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 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/

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.