Sorry, not convinced they are particularly ancient, compared to other conifers!

Larix and Pseudolarix have a shorter known fossil history than most other genera

Ginkgo - have they all, always, been deciduous? Some extinct Ginkgos could easily have been evergreen.

Why some plants became deciduous - three reasons:

Winter darkness at high latitudes north of the Arctic Circle; e.g. Metasequoia fossils on Axel Heiberg Island, palaeolatitude c.85°N. Also (in theory) south of the Antarctic Circle, though there are very few deciduous plants in the southern hemisphere (5 species of Nothofagus and a handful in other genera), maybe because most of what there might have been became extinct on Antarctica.

Dry season dought (e.g. deciduous forests of India, Brazil) - no extant conifers in this group, though.

Winter cold.

Resin

Yes it seems trees had a decision to make. Either stay green and produce some kind of anti freeze or develop a way of taking back the nutrients and dropping the leaves. Environment at the time would dictate which path to take.

One thing that's been pointed out, is that deciduous species are commoner in fertile soils, while evergreen species tend to occur more in nutrient-poor soils; if nutrient availability is very low, don't let go of what little you've been able to get.

Having said that, there's plenty of exceptions; e.g. larches do well on low nutrient soils.

Resin

Could deciduous conifiers have evolved to compete with non-conifer deciduous trees?

Seems like a lot of evergreen conifers live where other trees would struggle, maybe pushed out over time to harsher ground.

With all due respect to mr. resin, the habitat in which Pseudolarix is known today does not promote fossilization. If this species has always inhabited similar areas, it would fossilize rarely.

Such as with orchids. Despite recent spectacular finds, there is a dearth of fossils that can be conclusively attributed to this undeniably old lineage of flowering plants. Lack of fossils does not mean much.

"habitat in which Pseudolarix is known today does not promote fossilization"

Good point; fossils can be difficult to form. There are however abundant Pseudolarix fossils in European lignite deposits (Pliocene age). Checked up; the earliest reported Pseudolarix fossils are from the late Cretaceous in northeastern Siberia.

Resin

Farjon in "Natural History of Conifers" mentions the 1st of Resin's 3 reasons. He hypothesizes that that deciduousness in these conifers was an adaptation to the winter darkness in the arctic circle when that part of the world was warm. As the arctic circle became cold, these deciduous conifers migrated south.

He does not discuss Antarctica in this connection. Maybe, deciduousness never developed there as an adaptation to winter darkness. If it did develop there, another possibility might be that the connections to Australia and So. America might have been severed by the time Antarctica started growing cold, thereby blocking routes of possible migration northwards.

Well, the ginkgo is not closely related to the conifers. The conifers which are deciduous are in various branches. The Bald Cypress and Dawn Redwood are in Cupressaceae while The Larches and the Golden Larch are in Pinaceae although in different subfamilies. It seems like a parallel development. If you really want to see interesting conifer leaves the Phyllocladus have some really unique leaves, rather wide and leafy looking.

"If you really want to see interesting conifer leaves the Phyllocladus have some really unique leaves, rather wide and leafy looking"

Phyllocladus 'leaves' are actually modified flat shoots - the real leaves are tiny scale-like things about half a millimetre long.

Resin

Wow pineresin thanks for that info! What an interesting developments so are the leaves just vestigial leftovers with little purpose? So I guess the proto-Conifer would have had needle leaves for sure?

Resin

Are all the phyllocladus confined to southern Britain
I have the 3 NZ species and the one Tasmanian species
here.

"Phyllocladus 'leaves' are actually modified flat shoots - the real leaves are tiny scale-like things about half a millimetre long."

Same with sciadopitys, right? What other conifers are like this?

"What an interesting developments so are the leaves just vestigial leftovers with little purpose?"

Yep! Not sure they're even photosynthetic.

"So I guess the proto-Conifer would have had needle leaves for sure?"

Reasonable to assume, yes. All the various conifers with scale-leaves (cypresses, etc., etc.) all start off with needles in their juvenile phase, no conifer with needles starts off with scale leaves. So scale leaves are the derived feature, and needles the basal. It can however work the other way, e.g. Juniperus communis has gone back to needles, losing the scale leaves that its more immediate ancestors had.

"Are all the phyllocladus confined to southern Britain"

More western, than southern. They'll grow OK in e.g. western Scotland, and better there than in the southeast.

"Same with sciadopitys, right?"

Maybe; the precise derivation of its foliage is AFAIK still uncertain.

"What other conifers are like this?"

None. Unless one can argue a case for freak mutations like Cryptomeria japonica 'Cristata'.

Resin