Fossil Octopods Part 2: Pre-K/T

The first post of this series looked at fossil cephalopods whose inclusion in the order Octopoda (= Octobrachia) is a matter of debate. Pohlsepia mazonensis is an early Carboniferous coleoid with 10 appendages (including 2 tentacles!) which was interpreted as an octopod because of its sac-like body and lack of an apparent shell; the presence of fins indicates that it must have had some internal support and it is currently ignored in phylogenetic analyses because of its dubious preservation. Proteroctopus ribeti was a mid-Jurassic coleoid with 8 limbs, but it also curiously lacked a gladius despite having fins; it could be a stem-octopod, but affiliations with vampyromorphs are just as probable with the available evidence. Trachyteuthids are a mid-Jurassic to late Cretaceous family currently thought to be vampyromorphs (previously squids) but their beak and gladius morphology implies that the squid-like coleoids with eight cirrated appendages and four fins are in fact stem-octopods. Hopefully healthy debate in the future will solidify the phylogenetic positions of these organisms, but there are fossils with undoubted affinities to Octopoda.

Octopods

Palaeoctopus

First described in 1896 from Lebanon, the gladius vestiges of these Cretaceous cephalopods unambiguously indicate that they are octopods (Fuchs et al. 2008). Preservation of soft tissue shows that Palaeoctopus had fins; interestingly the gladius remnants do not resemble the clasp or butterfly-shaped structures of the finned cirrates, but the paired remnants of incirrates (Fuchs et al. 2008). The gladius remnants of Palaeoctopus differ from modern incirrates in being proportionally large, close-set, and stiffened - likely adaptations for providing muscle attachment for the fins (Fuchs et al. 2008). Fuchs et al. (2008) suggest that similarities in curvature in the lateral field of the gladius remnants/gladius of Palaeoctopus and teudopseids further demonstrates their theory about the derivation of the former from the latter... but keep reading.

P. newboldi was the only known species of Palaeoctopus for well over a hundred years, but recently Fuchs et al. (2008) described another species, P. pelagicus, from the early Turonian (~93 mya) of Mexico which differs from P. newboldi in the form and structure of the reinforcements and fields of their gladius remnants. The soft body morphology of P. newboldi indicates that it was probably capable of some benthic locomotion; this data is lacking for the earlier P. pelagicus, but the low oxygen of the sea floor and the distance from coasts strongly suggests that this species was entirely pelagic (hence the name) (Fuchs et al. 2008). I can't help but wonder if Palaeoctopus is paraphyletic or polyphyletic, considering the millions of years between the species and the possible lifestyle differences.

Palaeoctopus newboldi holotype. The soft body morphology of P. pelagicus is unknown, but likely to show more evidence of a pelagic lifestyle.

Keuppia

Palaeoctopus pelagicus was briefly the oldest unambiguous incirrate octopod until Fuchs et al. (2009) described five specimens from two genera and three species from the slightly older Upper Cenomanian (~95 mya). Keuppia was placed in the same family as Palaeoctopus, Palaeoctopodidae, on the basis of sharing blade-like medially isolated bipartite gladius vestiges (Fuchs et al. 2009). Unlike Palaeoctopus, the Keuppia species have a gladius vestige complex with a sub-triangular/semi-circular shape and linear growth patterns instead of concentric (Fuchs et al. 2009). The shape of their gladii remnants are more reminiscent of loligosepiid Octopodiformes, leading the authors to greatly revise their "teudopseid pathway" phylogeny proposed in earlier articles (Fuchs et al. 2009). Curiously, none of the three Keuppia specimens showed preserved fins (they did show suckers, ink sacs, gill lamellae, etc) - however circular encrustations imply that they had basal fin cartilage and were powerful swimmers (Fuchs et al. 2009). Palaeoctopus did not have preserved basal fin cartilage but it did have fins, Fuchs et al. (2009) suggest that it was a less powerful swimmer than Keuppia. I'd like to suggest the possibility that Keuppia recently lost its fins and still possessed a swimmer-like gladius - but I'm not the palaeontologist here. When more fossils turn up, it seems likely that they'll possess some bewildering array of characteristics that leads to more phylogenetic upheaval. The concept of morphological plasticity in early evolutionary "stages" is beginning to sound more plausible to me...

Styletoctopus

Another undoubted incirrate octopod from the Upper Cenomanian of Lebanon, incredibly this species already possesses stylets and appears to be a member of the extant family Octopodidae (Fuchs et al. 2009). Stylets (or rods) are gladius vestiges even more reduced and separated than those of the Palaeoctopodidae*; Fuchs et al. (2009) state that the stylets of Styletoctopus resemble those of Enteroctopus, Benthoctopus and Eledone in the possession of anterior and posterior "shoulders"**. Despite its otherwise modern morphology, Styletoctopus has circular structures which may be interpreted as small globular fins - rather unexpected for a cephalopod with such a reduced gladius (Fuchs et al. 2009). If fins were present (and that's a big "if"), it would seem to indicate that fins were lost multiple times within the incirrate octopods. Styletoctopus implies that Octopoda first derived at least in the Early Cretaceous and possibly the Jurassic (Fuchs et al. 2009).

* Interestingly, Keuppia has posterior shell sacs (remnants) while Palaeoctopus had more laterally placed ones transitional in placement between Keuppia and Styletoctopus; Fuchs et al. (2009) suggest there is some sort of functional difference associated with these placements.

** Strugnell et al. (2005) found Benthoctopus and Enteroctopus to form a clade despite being classified in different subfamilies. Strugnell and Nishiguchi (2007) noted that some previous authors considered Eledone basal - unfortunately Benthoctopus and Enteroctopus were not included in the analysis but Eledone tended to group with other octopods with one row of suckers.

Campanian Cirrate?

Fuchs et al. (2009) mentions a publication which described an unpaired saddle-shaped shell vestige possibly belonging to a cirrate Octopod. I cannot find this:

Fuchs, Dirk et al. 2007. Coleoid cephalopods from the Late Cretaceous North eastern Pacific. 131. In 7th International Symposium ‘Cephalopods – Present & Past’, abstract volume. Sapporo.

"Octopodida" (= Octopoda) Incertae sedis

Tanabe et al. (2008) describe a medium-sized lower jaw from the Santonian which shows the characteristic posteriorly expanded wings and ventrally projected inner lamella with a narrowly rounded crest typical of Octopoda - however it was not well preserved enough to determine any further relations.



Paleocirroteuthis

Two species, P. pacifica and P. haggarti, have lower jaws with a similar shape to modern cirrates, albeit with a posteriorly expanded lateral wall and greater size (Tanabe et al. 2008). P. haggarti has been found in the Santonian and Lower Campanian of Vancouver Island while P. pacifica is known from the Lower Campanian of Hokkaido and Vancouver Island, they are similar in size and morphology although the P. pacifica specimens were not as well-preserved (Tanabe et al. 2008). Since the authors also found a similarly sized vampyromorph from the Lower Campanian of Vancouver, Nanaimoteuthis jeletzkyi, they used a negative allometric equation scaled up from modern Vampyroteuthis to estimate that all of these species ranged between 11-57 kg (24-126 lbs) in weight and 24-37 cm (9.5" - 14.5") in mantle length. A Cirroteuthis magna with a 33 cm mantle length (13") and total length of 1.7 m (5'7") has been reported - but unfortunately not weighed (Collins et al. 2001). Judging from the photo, it probably weighed less than 10 kg - but then again, I'm not a teuthologist.

That's about it for interesting fossil octopods, no offense to the Argonauts. Considering how much this topic can change in a couple years I might as well start preparing for the re-reboot... if I didn't have a lot of other things to do.

References:

Collins, Martin A. et al. 2001. A large Cirroteuthis magna (Cephalopoda: Cirroctopoda) caught on the Cape Verde Terrace (North Atlantic). J. Mar. Biol. Ass. UK. 81, 357-358.

Fuchs, Dirk and Schultze, Hans-Peter. 2008. Trachyteuthis covacevichi n. sp., a Late Jurassic Palaeopacific coleoid cephalopod. Fossil Record 11, 39-49.

Fuchs, Dirk et al. 2008. A new Palaeoctopus (Cephalopoda: Coleoida) from the Late Cretaceous of Vallecillo, North-Eastern Mexico, and implications for the evolution of Octopoda. Palaeontology 51, 1129-1139.

Fuchs, Dirk et al. 2009. New Octopods (Cephalopoda: Coleoida) from the Late Cretaceous (Upper Cenomanian) of Hakel and Hadjoula, Lebanon. Palaeontology 52, 65-81.

Kluessendorf, Joanne and Doyle, Peter. 2000. Pohlsepia mazonensis, and early 'Octopus' from the Carboniferous of Illinois, USA. Palaeontology 43, 919-926.

Klug, Christian et al. 2005. Coleoid beaks from the Nusplingen Lithographic Limestone (Upper Kimmeridgian, SW Germany). Lethaia 38, 173–192

Strugnell, Jan and Nishiguchi, Michelle K. 2007. Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) inferred from three mitochondrial and six nuclear loci: a comparison of alignment, implied alignment and analysis methods. Journal of Molluscan Studies 73, 399-410.

Strugnell, Jan et al. 2005. Molecular phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) using a multigene approach; the effect of data partitioning on resolving phylogenies in a Bayesian framework. Molecular Phylogenetics and Evolution 37, 426-441.

Tanabe, Kazushige, et al. 2008. Late Cretaceous Octobrachiate Coleoid lower jaws from the North Pacific regions. J. Paleont. 82, 398-408.

Fossil Octopods Part 1: Possible Octopods

If this topic looks familiar, that's because it was covered back in 2007. Since those dark ages, much more information has become available and I realized a reboot was in order. Looking back at that old page was like watching Batman & Robin after Batman Begins.

So what is an "octopod"? For this post, I will consider an "octopod" to be everything more closely related to Octopus than Vampyroteuthis; this includes the cirrate and incirrate octopuses in Octopoda plus whatever stem-octopods are out there. Unfortunately, there is little consistency in the naming of major cephalopod taxonomic rankings in some recent literature. Mikko's phylogeny calls the order "Octopoida", but still refers to the animals as "octopods" instead of "octopoids". Fuchs et al. (2008) calls the order Octobrachia, the suborder containing incirrates Octopoda, and the suborder containing cirrates Cirroctopoda. The systematics used by Tanabe et al. (2008) have a superorder Octobrachia containing the orders Cirroctopodida, Octopodida, and Vampyromorphida. Young and Vecchione (2008) argue that cirrates and incirrates are well-supported sister taxa and this reorganization is not valid. So I'll stick with the more traditional naming scheme, but we'll see how this holds up with the re-reboot in a couple years.



Possible Octopods

Early cephalopod evolution was apparently rife with "morphological plasticity"; Carboniferous coleoid shells exhibited character recombinations not observed in Mesozoic individuals and previously thought to be impossible (Doguzhaeva et al. 2007). Assuming that this phenomenon effected parts of the cephalopod aside from the shell, caution should be used when assigning very early coleoids to groups.



Pohlsepia mazonensis

An upper Carboniferous fossil from the Mazon Creek Lagerstätte of Illinois, this "exceptionally well preserved" fossil in ventral view is interpreted to have a sub-circular and dorso-ventrally flattened sac-like body; two narrow posterior fins with a narrow, symmetric shape; a head indistinct from the body with mandibular architecture, eyes, and a funnel; an arm crown which is indistinct with no hooks or suckers visible, there appear to be short arms and long modified arms (tentacles) (Kluessendorf and Doyle 2000).

Stolen from Wikipedia. Abbreviations: e, eye; ef, expressed fluid; f, fin; fu, funnel; is?, ink sac (or gut trace); m, mandibles; ma, modified arm (tentacle); r, radula.

Kluessendorf and Doyle (2000) modify another author's figure to show Pohlsepia on the stem-line leading to the Vampyromorpha/Octopoda clade (text-fig 2); bizarrely they regard it as a possible member of Cirrata (= Cirroctopoda) - a group which the figure shows deriving more than a couple hundred million years after Pohlsepia. Since Pohlsepia reportedly lacks a shell, the authors compare it to octopods (cirrates and incirrates) which "lack any form of shell" - this is not true as shells are present in cirrates in the form of cartilaginous fin supports and in some incirrates as stylets. The presence of fins indicates that a shell-like structure must be present as a site of muscle attachment, so clearly either this fossil was not interpreted correctly or not everything fossilized. Klug et al. (2005) call this a poorly preserved fossil and suggest that the structures interpreted as fins could very well be the remnants of an internal shell. Considering the eight arms, two tentacles, dorso-ventral compression and possible shell remnant, could this be a decapodiform that was deformed (squished) during fossilization? Additional specimens will be needed to clear up all of these ambiguities since right now the absence of hard parts is viewed as a diagenetic artifact and Pohlsepia is ignored in phylogenetic analyses (Fuchs et al. 2008).



Proteroctopus ribeti

Very little literature on this species is available to me, but it is fortunately discussed by Fuchs et al. (2008). This mid-Jurassic coleoid has been viewed as an incirrate octopod by some, but its lack of a gladius us probably due to the deposit it was found in (where no gladii have preserved) (Fuchs et al. 2008). The presence of a pair of fins strongly supports the notion that the gladius failed to preserve. It is possible that the lack of cirri on the fossil is also an artifact of preservation (Fuchs et al. 2008). This article notes that the species has a sac-like body, two fins, eight equal arms and no indication of a modified appendage pair - but is it a stem-octopod? Fuchs et al. (2008) suggest that it could be a stem-line member of either "Octobrachia" (=Octopoda) or Vampyromorpha, since it has a vampyromorph-like body outline.

Proteroctopus ribeti, stem-octopod or stem-vampyromorph? Compare with Vampyronassa rhodanica, a contemporary vampyromorph and possible relative.

Teudopseina

I mentioned the peculiar coleoid Trachyteuthis hastiformis in a previous post - although not the one on fossil octopods. Although trachyteuthids have been assigned to a number of groups, the presence of two pairs of fins, eight arms, cirri, arm webbing, and the absence of a phragmocone has led to classification as a vampyromorph (Fuchs and Schultze 2008). However, the beak morphology bears a stronger resemblance to Octopus than Vampyroteuthis (Klug et al. 2005). Klug et al. (2005) note that beak morphology is not the most important character in coleoid phylogeny and suggest that more beaks from vampyromorphs will be needed to determine if other members of the group could exhibit Octopus-like beak morphology. Interestingly, Fuchs and Schultze (2008) place Trachyteuthis in the order Octobrachia (= Octopoda) and the suborder Teudopseina; they cited obscure sources which claimed that the gladius remnants of cirrate and incirrates derived from a teudopseid gladius. If this classification is correct (and it will certainly be debated in the future, then Trachyteuthis, Teudopsis, Glyphiteuthis and relatives are stem-octopods.

From Klug et al. (2005). This reconstruction presumes a close relation with Vampyroteuthis, although if Trachyteuthis is an octopod I doubt it looked much different. This looks a lot better than my effort.

Loligosepiidae

A group I forgot to add when I originally published this post, loligosepiids are another family of coleoids currently classified as vampyromorphs which may have octopod affinities. I unfortunately can't access this paper to give more of a background, but newly described octopod species hint that they may be derived from this family and not Teudopsidae (Fuchs et al. 2009). It is possible that loligosepiids are members of both the Octopoda and Vampyromorpha stem groups (Fuchs et al. 2009).



That's it for now, part 2 tomorrow will cover fossils that are without a doubt actual octopods.

References:

Doguzhaeva, Larisa et al. 2007. A Late Carboniferous Coleoid Cephalopod from the Mazon Creek Lagerstätte (USA), with a Radula, Arm Hooks, Mantle Tissues, and Ink. IN: N. H. Landman et al. (eds.) , Cephalopods Past and Present: New Insights and Fresh Perspectives, 121-143

Fuchs, Dirk et al. 2009. New Octopods (Cephalopoda: Coleoida) from the Late Cretaceous (Upper Cenomanian) of Hakel and Hadjoula, Lebanon. Palaeontology 52, 65-81.

Fuchs, Dirk et al. 2008. A new Palaeoctopus (Cephalopoda: Coleoida) from the Late Cretaceous of Vallecillo, North-Eastern Mexico, and implications for the evolution of Octopoda. Palaeontology 51, 1129-1139.

Kluessendorf, Joanne and Doyle, Peter. 2000. Pohlsepia mazonensis, and early 'Octopus' from the Carboniferous of Illinois, USA. Palaeontology 43, 919-926.

Tanabe, Kazushige, et al. 2008. Late Cretaceous Octobrachiate Coleoid lower jaws from the North Pacific regions. J. Paleont. 82, 398-408.

Young, Richard E. and Michael Vecchione. 2008. Octopodiformes Berthold and Engeser, 1987. Vampire Squid and Octopods. Version 21 April 2008 (under construction). http://tolweb.org/Octopodiformes/19405/2008.04.21 in The Tree of Life Web Project, http://tolweb.org/

Cephalopod Ageing and Gigantism

I was under the impression that just about every (non-Nautilus) cephalopod has a life history which involves growing at a blazing speed, reproducing, and then dying in about a year or two. The implications of such an ephemeral lifestyle on the growth of giant cephalopods is staggering, although it is possible that giants have a considerably longer lifespan than the norm. While the terminal "spawning once" strategy (formerly known as semelparity) is common amongst coleoids, intermittent terminal, multiple, and continuous spawnings are known to occur across various taxa (Rocha et al. 2001). An iteroparous strategy does not guarantee a longer lifespan, but they are generally thought of as longer lived (Rocha et al. 2001). With the abnormally long-lived and continuously spawning Nautilus excluded from data, degree-days to maturity and size are strongly correlated for coleoids (Wood and O'Dor 2000). The taxa used by Wood and O'Dor (2000) appeared to be simultaneous terminal and intermittent terminal spawning strategists; it could be potentially interesting to look at strategy and degree-days to maturity together, as nobody seems to have done it yet.


One of the "great mysteries of cephalopod biology" is the growth rate and lifespan of the giant squid Architeuthis (Grist and Jackson 2007). Architeuthis may no longer be considered the largest living cephalopod, but it is still a huge animal with average weights of 150 kg (330 lbs) for males and 275 kg (605 lbs) for females* (Grist and Jackson 2007). Cadmium concentrations in its digestive gland suggest that Architeuthis either feeds intensely while growing rapidly or is longer lived than most other cephalopods (Bustamante et al. 2008). ¹⁴C analysis of Architeuthis statoliths (inner-ear analogues) gave variable age estimates due to the assumed depths; depth calculations from ¹⁸O gave 95% confidence intervals of 0-37, 27-51, and 20-46 for 3 different specimens, depths estimated from captures gave figures of 0-33, 0-21, and 0-31 for the same specimens (Landman et al. 2004). The authors suggest that future studies should research the physical and chemical characteristics of the squids' environment and use more specimens in varying stages of growth (Landman et al. 2004). Steve O'Shea has an excellent article online on Architeuthis age determination from morphology; one squid with a 1.68 m mantle was estimated to be between ~1.5-4.8 years in age judging by daily(?)** growth rings on the statolith. O'Shea notes that layers on the eye lens and gladius both give ages close to 6 years, so clearly something here isn't being deposited on a daily basis.

* Wikipedia claims that these figures are maximums, but the source it cited has deleted these claims (figure 7).
** Deposits are known to be daily in at least some squids, but it is possible that others may do things differently. Landman et al. (2004) suggest that if their upper-bound estimates are correct, the rings could be formed from increased feeding in shallow water during a new or full moon.


Since none of the aforementioned methods provided a clear solution to this great mystery, Grist and Jackson (2007) applied growth models with energy balance taken into consideration. Cephalopod growth has two distinct stages, an exponential one for larvae and a linear one for adults (Grist and Jackson 2007). The various models gave a very wide estimate of lifespan (89 days to 753 years) but the authors used size-at-age data (from statoliths) in conjunction with this to estimate that females took 3 years to reach 275 kg and males took 6 years to reach 150 kg (Grist and Jackson 2007). In light of this, the authors suggest that there are behavioral (and presumably ecological) differences between the sexes (Grist and Jackson 2007).

This is certainly not the last we'll hear of this great mystery, more data will surely lead to a great deal of revision. If the average weights are found to be different, it could considerably alter the results of Grist and Jackson (2007), for instance. In all likelihood, it seems that Architeuthis does have a rather long lifespan for a cephalopod, but probably not one measured in decades. It would certainly help if at least juveniles could be raised in a lab, but perhaps I'm just partial to the idea of a captive Architeuthis...


So what about the other giant squids? If the "jumbo" ommastrephid Dosidicus gigas truly adds one layer a day to its gladius and statoliths, then it has an annual life-cycle in which it can reach a mantle length of 0.7 to 0.75 m (Nigmatullin et al. 2001). Particularly large specimens have been found up to 1.5-2 years in age with a mantle length of 1-1.2 meters (3'3"-3'11") and a weight of 30-50 kg (66-110 lbs) (Nigmatullin et al. 2001). Interestingly, the larger females show exponential growth while males have a slightly sigmoid growth pattern (Nigmatullin et al. 2001). D. gigas is of course an active, nektonic species with a monocyclic breeding strategy, so it probably isn't that comparable to Architeuthis.


I was originally going to talk about cirrate octopuses and the possible relation of their continuous spawning strategy and occasional gigantism, but I accidentally deleted it and realized it was rather nebulous at best. Rather than dote on it, I decided to at least get one thing posted this month.

References:

Grist, Eric P. M. and Jackson, George D. 2007. How long does it take to grow a giant squid? Rev Fish Biol Fisheries 17, 385-399

Landman, N. H. et al. 2004. Habitat and age of the giant squid (Architeuthis sanctipauli) inferred from isotope analysis. Marine Biology 144, 685-691.

Nigmatullin, Ch.M. et al. 2001. A review of the biology of the jumbo squid Dosidicus gigas (Cephalopoda: Ommastrephidae). Fisheries Research 54, 9-19

Rocha, Francisco et al. 2001. A review of reproductive strategies in cephalopods. Biol. Rev. 76, 291-304.

Wood, J. B and O'Dor R. K. 2000. Do larger cephalopods live longer? Effects of temperature and phylogeny on interspecific comparisons of age and size at maturity. Marine Biology 136, 91-99.

Strange Little Spirula

We can safely say that Spirula is an unusual coleoid cephalopod with a ventrally curved ("endogastric") planispiral shell, a vestigial radula, a photophore on the tip of the mantle, and oegopsid (cornea lacking) eyes (Warnke and Keupp 2005, Warnke 2007, Young 1996). That's about the limit of what can be said concisely...

The internal planispiral shell of Spirula, taken from scamazine's flickr. While this shell looks similar to those of the extinct ammonites, it curves ventrally rather than dorsally. This illustration shows how the shell fits into the animal.

Spirula was formerly considered to contain several species (see here) but now only S. spirula is valid. Spirula has two disjunct populations in the Atlantic and Indo-West Pacific Oceans; a molecular study of intraspecific variation suggests that individuals from Fuerteventura and New Caledonia are distinguished to a degree typical of separate species (Warnke 2007). The lifespan of the species is only ~20 months, making gene flow appear to be unlikely between the populations, but individuals closer geographically have not been investigated yet (Warnke 2007). With the sparse molecular and morphological data on Spirula variation, much more work needs to be done in order to (re-)establish multiple species.

So now that we haven't resolved the number of Spirula species, what exactly is it? Spirula certainly is a unique looking cephalopod and many sources (e.g. Wikipedia) place it in a monotypic order. Warnke and Keupp (2005) suggested that Spirula is the most basal decapodiform and further suggest that it can be used to study ammonite development! There are prominent morphological distinctions between the groups - ammonites tend to have shells with exogastric coils (heteromorphs are of course exceptions) and four prismatic layers while Spirula has a shell with endogastric coiling and two prismatic layers (Warnke and Keupp 2005). However, the initial chambers (protoconch) of ammonites and Spirula show morphological similarities and the mode of mineralization appears to be the same (Warnke and Keupp 2005). Warnke and Keupp (2005) cite prior preliminary molecular evidence to support the notion of Spirula being the most basal decapodiform and imply that similarities are plesiomorphies. Later molecular studies contradict the placement used by Warnke and Keupp (2005) but the issue of Spirula/ammonite similarities being homologies or homoplasies is still unclear. Spirula development will certainly be an interesting topic to investigate regardless.

More recent molecular analyses suggests that Decapodiformes consists of two orders (rather than 4) - Sepioidea (containing Sepiidae, Myopsida, Sepiolidae, Idiosepiidae, Spirula) and Teuthoidea (Strugnell et al. 2006). Spirula consistently grouped with Sepiidae and it should be noted that the proposed clade has the synapomorphies of sperm placement in females and the structure of the statoliths and tentacle clubs (Lindgren and Daly 2007, Strugnell et al. 2005). Their next nearest relative is either Myopsida or Sepiolidae, but either way Spirula is fairly nestled within the Decapodiformes (Lindgren and Daly 2007, Strugnell et al. 2005). The earliest probable member of Sepioidea is the early Carboniferous Shimanskya which is either a member of the Spirula-lineage or another taxa that convergently lost the nacreous layer (Strugnell et al. 2006). This fossil and the molecular clocks suggest that many clades are far older than previously thought, e.g. Sepiidae was previously thought to have originated in the Oligocene but apparently diverged around a couple hundred million years earlier (Strugnell et al. 2006)! Supporters of the Spirula-is-basal camp could argue that this incredible revision suggests that Spirula is not placed correctly, but other evidence in Strugnell et al. (2006) implies that many decapodiform lineages are similarly ancient. Undoubtedly this will undergo further revision, but it seems very unlikely that Spirula is the most basal of the Decapodiformes.

Despite apparently existing in large numbers, much of the life history of Spirula remains poorly known (Lukeneder et al. 2008). Study of shell isotopes suggests that the juveniles are born in waters >1000 m deep, migrate to warmer waters from 400-600 m as adults, and then migrate back down into deep and cold waters (Lukeneder et at. 2008). It's worth pointing out that Lukeneder et al. (2008) suggest that future studies of the Spirula life history can be applied to ammonites...



References:

Lindgren, Annie R. and Daly, Marymegan. 2007. The impact of length-variable data and alignment criterion on the phylogeny of Decapodiformes (Mollusca: Cephalopoda). Cladistics 23, 464-476.

Lukeneder, Alexander et al. 2008. Stable isotopes (18O and 13C) in Spirula spirula shells from three major oceans indicate developmental changes paralleling depth distribution. Marine Biology 154, 175-182.

Strugnell, Jan et al. 2006. Divergence time estimates for major cephalopod groups: evidence from multiple genes. Cladistics 22, 89-96.

Strugnell, Jan et al. 2005. Molecular phylogeny of coleoid cephalopods (Mollusca:Cephalopoda) using a multigene approach; the effect of data partitioning on resolving phylogenies in a Bayesian framework. Molecular Phylogenetics and Evolution 37, 426-441.

Warnke, Kerstin. 2007. On the Species Status of Spirula spirula (Linne, 1758) (Cephalopoda): A New Approach Based on Divergence of Amino Acid Sequences Between the Canaries and New Caledonia. IN: N. H. Landman et al. (eds.). 2007. Cephalopods Present and Past: New Insights and Fresh Perspectives, 144-155. Springer.

Warnke, Kerstin and Keupp, Helmut. 2005. Spirula—a window to the embryonic development of ammonoids? Morphological and molecular indications for a palaeontological hypothesis. Facies 51, 60-65.

Young, Richard E. 1996. Spirulida Haeckel, 1896, Spirulidae Owen, 1836. Spirula spirula Linnaeus, 1758. Version 01 January 1996. http://tolweb.org/Spirula_spirula/19989/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/

Spirula can also be seen bearing gifts on my Christmas card. Unusually among cephalopods, the buoyant shell puts the animal in a head-down orientation (presumably because it had bottom-based ancestors?). I accidentally depicted it without skin of the mantle.

Anomalous Cephalopod Appendages

Relative to other cephalopods, octopuses are reported with abnormal appendages* much more frequently. Symmetry and streamlining do not appear to be issues for animals that jet around infrequently and spend most of their time as benthic crawlers. It isn't fair to assume that every octopus is a benthic crawler, but as far as I can tell no pelagic octopuses were reported with abnormalities. Octopuses also seem capable of coping with arm morphologies quite divergent from the norm, one author reported seeing octopuses in the wild with the greater portion of seven arms missing (Toll and Binger 1991).

* The appendages are known as arms, regardless of how they're used. One recent study, which has not yet been peer reviewed as far as I can tell, reports that octopuses use arm pair IV as "legs" - but they primarily studied Octopus vulgaris and it is perfectly conceivable that different species have specialized their arms for different purposes.


Octopuses with subnumerary arm counts unrelated to natural losses have been reported. An article cited by Toll and Binger (1991) (Gleadall 1989 - see further reading) documented an Octopus sp. with seven arms*. Earlier this year it was claimed that the first "hexapus" was discovered, but somebody didn't bother checking the literature because I quickly found a description of a hexapodous specimen by Toll and Binger (1991). The aberrant Pteroctopus tetracirrhus entirely lacked arm pair II and there was a single adoral (near mouth) sucker located on the web between arms LI and LIII (Toll and Binger 1991). Arm pair I was observed with several other abnormalities: LI was narrower and shorter than RI, three of the first five suckers on LI were abnormally small, in the first ten rows of suckers on RI one third of them were abnormally small and there was widespread misalignment - some areas were even roughly tri-serial (Toll and Binger 1991). The authors reported that otherwise the specimen was normal and the abnormal appendages did not show signs of regeneration.

* Not to be confused with male Haliphron atlanticus


Octopuses with abnormally high counts of arms have also been reported. The Pink Tentacle posted on an octopus with 9 arms, which either has an extra RI or LIV (where's a hectocotylus when you need one?). The limb may be "split" off from another, I'll discuss this below. Kumph 1960 cited an earlier study (Parona 1900 - see further reading) which described an O. vulgaris with two thin arms in the place of LI and an Eledone cirrhosa* with an arm in between RII and RIII. Toll and Binger (1991) described the first decapodous octopus**, a lab-raised O. briareus which had a repeated arm pair IV. All of the arms were evenly spaced around the branchial crown, but the octopus still had a couple of other abnormalities. Male octopuses have a specialized arm for spermatophore transfer (RIII*** - the hectocotylized arm) and the Toll and Binger specimen had a supernumerary spermatophoric groove on LIII with no hectocotylus. A supernumerary diverticulum of the penis was also present.

* Toll and Binger 1991 cite this specimen as E. moschata, describes it as E. aldrovandi. Gonzalez and Guerra note that the species name has been changed.
** I can't help but mention the fact that there are octopodous decapods. Theirs' is a natural condition, however.
*** Some species have a hectocotylized LIII (Palacio 1973).


Abnormal hectocotylization is another abnormality recorded in octopuses. Palacio (1973) discussed some prior cases: hectocotylization was reported on RIII and LIII from an Eledone cirrosa (Appellof 1892 - see further reading) and on RIII and LII from Octopus briareus (Robson 1929 - see further reading). Palacio (1973) reported an O. vulgaris with hectocotylized RIII and RIV and an O. selene with hectocotylized RII and RIII. The extra hectocotylized arms all manifest with roughly the same morphology, they are not diminished in size and have proportional differences compared to the normal arms (Palacio 1973). Unlike the Toll and Binger decapodous octopus, none of these four specimens exhibited abnormalities with the genitalia (Palacio 1973). Palacio (1973) speculated that the extra hectocotylized arms were functional and were likely the result of mutations in sex-linked genes. It seems really odd that the mutation would occur on different arms each time, but how the hectocotylus wound up on RIII (for the most part) also seems rather odd. Another paper (Jereb et al. 1989) has discussed bilateral hectocotylization, but not exactly in a language that I can read.

So far I've only mildly alluded to the commonest and most bizarre condition that occurs in cephalopod arms - splitting. Bifurcation has been observed recently in the tentacle clubs of Onykia (= Moroteuthis) ingens by Gonzalez and Guerra (2007); polyfurcation was observed not-so-recently in the arms of a cuttlefish (Okada 1937 - see further reading). As can be predicted, octopuses are far more prone to demonstrating this trait - 7 were captured off Japan from 1884 to 1964 (Okada 1965a). Kumph (1960) described a bifurcation in LIII from O. briareus, both of the new arms had a biserial series of suckers and there was some webbing in between them. Kumph rejected the idea that it was the result of injury and interpreted it as a mutation or developmental oddity. This is a rather mild defect compared to some.

Around 8 years ago I found some diminutive quasi-cryptozoology book in a library (the downtown Naperville library) and I recall being extra dubious of the claim that octopuses have been found from extra "tentacles". Besides Toll and Binger (1991), the genesis of this post was a link my sister sent me to a post from Pink Tentacle which showed octopuses with up to 96 branching "armlets". The pattern of branching is quite complex: bifurcations have a continuous series of suckers, trifurcations have side branches with independently developed sucker series, then there are dorsal bifurcations, dorso-lateral mixed branching, dorsal branching and subcutaneous branching (with no suckers) (Okada 1965a, 1965b). Toll and Binger (1991) suggested that Okada's data indicates that the branching is not a random event. All of the specimens that Okada looked at were Octopus vulgaris from Japan, but it could be possible that this is due to sampling bias. If there is a regional tendency to be crazily polyfurcated I have no idea why.

Figures 4 and 5 from Okada 1965b. These are from the 1884 Uraga specimen with 90 branches total. Incredibly, RII did not have any branches. The left arm is LIII with five primary and thirteen secondary branches (21 total). The right arm is RIV with four primary and eighteen secondary branches (30 total). Ventral arms (III and IV) tend to have more furcations.

So what could possible cause these anomalous appendages? Gonzalez and Guerra (2007) note that in limb regeneration, an Apical Epidermal Crest covers the severed organ and Hox genes are activated to reproduce a limb as it was in the embryo. In their Onykia specimen, the tentacles appeared to have been regenerated but with clubs only (and bifurcate ones at that) - as such it had to get by with arms only (Gonzalez and Guerra 2007). Toll and Binger (1991) brought up amphibian regenerations with (surgically induced) supernumerary distal limb development but didn't reach firm conclusions on its relevance. These appendage abnormalities are likely due to developmental defects and/or regenerative difficulties, but the literature still is scant and I'm sure there's a lot more interesting work to be done.

Before I go, I should mention that five pairs of arms appears to be the ancestral conditions for cephalopods, including Nautilus. Pairs I and II turn into parts of the hood (!) and III-V turn into digital tentacles. I should probably mention the ocular and buccal tentacles in Nautilus which are not of homologous origin to these. Since there appears to have been a polyfurcation event in the past (albeit a less haphazard looking one), this could support the idea of some appendage anomalies being wholly genetic.

References:

González, Ángel F. and Guerra, Ángel. First observation of a double tentacle bifurcation in cephalopods. JMBA Biodiversity Records - Published Online

Kumph, H. E. 1960. Arm abnormality in Octopus. Nature 185, 334-335.

Okada, Y. K. 1965a. On Japanese octopuses with branched arms, with special reference to their captures from 1884 to 1964. Proc Jap Acad 41, 618-623. Available

Okada, Y. K. 1965b. Rules of arm-branching in Japanese octopuses with branched arms. Proc Jap Acad 41, 624-629. Available

Palacio, F. J. 1973. On the Double Hectocolyziation of Octopods. The Nautilus 87, 99-102. Available (staring on page 124).

Shigeno, Shuichi et al. 2007. Evolution of the Cephalopod Head Complex by Assembly of Multiple Molluscan Body Parts: Evidence from Nautilus Embryonic Development. Journal of Morphology 269, 1-17

Toll, Richard B. and Binger, Lynetta C. 1991. Arm anomalies: cases of supernumerary development and bilateral angensis of arms pairs in Octopoda (Mollusca, Cephalopods). Zoomorphology 110, 313-316

Further Reading:
For those with better access to materials than me


Appellof, A. 1892. Teuthologische Beitrage IV. Uber einem Fall von doppelseitiger Hectokotylisation bei Eledone cirrosa (Lam.) d'Orb. Bergs Mus Aarsb, 14-15

Gleadall, Ian G. 1989. An octopus with only seven arms: anatomical details. Journal of Molluscan Studies 55, 479-487.

Jereb, P. et al. 1989. Sue due esemplari anomali di Scaergus unicirrhus (Mollusca, Cephalopoda). Oebalia 15, 807–809.

Okada, Y. K. 1937. An occurrence of branched arms in the decapod cephalopod, Sepia esculenta Hoyle. Annot Zool Japon 17, 93-94

Parona, C. 1900. Sulla dichotomia delle braccia nei Cefalopodi. Boll Mus Zool Anat Comp Univ Genova, vol 4 (No 96), 1-7.

Robson, G. C. 1929b. On a case of bilateral hectocotylization in Octopus rugosus. Pro Zool Soc Lond. 95-97.

Oddly enough, I have a somewhat relevant shirt featuring an octadecapodous octopus. I got it from yonder (I feel contractually obliged). I also feel obliged to say that this was the best of several pictures, yeesh.

Integumentary Intrigue: Scaled Squids

Convergence is one of my favorite phenomena in biology. Evolution doesn't have a driving force to any sort of goal (like humanity), but on many occurrences unrelated groups have evolved very similar structures or even appearances. While cephalopods and fish have a fundamentally different body plan, squid have a streamlined body with camera-like eyes, fins, and a lateral line (in a few species). The females of one species of octopus even have a swim bladder. With this in mind, squids with scales don't sound nearly as bizarre...

I'm not sure if Cranchia scabra can be regarded as scaled or not; older authorities (Person, 1969) did but more recently the structures in question have been referred to as tubercles. These are also present to some degree on the unrelated genera Histoteuthis (occasionally) and Magnapinna talismani. Other odd textures such as "warts" have been recorded from some squids of the genus Onykia. These are not homologous of course, but they could shed light on why odd textures evolved in the first place. Relatives of Cranchia, Liocranchia and Leachia also have tubercles to a much lesser degree and other cranchiids occasionally have them on their funnel and nuchal locking mechanisms. If the tubercles are homologous within the cranchiids, then it appears that the tubercles were an external structure that was modified for other uses. But what use are they? I haven't seen any information on how hard the cartilaginous tubercles are, but Cranchia does have a behavior where it tucks its head and appendages into the mantle cavity and inks itself to turn opaque. Perhaps this is a re-evolving of a nautilus or ammonite-like strategy...but that isn't the focus. I purposefully neglected to mention another occurrence of tubercles.

Pholidoteuthis massyae was once grouped in its own genus and family, but was recently classified with P. adami in the family Pholidoteuthidae, itself part of the Lepidoteuthid families (O'Shea et al., 2007). Other members of the clade, the Octopoteuthidae and Lepidoteuthidae are distinguished by a lack of tentacles as adults. Well, the last one is distinguished by something else, but I'll get to that later. What makes P. massyae so curious is that it has papillate tubercles, some incredible pictures of it can be seen here. Curiously P. adami has structures, viewable here, that are termed "dermal cushions", a term O'Shea et al. synonymies with "scales". That paper discussed the confusing taxonomic history behind the two species (once each given a family, for instance), but (for?) now they seem to be part of the same genus. That would imply a close relation between tubercles and dermal cushions and makes the idea of a scaled squid seem a whole lot more plausible.

The structures on Pholidoteuthis look somewhat like scales, but the overlapping "dermal cushions" of Lepidoteuthis resemble fish scales to an uncanny degree (see here). Here at last is the Scaled Squid. Lepidoteuthis is a member of the Lepidoteuthid families of course, but possesses odd dermal structures like the Pholidoteuthidae and doesn't possess tentacles like the Octopoteuthidae. It seems like all of these families tend towards gigantism, Pholidoteuthids have a mantle length of ~0.7 meters, Lepidoteuthis has a 1 meter mantle and Taningia has one up to 1.7 m long. As if the notion of a near-giant tentacle-less scaled squid seems pretty bizarre, but the recently discovered males add yet another oddity. The first mention of a male is from Jackson & O'Shea 2003, and it is worth mentioning that this is a very cryptic species. The males are around half the size of the females and have an incredibly modified sucker ring on the dorso-lateral arm. The authors speculate that the saber-like hook could be used to "aid male purchase" by either hooking into the female's flesh or interlocking with the scales. Alternately, they also could have been used in male vs. male fighting - but either way the sudden modification of the hooks is noted as being without parallel in the cephalopod universe. Oh, and the males also have a penis half the length of their mantle...

Unfortunately, that's about it for the subject of squid scales. It would be fascinating if the overlapping scales of Lepidoteuthis were somehow related to the bizarre hook on the males - but it could very well be that both have uses more or less unrelated to mating. It still isn't really clear exactly what the tubercles/dermal cushions/scales do on members of the Lepidoteuthid families, and I'd be curious if the Octopoteuthids actually lost that characteristic somewhere along the road. I'm sure that with time we might have a few more surprises and maybe a better understanding of this exceptionally strange characteristic.


I really wish the Tree of Life was as complete for all groups as it is for cephalopods, it really is a remarkably valuable resource.


-Cameron



References:

Jackson, George D. & O'Shea, S. 2003. Unique hooks in the male scaled squid Lepidoteuthis grimaldi. J. Mar. Biol. Ass. U.K., 83, 1099-1100

O'Shea, S. et al. 2007. The nomenclatural status, ontogeny and morphology of Pholidoteuthis massyae (Pfeffer, 1912) new comb (Cephalopoda: Pholidoteuthidae). Rev Fish Biol Fisheries, 17:425–435

Person, Phillip. 1969. Cartilaginous Dermal Scales in Cephalopods. Science, Vol. 164, No. 3886, pp. 1404-1405.

Vecchione, Michael and Young, Richard E. 2007. Pholidoteuthidae Adam, 1950. Pholidoteuthis Adam, 1950. Version 18 December 2007 (under construction). http://tolweb.org/Pholidoteuthis/19835/2007.12.18 in The Tree of Life Web Project, http://tolweb.org/

Young, Richard E. and Mangold (1922-2003), Katharina M. 2007. Cranchia Leach 1817.
Cranchia scabra Leach 1817. Version 14 June 2007. http://tolweb.org/Cranchia_scabra/19542/2007.06.14 in The Tree of Life Web Project, http://tolweb.org/

Young, Richard E. and Vecchione, Michael. 1998. Lepidoteuthidae Pfeffer 1912. Lepidoteuthis grimaldii Joubin, 1895. The scaled squid. Version 01 January 1998 (under construction). http://tolweb.org/Lepidoteuthis_grimaldii/19833/1998.01.01 in The Tree of Life Web Project, http://tolweb.org/

Oh the Sea Monks, what a bizarre bestiary entity. The squid in the middle is supposed to be Architeuthis, but if these were based on squids and scaled they could possibly be our friend Lepidoteuthis. Of course, medieval artists tended to unnecessarily add scales to things and it would be out of range (Lepidoteuthis is tropical to sub-tropical) - so that's why I'm mentioning this here as a curiosity and nothing more.

Four Finned Cephalopods

On this old post, I mentioned the factoid that the vampire squid has four fins at one developmental stage. Vampire squids (Vampyroteuthis infernalis), as mentioned at this other old post, are a distinct group of cephalopods usually connected with octopodes - although this may not be the case. And yes, continuing with the recent trend this is the sole species of an entire order (superorder?) which may have originated as early as the Devonian.

Despite the very strange morphological feature of another pair of fins (briefly), I've seen no discussion of it and assumed it was some bizarre slip of the pen until I saw the picture I linked to earlier. Considering that all other cephalopods have either one pair of fins or none, this occurrence really should have raised eyebrows. Mercifully, the article by Donovan et al. (available on the Internet Archive) not only appears to be the first discussion of this oddity, but demonstrated that the vampire squid is not an isolated case.

For one thing, the Chiroteuthid Grimalditeuthis also possesses 2 pairs of fins as an adult and Chiroteuthis does in juvenile forms (Donovan et al 2003), although if you note from the links the secondary pair of fins are referred to as "fin-like flotation devices" and the larvae of Chiroteuthis are, well, extremely bizarre with siphonophore imitating growths which appear to be retained. Since this is not present in any other species of Chiroteuthid or decapodiform, we can fairly confidently say these are not homologous structures. It would be interesting to if the "fins" are modified portions of existing fins or non-homologous structures - or both maybe. But this is aside from the point.

Trachyteuthis is a fossil coleoid from the Upper Jurassic which was first described in 1896 (known since at least 1829) and subsequently reconstructed something like this. Other specimens hinted at the possibility of two pairs of fins; the specimen described by Donovan et al. made it clear that the species did posses them. The specimen was at the upper size limit for the species (~380 mm gladius length), so there is no question that this is an adult specimen. The animal was preserved showing the dorsal surface with the four fins present; they each appear have a base and the proximal pair has thicker muscle bundles. The fins appear to be directly attached to the gladius, although it is not clear if by a fin root pocket or directly by cartilage. Trachyteuthis, apparently had a well-muscled mantle and could presumed capable of jet propulsion, so these fins were likely used for stability or control of altitude rather than propulsion (Donovan et al 2003), like cirrate octopuses. The potential mechanics of why two pairs were needed was not discussed, although since Vampyroteuthis re-absorbs its extra fins presumably they don't offer that much of an advantage (for its lifestyle). Here's the obligatory link on many-finned fishes, which demonstrates that extra fins may sometimes have advantages.

So what exactly is Trachyteuthis? There is a noted resemblance between the three-part gladius of this species and Vampyroteuthis (plus Mesoteuthoidea and Prototeuthoidea), although Vampyroteuthis resembles Loligosepia much more, suggesting Trachyteuthis is a sort of side branch. The arm crown is a more definitive way of determining cephalopod identity; while fossil Trachyteuthis have left the impression of eight arms, it is possible for two more arms/tentacles/filaments to have been present and not preserved. The authors conclude that the four fin condition may have been primitive in Octobranchia, and it cannot be determined if all coleoids once possessed this feature (Donovan et al., 2003).

So there we go, we went from a factoid occasionally mentioned in books and websites to a potentially very old feature. Since vampyromorpha appears to be a very old lineage, I don't find the suggestion that all octopodes also started off with four fins. Would the extra fins be detectable in their embryos (do incirrates absorb fins?) as it is in juvenile vampire squid? I should mention that Pohlsepia was an incredibly old (~300 mya) "octopus" with eight arms, two fins, and no shell; although that last feature suggests it wasn't an ancestor of cirrates/incirrate octopodes which presumably split in the Jurassic from an ancestor with an internal shell. If the shell was mis-interpreted as something else and it was an octopod-ancestor maybe four fins wasn't an ancestral characteristic for octopodes, or vanished quickly. The lack of soft bodies preserved and the apparent fact the the gladii of fossil cephalopods tend to convergently evolve (Donovan et al., 2003) would seem to make fossil cephalopods a taxonomic nightmare. It could be possible that Trachyteuthis was an unrelated cephalopod that also possessed a feature one of Vampyroteuthis' ancestors evolved (and somewhat lost), but that coupled with gladius similarities does suggest a connection, albeit a rather tenuous one.


Ah, I like not having to look up a couple dozen articles. I've got a handful of post ideas at once here (most lengthy), so let's see what happens. Probably no more fossil cephalopods, yeesh.



Reference:


Donovan et al. 2003. Two pairs of fins in the late Jurassic Coeleoid Trachyteuthis from Southern Germany. Berliner Paläobiol. Abh. 03, p. 091-099. Available

Attempted re-re-reconstruction of Trachyteuthis. I chose to portray this as a pelagic Vampyromorphan - characteristics of this group include a broad gladius extending the full length of the mantle (~380 mm) and no clear head/mantle differentiation. Earlier reconstructions showed the latter feature, although that appears to be speculative. The body is reconstructed as being bullet-shaped like a pelagic squid (e.g. Loligo) assuming the fossils were somewhat flattened; the impressions support the idea of large eyes. I chose to portray it with 8 appendages (filaments hidden or lost) with a single row of suckers (ancestral to vampire squids and octopodes?) and no cirri (a deep water adaption?). An ink sac and chromatophores are probably not present, unless it converged upon decapodiformes. I'd suggest that one pair of fins could be held in a plat plane and the other somewhat upwards, perhaps in an analogy to the pectoral/pelvic fins of fishes or the wings of Microraptor; they are <70 mm long.

Fossil Octopodes

Dear Constant Readers,

As mentioned previously in the last post, this is an expansion of a subject not easily crammed in as a tangent. Sure there are only three examples of fossil octopodes (and some indirect evidence), but the story is shockingly complicated. As Persuasive and Analytical Writing has taught me, I really do have a tendency towards unnecessary broadness. Combating that will also probably give me a more respectable post output. So let us explore this little knot of a topic.

On an ironically placed tangent I should note the suspiciously changed title of the previous post. As far as the plural of "octopus" is concerned; "octopi" is hyper-corrected (note: pus/pod not present); "octopuses" is strange sounding and anglicized; and "octopodes" appears to be the proper plural. It is also the most international way of putting it, or so Wikipedia says to me. I try not being a typical 'murrican, I really do. All three (and "octopods") confusingly appear in recent scientific journals but from now on: octopodes.

With that nitpicking aside, yes, octopodes have a terrible fossil record. Way worse that choristoderans even. Despite having the advantage of extant species (and thus testable genetic material), the phylogenetics of "Octopodiformes" (octopodes and vampire squid) are currently quite confusing. Recent genetic analysis (Strugnell et al 2006) dealing with divergence times concluded that Octopoda and Vampyromorpha diverged some time in the Paleozoic; a diagram in the paper showed it as being in the Permian over 250 mya. As noted in the prior post, cirrate and incirrate octopodes diverged in the Jurassic, much earlier than anticipated. The paper also illustrated the major Decapodiform lineages diverging all the way back in the Devonian, perhaps around 400 mya. It should be noted that this test used examples from the fossil record in order to establish minimum ages for certain lineages and divergences. This paper did not estimate estimated the divergence of the major cephalopod divisions of nautiloids, Decapodiformes and Octopodiformes, nor did any other I could find. Things seemed peachy until...

An even more recent study by Yokobori et al 2007 discussed the relations of those major groups. Traditionally, the concept of Octopodiformes (= octopodes + vampire squids) has been morphologically supported but some genetic tests have concluded that Vampyromorpha is more closely allied with Decapodiformes. This reveals the problem with Strugnell et al 2006 of presuming the monophyly of the two traditional coleoid groups. The Yokobori et al study concluded that octopodes and vampire squids did have an mt organization closer to the proposed ancestral cephalopod condition the Decapodiformes. Interestingly, this does not support the notion that octopodes and vampire squids are necessarily sister groups. Yokobori et al conclude that there need to be three major divisions of coleoid cephalopods (Octopoda, Vampyromorpha, Decapodiformes) and that they all diverged rapidly at an ancient event before the Decapodiform radiation. So judging by the apparent Devonian (at least Carboniferous) radiation of Decapodiformes, this has to be an ancient radiation occurring relatively early in the history of cephalopods.

Now, how does this compare to what is known about fossil octopodes?


Pohlsepia mazonensis
Kluessendorf & Doyle, 2000

Most safely described as a coleoid cephalopod from the Pennsylvanian (~300 mya) Mazon Creek fauna of Illinois. Preservation of soft body parts from other cephalopods (and maybe one other specimen) are found in this formation, as is the famous and bizarre Tully Monster (Tullimonstrum gregarium). Despite these spectacular fossils, soft body preservation is still rare even in a formation such as this. The specimen is tiny (max body with 3.5 cm/1.4") with a flattened sub-circular body, two small fins, and small black eyes. The body is sac-like with an ill-defined head, characteristics typical of octopodes. Curiously the specimen does not possess 8 limbs, but has 2 additional arms longer than the rest (modified arms or tentacles). Decapodiformes modify/lose arm pair IV while Vampyromorphans and Octopodes modify/lose arm pair II, but it is never stated which arm pair is modified. This is where we begin to run into trouble. After some speculation that this may be a cuttlefish-like Decapodiform, the authors suggest that it is some sort of octopus, and compared it to cirrates. They classify it as ?Cirroctopoda, a suggestion I don't really buy. This would make cirrates paraphyletic (with incirrate and vampire squid offshoots), twice as old as indicated by genetic evidence, and would mean they re-evolved a shell somewhere along the line. Since the fins of cirrates use the shell as a muscular anchor, I was wondering if the "gut trace/ink sac" may have actually been a shell/gladius of some sort. The authors don't comment on and probably did not take into account the internal structures of "Octopodiformes". So what is Pohlsepia? I think that given the extreme separation of this fossil from any relatives and the apparent closeness to the Octopoda/Decapodiform/Vampyromorpha divergence this cephalopod may not be classifiable in any crown groups. I wouldn't give my opinion too much weight - but I think that more genetic and fossil evidence is certainly needed for this incredibly murky time period.


Proteroctopus ribeti

I tried avoiding the other fossil octopus article (here) but since I can't find the article for this species I guess I'm going to have to consult it. There certainly isn't anything wrong with the article, I just wanted to read things and put them in my own words. This specimen is from the mid-Jurassic (132 mya) of France, a time period near the divergence of cirrates and incirrates according to Strugnell et al 2006. Eyden's excellent article mentions that this specimen has suckers, a sac-like body, 8 equal appendages and fins. Strugnell et al 2006 notes that there was no shell present and they mentioned the possibility that this was a "teuthid" or stem-octopus. Eyden mentions that some authorities consider it a vampyromorph. While this has some superficial cirrate traits, the lack of a shell and cirri once again seems to be a considerable problem. Like Pohlsepia, with all traits considered it really isn't very clear what this specimen is.


Palaeoctopus newboldi

This is a Late Cretaceous (89-71 mya) octopus which bears strong resemblance to modern cirrate species. It has an indistinct head, sac-like body and 8 arms with suckers, fins, internal U-shaped fin supports and an ink sac (the last two from Voight, 1997). Judging from these characters, I would agree with the classification of this as a Cirrate/Cirroctopoda in the family Paleoctopodidae. The time period also strongly hints at this being a cirrate (as opposed to a basal Coleoid), although the ink sac hints at it not being as adapted towards a deep-water environment. While probably fairly basal in Cirrata, this is the least ambiguous fossil by far.

Table of Prominent Characteristics

	Shell/Gladius	MA	DH	Ink sac	Fins
Pohlsepia		x	-		x
Proteroctopus		-	x		x
Palaeoctopus	x	-	-	x	x
Cirrata	x	-	-	-	x
Incirrata	-	-	-	x	-
Vampyromorpha	x	x	-	-	x

MA = Modifed arms
DH = Distinct head

Argonauts

Before I leave, I should mention argonauts, usually listed separately from octopodes but certainly derived from them. While most species in the superfamily don't, in a few species the females secrete an egg case from their arms which bear an uncanny resemblance to ammonite shells. Obinautilus is the earliest known fossil argonaut from the Oligocene of at least 29 mya. Strugnell et al 2006 estimate that argonauts originated some time in the Jurassic, not much after the cirrates and incirrates diverged. This indicates that they actually did live at the same time as ammonites and may give hints as to the nature of their bizarre "shell". While not direct preservation of octopodes; Izumonauta, Kapal, Mizuhobaris, and Obinautilus certainly are the majority of fossil octopus species. Darnit, one of these days I'm going to have to do another tangent post (and one for Vampyromorphans too).



So there have it, a post on fossil forms of some of the least likely animals to be fossilized. This certainly is a rather confusing subject and unfortunately there is no definite word to be had on it. This goes to show that while books and webpages may write up some definite phylogenetic relationships, behind the scene there seems to be an immense amount of argument. With the perfection of genetic testing and the finding of additional specimens, the murky origins of octopodes may yet be discerned. Or not.


-Cameron


References:

Kluessendorf, Joanne & Doyle, Peter. 2000. Pohlsepia mazonensis, an early "octopus" from the Carboniferous of Illinois, USA. Palaeontology 43 (5) 919-926. Available: Here

Strugnell, Jan et al. 2006. Divergence time estimates for major cephalopod groups: evidence from multiple genes. Cladistics 22, 89-96. Available: Here

Voight, Janet R. 1997. Cladistic Analysis of the Octopods based on anatomical characters. J. Moll. Stud. 63, 311-325. Available: Here

Yokobori, Shin-ichi et al. 2007. Mitochondrial genome structure and evolution in the living fossil vampire squid, Vampyroteuthis infernalis, and extant cephalopods. Molecular Phylogenetics and Evolution 44 (2) 898-910. Available: Here