n g e x p e m m e n t s (App e n d i x I) h a v e p r o v e d h e l p f u l m r e a c h i n g a preliminary understanding of fern taphonomy i n n e u t r a l to a c i d e n v i r o n m e n t s .

Localities and material Almost all the spec]mens are from the type locahty, the Hasty Bank main plant bed ( N a t i o n a l g r i d r e f N Z 567 037; H i l l a n d V a n K o n i j n e n b u r g - v a n C l t t e r t , 1973) F i v e b l o c k s f r o m t h e s i l t s t o n e h o m z o n s (V 58747-51), w h m h i n c l u d e t h e l o n g e s t p l n n u l e k n o w n , w e r e col-

¢C',1987 Elsevier Science Pubhshers B V

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lected about 5 0 y e a r s ago by H. Hamshaw Thomas but were never described The poorly preserved holotype plnnule is also from the siltstone Persistent collecting at this locality between 1970 and 1976 yielded several hundred additional specimens, mainly from the uppermost meters of the siltstone in section C where A blackii is, very locally, fairly common Rare specimens were also collected from several horizons of the claystone of sections 1 and D. For locations of sections and relative abundance counts see Splcer and Hill (1979) and Hill (1980). Two additional pmnules (V.60635-6) were collected in 1976 from the Roseberry Topping plant bed (NZ 579 126), from the uppermost 50 cm of the slltstone. Besides the holotype, the State University of U t r e c h t collections (Museum of Palaeobotany and Palynology) include a further 7 specimens collected m 1972. All the fossil specimens figured here are in the Department of Palaeontology, British Museum (Natural History), London Exchanges have been made w i t h Nanking Institute of Geology and Palaeontology and with the Birbal Sahnl Institute of Palaeobotany, Lucknow (Further duplicate material is available, for exchange, on request ) Figured specimens and slides of extant material (Appendix II; Plate VI) are in the Botany Department, British Museum (Natural History)

Methods Standard methods of hght microscopy and scanning electron microscopy of compression/ impression material were used (Lacey, 1968). This included the use of transfers and Schulze's solution/dilute ammonia for preparation of sporangia and in situ spores. To increase their colour contrast for observation and for light photography, specimens were immersed under kerosene or crossed polar illumination was used. The thick nitrocellulose replica (see Plate III, 2) of the fertile pinnule impression shown

m Plate III, 1 was prepared as follows The impression surface was flooded with acetone and, while still wet, an acetone-based nail varnish was gently brushed on This was repeated to ensure t horough penetration of the varnish into cavities within the impression, in this case the buried tips of the sporangia. A solution of 1 1 "Durofix" glue amyl acetate was then applied until a tough film I mm thick was built up. This gives a thick and therefore rigid r e p h c a which is essential to prevent distortion during subsequent acid treatment. When set hard the replica (Plate III, 2) was pulled off the specimen and cleaned in 48% hydrofluoric acid for 24 hrs. Such replicas or "pulls" using materials dissolved in mobile organic solvents can give better penet rat i on of cavities in the substrate t han latex or silicone rubber, and at very high magnifications provide better resolution of detail (Hill, 1986). Unlike silicone rubber or latex they are permanent but are often more or less destructive of the original material For comparison with the fossil material (AppendlxII), herbarium specimens were bleached using 10% aqueous commercial bleach CDomestos"), followed by staining with gentian violet or 1% safranin m ethanol, subsequently differentiated by brief immersion in ethanol before transferring to water Safranm picks out cell walls with an acidic component, in this instance presumed to be lignm [For details of the bleaching technique see Hill and Camus (1986).] Rehydrated and stained son were subsequently detached from the lamina and mounted In glycerine jelly To prevent squashing, the cover slips were supported with tiny glass beads. Because it was impossible to heat the glycerine jelly without damaging the sori (Hill, 1983), some of these slides have partly dried out over an eight year period

Systematic description Order MARATTIALES Family MARATTIACEAE Berchtold et J S Presl, 1820; p 272 (see Plchl Serrnolh, 1970)

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G e n u s Angiopteris H o f f m a n n , 1796 n o m . c o n s . , s e n s u Hill et C a m u s , 1986

Angzopteris blacktl Van Konljnenburg-van Cittert (Plates I III, IV, 1 5, V, 1, 6 7; Figs 1 A-G, 2 A-D, 3 B) 1966 Angzopterts neglecta Van Clttert (non Chmg et Wang, 1959), pl IIB, holotype 1973 A neglecta Van Clttert, Hill and Van Konunenburgvan Clttert, p 60, name only 1975 A black~ Van Komjnenburg-van Clttert, change of name to correct the m v a h d homonymy of A neglecta Van Clttert with A neglecta Chmg et Wang

Description Frond assumed to be bl pm na t e but known only from fragments of final order plnnae and detached pinnules. Rachis of pinna incompletely known, finely striated longitudinally, up to 4 mm broad, with wings 0 5 1 mm broad at extreme apex. Plnnules elongatelanceolate, points of a t t a c h m e n t to rachm at intervals of up to 2 cm, angle of midrib to rachxs 40 80". Plnnule base poorly known, normally asymmetrically rounded, m a vegetative specimen which represents the extreme apex of a pinna or frond the basmcoplc margin is somewhat d ecu r r e nt on wing of rachis, pulvlni not preserved. Apical region of plnnule gradually tapered t h r o u g h 1 5 cm or more, apex itself obtusely pointed, not acuminate. Length of complete pinnules varied, 1 cm at apex of pinna to 7 cm further back; length of longest fragment of longer plnnules 8.3 cm, complete length of these 10 15 cm estimated from taper of margins. Width of middle region 4 12 mm, contracting more or less gradually In distal region to apex Margin usually flat, entire, or minutely and shallowly lobed (sometimes deeply), lobes equal in number to the veins and placed at their ends One fertile specimen, presumed to represent an abnormal pinna apex, has pinnatlfid divisions and thus appears deeply and coarsely lobed. Midrib more prominent on presumed abaxml surface, very finely striated longitudinally, up to 1.6 mm wide, tapering to pinnule apex. Veins simple or onceforked (very r ar ely twice-forked), arising from midrib at a small angle and curving away at

60-90 ° (20 60 ° near apex), reaching margin at a c o n c e n t r a t i o n of about 10 per cm (range 5--15 per cm). Point of forking usually near the midrib No fibrous strands seen between the veins. Fertile pinnules identical to vegetative but bearing two rows of sorl on abaxial surface Sori oval, situated over lateral vein or vein branches near pinnule margin, elongated in direction of veln; typically occupying about half the distance from mldrib to margin, 1.e half of the pinnule half-width, but occasionally i/3 and may be as low as 1/4 Sorus composed of 4-16, charactermtically 6-12, ovold sporangla~ each sporanglum attached separately at its base to the placenta, sometimes overlapping laterally, typically without lateral appresslon except near base. Sporangla spreading apart from one another distally to give sorus as a whole a stellate appearance. Sporangia typically broadest at or below the middle, narrowing distally to an obtusely pointed tip whlch is characteristically curved towards the ventral slde; normally twice as long as broad, 0.8 mm long×0.4mm wlde (range including more rounded immature or abortive sporangla 0 5 I.I × 0.3 0.6 mm) Spores shed through median longitudinal sht m ventral wall, sht slightly sunken, runni ng along most of length of wall Surface cells of whole sporangial wall longitudinally elongate, gradually becoming shorter towards the tip of the sporanglum, their walls uniformly thickened_ Spores at least 3000 per sporanglum, rounded, 20-30 #m wide; typically trilete but mark more or less asymmetrical_ E xm e about 1 pm thick, composed of a very thin continuous basal layer bearing closely placed wart-shaped granules; granules of uniform size (about 0.5-1 gm) both proximally and dmtally Neighbourmg granules often fused to form short rugulae. Holotype: No.1371, Museum of Pal aeobot any and Palynology, State Unlvermty of Utrecht, The Netherlands. Name: Honours the late Dr Maurice Black's discovery of the Hasty Bank plant bed in 1927 Hortzon and age: The exact stratigraphic

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Fig 1 A E S p o r a n g i a of Angtopterts blacku, scale b a r s 5 mm; A - C m a t u r e , D - E i m m a t u r e / a b o r t e d A C o m p r e s s e d d o r s l v e n t r a l l y , V 60588 B C o m p r e s s e d o b h q u e l y sideways, V 60588_ C C o m p r e s s e d sideways, V 60603 D, E C o m p r e s s e d d o r s l v e n t r a l l y , V 60589 F G D l a g r a m m a t m r e s t o r a t i o n s of h g h t l y c o m p r e s s e d (F) a n d h e a v i l y c o m p r e s s e d (G) fertile p m n u l e s of Angmpter~s blacktt, a p p r o x x 10 U p p e r r e g i o n of figures s h o w s l o n g i t u d i n a l s e c t i o n of l a m i n a (stippled), p a s s i n g t h r o u g h two s o n (black) H o m z o n t a l d a s h e d line r e p r e s e n t s p l a n e of s p h t t m g of r o c k m a t r i x on c o l l e c t i n g V e r t i c a l d a s h e d h n e s lead d o w n to e q u i v a l e n t p l a n v m w of sore, as s e e n on t h e p a r t a f t e r s p h t t m g _ T h e s p o r a n g i a in F a p p e a r b r o a d e r m r e l a t i o n to t h e i r l e n g t h t h a n t h o s e of G, s i n c e t h e s p o r a n g l a l apices in F are left burred m t h e c o u n t e r p a r t H - J D i a g r a m m a t i c views of e x t a n t Angtopterts s o r u s a n d s p o r a n g i a H P l a n view of sorus, a p p r o x × 15, s h o w i n g s p o r a n g i a m s e c t i o n t r a n s v e r s e to t h e i r long axis, x a n d y r e p r e s e n t m e d m n a n d t a n g e n t i a l l o n g i t u d i n a l s e c t i o n s s h o w n in I a n d J I is e q u i v a l e n t to A blacktt in F i g s 1 C a n d 2 C, J e q u i v a l e n t to Figs 1 A a n d 2_D, scale b a r s e a c h 5 m m

69 horizon of the Hasty Bank and Roseberry Topping plant beds is problematmal At Hasty Bank the mare bed occurs above the dark shale facms of the shallow marine Yorkshire Dogger F o rmatio n (Black, 1934, Rastall and Hemmgway, 1943) Based on ammonite occurrences elsewhere in N or t h Yorkshire these shales are considered to be of Aaleman, murchisonae zone age. The plant bed is separated from them by a sharp, weathered j u n c t m n presumed by Professor Harris to represent an unconformity_ At Roseberry the plant bed rests, still more unconformably, directly on weathered Lmssic shales of T o a r c m n age Both plant beds are succeeded by flUVlOdeltmc sediments of the Saltwick Formation ( = H a y b u r n F o r m a t m n of some authors, formerly Lower Deltaic Serms) These too may be A a l e m a n but without ewdence from ammonites may equally be considered to be younger, of Bajocian age. The sfltstones of the plant beds can be traced laterally into point-bar sandstones th at at least m fames terms may be assigned to the Saltwick For m at i on and have traditionally been so assigned. There is some redirect evidence, however, t hat these ear he s t of the fluvm-deltalc beds may be equivalent stratlgraphlcally to the sandstone facms of the Yorkshire Dogger ("Green Flags", ~Finkel House Group" etc. of Rastall and Hemmgway: for references and summary see Hemmgway, 1974). This evidence comes from relative abundances of mlcroplankton of marine origin m the plant beds (up to 10%), from distrlbutmn of supposed mangrove or otherwise pioneer plants and their drifted debris m the regmn as a whole, and from regional sedimentologlcal considerations as well as from the expected d m c h r o ms m of deltaic facms in general. The Dogger sandstone facies transitionally overhes the dark shales facms to the west, south and east of the Hasty Bank/Roseberry area and may represent delta-fringe clastics deposited from pioneer fluvio-deltaic channels, as at Hasty Bank and Roseberry, and whmh exploited the mare depo-basmal axis extending southeast to H a r t o f t in Rosedale (cf. Hemm g w ay and Riddler, 1982). The Green Flags

and their varied lateral equivalents, as with the dark shales, are dated by ammonites as murchtsonae zone (Cope et a l , 1980). This suggests both t h a t the famous inland plant beds at Hasty Bank and Roseberry Topping are of murchlsonae (Aalenian, Yorkshire Dogger) age, r a t h e r than Bajocian, and t hat they represent the earhest fluvlo-deltam sediments known from the Yorkshire basin. Compartson: Other records of fossils attributed to Angtopteris are few. Four species have been recorded from the Upper Trlas of China A antiqua Xu et Chen, A yungjenensts Xu et Chen (Xu et al., 1974, 1979), 9A taentopterotdes Yang (1978) and 9A hongniens~s Chen et Duan (Chen et a l , 1979) All are from Slchuan as that region is now defined. Angtopterts yungjenensis, 9A. taentopterotdes and 9A hongntens~s are known from vegetative materml only Although resembhng Angtopterts m form and venat i on they also resemble fossil Marattta specms in these characters and would thus appear to be Imperfectly distinguishable from such material in the vegetative condition. Furthermore, pinnule dimensions and details of venation are not particularly useful characters for separating extant specms of Angtopteris from Marattia there is considerable generic overlap All three of these Chinese specms, known only from vegetative material and characterlsable solely by reference to such characters, are therefore doubtfully attributable to either Angtopterzs or Marattia. Ang~opter~s antiqua in contrast is fertile. It is descmbed as having compact sorl of 5-8 sporangm situated over the lateral veins next to the plnnule margin. The sori occupy only a very small proportion of the lamina Qmte u n h k e normal Angtopterts, however, the sporangm are said to be radmlly arranged m the sorus, which is of exceptionally small s~ze, 05 0.6mm in diameter. The width of the sporangm w~thin the sorus is presumably less than half this, though no measurements are given, and is thus exceptmnally small These dlmensmns, together with the radml orgamsation of the sori, may indicate t hat A. anttqua is an abnormal, immature or abortive specimen

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such as may sometimes be seen in living material, r a t h e r than a distinct species of fundamental phylogenetlc sigmficance as claimed by its authors. U n f o r t u n a t e l y the pubhshed figures of A ant~qua do not show details of the sor~ clearly. Original photographs, kindly supphed by Dr Zhang Caifan, are of good q u a h t y but indicate that preservatmn is poor, and they look still less convincingly like Angiopteris than the published photographs Specimens were not available on loan for direct study.

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Of the specms of Marattza assocmted m the field with A antiqua, M. antiqua (sic) Chen et Duan (Chen et al., 1979; Chen and Duan, 1981) appears to be different from ;t but not strikingly so. The lateral veins and fibre bundles are more distract and the pmnules are broader, though as discussed above such vegetative characters are genermally of hmlted use The synangm are longer, though still troy, usually only 1 5 mm long and are described as rounded to elhptmal m shape. Once more, this radial orgamsatmn of synangm (which is generally found only m

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Fig 3 A E x t a n t Angmpter~s B R e c o n s t r u c t i o n ofAng~opter~s black~, scale b a r s 5 m m C o m p a r e w i t h Fig 2 E P m n u l e form was taemopter~d Fig 2 A D Angzopter~s blackll A P m n u l e s h o w n also m P l a t e V, 7, in w h i c h m o s t of t h e l a m i n a h a s d i s a p p e a r e d a n d the v e i n s a n d sorl h a v e b e c o m e d i s p l a c e d from t h e i r u s u a l position; V 60599, × 4 B P m n a t f f i d p m n u l e m P l a t e I, 3, s h o w i n g c o a r s e lobes w i t h well-preserved m i n u t e l y lobed m a r g i n s at l, s o m e of t h e c o a r s e lobes m a y h a v e been a c c e n t u a t e d by t e a r i n g (t) of t h e ~ m u s e s b e t w e e n t h e m , V 60625, a p p r o x × 2 5 C, D_ R e c o n s t r u c t e d m a t u r e s p o r a n g i a of A blackLl m m e d i a n l o n g i t u d i n a l (x) a n d t a n g e n t m l l o n g i t u d i n a l sect*on (y), scale b a r s 5 m m (see Fig 1 H for k e y to p l a n e s of section) E Eoang~opterts andrews~t M a m a y , r e d r a w n from M a m a y (1950), scale 5 m m C o m p a r e with Fig 3 A, B P m n u l e form was pecopterold

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PLATE I

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abnormally developed extant species of Marattia), coupled with their small size, indicates probable arrested development of pinnules at the extremit,,s of their normal range of variatmn. The problem if so is to identify what that normal range is. ~Marattia antiqua" may be merely an extreme var m nt of the widespread Asian specms M. astatica Kawasaki, whmh occurs assocmted with it in Baodmg; and "A ant~qua" may possibly represent a stall more extreme form Marattia asiattca is a normally developed and qmte typical Marattia, apparently representing a good species. This hypothesis of arrested and abnormal development for m at er m l I have not studied directly is entirely conjectural. It could be tested however by examining the conditmn of m situ spores as discussed below for A blackn and also by rumple statistical study based on unbmsed large collections of field assemblages In the latter case, my prediction is t hat typmal M. astattca as defined by Chen et Duan (1981) would represent most of the specimens, connected in the same sample by a series of increasingly rare or locahsed (and increasingly aberrant) forms, passing t hr ough ~'M. anttqua" to the extreme form '~A. antiqua" This does not rule out the possibility t hat some of these interesting specimens from China may be attmbuted mghtly to Angmpteris, but the exact positron remains to be demonstrated. The only other megafossil named Angmpteris is A. ruztncin~ana Palamarev, Petkova et Usu-

nova (1975) from the Tertiary (Upper Miocene) of Bulgaria The form and venation of its pinnules is quite unhke normal Angmpteris, as is the occurrence of presumed hmr bases on the adaxlal epidermis. The shapes of the upper epidermal cells and sizes of the guard cells also differ from those of extant species. The specms is clearly not correctly attributed to Angiopterts and is probably an Angiosperm leaf fragment_ Amongst Jurassic ferns t hat have been attributed to other genera the nearest is Marattmps~s boweri Seward (1911) from the Upper Jurassm of Sutherland, Scotland. It closely resembles A. blackii in the size, shape and venation of its pmnules. A very few spores obtained from V.12113 are almost identical to those of A. blackd (and thus u n h k e those of Marattta). The sori are so ill-preserved, however, t hat I am unwilling to identify this materml other t han as ?Angiopteris sp No other Jurassic fern known to me resembles A blackn when fertile. Marattza anghca (Thomas) Harris (1961) differs m its synangiate sorus, its mainly monolete spores and in having fibrous strands preserved between the veins. The pmnules are charactemstically much broader. Well preserved pinnules are therefore readily distinguished even when vegetative by their size and presence of fibrous strands, but poorly preserved small pmnules may resemble those of A. blackii. Such specimens can sometimes be attributed to one or the other species on grounds of field assocmtlon

PLATEI

Angmpter~s blacktt V a n K o n u n e n b u r g - v a n C l t t e r t 1 N o r m a l l y developed fertile p i n n a t e specimen; p m n u l e s still a t t a c h e d to o n e side of r a c h l s o n l y Note form of p m n u l e a p m e s V 60630, × 1 2 A b n o r m a l l y d e v e l o p e d v e g e t a t i v e p i n n a or f r o n d apex s h o w i n g w i n g e d r a c h l s L o w e r m o s t p m n u l e h a s a c o a r s e b a s a l lobe on t h e b a m s c o p l c m a r g i n V 60631, × 2 3 Deeply lobed ( p m n a t l i l d ) p m n u l e , see also F i g 2 B V 60625, × 1 4 P m n u l e s h o w i n g a s y m m e t r i c a l l y r o u n d e d b a s e a n d well p r e s e r v e d sorl of 6 - 8 s p o r a n g i a c o m p r e s s e d w i t h o u t t i l t i n g Lovls C o l l n , V 58551, × 2 5 G r a d u a l l y t a p e r e d p m n u l e apex, sorl c o m p o s e d of a b o u t 12 s p o r a n g i a w h i c h are m o s t l y c o m p r e s s e d w i t h o u t t i l t i n g V 60626, × 2 6 T h r e e p m n u l e s , two s h o w i n g t h e o b t u s e l y p o i n t e d p m n u l e apex D a r k e r r i n g s d e h m l t a r e a s of p r e s u m e d n e c r o s i s referred to in t h e text (see also P l a t e V, 1) V 60600, × 2 7 P m n u l e f r a g m e n t s h o w i n g t i l t i n g of sorl m d l r e c t m n t o w a r d s top of p h o t o g r a p h V 60608, × 3

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PLATE II

2

with the fertde pmnules, but at horizons where both specms occur together they can only be considered indeterminable. Pmnules of Cladophlebis aktashensts Turutanova-Ketova (Harms, 1961) are somewhat similar but have typically twice-forked veins and a more slender mldmb Discussion In attempting to describe A. blacki~ objecUvely it became clear that several of its characters (or lack of them) result from taphonomic 1 factors. This is now discussed, together with ewdence of posmble pathological attack and aspects of sporanglal development. The fossd is then compared with extant species and its phylogenetic status, nomenclature and palaeoecology are evaluated. Sporangtal shape: The shape of the sporangm of A. blackti is interpreted on the basis of Walton's compression theory (Walton, 1936, Rex and Chaloner, 1983). Sporangia of A blacki~ that are compressed dorsiventrally (Plate II, 3, 4, Plate III, 3-6; Plate IV, 3; Fig 1 A), whmh is usually the case, show their outline as it would have been originally m dorsiventral vmw (whdst in side view the shape is much flattened). The original shape m side view is seen only m sporangia at the ends of tdted sorl (Plate IV, 4, 5 at left; Figs.1 B, C) As the width of sporangia seen in these different planes of compression is equal I conclude that they were omgmally more or less c;rcular m transverse section, at any rate I T a p h o n o m y is the s t u d y of the processes (e_g decay transport, deposltmn, dmgenesls) i n t e r v e n i n g b e t w e e n the death of an o r g a m s m and its final state of p r e s e r v a t m n as a fossil

distally to the very basal region (Flg.3.B) This is supported by the absence of a thickened edge (compression border) from mature sporangia (Walton, 1936) Sporangia compressed sideways show that the dorsal wall of the sporangium is consistently more strongly convex than the ventral (Plate IV, 4, 5, Flgs.lB, C). Although less obvious this curve is still seen even m sporangia otherwme much flattened by dorsi-ventral compression, suggesting that most of the pmnules were preserved upside down compared to their pomtmn m hfe (Plate III, 2, 5, 6) As exposed on the parts, more than 95% of the sporangm appear to have lost their apices. Pmnules m whmh compression after burial was relatively shght show t h a t the sporangia stand away from the lamina at an angle of up to 30 °. (Presumably they were at a greater angle than this m hfe, more hke those of the h w n g species.) In such pinnules the parting planes normally pass t h r o u g h the substance of the sporangm. When the specimens are spht during collecting the tips of the sporangm are therefore broken off and left embedded at a low angle m the matrix of the counterpart, hidden from direct view (Plate III, 1, Fig I_F). Therefore the residual parts of the sporangia exposed flush with the surfaces of part and c o u n t e r p a r t often look shorter than they actually are, and appear broader m relation to their length (compare Plate III, 1 and III, 2). In the rare examples of more heavily compressed specimens the parting planes normally pass over the top of the more flattened sore Thus, m these pmnules the shape of the whole unbroken sporangm may be seen from the exposed surfaces of both part and c o u n t e r p a r t (Plates I, 3, 4, 7; II, III, 4, 6, IV, 3 5, Flg.I.G)

PLATE II

Angmpterts blackn V a n K o n u n e n b u r g - v a n C*ttert 1

Portion of a p m n u l e s h o w i n g venat*on and tilted sore In the lower region of the photo the t d t r i g h t of the m*dnb is m opposite directions M M J o n e s C o l l n , V 60640, × 4 2 Two s o n at b o t t o m mght of Plate II, 1, s h o w i n g shape of s p o r a n g i a and their dehiscence slit, 3, 4 P o r t i o n of p m n u l e m w h i c h the s o n are preserved w i t h o u t tilting and several stall r e t a i n t h e i r very clearly t h e i r elongate, more or less pointed shape and t h e stellate a p p e a r a n c e of the s o r u s ×4, 4, ×20

of the sore to left v e r s u s × 20 tips u n b r o k e n , s h o w i n g Lovls C o l l n , V 58554, 3,

76

PLATE III

77

This example of p r e s e r v a t m n in Angmpteris resembles t h a t for fossil lycopod shoots described by Rex and Chaloner (1983, text-fig.3) Cell outhnes of sporangial wall: H e a w l y compressed specimens hke those just referred to occur most freqently m the lower horizons of the claystone at Hasty Bank, where A. black~ is exceptmnally well preserved. Such pmnules show the outlines of the surface cells of the sporangmm wall with some clarity, the cell walls forming ridges and grooves on the compression and impressmn surfaces. These specimens usually split to expose only the ventral wall, and m m at ur e sporangm this shows more or less uniformly elongated cells becoming gradually shorter towards the sporang~al tip (Plate III, 3-6). Cell details of the dorsal wall were determined only with difficulty, from sporangia compressed sideways, from transfers, and by degagement, which show th at the surface cells over the whole of the dorsal wall appear to be similar m shape and m the thickness of their walls to those of the ventral, though ~t has so far proved impossible to prowde pubhshable photographic ewdence Immature sporangia and spores" Sporangia presumed to be immature or abortive were seen m only a few pmnules, mostly on block V 60589. The sporangia are uniformly small, either rounded or oval m shape and contain compact spore masses (Flgs.l.D, E) Using u l t r a s o m c w b r a t m n these proved impossible to separate without damage The spores have

little or no preservation of the granular sculpture. Spores: About 10% of the specimens examined for spores yielded spore masses, others had stray spores only. The spores generally show one or two arcuate compression folds (Plate IV, 1, 2). The number of spores per sporangmm was counted from five undehlsced sporangm of V 60587 macerated in cavity shdes. These sporangia were considered to have been mature and normally developed since they are of a typical size and the spore masses separated fmrly readily into individual spores with welldeveloped sculpture in the ammonia stage of, m a c e r a t m n It was impossible to prevent some loss of fragments during p r e p a r a t m n of the materml for counting and the counts are certainly too low. The two higher counts of about 3000 (highest exact count 3065) are more hkely to represent the real spore product m n than the lower three of about 1200, 1700 and 2000 A fuller description of the m sltu spores of A. blackiL and comparison with dispersed spores is to be pubhshed separately. FLbrous strands (venuli recurrentes): Fibrous strands between the lateral veins and runni ng parallel to them are not clearly visible in A_ black~ However, although occurring m most extant species a few lack them. Of more slgmficance is their widespread occurrence m Mesozoic Marattza, since scarcely any extant species of that genus has them (Harris, 1961 p 72; see also Hill et al., 1985) It ~s therefore of interest t hat the photographs of ~'Angmpter~s

P L A T E III

Angmpterzs black~L V a n K o m j n e n b u r g - v a n C l t t e r t 1, 2 I m p r e s s i o n s of h g h t l y c o m p r e s s e d sorl viewed before a n d after r e p h c a t l o n m m t r o c e l l u l o s e , V 60593 1, s h o w s o r i g i n a l s p e c i m e n p h o t o g r a p h e d m o b h q u e h g h t , i l l u s t r a t i n g a p p a r e n t l y s h o r t a n d s q u a t s h a p e of s p o r a n g i a , t h e i r tips are m o s t l y b u r i e d m t h e m a t r i x , × 20 2, r e p h c a c o a t e d w i t h m a g n e s m m oxide a n d p h o t o g r a p h e d m o b h q u e h g h t , s h o w i n g r e s t o r e d s h a p e of s p o r a n g i a w h i c h is m o r e e l o n g a t e a n d p o i n t e d t h a n m 1 T h e d e h i s c e n c e s h t s , s o m e of w h i c h gape open, are clearly visible, × 23 3, 4 S E M views of s p o r a n g i a from r e p h c a m 2, s h o w i n g t h e i r shape, d e h i s c e n c e s h t , a n d e l o n g a t e cell o u t h n e s of v e n t r a l wall_ L u m p s at tips of t h e s p o r a n g i a m a y be a r t e f a c t s 3, a p p r o x × 50, 4, × 80 5 D i r e c t S E M view of l m p r e s s m n of v e n t r a l wall n e a r tip of a s p o r a n g m m , s h o w i n g c u r v e of tip at left a n d o u t l i n e s of e l o n g a t e cells, a p p r o x × 130 6 Direct S E M view of h e a v i l y c o m p r e s s e d sorus, s h o w i n g c o m p r e s s m n l u m p at tip of t h e m o s t c o m p l e t e s p o r a n g m m Note o v e r l a p of b a s e of s p o r a n g m m at b o t t o m r i g h t over t h a t to left of it A p p r o x × 50_

78

PLATE IV

1 5 Angmpter~s black~ V a n K o n u n e n b u r g - v a n Clttert 1 2 3 4 5

6

Light m l c r o g r a p h of m sltu spores Note c h a r a c t e m s t l c a r c u a t e folding as a r e s u l t of c o m p r e s s i o n Shde V 60602, p r e p a r e d from CRH 2/2A, x 1600 SEM view of m sltu spore, a r c u a t e fold at left, a p p r o x × 2000_ S p o r a n g m m compressed dorslventrally, V_62058, × 25. S p o r a n g m m compressed o b h q u e l y sideways, s h o w i n g s t r o n g e r curve of dorsal wall compared to ventral, V 62058, × 25 Whole sorus tilted sideways, showing stellate appearance of sorus and elongate sporangia with their dehiscence hnes refilled with matrLx Lateral veto at bottom left, s p o r a n g m m above it compressed obhquely sideways as m 4 V 60606, approx × 20 Angmptens s p , extant, Chelsea P h y s m G a r d e n s n , p l a n t since deceased Comparable view to 5 of h e r b a r m m maternal r e h y d r a t e d w i t h commercial bleach and stained w i t h g e n t i a n violet Note the relatively c o m p a c t s o r u s composed of s q u a t s p o r a n g m t h a t are b r o a d e s t above the middle w h e r e a s t h o s e of 3 5 are b r o a d e s t below the middle A p p r o x × 30

79

-

antiquo" supplied by Dr Zhang show fibrous strands clearly, adding further to the argument though in a solely Mesozoic context - - t ha t it is a Marattia r a t h e r t han an Angioptens. Locahsed necroszs of the lamina" Circular or oval, r a t h e r thick rings of coal up to about 5 m m ~n diameter occur m six pmnules (PlatesI, 6, V, 1). They are also visible m omgmal photographs of "A ant~qua" from the Chinese Trias. Within the ring the lamina has apparently necrosed and this area presumably represents what in the Jurassic was a hole m the lamina, now infilled with matrix Cawtms of similar shape and size, delimited by a thickened and brown-coloured mm of Ussue, occur occasionally in pmnules of living species (Plate V, 2, 3). Sometimes m these only the mesophyll is destroyed and one or both of the epidermises is left intact (Plate V, 3). Presumably on compressmn the rams would form a thick ring of coal like that seen in the fossil Such localised necrosis of lamina tissue is in fact widespread in living plants and appears to have many causes, ranging from wind damage and viral or bacterial infectmn to insect or funga] attack (e.g. Miller et al., 1984). From a specimen of A. opaca Copeland [L.S. Gibbs (?)887, Fui (BM)] similarly necrosed to those in P l a t e s V , 2, 3, Dr D H a w ks w or t h (pers. comm., 1977) has identffied m y c e h u m (possibly of a rust fungus) as the hkel y causal agent I have seen similar locahsed dead areas in a specimen of Ctenis from the Middle Jurasmc of Oxfordshire. Similar but very much smaller holes have been reported by Watson (1977) m Pseudofrenelops~s varians (Fontame) Watson and may be fmrly widespread m fossil leaves. Tilted son. Besides other aspects of taphonomy, an interesting feature of A blacki~ is the occurrence of tilted sorL This also occurs m Maratt~a anghca and Qastmia Hill, Wagner et E1-Khayal (1986) (A. blackiv Plates I, 7; II, 1, 2; IV, 4, 5; M anghca. Plate V, 4, 5, Harms, 1961). The tilting occurs in about a third of the specimens of A blacki~ and is directed equally towards the bases of the pmnules and their apices. Out of a sample of 200pinnules a basally directed tilt was seen in 22 and an -

apical one m 24, whilst a few pmnules show tilting m both directions (Plate II, 1) Possibly the sporangia were tilted m life and permsted like this during bumal, but if so I would expect more of the specimens to show such tilting, with a marked bias m direction of the tilt towards either the pmnule base or apex Moreover, such tilting is not seen in living Angiopter~s or (most species of) Marattla I beheve instead t hat it was produced in the fossils by currents acting on the waterlogged, somewhat decayed and therefore softened maternal, either before burial or during its early stages (see Appendix I). Other post-mortem changes: In most of the pmnules the tissue between the veins has disappeared (e.g Plates I, 5, II, 3; V, 1, 6, 7) In some this has been caused by recent weathermg and in others by loss of fossil substance during and after collecting In several, however, the veins have become either widely separated from one anot her or squashed together at up to 20 per cm, and sometimes they have become widely displaced from their usual angles to the mldmb (Plate V, 1, 7; Fig 2.A). In places within some pmnules a whole group of otherwise normal looking veins has become detached as a u m t and then somewhat separated from the mldmb (Plate V, 7; Fig 2.A). The mldmb too m some cases has become separated into strands and the strands may be widely shifted apart from one anot her (Plate V, 6). Where the pinnules lie flat on the bedding planes such displacements must have occurred before final compresmon, following disintegration of the waterlogged mesophyll Amongst other Hasty Bank specms such extensive post-mortem changes are seen only in the related fern Marattm anglica (Plate V, 4, 5). Two explanations seem possible Either A blacku and M. anghca may have been carried somewhat further compared to other ferns m the fluvial channels and their overbank sediments at Hasty Bank and Roseberry, because they grew further away (and processes causing post mortem changes thus had longer to act); or they may simply have been more susceptible to such changes for anatomical or other

80

PLATE V

3w

8

81

r e a s o n s i n h e r e n t to them. I t is of i n t e r e s t to d e t e r m i n e w h i c h is the m o r e likely T h e field e v i d e n c e is weak: p i n n u l e s s h o w i n g no post mortem change occur together with those that do a n d t h e i r o v e r a l l f r a g m e n t size a n d robustness b o t h a p p e a r r o u g h l y s i m i l a r to t h o s e of o t h e r H a s t y B a n k ferns. C o n s i d e r i n g t h e locallsed o c c u r r e n c e of A. blacki~ at H a s t y B a n k a n d R o s e b e r r y T o p p i n g this indicates, if anything, t h a t a s i g n i f i c a n t l y l o n g e r d i s t a n c e of t r a n s p o r t IS u n l i k e l y . F o r r o t t i n g e x p e r i m e n t s r e l e v a n t to this p r o b l e m , please r e f e r to A p p e n d i x I.

Comparison with extant species of Angiopteris P i n n u l e s of A. blackd a g r e e w i t h t h o s e of s e v e r a l living species of Anglopteris in t h e i r gross form, d i m e n s i o n s , midrib, m a r g i n a n d v e n a t i o n . T h e basra f o r m of the s o r u s is also similar, w i t h a n u m b e r of l a r g e s p o r a n g i a a r r a n g e d In an o v a l s o r u s w h i c h e x t e n d s a l o n g the vein I n m a n y living species the n u m b e r of s p o r a n g i a in the s o r u s is m u c h g r e a t e r , t h o u g h in o t h e r s - - for e x a m p l e A pruinosa K u n z e - it m a y be as low as 4 12 as in A. blackn (Plates V, 8, VI, 1, 2, cf. Xu et al., 1974, 1979) In m o s t living species the sorus o c c u p m s a m u c h n a r r o w e r p r o p o r t i o n of the b r e a d t h of the

l a m i n a (Plate VI, 1), b u t a few are s i m i l a r (Plate V, 8) In t h e i r size, s h a p e and o r n a m e n t a t m n t h e spores of A blacktz are a l m o s t i d e n t i c a l to those of living species A n u m b e r of c h a r a c t e r s of A black~t differ f r o m t h o s e of e x t a n t m a t e r i a l , t h o u g h as discussed a b o v e some of t h e s e h a v e p r o b a b l y r e s u l t e d f r o m h m l t a t i o n s or effects of p r e s e r v a tion, s u c h as the a p p a r e n t l a c k of fibre bundles, o c c u r r e n c e of tilted sori a n d a r c u a t e folds of the spore wall. A few o t h e r differences c a n be a c c o u n t e d for by a b n o r m a l i t y of d e v e l o p m e n t whilst a residue of a few c h a r a c t e r s a p p e a r s on p r e s e n t e v i d e n c e to r e p r e s e n t differences of taxonomic significance (1) Further preservational dtfferences: Bemdes the c h a r a c t e r i s t i c t h o u g h n o t u m v e r s a l occurr e n c e of fibre b u n d l e s all h v l n g species b e a r tiny h a i r - l i k e scales on the u n d e r s u r f a c e of the pinnules, n o t a b l y a r o u n d the sorus S u c h scales h a v e n o t b e e n seen in A. blackii E v e n ff o r i g i n a l l y p r e s e n t t h e y are so d e l i c a t e as to m a k e t h e i r p r e s e r v a t i o n m the Y o r k s h i r e Jurassic unlikely, and their absence from A blackd is n o t n e c e s s a r i l y o r i g i n a l T h e p i n n u l e m a r g i n of A. blackil is r a r e l y c l e a r l y p r e s e r v e d a n d it m o s t often a p p e a r s to be flat and entire. S o m e t i m e s , h o w e v e r , it is r e c u r v e d , t h o u g h the c u r v e is d i r e c t e d e i t h e r u p w a r d or d o w n w a r d and s o m e t i m e s is m b o t h

PLATE V 1,6,7 1 6 7

2,3 2 3 4,5 4 5 8

Anglopter~s blackll V a n K o n u n e n b u r g - v a n C l t t e r t P l n n u l e s h o w i n g p a r t i a l loss of l a m i n a t i s s u e b e t w e e n t h e v e i n s a n d c i r c u l a r to oval a r e a s of p r e s u m e d necroms, e x a c t form of l o b m g of m a r g i n p o s s i b l y a l t e r e d by water-wear_ V 60600, a p p r o x × 3_5 P m n u l e m w h i c h the l a m i n a b e t w e e n t h e v e i n s h a s m o s t l y d m a p p e a r e d a n d the midrib h a s b e c o m e s e p a r a t e d into two s t r a n d s w h i c h h a v e drifted a p a r t R o s e b e r r y Topping, V 60635, x 4_ P m n u l e m w h i c h t h e l a m i n a h a s m o s t l y d m a p p e a r e d a n d t h e v e i n s h a v e drifted o u t of t h e i r u s u a l p o s i t i o n (see also Fig 2 A) A t top left a s e g m e n t of i n t a c t l a m i n a (arrowed) h a s b e c o m e d e t a c h e d as a u m t from t h e midrib at r i g h t V 60599, x 3 P m n u l e s of e x t a n t Angmpter~s s h o w i n g n e c r o s e s c o m p a r a b l e to t h o s e of A blacku A evecta H o f f m a n n , F a u n e 358, T a l w a n (BM), × 2 N o t e a c u m i n a t e p m n u l e apex c o m p a r e d to t h a t of 1 A w a l h c h m n a Presl, J P H o o k e r et T _ T h o m s o n 351-d, I n d m n C o l l e c t m n (BM), × 2 Marattta a n g h c a ( T h o m a s ) H a r m s S y n a n g l a tilted s i d e w a y s a n d l a m i n a lost from b e t w e e n t h e v e i n s L o w s Colln_, V 62045. × 3 S y n a n g m h k e t h o s e of 4 b u t s o m e w h a t d i s p l a c e d from t h e i r o r i g i n a l p o m t m n on t h e l a m i n a , V 62046. × 3 Angmpter~s pru~nosa K u n z e , M m h o h t z s n , Dec 1882, P h l h p p l n e s (K) Sore c o m p o s e d of r a t h e r few s p o r a n g m a n d o c c u p y i n g a b o u t 1/3 to 1/2 of the p m n u l e half-width, c o m p a r a b l e m t h e s e c h a r a c t e r s to A blackzz, × 2

82

PLATE VI

III

6

0

83

dlrectmns within one pinnule. Except where preservation is unusually good, a truly entire margin may be difficult to distinguish from such a recurved one (which may have been lobed). Certainly in some pmnules the margin is finely lobed (Plate I, 6; V, 1; Fig.2.B), with one lobe at the end of each veto as in extant species, though often rather more rounded. In some of these the lobes may have been rounded off by uneven wear of the pinnule margin, owing to the wear resistance of veins relative to intervening mesophyll. In others (e.g. Fig.2 B) the preservation is sufficiently good to lndmate that such loblng was certainly original. The mare uncertainty, therefore, concerns the extent and shape of lobing in the pmnules as a whole, and whether the pinnules were typically lobed or the lobes typically rounded. Similar uncertainty apphes to the few specimens that show evidence of the bases of the pmnules. Some of these may have become rounded by water wear rather t h a n representing the omginal shape In contrast, several specimens (including two in Utrecht, Van Konqnenburg-van Clttert, pers. comm., 1985) show the pinnule apmes clearly and I am confident that these were obtusely pointed rather than omgmally acuminate and subsequently rounded off by water wear.

The spores of A. blackd differ from those of hvlng species mainly m their arcuate folding and in the lack of a perispore Perispores are rarely preserved m fossil spores (Tschudy and Scott, 1969), and their absence is therefore not considered taxonomically significant. (2) Abnormal specimens Two of the specimens that represent the apex of a frond or pinna appear to have developed abnormally (Plate I, 2, 3) The fertile example m PlateI, 3 and Fig.2.B, is better descmbed as pinnatffid rather than pinnate. It has coarsely rounded lobes several mm broad which appear to be original rather than products of water wear, though there is evidence of tearing of the lamina between some of them. Occasmnal herbamum specimens of extant Angiopteris show similar coarse lobmg as an abnormality, for example A. evecta (Forster) Hoffmann, E V. Freeman, 401B, S n Lanka (BM). The vegetative apex m Plate I, 2, has the baslscoplc margin of all the plnnules, and first veto of the coarse basal lobe of the basal pmnule, decurrent onto the wing of the rachis. In the two specimens from Roseberry Topping (e.g. Plate V, 6) the sori occupy only about 1/4 to 1/3 of the pinnule half-width and are composed of only 4 or 5 small sporangm Rather than conmdermg them abnormal they seem to be

P L A T E VI S t r u c t u r e of s o r u s a n d s p o r a n g i a m e x t a n t Angmpter~s H o f f m a n n 1 A crasszpesWalhcher, E l m e r 6711, P h f l * p p m e s (K) P o r t i o n of a fertile p m n u l e s h o w i n g midrib, l a t e r a l veins, fibre b u n d l e s b e t w e e n veins, a n d s o n of 6 - 8 s p o r a n g i a T h e dry d e h i s c e d s p o r a n g i a c o n t r a c t a n d their walls gape widely T h i s gives t h e dined s o r u s a m o r e s t e l l a t e a p p e a r a n c e t h a n in f r e s h m a t e r i a l , m i s l e a d i n g l y like A blackn 2 A prutnosa K u n z e , M m h o h t z s n., Dec 1882, P h i l i p p i n e s (K) S E M v m w of u n u s u a l h e r b a r i u m s p e m m e n s h o w i n g some s p o r a n g i a of r a t h e r closely s , m f l a r s h a p e w h e n d r y to t h o s e of A blacktL A p p r o x × 40 3-5 A hypoleuca De V r m s e , 000-73 13071 (hort K) 3, 4, c m t l c a l p o i n t dried m a t u r e s o r u s j u s t before o p e n i n g of s p o r a n g i a , 3, p l a n view, 4, s~de v m w T h e sorus, typical of e x t a n t Angmpterzs, is c o m p a c t a n d c o m p o s e d of s p o r a n g i a t h a t are b r o a d e s t above t h e middle, × 30 5, p l a n view of dried s o r u s r e h y d r a t e d w i t h b l e a c h a n d s t a i n e d w i t h s a f r a n i n , for c o m p a m s o n of s p o r a n g l a l s h a p e w i t h critical p o i n t dined m a t e r i a l from s a m e p i n n a s h o w n m 3, 4 A p p r o x x 30 6, 7 A lactntata De Vmese, E S m i t h 2208, T h a i l a n d (BM) 6, s o r u s r e h y d r a t e d a n d s t a i n e d w i t h s a f r a n m , s h o w i n g Cs h a p e d " c r e s t " of m o d m m e t r m t h i n k - w a l l e d cells, v e n t r a l wall w i t h e l o n g a t e think-walled cells a n d d o r s a l wall w i t h t h i n - w a l l e d m o d m m e t n c cells A p p r o x × 30 7, S E M w e w s h o w i n g r o u n d e d cells of d o r s a l wall of a dried s p o r a n g m m , × 100 8 11 A ankolana De V r m s e , J u n g h u h n 698, S u m a t r a (BM)_ 8-10, sot1 r e h y d r a t e d a n d s t a i n e d w i t h s a [ r a m n , all a p p r o x × 35 8, p l a n view of s o r u s s h o w i n g v e r y s m a l l a r e a of t h i c k - w a l l e d m o d l a m e t m c cells at s p o r a n g l a l a p m e s 9, d o r s a l walls of s p o r a n g m s h o w i n g e l o n g a t e cells c o m p a r a b l e w*th t h o s e of v e n t r a l w a l l s s h o w n m 10 11, S E M w e w of d o r s a l wall of dry s p o r a n g m m , i l l u s t r a t i n g e l o n g a t e cells of d o r s a l wall, c o m p a r e w i t h 7, x 100

84

i m m a t u r e p m n u l e s at the extremes of the normal r a n g e of v a r i a t m n . Similar specimens, a l t h o u g h very scarce, o c c u r t o g e t h e r w~th more typical ones at H a s t y Bank, e.g.V.58555. (3) Taxonomically s~gnificant d~fferences: Differences from living specms t h a t c a n n o t be a t t m b u t e d to t a p h o n o m i c factors or to abnorm a l i t y are few. The p m n u l e apex, a l t h o u g h t a p e r e d as m e x t a n t species is o b t u s e l y p o i n t e d r a t h e r t h a n d r a w n out into an a c u m i n a t e tip (Plates I, 1, 6; V, I vs V, 2). W i t h the e x c e p t m n of this, all the differences are r e p r o d u c h v e characters of the sorus and sporangia. W h e n alive the m a t u r e , u n d e h l s c e d s p o r a n g i a m all e x t a n t specms of Angmpter~s are appressed in close m u t u a l c o n t a c t o v e r most of the area of t h e i r l a t e r a l walls. T h e s p o r a n g m are a s q u a t obovoid shape, r a t h e r like a pear; t h e y are b r o a d in r e l a t i o n to t h e i r l e n g t h and the b r o a d e s t point is t y p i c a l l y at or above the middle T h e s e characters of s p o r a n g i a l shape and the dense p a c k i n g of the s p o r a n g m combine to give a c o n s i s t e n t l y c o m p a c t sorus (Plates IV, 6, VI, 3, 4). As a r e s u l t the s p o r a n g i a along the sides of the sorus t y p i c a l l y h a v e a r o u n d e d s q u a r e to r e c t a n g u l a r o u t h n e m s e c t m n s of the middle r e g m n transverse to the longest axis of the sporangium, and those at the ends of the sore are n o r m a l l y r o u n d e d t r i a n g u l a r in such s e c t m n (Flg.I.H). T h e spore c o u n t given by B o w e r (1926) is 1500 per sporangium, t h o u g h C h a n g (1975) gives 2000 2500 B o b r o v (1973) gives up to 7000 for M a r a t t i a c e a e but w i t h o u t a n y m d i c a t m n as to w h i c h g e n e r a and specms this figure was based on, and the c o u n t s are d o u b t f u l l y a c c u r a t e . E a c h of these c h a r a c t e r s c o n t r a s t s with those of the fossil. In A. black~ the s p o r a n g i a are also in l a t e r a l c o n t a c t with one a n o t h e r , t h o u g h o n l y along the basal t h i r d or at most h a l f of t h e i r length. As in living specms the s p o r a n g m are obovold m shape, b u t t h e y are m u c h l o n g e r t h a n b r o a d and are b r o a d e s t at or below the middle T h e y m e a s u r e a b o u t h a l f as long a g a i n as those of h w n g species. T h e s e c h a r a c t e r s give the sorus a more spreading, stellate, a p p e a r a n c e t h a n is typical of any h w n g specms R e c o n s t r u c t e d t r a n s v e r s e sect m n s of the middle r e g i o n of the s p o r a n g i a are

fully circular, in c o n t r a s t to those of the h v m g species, w h i c h are t r m n g u l a r or square, t h o u g h m the appressed region n e a r e r the base t h e y m a y well h a v e been similar (Figs.2.C,D and 3.B) The spore c o u n t of 3000 is g r e a t e r t h a n t h a t for e x t a n t m a t e r i a l as r e p o r t e d on by B o w e r and by Chang. In w e w of the l a r g e r size of the s p o r a n g i u m m A blackii thin implies t h a t its s p o r a n g m l wall was not significantly t h i c k e r t h a n t h a t of e x t a n t specms. The low r a t i o of v e g e t a t i v e to fertile pmnules k n o w n for A. blackd is c o m p a r a b l e with t h a t of h w n g plants and t h e r e f o r e does not a p p e a r to r e s u l t from t a p h o n o m l c factors

Relationships and generic status Relationships" The a p p r o a c h adopted h e r e to d e t e r m i n e r e l a h o n s h i p s is based on cladlstlc m e t h o d (see e.g. Hill and Crane, 1982, and Wiley, 1981, for i n t r o d u c t i o n s to cladlstms and its t e r m i n o l o g y ) Because I wish to avoid u n n e c e s s a r y r e p e t i t i o n of p u b h s h e d information, the following should be studied t o g e t h e r with Hill and Camus (1986) Complete assessm e n t of the r e l a t i o n s h i p s of A blackn is m fact compromised by its high ' h n f o r m a t l o n gap" of 57~o. This is the e s t i m a t e d gap in a c t u a l l y k n o w n vs. p o t e n t i a l l y k n o w a b l e c h a r a c t e r r e f o r m a t i o n , t h e r e being only 29 c h a r a c t e r s k n o w n for A blackiz c o m p a r e d to a total of 68 as h s t e d by Hill and Camus (1986: table 2) for c o m p a r a b l e e x t a n t specms Nonetheless, on the basis of the c h a r a c t e r s t h a t are available, the a p p r o x i m a t e position of A. blackii on a prelimin a r y c l a d o g r a m of M a r a t t i a c e a e (Hill and Camus, 1986" fig.23) m a y be d e t e r m i n e d Referring to table 2 of Hill and Camus and excluding c h a r a c t e r states of u n c e r t a i n p o l a r i t y for A. black~l ( c h a r a c t e r s 6 and 20), A black~l shares eight derived c h a r a c t e r states with e x t a n t M a r a t t l a l e s : for c h a r a c t e r s 54, 57, 58, 60, 63, 65, 67 and 72 The o t h e r n i n e t e e n k n o w n characters out of the t o t a l of t w e n t y nine are all g e n e r a h s e d ( l e widely shared) c h a r a c t e r states, w h i c h are of no sigmficance m evaluating cladlstic r e l a t i o n s h i p s at this p a r t i c u l a r rank

85

Of the eight derived c h a r a c t e r states, t h r e e are shared with all or n e a r l y all e x t a n t g e n e r a (54, 58, 60), and one o t h e r is also shared widely (72). Out of the r e m a i n i n g four, two are shared exclusively with Angtoptens sensu stricto + Macroglossum C o p e l a n d + A r c h a n g t o p t e r t s Christ et G l e s e n h a g e n + Protomarattia H a y a t a , w h i c h t o g e t h e r c o n s t i t u t e Angmpteris sensu lato of Hill and Camus, and these c h a r a c t e r s c l e a r l y i n d i c a t e r e l a t i o n s h i p to t h a t genus These c h a r a c t e r states are 65 and 67: s p o r a n g i a l a t e r a l l y free from one a n o t h e r , e i t h e r vent r a l l y o n l y or b o t h dorsally and v e n t r a l l y . This leaves only two c h a r a c t e r s m the list of Hill and Camus w h i c h can be of use for d e t e r m i n i n g r e l a t i o n s h i p of A. blackii w i t h i n Angtopterts sensu lato. T h e s e h a v e b o t h g e n e r a h s e d and derived ( - / + ) c h a r a c t e r states for A blacktt and, to t h a t extent, are not c l e a r cut: 57, position of sori r e l a t i v e to m a r g i n e i t h e r n e a r to m a r g i n ( - ) or m i d w a y b e t w e e n midrib and m a r g i n ( + ) , and 63, typical n u m b e r of sporangla per sorus g r e a t e r t h a n 10 ( - ) or less t h a n 10 ( + ). F o r c h a r a c t e r 57 + , the n e a r e s t compar1son is found most widely m Archangiopteris, t h o u g h o c c a s i o n a l specimens of Angmpteris s.s. are also c o m p a r a b l e (e g. P l a t e V, 8, allowing for the reflexed margin) C h a r a c t e r 63 is s h a r e d with only one species of Angiopterts s.s. as selected by Hill and Camus (A annamensts C C h r i s t e n s e n et Tardmu), but r e f e r e n c e to a wider r a n g e of species indicates several t h a t can h a v e a c o m p a r a b l e n u m b e r of s p o r a n g i a per sorus (Plate VI). A n o t h e r c h a r a c t e r of r e l e v a n c e (not dealt with by Hill and Camus) is the l e n g t h of the s p o r a n g i u m of A. blackn (AppendlxII), w h i c h resembles Archangmpterts more closely t h a n Angtopterts s s., as is (for w h a t it is w o r t h ) a g e n e r a h s e d f e a t u r e - the lack of fibre bundles from A. blackii ( c h a r a c t e r 39) Conversely, as established m Appendix II for A. ankolana De Vrlese, comp a r a b l e surface s t r u c t u r e of the s p o r a n g i a l wall o c c u r s only in Angtopterts s s. Archangiopterts s p o r a n g i a u n i f o r m l y h a v e a dlfferentlated wall as in Angmpteris lactmata De Vriese (Plate VI, 6, 7, Hill and Camus, 1986 fig.20E) On the b a l a n c e of its s h a r e d derived charac-

ter

states

(synapomorphies),

therefore,

A.

blackii is clearly r e f e r a b l e to Angiopterts s 1 of Hill and Camus W i t h i n t h a t genus it resembles b o t h Angtopteris s s and Archangiopterts, and resembles t h e m m o r e closely t h a n Macroglossum or Protomarattia Like some living specms such as Angiopter~s annamensts, A. blackti as p r e s e n t l y k n o w n s o m e w h a t blurs the d i s t i n c t i o n b e t w e e n Angiopterts s s and Archangiopterts, but it is closest to Angtop-

terts. This i n t e r p r e t a t i o n of r e l a t i o n s h i p s is challenged by only one of the c h a r a c t e r states listed by Hill and C a m u s 59 ( + ) , close p a c k i n g of the s p o r a n g i a or s y n a n g l a l locules into the sorus or s y n a n g i u m In this f e a t u r e the relatively spread out, stellate a p p e a r a n c e of the sorus of A blackti differs from all o t h e r M a r a t t l a c e a e (Appendix II). On grounds of p a r s i m o m o u s i n t e r p r e t a t m n of the c h a r a c t e r s as a whole, this appears to be a u n i q u e l y derived c h a r a c t e r . D e p e n d i n g on how u m t c h a r a c t e r s are dehmited, the stellate a p p e a r a n c e of the A. blacktt sorus m a y be c o n s i d e r e d to r e p r e s e n t a complex of at least four distinct c h a r a c t e r states: (a) more s p r e a d i n g a t t i t u d e of the sporangia; (b) t h e i r r e l a t i v e l y long shape m r e l a t i o n to breadth; (c) t h e i r a b s o l u t e l y g r e a t e r l e n g t h c o m p a r e d to e x t a n t Angtopteris; and (d) width of s p o r a n g i a b r o a d e r at and below the middle, as opposed to at and above the middle m o t h e r M a r a t t l a c e a e . This h o w e v e r m a k e s no difference to the i n t e r p r e t a t i o n of r e l a t i o n s h i p s given h e r e and m a y involve some i n f o r m a t i o n r e d u n d a n c y To this e x t e n t the e v i d e n t l y g r e a t e r spore p r o d u c t i o n per s p o r a n g m m , a n o t h e r a p p a r e n t l y u n i q u e l y derived character, m a y reflect m e r e l y the g r e a t e r size of the s p o r a n g l u m A f u r t h e r h~ghly derived character (in the c o n t e x t of Angtopteris) is the u n i f o r m l y e l o n g a t e ceils of the s p o r a n g l a l wall On this view of r e l a t i o n s h i p s the evolutionary cladistlc retrodictxon 1 r e g a r d i n g the 1A retrodlctlon is a " p r e d i c t i o n " which a p p h e s to past r a t h e r t h a n f u t u r e events For an i n t r o d u c t i o n to "evolut i o n a r y c l a d l s t m s " see Hill and C a m u s (1986, p a r t II)

86 s t r a t i g r a p h y of Angiopterts is t h a t t h e e a r l i e s t o c c u r r e n c e of species m o s t closely r e s e m b l i n g t h o s e s u r v i v i n g t o d a y will be f o u n d to p r e d a t e A. blackn in t h e fossil record. T h i s u n f o r t u n a t e l y is left o p e n b y the C h i n e s e T r i a s s i c fossils as i n t e r p r e t e d here. T h e g e n e r a l position is c o m p a r a b l e to t h a t of the M a t o n l a c e a e , in w h i c h t h e first s t r a t i g r a p h m o c c u r r e n c e of the r e l a t i v e l y g e n e r a l i s e d g e n u s Matonta ( w h m h s u r v i v e s today) p r e d a t e s t h a t of t h e r e l a t i v e l y d e r i v e d g e n u s Weichselia w h i c h a r o s e l a t e r t h a n Matonta b u t b e c a m e e x t i n c t in the C r e t a c e o u s . A blackii, like Wetchseha, is considered a relatively highly evolved taxon t h a t w a s b o t h p r e d a t e d a n d o u t l a s t e d by o t h e r m o r e g e n e r a h s e d species. T h i s v i e w r e c e i v e s some s u p p o r t f r o m t h e o n t o g e n y of A. blacktt s p o r a n g m , since t h e i m m a t u r e ones are m o r e r o u n d e d m s h a p e t h a n t h e m a t u r e ones, as in m a t u r e s p o r a n g i a of e x t a n t Angiopteris (for a r g u m e n t a t i o n see Hill a n d C a m u s , 1986). This c h a r a c t e r a s s e s s m e n t a n d p h y l o g e n e t i c interpretation may seem strmghtforward but I am n o t c o n v i n c e d t h a t it is c o r r e c t r e g a r d i n g m t e r p r e t a t m n of t h e u n i q u e l y d e r i v e d (specialised) c h a r a c t e r s . T h e p r o b l e m is w h e t h e r t h e s e c h a r a c t e r s of e l o n g a t e s p o r a n g i a l s h a p e and length, a n d the u n i f o r m l y e l o n g a t e s u r f a c e cells of the s p o r a n g m l wall in A. blackii, are r e a l l y s p e c i a l i s e d or m a y possibly be r e t a i n e d g e n e r a h s e d c h a r a c t e r states. E w d e n c e t h a t t h e y m a y be g e n e r a h s e d c o m e s f r o m v a r i o u s P a l a e o z o i c fossils 1. O b s e r v a t i o n s on 20 s p e c m s of U p p e r C a r b o n iferous to P e r m i a n m a r a t t i a l e a n s by S c o t t (1932), M a m a y (1950), M i l l a y (1978, 1979) a n d M a p e s a n d S c h a b f l l o n (1979a, b) i n d i c a t e t h a t at l e a s t 14 of t h e s e h a d e l o n g a t e s p o r a n g i a of a s h a p e e i t h e r s i m i l a r to t h a t of A. blackii

JIt is generally beheved that extant Marattlales with taemoptend pmnules arose from Palaeozoic forms with pecopterold pmnules such as Scolecopterts Zenker and Acttheca Schlmper (e g Mamay, 1950, Stldd, 1974, Millay, 1979)_ Eoangtopterts Mamay (1950) m particular was a pecoptend that had elongate son (Flg2_E) and has therefore been regarded as an ancestral morphotype of

Angtopterts

s p o r a n g i a or still m o r e e l o n g a t e and p o i n t e d (Flg.2.E). M o s t of t h e 20 specms h a d s p o r a n g i a as long as or l o n g e r t h a n t h o s e of A blacktt m a b s o l u t e terms, e.g. I 7 - 2 . 0 m m m Mtllaya M a p e s et S c h a b i l i o n (1979b) a n d 1 3 2 m m l o n g × up to 0 4 4 m m wide m Scolecopterts o h v e n S c o t t (1932) K n o w l e d g e of the s u r f a c e cells of the s p o r a n g l a l wall m m o s t of these specms is i n c o m p l e t e , b u t a b o u t h a l f of t h e m a p p e a r to h a v e m o r e or less u n i f o r m l y e l o n g a t e cells as m A. blacklt. H o w e v e r , at l e a s t 7 species of Scolecopter~s have rather strongly differentiated surface cells, for i n s t a n c e m S mtnor H o s k m s (see M i l l a y , 1979) the g e n e r a l a p p e a r a n c e of t h e cells a n d of t h e squat, o b o v o i d s h a p e of the s p o r a n g i a , l o o k s s i m i l a r to ( t h o u g h is n o t i d e n t i c a l with) e x t a n t Angiopteris lac~ntata De V n e s e ( P l a t e VI, 6, 7). To t h i s e x t e n t the e v i d e n c e is u n c e r t a i n H o w e v e r , it r e c e i v e s s o m e i n d e p e n d e n t s u p p o r t f r o m the P e r m i a n Marattia-hke f e r n Qasimta schyfsmae (Lem o l g n e ) Hill et al. (1985) in its r e l a t i o n to e x t a n t Maratt~a Qas~mta h a d l o n g e r s y n a n glal l o c u l e s t h a n a n y e x t a n t species of Marattin, a n d - - a s s u m i n g t h a t t h e d o r s a l w a l l of the s y n a n g m m h a s b e e n c o r r e c t l y i n t e r p r e t e d as s u c h - - its s u r f a c e cells s h o w less different i a t i o n , a p p e a r i n g to be m o r e or less u m f o r m l y e l o n g a t e This, t o g e t h e r w i t h t h e g r e a t age of Qastmta a n d the o t h e r g e n e r a d i s c u s s e d above, s u g g e s t s t h a t s o m e of t h e c h a r a c t e r s i n t e r p r e t e d as s p e c l a h s e d for A blackn m a y i n d e e d h a v e b e e n r e t a i n e d primitive characters. F u r t h e r w o r k on cladlstxc a n a l y s i s of t h e s e P a l a e o z o m t a x a is n e e d e d b o t h to c l e a r up this p o i n t of u n c e r t a i n t y a n d m o r e g e n e r a l l y to c h a l l e n g e the v e r a c i t y of t h e c l a d o g r a m p r o d u c e d by Hill a n d C a m u s (1986), w h i c h was b a s e d m a i n l y on e x t a n t t a x a H o w e v e r , so far as t h e i m m e d i a t e q u e s t i o n of t h e r e l a t i o n s h i p s of A blackt~ w i t h Angtopter~s s 1 are concerned, the question whether the characters under consideratmn are uniquely d e r i v e d vs g e n e r a l i s e d is m i n o r . S i n c e cladlstic r e l a t m n s a r e e s t a b h s h e d on the b a s i s of s h a r e d d e r i v e d c h a r a c t e r s t a t e s , this q u e s t m n

87 is u n h k e l y to affect t h e i n t e r p r e t a t i o n of such c h a r a c t e r s t a t e s s h a r e d by A. black~i with e x t a n t specms. If t h e s e c h a r a c t e r s are i n d e e d g e n e r a l i s e d in r e l a t m n to Ang,opterm, the r a n k at w h i c h t h e y c o u l d be i n t e r p r e t e d as p o t e n t i a l l y s h a r e d would p r o b a b l y be a v e r y b r o a d one indeed. It is of i n t e r e s t t h a t b o t h A blackn and Qas~mia h a v e more r o u n d e d p i n n u l e apmes t h a n t h e i r n e a r e s t e x t a n t relatives, particularly so m Qas~mia. In A blackn 12 wellp r e s e r v e d p m n u l e apices are known, all of which closely resemble t h a t of P l a t e V, 1, m l a c k i n g an a c u m i n a t e tip In almost all e x t a n t m a t e r i a l of Angmpter~s s 1., the p m n u l e s h a v e a c u m i n a t e tips as m P l a t e V, 2 T h e tips are v a r m b l y developed but often h i g h l y conspicuous, t e n d i n g in general to be less well developed m p m n u l e s towards the bases of the p m n a e Some h e r b a r i u m specimens show more r o u n d e d apices as m A. blackii, but these are g e n e r a l l y a c c o m p a n i e d by clear e w d e n c e of a b e r r a n t d e v e l o p m e n t such as fungal infection. In only three sheets (out of several h u n d r e d examined) were p m n u l e apices found t h a t look v e r y like those of A. blackn" Angmpteris oldhamn H m r o n , W H a n c o c k 81, T a l w a n (BM), A flitgeliana Presl, Flugel 3243 (Type specimen), Asia (W) and "Archangiopterm varyabJts" Ching MS name, W u L l g o n g 4196-62, Y u n n a n (PE, 749079). In e a c h case most of the p i n n u l e apmes are a c u m i n a t e and only a few from n e a r the bases of the p l n n a e are like those of A blackii. I n t e r e s t i n g l y , some of those of the A oldhamn specimen h a v e t e r m i n a l sorl, as do apices of the A blackn specimen m P l a t e I, 1 Since the p m n u l e apices of A blackzi are uniform, two of them m e x t r e m e l y long pinnules and one from a p i n n a apex, it is e v i d e n t t h a t they do not c o n s t i t u t e a sample of p m n u l e s m e r e l y from the p i n n a bases of the plant. It m a y be c o n c l u d e d t h a t the difference m t h e i r shape from h y i n g m a t e r i a l was general and not as m these t h r e e e x c e p t i o n a l herbarium specimens. This d i f f e r e n c e in form of the p i n n u l e apex of A. blackn and Qastm~a from e x t a n t specms p r o w d e s some s u p p o r t for the idea t h a t t h e y

e v o l v e d from p e c o p t e r o l d a n c e s t o r s w h i c h h a d r o u n d e d p m n u l e apices If P s a r o m a c e a e is a c c e p t a b l e as an o u t g r o u p of M a r a t t l a c e a e (Hill and Camus, 1986), this c h a r a c t e r s t a t e is to be c o n s i d e r e d g e n e r a h s e d and t h e possession of an a c u m i n a t e apex as d e r i v e d A blackd is of general i n t e r e s t since it c u r r e n t l y provides the e a r h e s t and, as the a u t h o r believes, the only s u b s t a n t i a l fossil o c c u r r e n c e of Angiopteris s.1 This o c c u r r e n c e is l a t e r t h a n t h a t of Marattm, Qasim~a and "Radstock~a" k~dstoni~ T a y l o r (1967), and t h e r e f o r e m terms of r e l a t i v e ages of first o c c u r r e n c e s c o r r o b o r a t e s the o v e r v i e w of mara t t l a l e a n p h y l o g e n y based on cladistlc analysis by Hill and Camus (1986). Nomenclature: Since the c o m b i n a t i o n of characters found m A blackn is u n i q u e a m o n g s t M a r a t t i a l e s it m i g h t be a r g u e d t h a t a new genus is needed (Hill, 1974). As with " s e c t i o n s " of LycopodLum L or indeed of Anglopter~s s.1. as c o n s t r u e d by Hill and Camus (1986), w h e t h e r it should be t r e a t e d as a part of a genus or as a distinct genus involves a shifting of t a x o n o m m r a n k by one " r u n g " e i t h e r up or down the ~'ladder" of the classification hmrarchy. Views will i n e v i t a b l y differ, a l t h o u g h such differences seem to be trivial. The ~'lumping" a p p r o a c h adopted here in r e t a i n i n g A. blackn w i t h i n a b r o a d e n e d circumscription of Angiopterm is directly influenced by P r o f e s s o r T.M H a r r i s ' s (1964) p r a g m a t i c vmws on the u n d e s l r a b i h t y of "inflation of taxonomy". The most i m p o r t a n t biological cons i d e r a t m n is t h a t r e l a t i o n s h i p s a m o n g s t t a x a should be u n d e r s t o o d - - and the processes g o v e r n i n g those r e l a t i o n s h i p s - - based m p a r t on a p p r o p r m t e l y i n t e r p r e t e d d e t m l e d comparative study, i r r e s p e c t i v e of the names applied to the t a x a This w o r k has m a i n l y a t t e m p t e d to discover such r e l a t i o n s h i p s of A. blackit m c o m p a r i s o n with e x t a n t specms and with s c a n t r e f e r e n c e to P a l a e o z o i c r e l a t i v e s A. blackii has p r o v e d to be m u c h less s t r m g h t f o r w a r d t h a n m i t m l l y thought. In retrospect, to state t h a t J u r a s s i c M a r a t t i a l e s are ~dentlcal to m o d e r n g e n e r a (Stewart, 1983 p 202) is r a t h e r over-simphfied.

88 Palaeoecology

In its n atu r al habitats Angmpteris s.1. is hmited today to the eastern hemisphere, mainly Madagascar, India, Southeast Asia and Australia. Like all extant Marattiales it occurs only in tropical and subtropical environments. The o ccu r r en ce of A. black~ m Yorkshire suggests both t h a t the genus was more w~dely distributed m the past and t hat Yorkshire m Middle Jurassic times had a considerably warmer climate t h a n it does now A blacki~ adds to the small number of other Yorkshire Jurassic "ptemdophyte" genera that also still have ex tan t species, all of which as presently circumscmbed - - with the sole exceptmn of Equisetum - - are hm~ted to warm temperate or tropical chmates How humid those cond~tlons were is less settled, though we know that coals were formed on a limited scale. A. black~, for instance, lacks a "drip-t~p": the acuminate pmnule apex which occurs m most e xt a nt Marattmles. The lack of such apices from Qas~m~a, " Marattmps~s" macrocarpa (Oldham et Morms) Seward et Sahni (1920) and from A blacki~ may indicate that Mesophytlc chmates were perhaps less humid t h a n today. But it may merely represent an e v o l u t m n a r y lag effect, owing to only gradual evol ut i onar y divergence in this c h a r a c t e r from Palaeozoic pecoptero~d ancestors, It should be added t h a t the fossil record of Maratt~a (Hill, Wagner and El-Khayal, 1986) indicates mainly gradual evolution for th at genus. As for fossil Angmpter~s, mainly aspects t h a t are p u n c t u a t e d are the continuity of its record m time and space and the extent to which the maternal has been studied. Appendix I -- Rotting experiments on some extant ferns in neutral to acid conditions

Simple rotting expemments were begun m 1972 to provide an o t he r method of approaching the problem referred to on p.83. Living fern fronds comparable m their gross form to Hasty Bank ones were immersed m muddy pond

water of pH 5-7 with a diverse pond fauna. The t ank was kept well aerated. (Thin pH range was chosen since the pyritic matmx at Hasty Bank indicates t hat acid conditions probably occurred there during or after bumal ) Destruction of p m n a e of Angmpter~s evecta Hoffmann was compared with t hat of pm nae from hying species of Maratt~a sp. and Dicksoma sp, both of which are represented at Hasty Bank by fosmls (Harms, 1961). Over a 13 day period the Dtcksonia showed no visible damage or dmtortlon but m pm nae of Marattla and Angmpterls extensive destruction of the mesophyll occurred within 7 days. This allowed the veins to shift m response to the shghtest dmturbance of the water, r a t h e r more readily m Angmpter~s t han m Marattza. Indeed the appearance of the maternal at this time was remarkably hke t hat of the fossil species in Plate V, 1, 4 7 and in Fig.2 A. These results suggest that Maratt~a anghca and Angiopter~s blackil were more susceptible to decay and therefore to subsequent dlstortmn t han other ferns which occur at Hasty Bank Shedding of pm nul es from the rachls m the experi m ent al Angmpter~s and Maratt~a is also r e l e v a n t to i n t e r p r e t i n g the Hasty Bank fossils Pinnules of hvi ng M a r a t t l a l e s typically have swollen petmles, termed pul w m , These are p a r e n c h y m a t o u s , lacking the usual sheath of sclerenchyma, and may be more mchly supphed with mucilage cells t h a n the midmb Thus they are r a t h e r soft and fleshy Observations on cul t i vat ed plants at Kew and in the field indicate t h a t ageing fronds tend to shed t hei r p m n u l e s by s e p a r a t i o n at the pulvml, t h o u g h there does not appear to be a well defined absclssmn layer as m angiosperms Th~s may explain why m a r a t t i a l e a n spec~mens with pinnules or pm nae still attached to their rachmes are extremely rare m the Jurassic. There are only two such specimens each for M. angl~ca and A. blackd compared to many hundreds of detached pinnules seen in the field. The two specimens of pinnate M anglica show ewdence, from continuity of the coaly material, of a t t a c h m e n t of the pmnules to the

89 rachls, whereas only one of the comparable A blackn specimens is so preserved. This is an unusual specimen in which comparison with extant material suggests that pulvim would not have been mgmficantly developed (Plate I, 2). The other more normal specimen (Plate I, 1) lacks direct ewdence for continuity, the soft presumed pulvinar regmns evidently not having been preserved. Together with the absence of pmnules from the other sMe of the rachls (Plate I, 1) thin is conmstent with the results from the rotting expemments, m whmh the pulwni of Angiopteris evecta first became soggy and then rapidly disintegrated. At a fmrly advanced stage of dlsmtegratmn the rachis was left with a row of a few plnnules barely connected to ~t on one rode only, all the others having dropped off. Such a specimen would be preserved as a fossd just as m Plate I, 1 Prof. T.M. Harms pointed out to me that shrinkage because of loss of cell turgor on death is common m plant tissues today and has hardly been investigated in relation to taphonomy. Such shrinkage may explain why the two specimens of M anglica referred to above, whilst showing clear c o n t i n m t y of the petmle with the rachis, show no m d m a t m n that it was swollen to form a pulvinus For this reason pulvim can be difficult to detect even m herbarium material of extant species It nevertheless remains possible that they were originally lacking from M. anghca As far as I know, rotting experiments hke those descmbed here were first used by Prof. J Lindley (reported m Lmdley and Hutton, 1835-1837, Vol III, pp.l-12), followed by Stopes and Watson (1908) in their work on the omgm of coal-balls Those reported here are limited in scope, even m compamson with Lindley's remarkable enterprise of 150 years ago. They merely outhne what could be done, but they nonetheless appear to provide a useful approach for understanding taphonomm processes affecting plant materml. In 1983 I repeated the original experiment with comparable materml and pond water of pH 5 from Burton Mill Pond, West Sussex The findings were similar to the omginal experi-

ment except that the times taken for shedding of all pmnules from pmnae of Marattia and Angioptens were longer, ranging from 15 to 56days There was some evidence from a further repeat of the experiment that a high d~versity fauna speeds rotting, and pond snails seemed particularly fond of marattlalean mucilage. In the original experiment the Angiopterzs pinna shed its pinnules before Maratt~a, a finding that was reversed m the subsequent experiments. Experiments with calcareous water gave entirely different results, with no loss of pmnules even after many weeks Fresh mature fronds and rhlzomes of Matonia pectinata Maxon from Kuala Lumpur, kindly hand-carrmd by air to London by Mrs A. Plggott, remained virtually unchanged for over 18 months m these later experiments. This may explain why Matomaceae are particularly well represented m Mesozmc floras, often by relatively complete fronds. Under uniform conditions, plants clearly may behave very differently m terms of post-mortem changes, as was first estabhshed by Lmdley. This is given added weight by the observation that severed stems of Equisetum fluwatzle L. included m the experiments showed no post-mortem decay: indeed unlike the accompanying ferns they refused to die and even grew to produce new branch shoots. Equisetum is the most widespread and abundantly preserved fosml plant m the Yorkshire Jurasmc and is the only one found in abundance in growth position. This is because the ecologmal environment of its growth also happened to be its sedimentary enwronment of deposition, u n h k e most other plants in the Yorkshire flora. A p p e n d i x II - - S h a p e o f s p o r a n g i a a n d s u r f a c e cells o f s p o r a n g i a l wall o f e x t a n t material

The comparisons given on p.85 were based mainly on direct examinahon of herbarmm maternal at K (Kew) and BM [British Museum (Natural History)l, with loans generously made available from BKH, BO, KLU, L, M, MICH, P, PE, TI, and W (abbreviations from

90 Stafleu, 1981). T h i s w a s a u g m e n t e d by s t u d y of h v e p l a n t s at the R o y a l B o t a n i c G a r d e n s , K e w (hort K), w h e r e a n i n v a l u a b l e r a n g e of M a r a t t m l e s is n o w m c u l t i v a t i o n , u n d e r c o n d i t m n s t h a t m o r d i n a r y g r e e n h o u s e t e r m s are u n i f o r m . Special a t t e n t m n w a s g~ven to the r a n g e of v a r i a t m n of v a r i o u s c h a r a c t e r s , In p a r t m u l a r the s h a p e of t h e s p o r a n g i u m and also t h e d e t a i l s - - w h e n seen m s u r f a c e v i e w - - of t h e o u t e r m o s t l a y e r of cells of the s p o r a n g m l wall. I n f o r m a t m n on t h e s e c h a r a c t e r s m the h t e r a t u r e (e.g. De V r i e s e a n d H a r t m g , 1853; Campbell, 1911, Bower, 1926) is s p a r s e a n d m s e v e r a l cases w a s f o u n d to be i n a c c u r a t e . A p r o b l e m w i t h h e r b a r i u m m a t e r m l of Angiopter~s is t h a t t h e d e h i s c e d s p o r a n g m u s u a l l y g a p e widely o p e n v e n t r a l l y w h e n dry T h e d o r s a l wall s h r i n k s a n d t h e r e f o r e t h e l a t e r a l walls m o v e closer t o g e t h e r , s u c h t h a t the s p o r a n g i a m p l a n v i e w o f t e n a p p e a r l o n g e r in r e l a t i o n to t h e i r b r e a d t h t h a n t h e y a r e w h e n the d e h i s c e n c e s h t is closed ( P l a t e VI, 1). T h e s h a p e of t h e s p o r a n g m does n o t t h e r e f o r e r e p r e s e n t t h a t s e e n w h e n m a t u r e b u t before d e h i s c e n c e in h w n g fronds (Plate VI, 3, 4). A l t h o u g h o f t e n a p p e a r i n g s u p e r f i c i a l l y similar, n o r is the s p o r a n g i a l s h a p e d i r e c t l y c o m p a r able w i t h t h a t of A blackii, m w h i c h the sporangm presumably became waterlogged d u r i n g t r a n s p o r t a n d d e p o s l t m n a n d t h u s are n o r m a l l y closed or a l m o s t closed e v e n w h e n e m p t y of spores (for e x c e p t m n s see P l a t e III, 1, 2)_ F u r t h e r m o r e , details of the s u r f a c e cells of the s p o r a n g i a l wall in dined e x t a n t m a t e r m l , a l t h o u g h o b s e r v a b l e to some e x t e n t m t h e S E M (Plate VI, 7, 11) are often o b s c u r e d by collapse of the cells on d r y i n g For these reasons, herbarium m a t e r m l was routinely bleached and stained with saframn. As p r o b a b l y o c c u r r e d t h r o u g h w a t e r l o g g i n g of A black~, r a t h e r h k e b a s k e t - m a k e r s ' ' ~ r e t t m g " of Sahx twigs, t h e b l e a c h i n g r e h y d r a t e s a n d softens t h e s p o r a n g i u m and, as a result, closes the d e h i s c e n c e sht. T h e s p o r a n g i a l s h a p e a n d cell o u t l i n e s of the o u t e r m o s t l a y e r of cells of the wall are t h e r e b y r e s t o r e d to the c o n d i t m n seen m h v e p l a n t s j u s t b e f o r e d e h i s c e n c e (Plates IV, 6, VI, 5, 6, 8-10). T h e a c c u r a c y of

this w a s c h e c k e d by c o m p a r i n g s o n of b l e a c h e d a l r - d r m d A. hypoleuca De V r m s e w i t h c r l t m a l p o i n t dined fresh ones fixed m g l u t a r a l d e h y d e f r o m t h e s a m e p i n n a at the s a m e t i m e of c o l l e c t i n g (Plate VI, 3-5) M a t u r e s p o r a n g i a w e r e f o u n d on b l e a c h i n g to be r e m a r k a b l y u n i f o r m in s h a p e for all specms e x a m i n e d . This u n i f o r m i t y is m o r e p r o n o u n c e d t h a n i n d i c a t e d m the h t e r a t u r e , e g. by De V r m s e a n d H a r t m g (1853) w h o b a s e d t h e i r o b s e r v a t i o n s a l m o s t e n t i r e l y on h e r b a r m m maternal and w h o n o t o n l y confused i m m a t u r e w i t h m a t u r e sorl b u t m at l e a s t two i n s t a n c e s descmbed n e w specms n a m e s on t h a t basis T w o s p e c i m e n s labelled A. pruznosa K u n z e w e r e m f a c t f o u n d to s h o w in t h e i r dry s t a t e an e x c e p t i o n a l l y close a p p r o a c h to A. blacku (PlateVI, 2): M m h o h t z s . n , Dec. 1882, Philippines, and E l m e r 5930, Philippines, b o t h at K T h e s p e c i m e n s are at the e x t r e m e of the r a n g e of v a r i a t i o n of A. pru~nosa, w h i c h n o r m a l l y h a s sub-globose s p o r a n g i a e v e n w h e n dry, b u t o t h e r w i s e are t y p i c a l On b l e a c h i n g t h e i r s p o r a n g i a in f a c t l o o k e d n o r m a l in shape. I n d e e d w h e n r e h y d r a t e d no s p e c i m e n of e x t a n t m a t e r i a l was found w i t h s p o r a n g i a of a s h a p e at all h k e t h o s e of A blackd A r a n g e of m e a s u r e m e n t s by Miss J . M C a m u s of the l e n g t h of Angiopteris s s. s p o r a n g i a f r o m different s p e c m s g a v e 0.4 0.5 m m as t y p i c a l (excluding t h e h e i g h t of t h e p l a c e n t a ) , r a n g i n g f r o m 0.3 to 0.6 mm. T h i s is c o n s i s t e n t l y s h o r t e r t h a n m A black~ ( m e a n l e n g t h 0.8 m m r a n g i n g to 1.1 ram). A m o n g s t r e l a t e d g e n e r a the s p o r a n g m of Archangmptens w e r e found to p r o w d e a somew h a t closer m a t c h m s h a p e a n d l e n g t h T h e y are t y p m a l l y 0 5 - 0 . 6 m m long, r a n g i n g to 0 7(-0.8) ram. H o w e v e r , this is also s h o r t e r t h a n A blackn and, as m e x t a n t Angiopterzs s s., the s p o r a n g m are m u c h m o r e c o m p a c t e d into the sorus, g l w n g an o v e r a l l a p p e a r a n c e of the sorus u n h k e A blackd. T h e s u r f a c e l a y e r of the cells of the s p o r a n g i a l wall is a l w a y s s p e c m h s e d , as m P l a t e VI, 6, w h i c h is also u n l i k e A. black~i. Thin s u r f a c e l a y e r of cells m the s p o r a n g m l

91

wall of ex tan t species is described m the literature as speciahsed, i e. dlfferentmted at matumty into areas of thin vs thick-walled cells of varmus shapes (Strasburger, 1874, Luersson, 1875; Bower, 1898, 1926; Campbell, 1911). Bleached and stained sporangia confirm t h a t such specialisatlon is indeed widespread, occurring (though to varying extents) m most of the specimens of Angiopterts s s. investigated. For example, Plate VI, 6, 7, illustrates sporangm of A. lactntata De Vriese. The apical regmn of these sporangia is composed of lsodmmetrlc polygonal cells having thmkened a n t l c h n a l walls. The cells of the dorsal wall are also lsodmmetric but their walls are umformly thin, such t hat the perichnal walls on bleaching bulge strongly outwards Only those of the ventral wall (and in many other specms at the base of the dorsal wall) are uniformly elongated, with thmkened a n t l c h n a l walls In A blackit there appears to be no such speclahsatmn; the whole wall is composed of elongate cells with uniformly thmkened antlchnal walls_ The cell outhnes merely become shorter near the tip (Plate III, 3 6) However, m a few otherwise typical extant specimens a comparably unspecialised sporangium wall was found, for example m a specimen labelled A ankolana De Vriese, J u n g h u h n 698, Sumatra (BM) As in A. blackti the cell outhnes are more or less uniformly r e c t a n g u l a r polygonal t h r o u g h o u t the surface layer of the wall except at the extreme tip (Plate VI, 8-11). Those of the dorsal wall are generally broader and shorter t h a n those of the ventral, but the difference is slight and I beheve is too small to be clearly wsible after compressmn even if a comparable difference occurred originally m the fossil sporangia. There is no extensive crest of thickwalled ~sodmmetmc cells at the apex; simply a very few rounded cells with heavily thmkened a n t i c h n a l walls occur at the extreme apex, so few that again they would probably be undetectable in a compressmn fossil. There thus appears to be no demonstrable difference m the surface cells of the sporanglal wall of A blackLt compared to at least

some extant material of Ang~opterts s s However, the difference in sporangial shape ( F i g s l H I, 2C, D, 3.A, B) appears to be general, and is more marked than casual study of dried extant material alone would indicate

Acknowledgements Mr J G. B r u n t o n and the Hon. F.D.L. Astor kindly gave permission to excavate and collect at Hasty Bank and Roseberry Topping. Professor J.D_ Lovls and the late Morag M. Jones collected and kindly donated some of the specimens Dr J.M Pet t l t t is t hanked for freeze-drying sorl of extant material, BM(NH) photographers J Brown, P. York, P. Richens, P Crabb and P. Hurst for many of the photographs, and Dr Zhou Zhlyan for generous help with translation. Professor T M Harris, Dr W_A Sledge, Dr K.L. Alvin, Dr J. Watson, Dr W Punt, Dr J H.A van Komjnenburg-van Clttert, Mr A Wesley and Miss J.M. Camus have all provided helpful criticmm and other assistance The work is based on part of my PhD thesis It was financially supported m 1970-73 by a Parkm son Foundation Award at the University of Leeds, and m 1972 by a loan from Lloyds Bank plc towards transport costs during the mare excavations at Hasty Bank Subsequent field and laboratory work was supported by the British Museum (Natural History). Colorless kerosene (paraffin) used for photography and routinely for observation of the hand specimens was kindly provided by British Petroleum plc.

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