Reconstructing fossil cephalopods: Enchoteuthis (“Tusoteuthis” )

Enchoteuthis by Prehistorica

Enchoteuthis melanae drifts peacefully amongst a shoal of Baculites. Art by Prehistorica, used with permission.

The Enchoteuthinae are a subfamily of large cephalopods from the Cretaceous of North America and Australia. While frequently referred to as “giant squids”, they are not closely related to modern squids. Instead enchoteuthines are stem octopods belonging to the family Muensterellidae and superfamily Muensterelloidea. Enchoteuthines are part of a diverse Jurassic-Cretaceous radiation of octopus relatives and are close to the ancestry of octopuses themselves. Since they are known only from remains of the gladius (internal shell), their life appearance and ecology have gone largely unstudied. As with the previous entry in this series, I will reconstruct them here by examining the fossil evidence.

Tusoteuthis is the best known enchoteuthine in the popular consciousness and is portrayed as being similar to extant giant (Architeuthis) and colossal (Mesonychoteuthis) squids. It’s often depicted in combat with marine reptiles, mirroring artwork of giant squids fighting sperm whales (see collage below). However, this traditional view of Tusoteuthis is mostly incorrect. Based on a relationship with octopuses and preserved soft tissues from other muensterellids, enchoteuthines would have looked very different from squids. Additionally, enchoteuthines have a convoluted taxonomic history and the name Tusoteuthis should probably be replaced by Enchoteuthis.

Tusoteuthis collage

A collage of traditional squid-like depictions of “Tusoteuthis“, featuring artwork by Nobu Tamura10 Tons Studios, and two uncredited artists

A total of four genera and seven species of enchoteuthines have been named: Tusoteuthis longa (Logan, 1898), Niobrarateuthis bonneri (Miller, 1957), Enchoteuthis melanae (Miller & Walker, 1968), Kansasteuthis lindneri (Miller & Walker, 1968), Niobrarateuthis walkeri (Green, 1977), “Muensterellatonii (Wade, 1993), and Tusoteuthis cobbani (Larson, 2010). For a time most of these genera/species were synonymized with Tusoteuthis longa (Nicholls & Isaak, 1987; Stewart & Carpenter, 1990), although Larson (2010) tentatively considered them all valid. Fuchs et al. (2020) have recently revised the taxonomy of enchoteuthines, recognizing two valid genera with four species: Enchoteuthis melanae, E. cobbani, E. tonii, and Niobrarateuthis bonneri. They regard Kansasteuthis lindneri and N. walkeri as junior synonyms of Enchoteuthis, and Tusoteuthis longa as an undiagnostic nomen dubium.

Enchoteuthines mainly inhabited epeiric seas, namely the Western Interior Seaway in North America and the Eromanga Seaway in Australia. E. tonii is the earliest known species from the late Albian Toolebuc Formation of Queensland. E. melanae is known from the late Santonian Niobrara Formation of Kansas and middle-late Campanian Pierre Shale Group of Wyoming, North Dakota, and Manitoba. E. cobbani is known from the Niobrara Formation of Kansas and Pierre Shale Group of Wyoming and South Dakota. N. bonneri is only known from the Niobrara Formation of Kansas (Fuchs et al. 2020). Additional records of Enchoteuthis sp. from the late Campanian Northumberland Formation of British Columbia (Fuchs et al. 2020) and Ignek Formation of Alaska (YPM IP 038058, n.d.) indicate they also inhabited the Paleo-Pacific.

Munsterelloidea phylogeny

The phylogenetic relationships of the Enchoteuthinae and other muensterelloids, based on the analysis of Fuchs et al. (2020) with modifications.

Enchoteuthines had previously been placed in the families Palaeololiginidae (Miller, 1957; Miller & Walker, 1968) and Kelaenidae (Green, 1977; Nicholls & Isaak, 1987; Stewart & Carpenter, 1990). Palaeololiginidae is currently recovered as the sister clade to the Muensterelloidea (Fuchs et al. 2020). Kelaenidae is based on Kelaeno, a preoccupied synonym of Muensterella; both Kelaeno and Kelaenidae have been suppressed by the ICZN (ICZN, 1997) and Muensterella and Muensterellidae have replaced them. Enchoteuthidae was named as a distinct family by Larson (2010). The phylogenetic analysis of Fuchs et al. (2020) recovered Enchoteuthidae within Muensterellidae, rendering Muensterellidae a paraphyletic grade. Those authors overlooked that reducing the rank to a subfamily (Enchoteuthinae) would make Muensterellidae monophyletic, which is done here.

Muensterellids are most closely related to living octopuses, belonging to the octopod stem group. Octopuses are likely descended from patelloctopodids or a patelloctopodid-like ancestor, which places Octopoda firmly within Muensterelloidea (Fuchs & Schweigert, 2018; Fuchs et al. 2020). This affinity has only been recognized recently because of a paradigm shift to classifying groups formerly referred to as fossil “teuthids” (=decabrachians) as octobrachians. The muensterellid with the best preserved soft tissues, Muensterella scutellaris from the Late Jurassic Altmühltal and Painten Formations of Germany, shows many similarities to octopuses. These characteristics include eight arms, arm webbing, sessile suckers, and a fused head and mantle (Fuchs et al. 2003).

Muensterella

Line drawing of Muensterella scutellaris (BSPG MC‐21) showing preserved soft tissues, from Fuchs et al. (2003).

Since no enchoteuthines have preserved soft tissues, Muensterella is the closest taxon to reconstruct them. Both have a similar gladius comprised of an anterior stem (rachis) and spoon-shaped posterior (patella). Thus they likely had comparable mantle tissues, including the cuttlefish-like marginal fins known from Muensterella (Fuchs et al. 2003). Unlike most other cephalopods, the fins of Muensterella did not attach to the gladius but directly to the mantle (Fuchs et al. 2016) and presumably enchoteuthines had the same condition. [see addendum] They also would have had a completely fused head and mantle with no demarcation between them. Other shared features include eight arms with arm webbing and a single row of suckers. The arms were very short in proportion to the head and mantle (Fuchs et al. 2003). While no eyes are known from Muensterella, it can be assumed that they had camera-type eyes like all other coleoids.

Enchoteuthis diagram

Hypothetical anatomy of Enchoteuthis with soft tissues based on Muensterella and octopuses. “TL” is total length and “GL” is gladius length.

The largest enchoteuthine specimen is an almost complete gladius (NDGS 241) referred to E. melanae, which measures 1.87 meters as preserved (Hoganson, 2010; Fuchs et al. 2020). Hoganson (2010) estimated a total length of 28-35 feet (8.5-10.7m) for this individual using the proportions of Architeuthis. Because Architeuthis has elongated tentacles that Enchoteuthis lacks this size is grossly overestimated. For my reconstructions, I gave Enchoteuthis a conservative arm length-to-mantle length ratio of 0.3, slightly longer than the ratio of 0.2-0.28 for Muensterella (Donovan & Fuchs, 2016). I also gave it a head length-to-mantle length ratio of 0.2, so that the arms plus head equals half the length of the mantle.

To restore the gladius I used the patella length-to-gladius length ratio of 0.45 from complete specimens (Fuchs et al. 2020). Since the gladius spans the entirety of the mantle those lengths are equivalent. Using these proportions results in an estimated gladius/mantle length of 1.98 m and total length of 2.96 m for NDGS 241. The E. melanae holotype (FHSM 13049) is much smaller, with a preserved patella length of 22 cm (Fuchs et al. 2020), estimated gladius/mantle length of 49 cm, and total length of 74 cm. Even though this is significantly downsized from previous estimates, Enchoteuthis is still the largest coleoid cephalopod in the fossil record. The maximum gladius/mantle length of ~2 m is only exceeded by Architeuthis and Mesonychoteuthis.

Enchoteuthis skeletal

Skeletal reconstructions of the Enchoteuthis melanae holotype and largest referred specimen.

The evidence for enchoteuthine ecology is limited; exactly what habitats or prey they preferred is unknown. There is however a considerable amount of evidence for predation on enchoteuthines. This includes fish coprolites and stomach contents with gladius fragments and gladii with bite marks possibly from mosasaurs. The most striking example is a specimen of Cimolichthys nepaholica with a gladius lodged in its throat and stomach, likely having choked to death on it (Kauffman, 1990; Stewart & Carpenter, 1990). At least one defense against predators that enchoteuthines would have possessed is inking. Preserved ink sacs have been reported from the holotype of Tusoteuthis (Logan, 1898) and the paratype of E. cobbani (Larson, 2010), and are also present in Muensterella (Fuchs et al. 2003).

IMG_7356

The holotype gladius of Enchoteuthis cobbani (BHI 4138) on display at the Black Hills Institute. Photo taken by me in June 2018.

Once again I collaborated with paleoartist Prehistorica who created the artwork of Enchoteuthis based on my diagrams and the information behind them. The appearance was of course influenced by Muensterella but also by cirrate octopuses, which are the closest living relatives of enchoteuthines. We wanted to avoid the old trope of Enchoteuthis fighting marine reptiles so instead showed it passively floating through a shoal of Baculites. This is likely the most accurate depiction of Enchoteuthis to date since it incorporates the most fossil data. That being said there is still a fair amount of speculation here and hopefully future discoveries will reveal more about these enigmatic giants.

Addendum (8/20/2020)

Enchoteuthis diagram UPDATED

Enchoteuthis skeletal UPDATED

After finishing this post I contacted Dr. Dirk Fuchs, an expert on fossil octobrachians and coauthor of many of the papers I cited. He provided new information that led me to significantly revise my reconstructions of Enchoteuthis. Above are the updated versions of my charts, which should be used as references instead of the older versions.

Contrary to what had been previously published (and stated in this post), the fins of Muensterella attached to the patella of the gladius and not directly to the mantle. The condition likely would have been the same in enchoteuthines, so the fins would be limited to the size of the patella. Since the patella only makes up 45% of the gladius/mantle length, it’s unlikely that enchoteuthines had marginal fins like Muensterella. Instead Dirk suggested that they had triangular fins resembling pelagic squids. He also suggested a narrower, torpedo-shaped mantle, consistent with a more active lifestyle than the earlier benthic muensterellids.

I based the new fins on the Humboldt squid (Dosidicus), which reaches a similar mantle length and possibly has a similar ecology. I reduced the maximum mantle width to be only 1.5 times the maximum patella width. This consequently reduced the width of the head and arm crown. The proportional lengths of each of the body sections remains the same, so the previous size estimates are not affected. Altogether this results in a more squid-like appearance for Enchoteuthis, closer to basal octobrachians like plesioteuthids than to other muensterellids. This coincides with the fast swimming, open water habits of enchoteuthines as envisioned by Dirk.

Addendum (5/29/2021)

I visited the North Dakota Heritage Center and State Museum today and snapped some photos of the largest specimen of Enchoteuthis (NDGS 241). It’s even more impressive in person and really gives you an idea of the sheer size of enchoteuthines.

IMG_1233

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Previous entry: Endoceras

References

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4 thoughts on “Reconstructing fossil cephalopods: Enchoteuthis (“Tusoteuthis” )

  1. Hello mr. Greenfield, I’ve got a little question, would it be possible for the latest reconstruction of enchoteuthis to be uploaded on wikipedia? Permission from the original creator is needed and I’d like to know if you’re willing to give it to me.

    Thank you in advance

    Liked by 1 person

      1. Hey sir, thanks for uploading the picture to wikipedia! Oh and sorry for uploading it directly to the article and not in the plaeoart review page, I didn’t actually know that existed before so that was kind of embarrassing ._.

        Like

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