- The fossil record of cycads dates back to the Upper Paleozoic era, with more complete remains found from the Triassic and Jurassic periods. - Lyssoxylon, found in the Upper Triassic of Arizona, had features matching modern cycads like Dioon spinulosum including growth rings and araucarian-type bordered pits. - Leptocycas, from the Upper Triassic of North Carolina, was a slender-stemmed cycad up to 1.5 meters tall that lacked persistent leaf bases on its stem. - Reconstructions of Jurassic cycads combined foliage like Nilssonia leaves with reproductive structures like the ovulate cones

1. C.M.P. DEGREE COLLEGE , PRAYAGRAJ
DEPARTMENT OF BOTANY
Assignment Work
On:- Fossil history of cycdales
Submitted to :- Dr. Yashwant Singh
Submitted by :- Akash Maurya
M.Sc – I sem (2022-2023)

2. FOSSIL CYCADS
Introduction
 The beginning of Cycadales is not known.
 The fossil remains provisionally assigned to Cycadales are
meagre, in the Upper Palaeozoic. From the Triassic have been
reported undoubted cycads which spread rapidly over the
earth.
 Tertiary cycads mostly belonged to the modern genera. The
most complete and well-preserved remains are from the
Upper Triassic and Jurassic.

3. LYSSOXYLON.
 Gould (1971) described a well-preserved permineralized specimen
of Lyssoxylon, a stem genus, from the Upper Triassic of Arizona.
 The stem has a large central pith, a cylinder of compact secondary
wood, and an outer cortical region surrounded by persistent spirally
arranged leaf bases.
 The stele has well-defined "growth rings", rays of two types, and
tracheids with multiseriate alternate circular bordered pits of the
araucaroid type, on the radial walls (cf. extant Dioon spinulosum).
 These characteristics indicate that the affinities of Lyssoxylon are
with the Cycadales.

4. LEPTOCYCAS.
 Delevoryas and Hope (1971), from the Upper Triassic beds of North Carolina,
described a remarkably complete compression-impression fossil of a cycad
stem with leaves and pollen cone attached.
 The stomata are haplocheilic, and other characteristic features are also
cycadean.
 The attachedfronds are comparable to the isolated cycad frond type
Pseudoctenis. A new genus Leptocycas has been established. The
reconstruction depicts a slender stem, ca.1.5 m tall, bearing a crown of leaves,
some exceed 30 cm in length. Persistent leaf bases on the stem are absent.
 The general morphology of Leptocycas suggests that primitive cycads had
slenderstems; the bulky, fleshy stem of a typical extant cycad is derived.

5. Reconstruction of extinct Cycad plant. A.Leptocycas B.Leptocycas Fossil

6.  Harris (1961) placed the reproductive organs and foliage on an
imaginary branched stem which had an armour of leaf bases, and
reconstructed a Jurassic cycad.
 It had crown of Nilssonia tenuinervis leaves, ovulate cones of
Baenia sp. (described later), and pollen cones of Androstrobus sp.
(described later). All the genera are from the Jurassic Cayton Bay
beds of Yorkshire.

7.  Cycad bearing Beania ovulate cones and
Nilssonia type foliage.

8. NILSSONIA
 This is one of the most common and widely distributed Mesozoic
cycadean
 leaf types-slender, 60 cm long, 10 cm wide.
 The lamina is entire or dissected into pinnule-like segments and is
supported on a strong mid-rib from which simple veins pass
obliquely or at right angles to the margin.
 The veins are rarely forked. There is considerable variation within a
species.
 The stomatal characters display cycadean affinity. The genus is
nearly worldwide in distribution from Triassic to Cretaceous.

9. NILSSONIA. LEAF

10. BAENIA.
 Two species are known. In B. Gracilis, peltate sporophylls (1.5- 2.5 cm) are
arranged spirally in a loose cone (10 cm long) around a central axis, each
bearing two ovules with their micropyle towards the cone axis.
 The mature seeds (detached seeds are also called Baenia) are 7 × 7 mm to 16
x 16 mm. On maceration, four cutinized layers have been observed.
 Their distribution indicates that the integument is fused to the nucellus
throughout the lower two-thirds of the seed, and is free at the apex.
 There is an outer fleshy, middle stony, and an inner fleshy layer.
 There is evidence of vascular bundles running longitudinally up to the level
where the integument became free from the nucellus.
 The remains of pollen grains (identical with those of Androstrobus manis)
have been observed inside the micropyle.

11. A SEED “CONE”. B MEGASPOROPHYLL WITH ONE SEED IN
LONGISECTION.
A. B.

12. ANDROSTROBUS
 The cones are compact, ca. 5 cm long and 2 cm broad.
 Each cone has a large number of spirally arranged peltate
microsporophylls, each is terminated by a rhomboidal scale and
has numerous finger-like pollen sacs on the abaxial side .
 They are arranged in sori with dehiscence slits along their inward-
facing walls.
 The pollen isolated from the microsporangia are small, ovoid and
monocolpate, as in extant cycads.

13. ANDROSTROBUS MANIS.
D. MICROSPORANGIATE CONE. E MICROSOROPHYLL.

14. THANK YOU