Up the Andes and back in time

In 1924 Lincoln Ellsworth funded a John’s Hopkins University expedition to the Peruvian Andes and among the items that were brought back was a small collection of Lower Cretaceous plant fossils. They were described by paleobotanist E.W. Berry in 1939 and about two weeks ago I found them in the Smithsonian’s paleobotanical collections. When I find an interesting old collection like this one I like to get a little bit of background information on the people who made it, or in this case who made it possible. Lincoln was the only son of James Ellsworth, who made millions as a banker and owner of coal mines across Ohio, West Virginia and Pennsylvania in the late nineteenth and early twentieth century. As an adult Lincoln ended up living and traveling on a trust set up for him by his father. While working for years to set up an expedition to the North Pole, which finally happened in 1925, Lincoln financially supported the Johns Hopkins University trip to the Peruvian Andes in 1924.

In the 1939 report Berry reported the following taxa collected near Huallanca, Peru: Equisetities sp. Coniopteris peruviana, Cladophlebis browniana, Cladophlebis sp. Ruffordia goepperti, Klukia raciborski, Onychiopsis sp. Weicheselia retculata, Thinnfeldia sp. Sagenopteris cf. paucifolia, Otozamites peruvianus, Pterophyllum sp. Cycadolepis bonnieri, Podozamites sp. Brachyphyllum peruvianum, and Thujites pompeckji

When I read old species names from people like Berry and other early 1900′s american paleobotanists for the first time I pay little attention to the specific epithet (the second part of the species names) for a variety of reasons. Many of those old authors were over-splitters, increasing the number of species based on a few or uninformative characters, or based on geographic location. The generic names tell me what major group (e.g. fern, conifer, etc.) the fossil belongs to, but are often also outdated and require taxonomic revision. This is primarily a collection of ferns, cycads, and conifers. When I found the specimens in the museum’s collection, what struck me about them (and stuck Berry as well) was their familiarity. They were deposited sometime in the early part of the Early Cretaceous (145-125Ma) when South America and Africa were united in a single continent, but separated from North America and Eurasia. Nonetheless, Barry’s Weichselia, Sagenopteris, Cladophlebis, Ruffordia, and Coniopteris peruvianus are all indistinguishable from forms found in Europe and North America that I am familiar with. Others probably fit the same pattern, given that Barry chose to give them familiar generic names.

I said that I was struck by the familiarity of the fossils, but it is important to remember that the early part of the Early Cretaceous was globally warm time and therefore the climate gradient from the equator to the poles would have been less steep that it is today. The kinds of plants and the fine-grained, dark nature of the rock suggest that these plants probably grew in a swampy or wetland habitat, as did their northern counterparts. Under similar temperatures, similar water-availability conditions, and similar soil conditions, finding similar plants is not that surprising. Still, were talking across continents here (final separation from North America was in the Middle-Late Jurassic). With more fossils and a better understanding of the taxa that I am not yet familiar with, I wonder if it is even be possible to tell whether a given collection from the early part of the Early Cretaceous is from South America or North America/Europe based on relatively common leaf fossils alone.

Berry, E.W 1939. The fossil plants from Huallanca, Peru. in Contributions to the paleobotany of middle and South America. Johns Hopkins University Press.

http://www.bookrags.com/biography/lincoln-ellsworth/

http://pabook.libraries.psu.edu/palitmap/bios/Ellsworth__Lincoln.html

Cycadeoidea

Cycadeoidea is one of the classic genera of extinct Mesozoic plants. A 1971 reconstruction is widely reproduced online, and there was even a Fossil Cycad National Monument dedicated to these fascinating plants in South Dakota where many were preserved in place. Unfortunately, it was officially closed in 1975 because poachers had taken nearly all of the fossils.

Readers with something of a paleobotany background may already know that cycadeoids are not the same as modern cycads, and that early interest in these plants was driven by the hypothesis that they are closely related to flowering plants. Today it appears that cycadeoids were part of their own distinct lineage of seed plants, and the sister group of flowering plants continued to be debated.

Cycadeoids grew somewhat like palms, cycads, and some cacti today. These plants all have a primary thickening meristem. In other woody plants the growing shoot tip adds height to a plant whereas the vascular cambium adds thickness by producing wood and bark. In plants with a primary thickening meristem the growing tips add both height and girth. They either don’t produce wood at all (palms) or the vascular cambium produces relatively little wood (cycads and cycadeoids). Like many cycads, Cycadeoidea stems are covered in the hard, persistent bases of the old, shed leaves.  Unlike in modern cycads where seed cones or pollen cones are produced terminally as a dichotomous branch, the outer armor of leaf bases in a Cycadeoidea is interspersed with the cones that produced both pollen and seeds (you may see them referred to as flowers).

The images here are taken from slides made in the early 1900’s for publications by Wieland (1916). The slides come from one silicified Cycadeoidea trunk. Images of similar petrified trunks are not hard to find online; however, it can be fairly difficult to see detailed pictures of the internal anatomy without subscriptions to a few different scholarly journals.

First I have a longitudinal section of a Cycadeoidea trunk, as though the stem was in half along the axis. Look at how small the seeds were! In some cycadeoids there were cones associated with every leaf. These plants had high fecundity. [UPDATE: I just wanted to point out that the little gray or brown bodies in the seeds below and in the second image are the cute little baby cycadeoids. In some of them you can make out a couple cotyledons.]

Here is a tangential section of the trunk through the outer armor of leaf bases and cones. Because the cones are borne laterally, you are looking at cross sections of the cones, as though the cone was cut in half perpendicular to the axis.

Last is a near-longitudinal section through a stem apex. Most of the stem tissue is opaque (black), but you can see the pith bounded by vascular tissue at the bottom of the photo, and the armor of leaf bases along the sides with a cone base in the lower left. The tip is where we would expect to see immature leaves developing, but I’m not sure precisely what the wavy, hair-like lines are, but I will come back to them in a future post, after I’ve done a little more research. Mature leaves have never been found attached to permineralized Cycadeoidea trunks, but we know they were thick pinnate leaves similar to cycads because the arrangement of the vascular bundles in the petiole or rachis of detached leaves can be matched with the pattern in the persistent leaf bases (Yamada et al. 2009)

Wieland, G.R. 1916 American Fossil Cycads. Vol. 1. Carnegie Institute of Washington, Washington D.C.

Yamanda, T. J. Legrand, and H. Nishida 2009. Structurally preserved Nilssoniopteris from the Arida Formation (Barremian, Lower Cretaceous) of southwest Japan. Review of Palaeobotany and Palynology 156: 410-417

North America’s oldest flowering plants

The earliest evidence of flowering plants in North America comes from the Potomac Group deposits of Virginia and Maryland. The plant fossils found there provide a picture of what some of the earliest angiosperms looked like and how they grew. In addition to being of general interest, I hope that the pictures and information that I put up here will be of use to some students and teachers out there. Scale bars are always 1cm.

The Potomac Group includes the Patuxent Formation (Fm.), the Arundel clay, and the Patapsco Fm. It stretches out in an arc from Petersburg, VA, north through Fredericksburg, VA and into Northernmost Delaware along the coastal plain. A few years back Hochuli et al. (2006) published an update of the age of the Potomac Group deposits. They correlated the Potomac Group with well-dated deposits in Portugal by comparing the first occurrences of certain pollen taxa and the overall diversity-abundance patterns of pollen and spores. The Patuxent Fm. was assigned an Aptian age because of the presence of certain species of monocolpate pollen that have been found in the Aptian deposits of Portugal and around the world. At least one of these (Pennepollis peroreticulatus) is not found in pre-Aptian deposits. Tricolpate pollen grains, indicative of the eudicots, have not been reported from the Aptian section used by Hochuli et al., or in the Patuxent Fm. (see update below!)

Interestingly, tricolpate pollen is reported from Earliest Aptian deposits in England and Brazil (Friis et al. 2011) roughly 125-120Ma. According to Hochuli et al., in Portugal there is a well dated section through the Aptian that does not have any tricolpate grains. Hochuli et al. cited the absence of tricolpate pollen in the Patuxent Fm. and the Aptian portion of the Luz section as further evidence for the correlation. However, the latest Barremian-Early Aptian sites Torres Vedras and Catefica, also in Portugal, do have tricolpate pollen grains (Friis et al. 2011). So, no eudicots have been found in the Luz section, but they’re around in Portugal as well as England and Brazil. A little later in the Aptian, eudicot pollen and leaves are found in more places including Israel, Tunisia, China, and Argentina. So why aren’t they in the Patuxent Fm? Is it actually older? Are they so rare that we just missed them? We will return to the case of the missing Patuxent Fm. eudicots below.

Only a handful of plant fossil collections made over the last ~130 years have resulted in published records of Patuxent Fm. angiosperm leaves. Doyle and Hickey (1976) and Hickey and Doyle (1977) mention some these sites and discuss five distinct types of leaves. These are Acaciaephyllum longifolium, Proteaephyllum reniforme, Ficophyllum sp. Quercophyllum sp., and Rogersia sp. These are all simple leaves. (The names of these are unfortunate; the plants are only distantly related to the modern genera Acacia, Protea, Ficus, and Quercus.)

  

Acaciaephyllum leaves are narrow with a smooth margin but a glandular tip. They appear to have acrodromous venation. One or two pairs of lateral veins diverge from the midvein and then curve together again toward the apex. At the apex the midvein terminates in a gladular tooth that is also fed by two of the lateral veins.

Proteaephyllum reniforme is a challenging species. As far as I know there is only one specimen and it doesn’t seem to be standing the test of time very well. The midvein bears closely spaced, pinnately-arranged secondary veins near the base of the leaf, and then about halfway up the leaf it seems to transition into a spray of about 6 (but maybe 5 or 7) different veins that fan out. I can’t make out much of a margin, but by following some of the most basal secondary veins with very high magnification, it becomes clear that the base widens rapidly above the transition from petiole to lamina.

So far, I’ve found only one specimen of Ficophyllum labeled the Patuxent Fm. in the Smithsonian’s collections. It is the base of a relatively large pinnate leaf with an entire margin as far as is visible. It has secondary veins near the base that sweep away from the midvein (decurrent) and secondary veins higher up that come straight out (excurrent). Another leaf, labeled Proteaphyllum tenuinerve, looks more like the Ficophyllum leaves found in the Arundel Clay. A third leaf labeled Proteaephyllum tenuinerve looks different yet again, but could be a member of either of the other two types with different preservation.

Rogersia (not pictured) was mentioned as a Patuxent Fm. taxon in Doyle and Hickey 1976 based on “recent” collections as well, but the Patuxent Formation specimen was not figured. It appears that the specimen is not housed at the Smithsonian. Rogersia is an entire, pinnate leaf with decurrent secondary veins. The petiole is not always well differentiated, suggesting it may have been an herb. Quercophyllum (not pictured) is a pinnate leaf with glandular teeth, but the Patuxent Fm. specimens were housed at the University of Michigan Museum of Paleobotany in 1976. They may still be there, but I didn’t check.

In looking through these collections, I have come across specimens that are distinct from those original five. The total, it seems to me, is in fact eight. In addition, Upchurch (1984) figured at least four types of Patuxent Fm. angiosperm cuticle from one site, and there are a few mentions here and there in the literature that diverse angiosperm fruits and seeds have been recovered from the Patuxent Fm. as well, but I haven’t read about these yet. In any case, the sampled angiosperm diversity in the Patuxent Fm. is higher than is often discussed. But where are the eudicots? Well, I think I’ve found one, but I’ll have to post about it sometime in the future. I promise it will be exciting!

UPDATE! It turns out that I missed an important detail. Doyle (1992) briefly mentioned that a few rare tricolpate grains were reported from one Patuxent Fm. site, and it is the same site as the new leaf fossil I hinted at the end of this post!

Doyle, J.A. 1992. Revised palynological correlations of the Lower Potomac Group (USA) and the Cocobeach sequence of Gabon (Barremian-Aptian). Cretaceous Research 13:337-349

Doyle, J.A., Hickey L.J. 1976. Pollen and leaves from the Mid-Cretaceous Potomac group and their bearing on early angiosperm evolution. In: Beck, C.B. ed. Origin and Early Evolution of Angiosperms. Columbia Univ. Press: New York & London. pp. 139-206.

Friis, E.M., P.R. Crane, and K.R. Pedersen 2011. Early Flowers and Angiosperm Evolution. Cambridge University Press: New York.

Hickey, L.J. and J.A. Doyle 1977. Early Cretaceous evidence for angiosperm evolution. Botanical Review 43(1):2-104

Hochuli, P.A., U. Heimhofer, and H. Weissert 2006. Timing of early angiosperm radiation: recalibrating the classical succession. Journal of the Geological Society, London 163:587-594.

Upchurch, G.R. 1984. Cuticular anatomy of angiosperm leaves from the Lower Cretaceous Potomac Group. I. Zone I Leaves. American Journal of Botany 71(2):192-202

Just gorgeous

This is a polished cross section of a fern trunk that I came across in the Natural History Museum while looking for other fossils. What great colors and anatomy! If you aren’t sure what you’re looking at, think of a typical tree first, like an oak tree. If you cut it down look down at the stump you would be looking at a cross-section of the trunk. You would see outer ring of bark surrounding wood with growth rings, and maybe a bit of pith tissue in the very center. If you cut down a tree fern like this one, this is what you’d see. There is no wood. The thick outer zone of small circles is a mantle of tough roots that provided support to the stem. The stem is the circular structure surrounded by the root mantle, and it has a lot of C-shaped leaf traces in the cortex. In the middle of the stem is another ring of little bundles. This is the stele, where the xylem and phloem is, and in the middle of the stele is that sort of pale-yellow area. That is the pith.

So who is this? This plant is a relative of modern Osmundaceae, a small but widely distributed family of ferns that includes the cinnamon fern, the interrupted fern, and the royal fern. This fossil would probably be assigned to the extinct subfamily Guaireoideae (woah, too many vowels, I know), but the taxonomy of Paleozoic and Mesozoic Osmunda-like ferns is not fully worked out, and so I don’t worry too much about subfamilies. This fossil comes from near the city of Rio Pardo in Rio Grande do Sul, Brazil. It was described by Henry Andrews in 1950 as Osmundites braziliensis. But today is called Guairea carneiri because trunks called Osmundites were transferred to Osmundacaulis, and then Osmundacaulis was divided up into three groups, Osmundacaulis, Millerocaulis, and Guairea; and then G. brasiliensis turned out to be indistinguishable from the earlier species G. carneiri.

In the late Paleozoic and during most of the Mesozoic the Osmudaceae was an impressive family in terms of growth form. Many of these plants were tall tree-ferns, and in some places quite abundant. Today we have shorter, though stately, ferns with mostly subterranean stems. Todea spp., though, can get somewhat “trunky” and may be the best plant to help give an image of the plant this colorful trunk came from. Here are two links to another site with pictures of an impressive Todea barbara. image 1 image 2

Here’s the reference for the original paper.

Andrews, H. 1950. A Fossil Osmundaceous Tree Fern from Brazil. Bulletin of the Torrey Botanical Club 77(1): 29-34

Patuxent Formation plants

The Early Cretaceous marks the beginning of the transformation of terrestrial ecosystems by flowering plants. I think that to understand the early evolution of flowering plants we have to have a picture of what kinds of ecosystems the earliest flowering plants encountered. Here in Maryland is the Patuxent Formation, an Aptian deposit of sands, clays, and sandy clays. There happens to be an outcrop of this layer right near the University of Maryland Campus. A while back I was preparing for an introductory course on aquatic ecology in a local stream when I noticed what looked like burned wood on the banks. At first I thought it was leftover from a bonfire or something, but when I picked it up I realized it was heavy with mineralization. I started looking up stream, and along the bank was a thin layer of clay with more of the black, compressed, lignified wood sticking out. Later I walked further upstream and found a cutbank with large logs sticking out. Some were more than two feet wide, and within a few minutes of poking around I was pulling out compressed conifer cones that were circular and a little smaller than a dime.

This particular spot is now covered up to prevent further erosion, but with a little research I began to paint a picture. About 125-115 million years ago, when flowering plants were still quite rare, the University of Maryland College Park Campus was a warm, subtropical forest dominated by large Taxodium-like conifers with an abundance of ferns in the understory. One of these was Anemia dicksonioides. Modern species of Anemia are tropical to subtropical, mostly new world ferns. Another, Loxsomatopteris, has living relatives in New Zealand, Costa Rica, and along the tropical Andean corridor from Columbia to Bolivia. Both of these fossil ferns were described from collections made very near the large cutbank where I found the wood and cones.

Other fossils the same level in the D.C. and Virginia area provide evidence of other ferns, other kinds of conifer wood and foliage, cycads such as Doonites, and rare flowering plants that I may discuss in a future post.

  

Fossils are fun!

reallyoldplants is a blog about plant fossils and evolution, usually with a focus on the Cretaceous period and early flowering plants. My name is Nathan, I am a graduate student at the University of Maryland and the National Museum of Natural History where I am working on a thesis that centers around Early Cretaceous plant fossils which I collect each summer in Wyoming. I envision this as a place where people can read about interesting or unique plant fossils as a means to think about evolution, extinction, and how the plants around us came to be. I expect this vision to develop and change with time, but I hope you enjoy looking and thinking about fossils with me along the way.