Name the Bug: Fouquieria columnaris

Fouquieria columnaris. Photo by Josiah.

"But oh, beamish nephew, beware of the day,
If your Snark be a Boojum! For then
You will softly and suddenly vanish away,
And never be met with again!"

--Lewis Carroll, The Hunting of the Snark

Congratulations to Pat who identified the subject of the above photo right off the bat as Fouquieria columnaris (or Idria columnaris), a desert plant of southwest North America commonly known as the cirio (Spanish for 'candle') or boojum tree. The name 'boojum' comes from Lewis Carroll's allegorical* poem The Hunting of the Snark in which a company of mismatched adventurers attempts to capture a mysterious (and possibly non-existent) creature only to have one of their party disappear under puzzling circumstances.

*Many authors refer to The Hunting of the Snark as allegorical. 'Allegorical' may be shorthand for 'no, we don't know what he's on about, either'.

It is not hard to see how Carroll's eerie, creepy boojum became associated with this strange, eerie plant (though, to the best of my knowledge, F. columnaris has never been party to mysterious disappearances). The boojum has a restricted range, found on granite ranges in the Mexican states of Baja California and Sonora. Rainfall in these areas is low, averaging 120 mm per year (Bashan et al., 2007). Boojums can reach heights of up to 12 metres (Humphrey, 1935) but grow slowly, about three or four centimetres in a good year (Bashan et al., 2007). It can take 100 years for a boojum to reach maturity and begin flowering and large individuals may be more than 700 years old.

The usual growth form of a boojum is as a single tapering trunk - Pat's description of it as a "living telegraph pole" is appropriate, while Humphrey (1935) regarded it as "not unlike a greatly elongated inverted parsnip". The central stem may or may not divide into candelabra-like branches while individuals may deviate from the usual vertical growth to form strange loops or arches. The central stem is covered by short side branches arranged in a spiral pattern and carrying spines and small leaves.


An example of the unusual growth habits adopted by some boojums. From Bashan et al. (2007).

The genus Fouquieria includes eleven species of North American succulents that have been placed in their own separate family (the other Fouquieria species, the ocotillos, are low radiating shrubs). Recent studies have placed Fouquieria among the Ericales and most (but not all) molecular analyses support a sister-group relationship between Fouquieria and Polemoniaceae (the phlox family; Geuten et al., 2004).

REFERENCES

Bashan, Y., T. Khaosaad, B. G. Salazar, J. A. Ocampo, A. Wiemken, F. Oehl & H. Vierheilig. 2007. Mycorrhizal characterization of the boojum tree, Fouquieria columnaris, an endemic ancient tree from the Baja California Peninsula, Mexico. Trees 21: 329-335.

Geuten, K., E. Smets, P. Schols, Y.-M. Yuan, S. Janssens, P. Küpfer & N. Pyck. 2004. Conflicting phylogenies of balsaminoid families and the polytomy in Ericales: combining data in a Bayesian framework. Molecular Phylogenetics and Evolution 31 (2): 711-729.

Humphrey, R. R. 1935. A study of Idria columnaris and Fouquieria splendens. American Journal of Botany 22 (2): 184-207.

Name the Bug # 13

Been a while since we last had one of these. Anyone care to identify this beastie?



Okay, it's a shrub, not a beastie, but you get the idea. Attribution to follow.

Update: Identity available here. Photo by Josiah.

Taxon of the Week: Rhaphidophora

Rhaphidophora decursiva growing in the Sydney Botanical Gardens. Photo by Tony Rodd.

As currently recognised, Rhaphidophora is a large genus of about 100 species of lianes (woody climbers) of the family Araceae found in the tropics of the Old World from Africa to northern Australia. Rhaphidophora forms part of the tribe Monstereae whose most familiar member is probably Monstera deliciosa, the Swiss cheese plant of many a garden, and the flowers and fruit of Rhaphidophora are similar to those of Monstera. Some Rhaphidophora species have pinnate or perforated leaves while others have entire leaves. Most Rhaphidophora species do not seem to currently have a great deal of economic significance except as ornamental plants though a small number have been investigated in recent years for their pharmacological properties. Rhaphidophora pertusa stems are chopped up and mixed with rice gruel before being fed to cattle or buffaloes in India to induce oestrus (Santosh et al., 2006).


Rhaphidophora foraminifera. Photo by Eric in SF.

The genera of the Monstereae such as Rhaphidophora, Monstera and Epipremnum have not had their definitions substantially revised since 1908 and are currently regarded by many authors as problematic. They have been primarily distinguished on the basis of reproductive anatomy (Rhaphidophora, for instance, has numerous ovules, punctate stigmas and minute albuminous seeds) but reproductive characters are often at odds with vegetative characters (Hay, 1993) and a revision of the group is overdue (matters were not helped by the suggestion - since shown to be mistaken - that Rhaphidophora and Epipremnum shared the same type species). A molecular study by Tam et al. (2004) also identified polyphyly of Rhaphidophora, with the majority of Rhaphidophora species forming a single clade but a significant minority forming clades with species of other genera.

REFERENCES

Hay, A. 1993. Rhaphidophora petrieana - a new aroid liane from tropical Queensland; with a synopsis of the Australian Araceae-Monstereae. Telopea 5 (2): 293-300.

Santosh, C. R., N. B. Shridhar, K. Narayana, S. G. Ramachandra & S. Dinesh. 2006. Studies on the luteolytic, oestrogenic and follicle-stimulating hormone like activity of plant Rhaphidophora pertusa (Roxb.). Journal of Ethnopharmacology 107 (3): 365-369.

Tam, S.-M., P. C. Boyce, T. M. Upson, D. Barabé, A. Bruneau, F. Forest & J. S. Parker. 2004. Intergeneric and infrafamilial phylogeny of subfamily Monsteroideae (Araceae) revealed by chloroplast trnL-F sequences. American Journal of Botany 91 (3): 490-498.

A Beginner's Guide to Blastoids

No, not that. These (photo by DanielCD):



Blastoids are small but reasonably common Palaeozoic (Silurian to Permian) fossils. The name means, roughly, 'bud-like' and refers to the common resemblance of the fossils to flower buds. However, blastoids were not plants but echinoderms, animals of the same phylum as modern crinoids, starfish and sea urchins.


Pentremites, the best-known blastoid. Photo from here.

Most blastoid fossils are less than an inch in diameter, and all have a very clear pentaradial arrangement (the following account is primarily based on Beaver et al., 1967). The theca (the main body) is very solidly built from a very regular arrangement of plates, with five ambulacra (feeding grooves) running down the sides (the ambulacra are what house the tube feet in living echinoderms). At the top of the fossil where the ambulacra meet is a central opening that in life would have led to the mouth, with a number of other openings around it. The largest of these was the anus while the smaller openings are known as the spiracles.



The spiracles are connected to the hydrospires, a series of folds of the internal body wall underlying the ambulacra (reconstruction above from Schmidtling & Marshall, 2010) that are generally believed to have function in respiration. Presumably, water was drawn into the hydrospires on either side of the ambulacra and expelled through the spiracles. Two orders of blastoids are distinguished based on the arrangement of the hydrospires and spiracles. In members of the order Fissiculata, the hydrospires open directly to the outside world through a series of slits in the thecal plates; the spiracles are often small or slit-like and may not be readily distinguishable from the hydrospire slits (as far as I can see, anyway). In members of the order Spiraculata, such as Pentremites, the hydrospire slits were internal and entry to the hydrospires was through minute pores on either side of the ambulacra while the spiracles were much larger and more distinct. The remaining internal anatomy (such as the mode of reproduction) remains largely unknown.


In life the theca was only a small (but significant) part of the whole. A slender stem (up to about 25 cm long) attached the blastoid to the substrate while on either side of each ambulacrum was a row of arm-like structures known as brachioles. The brachioles would have captured food particles in the water, transporting the particles down a groove on the underside to the ambulacrum below. The stem and brachioles were comparatively delicate and rarely preserved but the positions of the brachioles can still be otherwise distinguished by the presence of attachment sockets alongside the ambulacra.

Brachioles are also found in a number of other extinct echinoderm groups (such as cystoids and eocrinoids) but are not found in any living echinoderms. Despite a certain superficial resemblance, brachioles are not comparable to the arms of living crinoids. In recent years, it has been proposed that the echinoderm exoskeleton can be divided on morphological and developmental grounds into two distinct components, the axial skeleton which grows through the alternating addition of plates at the distal points and the extraxial skeleton which can grow through the addition of new plates in between pre-existing ones (David et al., 2000). The axial skeleton makes up the ambulacra and associated structures while the extraxial skeleton makes up the remainder of the body wall. Crinoid arms, which carry the ambulacra along their axis and contain radial extensions of the internal coelom, are made up of both axial and extraxial components. Blastoid brachioles, which sit alongside the ambulacra and do not contain coelomic extensions, are entirely axial*. While many authors have suggested that crinoids may be derived from brachiolar echinoderms (particularly cystoids, some of which have a similar arrangement of thecal plates to early crinoids - e.g. Ausich, 1998), proponents of the extraxial-axial division regard the similarities between the groups as convergent; indeed, the phylogeny proposed by David et al. (2000) would place brachiolar echinoderms such as blastoids entirely outside the echinoderm crown group.

*If I understand things correctly, deriving crinoid arms from blastoid brachioles would be a little like deriving human arms from lemur fingernails.

REFERENCES

Ausich, W. I. 1998. Early phylogeny and subclass division of the Crinoidea (phylum Echinodermata). Journal of Paleontology 72 (3): 499-510.

Beaver, H. H., R. O. Fay, D. B. Macurda Jr, R. C. Moore & J. Wanner. 1967. Blastoids. In Treatise on Invertebrate Paleontology pt. S. Echinodermata 1. General Characters. Homalozoa-Crinozoa (except Crinoidea) (R. C. Moore, ed.) pp. S297-S455. The Geological Society of America, Inc. and The University of Kansas.

David, B., B. Lefebvre, R. Mooi & R. Parsley. 2000. Are homalozoans echinoderms? An answer from the extraxial-axial theory. Paleobiology 26 (4): 529-555.

Schmidtling, R. C., II & C. R. Marshall. 2010. Three dimensional structure and fluid flow through the hydrospires of the blastoid echinoderm, Pentremites rusticus. Journal of Paleontology 84 (1): 109-117.

Beginning to Grasp Things (Taxon of the Week: Euprimateformes)

Skull of Plesiadapis tricuspidens, from Gingerich (1976).

The name Euprimateformes was coined fairly recently by Bloch et al. (2007) for a clade uniting crown-group Primates and the extinct plesiadapoids (the exact definition was "the clade stemming from the most recent common ancestor of Carpolestes simpsoni and Homo sapiens), excluding even more basal stem Primates such as paromomyids. The plesiadapoids include the taxa Plesiadapidae, Carpolestidae, Saxonella and Chronolestes and were found in North America and Eurasia from the late Early Palaeocene to the end of the Early Eocene (a possible plesiadapoid has also been described from Africa).


Reconstruction of Carpolestes from here.

Plesiadapoids would have been not dissimilar to squirrels or modern tree shrews in size and appearance. They possessed large, forward-pointing lower incisors and originally fairly long skulls. Few plesiadapoids are known from extensive postcranial remains but what we do know indicates a fair amount of ecological divergence (Bloch et al., 2007). Carpolestes possessed a nail rather than a claw on its hallux (opposible big toe) and shorter claws overall, indicating that it was a grasping climber (wrapping its digits around branches) like modern primates rather than a clinging climber (hanging onto branches with its claws) like squirrels. Plesiadapis, on the other hand, had long narrow claws and was probably more of a clinging climber. Some authors have suggested a more terrestrial lifestyle for Plesiadapis; such interpretations are not currently popular (Kirk et al., 2008) but it would be interesting if postcrania were available for the largest and one of the latest of the plesiadapids, the European Platychoerops, which was comparable in size to a groundhog (Gingerich, 1976). Also notable among plesiadapids was Chiromyoides which appears to have been a specialised seed-eater with a short and deep jaw (and presumably skull) and massive incisors.


Lower jaw of Carpolestes simpsoni from Bloch & Gingerich (1998).

Carpolestids also showed a trend towards reduction in the length of the skull, but the really neat thing is what they did with their teeth, for which Carpolestes simpsoni can be taken as one of the best-known examples (Bloch & Gingerich, 1998). In the lower jaw, the anterior teeth were greatly reduced except the large first incisors which were followed by two teeth reduced to mere nubbins (identified as the second incisor and the canine). Only a single premolar remained (identified as the fourth) but to make up for it that tooth was huge, a massive blade-like multi-cusped structure that ground against the similar obscenely complex third and fourth premolars in the upper jaw (another derived carpolestid, Carpomegodon jepseni, retained a small third premolar in the lower jaw - Bloch et al., 2001). In comparison to all this, the three molars that followed were rather pedestrian. Biknevicius (1986) interpreted this tooth arrangement (comparable only to the multituberculates among other mammals) as indicative of a diet of foods with a tough exterior that would have been pierced by the premolars but a soft interior that did not require a huge amount of molar processing. Carpolestids were probably omnivorous, feeding on insects, seeds and fruit, with later forms becoming increasingly frugivorous.


Upper dentition of Carpolestes simpsoni from Bloch & Gingerich (1998).

REFERENCES

Biknevicius, A. R. 1986. Dental function and diet in the Carpolestidae (Primates, Plesiadapiformes). American Journal of Physical Anthropology 71 (2): 157-171.

Bloch, J. I., D. C. Fisher, K. D. Rose & P. D. Gingerich. 2001. Stratocladistic analysis of Paleocene Carpolestidae (Mammalia, Plesiadapiformes) with description of a new Late Tiffanian genus. Journal of Vertebrate Paleontology 21 (1): 119-131.

Bloch, J. I., & P. D. Gingerich. 1998. Carpolestes simpsoni, new species (Mammalia, Proprimates) from the Late Paleocene of the Clarks Fork Basin, Wyoming. Contributions from the Museum of Paleontology, The University of Michigan 30 (4): 131-162.

Bloch, J. I., M. T. Silcox, D. M. Boyer & E. J. Sargis. 2007. New Paleocene skeletons and the relationship of plesiadapiforms to crown-clade primates. Proceedings of the National Academy of Sciences of the USA 104 (4): 1159-1164.

Gingerich, P. D. 1976. Cranial anatomy and evolution of Early Tertiary Plesiadapidae (Mammalia, Primates). The Museum of Paleontology, University of Michigan, Papers on Paleontology 15: 1-141.

Kirk, E. C., P. Lemelin, M. W. Hamrick, D. M. Boyer & J. I. Bloch. 2008. Intrinsic hand proportions of euarchontans and other mammals: implications for the locomotor behavior of plesiadapiforms. Journal of Human Evolution 55: 278-299.


This has nothing to do with the above post but as soon as I found it (here) I thought it was too fantastic not to share. From a German book published in the early 1900s, illustrated by one F. John, comes perhaps the creepiest reconstruction of the giant lemur Megaladapis ever.

Crinoids of the Open Seas

Lateral view of calyx of Saccocoma tenella from Brodacki (2006) showing the emergence angle of the arms.

Living crinoids can be divided morphologically between the stalked sea lilies and the stemless feather stars but, as described in an earlier post, the feather stars are not really entirely stemless. Rather, the column has been reduced to a single plate that still functions as the point of attachment for the cirri, the small tentacle-like appendages that the feather star uses to hang onto the substrate or move about. There were two groups of Mesozoic crinoids that went a step further, completely losing both column and cirri.

The Uintacrinida (of the late Cretaceous) and the Roveacrinida (throughout the Mesozoic) were both subgroups of the Articulata, the clade that includes all living crinoids, but they are very distinct from each other and probably lost their stalks independently. Milsom et al. (1994) placed the Uintacrinida as a derived subgroup of the feather stars while the relationships of the Roveacrinida remain mysterious. Because of the lack of any means of attachment to the substrate, both have been regarded as pelagic; as I'll explain below, this seems likely for the roveacrinidans but not for the uintacrinidans.


Ventral reconstruction of Saccocoma from Milsom (1994) showing the arrangement of lateral plates in the proximal part and long branches in the distal part of the arms.

The roveacrinidans were absolutely tiny animals with the central cup only a couple of millimetres across and the total armspan up to a few centimetres. In the best-known example, Saccocoma, broad wing-like plates were attached to either side of the proximal part of the slender multi-branched arms while the skeleton as a whole was very thin and light. In an influential interpretation of Saccocoma, Otto Jaekel referred to the lateral plates on the arms as "Schwimmplatten" and suggested that they were used to propel the animal through the water. However, Brodacki (2006) pointed out that the mobility of the proximal part of the arms would not have been sufficient for the plates to be used in swimming. Instead, the distal branched parts of the arms would have provided the swimming force while the Schwimmplatten would have provided extra friction to reduce the rate of sinking. Because roveacrinidans would have been heavier than the surrounding water even with their lightened plates, they must have been active (and fairly continuous) swimmers rather than passive floaters. Swimming was probably done by slowly coiling the distal part of the arms inwards then rapidly straightening them outwards so the animal flicked itself through the water. An alternative suggestion (Milsom, 1994) that Saccocoma was benthic on soft mud with the "Schwimmplatten" protecting the animal from being buried is contradicted by the fact that the arms would have emerged from the top of the theca at an angle of 45° rather than being flat. Also, Saccocoma plates are commonly found in coprolites whose mode of deposition indicates that they were produced by pelagic animals (Hess, 1999a).


Fossil assemblage of the very aptly named Uintacrinus socialis, from Hess 1999b.

In contrast to the minute, light roveacrinidans, the two uintacrinidan genera Uintacrinus and Marsupites were very large crinoids with sack-like, flexible thecas up to 75 mm in diameter and arms up to a metre or more in length. Unlike roveacrinidans, uintacrinidan plates are not reduced but remain robust and heavy. The proximal parts of the arms were integrated into the theca which would have limited their ability to spread outwards as in Saccocoma. Orientation of preserved specimens (and Uintacrinus can sometimes be preserved in extraordinarily dense concentrations) indicates that the habitual life position of uintacrinidans was with the mouth upwards, contradicting suggestions that the theca could have contained some sort of buoyancy organ. Despite the lack of any means of attachment, without any clear adaptations for increasing buoyancy it seems that uintacrinidans would have been benthic rather than pelagic. They would have lived in soft mud with the theca buried (hence the lack of attachment structures) and the arms extending upwards from the substrate to collect food particles. Hess (1999b) compares the possible life appearance of Uintacrinus assemblages to "dense patches of tall eel grass".

REFERENCES

Brodacki, M. 2006. Functional anatomy and mode of life of the latest Jurassic crinoid Saccocoma. Acta Palaeontologica Polonica 51 (2): 261–270.

Hess, H. 1999a. Upper Jurassic Solnhofen Plattenkalk of Bavaria, Germany. In Fossil Crinoids (H. Hess, C. E. Brett, W. I. Ausich & M. J. Simms, eds) pp. 216-224. Cambridge University Press.

Hess, H. 1999b. Uintacrinus beds of the Upper Cretaceous Niobrara Formation, Kansas, USA. In Fossil Crinoids (H. Hess, C. E. Brett, W. I. Ausich & M. J. Simms, eds) pp. 225-232. Cambridge University Press.

Milsom, C. V. 1994. Saccocoma: a benthic crinoid from the Jurassic Solnhofen Limestone, Germany. Palaeontology 37 (1): 121-129.

Milsom, C. V., M. J. Simms & A. S. Gale. 1994. Phylogeny and palaeobiology of Marsupites and Uintacrinus. Palaeontology 37 (3): 595-607.

Prototaxites: A Giant that Never Was?

Reconstruction of Prototaxites as columnar perrenial fungus from Hueber (2001), painted by Mary Parrish.

Nearly two years ago, I presented a post on Prototaxites, a mysterious fossil of the late Silurian, the earliest truly large terrestrial organism known from the fossil record. In that post (which I'd recommend reading before this one) I discussed the possibility that Prototaxites might have represented a giant fungus but a recent publication by Graham et al. (2010) presents a new alternative interpretation of Prototaxites. If they are correct, the Silurian may never be the same again.


Thalli of the liverwort Marchantia. Photo from here.

In Graham et al.'s estimation, Prototaxites should not be classed with the fungi but with the liverworts. Liverworts are small, often mosslike plants of moist habitats. Members of one group of liverworts, the thallose liverworts, lack any distinction between leaves and stem but grow as a flattened thallus anchored to the ground by rhizoids (rootlets) on the lower surface. Liverworts are one of the earliest diverging groups of land plants and they or their ancestors would have certainly been part of the Silurian flora. One group of Silurian plant fossils, the nematophytes, possess a microstructure of criscrossing tubular filaments; Graham et al. (2004) demonstrated that this structure was also found in the decaying remains of modern thallose liverworts, as the upper tissue of the thallus rotted away to leave the more resistant rhizoids and connective tissue. The microstructure of Prototaxites is also similar to that of nematophytes, to the extent that some palaeontologists have regarded nematophytes as Prototaxites leaves (this interpretation is not currently supported as nematophytes have never been found actually attached to Prototaxites). But modern liverworts lack strong supporting tissue and would be pushing to reach an inch in height - how could they have produced the eight-metre columns recorded for Prototaxites?


The largest known Prototaxites fossil (at least as of 2001), photographed by Charles Meissner in Saudi Arabia. From Hueber (2001).

A transverse section of Prototaxites shows a ring structure like that found in a tree trunk. Hueber (2001), who interpreted Prototaxites as a perennial fungal fruiting body, felt that this ring structure also resembled tree rings in indicating discontinuous growth by the organism. Graham et al. (2010) interpret the ring structure differently. They suggest that large mats of thallose liverworts covered the Silurian landscape. These mats could become detached from their substrate by agents such as wind and rain, and start to roll up as they decayed. As they rolled, they would form the large columns that, after being compressed by burial and fossilised, would eventually be identified as Prototaxites.


Reconstruction by Kandis Elliot of Silurian liverwort mats being rolled by wind, gravity and/or water movement to form 'Prototaxites'. From Graham et al. (2010).

Under this interpretation of Prototaxites, the fungal hyphal structures identified by Hueber (2001) within Prototaxites sections would be those of fungi growing among the liverwort mats. Boyce et al. (2007) identified significant variations in carbon isotope ratios between Prototaxites individuals as supportive of fungal identification because they suggested heterotrophy (nutrients being obtained from the surrounding environment rather than being produced by the organism itself); however, Graham et al. (2010) establish that thallose liverworts may grow heterotrophically when conditions encourage it. The liverwort interpretation is also more consistent with the size of most Prototaxites filaments (much larger than found in modern fungi) and also explains the occasional discovery of other land plants embedded in Prototaxites columns - these would have been growing among the mats and become swept up when the mats became rolled, like Silurian Cleopatras.

I find this new interpretation intriguing, if a little difficult to accept outright. Prototaxites is represented by a reasonable number of specimens (I don't know the actual number, but thirteen species have been named from numerous localities around the world) - were the conditions that would have lead to mat-rolling common enough to have produced that number of fossils? I wonder if it would be worth investigating how Prototaxites specimens compare in abundance to nematophyte specimens and what that might tell us about the likelihood of 'Prototaxites' formation from liverwort mats. Certainly, the only thing that could be more intriguing than the existence of these giant pillars from so early in the earth's history would be if it turned out that they never existed at all.

REFERENCES

Boyce, C. K., C. L. Hotton, M. L. Fogel, G. D. Cody, R. M. Hazen, A. H. Knoll & F. M. Hueber. 2007. Devonian landscape heterogeneity recorded by a giant fungus. Geology 35: 399–402.

Graham, L. E., M. E. Cook, D. T. Hanson, K. B. Pigg & J. M. Graham. 2010. Structural, physiological, and stable carbon isotopic evidence that the enigmatic Paleozoic fossil Prototaxites formed from rolled liverwort mats. American Journal of Botany 97 (2): 268-275.

Graham, L. E., L. W. Wilcox, M. E. Cook & P. G. Gensel. 2004. Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils. Proceedings of the National Academy of Sciences of the USA 101 (30): 11025-11029.

Hueber, F. M. 2001. Rotted wood–alga–fungus: the history and life of Prototaxites Dawson 1859. Review of Palaeobotany and Palynology 116 (1-2): 123-158.