Mario Coiro

While doing some doomscrolling on Twitter, I came across this absolutely spectacular reconstruction of the Triassic Fremouw Formation by Liam Elward. The main focus of the piece are a couple of Lystrosaurus, but the attention to the flora of this formation is stunning. Many plants are known from the Fremouw formation, with many having been reconstructed as whole plants (see the Extinct Plant Paleoart database for references). This gave the artist the opportunity to pay extreme attention to the flora, including many living plants as well as foliage in the litter.

Many other formations with well-known floras receive less attention mostly because they often lack charismatic fauna. This is due to the different conditions that favour the preservation of vertebrate fossil compared to plants. In this new series, I am going to describe some of these localities and their floras, in the hope of inspiring paleoartists to try and reconstruct such paleoenvironments (or use some of the elements in other reconstructions). I will start with a formation that is close to my heart, since I started my paleobotanical investigations by reexamining material from this formation. Moreover, the complete absence of vertebrate fossils from this formation makes it easy to overlook it, even if it can give us an incredible look at the biomes and vegetation of the Early Cretaceous.

The Anfiteatro de Ticó is one of the three formations which compose the Baqueró group, a continental succession cropping in the center of the Deseado Massif, in the provice of Santa Cruz, Argentina. The age of this formation is Aptian (Early Cretaceous), with the lower limit constrained to 119 millions of years ago by radiometric dating. These sediments were probably deposited in a river system with numerous lakes.

The flora of this formation has been studied since the 1960s, with the first treatment published by Sergio Archangelsky in 1963. Numerous successive studies have identified one of the most rich floras from the Early Cretaceous, including a mixture of different elements with various affinities.

Here I will focus on the macrofloral elements of the formation, and quickly touch the palynoflora. Reconstruction of some of the elements of the flora were kindly provided by Julian Kiely. The help of Ezequiel Vera was unvaluable in drafting this post, and he provided the spectacular picture of the locality.

Non-seed plants

The Anfiteatro de Ticó does not present a high richness of bryophytes, ferns and fern allies. It includes the liverwort Ricciopsis grandensis, the horsetail Equisetites pusillus, as well as the ferns Cladophlebis tripinnata, Cyathea cyathifolia, Baqueroites padulae, Adiantopteris tripinnata, Korallipteris vegagrandis, Cladophlebis antarctica, and some other schizaeaceous fern remains.

Bennettitales

Bennettites are not uncommon in the Anfiteatro de Ticó formation, with multiple foliage species assignable to the genera Ptilophyllum, Dictyozamites, Otozamites, Zamites, and Pterophyllum, as well as reproductive material assignable to the genus Williamsonia.

Ginkgoales

The ginkgoales are represented by the ovulate structure Karkenia, dispersed seeds (Allicospermum patagonicum) and two species of foliage assigned to the genus Ginkgoites.

Cycadales

Many species of foliage and other organs assigned to the Cycadales are retrieved from the Anfiteatro de Ticó, including taxa only known from this locality. These include species of Pseudoctenis, as well as the bipinnate leaves Mesosingeria, the entire leaf Sueria, the probably zamiaceous leaflet Restrepophyllum chiguoides and Almargemia dentata (that me and Christian Pott proposed to transfer in the new genus Eobowenia). Another taxon assigned by Archangelsky to the Cycadales, Ticoa, has pecopteroid pinnules, and other authors consider it to be a seed fern with uncertain affinities.

‘Seed ferns’

The formation includes the seed fern Ruflorinia and its reproductive organs Ktalenia. The Ruflorinia–Ktalenia plant was a member of the Caytoniales, the group including Sagenopteris and Caytonia. However, the morphology and venation of Ruflorinia differs substantially from Sagenopteris in being a bipinnate leaf with no vein fusion (anastomosis). A reference with a reconstruction of Ruflorinia/Ktalenia can be found here.

Conifers

The conifers known from the formation include compression fossils including vegetative and reproductive material of Cheirolepidiaceace (Tomaxellia, Brachyphyllum, Tarphyderma), Araucariaceae (Alkastrobus,Brachyphyllum) and Podocarpaceae (Podocarpus, Trisacocladus, Morenostrobus, Apterocladus). Moreover, preserved fossil trunks are also found in the formation. Of these, Agathoxylon represents aracauriacean wood, while Brachyoxylon could have affinities with the Cheirolepidiaceae.

Gnetales

Unlike many other Early Cretaceous formations, the Anfiteatro de Ticó only has one species of Ephedra as representative of the Gnetales.

Angiosperms

Few angiosperms are known from the formation. One of such leaves (Morphotype A) has a ‘nymphaeaphyll’ morphology, while others have a lobate serrate margin. We have recently proposed that Mesodescolea plicata, which was previously described as a cycad leaf, represents another angiosperm taxon in the formation.

Pollen flora

The pollen flora of the formation shows the presence of many elements which are not preserved in the macrofossil record. Spores of hornworts and Lycopodiales are recovered, as well as more diverse fern assemblages including Gleicheniaceae, Lophosoriaceae, Schizaeaceae, Osmundaceae, Dicksoniaceae, Pteridaceae, and other groups. Angiosperm pollen is also present, including Clavatipollenites (usually assigned to the Chloranthaceae), Retimonocolpites, Jusinghipollis and Lethomasites.

Associations and fossiliferous levels

Even though we have described all the species found in the formation, this does not indicate that all these actually grew together. In fact, it could well be that many of these species were separated by hundred of thousands of years!

However, we can identify some fossiliferous levels that potentially preserve actual ecological associations. One of this levels includes Ginkgoites ticoensis, the seeds Allicospermum patagonicum, and the dennstaedtiaceous fern Cladophebis tripinnata. Another includes different lenses, one including Ticoa harrisii and Tomaxiella deguistoi and another including Ruflorinia/Ktalenia and Mesodescolea plicata together with Brachyphyllum. The bennettitalean remains are usually found together in different fossiliferous layers. The fern Adiantopteris tripinnata and Ephedra are found always in association in the Bajo Grande locality outcrops.

These cooccuring plants probably occupied different roles in the vegetation. Large coniferous trees (Aracuariaceae, Podocarpaceae) would have made up the canopy of forested environments, while smaller trees such as ginkgoes, cycads, bennettitaleans, and tree ferns (and potentially some of the seed ferns) would have occupied either the understorey or more distrurbed or open environments. A layer of non-arborescent ferns and (few) angiosperms would have occupied the ground layer of the understorey, with Gnetales such as Ephedra occupying more open habitats.

All this indicates presence of different environments and association through the depositional history of the formation, and offers paleoartists the opportunity of using any of these to portray different scenes.

References:

Archangelsky, S., 1963. A new Mesozoic flora from Ticó, Santa Cruz Province, Argentina (Vol. 8, No. 2). British Museum (Natural History).
Archangelsky, S., 1968. On the genus Tomaxellia (Coniferae) from the Lower Cretaceous of Patagonia (Argentina) and its male and female cones. Botanical Journal of the Linnean Society, 61(384), pp.153-165.
Archangelsky, S., Barreda, V., Passalia, M.G., Gandolfo, M., Pramparo, M., Romero, E., Cúneo, R., Zamuner, A., Iglesias, A., Llorens, M. and Puebla, G.G., 2009. Early angiosperm diversification: evidence from southern South America. Cretaceous Research, 30(5), pp.1073-1082.
Del Fueyo, G.M., Guignard, G., de Seoane, L.V. and Archangelsky, S., 2013. Leaf cuticle anatomy and the ultrastructure of Ginkgoites ticoensis Archang. from the Aptian of Patagonia. International Journal of Plant Sciences, 174(3), pp.406-424.
Limarino, C.O., Passalia, M.G., Llorens, M., Vera, E.I., Loinaze, V.S.P. and Césari, S.N., 2012. Depositional environments and vegetation of Aptian sequences affected by volcanism in Patagonia. Palaeogeography, Palaeoclimatology, Palaeoecology, 323, pp.22-41.
Llorens, M. and Loinaze, V.S.P., 2016. Late Aptian angiosperm pollen grains from Patagonia: earliest steps in flowering plant evolution at middle latitudes in southern South America. Cretaceous Research, 57, pp.66-78.
Passalia, M., Archangelsky, S., Romero, E. and Cladera, G., 2014. A new early angiosperm leaf from the Anfiteatro de Tico Formation (Aptian), Santa Cruz Province, Argentina. Revista del Museo Argentino de Ciencias Naturales nueva serie, 5(2), pp.245-252.
Taylor, T.N. and Archangelsky, S., 1985. The Cretaceous pteridosperms Ruflorinia and Ktalenia and implications on cupule and carpel evolution. American Journal of Botany, 72(12), pp.1842-1853.
Vera, E.I. and Césari, S.N., 2012. Fossil woods (Coniferales) from the Baqueró Group (Aptian), Santa Cruz Province, Argentina. Anais da Academia Brasileira de Ciências, 84(3), pp.617-626.