Anisopteris shuteana HAYES et H.L. PEARSON

Hayes, Peta Angela & Pearson, Hugh Lance, 2024, Anisopteris Shuteana Sp. Nov., A Fertile Adpression Fossil From The Mississippian (Lower Carboniferous) Of Teilia Quarry, North Wales, Uk, Fossil Imprint 80 (1), pp. 125-134 : 127-129

Anisopteris shuteana HAYES et H.L. PEARSON sp. nov.

Text-figs 1–3

H o l o t y p e. V 25790, Palaeobotany Collections,

NHMUK.

P l a n t F o s s i l N a m e R e g i s t r y N u m b e r.

PFN003401 (for the new species).

E t y m o l o g y. This species is named in honour of Cedric H. Shute, former Curator of Palaeobotany at the Natural History Museum, London.

T y p e l o c a l i t y. Teilia Quarry, Gwaenysgor,

Flintshire, North Wales , United Kingdom [ SJ 0793 8137] .

T y p e h o r i z o n. Teilia Formation, Craven Group.

A g e. Brigantian, Visean, Middle Mississipian (lower

Carboniferous).

D i a g n o s i s. Rachis covered with longitudinal striations spaced approx. 0.1 mm apart. Primary rachis width approx. 2.5 mm, narrowing slightly to 2 mm after the first dichotomy. Angle of divergence of first dichotomy narrow acute; angle of divergence of subsequent repeated dichotomies wide acute to obtuse. Ultimate rachises up to 0.6 mm wide. Clusters of pedicellate sporangia attached terminally on ultimate rachises. Sporangia narrow ovate in outline, each sporangium roughly symmetrical and approx. 2.1 mm in length and 0.8 mm in width.

D e s c r i p t i o n. The specimen is a fertile portion of a plant, with the maximum dimensions of this fragmentary specimen approx. 6 cm in length and 3 cm in width ( Text-fig. 1a, b). There is no attachment to a sterile section of frond bearing pinnules. The rachis appears slightly flexuous. The primary rachis is approx. 2.5 mm wide, narrowing slightly to 2 mm after the first dichotomy, which is approx. 2 cm above the base of the fossil, with ultimate rachises of up to 0.6 mm wide. The rachis is covered with longitudinal striations spaced approx. 0.1 mm apart ( Text-fig. 2a, 3a). The first dichotomy preserved in this specimen is narrow acute (42°). The rachis then dichotomizes at least two more times at an angle of divergence of 70–110° (mean 94°) ( Text-fig. 2b). The irregularity of the branching preserved in this adpression fossil is suggestive of a three-dimensional branching axis rather than a two-dimensional frond. The sporangia are attached to the ultimate rachises in clusters of at least four, but the state of preservation does not allow them to be counted precisely ( Text-fig. 2b). The majority of the pedicellate sporangia observed appear pendent ( Text-fig. 2c, d). The pedicel appears to be approx. 0.5 mm long and 0.1 mm wide ( Text-fig. 2d). The sporangia are narrow ovate in outline, with an average length:width ratio of approx. 2.5:1 ( Text-fig. 2b, c, d). Each sporangium appears roughly symmetrical. As a result of the clustering and overlapping of the sporangia precise measurement of each sporangium is difficult. The sporangia appear to range in size from 2.0 to 2.7 mm long (mean 2.1 mm) and 0.7 to 1.0 mm wide (mean 0.8 mm) ( Text-fig. 2b, c, d). The surfaces of the sporangia are covered with fine striations ( Text-fig. 3b).

A d d i t i o n a l m a t e r i a l. V 25777. Specimens that appear similar to these fertile organs have been found in association with sterile fronds, but organic connection has not been observed ( Text-fig. 4a, b).

D i s c u s s i o n. The report of Benson’s collecting recording the association of many specimens of Rhacopteris fronds, now assigned to Anisopteris , with this fertile material at Teilia Quarry supports the assignment of this species to Anisopteris , but no sterile fronds have been found in organic connection with this fertile specimen. This species is assigned to the genus Anisopteris on the basis of observed similarities with Anisopteris fertilis (J. WALTON) HIRMER, 1940 , a single specimen that was also collected from Teilia Quarry and originally described as Rhacopteris fertilis WALTON, 1926 ( Text-fig. 4c, d). Hirmer (1940) included R. fertilis within Anisopteris due to its similarity to the fertile frond section of Anisopteris lindseaeformis (BUNBURY) HIRMER, 1940 , the only species which includes both sterile and fertile material since Kidston (1923) synonymized Rhacopteris paniculifera STUR, 1875 with Rhacopteris lindseaeformis (BUNBURY) KIDSTON in Patton (1884) and which Hirmer transferred to Anisopteris remarking on the asymmetry of the sterile pinnules. There are therefore two fertile species of Anisopteris available for comparison with A. shuteana .

Anisopteris shuteana is similar to A. fertilis in that both species possess a longitudinally striated, flexuous, dichotomizing rachis, that is approximately 2.5 mm wide. The two species are of a similar size, with the fertile part of the branching system from the first dichotomy to the termination of the ultimate rachises for both species approximately 4 cm in length. The sporangia for both species are borne in clusters and are similar in shape, with the sporangia of A. fertilis reported as ovoid, with a length:width ratio of over 2:1, comparable with the narrow ovate outline of the sporangia in A. shuteana . However, the sporangia of A. fertilis are sessile and asymmetrical, while the sporangia of A. shuteana are pedicellate, pendent, and symmetrical in form. Unfortunatelly the illustration of A. lindseaeformis ( R. paniculifera STUR, 1875 ) is inadequate for detailed comparison. The new specimen cannot be placed in A. lindseaeformis because it differs in the nature of branching, with the branches of A. lindseaeformis shown to diverge at a narrow acute angle compared to the wide acute to obtuse dichotomizing of A. shuteana , and the different shape of the sporangia, as the sporangia of A. lindseaeformis are described as globular. These differences in the nature of branching and the attachment and shape of the sporangia means that it is not possible to place this new specimen in either A. fertilis or A. lindseaeformis and that it represents a new taxon.

There has been a long history of differing interpretations of the botanical affinities for Anisopteris . In her unpublished typescript, Benson agreed with Stur (1875) and Walton (1926) that the affinity of this type of frond is most likely with the ferns. Corsin (1960) classified Anisopteris under the Archaeopteridales, and Cleal and Thomas (1995) also remarked on the similarity of the fertile frond of A. fertilis ( Rhacopteris fertilis ) from Teilia Quarry to Archaeopteris fructifications and suggested that these may be representatives of progymnosperms. However, Galtier et al. (1998) analysed permineralized foliage material of A. lindseaeformis ( Rhacopteris lindseaeformis ) from the Visean of Scotland that revealed anatomical detail in addition to external morphology. They concluded that the sterile foliage of A. lindseaeformis showed Lyginorachis - type anatomy and suggested that the fronds represented the remains of arborescent seed ferns. A. shuteana is therefore included within the Lyginopteridales , but it has not been possible to assign this new species to a family.