Eocetus, "Eocetus", and Friends

Update (January 28, 2014): "Eocetus" wardii is now Basilotritus wardii. More on my new post, The Third King.


I was shocked that Uhen (2010) remarked that Basilosaurus drazindai and Basiloterus hussaini "probably represent protocetids... akin to Eocetus". This would place the whales outside Pelagiceti and imply that the now-questionable basilosaurids were potentially capable of walking on land, despite being enormous. Unfortunately, other mentions of this revised placement give no further details (Uhen 2008, Uhen et al. 2011) and Uhen (2010) further states the placement is "difficult to determine with certainty" due to scarce materials. I suspect the hypothesis will not be officially discussed until further material is found and/or described... which won't stop me from wildly speculating.

Lumbar vertebrae in right lateral view. From left to right: "Eocetus" wardii (from Uhen 1999), Basiloterus hussaini, and Basilosaurus drazindai - note that the latter-most may be an anterior caudal (from Gingerich et al. 1997). For comparison: Basilosaurus isis vertebrae.

In the description of Basilosaurus drazindai, Gingerich et al. (1997) note a number of "primitive retentions" which resemble the morphology of "generalized archaeocetes": long neural spine and arch; broad, almost-horizontally placed, anterior-projecting metapophyses which project beyond the anterior edge of the vertebral centrum; and paired, posterolateral processes of the neural arch. Aside from the last trait (which I can't confirm without a dorsal view), all of these traits are present in "Eocetus" (Uhen 1999). Additionally, "Eocetus" has elongated transverse processes, unlike the condition of Basilosaurus (Uhen 1999); however, B. drazindai has processes with a 15.5 cm long base (they broke off) relative to the 30 cm centrum (Gingerich et al. 1997), and so probably had a similar, albeit slightly less extreme, condition. The only criterion for placing B. drazindai in the genus Basilosaurus was the size and shape of the centrum (Gingerich et al. 1997), and while they are uncannily similar in shape, everything else seems to be pointing towards a relationship with "Eocetus".

Lumbar vertebrae in anterior view. Ditto order.

As for awkward middle-child Basiloterus, it appears to have a centrum which is slightly more elongated than that of "Eocetus", however the neural arch and maybe the neural spine appear to be narrower. The metapophyses are upwardly-angled (Gingerich et al. 1997), less broad, less anterior-projecting, but still appear to extend past the centrum. The posterolateral processes are absent (Gingerich et al. 1997). The base of the transverse process is 9.3 cm long relative to a 19.5-20 cm centra (Gingerich et al. 1997), proportionally similar to Basilosaurus drazindai. The placement of Basiloterus is thus not clear, and perhaps it was a basilosaurid or an even more derived protocetid.

Maiacetus inuus, a basal "protocetid" (Uhen 2011). From Wikipedia Commons.

Protocetidae is a blatantly paraphyletic "family" of extinct cetaceans from Eocene coastal marine deposits with hip and femur morphology indicating amphibious capabilities (most of the time) and no evidence of flukes (Uhen 2010). Uhen (1999) appears to think that "Eocetus" wardii had weight-bearing hips, however Uhen (2010) refers to them as "moderately reduced" and regarded the species as possibly non-amphibious. This is perhaps not surprising since Eocetus, "Eocetus", and an unnamed Pisco Formation species are the sister group of Pelagiceti (Uhen et al. 2011). This could make them closer relatives of Dorudon than Maiacetus, and raises the question of how many typical protocetid traits they actually exhibited. Perhaps they were entirely aquatic tail-based swimmers which just happened to have fairly large vestigial legs.

Dorudon atrox. From Wikipedia Commons.

The scare quotes around "Eocetus" hint at a taxonomic misadventure. "E." wardii was assigned to its genus by Uhen (1999) based on comparisons of its skull and vertebrae to Eocetus schweinfurthi; the problem is, the holotype of E. schweinfurthi is an isolated skull and it is not possible to determine whether the vertebrae referred to it actually represent the species (Geisler et al. 2005). There is overlapping skull material (Uhen 1999), but Geisler et al. (2005) apparently regarded it as too incomplete to warrant unambiguous placement in the genus. Somehow, "Eocetus" and Eocetus formed a clade in phylogenetic analyses (Geisler et al. 2005, Uhen et al. 2011), making it probable that future discoveries will confirm their close relationship.

"Eocetus" wardii is clearly related to unnamed Pisco Formation material which exhibits the same distinctive traits (moderate centrum elongation, elongated neural arches and spines and transverse processes, strange pock-marked texture) with the only difference being that the unnamed material is 35% smaller (Uhen et al. 2011). The Egyptian vertebrae dubiously assigned to Eocetus schweinfurthi (figured in Uhen 1999) also seem quite similar (including the pock-marks), and if it is also a member of this clade, it would indicate a sizable trans-oceanic range. This in turn could be taken as evidence of the whales being largely pelagic... of course this is quite speculative.

There of course remains much to be known about these cetaceans, and perhaps future discoveries will be enlightening as to how similar they were to the pelagic cetaceans, as well as the origins of Pelagiceti. I really hope it turns out that a Basilosaurus-sized animal could walk on land.


References:

Geisler, J. H., Sanders, A. E., and Luo, Z-X. (2005). A New Protocetid Whale (Cetacea: Archaeoceti) from the Late Middle Eocene of South Carolina. American Museum Novitates 3480, 1-65. Available.

Gingerich, P. D., Arif, M., Bhatti, M. A., Anwar, M., & Sanders, W. J. (1997). Basilosaurus drazindai and Basiloterus hussaini, new Archaeoceti (Mammalia, Cetacea) from the middle Eocene Drazinda Formation, with a revised interpretation of ages of whale-bearing strata in the Kirthar Group of the Sulaiman Range, Punjab (Pakistan). Contributions from the Museum of Paleontology, University of Michigan 30 (2), 55-81. Available.

Uhen, M. D., Pyenson, N. D., Devries, T. J., Urbina, M., and Renne, P. R. (2011). New middle Eocene whales from the Pisco Basin of Peru. Journal of Paleontology 85(5), 955-969. doi: http://dx.doi.org/10.1666/10-162.1

Uhen, M. D. (2010). The Origin(s) of Whales. Annual Review of Earth and Planetary Sciences 38, 189–221. Available.

Uhen, M. D. (2008). Basilosaurids. In: Perrin, W. F., Würsig, B., and Thewissen, J. G. M. (eds.) Encyclopedia of Marine Mammals, Second Edition. Elsevier: Burlington, Massachusetts. Available.

Uhen, M. D. (1999). New Species of Protocetid Archaeocete Whale, Eocetus wardii (Mammalia: Cetacea) from the Middle Eocene of North Carolina. Journal of Paleontology 73(3), 512-528.

Weems, R. E., Edwards, L. E., Osborne, J. E., and Alford, A. A. (2011). An occurrence of the protocetid whale "Eocetus" wardii in the Middle Eocene formation of Virginia. Journal of Paleontology 85(2), 271-278. Available.

Billfish Bills - What Are They Good For?

In the prior article, I discussed long-beaked "dolphins" (Eurhinodelphidae) and noted that I couldn't find hypotheses on the function of their uneven jaws in the literature... aside from a weird proposal involving Skimmers. The Theatrical Tanystropheus mentioned a couple ("digging for small, sand-dwelling organisms or as a bat with which to stun fish") which are plausible, but I don't know where they are from or what lines of reasoning are behind them. There are extant species with a superficially similar condition - billfishes - and it could be relevant to review what they do with their bills.

Atlantic White Marlin (Tetrapturus albidus) from Wikipedia Commons.

Swordfish (Xiphiidae) and Marlins/Sailfishes/Spearfishes (Istiophoridae) are living sister taxa¹ in the clade Xiphioidea; while traditionally included in Scombroidei, billfishes are presently regarded as phylogenetically distinct (Orrell et al. 2006) and possibly close relatives of jacks and... flatfishes (Little et al. 2010). Fish phylogenetics is scary business, and I suspect billfish relations will undergo further revisions as the monstrosity known as "Perciformes" is reasoned into pieces. Anyways, while xiphiids² and istiophorids look superficially similar, they actually have rather distinctive morphology. Swordfish have a bill which is flat in cross-section, toothless, blunt-tipped, and with central chambers (compared to rounded, denticulated, pointed, and chamber-less for istiophorids), a weak mandible much shorter than the rostrum, no scales, and no pelvic fins (Collette et al. 2006; Fierstine 2006; Fierstine and Voight 1996 citing Nakamura 1983). Strangely, most extinct billfishes have jaws of equal length, and if the proposed (Istiophoridae + Hemingwayidae) and (Xiphias + Xiphiorhynchus) clades (Fierstine 2006) are correct (see note 1), this would mean the unequal jaws of extant billfishes evolved twice. 

¹ A detailed cladistic analysis with the fossil members of the group has yet to be undertaken (Fierstine 2006).
² As for what the deal with them and ziphiids is, I have no idea.

Swordfish (Xiphias gladius) from Wikipedia Commons.

One infamous use of the billfish bill is impaling unexpected objects. One Blue Marlin was found with rostrum fragments from two other, different billfish species (Fierstine 1997). Other unfortunates include large fish, whales, bales of rubber, boats, ships, deep-diving vessels, people, and turtles (Frazier et al. 1994 - citing various). The billfish-on-billfish impaling has been interpreted as defense against predators (Fierstine 1997) and in the case of the turtles, it was hypothesized that the billfish accidentally impaled them when aiming for fish aggregated nearby (Frazier et al. 1994). Istiophorids can survive with a foreshortened rostrum (Fierstine 2006) so apparently these accidents are survivable. But this raises another question - do they need an elongated rostrum at all?

One study of 227 Blue Marlins (Makaira nigricans) stomach contents found that 38% of prey items showed evidence of damage from the bill, 11% of which were speared and 81% of which were slashed, and the rest of which were in multiple pieces (Shimose et al. 2007). Bizarrely, another study with 226 Blue Marlins found no evidence of prey being struck or speared (Vaske et al. 2011). Vaske et al. (2011) offered no explanation for this anomaly, and I can't see an obvious one either. Both populations (from Japan and Brazil, respectively) even primarily preyed on Skipjack Tuna (Katsuwonus pelamis), which were normally killed with the bill in the former population. I'm stumped.

Fierstine (2006) hypothesized that unequal jaw length in billfishes may have evolved to avoid suffocation when impaling large objects (predator or prey) and to avoid damage to the mandible. I don't buy the mandibular reasoning since extant billfishes get by just fine with them naturally foreshortened. The available evidence suggests impaling is a rather rare event and thus unlikely to be the main factor in the evolution of the characteristic billfish bill. An alternate hypothesis could be that the mandible was shortened so the rostrum could be "weaponized" (sword-like flattening in xiphiids and denticles in istiophorids³) to slash at prey. However, the population which apparently doesn't use bills to feed and healthy individuals with damaged rostra are problematic for both of these hypotheses. Perhaps future studies will show that the bill is generally important for feeding in the group and that the counterexamples are just freaks, but either way, it seems premature to make any conclusions about why billfish have their striking morphology.


³ The ichthyosaur Eurhinosaurus has teeth on the upper jaw which could be a similar instance of "weaponization". 

I really have no idea how eurhinodelphids fit into this framework since Fierstine's hypothetical suffocation would not be an issue (if they could impale at all) and the rostrum does not seem particularly dangerous (no teeth, denticles, or flattening). I wonder if this morphology evolved for different reasons, or if it evolved for reasons that have yet to be hypothesized.

References:

Collette, B. B., McDowell, J. R., and Graves, J. E. (2006). Phylogeny of Recent Billfishes. Bulletin of Marine Science 79(3), 455-468. Available.

Fierstine, H. L. (2006). Fossil history of Billfishes (Xiphioidea). Bulletin of Marine Science 79(3), 433-453. Available.

Fierstine, H. L. (1997). An Atlantic Blue Marlin (Makaira nigricans), impaled by two species of billfishes (Teleostei: Istiophoridae). Bulletin of Marine Science 61(2), 495-499. Available.

Fierstine, H. L., and Voight, N. L. (1996). Use of Rostral Characters for Identifying Adult Billfishes (Teleostei: Perciformes: Istiophoridae and Xiphiidae). Copeia 1996(1), 148-161. Available.

Frazier, J. G., Fierstine, H. L., Beavers, S. C., Achaval, F., Suganuma, H., Pitman, R. L., Yamaguchi, Y., and Prigioni, C. M. (1994). Impalement of marine turtles (Reptilia, Chelonia: Cheloniidae and Dermochelyidae) by billfishes (Osteichthyes, Perciformes: Istiophoridae and Xiphiidae). Fisheries Science 39(1), 85-96. Available.

Little, A. G., Lougheed, S. C., and Moyes, C. D. (2010). Evolutionary affinity of billfishes (Xiphiidae and Istiophoridae) and flatfishes (Plueronectiformes): Independent and trans-subordinal origins of endothermy in teleost fishes. Molecular Phylogenetics and Evolution 56(3), 897-904. doi:10.1016/j.ympev.2010.04.022

Nakamura, I. (1983). Systematics of billfishes (Xip­hiidae and Istiophoridae). Publications of the Seto Marine Biological Laboratory 28, 255-396.

Orrell, T. M., Collette B. B., and Johnson, G. J. (2006). Molecular data supports separate scombroid and xiphioid clades. Bulletin of Marine Science 79(3), 505-519. Available.

Shimose, T., Yokawa, K., Saito, H., and Tachihara, K. (2007). Evidence for use of the bill by blue marlin, Makaira nigricans, during feeding. Ichthyological Research 54(4), 420-422. DOI: 10.1007/s10228-007-0419-x

Vaske, T., Travassos, P. E., Pinheiro, P. B., Hazin, F. H. V., Tolotti, M. T., and Barbosa, T. M. (2011). Diet of the Blue Marlin (Makaira nigricans, Lacepède 1802) (Perciformes: Istiophoridae) of the southwestern equatorial Atlantic Ocean. Brazilian Journal of Aquatic Science and Technology 15(1), 65-70. Available.

Picture of the Indiscriminate Interval #000008 - Eurhinodelphis longirostris

Eurhinodelphis longirostris at the American Museum of Natural History.

The most striking trait of Eurhinodelphidae is a toothless extension of the rostrum beyond the mandible (Lambert 2005), superficially similar to the bills of Billfish and Swordfish. Oddly, this morphology was speculative for a period of time (Kellogg 1925) although it has apparently been confirmed in several species as of Lambert (2005). Unfortunately, information on eurhinodelphids is scant and/or difficult to access and, among numerous other basics of their biology, I really don't know what the function of the extended rostrum would be. The only suggestion I could find is from one professor Abel who speculated that the cetaceans "swam on the surface of the sea, where they captured food - probably fishes - in much the same manner as does the skimmer (Rhynchops) [sic] among birds" (Anonymous 1909). Somehow, I find this even less plausible than azhdarchids-as-skimmers. On a curious note, there is a cetacean with the reverse of eurhinodelphid morphology (mandible extending past rostrum) unofficially known as the... skimmer porpoise.

Phylogenetically, eurhinodelphids have bounced around from being considered stem-ziphiids, the sister group to Delphinida, and the sister group to Squalodontidae + Squalodelphidae (Geisler et al. 2011 - citing various); within Geisler et al. (2011), they were placed outside crown-Odontoceti¹ in an unconstrained analysis and as the sister group of platanistoids in a constrained analysis. The authors regarded the latter position as more probable and placed eurhinodelphids within the new group Synrhina, which includes most odontocetes except for Sperm Whales and assorted extinct taxa. Whatever their placement, eurhinodelphids are certainly close relatives of living toothed whales, despite that whole extinct thing.

¹ It actually states they "did not fall inside crown Cetacea", but this is a typo. Otherwise, they'd be Miocene Archaeocetes. 

Eurhinodelphis longirostris seems to have an unusually long neck for a cetacean. The cervical vertebrae are not fused (Kellogg 1925), however this is a surprisingly common trait shared with river dolphins, monodontids, rorquals, and gray whales (Tinker 1988). The neck of E. longirostris appears to be proportionally longer than those of the baleen whales and Narwhal and is probably comparable to those of the Beluga and Dorudon. River dolphin skeletons are hard to find, but it seems likely they have similarly proportioned necks. It seems that Eurhinodelphis wasn't a total freak, well, except for the snout.

The Theatrical Tanystropheus covered Eurhinodelphis as well, and it doesn't even overlap that much!

References:

Anonymous. (1909). Notes. Nature 2088 (82), 16. Available.

Geisler, J. H., McGowen, M. R., Yang, G., Gatesy, J. (2011). A supermatrix analysis of genomic, morphological, and paleontological data from crown Cetacea. BMC Evolutionary Biology 11 (112). Available.

Kellogg, R. (1925). On the occurrence of fossil porpoises of the genus Eurhinodelphis in North America. Proceedings of the U. S. National Museum 66(26), 1-40. Available.

Lambert, O. (2005). Les dauphins longirostres et les baleines à bec du Néogène de la région d’Anvers: systématique, phylogénie, paléo-écologie et paléo-biogéographie. Doctoral Thesis. Partially Available.

Tinker, S. W. (1988). Whales of the World. E. J. Brill Publishing Company: New York. Partially Available.

The Giant Turtle Therizinosaurus

Therizinosaurus, you look... unwell. Reconstruction by K. K. Fierova, from Maleyev (1954).

I am quite fond of old, weird reconstructions, and the initial classification of Therizinosaurus cheloniformis as a "turtle-like reptile"¹ resulted in the magnificent specimen above. So how could the veritable Jabberwocky we're all familiar with be misinterpreted to such a colossal degree?

¹ This odd phrasing is mirrored in the scientific name ("saurus" = lizard, "cheloniformis" = turtle-like). Malayev (1954) linked Therizinosaurus with members of Protostegidae and thus (probably) didn't intend to suggest another clade of reptiles which converged on turtles. Bizarrely, Rozhdestvensky (1974) claimed Malayev/Maleev classified Therizinosaurus as a "turtle-like pangolin"! Rozhdestvensky (1977) does not reiterate that statement, and further notes that another worker (Sukhanov) classified Therizinosaurus as a turtle; I unfortunately cannot find that source ("The subclass Testudinata" in Osnovy Paleontologii).

Therizinosaurus in its non-turtle form. From Wikipedia Commons.

Malayev (1954) described Therizinosaurus from scrappy remains: a metacarpal fragment, 3 manual unguals, and rib fragments (Zanno 2010). One of the ribs was an estimated 1.5 meters long when complete and was used to calculate a maximum body width of 3.25 meters (10'8") and body length of 4.5 m (14'9") (Malayev 1954); this is of course quite a bit larger than even the largest known Stupendemys geographicus. The rib was noted to lack costal elements, which is curious since turtle skeletons generally look like this:

 

Common Snapping Turtle (Chelydra serpentina) skeleton. Note the plastron is missing. From Wikipedia Commons.

Surprisingly, this is not necessarily a critical flaw, as (all?) turtles have distinct ribs during development before the carapace is fully formed (Wyneken 2001, fig. 90; Sánchez-Villagra 2009, figs. 3, 4). Malayev (1954) did not mention this nor the obvious possibility of a multi-ton hatchling. Instead, the "form of the ribs" was compared to Archelon and Protostega:

Archelon skeleton. From Wikipedia Commons.

The similarity is very general and Malayev (1954) does not list any specific shared characteristics. Due to the lack of costal elements, Malayev (1954) speculated that Therizinosaurus was in a distinct clade and in life had "barely developed or almost completely absent bony armor". It is incredibly strange that the Leatherback Seaturtle (Dermochelys coriacea) was not mentioned, as it entirely lacks costal elements and instead has thousands of dermal ossicles (Cebra-Thomas et al. 2005). The skeleton (sans ossicles) looks like an attempt by turtles to become "normal" tetrapods again.. until you notice the pectoral girdle within the ribcage:

From Wikipedia Commons

The rib material used to describe Therizinosaurus cheloniformis is apparently not from a therizinosaur at all, but a sauropodomorph (Zanno 2010 citing Rozhdestvensky 1970). Isn't it a major problem that the holotype is a chimera? Whatever the case, Therizinosaurus cheloniformis has been re-described a few more times and other rib material has been referred to the species (Zanno 2010). However, all of the diagnostic traits (and most of the material) are from the forelimbs (Zanno 2010).

From Wikipedia Commons.

Malayev (1954) interpreted the metacarpal and phalanges to be "powerful swimming organs" and suggested the huge claws were used for "cutting aquatic vegetation or for another functions, constrained by movement and acquiring food". The longest phalanyx was 60-65 cm long, not including the keratin covering (Malayev 1954), which suggests that the claws were ridiculously huge in life, even for a turtle-like reptile with a 4.5 meter body. I have observed turtles using their claws to climb and tear apart food (maybe what Malayev had in mind...), but clearly claws this disproportionate were doing something special. Something like this:

I like to think that Therizinosaurus, despite not being turtle-shaped anymore, waved its giant claws seductively in the faces of prospective mates.

References:

Cebra-Thomas, J., Tan, F., Sistla, S., Estes, E., Bender, G., Kim, C., Riccio, P., and Gilbert S. F. (2005). How the Turtle Forms its Shell: A Paracrine Hypothesis of Carapace Formation. Journal of Experimental Zoology 304B, 558-569. Available.

Maleyev, E. A. (1954). A new turtle-like reptile from Mongolia. Priroda 3, 106-108. Available.

Rozhdestvensky, A. K. (1977). The study of Dinosaurs in Asia. Journal of the Palaeontological Society of India 20, 102-119. Available.

Rozhdestvensky, A. K. (1974). History of the dinosaur fauna of Asia and other continents and questions concerning paleogeography. Transactions of the Joint Soviet–Mongolia Paleontological Expedition 1, 107–131. Available.

Rozhdestvensky, A. K. (1970). On the gigantic claws of mysterious Mesozoic reptiles. Palaeontological Journal 1, 131-141.

Sánchez-Villagra, M. R., Müller, H., Sheil, C. A., Scheyer, T. M., Nagashima, H., and Kuratani, S. (2009).  Skeletal Development in the Chinese Soft-Shelled Turtle Pelodiscus sinensis (Testudines: Trionychidae). Journal of Morphology 270, 1381-1399. Available.

Wyneken, J. (2001). The Anatomy of Sea Turtles. U.S. Dept Commerce NOAA Tech Mem NMFS SEFSC-470. Available.

Zanno, L. E. (2010). A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4), 503-543. Draft Available.

Picture of the Indiscriminate Interval #000004b - Megalocnus rodens

The unusual skull from the last article does not belong to some huge rodent, glyptodont, diprotodontid, or Thylacoleo - it is from the extinct Cuban sloth Megalocnus rodens. This particular specimen was part of a panoply of sloths at the American Museum of Natural History:

Megalocnus is in the foreground, with Megalonyx facing towards it, Scelidotherium facing away, and Lestodon rearing up in the background. 

Megalocnus is probably a member of the clade Megalonychidae, which can be distinguished (in part) by canine- or incisor-like first upper and lower teeth (Gaudin 2004). It may come as a surprise that megalonychids are still with us, as Choloepus (Two-Toed Sloths) are living representatives, and grouped closely (albeit not strongly) with Megalocnus and other Antillean sloths in at least one phylogeny (Gaudin 2004). Yes, this means that Two- and Three-Toed Sloths are distant relatives, with the former being far more closely related to large-bodied 'ground sloths'. I'd recommend this article from the old Tet Zoo for a sloth primer - they're far more diverse and interesting than they're often given credit for, although I suppose that's true of just about any group.

Note the radically different skull of Scelidotherium - it is a mylodontid unlike the other two megalonychids. 'Ground Sloths' are far from a homogeneous group. 

The most striking aspect of Megalocnus rodens is the vaguely rodent-like skull, and it was in fact initially described as a giant rodent from an incomplete mandible (de Paula Couto 1967). While the chisel-like first teeth look particularly rodent-y, the overall dentition is similar to Megalonyx (de Paula Couto 1967). Compared with the other sloths on display, M. rodens displays an elongated neck, heavy body, short tail, and plantigrade hands and feet (de Paula Couto 1967). M. rodens may have been the second-smallest 'ground sloth' on display at the AMNH (Hapalops is slightly out of view), however it was still a large animal which may have weighed about 150 kg (330 lbs) in life (van der Geer et al. 2010). Not bad for a terrestrial Cuban mammal


Megalocnus rodens is most notable for when it went extinct - the latest fossil dates from 4200 years before present (MacPhee et al. 2007). These sloths were still trundling about when the Great Pyramid of Giza was hundreds of years old. All mainland sloths, except of course Bradypus and Choloepus, were extinct by about 10,000 years ago; in contrast, the Antilles had 13 species of sloths in the late Quaternary (Steadman et al. 2005). Most remarkable of all, M. rodens appears to have co-existed with humans on Cuba for over a millennium (MacPhee et al. 2007). There does not appear to be any clear evidence for how the sloths went extinct, although a 'long-fuse' model of human predation would appear to be the most likely. If only they held on for a few more millennia.


References:

Gaudin, T. J. (2004). Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 255–305. Available.

van der Geer, A., Lyras, G., de Vos, J., and Dermitzakis, M. (2010). Evolution of Island Mammals: Adaptation and Extinction of Placental Mammals on Islands. John Wiley and Sons. Partially Available.

MacPhee, R. D. E., Iturralde-Vinent, M. A., and Vazquez, O. J. (2007). Prehistoric Sloth Extinctions in Cuba: Implications of a New “Last” Appearance Date. Caribbean Journal of Science 43(1), 94-98. Available.

de Paula Couto, C. (1967). Pleistocene edentates of the West Indies. American Museum Novitates 2304: 1–55.

Steadman, D. W., Martin, P. S., MacPhee, R. D. E., Jull, A. J. T., McDonald, H. G., Woods, C. A., Iturralde-Vinent, M., and Hodgins, G. W. L. (2005). Asynchronous extinction of late Quaternary sloths on continents and islands. PNAS 102(33), 11763-11768. Available.

Picture of the Indiscriminate Interval #000004a - Not A Rodent

I'll try something new here - can anyone out there identify this skull? As the title hints, this is not a rodent...

Dorudon Was Not A Monster

The external shape of cetaceans is very much defined by blubber and other soft tissues†. In a previous article, I argued that if a cetacean were to be naïvely reconstructed by what the skeleton (or rotten carcass) 'suggests', it could end up looking more like a reptilian horror than, say, a fat, charismatic monodontid we all know and love. It's below the monstrous footnote.

† But don't just take my word for it - the Woods Hole Oceanographic Institution has excellent CT scans showing the interplay between skeleton and external shape. Aside from the caudal peduncle and (occasionally) the tip of the snout, toothed whales are cocooned in blubber. The heads of the False Killer Whale and Narwhal provide sufficiently extreme examples. Contrarily, the Minke Whale has a skull which roughly correlates with the external shape... in a dorsal view; shrink-wrapping the skull at a different angle shows that soft tissue still plays a considerable role in determining overall shape. Dorudon probably looked a great deal more like toothed than baleen whales, however more basal 'baleen' whales (stem-Mysticeti) lacking the hyper-derived skull are potentially very informative. Thanks to Markus Bühler for the link.

This intentionally incompetent Beluga bears an unexpected similarity to some reconstructions of Dorudon... notwithstanding the blowhole and fur, of course. This is partially due to the offending illustrations depicting Dorudon atrox with almost no blubber, which makes as much sense as reconstructing a fossil bird without feathers. The other factor is that skeletally, Dorudon is broadly similar to modern toothed whales, despite being basal to the toothed/baleen whale split:

Delphinapterus leucas skeleton from Wikipedia Commons.

Dorudon atrox2, taken and modified from Wikipedia Commons. Note that the arm is held at an angle and was not, in fact, really really short.

White-sided dolphin, taken and modified from Wikipedia Commons.

Above Dorudon is a Beluga, which is similar in size and also has non-fused neck vertebrae (Uhen 2004). What I find particularly striking is the similar depth of the ribcages and the comparatively short spinous processes of Dorudon. Beaked whales also have non-fused neck vertebrae and Ziphius in particular has been compared in size to Dorudon (Uhen 2004) - judging by this photo of Ziphius, the species also has a deep ribcage and relatively enormous spinous processes†. Below Dorudon is a Lagenorhynchus dolphin (either L. acutus or L. obliquidens) which has numerous highly derived characteristics (Buchholtz and Schur 2004), and thus makes for strong contrast. The ribcage seems relatively streamlined and shallower and the spinous processes of the vertebrae are extremely developed. There's still a broad similarity between Dorudon and that highly derived taxon, which makes portrayals of Dorudon as some anguilliform quasi-reptilian horror appear increasingly bizarre.

† Aside from which, the lumbar/anterior caudal region gives off a strong Basilosaurus vibe due to the elongated vertebral bodies and lack of interlocking processes. Hmm.


So why have I been talking so much about Dorudon atrox as opposed to D. serratus, Chrysocetus, Ancalecetus, or some other 'dorudontine'? Dorudon atrox is the best-known 'archaeocete', and at present "[r]elationships among the Dorudontinae are not well-defined, either by morphology or stratigraphy... [i]n addition, the relationships among the Dorudontinae cannot be determined until the taxa within the Dorudontinae are clearly delimited" (Uhen 2004). Additionally, it's become apparent that I've been citing Uhen (2004) quite a bit so far, and that source just so happens to be a massive, book-length treatise on D. atrox which is freely available. The publication is outstanding... aside from the frontispiece, which was credited as being made in cooperation with the author, but seems to contradict several points made within the publication and looks more like a zombie than a fairly close relative of extant cetaceans.

I think I can do Dorudon a bit more justice... next post.

Well, I've actually already done it for the banner - but the explanation will be in the following post! Which won't be in a month, I swear.

References:

Buchholtz, E. A., and Schur, S. A. (2004). Vertebral osteology in Delphinidae (Cetacea). Zoological Journal of the Linnean Society 140, 383–401. Available.

Uhen, M. D. (2004). Form, Function, and Anatomy of Dorudon atrox (Mammalia, Cetacea): An Archaeocete from the Middle to Late Eocene of Egypt. University of Michigan Papers on Paleontology 34, 1-222. Available.

An Interlude Of Poorly-Reconstructed Bears

There's too much on my plate right now to allow for a proper followup on the Bad-Ass Mega-Bear Arctotherium angustidens - now one of my most visited posts, wow! - so I figured to do some recycling in the interim. I have a lot of unfinished posts, one of which on deceptive soft tissue so happens to have a section on bears. So, I excised the opening paragraphs and expanded on the bear section a bit to serve as an introduction to the topic in general and tie in with a cryptic statement in the prior post. Don't worry, it gets to bears soon.

For all of the awesome, mind-blowing fossil reconstructions out there, some are incredibly lazy. Particularly noxious offenders include mimeographing inaccurate morphology from prior works (e.g. pronated theropod hands, elephantine sauropod hands), portraying extinct animals as identical to distant modern relatives (e.g. Teratorns-as-Condors, Kayentachelys-as-Snapping-Turtle, Prosalirus-as-Bullfrog...), and of course portraying live animals as shrink-wrapped skeletons:

*Cough*

SV-POW!'s kickass articles on sauropod life reconstructions (Part 1, Part 2) served as a major catalyst for my interest in this topic, particularly the second part which explains how portraying 'pods with freakish shrink-wrapped skull-heads has become common, if not expected in palaeo-art. I'd like to suggest that Shrink Wrapped Dinosaur Syndrome (SWDS) is but a facet of a larger phenomenon in which an animal's appearance as determined by skeletal structure, soft tissue, and external cover (hair, feathers) is improperly depicted and/or misunderstood*. Just look at that poor Dimetrodon up top (from Cleland 1916), yeesh. This phenomenon is not limited to fossils, as it can afflict carcasses still in the process of rotting or even live animals.

*Snazzy acronym pending

Since I'm not exactly a skilled re-constructionator, I figured I could put my not-skills to use and concentrate on reconstructing animals incompetently, in the hope of deconstructing some reconstruction myths. Or something.

...

Let's say a clever yet ignorant individual finds a decomposed corpse out in the woods, perhaps reduced to a skeleton with a few globs of flesh and hair still attached. It doesn't remind them of any animals they've ever seem, so they take a stab at reconstructing the presumed cryptid:

The person posts the reconstruction online, along with some blurry photographs of the remains taken at surreal angles typical of German Expressionism. Commenters suggest seemingly random and inexplicably specific taxa for the animal's identity, including the weird mustelid Ekorus, Bigfoot, the weird peccary Mylohyus, non-mammalian synapsid Titanophoneus, and a werewolf. Eventually, a near-consensus is reached suggesting that the carcass is of a late-surviving juvenile "short"-face bear Arctodus. Of course, the animal in question is actually this:

From Wikipedia Commons.

The contrast between the popular conception of bears being stumpy-legged fatties and their skeletons is truly remarkable. My "reconstruction" is cribbed from a skeleton figured in The Royal Natural History: Mammals (page 2) which unfortunately does not have a label, but appears to be an American Black Bear (Ursus americanus) as opposed to some fictional generalized bear. If the "reconstruction" looks familiar, that's because a mangy U. americanus was once confused for Bigfoot, and no, the legs of the creature are most certainly not "too long" to be from a bear. And since when is Bigfoot a quadruped?

Arctodus is typically portrayed as a bear on stilts, in sharp contrast to other species, but is truly not that different. It is almost always shown with rather short hair, which does occur in the Sun Bear, but is highly unlikely to occur out of the tropics; see serchio25's Deviant Art for an intriguing portrayal of Arctodus with more probable hair. It also doesn't help that when Arctodus is compared with other bears or people, it is shown at maximum size. It is now known that Arctodus simus has legs that are not elongated in comparison with other bears, and that the appearance of long legs is probably an optical illusion caused by a rather short back (Figueirido et al. 2010). Arctodus does seem to be rather gracile in build, at least in comparison with Arctotherium angustidens. Grrrraaaahhhh of Shaggy God (citing Nelson and Madsen 1983) informed me of the A. simus specimen UVP 015 with a femur 72.3 (28.5") in length, 6.4 cm (2.5") in mid-shaft width and (as estimated by Figueirido et al. 2010) a weight of 957 kg (2110 lbs); the largest Arctotherium angustidens (see the prior post) has a humerus length* of 62 cm (24.5"), a mid-shaft width of 9 cm (3.5"), and an amazing weight of 1588-1749 kg (3500-3855 lbs). It seems strange that two closely related and similarly sized bears would differ so much in build, especially when bears in general seem conservative in their body plan variation, as demonstrated below.

* Bear humeri seem to be slightly shorter than femurs. UVP 015 is still certainly the tallest bear ever.

And now, bears, bears, bears!

Arctodus simus from Figueirido et al. 2010. Note the outline, which includes hair.

Ursus americanus (Black bear) (?) modified from Wikipedia Commons. It seems to be somewhat shorter-bodied and leggier than Arctodus - is it a juvenile?

Ursus spelaeus ("cave bear") from Wikipedia Commons. Note the long body relative to A. simus and the similar leg length.

Helarctos malayanus (Sun bear) modified from Wikipedia Commons. Note the very short fur.

So yeah, Arctodus simus is certainly not long-legged or feline-like. Did the originators of the claim even bother to compare it with other bears?

References: 

Cleland, H. F. (1916). Geology Part II. Historical. American Book Company: New York, Cincinnati, Chicago. Available.

Figueirido, B. Perez-Claros, J. A., Torregrosa, V., Martin-Serra, A., Palmqvist, P. (2010). Demythologizing Arctodus simus, the 'short-faced' long-legged and predaceous bear that never was. Journal of Vertebrate Paleontology 30(1), 262 - 275. Available.

Lydekker, R. (1894). The Royal Natural History: Mammals. Frederick Wayne and Co: London. Available.

Nelson, M. E. and Madsen, J. H. (1983). A Giant Short-Faced Bear (Arctodus simus) from the Pleistocene of Northern Utah. Transactions of the Kansas Academy of Science 86(1), 1-9.

Arctotherium angustidens: Biggest Bear Ever?

I have a bit of an obsession with animal size superlatives, and megabears* are among my favorites - that's right, I have interests beyond testudines. Anyways, in this blog's even more poorly-written past, I discussed purported giant hypercarnivores wherein I argued that the One-Ton(ne)-Hyperpredatory-Arctodus meme is unsubstantiated Godzillafication which somehow managed to infect even some peer-reviewed literature. Brian Switek wrote an article at the old Laelaps covering newer research which further demolished the mythology of the Giant Short-Faced Bear: it didn't have a short face (it did have a deep snout), or particularly long legs (somewhat of an optical illusion caused by a short back), and was probably a generalist omnivore like extant bears (presumably with some differences in niche, of course). Just as it seemed that speculations about One-Ton(ne)-Hyperpredatory-Bears would be a thing of the past, this happened:

* Definition pending.

Figure 2(1) from Soibelzon and Schubert (2011). The bear's height is ~ 3.3 meters (10' 10") and note how the legs are realistically flexed.

Arctotherium is composed of 5 South American species - of which A. angustidens is the earliest, largest, and apparently most predatory - and is the sister clade of Arctodus; the two are in turn part of the clade Tremarctinae which further includes Tremarctos (spectacled bear and kin) and Plionarctos (Soibelzon and Schubert 2011). The Arctotherium angustidens specimen of concern is not a new discovery, as it was found prior to 1935 during construction of a hospital in La Plata, Argentina (Soibelzon and Schubert 2011). It is presently composed of radii, ulnae, and humeri from both forelimbs; metacarpals, phalanges, and a scapula fragment were also recovered but unfortunately lost (Soibelzon and Schubert 2011). The dimensions of the bones* are incredible, the humerus has a length of 62 cm (2' 0.4") and the mid-shaft humerus width is 9 cm (3.5"); comparable maximum measurements of other giants bears are: Arctodus simus - 59.4 cm/6.4 cm; Ursus spelaeus - 44.8 cm/5.6 cm; and Ursus maritimus - 38.5 cm/4.65 cm (Soibelzon and Schubert 2011). For those who would prefer a more graphical comparison:

* The limbs had somewhat different measurements - the left was shorter and wider and the right vice versa. See below for why.

Humerus length in cm:

The number of specimens is in parenthesis. This does not include both limbs from the Arctotherium specimen in question, subsequently the average was re-calculated from Table 3.

Humerus mid-shaft width in cm:

Table 5 figures kept the specimens in question separate (unlike the prior example) so the range and average have been re-calculated. Even without the newly measured specimen, the average for Arctotherium was substantial (5.88 cm).

Using humerus greatest length, humerus mid shaft circumference, humerus greatest distance of distal epiphysis, and radius proximal epiphysis greatest diameter, the estimated weight for the giant Arctotherium angustidens specimen ranged from 983-2042 kg (2,167-4,502 lbs), with the value likely around the mean and median of 1588 and 1749 kg (3501-3856 lbs), respectively (Soibelzon and Schubert 2011). The other known specimens were given the same treatment (when possible), and a couple of them appeared to mass around a tonne (Soibelzon and Schubert 2011). This would seem to suggest that the giant Arctotherium angustidens specimen was not an outsized freak, and could represent a "normal" maximum size for the species. Before too many conclusions can be made, some more discussion of the specimen is in order.

Left humerus in caudal view. The scale bar is 10 cm (~ 4 inches) and the arrow points to a pathology.  Taken from Figure 3(1), Soibelzon and Schubert (2011). Compare with the humerus of Arctodus: here.

The most striking aspect of this specimen are the osteogenic changes to the deltoid crests of both humeri - more apparent in the left humerus pictured above, see arrow - and the distal third of the left radius shaft, which suggest a deep injury followed by infection and then new vascular growth over a long period of time (Soibelzon and Schubert 2011). Judging by the high degree of epiphyseal fusion, the specimen managed to become an old adult (Soibelzon and Schubert 2011). Humeral mid-shaft measurements gave on average larger estimated masses (Soibelzon and Schubert 2011 - Table 3), which makes me wonder if the measurements were artificially inflated by the injury and subsequent pathological growth. However, the limited data on Table 3 shows similar proportions with a somewhat smaller specimen:

	HMSC	HGL	HMSC/HGL
MLP 35-IX-26-5	26.5	61.5	43%
MLP 35-IX-26-6	26.2	62	42%
MACN 5132	22	54	41%
MLP 82-X-22-2	16	49.5	32%

Measurements in cm: HMSC = Humerus mid shaft circumference; HGL = Humerus greatest length. The first two rows are from the specimen in question.

Curiously, specimens of Arctotherium angustidens appear to differ considerably in limb proportions, for instance, two specimens have the same humeral circumference (22 cm) but the greatest diameter of the distal humeral epiphysis differs considerably (20.5 vs. 18 cm), one of which is larger than the giant specimen's maximum measurements (18.5 cm) (Soibelzon and Schubert 2011)... this is certainly confusing, and the value of compiling median and mean figures is readily apparent. While the mass of the giant Arctotherium angustidens cannot be precisely pinned down, the available evidence suggests it exceeded all other bears in size.

... or does it?

Incredibly, one mass regression of Indarctos atticus exceeded 3 metric tonnes, although predictably it was found to be highly improbable (Finarelli and Flynn 2006) and, along with fellow Mio-Pliocene bear Agriotherium, they are not believed to have reached the same size as Arctodus simus or Arctotherium angustidens (Soibelzon and Schubert 2011). Polar bears (U. maritimus) can get extremely large*, with one specimen shot in Alaska in 1960 purportedly standing 3.39 m (11' 1.5") and weighing 1002 kg (2210 lbs); the whereabouts are apparently unknown and the skull was never submitted for measurement (Wood 1981). Assuming the record is genuine, I'm wondering if the height included unnaturally straitened legs or was in fact the length lying down and outstretched, which would certainly be easier to take. Considering the largest Arctotherium angustidens humeral length is about 160% as large as the largest polar bear measurement included in Soibelzon and Schubert (2011), it would take one freakish polar bear to get that tall, and it would probably weigh a lot more than a tonne. Polar bears reached their largest sizes in the late Pleistocene (Soibelzon and Schubert 2011) and Ursus maritimus "tyrannus" apparently had an ulna 44 cm in length (see Markus Bühler's Bestiarium, comment #5), which is of course smaller than that of the specimen in question's (57 cm), but still surprisingly large for a single specimen. Information on these giant polar bears is unfortunately quite hard to come by, but I think it's safe to assume it didn't exceed Arctotherium angustidens in size, at least regularly.

* DeMaster and Stirling (1981) give maximum figures of: mass 800 kg (1764 lbs), nose-tail length 2.5 m (8' 2"), and shoulder height 1.6 m (5'3").

Exactly how the average sizes of the giant bears compare is difficult to determine at the present time - particularly when gender isn't obvious. However, as weights of a tonne or more appear to have been reached by Arctotherium angustidens regularly, the average must have considerably exceeded that of other giant bears, which have only been demonstrated to exceed a tonne in one instance. The authors' assertion that Arctotherium angustidens was the biggest bear ever is well-supported, until something bigger turns up.

---

This post has run long enough, I'll write a followup on the proposed ecology of Arctotherium angustidens shortly.


References:

DeMaster, D. P., and Stirling, I. (1981). Ursus maritimus. Mammalian Species 145, 1-7. Available.

Finarelli, J. A., and Flynn, J. J. (2006). Ancestral State Reconstruction of Body Size in the Caniformia (Carnivora, Mammalia): The Effects of Incorporating Data from the Fossil Record. Systematic Biology 55(2), 301-313. doi: 10.1080/10635150500541698. Available.

Soibelzon, L. H., and Schubert, B. W. (2011). The Largest Known Bear, Arctotherium angustidens, from the Early Pleistocene Pampean Region of Argentina: With a Discussion of Size and Diet Trends in Bears. Journal of Paleontology 85(1), 69-75. doi: 10.1666/10-037.1

Wood, G. L. (1981). The Guinness Book of Animal Records. Guinness Superlatives: Middlesex, Great Britain.