Wednesday, December 25, 2013

2013 in review: Advances in marine mammal paleontology

Edit: as it turns out, there are still a few articles I need to include on here, including Koretsky and Rahmat (2013) on Pachyphoca, Flynn et al. (2013) on a pathologic dolphin tooth, Montgomery et al. (2013) on the evolution of brain size in modern and fossil cetaceans, and Uhen's (2013) review of the North American fossil record of Basilosauridae. I'll get these done soon, but have been "distracted" by dissertation eomysticetid research and a just-submitted manuscript on an Early Pleistocene gray whale earbone from California with my labmate Cheng-Hsiu Tsai.



Happy Holidays, Merry Christmas, Happy Hannukah, Kwanzaa, etc. – and happy Boxing Day from New Zealand. As an American, I’m not really sure what I’m supposed to do today, so other than recoup from consuming a disgusting amount of chicken, potatoes, cobbler, and berry pie, I’m completing my longest ever blog post. I’ve summarized every paper in marine mammal paleontology that has come out in 2013 (either published or appeared online as an in press manuscript). I did this last year for 2012, and it quickly became apparent that I left quite a few out. So, I’ve put this rather large body of text and images together, and I’m quite frankly a bit embarrassed with how much time I put into it, but to be fair – there were quite a few studies that came out this year, and it forced me to read or skim several that I had not yet had a chance to flick through. There are also several new papers I’ve put out this year which have also inflated the list a little bit (and there is one more yet to come this year). I hadn’t originally considered to include my own work, but my wife convinced me to at the last minute.


            This year’s only new species of fossil pinniped is a new species of monachine true seal from the latest Miocene Pisco Formation of Peru (Sud-Sacaco level). The material is pretty well preserved, and includes several complete skulls and mandibles, in addition to postcrania (much of which remains to be figured). Hadrokirus – meaning stout tooth – shares a sister-taxon relationship with another Pisco Formation phocid, Piscophoca pacifica. The cheek teeth of Hadrokirus are very robust, and owing to this – and some robust muscle attachments on the cervical vertebrae – Hadrokirus was interpreted as having durophagous diet, potentially feeding on hard shelled prey like crustaceans, or even other vertebrates. I’ll admit I was initially a bit skeptical of the feeding ecology hypothesis, since dental features were the rationale behind the “killer walrus” macrophagous apex predator hypothesis initially proposed for Pelagiarctos, and criticized in the PLOS One article published by Morgan Churchill and myself early this year. However, in the case of Hadrokirus, there are some peculiarities of the neck muscle attachments that add some credence to the hypothesis. Another interesting aspect of the study is that it recovered Acrophoca as sister to extant lobodontines (Antarctic phocids), and Hadrokirus, Piscophoca, and Homiphoca (South Africa) as a clade sister to the lobodontines. If this group gets further support in the future, we could very well see a “Piscophocinae” or “Homiphocinae”.


Subfossil bowhead whale remains from Sweden.


This study reports a latest Pleistocene bowhead whale skeleton from marine sediments along the coast of Sweden. The skeleton is approximately 13,800 years old based on radiocarbon dating, and includes mandibles, vertebrae, and ribs. Ancient DNA was recovered from the specimen, which indicated that the skeleton was in fact from a bowhead whale, Balaena mysticetus. Previously reported subfossil bowhead remains had been used to erect the fossil species Balaena swedenborgii; morphologically, the specimen did not appear to represent Balaena swedenborgii, but this fossil species has been interpreted by some to perhaps be a synonym of Balaena mysticetus or perhaps a subspecies of it (or alternatively Eubalaena glacialis). The new fossil is probably not complete enough to weigh in on the taxonomic distinctiveness of B. swedenborgii anyway. The authors also inspected the specimen for any evidence of colonization by the bone-eating worm Osedax – and found none. They concluded that this skeleton was deposited in at least 100 m water depth, but regardless – this specimen was certainly deposited on the Pleistocene shelf (…because the specimen was found 72 m above sea level). Modern studies of whale falls have demonstrated that Osedax has a difficult time colonizing carcasses on the continental shelf, owing to intermittent currents and sedimentation events. However, Anderung et al. speculate that rapid sedimentation caused by retreating ice pack along the saline front (where clay flocculation is accelerated). This is difficult to test, and to be fair – perhaps 1 out of 1,000 Neogene marine mammal fossils I have ever seen have convincing evidence of Osedax bioerosion, probably resultant from their deposition on the shelf – and I think this is a more likely reason for the lack of Osedax colonization.


Fossil ambergris from the Pleistocene of Italy.


One of the most fascinating taphonomic discoveries in years was the report of fossil ambergris from the early Pleistocene of Italy. Numerous large coprolites – a few dozen bearing cephalopod beaks and hooklets – were found in Pleistocene muddy strata. Admittedly, this was pretty unexpected – ambergris is known to be positively buoyant (although, admittedly – the buoyant examples are those we see – who knows what proportion sinks rather than floating) – and there is currently debate regarding how hard it is when it is inside the digestive tract; it is thought by some that while in the body it remains somewhat ‘compliant’ and only hardens after floating at sea for extended periods of time. Ambergris is only known to occur in giant sperm whale guts (Physeter macrocephalus), although in this case no cetacean body fossils exist to corroborate such an association. I've already discussed this exciting find.


Skeleton of the holotype of Neoparadoxia cecilialina.

Barnes, L.G. 2013. A new genus and species of Late Miocene paleoparadoxiid (Mammalia, Desmostylia) from California. Natural History Museum of Los Angeles County Contributions in Science 521:51-114. Direct link to pdf.

One of the studies published this year that is more geographically relevant to this blog is the new monograph on desmostylians by Larry Barnes (LACM). The main fossil in the paper is a new, absolutely gorgeous paleoparadoxiid from the Monterey Formation – this specimen includes a complete skull, mandibles, complete vertebral column, and appendicular elements. Barnes named this as a new genus – Neoparadoxia cecilialina. I had heard ahead of the publication that it would be named as a new genus, and I was unsure of the rationale prior to reading the paper. A quick skim of the paper revealed no solid rationale for splitting the genus Paleoparadoxia into three, cladistic or otherwise: all four species – the new species, and formerly P. repenningi, P. weltoni, and P. tabatai – all form a monophyletic group in Barnes’ cladistic analysis anyway, which Barnes named the Paleoparadoxiinae. Why not just keep things simpler and leave it as one genus? I haven’t read the entire monograph, so I’m not quite ready to judge whether or not this is a case of oversplitting. In addition to erecting a new genus name, Barnes also referred the Stanford skeleton – Paleoparadoxia repenningi – to the new genus, recombining it as Neoparadoxia repenningi. He also established a new genus for the latest Oligocene-earliest Miocene paleopardoxiid from the Skooner Gulch Formation, recombining it as Archaeoparadoxia weltoni. The paper includes many dozens of beautiful figures and illustrations, and certainly appears to be one of Barnes’ more significant contributions to our field. I think I’ll have to cover this study with a dedicated blog post in the future, after I have more time to read and digest the paper.


Phlogenetic and geographic placement of the Tunisian sea cow specimen.


Archaic sirenians are probably not my strong point. The only sirenians I’ve ever dug up are all hydrodamalines – which represent, I would say, the tragic pinnacle of sirenian evolution. So, as a result of reading mostly about crown sirenians, I’ve not strayed much into the literature on archaic sirenians – so this paper was a bit new to me. The problem with sirenians is that they are members of the Afrotheria – a group of mammals with African origins – but the earliest and most primitive known sirenian is Prorastomus from the early-middle Eocene of Jamaica. So, we’re missing the earliest representatives of the group from where they should be – Africa. The earliest known and most primitive sirenians – Prorastomus, Pezosiren – are quadrupedal sirenians that had not yet lost their hindlimbs (Pezosiren in particular, in terms of its phylogenetic placement and terrestriality, is a sirenian analog of Pakicetus). These two sirenians from Jamaica have been found in estuarine sediments. Benoit et al. report a new sirenian earbone from the late early Eocene (late Ypresian to early Bartonian) of Tunisia, in a lacustrine limestone. The anatomy of this earbone is relatively more primitive than Prorastomus from Jamaica, making the Tunisian specimen the most primitive known sirenian. Unfortunately, the new specimen is far too incomplete to be named – but the earbones of mammals – particularly of cetaceans – are very informative and isolated earbones such as this can often be accurately identified (for example, in some morphological cladistic analyses, up to 1/3 of all phylogenetic characters are periotic or tympanic bulla characters). In this study, Benoit et al. were able to conduct a phylogenetic analysis, corroborating the stem position of this taxon. They suggest that pachyostosis of the periotic is tied to aquatic adaptation in this early sirenian (as in other sirenians and cetaceans). Another study by Mark Clementz on isotopes suggested that sirenians took a direct route to marine life, instead of having a prolonged intermediate freshwater aquatic stage. The presence of the Tunisian specimen in freshwater settings, however, suggests that sirenians may have indeed adapted to a transitional freshwater environment before leaving Africa. On a humorous parting note, this paper has to have the record for the number of authors per single fossil bone in paleo literature.


Skull of the extremely strange ziphiid Globicetus from offshore Portugal.

 
In 2007, Giovanni Bianucci, Olivier Lambert, and Klaas Post published a large number of fossil beaked whales (Ziphiidae) trawled from offshore South Africa, which included multiple strange new genera and species. Most of these were found inside phosphorite nodules on the seafloor, and unfortunately because of this no detailed age data is known.
A new study published this year Is sort of a followup to that South African study, and reports many new – and also strange – ziphiids from offshore Portugal. These include a new species of Tusciziphius, known from Portugal and also South Carolina – that has a large ossification formed as a posteriorly-rising “fin” of bone on the rostrum, somewhat similar to Aporotus (although in Aporotus it is formed by the paired premaxillae and is transversely bilobed). Several new skulls are referred to Tusciziphius atlanticus. Another strange ziphiid, Imocetus, bears a strangely elongate facial region and a rostrum with a very wide, triangular base, vaguely reminiscent of the overall shape of a beluga skull in dorsal view; however, it bears elongate maxillary ridges, and a pair of short conical crests on the base of the rostrum. Other ziphiids include new records of Caviziphius, Ziphirostrum, and a new species of Choneziphius. Arguably the strangest new cetacean, however, is Globicetus – a robust beaked whale with a bizarre football-shaped ossification on the middle of the rostrum. I remember at the 2011 Aquatic Tetrapods conference in San Diego, Ted Cranford asked if the spherical structure could be a fossilized melon – unfortunately the chances of that happening are remarkably slim, although some soft tissue structures such as baleen and intervertebral disks have been preserved in Peruvian mysticetes. The structure is actually bone, and is formed by the medially fused premaxillae. Many ziphiids bear strange rostral ossifications and crests, and they probably have some function in reflecting sound (air is an effective acoustic barrier, but bone makes for a close second); the ossifications appear to be distinctive amongst various species, and are also known to arise via different developmental means (a paper by Olivier Lambert in Comptes Rendus Palevol reviews this nicely, and would be a good topic to cover on here at some point). In a way, Globicetus isn’t really any stranger than extant Hyperoodon (bottlenose whales), which has a pair of tall maxillary crests on either side of the melon; it’s just that Hyperoodon is “familiar” but strange, and Globicetus is “unfamiliar” and strange, so to speak.


Fossil platanistine periotic from Amazonian Peru.


This short communication presents a pretty surprising discovery, even if it’s just a single earbone: a record of a Platanista-like dolphin (identified to Platanistinae) from the Peruvian Amazon. Most of us probably think of the Pisco-Ica region on the Pacific side, which is dry and dusty and effectively a big desert; however, it’s easy to forget about the part of Peru on the other side of the Andes, which is technically part of Amazonia. A single periotic was collected from late middle Miocene fluvial rocks here, and the periotic shares numerous features in common with extant Ganges river dolphin, Platanista gangetica. For the geographically uninformed, this may not seem like anything huge: the Ganges river is in India, and Platanista is currently relegated to Pakistan, India, and Bangladesh, and is totally riverine in distribution. Although G.G. Simpson placed all river dolphins into a single subfamily Platanistoidea, it now appears that each river dolphin really needs its own family: Pontoporiidae (Franciscana/La Plata river dolphin), Iniidae (Amazon river dolphin/Boto), Lipotidae (Chinese river dolphin/Baiji), and Platanistidae (Ganges river dolphin/Susu), as these occur as a paraphyletic group in most molecular and many morphological cladistic analyses of odontocete relationships. So, this new record indicates that three of these families – Pontoporiidae, Iniidae, and Platanistidae – were all swimming around in coastal waters or rivers of South America during the Miocene. This has some curious biogeographic implications; it’s thought that these reflect independent adaptation to riverine life amongst archaic odontocetes, with many of their oceanic relatives going extinct and being replaced (passively or competitively) by more recently evolved delphinoids. This new find demonstrates that platanistines were not restricted to Asia, and an early Miocene specimen from Oregon indicates they were not uniformly riverine during the Miocene. Bianucci et al. hypothesized that platanistines had a marine, North Pacific origin, followed by invasion of rivers in South America and southern Asia, and subsequently going extinct in South America. Bianucci et al. also suggested that the long rostra of “platanistoids” (sensu Simpson) was a preadaptation for freshwater existence – perhaps suggesting a limited ability of delphinoids to colonize freshwater environments (although plenty of freshwater brevirostrine delphinoids exist: Orcaella spp., and Neophocaena, and a couple of other more longirostrine delphinids).


Holotype skull of the new Pliocene dolphin Septidelphis.


Giovanni Bianucci’s Ph.D. thesis and eventual publications in the late 1990’s dealt with a comprehensive reassessment of the Pliocene odontocete assemblage from Italy, which is a pretty sizeable assemblage and certainly no small feat. Of many of the historical specimens, there was one he was never able to track down and examine: a specimen of Stenella cf. frontalis reported in 1980; unfortunately the author of the study did not report where the specimen was reposited, and died before Bianucci could contact him about it. After recently learning the whereabouts of the specimen, Bianucci examined and reevaluated the specimen. Owing to some cranial differences, he named it Septidelphis morii – one peculiar feature is the presence of a fairly wide mesorostral groove, which is quite a bit wider than in other delphinids (elegantly shown graphically within the paper). Instead of conducting a dedicated morphological cladistic analysis of small bodied delphinine delphinids – no doubt a difficult undertaking thanks to the skulls of modern delphinines looking damned near identical (if I tried it, it would surely result in tears and hair being pulled out) – Bianucci used a molecular “scaffold”, constraining the tree topology and phylogenetic position of extant delphinids based on their occurrence in molecular phylogenies. 14 morphological characters were used to place the fossil taxa on the tree, with Pliocene fossil delphinids Astadelphis, Etruridelphis, and Septidelphis forming a paraphyletic stem group of delphinines. Each of these taxa were formerly identified as fossil Stenella; Bianucci suggests that, based on his results and the molecular phylogenetic results of others, that extant genera of delphinids probably did not arise until the Pleistocene, and that the majority of Pliocene delphinids are probably better attributed to extinct genera. Interestingly, given the recent proposal by William Perrin and others to combine Delphinus, Tursiops, Stenella, Lagenodelphis, and Sousa under Delphinus – which would no doubt make all of these extinct delphinine genera from Italy Delphinus as well. Is this a case – modern and fossil species alike - of taxonomic oversplitting, with recombining everything as Delphinus as the solution? I’m not sure, and certainly more morphological work on delphinines is necessary. To be fair, I have a hard time swallowing the idea that extant delphinid genera were not present at all during the Pliocene, but that’s just a gut opinion.


Holotype skull of the new baleen whale Parietobalaena campiniana.


During the late 19th century, a number of fossil baleen whales were named from the Miocene and Pliocene of Belgium. Many of these are of debatable utility and diagnosability, and many have been demonstrated to be chimaeras – collections of isolated, non-associated bones which the author interpreted to belong together. One of these fragmentary baleen whales was described as Isocetus depauwi – it includes a series of cervical and thoracic vertebrae, a partial mandible, a tympanic bulla, and an ulna. Reevaluation of the type specimen indicated that it is indeed a distinct genus and species, albeit difficult to compare with more complete fossil mysticetes; a nearly complete skull, periotic, tympanic bulla, mandible, and vertebrae was referred by the German paleontologist Abel to Isocetus depauwi. This specimen was described in detail and figured by Bisconti et al., who named it as a new species of ParietobalaenaParietobalaena campiniana. Interestingly, this study proposed some of the first synapomorphies for the genus Parietobalaena, including numerous earbone features. Two poorly known mysticetes which were transferred to Parietobalaena by Steeman in 2010 – Heterocetus affinus and Idiocetus laxatus – were concluded to likely be valid genera owing to periotic differences. Most significantly, a new clade of mysticetes was named: it includes all mysticetes crownward of right whales (Balaenidae), including Balaenopteridae (rorquals), Eschrichtiidae (gray whales), Cetotheriidae sensu stricto (true cetotheres), and cetotheres sensu lato, jokingly referred to as kelloggitheres (e.g. Kellogg’s cetotheres – Parietobalaena, Diorocetus, Aglaocetus, Thinocetus, Halicetus, Pelocetus, etc.). Admittedly, kelloggitheres are my least favorite group of mysticetes – they all look the same to me. There’s only one problem with the proposal of this new taxon – depending upon which phylogenetic result is achieved, it may or may not be equivalent (or mutually exclusive) with Balaenopteroidea, sensu Deméré et al. (2005). In Deméré et al. (2005), Cetotheriidae ss. appear on the stem relative to balaenids, but in this study, cetotheriids occur crownward of balaenids; in Deméré et al., everything crownward of balaenids belongs to Balaenopteroidea, whereas everything crownward of Balaenidae in this new study is termed Thalassotherii. By the way, I was pretty pleased and entertained to hear the term kelloggithere used in at least one SVP talk this year.


The Pliocene marine vertebrate assemblage from the San Gregorio section 
of the Purisima Formation.


Boessenecker, R. 2013. A new marine vertebrate assemblage from the Late Neogene Purisima Formation in central California, part II: Pinnipeds and Cetaceans. Geodiversitas 35:815-940.

This new study which came out on Dec. 27 was almost in time for Christmas. It marks the culmination of 8 of research on my part. In 2004 I received a tip to check out some bones at a beach by a local surfer, and when I got out there I found numerous bonebeds and hundreds of bones sticking out of the cliffs. It was my first summer home from college in Montana, and I had an idea for fieldwork – virtually nothing had been published on fossil marine mammals from the Purisima Formation, and literally nothing had been published on material outside the Santa Cruz area – so this was a ripe piece of fruit to pick. I received my first permit in 2005, had it renewed for 2006, and received another permit for 2010 to 2011. During these periods I collected a rather large number of marine vertebrate fossils, which would eventually represent over thirty species of sharks, bony fish, marine birds, pinnipeds, and cetaceans. Two earlier papers published all of the sharks, bony fish, and birds, including the embarrassingly large pelagornithid humerus which Adam Smith and I published in 2011 (the drawer label at UCMP is titled “Bobby’s big bird”). This new paper is concerned with the fossil marine mammals, and includes three pinnipeds, several baleen whales including Eubalaena (right whale), Herpetocetus, and a new species of Balaenoptera Balaenoptera bertae, which I’ve named in honor of Dr. Annalisa Berta. Odontocetes include delphinids, a globicephaline, an indeterminate sperm whale, Parapontoporia sternbergi, and several phocoenids including the strange “skimmer porpoise” as well as a harbor porpoise like fossil I’ve identified as cf. Phocoena. In addition to reporting all of these marine mammals, the paper includes a review of various Pliocene marine mammal assemblages from around the globe. Interestingly, I found that when I tallied up the proportion of extant to extinct genera in various assemblages, Pliocene marine mammal assemblages from the Pacific consistently had fewer extant genera than the North Atlantic. The Yorktown Formation of the eastern US, for example, is approximately 55% extant, whereas it is about 30-35% or so for the eastern North Pacific, and about 17% for the eastern South Pacific. This suggests that many extant marine mammals appeared earlier in the Atlantic than they did in the Pacific. Furthermore, many Pliocene assemblages seem to have all sorts of non-cosmopolitan “bizarre” species without modern ecological analogs in the region. All of these data, in concert with a Pleistocene marine mammal assemblage that is mostly comprised of extant taxa, indicate that a higher degree of faunal provinciality prevailed during the Pliocene and that various extinctions occurred amongst these groups sometime during the early Pleistocene.
 


Revised stratigraphic range of Herpetocetus with some other charismatic megafauna added for context.


This study published in Naturwissenschaften early this year reports a surprisingly late surviving example of the archaic mysticete Herpetocetus - the specimen may be as young as 700 thousand years. This has some interesting implications for how we think about marine mammal faunal change during the Pleistocene. Read about it here.


A collage initially intended for a cover image - barnacle encrusted sea lion bones and their locality.


This paper published earlier in the year in Journal of Paleontology is another taphonomic contribution of mine, and reports a new occurrence of barnacle encrusted marine mammal bones - and expands on the possible data we can squeeze out of the fossil record from encrusting invertebrates. Read about it here.


Life restoration of the extinct "killer" walrus Pelagiarctos.

This paper by myself and Morgan Churchill describes a new fossil of Pelagiarctos and reevaluates the problematic "killer walrus" hypothesis for the original Pelagiarctos thomasi material from Sharktooth Hill. Read more about it here, here, here, here, and here.


Life restoration of a globicephaline whale from the Purisima Formation.


This paper describes new records of globicephaline whales from the Purisima Formation of central/northern California. Read more about it here.



The holotype skull of the new beaked whale Notoziphius from Argentina.


This is one of the few papers published this year which I had the fortune to review. This study reports a new genus and species of beaked whale from the late Miocene of Argentina, collected by (late) local fossil collector Rodolfo Brunet. The specimen includes a relatively large skull, approximately Mesoplodon sized – missing the anterior part of the rostrum, and also some mandibular fragments. Monica Buono and Mario Cozzuol named this new genus Notoziphius, and named it after the collector – Notoziphius bruneti. Phylogenetic analysis indicates that this new ziphiid forms a clade with Messapicetus, Ziphirostrum, Beneziphius, and Aporotus. This new beaked whale is the first record of a fossil ziphiid from the southwestern Atlantic, and demonstrates that ziphiids were widely dispersed and diverse during the Miocene.


Fossil pygmy right whale mandible from the late Miocene of Argentina.


This new paper continues last year’s Caperea frenzy: this is the third fossil neobalaenid/neobalaenine to be reported in the last 16 months: the paper reports a partial mandible from the late Miocene of Argentina that is most similar to that of the extant pygmy right whale, Caperea marginata. It notably differs in having a larger coronoid process (reduced to absent in adult, modern Caperea, but retained in juveniles – see Marx et al., below), and in having a slightly less dorsally arched mandible; however, the features preserved are unique to neobalaenines. This specimen is the oldest known pygmy right whale, at approximately 9-10 million years old; it is about 3-4 million years older than the recently described Miocaperea from Peru. These attest to an old origin for pygmy right whales, and this specimen is just slightly younger, for example, than the oldest well-demonstrated fossil balaenopterids. Fossil balaenids, on the other hand, extend back to the early Miocene (~10 Ma).


Fossil skull of an undescribed kekenodontid from the Oligocene of New Zealand, currently being studied by labmate Josh Corrie.


Although published in 2013, this paper came out “online early” in 2012 and I covered it in last year’s post, which you can read here.


The strange taxonomic and phylogenetic framework for sharks in Diedrich 2013.


This paper by Cajus Diedrich is a followup to the 2011 paper on a supposed pinniped from the Eocene (a highly unlikely and poorly supported case which I summarized on this blog a couple years ago). This new paper reports the co-occurrence of the aforementioned “pinniped” in addition to a purported Protosiren rib, and a couple of bone fragments questionably identified as protocetid remains (which had been more appropriately identified by Diedrich as indeterminate mammalian remains in a previous paper); rationale for these identifications is not provided in the paper (which admittedly is not a solid foundation). Curiously, he uses a rather bizarre taxonomic framework for sharks, concluding – again without evidence – that the Carcharodon carcharias lineage can be traced back to the Eocene, and that both Carcharodon and Carcharocles were separate entities during the Eocene. The teeth identified as Carcharodon are clearly just small Carcharocles teeth that have been misidentified; the earliest taxon that can be reliably ascribed to Carcharodon is Carcharodon hastalis in the Miocene, as shown by Dana Ehret’s careful work. Diedrich argues that the co-occurrence of three marine mammals, and the earliest appearance of serrated Carcharodon and Carcharocles – is indirect evidence that the latter evolved after marine mammals first appeared in the North Sea. Is correlation = causation in this case, assuming for one moment the marine mammals are correctly identified (or even identifiable)? Or does the co-occurrence of these specimens in a time averaged, taphonomically concentrated horizon instead indicate a physical control on their occurrence simply by virtue of these sharing a calcium phosphate mineralogy which may be concentrated in certain sedimentological circumstances such as this? From a taphonomic perspective, any claim that there is a causal link is a bit of a stretch. It’s not really clear what the science was here aside from storytelling, and the puzzling taxonomic framework for sharks and lack of defense for marine mammal identifications undercuts this paper’s significance.
Full disclosure: I reviewed this paper twice for two different journals, and was more than a little surprised to see it published – effectively unabridged replete with all of its original typos – in a third journal, less than a month after it was rejected from the second journal. Despite not utilizing a shred of my constructive review comments, I was the only reviewer thanked in the published paper…


Hand-drawn speculative cladogram of diphyletic sirenian evolution by Diedrich.


This new study by Cajus Diedrich is a followup to the above study and the 2011 paper on a very dubious report of an Eocene pinniped fossil, and purports to document a new record of Protosiren from the proto-North Sea, and demonstrate evidence that sirenians are biphyletic (not monophyletic, and had two separate origins and is therefore not a biologically real group). The new fossil of Protosiren is just a rib – although ribs are diagnostic for sirenians as a whole, they are not exactly a rich treasure trove of morphological features, and I’m skeptical that such an identification is based on well-founded reasoning. Apparently Protosiren does have distinctive bone histology (thanks to Jorge Velez-Juarbe for the heads up), but no attempt at sectioning the specimen was made (in fact, the fossil remains in a private collection – which is not so good). Little morphological evidence is marshaled to support the identification as Protosiren. The central tenet of the paper – the identity of the main fossil reported within – is not solidly founded, in other words. The rationale behind the other point of the article – is not clearly accessible in the article – no attempt at conducting a phylogenetic analysis which reflects sirenian biphyly is made, although a pretty diagram showing sirenian diphyly is included. Importantly, no cladistic analysis was executed or reported upon – it is necessary to note here that the reported tree is a hand-drawn cladogram. That’s fine, it’s still a hypothesis, but not one that was tested by the author. It’s unclear after reading just where the “science” was in this study.


Cluster diagram of various fossil and modern marine and terrestrial mammals, grouped together based on microwear data.


This new paper by Julia Fahlke and colleagues investigates dental microwear on the teeth of archaeocete whales to document changes in diet during the land to sea transition in early cetaceans. Fahlke et al. investigated a pakicetid, several protocetids, and basilosaurids – fully bridging the terrestrial to marine transition. The habitat and locomotion of archaeocetes are already well known thanks to functional and isotopic studies, but it’s unclear exactly what archaeocetes were eating. For example: did aquatic feeding or adaptation for aquatic locomotion occur earlier in whale evolution? Or vice versa? The study of microwear is the microscopic analysis of damage to enamel, which is broadly correlated with diet. In extant herbivorous mammals, the number of pits and scratches is tied to how much silica is ingested and chewed – often in the form of phytoliths that grow in grass, and information like this can tell you whether or not a mammal was a browser or grazer. Dental microwear has historically been applied more frequently to herbivorous mammals, but recently a number of studies  by Brian Beatty and others have applied microwear to marine reptiles in order to evaluate feeding ecology – so there is scope for applying these methods to toothed marine mammals (sorry, chaeomysticetes). As it turns out, pakicetids and semiaquatic (pinniped equivalent semiaquatic-ness) protocetids share similar microwear patterns, suggesting that pakicetids were indeed feeding in the water. Basilosaurids, on the other hand, were found to have microwear indicating feeding on occasional harder prey – marine mammals, sea birds, etc., in addition to exhibiting extensive tooth damage related to contact with the bones of prey items. One protocetid, Qaisracetus, had microwear patterns similar to hyenas and killer whales, suggesting a large component of warm-blooded prey in its diet (e.g. other marine mammals, sea birds, large fish, etc.). In summary, they concluded that specialized piscivory and teuthophagy in extant odontocetes is derived from what was formerly a much more generalized diet during the Eocene – perhaps permitted by a dentition that could still shear, as opposed to modern odontocetes which predominantly swallow prey whole (killer whales being an exception).


Fossil sea cow as discovered in 1975 in a cave in New Guinea.

It’s always difficult finding vertebrate fossils in the tropics; carbonate rocks predominate in equatorial latitudes, and are not a great environment for preserving abundant marine vertebrate skeletal material – coastal carbonate systems tend to be characterized by relatively rapid, aggradational deposition, as opposed to vertebrate-rich low subsidence settings in siliciclastic basins where bones can be concentrated quite densely. As such, the marine vertebrate fossil record from Oceania – outside Australia and New Zealand – is quite limited. Occasionally, interesting gems are found though. A caving expedition in the mid 1970’s came across a series of bones in early-middle Miocene limestone in New Guinea (admittedly, not a very small island). As it turns out, this partial skeleton belongs to a small but indeterminate sirenian (sea cow). The extant Dugong currently inhabits Australasian, Indonesian, and Philippine waters, but has a crappy fossil record- it’s known from various Holocene localities in Australia and New Guinea, but only scraps of sirenians are known from earlier rocks in Australia. Eocene sirenians are plentiful further north and west in the Indian subcontinent as well as Java, but little evidence can be marshaled even to say that sirenians were present (or absent) during the intervening time. This new discovery suggests that sirenians indeed probably inhabited this region, and fossils of them from rocks of this time have so far gone undiscovered. Fitzgerald et al. suggest that this is due to incomplete sampling, and that other rocks in Australia may yet yield additional sirenian material.


Location and radiocarbon ages of fossil and subfossil Eubalaena (purple) and Balaena (blue) occurrences in the eastern North Atlantic.



This fascinating new study utilized ancient DNA from relatively young fossils of North Atlantic balaenids – bowhead whales (Balaena mysticetus) and right whales (Eubalaena glacialis) to examine evolutionary dynamics of the two whales during the late Pleistocene. They used about 44 samples from subarctic and cold temperate latitudes in the North SeaUnited Kingdom, Denmark, Sweden, and Norway. Specimens of late Pleistocene age turned out to all represent Balaena mysticetus, while those from the same latitudes – but from the Holocene – all represented Eubalaena glacialis. Currently, Balaena mysticetus is an arctic mysticete and is tied to ice-bound regions, whereas Eubalaena – all three putative species – are temperate water whales. The combination of identity (based on ancient DNA) and radiocarbon dates, in concert with paleoclimate suggests that during the last glacial period of the late Pleistocene, bowhead whales inhabited latitudes much further south than at present. During the Holocene, as icepack receded North and the earth recovered from the last glacial maximum, warmer water (note: still cold temperate and temperate – warmer, but still not “warm” or warm temperate) Eubalaena replaced the bowhead whale in those latitudes. This is a rather nice demonstration of habitat tracking in the fossil record of an extant mysticete.



The novel phylogenetic hypothesis of Caperea relationships.


Another paper from Caperea fever. This new paper by my adviser R. Ewan Fordyce and former labmate Felix Marx presents a provocative new hypothesis on the phylogenetic relationships of the pygmy right whale, positing that it is most closely related to extinct herpetocetine cetotheriids such as Herpetocetus and Nannocetus, which resurrects the Cetotheriidae from extinction. I’ve already covered this paper here.


Morphological changes in cetacea. There's a lot of labels here, so you can go ahead and consult the actual paper.


This large study is a review paper of sorts, and reviews various aspects of molecular and morphologic evolution of cetaceans. The study does reanalyze molecular and morphological data, but this is one of the more robust and up to date reviews of cetacean evolution and nicely summarizes current ideas on changes in locomotion, feeding ecology, sensory biology, sound production, brain size, diving adaptations, respiration, habitat (e.g. terrestrial v. aquatic v. marine), and other various aspects. There’s really too much to cover here, but if you’re looking for an excellent review of cetacean evolution within a phylogenetic framework, peppered with beautiful artwork by Carl Buell thrown to boot – look no further than this paper.


Partial skull attributed to Stromerius by Gingerich.


Historically collected specimens can often be problematic, even if they have been cited and discussed by various earlier researchers. There can be many changes in schools of thought and practice within a discipline over a century or so; as a result, many early specimens – types or otherwise – have a dramatically changed meaning to us relative to Victorian scientists. A new paper by Phil Gingerich illustrates quite nicely why old museum labels should never be trusted at face value. A skull and mandible of an archaeocete at the Field Museum in Chicago was historically identified as Prozeuglodon osiris (=Saghacetus osiris of current usage). It was sold to the Field Museum in 1914 or 1915 by Richard Markgraf. However, detailed study by Gingerich indicated that the two specimens differ in preservation and appear to represent two differently sized individuals. The skull is too small to represent Saghacetus or Dorudon, and Gingerich tentatively referred the specimen to the smaller basilosaurid Stromerius (the type specimen of which is represented by a vertebral column – albeit smaller than other basilosaurids). The mandible is in fact referable to Dorudon atrox. Gingerich points out that Richard Markgraf was not a paleontologist or a stratigrapher, and highlights problems with accepting museum labels at face value. This issue is familiar to me, and was hammered into my brain during the first few years of research, and as a result of questioning previous identifications while visiting various west coast museum collections, I developed a photographic and mental atlas of Neogene marine mammal fossils from UCMP, SDNHM, LACM, and others to construct a body of knowledge that I could use to evaluate and reidentify museum specimens (and, my own collected material).


Reconstructed olfactory apparatus of extinct protocetid archaeocete.


One of the most fascinating papers in marine mammal functional morphology this year was a paper by Stephen Godfrey, Erich Fitzgerald, and Jonathan Geisler on olfaction in archaeocetes and mysticetes. This study examined a fragmentary archaeocete skull from Virginia, mostly consisting of a frontal shield; they reasonably make the case that the specimen represents a protocetid rather than a basilosaurid. The specimen was found by a private collector who has been really generous in donating material from his collection to various institutions; it was found on a riverbank, with no adhering matrix, although its protocetid morphology suggests it is Eocene and may have been derived from the Piney Point Formation. The specimen includes well preserved olfactory structures. The olfactory apparatus of this protocetid is well-developed, in contrast to extant odontocetes – which appear to lack many of the structures found in this archaic whale and other “macrosmatic” mammals (macrosmatic means mammals with well-developed olfactory senses, such as dogs); odontocetes are widely considered to lack a sense of smell. The protocetid appears to have a well-developed sense of smell, probably far more sensitive than in humans. Interestingly, sectioned skulls of modern minke whales have an olfactory apparatus that is strikingly similar and functionally identical to the Eocene protocetid, leading Godfrey et al. to state that the protocetid had effectively modern olfactory anatomy. While it is clear that well-developed olfaction is probably primitively retained in some modern mysticetes (possibly all) and lost in odontocetes, the discovery of probable well-developed olfaction in mysticetes is somewhat surprising, given that when diving and foraging, the nostrils of cetaceans are closed off by the nasal plugs so as to prevent ingestion of water (and drowning). Godfrey et al. indicate that krill give off a particular odor, and it has recently been proposed that bowhead whales use their retained sense of smell to identify other whales, and locate “clouds” of planktonic prey; they suggest that olfaction – when the whales are at the surface, of course – could be used for finding dense accumulations of prey items.


Skull outlines of fossil squalodontids. The grayed area on the right hand side is the preserved portion of the partial skull described by Godfrey.


As a followup to the above article, Stephen Godfrey published another great paper on olfaction – but this time in an archaic odontocete – Squalodon, from the middle Miocene of Maryland. The cross-sectional area of the olfactory epithelium is about 7 times than the area of the ethmoid bone, whereas in most terrestrial mammals it’s about 16 times larger; this demonstrates that (unsurprisingly) Squalodon had an intermediate olfactory sense between archaeocetes and extant odontocetes – and, that olfaction was probably gradually lost within odontocetes during the Miocene.


Part of the holotype of the new basilosaurid Basilotritus uheni.


This new paper by Pavel Gol’Din and Evgenij Zvonok describes a new genus and species of basilosaurid archaeocete from the late Middle Eocene of Ukraine. This new fossil consists only of a partial tympanic bulla and several vertebrae. The vertebrae are grossly pachyosteosclerotic and inflated (vaguely resembling sirenian vertebrae), and bear a strange punctate texture on the external bone surface. This skeleton was given the name Basilotritus uheni, and named after archaeocete researcher Mark Uhen, and represents the oldest fossil cetacean from Eastern Europe. Phylogenetic analysis recovered Basilotritus uheni as an early diverging basilosaurid. Interestingly, Gol’Din and Zvonok noted the similarity between the vertebrae of Basilotritus uheni and “Eocetuswardii from the eastern USA, and recombined the latter as Basilotritus wardii. Several other fragmentary and problematic fossil cetaceans, such as Platyosphys, may have something to do with this new genus.


Sperm whale teeth from the late Miocene of Moldova.


Gol’Din, P. and V. Marareskul. 2013. Miocene toothed whales (Cetacea, Odontoceti) from the Dniester Valley: the first record of sperm whales (Physeteroidea) from the Eastern Europe. Vestnik Zoologii 47:21-26.

This short study reports several isolated teeth from an indeterminate physeteroid from the Tortonian (~9-12 Ma) of Moldova (a small country sandwiched between Ukraine and Romania). Two teeth apparently representing the same taxon are similar to teeth of the wastebasket taxon “Scaldicetus” in having a large enamel cap and swollen roots, and another tooth with an elongate and narrow root looks a bit like some “physeterines” (=Physeteridae of some workers), potentially indicating that two sperm whales were present. In the grand scheme of things, these are admittedly not very old, since there are plenty of examples of middle Miocene sperm whales (e.g. Aulophyseter from California), and Ferecetotherium from the Caucasus is potentially late Oligocene. These are, however, the first records of physeteroids from eastern Europe, a region which is becoming better known in terms of cetacean fossils thanks to recent efforts by the author, Pavel Gol’Din.


Skull and subantarctic locality of Africanacetus from the seafloor.


A second paper forms a followup to the 2007 paper on fossil ziphiids trawled from th seafloor off South Africa (This paper was covered last year as it was evidently online early in 2012 and only published this year, but I’ve typed up a longer and more fitting summary this year). This study by Pavel Gol’Din and Karina Vishnyakova reports two partial skulls of the beaked whale Africanacetus from offshore Antarctica, at a remarkably high latitude – approximately 60º south, and about midway (longitudinally speaking) between Australia and South Africa. The two skulls are slightly larger than the skulls reported from offshore South Africa, and differ in having a more well-developed mesorostral ossification of the vomer, leading the authors to simply identify the skulls as Africanacetus sp. These authors further hypothesize a circum-Antarctic distribution of Africanacetus, and also note that it is so far the highest latitude fossil ziphiid yet known; an interesting parallel is the Pliocene ziphiid-convergent delphinid Australodelphis from Antarctica named by Ewan Fordyce about a decade ago.


Articulated skeleton of the holotype of Cetotherium riabinini from the late Miocene of Ukraine. Scale bar = 1 meter.

It’s been a good year for Pavel Gol’Din – this study, also published this year in Acta Palaeontologica – reevaluates the skeletal anatomy of Cetotherium riabinini, a well preserved cetotheriid sensu stricto from the late Miocene of Paratethys (collected in Ukraine). I had the pleasure of reviewing this article last fall – and actually conducted my peer review during Hurricane Sandy when I was shuttered in my friend’s brownstone apartment in Washington D.C. (I was unable to go into the Smithsonian for about four days). Cetothrium riabinini is a more obscure species of Cetotherium from Paratethys; the genus is based on Cetotherium rathkei, which is known from a skull – but when Brandt described it initially, there was apparently a very narrow and tapering maxilla, which I and others did not really think was complete. As it turns out, the more complete skull of Cetotherium riabinini indicates that the narrow rostrum was in fact accurate as illustrated by Brandt. Cetotherium riabinini is small – about four meters body length, with a tiny skull with an elongate rostrum. The postcranial skeleton is well preserved, and includes Caperea-like platelike pachyosteosclerotic ribs. The rostrum is “bent” slightly anteroventrally, and it shares some peculiar features of the mandibular articulation with Herpetocetus. Owing to some of these features, Gol’Din and others argued that Cetotherium riabinini was adapted for benthic suction feeding much like today’s gray whale (Eschrichtius robustus). On a similar note, an in press article by Joe El Adli, Tom Deméré, and myself makes the same case for Herpetocetus from the Pliocene of California.


Bony tumor in the late Miocene balaenopterid "Megaptera" hubachi.



This new paper by German colleague Oliver Hampe and others is literally hot off the press, and came out just a couple of days ago in Alcheringa. This paper is concerned with large bony protrusions on the occipital shield of the skull of “Megapterahubachi, a fossil baleen whale from the late Miocene of Chile which was initially thought to be a fossil humpback whale relative. “Megapteramiocaena is generally plesiomorphic and shares various primitive characters with extant Megaptera, explaining why the original author placed it in the same genus. Regardless, it needs a new genus, as has been concluded by several researchers. The skull of “Megapteramiocaena has a strange bony lump on its occipital bone, in about the same position as small tubercles in rorquals (Balaenoptera) and even larger tubercles in the gray whale (Eschrichtius). In “Megapteramiocaena, it is only developed on the left side, whereas in gray whales it is bilaterally symmetrical – which Hampe et al. indicate is likely evidence that it is pathologic, and not a gray whale-like muscle attachment as suggested by Michelangelo Bisconti. Hampe et al. identify the strange structure as a benign bony tumor or osteoma – which apparently is the first known example of this in cetaceans. The inside of the structure is homogeneous and very dense. Previously reported pathologies identified as osteomas in extant cetaceans reported that the structures were very porous, and Hampe et al. suggest that these extant examples are probably not osteomas and represent some other type of abnormal bone growth such as spondylitis.           


Osteohistologic sections of fossil desmostylians.


Bone histology has been an excellent tool to gauge aquatic-ness of fossil marine tetrapods; multiple groups have acquired extremely dense bones upon invasion of the aquatic realm, thought to aid as ballast or to modify trim (orientation while swimming). This study by my Japanese friend and colleague Shoji Hayashi took postcranial bones of various desmostylian specimens from Japan. They found that the early desmostylian Ashoroa laticosta had pachyosteosclerotic bones – that is, bones with a reduced medullary cavity and an outwardly expanded cortex (e.g. inflated bones). The earlier diverging desmostylian Behemotops, and Paleoparadoxa both showed evidence of pachyostosis (inflated cortical bone). The most derived desmostylian, Desmostylus, on the other hand, showed evidence of osteoporosis – decreased bone density (the opposite of osteosclerosis). An increase in bone mass is tied to hydrostatic buoyancy and body trim and correlated with inefficient swimmers. However, decreased bone mass is related to hydrodynamic buoyancy control in active swimmers. This trend parallels that seen in cetaceans and pinnipeds, indicating all desmostylians have osteologic adaptations for aquatic life. Desmostylus in particular appears to have been a more active swimmer and more adapted for marine life than others – which does appear at odds with its inferred ecology as a seagrass or kelp grazer (i.e. since aquatic plants and algae grow in the photic zone and along the shoreline in shallow water). The spongy bone in Desmostylus parallels most modern cetaceans, in addition to elephant seals.
 

Referred skull of Haborophocoena toyoshimai.


This paper reports a new specimen of the fossil porpoise Haborophocoena toyoshimai. Haborophocoena is a porpoise that differs from extant porpoises in retaining an asymmetrical skull: the right premaxilla is wider than the left and extends further posterior to the left, in addition to the right maxilla being wider than the left, and the vertex being offset to the left side of the midline. A second species, Haborophocoena minutis, was reported by the same authors in 2009 from a different locality – and from this locality originated the new, second specimen of Haborophocoena toyoshimai. The new specimen yields additional insights into the skull anatomy of this porpoise.


Beautiful life restoration of the fossil ziphiid Ninoziphius from Peru.


Ninoziphius is an archaic beaked whale described by Christian de Muizon in the early 1980’s from the early Pliocene Pisco Formation of Peru. It was initially described in a brief article in French, and subsequently a longer description was published as part of a monograph on Pisco Fm. odontocetes – but again, in French. This new study redescribes the type specimen in even more detail (and in English!), and reports new skulls which preserve the vertex, which is damaged in the holotype. The cladistic analysis in this study confirms that Ninoziphius is the most archaic known fossil ziphiid. The feeding apparatus of Ninoziphius is less specialized for suction feeding than extant ziphiids, owing to the retention of a homodont dentition and elongate rostrum. Extensive tooth wear in Ninoziphius is interpreted to correspond to benthic feeding, or capture of prey near the sea floor. Based on facial cranial anatomy, Ninoziphius evidently was as capable of echolocation as extant ziphiids; it also exhibited relatively enlarged pterygoid sinuses, which appear to correspond to deep diving in ziphiids and physeteroids. Despite all this, the vertebral column of Ninoziphius is more flexible than extant ziphiids, with a longer cervical series; these suggest a less stiffened vertebral column that is less well adapted to deep diving than extant beaked whales.


The holotype skull of Brachydelphis jahuyaensis from the late Miocene of Peru.


This new study by Olivier Lambert and Christian de Muizon reports a new species of pontoporiid dolphin from the Pisco Formation of Peru. The dolphin is a new species of Brachydelphis. Brachydelphis mazeasi is a short-snouted relative of the extant La Plata River Dolphin Pontoporia blainvillei, notable for having an extremely short snout; it was described in the late 1980’s by Christian de Muizon. This new species is somewhat younger than B. mazeasi, and named Brachydelphis jahuayensis. Curiously, it has a somewhat longer rostrum than the older species – although it is still a notably short rostrum for a pontoporiid. If these two species belong in a single lineage, it implies that this lineage developed a short rostrum from a longirostrine ancestor (the primitive condition for pontoporiids), and subsequently evolved towards having a longer rostrum.


The ascending process of the maxilla and coronoid process of the mandible in various mysticetes.


Yet another paper from Caperea mania. This paper looked at juvenile and adult specimens of fossil and modern mysticetes to examine the ontogenetic polarity of a few characters that influence the phylogenetic position of the pygmy right whale. One feature is the lack of a coronoid process in adult Caperea, which it shares with right and gray whales to the exclusion of other mysticetes; however, juvenile specimens have a triangular coronoid, whereas juvenile balaenids – and juveniles of archaic balaenids – still lack one, suggesting that Caperea evolved from an ancestor with a triangular coronoid. The other character, lack of an ascending process of the maxilla, is shown to actually be present in juvenile Caperea, but absent in juvenile balaenids. Again, this suggests that Caperea evolved from an ancestor with an ascending process, which appears to have never been present in balaenids. Both features then are not really synapomorphic, and cloud our ability to effectively use them in phylogenetic analyses. As a bonus, there’s a figure of a mandible and skull of Herpetocetus bramblei provided by yours truly.



Periotics of the new albireonid from Japan (top) and Albireo whistleri from Cedros Island, Baja California (bottom).


Murakami, M., and Y. Koda. 2013. The first Pliocene albireonid (Cetacea, Delphinoidea) periotic from the western North Pacific and paleobiogeographic significance of fossil delphinoid ear bones of Na-arai Formation of Choshi, Chiba, central Japan. Japan Cetology 23:13-20.

This study by my colleague Mizuku Murakami reports the first record of an albireonid dolphin from Japan. Albireonids are thus far only known from two species in one genus – Albireo whistleri and Albireo savagei, from the late Miocene Almejas Formation of Baja California (Mexico) and late Pliocene Pismo Formation of California (respectively). Although the late Miocene species is represented by a beautiful skull, mandibles, earbones, and well preserved postcranial skeleton, the Pliocene species is represented only by a partial vertebral column and ribs. Albireo looks a bit like a cross between a phocoenid, monodontid, and a kentriodontid, and are some strange basal offshoot of delphinoids that didn’t quite make it to the modern day (but almost did). Murakami’s new study reports a diagnostic earbone – the periotic in particular – from the Pliocene of Japan. This new find establishes a circum North Pacific distribution for albireonids during the Pliocene. There are more complete remains of albireonids from Japan, but these have yet to be described. 



Vertebral columns of fossil and modern phocoenids.


Mizuki Murakami and colleagues report on another Pliocene porpoise (Phocoenidae) from Japan. This one, unfortunately, is too incomplete to be identified or named, but includes teeth, a strange rostrum, and quite a bit of the vertebral column. The phocoenid was relatively small, with an abnormally narrow rostrum for a phocoenid; sectioning of its teeth indicate that it was about four years old when it died. The young age and skeletal maturity of this specimen suggest that skeletal maturity was achieved quite early on during its ontogeny. The vertebral column of this specimen is morphologically intermediate between that of more primitive porpoises like Numatophocoena, and extant phocoenids like Phocoenoides. This finding suggests that postcranial evolution amongst phocoenids has been mosaic rather than gradual and ‘directed’.



Fossil gray whale mandible collected from the seafloor off Georgia.


This paper is a followup to a Palaeontologia Electronica article by Garrison et al. (2012), and reports on several fossil gray whale specimens recovered from the sea floor off of Georgia (U.S.A.). Two gray whale specimens are represented by mandibles with radiocarbon dates of about 30 Ka, and appear to represent juveniles, possibly under one year old. These fossils demonstrate that at about 30 Ka, Eschrichtius robustus was calving along the eastern coast of North America, in addition to being the oldest known specimens of the now-extinct North Atlantic population of gray whales (in the western North Atlantic, anyway).


Restricted distribution of sirenians during the Pliocene in Europe and North Africa (yellow spots).


This new study summarizes the known fossil record of sirenians (sea cows) in Europe and North Africa. This region is now totally devoid of sirenians, although they inhabited the Mediterranean from the Oligocene through to the Pliocene. The disappearance of sirenians is an interesting phenomenon, and one facet of late Neogene faunal change in marine mammal assemblages. Prista et al. concluded that sirenians became extinct in the eastern North Atlantic first, due to oceanic cooling and fragmentation of seagrass habitats. Seagrass habitats were inferred to persist in the Mediterranean, and extinction of Mediterranean sirenia was concluded to be caused by glacially induced cooling.


Mandibles and measurements - gigantic jaws of Balaenoptera.


This study examined the mandibles of balaenopterid whales (rorquals) to determine how they scaled with body size. They also point out that the mandible of the blue whale is the largest vertebrate skeletal element; perhaps an unremarkable finding, since blue whales are widely known to be the world’s largest vertebrate animal, fossil or modern (some dinosaur fan boys have proposed several sauropod dinosaurs that may be larger, but have produced insufficient evidence to dethrone Balaenoptera musculus). They report that a specimen of Balaenoptera musculus, USNM 268731, was from a 28 meter long female, and measure 6.8 meters in length. Damn, that’s huge. The more interesting aspect of this study was their use of scaling relationships to estimate body length from mandible size; many fossil balaenopterids are incomplete, few with skeletons or any postcrania, although isolated mandibles are abundant (they have a very high preservation potential owing to their large size). Mandible length corresponds to skull length, and skull length correlates well with body size in balaenopterids. They used three measurements – chord length (i.e. straight line from tip to tip), curvilinear length, and condyle to coronoid distance. They found that the relationship between mandibular length and body length is nearly isometric, and also that condyle-coronoid length decreases with increasing size. Although based on skeletal length and mandibular measurements of extant mysticetes, they tested their mandibular estimates with skull-based estimates for two fossil mysticetes with postcranial skeletons. Mandibular estimates were comparable with skull-based estimates, which is encouraging. Pyenson et al. then used two partial balaenopterid mandibles from the Purisima Formation (my favorite rock unit) to give examples of applying this method. The two mandibles from the Purisima Formation ended up being reconstructed as 3.26 and 4.83 meters in length, total – smaller than extant minke whales.


Physeteroid teeth from the Miocene of Spain.


This study reports some isolated teeth of a physeteroid sperm whale from the Late Miocene of southern Spain. They identify the teeth to the problematic genus Scaldicetus. Scaldicetus is supposedly diagnosed by having robust teeth with primitively retained enamel caps. However, teeth of the Scaldicetus morphotype have been found among various skull morphologies – and teeth of this morphotype belong to several extinct genera including Zygophyseter, Acrophyseter, Brygmophyseter, and Livyatan. Scaldicetus as a taxonomic entity is virtually meaningless. Admittedly, I only have a Spanish language version of the paper, and am unable to read the rest of the work.


Map of fossil cetacean localities in Taiwan.


Tsai, C., Fordyce, R., Chang, C., and L. Lin. 2013. A review and status of fossil cetacean research in Taiwan. Taiwan Journal of Biodiversity 15:113-124.

This new study by my labmate and fellow mysticete enthusiast Cheng-Hsiu Tsai and colleagues summarizes current and former research on fossil cetaceans from Taiwan. This study is derived in part from Tsai’s master’s thesis – the other half of which will be coming out in the Japanese journal Paleontological Research sometime next year on fossil gray whales from the Penghu Channel (along the western shore of Taiwan). Tsai et al. report the occurrence of numerous mysticetes including balaenopterids, balaenids, and Eschrichtius (again, to be considered in more depth in a following study) as well as delphinids, all from Miocene through Pleistocene rocks. A fossil pilot whale (Globicephala macrorhynchus) was trawled out of the Penghu Channel, and a well-preserved globicephaline skeleton which was previously named Pseudorca yuanliensis in an abstract-length publication. However, Tsai et al. pointed out that in the absence of a description this name is a nomen nudum. They also indicate that the taxon Balaenoptera taiwanica is based only on a tympanic bulla, meaning that some caution needs to be exercised when using the name. Tsai et al. conclude that although only a meager cetacean fossil record has been established in Taiwan in contrast to Japan, there has been very little research focus as well; preliminary field observations suggest a richer record than has been published, and that much more field work needs to be done in order to flesh out the cetacean fossil record of Taiwan.
 

Pinniped localities in South America and fossil southern sea lion remains from Chile.


This new paper marks Anita Valenzuela-Toro’s publishing debut, and describes several new pinniped fossils from the late Pliocene and Pleistocene of Chile. Most are fragmentary, but nonetheless tell an important story. The Pliocene specimens are a couple of ankle bones that are undoubtedly those of extinct true seals, several genera of which (like Hadrokirus mentioned above) inhabited the southeast Pacific during the Pliocene. However, the Pleistocene specimens – probably late Pleistocene at that – are all otariid specimens, most of which are identifiable to the extant South American sea lion, Otaria byronia. The modern pinniped assemblage in South America is entirely composed of otariids (Otaria, Arctocephalus) in addition to the southern elephant seal (Mirounga) – but none of these genera are known from the Pliocene marine mammal record there. Instead, we have extinct phocids like Hadrokirus, Piscophoca, and Acrophoca; these pinnipeds are known from both Peru and Chile (with the exception of Hadrokirus, which is so far only known from Peru). Numerous other strange late Neogene marine mammals that are now extinct are known from both Chile and Peru, including Brachydelphis (short snouted river dolphin - see above), Odobenocetops (walrus faced whale), and Thalassocnus (aquatic sloth). These faunal similarities attest to some sort of faunal turnover during the Pliocene-Pleistocene interval. Valenzuela-Toro et al. suggested that phocids were extirpated in this region as a result of sea level changes and changing coastal geomorphology, with otariids repopulating the region as rocky shorelines proliferated during the Pleistocene. I really enjoyed this paper, and this was one of my first reviews for a paper in JVP; additionally, I had the good fortune of meeting Anita in person at SVP in Los Angeles this year; we spent some time looking at pinniped fossils at the Cooper Center, something I ought to write some blog posts about.


Miocene seagrass and sea cow fossil records.


The fossil record of seagrasses is relatively limited, and little can be said directly from the fossil record of seagrasses regarding their paleogeographic distribution. Seagrasses are the primary food source of sirenians, and their modern distribution is tied to the distribution of seagrasses. This new study by Jorge Velez-Juarbe uses the fossil record and paleogeographic distribution of sea cows to reconstruct the paleogeography of seagrasses through Cenozoic history. The sirenian fossil record suggests that seagrasses were already distributed widely in the western North Atlantic and Caribbean by the middle Eocene. Oligocene cooling appears to have contracted the range of seagrasses and sea cows, which soon expanded again early in the Miocene. Later in the Miocene both groups expanded west and south into the eastern Pacific and the western South Atlantic. The distribution of seagrasses – as reconstructed from sea cow fossils – reached its modern pattern during the Miocene.

8 comments:

Richard White said...

Bobby, instead of going to sleep at a reasonable time, I spent the last several hours reading through your impressive blog from beginning to end. Well done, and I feel like I'm actually aware of some of the marine mammal stuff going on now. Thanks, and I look forward to seeing more!

Robert Boessenecker said...

Hey Rich, Glad I could contribute to sleep deprivation! Few things are better than that for a writer to hear.

Some of these papers are definitely interesting enough to necessitate a bit more of a detailed look, so check back. I've also got a lot of posts to do about my trip to the US, and the Marine Mammal conference here in Dunedin.

Davidow said...

Hi Bob,

Hadrokirus isn't the only fossil pinniped genus that was described in 2013 --- Koretsky and Rahmat (2013) have described Pachyphoca as a new genus of fossil phocid closely related to the hooded seal. Paradoxically, only a teeny tiny number of extinct pinniped species are named once in a while b/c the skeletons of fossil seals are somewhat fragile and subject to erosion or distortion.

I. A. Koretsky and S. J. Rahmat (2013). "First record of fossil Cystophorinae (Carnivora, Phocidae): Middle Miocene seals from the northern Paratethys". Rivista Italiana di Paleontologia e Stratigrafia 119 (3): 325–350.

Robert Boessenecker said...

Davidow,

At the time of writing I wasn't aware of the new paper by Irina, but Jorge Velez-Juarbe kindly emailed me a pdf of the article - I'll be incorporating it as soon as I've gotten a chance to read through it.

Regarding preservation, there's nothing inherently different in the skeletal anatomy of pinnipeds that makes them any more or any less susceptible to preservational bias relative to odontocetes of the same size. In fact, I'd argue that since the skeleton of a pinniped is not osteoporotic like a dolphin's is, pinnipeds would have a higher preservation potential. The low number of publications on fossil pinnipeds is arguable related to the fact that there are not very many researchers who work on fossil pinnipeds - and fewer yet who work exclusively on them. Trust me, there are tons of amazing but as yet undescribed fossil pinnipeds.

Johannes Albers said...

Hi Robert Boessenecker,
thanks a lot (really!), but what about this paper:

Flynn, S.S., Moses, R.J., and J.H. Connolly (2013). Indications of periodontal disease in a fossil Odontoceti (Mammalia: Cetacea) from the late Miocene Monterey Formation at San Clemente Island, southern California. - Contributions in Science 521: 1-12.

Best regards,
Johannes Albers, Germany

Robert Boessenecker said...

Johannes, Thanks! I had totally forgotten about that one. To be honest, it had crossed my mind, but I subconsciously thought it had been published in 2012. I'll have to add that and the Koretsky article, pronto.

Cameron McCormick said...

Awesome collection!

In a way, Globicetus isn’t really any stranger than extant Hyperoodon (bottlenose whales)

Nah, Globicetus is way weirder. Hyperoodon (and Platanista) may look strange with an arch of bone surrounding their melons, but it's worth remembering that other odontocetes coat the top and sides of their melons with a sound-reflecting layer of dense connective tissue called the theca. Globicetus... just has a lump of dense bone where any sane cetacean would put a melon. Bianucci et al. are reasonable in concluding that the entire melon had to be above that lump in order to function, but this is way more dorsal than the position for any other odontocete. There's really no clear advantage for such a position and — comparing with the known sound transmission information for Ziphius — it's puzzling how such a setup would even work, especially considering the vertex doesn't look particularly weird.


Cetotherium riabinini is small – about four meters body length, with a tiny skull with an elongate rostrum. The postcranial skeleton is well preserved, and includes Caperea-like platelike pachyosteosclerotic ribs.

Neat! I see it also has a low number of lumbars for a non-Caperea baleen whale (8, Balaena glacialis is the next-lowest with 10–12) although the thoracic count is unremarkable.

Mike said...

Just. Wow. Fantastic review Mr. Boessenecker! Thanks for doing all this work to author this impressive piece. Very enjoyable.