The best known fossil pinniped, part 3: life habits, paleoecology, and biogeography of Allodesmus

 

An undescribed skeleton of Allodesmus from the Miocene of Japan, on display at the National Museum of Nature and Science in Tokyo.

The abundance of Allodesmus in the Neogene marine record in concert with its completeness made investigation of its paleoecology and life habits inevitable. However, most of what follows is scoured from a few publications, and ample scope for further studies of functional morphology, ontogeny, and sexual dimorphism exist for future researchers.

 

This doesn't really belong anywhere in here, but when I found this strange photo I knew I couldn't leave it out. Ignoring the bizarre pose and composition of the slab and the unecessarily included models, this picture does actually give you an idea of how large Allodesmus was.

Ontogeny and Body Size

A few studies have touched upon growth in Allodesmus, and have mostly discussed issues of age determination rather than growth-related changes in morphology. Mitchell (1966) briefly investigated epiphyseal fusion in Allodesmus, and found that (unsurprisingly), in the forelimb epiphyses fused at the elbow before other parts of the forelimb, and that in the hindlimb, fusion begins at the hip and ankle before progressing to the knee joint (for casual readers, epiphyses are the ends of long bones that begin as separate osteological units and later fuse to the shaft – known as the diaphysis – the radius and ulna have a proximal epiphysis, a distal epiphysis, and the diaphysis; the diaphysis generally composes most of the bone).

            A classic and widely used method for age determination in pinnipeds and other marine mammals is counting periodic growth marks in teeth in sectioned teeth under a microscope. Additionally, in pinnipeds (and presumably other carnivores) preserve a series of annular ridges/grooves in the root, corresponding to periodic growth marks in the cross section of the tooth. Mitchell (1966) was one of the earliest researchers to apply this method to fossil pinnipeds, and sectioned teeth of Allodesmus from the Sharktooth Hill Bonebed. Although the canines of the Allodesmus kelloggi holotype did not yield good results owing to “varying replacement phenomena” (unclear if this refers to an in vivo process or diagenesis), canines of similar size (and presumably root closure) were sectioned and exhibited a minimum of 13 growth marks, suggesting a minimum age of 13 years for Allodesmus kelloggi.

            Allodesmus kelloggi was estimated to be 2.6 meters in length by Mitchell (1966); this is the most complete skeleton of a desmatophocid known, so other Allodesmus (=Allodesminae of Barnes and Hirota, 1995) may be scaled from this species. It should be pointed out here that Allodesmus kelloggi is the smallest known species of Allodesmus. Mitchell (1966) pointed out that other specimens from Shartooth Hill would be much larger (up to 3.35 meters), surpassing even the Northern sea lion Eumetopias jubatus (3+ meters) in size. Taking measurements of other skulls of Allodesmus, small body sizes for Allodesmus sadoensis (2.1 meters) and Allodesmus packardi (2.2 meters) are probable. A much larger body size is indicated for LACM 9723 – the largest known Allodesmus kernensis/gracilis specimen – this individual, scaled up from Allodesmus kelloggi, would have been 3.8 meters in length. Lastly, the positively enormous adult rostrum of Allodesmus sinanoensis (=Allodesmus megallos of Barnes and Hirota 1995) would have been a whopping 4.8 meters in length! To put this in context, this would be an animal the size of the largest male Northern Elephant Seal (Mirounga angustirostris – 4.3-4.9 meters), and surpassed only by the Southern Elephant Seal (Mirounga leonina – 4.2-6 meters).

            Despite having a relatively large sample size from the Sharktooth Hill Bonebed, little investigation of sexual dimorphism has been attempted – and remains a lucrative research topic for future researchers.

Mitchell's (1966) elephant seal-like reconstruction of Allodesmus. Although some have criticized the addition of a proboscis (Adam and Berta, 2001) I don't feel like it's such a bad call myself. However, more time looking at the structure of the prenarial shelf in this pinniped would permit me to make a more informed interpretation.

Life Restoration

This is by far the most speculative part of this post. Mitchell (1966) hypothesized that due to the large size of Allodesmus, and relatively short forelimbs (although that really remains to be established), Allodesmus likely had thick layers of blubber, and further speculated that Allodesmus lacked fur and was possibly hairless like elephant seals. Another observation first made by Mitchell (1966) with the first skull of Allodesmus was that it exhibited a peculiar prenarial shelf, somewhat similar to elephant seals. Based on the size of this prenarial shelf, and the position of muscle attachment scars, Mitchell (1966) speculated that Allodesmus had a short proboscis like extant elephant seals. However, Berta and Adam (2001) suggested that Allodesmus may not have a proboscis, citing as yet unpublished research. The question of whether or not Allodesmus had a proboscis has barely been answered, and future studies could certainly go further.

 

The teeth of Allodesmus, from Mitchell (1966). J-M are classic examples of "phallic" Allodesmus cheek teeth.

Feeding Ecology

The skull of Allodesmus is quite different from many other pinnipeds. It has one of the proportionally longest palates of any known pinniped, fossil or modern. All of the teeth of Allodesmus are single-rooted with bulbous, simple cheek teeth bearing a single cusp; isolated Allodesmus teeth are frequently found by fossil collectors at Sharktooth Hill and appear “phallic” to many amateurs (check out the photo; you can do the math). The canines are relatively small in Allodesmus in comparison to similarly sized otariids and odobenids (with the exception of the adult “snout” of Allodesmus sinanoensis; =Allodesmus megallos of Barnes and Hirota, 1995). The mandible is relatively gracile but bears a well developed flange for the digastric insertion, as in modern elephant seals (Mirounga). Allodesmus curiously lacks well developed nuchal and sagittal crests as in many fossil and modern otariids and many odobenids, and also has an unusually small coronoid process of the mandible – suggesting reduced temporalis musculature (the temporalis is the primary jaw closing muscle; those of you who are dog owners can feel it by petting the top of your dog’s head while it is chewing; cat owners should not try this). Lastly, the eye sockets of Allodesmus are proportionally enormous; they are so large, that Debey and Pyenson (2011) suggested that Allodesmus was a deep diver, like modern elephant seals.

The lengthening of the palate is probably related to suction feeding (Adam and Berta, 2002), and Allodesmus was reconstructed as a pierce/raptorial feeder by Adam and Berta (2002). The simplification of the postcanine teeth and reduction in size of the posterior postcanine teeth suggests reduced utility of the dentition, potentially even more so than other pinnipeds. The underdeveloped cranial crests and small coronoid process suggests a decreased importance of jaw closing musculature relative to many other pinnipeds. All of this, in concert with the enormous eye size and potential deep diving ecology, in my opinion, suggests a possible suction feeding elephant seal-like habitus. However, it is important to note that craniodental morphology correlates poorly with diet in pinnipeds.

 

Allodesmus kernensis (=Allodesmus gracilis of Hirota and Barnes, 1995) at the San Diego Natural History Museum reconstructed in a very sea lion like pose. Check out the length of the forelimb - at first glance, it screams "sea lion" in terms of function.

Locomotion

Osteological characteristics of limb bones and the hypothesized monophyletic clade formed by desmatophocids and phocids (Phocoidea) led Berta and Adam (2001) to interpret Allodesmus as a hindlimb-dominated swimmer. However, a subsequent study by former Gingerich student Ryan Bebej (2009) based on proportions of limb bones identified that Allodesmus was most similar to modern fur seals and sea lions, which are forelimb-dominated swimmers. In fact, fur seals and sea lions swim in a somewhat similar fashion to penguins (although have a forelimb that bends more at the elbow). Interestingly, Allodesmus was found to be slightly less aquatically adapted than extant pinnipeds by Bebej (2009), which is borne out by the fact that Allodesmus first appeared within the first 10 million years of the evolutionary history of pinnipeds. Significantly, Allodesmus has an otariid/odobenid like ankle, indicating that this pinniped could terrestrially "walk" as opposed to wriggle like modern earless seals (Phocidae). Modern true seals cannot rotate their ankle forwards, meaning their hindflippers are always pointing posteriorly and cannot be used for locomotion, and so they must wriggle around awkwardly on beaches like a kid trapped in a sleeping bag.

Biogeography

Lastly, Allodesmus is now known from the middle and late Miocene of California, Baja California, Washington, and Japan. This indicates that this genus was widely distributed across much of the Northern Pacific, including most of the west coast of North America. Allodesmus had a circum-North Pacific distribution, paralleled with many other Mio-Pliocene marine mammals (Desmostylus, Paleoparadoxia, Albireo, Kentriodon, Thalassoleon, Callorhinus, Hydrodamalis, Dusisiren, and many others), and many modern cetaceans and pinnipeds. Allodesmus courseni (=Atopotarus of some authors) and Allodesmus kernensis are known from both California and Japan, suggesting that some species of Allodesmus may have enjoyed a wide geographic range. Curiously, desmatophocids never escaped the north Pacific. Why? My hypothesis would be that Allodesmus was cold-water adapted, and unable to cross the warm equatorial waters that serve as a formidable thermal barrier to north-south dispersal even today. Similarly, Allodesmus never invaded the Atlantic, suggesting it was unable to disperse through the Central American Seaway, although many pinnipeds and other marine mammals were able to disperse from the western North Atlantic to the eastern South Pacific during the Miocene.

Next up: part 4, the controversial phylogenetic position of Allodesmus, and future directions for research.

P.J. Adam and A. Berta. 2002. Evolution of prey capture strategies and diet in the Pinnipedimorpha (Mammalia, Carnivora). Oryctos 4:83-107.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

 

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360.

 

R.M. Bebej. 2009. Swimming mode inferred from skeletal proportions in the fossil pinnipeds Enaliarctos and Allodesmus (Mammalia, Carnivora). Journal of Mammalian Evolution 16:77-97.

A. Berta and P.J. Adam. 2001. Evolutionary history of pinnipeds. In Mazin J.M., Buffrenil V. de (eds), Secondary Adaptation of Tetrapods to Life in Water. Verlag Dr. Friedrich Pfeil, Munich, pp. 235-260.

 

L.B. Debey, and N.D. Pyenson. 2013.Osteological correlates and phylogenetic analysis of deep diving in living and extinct pinnipeds: what good are big eyes? Marine Mammal Science 29:48-83

 

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

 

The best known fossil pinniped, part 2: How many species (...and genera) are there of Allodesmus, anyway?

Last week I summarized the history of research on Allodesmus (and Atopotarus). How many species of Allodesmus exist? And how many genera of desmatophocids are there? On one extreme, one could take the view that there are only two genera – Allodesmus and Desmatophoca – and that Atopotarus, Megagomphos, and Brachyallodesmus are all synonyms of Allodesmus. On the other hand, a more diverse view of the Desmatophocidae would include as many as 10 species in the aforementioned 5 genera. We’ll start with genera – and then look at the species level.

How many genera of desmatophocids are there?

I won’t bother with Allodesmus and Desmatophoca, since these are both clearly “real” and the oldest available names for generic concepts.

Atopotarus – Atopotarus is largely diagnosed by the retention of primitive characteristics in comparison to Allodesmus spp. For example, Atopotarus lacks the prenarial shelf of more derived Allodesmus such as Allodesmus kernensis/kelloggi/gracilis, has a less inflated braincase, and retains double-rooted postcanine teeth (premolars and molars). In contrast, the teeth of Allodesmus are single rooted. All these features were listed by Barnes and Hirota (1995) as distinguishing A. courseni from Allodesmus at the generic level. Mitchell (1966) was the first to suggest that Atopotarus courseni was possibly a species of Allodesmus – prior to his description of Allodesmus kelloggi, insufficient cranial and postcranial material was known to really evaluate the generic validity of Atopotarus. This skepticism was echoed by Barnes (1972), Kohno (1996) and Deméré and Berta (2002) – although its generic distinctiveness was endorsed by Barnes and Hirota (1995). I’ve always been on the fence about Atopotarus – it’s barely distinguishable from Allodesmus as it is slightly more plesiomorphic and its morphology – with the exception of the possibly lost second lower molar – could reflect the ancestral morphology of the entire genus. Amongst extant pinnipeds, including phocids – closely related clusters of species (e.g. Zalophus, Arctocephalus, Monachus), with the exception of the Phoca-Pusa-Halichoerus complex – tooth rooting doesn’t vary this much between species, potentially suggesting that Atopotarus might be real. More fossil material of Atopotarus is necessary to further evaluate it, since the holotype is a somewhat flattened articulated specimen exposed in relief in a large slab.

The holotype specimen of Atopotarus courseni, from Downs (1956).

Brachyallodesmus: this genus was erected by Barnes and Hirota (1995) for Allodesmus packardi, the skull from Portola Valley in southern San Mateo County. Features used by these authors to distinguish it from other Allodesmus include canines with an oval cross section (rather than round), an inflated braincase lacking strong nuchal crests, enormous orbits with an extremely narrow intertemporal region, and some primitively retained characteristics such as bilobed premolar roots, a furrow on the side of the braincase marking the position of the pseudosylvian sulcus on the brain, and a less flattened tympanic bulla. This species is arguably much less primitive than Atopotarus courseni, and while I’m on the fence about the generic distinction of Atopotarus, the claim that Allodesmus packardi is generically distinct is spurious in my opinion, and in my preference for taxonomic conservatism (aka lumping), I’ve always held the consideration that this is a species of Allodesmus.

Megagomphos: This genus of desmatophocid was also erected by Barnes and Hirota (1995) for a fragmentary rostrum previously known as Allodesmus sinanoensis (originally erroneously placed in Eumetopias). This specimen is the same size as the largest specimens of Allodesmus from California. Characteristics used by Barnes and Hirota (1995) to elevate it to a separate genus include the lack of a prenarial shelf (like Atopotarus) and the presence of larger canines than other Allodesmus. Kohno (1996), however, identified several features of this specimen suggesting that it was immature, such as unworn teeth that have large pulp cavities and are not completely erupted. In contrast, Barnes and Hirota (1995) thought that this specimen was an adult because of the shape of the tooth roots and purported fusion of the premaxilla-maxilla suture, but didn’t discuss the ontogenetic stage of this specimen any further. In contrast, Kohno (1996) interpreted the specimen to have a large prenarial shelf, eliminating one purported feature excluding it from Allodesmus; similarly, it exhibits single rooted postcanine teeth and no features of the dentition preclude it from being Allodesmus. Furthermore, one Allodesmus synapomorphy – the prenarial shelf – unequivocally links this specimen with Allodesmus to the exclusion of all other pinnipeds. Although Barnes and Hirota (1995) considered this specimen to lack a shelf, it is present but since the specimen is bilaterally compressed and crushed, which has made the shelf appear less apparent than in life. While this specimen has a few minor differences with other described species of Allodesmus such as procumbent, large canines – no features suggest that establishment of Megagomphos was necessary.

In conclusion, evidence supporting the generic distinction of Megagomphos and Brachyallodesmus is limited to non-existent – but Atopotarus may be “real”, although more cranial material is necessary to evaluate Atopotarus.

How many species of Allodesmus?

Allodesmus from Japan: To date, four species of Allodesmus have been described from Japan. These include the aforementioned Allodesmus sinanoensis, the well-preserved Allodesmus sadoensis, and the more fragmentary Allodesmus naorai (the “Mito seal”) and Allodesmus megallos. Allodesmus sadoensis is known from a nearly complete skull and partial mandibles, and is readily distinguished from all other Allodesmus by having anteriorly crowded and procumbent (forward pointing) postcanine teeth, more vertically oriented mandibular symphysis, and lower postcanine teeth without gaps between them. Allodesmus naorai is similar to Allodesmus packardi, and differs only in a few minor features such as having a slightly wider interorbital region and supraorbital processes positioned further posterior – potentially diagnostic features. The fourth species, Allodesmus megallos, was also named by Barnes and Hirota (1995) and diagnosed based on its enormous size, procumbent tusk-like canines and proportionally larger incisors. However, Kohno (1996) independently referred this specimen to Allodesmus sinanoensis, based upon the shared large size, large procumbent canines, and enlarged incisors, and considered this specimen to be an adult – it is substantially larger than the holotype of A. sinanoensis, now recognized to be a juvenile. Furthermore, Kohno (1996) pointed out that both this specimen and the juvenile A. sinanoensis type specimen were from the same rock unit. This specimen, by the way, represents one of the most gigantic of all pinnipeds – it has an estimated skull length of 55-59 centimeters, just a hair smaller than the giant walrus Pontolis (60 cm), and even larger than the double tusked walrus Gomphotaria (40 cm). I think Kohno (1996) makes a reasonable case that this specimen is an adult of Allodesmus sinanoensis, and therefore that Allodesmus megallos is a junior synonym. In conclusion, three species of Allodesmus appear to be known from Japan.

A size comparison with casts of the partial gigantic rostrum of Allodesmus sinanoensis (=Allodesmus megallos) and the type specimen of Allodesmus kelloggi.

Allodesmus from Sharktooth Hill, California: Five species of Allodesmus are known from the middle Miocene of California, and three of them have all been named from the Round Mountain Silt: Allodesmus kernensis, Allodesmus kelloggi, and Allodesmus gracilis. As stated in the previous post, Allodesmus kernensis was described from a partial mandible with an erect canine, a deep mandibular symphysis, and a somewhat double-rooted lower molar. Mitchell (1966) originally drew attention to the observation that the mandibles of Allodesmus kelloggi and other mandibles from the Sharktooth Hill Bonebed consistently differed from Kellogg’s type specimen in having a shallower mandibular symphysis, having a more erect canine, and having a single rooted lower molar. Mitchell (1966) also pointed out that the locality data for the Allodesmus kernensis holotype actually pointed to two different, mutually exclusive localities, and suggested that the locality data indicated that the Allodesmus kernensis holotype was collected somewhat below the stratigraphic level of the Sharktooth Hill Bonebed, lower down within the Round Mountain Silt. Because of these perceived differences, Mitchell restricted A. kernensis to the type specimen, named his new skeleton A. kelloggi, and referred all known Allodesmus material from the bonebed to his new species.

 

The holotype skull of Allodesmus kelloggi. Check out the size of that orbit!

            Many of these claims were criticized by Barnes (1970, 1972). He pointed out that in the context of variation of modern Zalophus (California Sea Lion), the features identified by Mitchell as separating Allodesmus kernensis from the rest of the bonebed sample are within the range of variation expected for a pinniped species, with the exception of shape of the mandibular symphysis – which varies less within extant Zalophus than it does within the bonebed sample of Allodesmus. Regardless, Barnes (1970) pointed out that all of the morphologic features used by Mitchell (1966) to separate Allodesmus kernensis actually fell within the range of variation of Allodesmus mandibles from within the bonebed itself. Barnes (1970, 1972) then synonymized A. kelloggi with A. kernensis, and referred all known material from the bonebed to A. kernensis. Barnes further pointed out “no conclusive arguments that the holotype of A. kernensis was collected from some formation other than the Round Mountain Silt”. Although this does not really negate Mitchell’s suggestion that the holotype came from an older horizon, Barnes correctly points out that there is uncertainty regarding the A. kernensis type locality – which in my mind means that Mitchell’s hypothesis is speculative. In the context of known Allodesmus variation and the fact that the A. kernensis holotype falls within the range of variation reported for mandibles from the bonebed – I think the idea that the A. kernensis type is more primitive than the bonebed sample falls on its face, and that the hypothesis that A. kernensis was really collected from a lower, older horizon need not be invoked. After all, the type specimen was (thought to be) collected in 1911 by R.C. Stoner, according to the specimen label, or by Charles Morrice (according to Kellogg, 1922), in 1909-1912; locality data were not always accurate in those days. Given the two sets of contradictory data regarding the provenance of the type specimen, any argument being made about the locality of this specimen should be considered to be speculative at best. I speculate that, given how abundant vertebrate fossils are within the bonebed, and how rare they are outside the bonebed, that it is more likely that the specimen was in fact collected from the bonebed and that the locality data is inexact. This seems more reasonable to me, but I note that it is not falsifiable – and that Mitchell’s (1966) arguments are not falsifiable either (although perhaps less parsimonious than my suggestion).

 

Fifty years of taxonomic disagreement contained in a single photograph. How many species of Allodesmus are represented here? One? Two? or Three? From top to bottom, holotype mandible of Allodesmus kelloggi, cast of holotype of Allodesmus kernensis, and cast of referred mandible of Allodesmus gracilis.

Despite the rather sober arguments made earlier, Barnes and Hirota (1995) indicated that the wider variation within the “Allodesminae” resulted in the recognition that the seemingly minor differences between Allodesmus kernensis and the bonebed sample were in fact meaningful. In the absence of quantitative study (as Barnes, 1970, had done) they resurrected Allodesmus kelloggi – a name which they restricted to Mitchell’s type specimen – and went so far as to establish a third species, Allodesmus gracilis, for the remainder of material from the bonebed. Barnes and Hirota (1995) echoed many of Mitchell’s (1966) arguments and casually dismissed Barnes (1970, 1972) earlier, and in my opinion well-reasoned observations. They further pointed out that the holotype mandibles of Allodesmus kelloggi have a strange, widened flange of bone on the anterior part of the coronoid process, in addition to having a single-rooted lower molar, apparently unique amongst specimens from Sharktooth Hill. However, it is well known that modern pinnipeds have tooth roots that vary quite a bit – the short version is that arctoids primitively have triple or double-rooted premolars and molars, and that in the transition to aquatic life, many pinnipeds have lost their carnassial teeth in favor of simplified teeth for catching fish, roughly similar to what happened with dolphins. Dental simplification, in concert with crowding the teeth in the front of the jaw, has resulted in double rooted teeth of archaic pinnipeds fusing together, generally starting from the front of the jaw. In my 2011 paper on fossil Callorhinus, I noted that there is a fair amount of variation in the tooth roots of extant Callorhinus ursinus (Northern Fur Seal). In the context of extant pinniped dental variation (which is considerably more than terrestrial carnivores, probably because pinnipeds do not chew and thus do not require precise occlusion), this observation on Allodesmus kelloggi does not preclude it from being a member of Allodesmus kernensis.

 

The holotype skull of Allodesmus gracilis.

Deméré and Berta (2002), although not focused on Allodesmus taxonomy, noted that the occurrence of three species of Allodesmus within a narrow stratigraphic interval in the Round Mountain Silt is a bit hard to swallow, and I agree. I can understand the rationale behind restricting names to seemingly oddball specimens like the holotypes of Allodesmus kelloggi and Allodesmus kernensis – these are decisions done in spirit of taxonomic stability. However, any argument that these three perceived species are distinctive enough to be recognized as separate taxonomic entities needs to be done quantitatively – which has been done exactly once - by Barnes (1970). There is a huge discrepancy between the rather taxonomically conservative conclusions of Barnes (1970) and the rather optimistic splitting of Allodesmus into several genera.

 

The holotype mandible of Allodesmus gracilis - or a referred specimen of Allodesmus kernensis?

So, how many species and genera are there? I tend to be on the taxonomic lumping side of things, as modern pinnipeds show quite a bit of variation – and keeping this variation in mind, I think a bit of skepticism is in order regarding new taxonomic names for the densely sampled and well published record of pinnipeds from the eastern North Pacific. I think the following list best summarizes my opinions on which genera and species are real:

Atopotarus? Allodesmus? courseni

Allodesmus packardi (syn: Brachyallodesmus)

Allodesmus kernensis (syn: A. gracilis, A. kelloggi)

Allodesmus sadoensis

Allodesmus sinanoensis (syn: Megagomphos sinanoensis, Allodesmus megallos)

Allodesmus naorai

Next up: we still have at least two more parts to this, including the paleoecology of Allodesmus and the phylogenetic position of the family Desmatophocidae.

References

L. G. Barnes. 1970. A re-evaluation of mandibles of Allodesmus (Otariidae, Carnivora) from the Round Mountain Silt, Kern County, California. PaleoBios 10:1-24.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360.

Demere, T. A., and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon 1906 (Mammalia: Carnivora), from the Astoria Formation of Oregon; pp. 113–147 in R. J. Emry (ed.), Cenozoic
Mammals of Land and Sea: Tributes to the Career of Clayton E. Ray. Smithsonian Contributions to Paleobiology 93.

T. Downs. 1956. A new pinniped from the Miocene of southern California: With remarks on the Otariidae. Journal of Paleontology 30(1):115-131.

R. Kellogg. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications in Geological Sciences 13(4):23-132.

N. Kohno. 1996. Miocene pinniped Allodesmus (Mammalia: Carnivora); with special reference to the "Mito seal" from Ibaraki Prefecture, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 181:388-404.

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

The best known fossil pinniped, part 1: a review of research and taxonomy of the Miocene pinniped Allodesmus

 

 

What to call this animal? Allodesmus kernensis, kelloggi, or gracilis? This very topic remains one of the major bones of contention in marine mammal paleontology. Skeletal reconstruction (by yours truly, 2009) of a mounted skeleton at the San Diego Natural History Museum, and beautiful life reconstruction based on my skeletal illustration by Roman Yevseyev.

Four fossil pinnipeds were discovered from California and Oregon during the early 20^th century: Pontolis magnus, from the Empire Formation of Oregon, described by Frederick True in 1905, Desmatophoca oregonensis, from the Astoria Formation of Oregon, described by Thomas Condon in 1906, Pliopedia pacifica, from the Paso Robles Formation of Oregon, described by Remington Kellogg in 1921, and Allodesmus kernensis, from the Round Mountain Silt, named by Remington Kellogg in 1922. Desmatophoca and Pontolis were originally known from partial skulls, but neither specimen was well preserved or well-prepared, and hailed from localities with vertebrate fossils embedded largely within hard concretions – it would not be until the late 1980’s that more research on fossil pinnipeds from these localities would continue again. In short, neither specimen seriously influenced the early understanding of pinniped evolution. Pliopedia was only known from a partial forelimb, and it wasn’t until the late 1970’s that it was identified as an odobenine walrus. At the time of its discovery, Allodesmus was only known from a partial, not very well-preserved mandible. In 1931, Kellogg referred several mandibular and skull fragments and postcrania to Allodesmus.

 The fossil that started it all. The holotype mandible of Allodesmus kernensis.

            Elsewhere worldwide, few fossil pinnipeds had been discovered; the early seal Leptophoca had been named, in addition to a bunch of fragmentary fossil true seals (Phocidae) with problematic taxonomic history from the North Sea named by Van Beneden in the late nineteenth century. As a result, none of these fossils influenced the understanding of pinniped evolution much, either. And while Allodesmus at first was less completely known at the time of discovery, it would soon dominate discussions of pinniped phylogeny for decades. A problem facing these early workers in North America was that they were Otariidae-centric – many of these early fossils were assumed, a priori, to represent ancestors of sea lions, rather than featuring in walrus or true seal evolution – or representing completely extinct groups of pinnipeds.

            In the 1950’s, LACM paleontologist Theodore Downs reported a series of discoveries of new Allodesmus material. In 1953, he reported a nearly complete mandible from Sharktooth Hill, and then in 1955, he reported some associated postcrania from the Monterey Formation in Orange County. And then, in 1956, he reported an Allodesmus-like skeleton including a nearly complete skeleton, lacking parts of the hindlimbs. He named it Atopotarus courseni, and its distinction as a truly separate genus from Allodesmus has been controversial.

            A few years later, Earl Packard (1962) reported on a partial skull in a concretion collected from unnamed middle Miocene rocks of Portola Valley in southernmost San Mateo County, right near where I grew up – he tentatively referred this specimen to Atopotarus courseni.

 One of the first complete skulls of Allodesmus: the holotype specimen of Allodesmus/Brachyallodesmus packardi, from unnamed middle Miocene rocks of Portola Valley, San Mateo County, California.

 Life restoration of Allodesmus kelloggi from Mitchell (1966).

            In 1966, Ed Mitchell published a monograph on a newly discovered skeleton (actually collected in 1960) from Sharktooth Hill. This skeleton was nearly complete, missing only a few bones from the hindflipper. A baculum unequivocally indicates it was a male. This specimen represented the first good skull referable to Allodesmus (not including Atopotarus), and demonstrated how the postcranial skeleton was very convergent with extant otariids – but the skull was not. The skull of Allodesmus is about as different from an otariid as you can get – an elongate, narrow rostrum with a prenarial shelf, similar to elephant seals, an elongate palate, enormous orbits, a vertically expanded zygomatic arch, absent supraorbital shelves (a distinctive feature unique to fur seals and sea lions), a shallowly sloping mandibular symphysis, and a retained lower second molar (this tooth position has been lost in modern fur seals and sea lions). Many of these skull features occur in true seals – and aside from simplified teeth and a primitively otariid-like basicranium, few features are evocative of otariids. Mitchell admitted that these differences precluded Allodesmus from having an ancestral role in the evolution of the Otariidae. Regardless, Mitchell concluded that the holotype jaw of Allodesmus kernensis was collected from somewhat below the Sharktooth Hill Bonebed, but within the Round Mountain Silt – and also noted that Allodesmus specimens from the bonebed consistently had a shallower mandibular symphysis, lower incisors that were positioned differently, a less vertical canine, a single rooted lower first molar, and a slightly more robust mandible. Because of this, Mitchell restricted Allodesmus kernensis to the type specimen, named the skeleton from the bonebed as the holotype of Allodesmus kelloggi, and referred all material from the bonebed to this new species.

The modern mount of the holotype skeleton of Allodesmus kelloggi, as it can be seen today hanging in the hall of mammals at the Los Angeles County Museum. Unfortunately much of the actual skeleton is hanging there and totally inaccessible for study; cardinal elements, such as the skull, mandibles, scapula, humerus, femur, and baculum, are mounted as casts so that they may be studied.

The next two publications in the saga were published by Larry Barnes in 1970 and 1972. The first study was an analysis of mandibles, including the types of Allodesmus kernensis and Allodesmus kelloggi. Barnes (1970) concluded that the differences between these were minimal, and that they easily fell within the range of variation expressed by modern pinnipeds. Barnes (1972) described new skulls, mandibles, and postcrania of Allodesmus, and reiterated his earlier conclusion (based on quantitative analysis!) that Allodesmus kelloggi was a junior synonym of Allodesmus kernensis. He also transferred Atopotarus courseni to Allodesmus, recombining it as Allodesmus courseni, and reported on the skull reported earlier by Packard (1962) – which was now fully prepared, and designated it as the holotype specimen of Allodesmus packardi. For another 20 years, this study constituted the last word on Allodesmus taxonomy.

The first, and only quantitative study of morphological variation in Allodesmus - from Barnes (1970).

            In 1995, Larry Barnes and Kiyoharu Hirota published an article in the special volume (mostly marine mammal-themed) of The Island Arc on “allodesmine” pinnipeds from the North Pacific. In the intervening decades, Barnes changed his mind on Allodesmus from Sharktooth Hill – and (without executing any sort quantitative analysis using the large sample of Allodesmus mandibles) not only reaffirmed Mitchell’s (1966) conclusion that Allodesmus kernensis was different from those specimens from the bonebed, but also restricted Allodesmus kelloggi to Mitchell’s type specimen, and named a well-preserved skull and mandibles originally described by Barnes (1972) as a new species – Allodesmus gracilis – to which they referred the rest of known bonebed Allodesmus specimens. In addition to this decision, they also resurrected Atopotarus as a distinct genus, and named the new genus Brachyallodesmus to contain the Portola Valley skull – recombined as Brachyallodesmus packardi. Material from Japan was considered to represent three species in two genera. A large but fragmentary roustrum and mandible fragments, similar in size and morphology to Allodesmus kernensis, was named Megagomphos sinanoensis (originally named in the 1950’s as Eumetopias sinanoensis). A far more enormous snout – comparable in size to a steller’s sea lion or small elephant seal – was named as the holotype specimen of Allodesmus megallos. Lastly, a somewhat more complete specimen with skull and mandibles was named as the new species Allodesmus sadoensis. Their use of the subfamily name Allodesminae was necessitated by the splitting of the generic concept into eight named (and three unnamed) species in four genera.

 The holotype skull of Allodesmus gracilis, from Barnes (1972).

            A paper by Naoki Kohno that came out in 1996 was evidently submitted and accepted prior to publication of the Barnes and Hirota (1995) paper. This study by Kohno (1996) was a bit more sober in its taxonomic conclusions, considering the gigantic snout of Allodesmus megallos as an adult specimen of Allodesmus sinanoensis (=Megagomphos sinanoensis of Barnes and Hirota), and considered only one species of Allodesmus from the Round Mountain Silt to be valid (Allodesmus kernensis), following Barnes (1970, 1972). Kohno (1996) also considered Atopotarus courseni to be a species of Allodesmus. In this article, Kohno (1996) named the “Mito seal” – a partial skull thought to be lost due to Allied bombing of Japan during the second world war, but figured and discussed by Repenning and Tedford (1977) based on a cast at the Smithsonian. In fact, the specimen had not been destroyed but was rediscovered – and the specimen He named the “Mito seal” Allodesmus naorai, and considered it to be closely related to Allodesmus packardi. Kohno also summarized other fragmentary occurrences of Allodesmus from Japan.

An alternate view of desmatophocid/allodesmine diversity published by Kohno (1996); this idea was published in parallel and independent from Barnes and Hirota (1995).

In 1998, a paper by Kimura et al. reported a mandible of Atopotarus sp. from the middle Miocene of Hokkaido. It is very similar to the holotype of Atopotarus courseni - but under a different paradigm of Allodesmus taxonomy, it could also be identified as Allodesmus courseni rather than Atopotarus sp.

            The most recent paper weighing in on the subject was Deméré and Berta (2002), which actually focused on the closely related Desmatophoca oregonensis. They argued that Allodesmus was oversplit, and emphasized the problematic recognition of three species of Allodesmus from a narrow stratigraphic interval in a single rock unit in California – Allodesmus kernensis, Allodesmus kelloggi, and Allodesmus gracilis from the Round Mountain Silt. However, a discussion of Allodesmus taxonomy was clearly beyond the scope of the study, and they elected to not discuss the topic further.

Next up: How many species of Allodesmus are there, any way? I've given out a brief sketch of the history of work on Allodesmus, but there's quite a bit more to the story than this.

References

L. G. Barnes. 1970. A re-evaluation of mandibles of Allodesmus (Otariidae, Carnivora) from the Round Mountain Silt, Kern County, California. PaleoBios 10:1-24.

L. G. Barnes. 1972. Miocene Desmatophocinae (Mammalia: Carnivora) from California. University of California Publications in Geological Sciences 89:1-76.

L. G. Barnes and K. Hirota. 1995. Miocene pinnipeds of the otariid subfamily Allodesminae in the North Pacific Ocean: Systematics and relationships. The Island Arc 3:329-360.

T.A. Demere, and A. Berta. 2002. The Miocene pinniped Desmatophoca oregonensis Condon,
1906 (Mammalia: Carnivora) from the Astoria Formation, Oregon. Smithsonian Contributions to Paleobiology 93: 113–147.

T. Downs. 1953. A mandible of the seal Allodesmus kernensis from the Kern River Miocene of California. Bulletin of the Southern California Academy of Sciences 52:93-102.

T. Downs. 1955. A fossil sea lion from the Miocene of the San Joaquin Hills, Orange County, California. Bulletin of the Southern California Academy of Sciences 54:49-56.

T. Downs. 1956. A new pinniped from the Miocene of southern California: With remarks on the Otariidae. Journal of Paleontology 30(1):115-131.

R. Kellogg. 1922. Pinnipeds from Miocene and Pleistocene deposits of California. University of California Publications in Geological Sciences 13(4):23-132.

M. Kimura, K. Hirota and C. Kiyono. 1998. Fossil pinniped mandible from the Middle Miocene of Haboro-Cho, Hokkaido. The Bulletin of the Hobetsu Museum 13:1-7.

N. Kohno. 1996. Miocene pinniped Allodesmus (Mammalia: Carnivora); with special reference to the "Mito seal" from Ibaraki Prefecture, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan, New Series 181:388-404.

E. D. Mitchell. 1966. The Miocene pinniped Allodesmus. University of California Publications in Geological Sciences 61:1-105.

Update to research trends, 1960-2014

First of all, it's been over a month since I've posted anything, and I feel that apologies are in order. I have been devilishly busy with dissertation writing, and feel like I am finally at about the halfway point. Things have relaxed somewhat, and I've got a few ideas for quicker posts and some longer ones. Relatively soon I'll be tackling an issue I've always wanted to talk about but have never had the time to read all the relevant papers in depth - controversies surrounding the highly derived, extinct pinniped Allodesmus from the Miocene of California, Mexico, Washington, and Japan.

Before I do any of that, it's been about six months since I posted the review of publishing trends for marine vertebrates from the eastern North Pacific. In the meantime, eleven (11!) new articles have been published (that I know of). The newest addition to the list is a new kentriodontid dolphin from the middle Miocene Rosarito Beach Formation - I had updated the list over the weekend, but thanks to this new paper (in Spanish with English abstract - pdf freely available online here) I had to update it again this evening.

Here's the updated chart:

There are two things you should notice. 1) 2013 has the largest number of publications on record dealing with marine vertebrates from our corner of the globe. There are five papers on fossil birds, mostly by colleague N. Adam Smith at NESCENT. 2) We're only four months into 2014, and at this rate we're already looking to beat the record of 2013 (although it is very possible that things may slow down). Regardless, 8 publications is fairly high for any year - only a handful reach 8 or higher.

Unlike the last time I posted this in October, I've now placed my excel file up on the web - so, you are free to download it, and if you so desire, notify me of glaring errors or omissions. Click here to download the excel file. At the moment, it's set up very simply: just four columns, with the aforementioned subjects (Taphonomy, Sirenia, Osteichthyes, Odontoceti, Mysticeti, Elasmobranchii, Desmostylia, Chelonia, Aves, Assemblages, and Aquatic Carnivora).

A publication need not be alphataxonomic in scope to merit inclusion - those certainly count, but minimum requirements for inclusion in this list include any of the following: 1) extensive discussion of the morphology, functional anatomy, age, or biogeography of marine vertebrates from Cenozoic rocks in the eastern North Pacific (e.g. Smith and Clarke, 2013, who used bones of the flightless auk Mancalla for histologic study); 2) published figures of said marine vertebrates, even if focusing on fossils from elsewhere (e.g. Velez-Juarbe and Pyenson 2012, in their paper on Bohaskaia - an Atlantic odontocete - figure the holotype skull of Denebola brachycephala); 3) extensive sampling of ENP marine vertebrates for any sort of quantitative study (e.g., Ando and Fordyce 2014, who used data on fossil occurrences from many ENP vertebrates for a large part of their analysis). If you are confused by a particular inclusion or omission, at least you can make some sense out of my strategy.

Future efforts: it would be nice to include a proper citation for each publication, but boy there are a lot of them, and it would take me a lot of time that I don't have. If there is a paper you see but were unaware of, shoot me an email - I've either got a pdf of it, or a paper copy in a box back in California (in which case you should use interlibrary loan, since it's going to be another 12 months until I'm home again).

Other future tweaks I might investigate and post in the future: the ratio of marine mammal to non-mammal publications, and the ratio of regular articles to book chapters/edited volumes. I believe that 90% of the big 1994-1995 spike is because of the 1994 Frank Whitmore marine mammal paleontology volume and the 1995 Island Arc volume (also heavily marine mammal-themed).

Science Fiction Double Feature: Two new papers on the same day – a strange new fossil porpoise, and vertebrate taphonomy of the Purisima Formation

Yesterday saw the publication of two new papers: the first of which is about a new genus and species of bizarre porpoise from the Pliocene of California, and the second is the published version of my master’s thesis.

The first paper is a collaboration with Rachel Racicot, Brian Beatty, and Tom Deméré and finally describes the extinct odontocete informally known as the “skimmer” or “half-beaked” porpoise. The new fossil phocoenid is named Semirostrum ceruttii, the genus name referring to the dramatically shorter rostrum, and is also an homage to the half-beak fish, Hemiramphus. The species name is in honor of Richard Cerutti, longtime field paleontologist and preparatory for the San Diego Natural History Museum. Mr. Cerutti collected the holotype in the early 90’s from the Pliocene San Diego Formation – I met him during a 2012 visit to the SDNHM.

The holotype skull, earbone, and mandible of Semirostrum ceruttii, and a composite skeletal reconstruction from three specimens. From Racicot et al. (2014); skeletal reconstruction by yours truly.

The new fossil porpoise has a somewhat longer rostrum than modern phocoenids, and is slightly more delphinid-like than modern porpoises as well. Most obviously, Semirostrum has a bizarre lower jaw with an elongate, fused mandibular symphysis that is developed into a laterally flattened and expanded, paddle-shaped process that juts far beynd the edge of the rostrum. The teeth in the mandible do not extend past the rostrum, so the majority of the symphysis is edentulous. The preserved teeth have labial wear facets, which we interpret as being the result of substrate abrasion – the observed patterns of tooth wear differ from extant phocoenids in lacking apical wear facets. When articulated, the wear facets do not match up with occluding upper teeth – indicating that regular tooth wear does not account for the observed pattern. We hypothesize that the elongate mandibular symphysis is a benthic probe, and that Semirostrum pushed its “chin” through the substrate, with sediment streaming along the lateral sides of the toothrow – snatching up any burrowing prey that came into contact with the “chin” or rostrum. In my life restoration, I illustrated Semirostrum as using it’s mandibular symphysis like a benthic plough, ploughing through the uppermost layer of the sediment in its search for burrowing invertebrates. The type specimen consists of a complete skull and mandible with periotic, tympanic bulla, and postcrania – an absolutely gorgeous set of fossils which I first had the opportunity to examine on my first visit to the SDNHM back in 2007.

 

Life restoration of Semirostrum ceruttii, from Racicot et al. (2014) - by yours truly.

My contribution to the paper was describing fossil material of Semirostrum from the Purisima Formation. Although the holotype specimen of Semirostrum ceruttii is from the San Diego Formation, multiple specimens of Semirostrum have been collected from contemporaneous sections of the Purisima Formation. In fact, one of the earliest known specimens of Semirostrum – collected in the mid 1980s by local collector Wayne Thompson – consists of a pair of fused mandibles. The specimen still unpublished and is now at LACM, but I was not able to see it on my last museum visit in November 2013. Material from the Purisima Formation includes a nearly complete skull and isolated mandible, a partial rostrum, and a couple of isolated periotics. None of the material is associated – it’s all scattered material preserved in bonebeds and other inner shelf sediments, presumably scattered across the seafloor by currents or from drifting carcasses. Nevertheless, every referred element exhibits morphological features unique to Semirostrum. Some specimens – including the periotics and the mandible – are morphologically indistinguishable from and identical in age to Semirostrum ceruttii. However, the skull and partial rostrum are somewhat older, from about the Mio-Pliocene boundary; furthermore, the skull exhibits a slightly asymmetrical facial region – which is a bit more primitive than extant phocoenids, and Semirostrum ceruttii. For these reasons, we interpreted this slightly older material as representing an as yet unnamed, slightly older species, and chose to simply identify it as Semirostrum sp.

 

Examples of different preservational features on shark teeth (A), odontocete vertebrae (B), auk (Alcidae) humeri (C), and odontocete periotics (D) - specifically, the top periotic is Parapontoporia wilsoni, and the bottom periotic is a referred periotic of Semirostrum ceruttii figured by Racicot et al. (2014:figure 2).

The second paper is the publication derived from my master’s thesis research at Montana State University. My master’s thesis dealt with the taphonomy of Miocene and Pliocene marine vertebrates preserved in the Purisima Formation of Northern California. I initially got hooked on taphonomy – the science of fossil preservation – thanks to my undergraduate adviser Dave Varricchio, who did his Ph.D. on the formation of “Jack’s Birthday Site”, a multispecies bonebed assemblage from the late Cretaceous Two Medicine Formation. I took his taphonomy course in fall 2005, and read a few articles on the taphonomy of modern whales. At that time, I had just returned from my first summer season of permitted field work in the Purisima Formation, so I was naturally interested in looking into the taphonomy of the unit. Further piquing my interest was marine reptile researcher Pat Druckenmiller’s return to MSU to teach for a year. Pat did his master’s thesis at MSU, where he published the short necked plesiosaur Edgarosaurus from the Thermopolis Formation near Bridger, Montana. Pat had an interest in marine vertebrate taphonomy – and we talked quite a bit about it.

 

Histograms of taphonomic characteristics of bones, teeth, and cartilage from different lithofacies of the Purisima Formation. In general, highest energy conditions are on left, lowest energy on right.

As it turns out, the Purisima Formation had already been the focus of a taphonomic study of fossil invertebrates in the 1980’s. The Purisima Formation is rather unique in that, unlike most rock units which have received taphonomic study, it preserves invertebrate and vertebrate fossils in a number of different depositional environments. This provided Norris (1986) with the unique opportunity of examining across-shelf trends in preservation of marine invertebrate fossil concentrations. Even with such an expansive shelly fossil record, similar studies have been few and far between. No studies investigating across-shelf trends in marine vertebrate taphonomy had ever really been attempted. My own limited field experience at the time indicated that a study of similar scope as Norris’s original paper – but analyzing marine vertebrates from the Purisima Formation instead – would uniquely permit the examination of cross-shelf changes in vertebrate preservation. All previous studies had sampled vertebrates from a single marine unit reflecting a single depositional environment, or a single fossil bed, or a single skeleton. These studies are of course necessary and make up the bread and butter of marine vertebrate taphonomy, but investigating larger scale processes that control or influence the spatial distribution and preservation of vertebrate bones and teeth in the marine environment is (or, was) virgin territory.

I’ll discuss the highlights later on in a dedicated series of posts, but these are takeaway points:

1) vertebrate material is most abundantly concentrated along time-rich hiatal or erosional surfaces – namely, bonebeds and shell beds.

2) taphonomic damage – abrasion, phosphatization, fragmentation, polish – are all positively correlated with both high-energy, shallower water deposits, and time-rich surfaces.

3) this indicates a systematic relationship between sedimentary architecture and marine vertebrate preservation, and that the sheer majority of the marine vertebrate fossil record is controlled by physical sedimentary processes, rather than biotically controlled. From a paleoecological perspective, there is not much hope that using any sort of specimen counting methods (e.g. relative abundance) for faunal analysis will be able to backstrip the rather severe taphonomic overprint.

Megachasma applegatei: A new megamouth shark from the Oligocene and Miocene of California and Oregon

In 1976, a strange large bodied shark with a wide mouth and a multitude of tiny, unicuspate teeth was discovered after being entangled in an anchor of a US Navy ship off the coast of Hawaii. Preliminary examination indicated it was an entirely new genus and species of filter feeding shark, not similar or closely related to basking sharks (Cetorhinus) and whale sharks (Rhincodon). It was named several years later as Megachasma pelagios – the megamouth shark. Megachasma is approximately 4-6 meters in length, inhabits temperate waters of the Atlantic, Pacific, and Indian Oceans, and extraordinarily rare – only 55 specimens have been observed since its discovery, explaining why this shark took so long to discover (in contrast, most other large bodied sharks at temperate latitudes have been known to science since the 18^th century).

The modern megamouth shark, Megachasma pelagios.

This week, a new species of fossil megamouth – named Megachasma applegatei after the late paleoichthyologist Shelton Applegate – was described by Kenshu Shimada, Bruce Welton, and Doug Long. Fossil teeth of M. applegatei occur in the late Oligocene-early Miocene Pyramid Hill member of the Jewett Sand near Bakersfield (California), the Skooner Gulch Formation in Mendocino County (California), and the Yaquina Formation and Nye Mudstone of coastal Oregon. Oddly enough, despite being named recently, the first fossils of this new species were discovered (at the Pyramid Hill locality) fifteen years prior to the discovery of the modern megamouth shark – which sort of makes the modern megamouth shark a living fossil.

The holotype and some paratypes of Megachasma applegatei.

Shimada et al. (2014) describe in total a series of 67 teeth (see above) – virtually every specimen present in museum collections. Many more specimens are present in private collections, but are useless to paleontologists interested in publishing as they are not publishable specimens. Private specimens include many published in an earlier study by de Schutter (2009), who unfortunately published photographs and descriptions of specimens in private collections. The 67 specimens reported by Shimada et al. (2014) include all publishable specimens, and constitutes a fairly large sample set. Other Cenozoic sharks are represented by tens of thousands of specimens – but a fair amount of variation is recorded in this sample. This large sample demonstrates two primary morphological differences between Megachasma applegatei and extant Megachasma pelagios: relatively shorter crowns (relative to root size) and the primitive retention of lateral cusplets in M. applegatei. The lateral cusplets and overall morphology of the teeth of M. applegatei are reminiscent of sand tigers (Odontaspididae), and appear to retain some primitive lamniform tooth morphology.

The rather large sample size of Megachasma applegatei. Serious kudos to the authors for figuring every single specimen!

The authors also review the rest of the published fossil record of Megachasma, and demonstrate that most Cenozoic teeth fall into two categories: Megachasma applegatei and similar teeth from Belgium from Mio-Pliocene deposits, and younger Pliocene specimens much more similar to extant Megachasma pelagios (e.g., Pliocene Yorktown Formation, Lee Creek Mine, North Carolina). The third species, Megachasma comanchensis, was described earlier by Shimada (2007) from the Cretaceous of the western interior (USA) but has been challenged by other authors as not genuinely representing a Cretaceous megamouth shark.

Proportional differences between M. applegatei and M. pelagios. Note the overlap between the two. From Shimada et al. (2014).

This study and two recent papers on fossil basking sharks mark the return of paleoichthyologist Bruce Welton, who published quite a bit during the 1970’s and 1980’s, but was less productive prior to his retirement from the petroleum industry. I’m truly pleased that this paper is finally out, and am eagerly looking forward to more papers on fossil sharks from the North Pacific. On that note, I will conclude that I have just submitted my own paper on fossil sharks from the region – with Dana Ehret, Doug Long, Evan Martin, and my wife Sarah – so, there will be more to read in the somewhat distant future!

References

De Schutter, P. 2009. The presence of Megachasma (Chondrichthyes: Lamniformes) in the Neogene of Belgium, first occurrence in Europe. Geologica Belgica, 12: 179–203.

Shimada, K. 2007. Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology, 27: 512–516.

Shimada, K., Welton, B.J., and Long, D.J. 2014. A new fossil megamouth shark (Lamniformes, Megachasmidae) from the Oligocene-Miocene of the western United States. Journal of Vertebrate Paleontology 34:281-290.

 

Radio interview on Radio Live NZ - fossil marine mammals from Northern California

Last weekend I was interviewed by Graeme Hill for the New Zealand station Radio Live, which broadcasted here over the weekend. For those of you who live elsewhere and probably missed it, you can listen to a podcast [9:55 min], linked below:

Ancient Sea Mammals - Radio Live

The interview covers the results of a recently published paper in Geodiversitas regarding fossil marine mammals from the Pliocene Purisima Formation of California. It covers some of the behind the scenes stuff - the discovery of the fossil site, some details of the ten years of laboratory work involved, in addition to discussing the broader implications of the fossilized fauna, and potential insights into the appearance of modern marine mammal species in the North Pacific.