Krassilovia: An Amazing Cretaceous Conifer

Reconstructing extinct organisms based on fossils is no simple task. Rarely do paleontologists find complete specimens. More often, reconstructions are based on fragments of individuals found either near one another or at least in similar rock formations. This is especially true for plants as their growth habits frequently result in fragmentary fossilization. As such, fossilized plant remains of a single species are often described as distinct species until subsequent detective work pieces together a more complete picture.

Such was the case for the fossil remains of what were described as Krassilovia mongolica and Podozamites harrisii. Hailing from the Early Cretaceous (some 100-120 million years ago), Krassilovia was only known from oddly spiny cone scales and Podozamites was only known from strap-shaped leaves found in a remote region of Mongolia. Little evidence existed to suggest they belonged to the same plant. That is, until these structures were analyzed using scanning electron micrographs.

(A–C) Articulated seed cones, (D) Isolated cone axis, (E) Incomplete leafy shoot showing a cluster of three attached leaves, (F) Three detached strap-shaped leaves, G) Detail of A showing tightly imbricate interlocking bract-scale complexes, (H) Detail of leaf apex showing converging veins, (I) Three isolated bract-scale complexes showing abaxial (top) and adaxial (bottom) surfaces, (J) Two isolated seeds showing narrow wings. [SOURCE]

These fossilized plant remains were preserved in such detail that microscopic anatomical features such as stomata were visible under magnification. By studying the remains of these plants as well as others, scientists discovered some amazing similarities in the stomata of Krassilovia and Podozamites. Unlike other plant remains associated with those formations, the Krassilovia cone scales and Podozamites leaves shared the exact same stomate morphology. Though not without some uncertainty, the odds that these two associated structures would share this unique morphological trait by chance is slim and suggests that these are indeed parts of the same plant.

The amazing discoveries do not end with stomata either. After countless hours of searching, fully articulated Krassilovia cones were eventually discovered, which finally put the strange spiky cone scales into context. It turns out those spiked scales interlocked with one another, with the two bottom spikes of one scale interlocking with the three top spikes of the scale below it. In life, such interlocking may have helped protect the developing seeds within until they had matured enough to be released. Also, the sheer volume of cone scales coupled with other minute anatomical details I won’t go into here indicate that, similar to Abies and Cedrus cones, Krassilovia cones completely fell apart when fully ripe.

Though not related, the cone scales of the extinct Krassilovia (left) show similarities with the cone scales of modern day Cryptomeria species (right).

Interestingly, the ability to resolve microscopic structures in these fossils has also provided insights into some modern day taxonomic confusion. It turns out that Krassilovia shares many minute anatomical similarities with present day Gnetales. Gnetales really challenge our perception of gymnosperms and their superficial resemblance to angiosperms have led many to suggest that they represent a clade that is sister to flowering plants. However, more recent molecular work has placed the extant members of Gnetales as sister to the pines. Evidence of shared morphological features between extinct conifers like Krassilovia and modern day Gnetales add some interesting support to this hypothesis. Until more concrete evidence is described and analyzed, the true evolutionary relationships among these groups will remain the object of heated debate for the foreseeable fture.

What we can say is that Krassilovia mongolica was one remarkable conifer. Its unique morphology clearly demonstrates that conifers were once far more diverse in form and function than they are currently. Even the habitat in which Krassilovia once lived is not the kind of place you can find thriving conifer communities today. Krassilovia once grew in a swampy habitat. However, whereas only a few extant conifers enjoy swamps, Krassilovia once shared its habitat with a wide variety of conifer species, the likes of which we are only just beginning to appreciate. I for one am extremely excited to see what new fossil discoveries will uncover in the future.

LISTEN TO EPISODE 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS FOSSIL AND THE ECOSYSTEM IN WHICH IT ONCE EXISTED.

Photo Credits: [1] [2] [3]

Further Reading: [1]

The Ginkophytes Welcome a New Member

Despite their dominance on the landscape today, the evolutionary history of the major seed-bearing plant lineages is shrouded in mysteries. We simply don't have a complete picture of their evolution and diversification through time. Still, numerous fossils are turning up that are shedding light on some of these mysteries, including some amazingly well-preserved plant fossils from Mongolia. One set of fossils in particular is hinting that the part of the seed-bearing family tree that includes the Ginkgo was much more diverse in both members and forms.

The fossils in question were unearthed from the Tevshiin Govi Formation of Mongolia and date back to the Early Cretaceous period, some 100 to 125 million years ago. Although these fossils do not represent a newly discovered plant, their preservation is remarkable, allowing a much more complete understanding of what they were along with where they might sit on the family tree. The fossils themselves are lignified and have preserved, in extreme detail, fine-scale anatomical details that reveal their overall structure and function.

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The paleobotanical team responsible for their discovery and analysis determined that these were in fact seed-bearing cupules of a long-extinct Ginkgophyte, which they have named Umaltolepis. Previous discoveries have alluded to this as well, however, their exact morphology in relation to the entire organism has not always been clear. These new discoveries have revealed that the cupules (seed-bearing organs) themselves were borne on a stalk that sat at the tips of short shoots, very similar to the shoots of modern Ginkgo. They opened along four distinct slits, giving the structure an umbrella-like appearance.

The seeds themselves were likely wind dispersed, however, it is not entirely clear how fertilization would have been achieved. Based on similar analyses, it is very likely that this species was wind pollinated. Alongside the cupules were exquisitely preserved leaves. They were long, flat, and exhibit venation and resin ducts similar to that of the extant Ginkgo biloba. Taken together, these lines of evidence point to the fact that this group, currently represented by a single living species, was far more diverse during this time period. The differences in seed bearing structures and leaf morphology demonstrates that the Ginkgophytes were experimenting with a wide variety of life history characteristics.

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Records from across Asia show that this species and its relatives were once wide spread throughout the continent and likely inhabited a variety of habitat types. Umaltolepis in particular was a denizen of swampy habitats and shared its habitat with other gymnosperms such as ancient members of the families Pinaceae, Cupressaceae, and other archaic conifers. Because these swampy sediments preserved so much detail about this ecosystem, the team suggests that woody plant diversity was surprisingly low, having turned up fossil evidence for only 10 distinct species so far. Other non-seed plants from Tevshiin Govi include a filmy fern and a tiny moss, both of which were likely epiphytes.

Whereas this new Umaltolepis species represents just one player in the big picture of seed-plant evolution, it nonetheless a major step in our understanding of plant evolution. And, at the end of the day, fossil finds are always exciting. They allow us a window back in time that not only amazes but also helps us understand how and why life changes as it does. I look forward to more fossil discoveries like this.

LISTEN TO EP 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS DISCOVERY AND MORE!

*Thanks to Dr. Fabiany Herrera for his comments on this piece

Photo Credits: [1]

Further Reading: [1] [2]

Ferns Unchanged

Ferns are old. Arising during the late Devonian period, some 360 million years ago, ferns once dominated the land. These ancient ferns were a bit different than the ferns we know today. It wasn't until roughly 145 million years ago, during the late Cretaceous period, that many extant fern families started to appear. However, a recent fossil discovery shows that at least one familiar fern was hanging out with dinosaurs as far back as 180 million years ago!

A team of scientists in Sweden recently unearthed an exquisitely preserve fossil of a fern from some early Jurassic deposits. Usually the fossilization process does not preserve very fine details, especially not at the cellular level, but that is not the case for this fossil. Falling into volcanic hydrothermal brine, the fern quickly mineralized. The speed at which the tissues of the fern were replaced by minerals preserved details that paleontologists usually only dream about. Clearly visible in the fossilized stem are subcellular structures like nuclei and even chromosomes in various stages of cell division!

 

A) Section of the fossil rhizome. B-J) Exquisitely preserve cellular details [SOURCE]

Using sophisticated microscopy techniques, the team was able to analyze the properties of the nuclei undergoing division. What they discovered is simply amazing. The number of chromosomes as well as other properties of the DNA matched a fern that is quite common in eastern North America and Asia today. This fossilized fern, as far as the team can tell, is a close relative of the cinnamon fern (Osmundastrum cinnamomeum), placing it in the royal fern family (Osmundaceae). Based on the fossil evidence, relatives of these ferns were not only around during the early Jurassic, they have remained virtually unchanged for 180 million years. Talk about living fossils!

Further Reading: [1] [2]

Paleo Pinus

Photo Credit: Howard Falcon-Lang, Royal Holloway University of London

What you are looking at here is the oldest fossil evidence of the genus Pinus. Now, conifers have been around a long time. I mean really long. Recognizable members of this group first came onto the scene sometime during the late Triassic, some 235 million years ago. Today, one of the most species-rich genera of conifers are those in the genus Pinus. They dominate northern hemisphere forests and can be found growing in dry soils throughout the globe. For such a commonly encountered group, their origins have remained a bit of a mystery. 

The fossil was discovered in Nova Scotia, Canada. Unlike the rocky fossils we normally think of, this fossil was preserved as charcoal, undoubtedly thanks to a forest fire. The degree of preservation in this charcoal specimen is astounding and provides ample opportunity for close investigation. 

I mentioned that this fossil is old. Indeed it is. It dates back roughly 133 –140 million years, which places it in the lower Cretaceous. What is remarkable is that it predates the previous record holder by something like 11 million years. Even more remarkable, however, is what this tiny fossil can tell us about the ecology of Pinus at that time. 

Firstly, the leaf scars indicate that this tree had two needles per fascicle. This implies that the genus Pinus had already undergone quite the adaptive radiation by this time. If this is the case, it pushes back the clock on pine evolution even earlier. Another interesting feature are the presence of resin ducts. In extant species, these ducts secrete highly flammable terpenes, which would have potentially promoted fire. 

Species that exhibit this morphology today often utilize an ecology that promotes devastating crown fires that clear the land of competition for their seedlings. Although more evidence is needed to confirm this, it nonetheless suggests that such fire adaptations in pines were already shaping the landscape of the Cretaceous period. All in all, this fossil is a reminder that big things often come in small packages. 

Photo Credit: Howard Falcon-Lang, Royal Holloway University of London

Further Reading:

http://bit.ly/1QP85zm

Cretaceous Seeds Shine Light on the Evolution of Flowering Plants

What you are looking at here are some of the earliest fossil remains of flowering plants. These seeds were preserved in Cretaceous sediments dating back some 125–110 million years ago. Fossil evidence dating to the early days of the angiosperm lineage is scant, which makes these fossils all the more spectacular. Thanks to a large collaborative effort, Dr. Else Marie Friis is shining light on the evolution of seeds.

Finding these fossils is not a matter of seeing them with the naked eye. These seeds are tiny, ranging from half a millimeter up to 2 millimeters in length. They were discovered using an advanced form of X-ray microscopy. The advantage of this technique is not only that it is nondestructive but it also allows researchers to investigate the internal structures of the seeds that would otherwise be impossible to see. Their preservation is mind blowingly delicate, allowing researchers to see minute details of the embryo and even subcellular structures like nuclei. 

Dr. Friis' team was able to look at over 250 fossil seeds from 75 different taxa. They were able to make 3D models of the embryos, allowing for more detailed studies than ever before. For some of the fossils, the detail was such that they were able to match them to extant lineages of flowering plants. For others, this technique is allowing for better reclassification of now extinct species. 

By far the most exciting part about these fossils are what they can tell us about the ecology of early flowering plants. In all instances, the embryos within the seeds were small, immature, and dormant. This suggests that seed dormancy is a fundamental trait of flowering plants. What's more, this lends support to the hypothesis that angiosperms first evolved as opportunistic, early successional colonizers. Seed dormancy allows flowering plants to wait out the bad times until favorable environmental conditions allowed for germination and seedling establishment. 

Photo Credit: Dr. Else Marie Friis

Further Reading:
http://www.nature.com/nature/journal/v528/n7583/full/nature16441.html

Aquatic Angiosperm: A Cretaceous Origin?

Via Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro [SOURCE]

It would seem that yet another piece of the evolutionary puzzle that are flowering plants has been found. I have discussed the paleontological debate centered around the angiosperm lineage in the past (http://bit.ly/1S6WLkf), and I don't think the recent news will put any of it to rest. However, I do think it serves to expand our limited view into the history of flowering plant evolution.

Meet Montsechia vidalii, an extinct species that offers tantalizing evidence that flowering plants were kicking around some 130–125 million years ago, during the early days of the Cretaceous. It is by no means showy and I myself would have a hard time distinguishing its reproductive structures as flowers yet that is indeed what they are thought to be. Detailed (and I mean detailed) analyses of over 1,000 fossilized specimens reveals that the seeds are enclosed in tissue, a true hallmark of the angiosperm lineage.

On top of this feature, the fossils also offer clues to the kind of habitat Montsechia would have been found in. As it turns out, this was an aquatic species. The flowers, instead of poking above the water, would have remained submerged. An opening at the top of each flower would have allowed pollen to float inside for fertilization. Another interesting feature of Montsechia is that it had no roots. Instead, it likely floated around in shallow water.

Via Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro [SOURCE]

This is all very similar to another group of extant aquatic flowering plants in the genus Ceratophyllum (often called hornworts or coon's tail). Based on such morphological evidence, it has been agreed that these two groups represent early stem lineages of the angiosperm tree. Coupled with what we now know about the habitat of Archaefructus (http://bit.ly/1S6WLkf), it is becoming evident that the evolution of flowers may have happened in and around water. This in turn brings up many more questions regarding the selective pressures that led to flowers.

What is even more amazing is that these fossils are by no means recent discoveries. They were part of a collection that was excavated in Spain over 100 years ago. Discoveries like this happen all the time. Someone finds a interesting set of fossils that are then stored away on a dark shelf in the bowels of a museum only to be rediscovered decades or even centuries later.

All in all I think this discovery lends credence to the idea that flowering plants are a bit older than we like to think. Also, one should be wary of anyone claiming to have found "the first flower." The idea that there could be a fossil out there that depicts the first anything is flawed a leads to a lot of confusion. Instead, fossils like these represent snapshots in the continuum that is evolution. Each new discovery reveals a little bit more about the evolution of that lineage. We will never find the first flower but we will continue to refine our understanding of life on this planet.

Photo Credits: Bernard Gomeza, Véronique Daviero-Gomeza, Clément Coiffardb, Carles Martín-Closasc, David L. Dilcherd, and O. Sanisidro,

Further Reading:
http://www.pnas.org/content/112/35/10985.abstract