Dorsal and ventral views of Monogalumnella neotricha, with legs removed. Figures from Balogh & Balogh (1992).
In a previous post, I introduced you all to the oribatid mites. Oribatids come in a wide range of varieties, and the animal in the figures above is a member of the oribatid family Galumnellidae. Galumnellids belong to a group of oribatids, the galumnoids, marked by their well-developed pteromorphs: the roughly triangular structures at either side of the front of the body. Many oribatids have pteromorphs developed to a greater or lesser degree, but the pteromorphs of galumnoids are particularly noteworthy for their size and for the development of a hinge between the pteromorph and the main body, so that the pteromorph can be folded down to cover the legs for protection (other species have the pteromorphs as fixed outgrowths of the body). The name 'pteromorph', of course, means 'wing-shaped', and you can readily find cases where galumnoids have been referred to as 'winged mites' (especially in older publications). Woodring (1962) even suggested that galumnoids might provide a useful analogy for the evolution of wings in insects. However, pteromorphs are not actually wings like those of insects, being used only for protection, not flight. In animals as small as oribatids, the relative viscosity of the air becomes very high, not to mention the relative force of small air movements. Vary small arthropods that move aerially either develop long hairs or similar structures so that they can be passively lifted and carried by the breeze (like the line of silk produced by ballooning spiders) or have reduced wings with long fringes of hairs to maintain wing surface area while minimising air resistance (such as mymarid wasps, thrips or ptiliid beetles). A solid plate like the galumnoid pteromorph would be to difficult to move*.
*Similar issues affect suggestions that the absent fossil record of the earliest winged insects may indicate that flight evolved at small sizes. It seems almost certain that the first flying insects were relatively large.
The Galumnellidae can be distinguished from other galumnoid mites by the lack of protruding lamellae on the prodorsum (the top of the 'head'), the pointed rather than rounded rostrum, and the shape of their chelicerae. The chelicerae of galumnellids are long and slender, compared to the shorter, stronger chelicerae of their relatives in the Galumnidae. Galumnella has been shown in the laboratory to be panphytophagous (Badejo & Akinwole 2007)—that is, it will accept any type of plant or algal food, both living and dead.
Vertical (1-3, 7) and transverse (4-6) sections of Miogypsinoides dehaarti. Figure from Cole (1939).
Miogypsinoides dehaarti was a large calcareous foraminiferan (up to a few millimetres in length) that lived during the Aquitanian period (lower Miocene). The test of M. dehaarti and other species of Miogypsinoides was divided vertically into three distinct layers: the chambers were laid in a plane along the midline of the test with a thick unchambered wall above and below. The ventral wall contained a lattice system of canals that in life may have contained cytoplasm running between the chambers and the outside world (de Bock 1976); the upper wall was unperforated. The first part of the test to grow is visible in the lower point of the transverse sections above: from the embryonic chambers, the juvenile test initially grew in a spiral (with the size and proportions of the spiral varying between species). After the juvenile test reached maturity*, new chambers were added in a fan from one side of the juvenile test, so the eventual form of Miogypsinoides was not dissimilar to a piece of candy corn (though we do not know whether it, too, tasted of sweetness and death). The juvenile test of Miogypsinoides is similar to the adult form of other rotaliid forams, and it probably evolved from such forms through a process of hypermorphosis (the addition of new adult stages to development).
*Developmental maturity, that is. Obviously, we have no idea when the foram reached reproductive maturity.
Sectional diagram of the apical end of Miogypsinoides, showing the chambers in the equatorial plane and with some sections of the canal system visible below. Figure from Bock (1976).
The genus Miogypsinoides may have been ancestral to other genera in the family Miogypsinidae (Hanzawa 1964), from which it differs by the presence in the latter of accessory lateral chambers in the dorsal and ventral walls (and hence the loss of the canal system in the ventral wall). In the genera Miolepidocyclina and Heterosteginoides, the juvenile test moved from the apical position of Miogypsinoides to a a central position, and the adult test became conical (Hanzawa 1962). Some authors treat some or all of these genera as subgenera of Miogypsina (which, in the sense of Hanzawa 1962, had lateral chambers like Miolepidocyclina but an apical juvenile test like Miogypsinoides). Hanzawa (1964) treated them as separate but nevertheless derived both Miogypsina and Heterosteginoides from Miogypsinoides polyphyletically, evidently basing his classification on the overall shape of the adult test but his phylogeny on stratigraphy and the juvenile test. The Miogypsinidae as a whole became extinct in the middle Miocene.
Bock, J. F. de. 1976. Studies on some Miogypsinoides-Miogypsina s.s. associations with special reference to morphological features. Scripta Geologica 36: 1-135.
Cole, W. S. 1939. Large Foraminifera from Guam. Journal of Paleontology 13 (2): 183-189.
Hanzawa, S. 1962. Upper Cretaceous and Tertiary three-layered larger Foraminifera and their allied forms. Micropaleontology 8 (2): 129-186.
Hanzawa, S. 1964. The phylomorphogeneses of the Tertiary foraminiferal families, Lepidocyclinidae and Miogypsinidae. Science Reports of the Tohoku University, second series, Geology 35 (3): 295-313.
The Lower Carboniferous gastropod Phanerotinus cristatus. Figure from Knight et al. (1960) [Treatise on Invertebrate Paleontology pt. I].
About two weeks ago, I started putting up a series of very brief posts, each figuring and giving characteristics of a particular taxon. There was a point to doing so: if you were to ask me what was the number one issue in most people's understanding of biodiversity, I would say that most people have no idea just how much of it there is. Indeed, there is so much that it might just be incomprehensible. The short posts allowed me to exhibit more variety of organisms than I could in my usual longer posts.
However, a couple of readers voiced concern that the more detailed posts (which they preferred to read) were being lost in the mix. Their point has been noted, and granted. Which is why, with the welcome assistance of Field of Science's puppet-master Edward, I have launched the Catalogue of Organism's new sister blog, The Variety of Life. The short posts will be put up there, and it is my hope that over time I can build it up to a useful guide to the diversity of (at least some) organisms that inhabit, or have inhabited, our world. Meanwhile, Catalogue of Organisms will continue in its previous fashion, bringing you in depth discussion of matters systematical (at least as far as I am able). I hope that both sites will please at least somebody.
Some of you may remember this post from back in May, in which I critiqued Smith & Caron's (2010) interpretation of Nectocaris as an early cephalopod. I was not convinced. Nor am I the only one: a paper recently released by Mazurek & Zatoń (in press) comes to much the same conclusions. They point out that Smith & Caron's proposed model of cephalopod evolution conflicts strongly with what we previously knew from the cephalopod fossil record (and that's no small amount—there are few groups of organisms whose fossil record has been as intensely studied as cephalopods), and that most of the characters supposedly shared between Nectocaris and cephalopods are in fact only shared between Nectocaris and coleoids (modern octopods and squid) that did not appear in the fossil record until during the Mesozoic, considerably later than the Cambrian Nectocaris. Smith & Caron (2010) suggested that the absence of a shell in Nectocaris indicated that the cephalopod shell had been evolved independently to that of other molluscs, but Mazurek & Zatoń point out that the only known cephalopods to completely lack any trace of a shell are octopods, and that octopods are secondarily shell-less is indicated, not only by their phylogenetic position, but also by the presence of a remnant shell in Cretaceous stem-octopods.
What I find particularly interesting about Mazurek & Zatoń's paper, however, is how much it brings up the same points already raised by commenters here. The primary feature cited by Smith & Caron (2010) as connecting Nectocaris with cephalopods, the presence of a funnel, is contradicted by the apparent difference in functional structure between a cephalopod siphon and Nectocaris' 'funnel', as noted by Adam Yates. Aydin Örstan commented on the absence of a radula. Just goes to show that I've got some pretty clever readers here. Mind you, I'm not happy with everything in Mazurek & Zatoń's paper. They make the argument that Nectocaris could not have evolved from a shelled and radula-possessing ancestor because it was 'too early', but the known fossil record of molluscs pre-dates Nectocaris by about twenty million years, more than long enough for shell loss to potentially occur. The absence of a beak in Nectocaris is also of doubtful significance as this is a cephalopod autapomorphy.
I am also not swayed by Mazurek & Zatoń's (provisional) alternative placement for Nectocaris as a dinocarid. Though it is tempting to compare the funnel of Nectocaris to the proboscis of dinocarids such as Opabinia, and dinocarids have the advantage over coleoid cephalopods of being coeval with Nectocaris, no dinocarid has cephalic tentacles like Nectocaris. Also, some of the figures in Smith & Caron (2010) appear as if the pharynx might pass through the funnel; in Opabinia, the proboscis was a separate structure in front of the mouth. I can think of two groups of animals for which cephalic tentacles are definitely known: annelids and molluscs (presuming that the tentacles of Nectocaris are not a unique autapomorphy of its own). The lack of obvious segmentation makes it unlikely that Nectocaris is an annelid. That leaves us with mollusc. While Smith & Caron's identification of a pinhole camera eye in Nectocaris could still connect it to cephalopods, I believe that this is outweighed by the arrangement of the gut. The presence of an apparent through-gut, opening with a terminal anus, was identified by Chen et al. (2005) in Vetustovermis (now recognised as a synonym of Nectocaris)*. Cephalopods, however, have a U-shaped gut, opening in the mantle cavity not too far from the head. This is related to the 90° shift that the cephalopod body plan has gone through during its evolution: the apparent "front-back" axis of a squid actually represents the "top-bottom" axis of other molluscs. A similar U-shaped gut is present in scaphopods, the probable living sister group of cephalopods, so a molluscan Nectocaris would have to sit outside the scaphopod-cephalopod clade. As far as is known, cephalic tentacles are a possible synapomorphy of the clade uniting cephalopods, scaphopods and gastropods**, so a molluscan Nectocaris would probably have to be either a stem representative of this clade, or just possibly a stem gastropod.
*My apologies to the commenter somewhere whose identity I've forgotten who brought my attention to this point.
**Cephalic tentacles are definitely absent in polyplacophorans and tryblidiids***. They are also absent in bivalves, but bivalves don't have a head to have cephalic tentacles on in the first place, so the absence of tentacles is probably best treated as ambiguous for bivalves.
***Or whatever Neopilina and its ilk are going by these days.
Pity the poor Liliaceae. At one time, the family stood as the repository for almost all monocots with large-petaled flowers except orchids. Over the years, successive reclassifications have steadily whittled it down until the current Liliaceae is left with a mere ten to sixteen or so genera (depending on whether or not the Calochortaceae are treated as a separate family) found in the Holarctic region. Of course, these genera still include such luminaries as Lilium (lilies) and Tulipa (tulips), so even in its minority the Liliaceae can still draw its share of attention.
Greig's tulip Tulipa greigii growing wild in Kazakhstan. Photo by Rustem Vagapov. I have to admit that the thought of such horticultural wonders as tulips and orchids growing wild has always been a strange one to me.
Molecular studies of the Liliaceae have agreed on the monophyly of Liliaceae sensu stricto (excluding 'Calochortaceae') but differ on the relationships of the 'Calochortaceae', whether a monophyletic sister to Liliaceae s. s. (Patterson & Givnish 2002) or paraphyletic to the latter (Rønsted et al., 2005). Within Liliaceae s. s., there is a well-supported division between the Lilioideae and a small clade Medeoloideae. Whatever the phylogeny, it seems likely that the ancestor of the Liliaceae in the broad sense was a shade-loving, rhizomatous plant with broad reticulate leaves, as is characteristic of Medeoloideae and 'Calochortaceae' other than Calochortus (Patterson & Givnish 2002). Calochortus and Lilioideae independently became adapted to more open habitats, developing narrower leaves and bulbs instead of rhizomes (hence a more seasonal growing cycle). Both lineages also developed more showy flowers than their relatives (showy flowers are also found in the genus Tricyrtis, which may or may not be closely related to Calochortus) and replaced the berries of their ancestors with dehiscent capsules, so that their seeds became dispersed by wind instead of by animals. Again, capsules are also found in Tricyrtis, as well as in the genus Scoliopus that has distinctive fleshy capsules that are believed to encourage seed dispersal by ants (Patterson & Givnish 2002).
The Indian cucumber (because of its edible rhizome) Medeola virginiana, a North American representative of the forest-dwelling Medeloideae. Photo by David Smith.
As well as reproducing by seeds, some Liliaceae also reproduce asexually. A number of bulbiferous species produce bulbils, small lateral offshoots of the bulb. These may break off and grow into new plants elsewhere, generally when carried by the action of burrowing animals such as moles and mole-rats.
Patterson, T. B., & T. J. Givnish. 2002. Phylogeny, concerted convergence, and phylogenetic niche conservatism in the core Liliales: insights from rbcL and ndhF sequence data. Evolution 56 (2): 233-252.
The mandible of Khoratpithecus piriyai from Chaimanee et al. (2004). Scale bar equals 1 cm.
The subject of today's Taxon of the Week post is the Ponginae. Rather than comment directly on the prolonged, bitter and largely pointless arguments on ape beta taxonomy, I'll simply note that for this post I'm restricting Ponginae to the clade including the modern orangutans and fossil apes closer to orangs than other modern apes.
I say 'orangutans' because there are two distinct modern varieties that are listed as separate species by Groves (2005), the Sumatran Pongo abelii and the Bornean P. pygmaeus. During the Pleistocene, orangutans were also found in continental south-east Asia and southern China (Bacon & Long 2002). Previous to the Pleistocene, however, a gap of six or seven million years separates Pongo from their generally accepted relatives in the Miocene genera Sivapithecus and Khoratpithecus (Finarelli & Clyde 2004; Chaimanee et al. 2004). Other possible pongine genera whose position is less firm include Lufengpithecus, Ankarapithecus and Gigantopithecus. In the phylogenetic analysis by Finarelli & Clyde (2004), the Miocene Lufengpithecus and Ankarapithecus were initially placed on the orangutan stem on the basis of morphology, but switched over to the base of the stem of the African ape-human clade under an analytical method that attempted to reduce stratigraphic incongruence.
Sumatran orangutan Pongo abelii drinking while neatly concealing its baby. Photo from here.
Sivapithecus is the best-known of the fossil pongines, with a number of species assigned to it from India dating from about 12.8 to 7.4 million years ago. Though Sivapithecus was similar to modern orangutans in skull morphology, it differed in its dentition and postcranial morphology. Sivapithecus lacked the adaptations for brachiation of orangutans; when moving in trees, it would have run along the top of branches in the manner of a monkey rather than swinging underneath the branches like an orangutan. Arm-swinging was probably a later innovation on the orangutan line (and would have therefore developed independently from other arm-swingers such as gibbons). Khoratpithecus, currently known only from teeth and jaw bones, had dentition more similar to Pongo and is probably more closely related to modern orangs than Sivapithecus; unfortunately, we do not yet know whether it retained the plesiomorphic postcranial morphology of Sivapithecus.
Ankarapithecus is a smaller ape that, as its name suggests, was found in Turkey. If it is a pongine, it would increase the known range for that clade. An even greater range has been suggested by the assignation of the Spanish Hispanopithecus to the pongine line (Cameron 1997), though it was instead assigned to a non-pongine clade of European apes by Begun (2009). As indicated above, Ankarapithecus and the Chinese Lufengpithecus show features that could be interpreted as showing relationships to either pongines or hominines. Indeed, some fossils now regarded as Lufengpithecus were initially assigned to Homo (Harrison 2002), though possibly that may say more about the expectations of Chinese palaeoanthropology than about Lufengpithecus itself.
Reconstruction of Gigantopithecus herd. Image from here.
The only potential pongine other than Pongo itself known from later than the Miocene is Gigantopithecus. Three species have been assigned to this genus: the Pleistocene Gigantopithecus blacki from China and two Miocene species from Indo-Pakistan (the Indo-Pakistan species were smaller than G. blacki, but still larger than most other apes). A significant time gap separates the Chinese and Indo-Pakistani species, and it has been suggested that they may represent two separate lineages that independently attained large size (in which case the Indo-Pakistani species are placed in the genus Indopithecus). Gigantopithecus blacki had the largest teeth of any known ape, but without any post-cranial remains it is difficult to know its overall size. Johnson (1979), assuming the proportions of Gigantopithecus blacki to be similar to those of a modern gorilla, suggested that it may have weighed around 270 kg (vs about 160 kg for a gorilla) with long bones about 20% longer than those of a gorilla. However, it has been suggested that the large teeth of Gigantopithecus were specialised for feeding on bamboo (Kupczik & Dean 2008), in which case it may have had larger teeth relative to body size than other apes (it is notable in this light that the incisors of Gigantopithecus were actually smaller than a modern great ape's: Woo 1962). At any case, estimates that Gigantopithecus was more than twice the size of a modern gorilla seem unlikely.
Bacon, A.-M., & V. T. Long. 2001. The first discovery of a complete skeleton of a fossil orang-utan in a cave of the Hoa Binh Province, Vietnam. Journal of Human Evolution 41 (3): 227-241.
Begun, D. R. 2009. Dryopithecins, Darwin, de Bonis, and the European origin of the African apes and human clade. Geodiversitas 31 (4): 789-816.
Cameron, D. W. 1997. A revised systematic scheme for the Eurasian Miocene fossil Hominidae. Journal of Human Evolution 33 (4): 449-477.
Groves, C. P. 2005. Order Primates. In: Wilson, D. E., & D. M. Reeder (eds) Mammal Species of the World: a taxonomic and geographic reference, 3rd ed., vol. 3 pp. 111-184. John Hopkins University Press.
I've written posts before on the Bryozoa, the aquatic (mostly marine) colonial animals sometimes known as 'lace animals'. On both previous occasions, the bryozoans in question have belonged the the group known as Cheilostomata. For this post, I'll be looking a members of another major bryozoan group, the Ctenostomata. While cheilostomes have their colony enclosed in a calcified body wall, ctenostomes have a soft chitinous or gelatinous body wall. Most ctenostomes do not form the tightly arranged colonies of cheilostomes, and the orifice of each individual zooid is not closed by an operculum as in cheilostomes (but read on). It is the delicate tracings of cheilostome colonies that lead to the name of 'lace animals'; if ctenostomes are to be compared with lace, it is with a mucky forgotten rag that has been allowed to rot in the mud.
The Arachnidiidae are a family of ctenostomes that form trailing colonies across their substrate; the type genus Arachnidia was originally named for its resemblance to a spider's web (Harmer 1915). An individual arachnidiid zooid is roughly teardrop-shaped with the orifice at the bulbous end. The branching pattern of the colony is roughly cross-shaped with the thin stolons of three daughters attached to the bulbous end of their parent. Both marine and freshwater species of arachnidiid have been described. It is primarily their colony structure that distinguishes them from other ctenostome families.
Fossil arachnidiid colony, Arachnidium smithii, preserved on a bivalve shell. From Taylor (1990).
Lacking a calcified skeleton, it is not surprising that the fossil record of ctenostomes is somewhat sparse. Ctenostomes are generally preserved as imprints on other fossils, either as borings or by a process called bioimmuration where another hard-bodied organism (such as a coral or another bryozoan) grows over the top of a ctenostome colony. Ctenostome borings date back to the Ordovician, and arachnidiids preserved by bioimmuration are known from the Jurassic (Taylor 1990). However, although cheilostomes and ctenostomes are generally accepted as more closely related to each other than to other bryozoans, the cheilostome fossil record only dates to the Jurassic. It has therefore been suggested that cheilostomes were derived from ctenostome-type ancestors, making ctenostomes potentially paraphyletic (interestingly, this would imply that calcification arose independently in cheilostomes from Stenolaemata, the other major calcified bryozoan group). Among the Jurassic arachnidiids described by Taylor (1990) was one genus, Carboarachnidium, with a D-shaped orifice that Taylor interpreted as indicative of the presence in life of an operculum. As an operculum is a distinctively cheilostome characteristic, Taylor suggested that Carboarachnidium could represent a stem cheilostome. This could make arachnidiids the closest known relatives of cheilostomes among the 'ctenostomes' (though it has to be admitted that, as supporting links go, it's not the most robust), and potentially crucial in understanding the origins of that significant bryozoan clade.
Harmer, S. F. 1915. The Polyzoa of the Siboga Expedition – Part I. Entoprocta, Ctenostomata and Cyclostomata. E. J. Brill: Leyden.
Taylor, P. D. 1990. Bioimmured ctenostomes from the Jurassic and the origin of the cheilostome Bryozoa. Palaeontology 33 (1): 19-34.
Because of the Christmas period lull, you're getting a double whammy:
Attributions to follow. Both images are worth full points as if they were in separate posts. I won't be putting up the follow-up posts for each at the same time, so the second image will be open to challenge until its own post is up, not when the post for the first image appears.
Update: Identity of #41 now available here. Image from here. Identity of # 42 now available here. Figure from Chaimanee et al. (2004).