Fusulinoids: Complex Forams of the Late Palaeozoic

Among the most characteristic fossils of the latter part of the Palaeozoic are the group of Foraminifera known as the fusulinoids. These forams, known from around the middle of the Carboniferous to the end of the Permian, can be extremely abundant. Indeed, I get the impression that some fossil deposits are pretty much made of fusulinoids. Fusulinoids did not merely thrive in their environment; they were the environment.

Limestone block dominated by fusulinids, copyright James St John. Field of view is about 3.9 cm across.

Fusulinoids are distinguished from other forams by their test composition, built from minute granules of calcite, and complex internal structure. Externally, fusulinoids (defined here to exclude their forerunners, the endothyroids) were fairly conservative, with a planispiral, usually involute test (that is, each successive whorl covers the last). The last whorl ended on a transverse wall without a defined aperture; instead, the only connection between the interior and exterior of the test was by a series of pores in said wall. Early forms were disc-shaped; later species could be more globular or fusiform. Some of the later fusulinoids also reached gigantic sizes by single-celled organism standards: whereas the earliest fusulinoids were only a fraction of a millimetre across, the late Permian Polydiexodina could be up to six centimetres along their longest axis (Loeblich & Tappan 1964). Internally, fusulinoids had an incredibly complicated and varied structure which I'm not going to go into too much detail about here, primarily because I barely understand a word of it myself. Any description of fusulinoid morphology quickly devolves into madly throwing about terms like chomata, parachomata, spirotheca, tectorium, and the like, and your humble narrator feeling the need to go look at something else.

Cutaway diagram of a fusulinid, showing an example of internal structure, from here.

I have to go into some detail, though, because some features of the fusulinoid wall structure may explain their success. The ancestral state for the fusulinoid test wall involved a thin layer of solid calcite, the tectum. In most species, the inside of the tectum was coated with a thicker, less dense layer. As the test wall becomes more derived, this inner layer becomes more or less translucent, or pierced by tubular alveoli to produce a honeycomb-like appearance. It has been suggested that these modifications may have been adaptations to accomodating symbiotic microalgae, striking a balance between maintaining the protective test and allowing optimal transmission of light. Microalgal associations with fusulinoids may be corroborated by the discovery of minute fossils of probable planktonic relationships such as Ovummuridae preserved within fusulinoid tests (Vachard et al. 2004).

Ecologically, fusulinoids were restricted to off-shore marine habitats, being mostly found preserved in limestones and calcareous shales. They are absent from deposits that would have been formed in brackish water, and while they may be found in sandstones it is debatable whether such occurrences represent life associations or post-mortem transport (Loeblich & Tappan 1964). Fusulinoids would therefore have been ecologically similar to the inhabitants of modern-day photic zone coral reefs, another reflection of their probable co-dependence with photosynthetic microalgae. However, as successful as the advanced fusulinoids were in their time, they did not make it past the massive extinction event at the end of the Permian. This was not the end of giant and complex forams entirely—indeed, some later forms such as the alveolinids would evolve morphologies very similar to those of fusulinoids—but it was the end of these particular giant forams.

REFERENCES

Loeblich, A. R., Jr & H. Tappan. 1964. Treatise on Invertebrate Paleontology pt C. Protista 2. Sarcodina, chiefly "thecamoebians" and Foraminiferida vol. 1. The Geological Society of America and The University of Kansas Press.

Vachard, D., A. Munnecke & T. Servais. 2004. New SEM observations of keriothecal walls: implications for the evolution of Fusulinida. Journal of Foraminiferal Research 34 (3): 232–242.

Hyopsodontids: Little Slinkers of the Palaeogene

The oft-repeated quote about mammalian palaeontology is that it tends to be focused on "the tooth, the whole tooth, and nothing but the tooth". This is primarily the result of pragmatic constraints: because they are much harder than the other bones of the mammalian skeleton, teeth are much more likely to be preserved in the fossil record. There are a great many fossil mammals for which the teeth remain pretty much the only part of the animal known. However, there is no question that this focus tends to limit our understanding of mammalian evolution. On the one hand, the complex morphology of many mammalian teeth means that they provide a wealth of characters for analysis. On the other, the morphology of teeth is heavily influenced by their bearer's diet and lifestyle, meaning that phylogenetically informative features are probably outweighed by the products of ecological convergence.

Reconstruction of Hyopsodus from Savage & Long (1978), via here.

All of which is pretty important background to keep in mind for any discussion of the Hyopsodontidae, a group of small (mostly rat- or weasel-sized) mammals recognised from the Palaeogene, the early part (Palaeocene and Eocene epochs) of the Caenozoic era. Hyopsodontids are generally assigned to the 'Condylarthra', a group of mammals that has long been recognised as one of the classic examples of a 'wastebasket taxon'. Condylarths were originally united as primitive relatives of the ungulates, the hoofed mammals. However, the individual condylarth families themselves have not got much in common otherwise, and (particularly with the current acceptance that 'ungulates' are probably not a monophyletic group) it is hard to come up with a definition for 'condylarths' that amounts to much more than 'medium-sized, unspecialised Palaeogene placentals'.

The hyopsodontids have been recognised as one of the longest-lived groups of 'condylarths', with assigned members extending from close to the start of the Palaeocene right up to near the end of the Eocene. Here again, though, we come up against the question of definition. The majority of taxa that have been aligned with the hyopsodontids are among those known only from teeth. Features of the hyopsodontid dentition include fairly simple incisors and premolars, small canines, and molars that are more or less bunodont (that is, the cusps are rounded or conical and clearly separate from each other rather than being connected by lophs). The problem is that these are all primitive, unspecialised features. Hyopsodontids are therefore defined more by their lack of alternate specialisations than anything positive, making them something of a wastebasket within a wastebasket.

Until recently, the only hyopsodontid known from much in the way of postcranial material was the type genus Hyopsodus, a number of species of which are known from an extended period of the Eocene. Indeed, Hyopsodus was one of the most abundant mammalian genera of its time, accounting for over a quarter of mammalian remains in a number of deposits where it is found (Rose 2006). These remains combine to give a picture of Hyopsodus as a long, low-bodied animal that has been compared in its proportions to a dachshund, a weasel, or a prairie dog. Hyopsodus would have been a ground-hugging slinker of an animal, build for concealment rather than speed. Short claws on the forelegs may be consistent with a certain degree of digging ability, whether in search of buried tubers or to scrape shallow burrows. Overall, Hyopsodus was probably a generalist, able to make a living wherever it may find itself: the real rat of the Eocene.

It was only relatively recently that Penkrot et al. (2008) provided further descriptions of limb-bone material from two other genera associated with the hyopsodontids, Apheliscus and Haplomylus. And despite the dental similarities between these genera and Hyopsodus, their postcranial anatomy indicates a quite different animal. Though small, the apheliscines were relatively long-legged, speedy runners: sprinters rather than slinkers. Penkrot et al. interpreted the apheliscines as relatives of the modern elephant shrews of Africa; whether or not there was a valid phylogenetic connection, the two would have certainly been ecologically similar.

Both Hyopsodus and Apheliscus were included in the broad-scale analysis of early placental phylogeny by Halliday et al. (2017). The results of the analysis corroborate the implications of the postcranial anatomy: despite dental similarities, the 'hyopsodontids' in the broad sense are not a monophyletic group. Over a dozen other genera are known of candidate hyopsodontids, but so long as they are known only from dental characters their true position remains uncertain. Without postcranial data, it seems, we can't handle the tooth.

REFERENCES

Halliday, T. J. D., P. Upchurch & A. Goswami. 2017. Resolving the relationships of Paleocene placental mammals. Biological Reviews 92 (1): 521–550.

Penkrot, T. A., S. P. Zack, K. D. Rose & J. I. Bloch. 2008. Postcranial morphology of Apheliscus and Haplomylus (Condylarthra, Apheliscidae): evidence for a Paleocene Holarctic origin of Macroscelidea. In: Sargis, E. J., & M. Dagosto (eds) Mammalian Evolutionary Morphology: A Tribute to Frederick S. Szalay pp. 73–106. Springer.

Rose, K. D. 2006. The Beginning of the Age of Mammals. JHU Press.

Platyschismatinae

Platyschisma helicoides, from Knight et al. (1960).

In an earlier post on this site, I commented on some of the various ways that gastropods deal with the fact that their development tends to put their anus uncomfortably close to their mouth. A common solution is the development of a sinus or slit in the shell that provides spaces for the anus to be moved backwards.

One of the major gastropod groups exhibiting such a feature is known as the Pleurotomarioidea. In the modern fauna, pleurotomarioids are not hugely abundant, with living species restricted to deep waters. However, they were one of the dominant gastropod groups back in the Palaeozoic when they were represented by a number of families. One Palaeozoic pleurotomarioid group is the Platyschismatinae, known from the Lower Ordovician to the Middle Permian (Knight et al. 1960). Platyschismatines went with the sinus option, with a sinus present at or above the midpoint on the outer edge of the shell opening. Knight et al. (1960) included five genera in the Platyschismatinae. The type genus, Platyschisma, has a slightly flattened spiral and a relatively thin shell. Some of the other platyschismatines were also relatively flat.

REFERENCE

Knight, J. B., L. R. Cox, A. M. Keen, R. L. Batten, E. L. Yochelson & R. Robertson. 1960. Gastropoda: systematic descriptions. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt I. Mollusca 1: Mollusca—General Features, Scaphopoda, Amphineura, Monoplacophora, Gastropoda—General Features, Archaeogastropoda and some (mainly Paleozoic) Caenogastropoda and Opisthobranchia pp. I169-I331. Geological Society of America, and University of Kansas Press.

Jewels among Beetles

There are many contenders for the title of most stunning-looking insect but there is no question that the jewel beetles have a place among the line-up. Some of these brilliantly coloured insects look as if they could have been sculpted from gleaming metal:

Buprestis niponica, copyright Kohichiro Yoshida.

Buprestis is a genus of jewel beetles found in the Holarctic region, with the greater diversity around the Mediterranean and North America. Somewhere between forty and eighty species are recognised, depending on whether the closely related genera Cypriacis and Yamina are regarded as distinct or not. Species of Buprestis come in a variety of colours, with green, blue or black backgrounds often patterned with yellow or red.

Female Buprestis octoguttata ovipositing, copyright Christian Fischer.

Despite their attractive appearance, jewel beetles are not always welcome. They spend the larval part of their life cycle burrowing into wood so some are known for damaging timbers. The preferred hosts of most Buprestis species, where known, appear to be conifers such as pine, spruce and larch. They primarily attack dead and dying wood, and females of some species are known for searching the trunks of trees following fires to find where protective bark has cracked open (some jewel beetle species in other genera are commonly known as 'fire beetles' in reference to this habit). Buprestis larvae have been claimed to live for extraordinarily long periods. Mature beetles have been observed emerging from furniture and the like multiple decades after the original tree was felled, leading to claims of larval life spans of up to 51 years! It almost goes without saying that such inferences have attracted their share of scepticism, with detractors suggesting the possibility of eggs being laid after the wood was already worked. It is true that the low nutritious value of dry wood might be expected to lead to slow development, but how slow are you willing to believe?

Hairy-Winged Barklice

Forewing and fore tibia of Siniamphipsocus fusconervosus, from Mockford (2003). Scale bar for the femur = 0.1 mm.

For my next semi-random post, I drew Siniamphipsocus, a genus of more than twenty species of barklice known from eastern Asia. Most of these species were described by China by the almost ludicrously prolific psocopterologist Li Fasheng who over the course of his career has described close to 1000 psocopteran species—nearly a fifth of the world's barklouse fauna. It should be noted, though, that this productivity has not entirely come without criticism: for instance, in the case of the Siniamphipsocus species, most if not all are known from a single sex with some described from males and others from females (Li 2002).

Siniamphipsocus is a genus of the Amphipsocidae, a family of barklice most easily recognised by their wings which have a double row of setae along each of the veins. Amphipsocids can be relatively large as barklice go: the largest Siniamphipsocus species, S. aureus, has a body length of four millimetres, with the forewings being up to 6.75 millimetres long. Features distinguishing Siniamphipsocus from other amphipsocids include the absence of the brush of hairs present at the base of the hind wing in many other species, the absence of a spur vein in the rear of the forewing pterostigma, and the presence of a row of minute spines along the fore femur (Li 2002). Distinguishing the individual species of the genus requires fine attention to details such the patterns of markings on the face, the proportions of the wing veins, and details of the genitalia.

REFERENCES

Li F. 2002. Psocoptera of China (2 vols). Science Press: Beijing.

Mockford, E. L. 2003. New species and records of Psocoptera from the Kuril Islands. Deutsche Entomologische Zeitschrift 50 (2): 191–230.

Sordariomycetidae: Soil Fungi A-Plenty

I'm pretty sure I've commented before that, although most of us tend to associate the word 'fungi' with mushrooms and other eye-catching fruiting bodies, the vast majority of fungal diversity is minute and tends to go unnoticed. Nevertheless, despite their obscurity, many of these microfungi are crucial to our own continued existence. These are the decomposers, the organisms that break down fallen plant matter and animal wastes in their own search for nourishment and so contribute to the release of locked-up nutrients back into the environmental cycle.

Neurospora growing on sugar cane waste, from here.

The group of fungi that I drew for today's post, the Sordariomycetidae, is primarily made up of these minute decomposers. Sordariomycetids have already made an appearance here at Catalogue of Organisms, in a post from ten years ago on black mildews. Depending on how broadly the group is circumscribed, the Diaporthales could also be included. Due to a simple morphology that provides few distinct characters, the Sordariomycetidae are primarily defined on the basis of molecular phylogenies. The difficulty of classifying microfungi by morphology alone is underlined by cases where species previously classified within the same genus have proven to belong to entirely distinct fungal lineages.

In general, the vegetative body of most Sordariomycetidae consists of little more than disassociated hyphae embedded in their substrate, with the only distinct structures being the reproductive fruiting bodies. These are perithecia: that is, globular or flask-shaped fruiting bodies with a single small opening or ostiole at the top through which the mature spores are released. In some cases, the internal structure of the mature perithecium will simply dissolve, freeing the spores to escape through the ostiole in the manner of a miniature puffball. In others, the spores become entangled in a long strand or seta that is then extruded through the ostiole like toothpaste being squeezed out of a tube.

Perithecium of Chaetomium extruding spore-bearing setae, from here.

Sordariomycetids are found in almost every habitat imaginable: as well as soil- and dung-dwelling forms, they may also be found in aquatic and even marine habitats. Perhaps the best-known sordariomycetid is Neurospora crassa, red bread mould, which is widely used in laboratories as a model organism for genetic research. Indeed, it was investigations into N. crassa in the 1950s that first led to the proposal of the 'one gene, one enzyme' model that became a cornerstone of molecular genetics.

A Western Rockweed

Rockweed Silvetia compressa, from here.

Silvetia compressa is a species of brown alga found on shorelines on the western coast of North America, from British Columbia to Baja California. It is a member of the wrack family Fucaceae that I covered in an earlier post. Silvetia compressa is found in midtidal habitats, generally higher up on the shoreline than other large seaweeds. Individual thalli can reach a maximum length of about three feet (90 cm) but are often smaller. This is a slow-growing species, so patches of Silvetia are slow to recover from damage due to trampling and other disturbance. Please try to avoid walking on the rockweed!

Thalli of Silvetia compressa are composed of thin strands a few millinetres in width with irregular, dichotomous branching. Strands of the thalli lack a midrib (distinguishing them from some other Fucaceae species found in the same area). The width of the strands and regularity of the branching varies with environmental conditions: for instance, individuals growing in locations with stronger wave action have more robust strands that branch more frequently. As with other Fucaceae, the reproductive structures a produced on swollen branch tips called receptacles, but these receptacles do not become inflated with gases and buoyant like those of other species. The exact size and shape of the receptacles is, again, variable.

In many older references, Silvetia compressa may be referred to as Pelvetia fastigiata. The supposed species 'Fucodium compressum' and 'F. fastigiatum' were originally distinguished on the basis that the latter was smaller than the former with more fastigiate branches (that is, the branches remained subparallel). As indicated above, these characters represent the effects of environmental conditions, not fixed differences (Silva 1996). They were eventually included in the genus Pelvetia, together with the Atlantic species P. canaliculata, on the basis of the thalli without a midrib, and the production of just two eggs from each oogonium in the receptacles. However, later analyses supported the separation of the Atlantic and Pacific species of Pelvetia. Not only did they not form a clade in molecular analyses, the eggs in the oogonia were separated by a horizontal division in the Atlantic species but a longitudinal or oblique division in the Pacific species (Silva et al. 2004). As such, the Pacific Pelvetia were transferred into a new genus Silvetia.

Further taxonomic complications involved subspecific variation in Silvetia compressa. A distinctive form of 'Pelvetia fastigiata' found at Pebble Beach in California's Monterey Bay, with smaller, finer thalli and more abundant, regular branching, was labelled as a separate forma gracilis. Similar individuals were also found on the islands off California's coast. However, when Silva (1996) examined the original type specimen of P. fastigiata, he discovered that it was an individual of this 'gracilis' form, not the more typical larger form. Later, Silva et al. (2004) examined genetic variation within the Silvetia compressa of California and Baja California. They found that the individuals of the offshore islands were indeed genetically distinct from continental individuals. As well as the differences in growth habit, there was also some difference in receptacle shape: the continental form had receptacles that tended to be linear and pointed whereas those of the island form were ellipsoidal and blunt. However, the island form still could not be labelled with either of the 'fastigiata' or 'gracilis' monikers, as individuals from the type locality of Pebble Beach did not align genetically with insular individuals but with other continental forms. As such, yet another name had to be coined for the insular form which now goes by the name of Silvetia compressa ssp. deliquescens. Let's see if it sticks this time.

REFERENCES

Silva, P. C. 1996. California seaweeds collected by the Malaspina expedition, especially Pelvetia (Fucales, Phaeophyceae). Madroño 43 (3): 345–354.

Silva, P. C., F. F. Pedroche, M. E. Chacana, R. Aguilar-Rosa, L. E. Aguilar-Rosa & J. Raum. 2004. Geographic correlation of morphological and molecular variation in Silvetia compressa (Fucaceae, Fucales, Phaeophyceae). Phycologia 43 (2): 204–214.