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2019 in review: advances in marine mammal paleontology

Oi, it's been a long time since I've done this. We're five months late here, but let's just say 2019 was not a great year for me professionally and it's taken me about a year to mentally catch up, accept the new normal, and re-motivate me to do research. Have you ever seen Office Space? I was Peter Gibbons for quite a while (still am, and my students love it). Anyway, I'm going to get back into this blogging thing. Truth be told, winter was very busy for me, and so I genuinely did not have any time to write this post on time - all of December was spent working on getting a cast of a whale skeleton repaired and painted and ready for mounting. I reviewed like 16 manuscripts in 2019, and didn't submit a single one of my own! I finally, for the first time in my career, declined a few requests to keep my stress levels down. I taught my first giant lecture with about 100 students - which was not a whole lot harder than our typical 50 student lectures (more emails, though). And, now we're stuck in quarantine - and I've been catching up on various things in a big way, so without further ado, brought to you by Covid19, the very belated 2019 in marine mammal paleontology post!

Albright et al.: Cenozoic vertebrate biostratigraphy of South Carolina, U.S.A., and additions to the fauna. Bulletin of the Florida Museum of Natural History.

Link: https://digitalcommons.unf.edu/facultyshowcase/2020/Showcase/1/

Abstract: Study of vertebrate fossils from the South Carolina Coastal Plain played a significant role in the early history of vertebrate paleontology as a scientific discipline in North America. However, a clear understanding of the state’s vertebrate biostratigraphy has been greatly hindered by the paucity of well-exposed fossil-bearing stratigraphic sections and a complicated subsurface stratigraphy. Most units, particularly those of Neogene and Quaternary age, exist as thin veneers of marine or estuarine sediments that typically occur as infilled topographic lows or erosional remnants as determined primarily from borehole stratigraphy. Hence, lateral continuity can be difficult to confirm over broad geographic areas often resulting in confusion insofar as vertebrate fossil provenance is concerned. The evaluation of vertebrate fossils from the South Carolina Coastal Plain presented here, and of the geologic units from which they originated, or are thought to have originated, results in the first modern biostratigraphic framework for the known Cenozoic record of the state. Results provide (1) updated correlations of many units to the most recent, astronomically-tuned marine oxygen isotope stages; (2) the first viverravid from the Atlantic Coastal Plain, Didymictis proteus; (3) new information on the timing of certain Neotropical immigrants into the Southeast during the Great American Biotic Interchange, including the oldest record of Erethizon in this region and the oldest records of capybara in the USA; (4) the possible oldest record of the microtine rodent Allophaiomys pliocaenicus in the USA; (5) new details on the unit of origin for the type specimen of the archaeocete Dorudon serratus; and (6) new details on the ontogeny of the early odontocete Agorophius pygmaeus. New taxonomic records from South Carolina include Glyptotherium texanum, Holmesina floridanus, Ondatra idahoensis, Erethizon ?bathygnathum, Leopardus amnicola, Miracinonyx ?trumani, Canis lepophagus, Canis latrans, Phocanella pumila, Callophoca obscura, Monatherium sp., Anchippus texanus, Subhyracodon mitis, Aphelops ?malacorhinus, Teleoceras ?guymonense, and Perchoerus sp. New specimens of previously recorded taxa are also noted.

Comments: This behemoth of a paper has a LOT in it, and once I have barely had time to scratch the surface of - but discusses the South Carolina marine vertebrate fossil record in detail, including all sorts of obscure historical references I wasn't aware of. Also, it's worth noting that because South Carolina is so anomalously fossiliferous, and there are also no cliffs, that the history of paleontology here is dominated by tons and tons and tons of very neat but context-less ex situ fossils with uncertain ages and disagreements over provenance.

Bianucci et al: A new Monodontidae (Cetacea, Delphinoidea) from the lower Pliocene of Italy supports a warm-water origin for narwhals and white whales. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/abs/10.1080/02724634.2019.1645148?journalCode=ujvp20

Abstract: A new taxon of monodontid cetacean, Casatia thermophila, gen. et sp. nov., is here described on the basis of a partial skull from lower Pliocene (5.1–4.5 Ma) marginal-marine deposits of Tuscany (central Italy). This new taxon belongs to Monodontidae based on the presence of a medial exposure of the maxillae anterior and lateral to the external bony nares; it mainly differs from all other named monodontids by the presence of a median depression of the premaxillae anterior to the premaxillary sac fossae and by a medial margin of the premaxillary-maxillary suture that does not parallel the anterolateral profile of the external bony nares. Our phylogenetic analysis, the first including all taxa of Monodontidae, recovers Casatia as a crown monodontid, more closely related to Delphinapterus than to Monodon and sister group of an unnamed taxon from the North Sea. The holotype of Casatia represents the first and only fossil monodontid from the Mediterranean Basin. Taking its place beside abundant fossils of strongly thermophilic marine vertebrates, such as the bull shark Carcharhinus leucas, the tiger shark Galeocerdo cuvier, and the extinct sirenian Metaxytherium subapenninum, Casatia thermophila represents the strongest evidence supporting the hypothesis that monodontids once thrived in low-latitude, warm-water habitats. On the basis of our phylogenetic reconstruction, early relatives of the extant monodontids might have adapted independently to the high-latitude, cold-water environments they currently master. The definitive disappearance of the Neogene thermophilic monodontids could be attributed to the cooling episode that accompanied the onset of long-term Northern Hemisphere glaciation around 3 Ma.

Comments: This paper is sort of a response to the 2018 paper by Ichishima et al. on Haborodelphis, a beluga-like monodontid from the Pliocene of Hokkaido. Previously reported temperate to subtropical latitude monodontids (e.g. Denebola, Bohaskaia) suggested that the earliest belugas were actually warm water cetaceans - but Ichishima et al. found a cold water invertebrate assemblage, and indicated that since there are some quite cold (albeit brief) periods in the Pliocene, greater care was needed to demonstrate paleoclimate aside from "ahhh, yeah it's from Mexico so it's gotta be warm". Casatia thermophila (great species name!) was recovered with a nice assemblage of warm water taxa, in the Mediterranean! Given the timing and incomplete preservation of Casatia I do wonder if Bianucci et al. saw the Ichishima paper and thought "well now is the perfect time to get this thing published" and wrote it up. Fascinating little back and forth.

Bianucci et al. Rise of the titans: baleen whales became giants earlier than thought. Biology Letters.

Link: https://royalsocietypublishing.org/doi/10.1098/rsbl.2019.0175

Abstract: Baleen whales (Mysticeti) are major ecosystem engineers, thanks to their enormous size and bulk filter feeding strategy. Their signature gigantism is thought to be a relatively recent phenomenon, resulting from a Plio-Pleistocene mode shift in their body size evolution. Here, we report the largest whale fossil ever described: an Early Pleistocene (1.5–1.25 Ma) blue whale from Italy with an estimated body length of up to 26 m. Macroevolutionary modelling taking into account this specimen, as well as additional material from the Miocene of Peru, reveals that the proposed mode shift occurred either somewhat earlier, or perhaps not at all. Large-sized mysticetes comparable to most extant species have existed since at least the Late Miocene, suggesting a long-term impact on global marine ecosystems.

Comment: This paper is a response of sorts to earlier studies, chiefly Slater et al. 2017, which proposed that baleen whales did not become gigantic (e.g. over 15 meters) until the last 2-3 million years - the analysis was based on skull size and found that gigantism evolved independently and late in balaenids and balaenopteroids. How late, nobody was sure, because most Pliocene fossil mysticetes are still on the small side and our Pleistocene record is terrible. I always thought the Slater hypothesis was correct, based on the lack of large mysticete *crania*. This new study reported a nearly full size fossil blue whale skull from the middle Pleistocene of Italy, and a few gigantic mysticetes from the latest Miocene of Peru (Pisco Fm., of course) and it pulled the onset of gigantism back a few million years - same overall pattern, just slightly earlier. Now: I think a better way around this, to get a better sample size, is to get a regression for body length based on vertebral size (which, based on my last project, is eminently possible) and measure hundreds and hundreds of isolated vertebrae. Granted, vertebrae are non-diagnostic, so they will be devoid of phylogenetic context, but may show a very different pattern as I have seen gigantic vertebrae in cliffs, backyards, and museum collections from late Miocene and Pliocene localities, and I believe there is certainly collecting bias against large mysticetes (too big to excavate).

Bisconti et al. A new balaenopterid whale from the late Miocene of the Southern North Sea Basin
and the evolution of balaenopterid diversity (Cetacea, Mysticeti). PeerJ.

Link: https://peerj.com/articles/6915/

Abstract: Balaenopterid mysticetes represent the most successful family-rank group of this clade. Their evolutionary history is characterized by a rich fossil record but the origin of the living genera is still largely not understood. Recent discoveries in the southern border of the North Sea revealed a number of well preserved fossil balaenopterid whales that may help resolving this problem. In particular, skull NMR 14035 shares morphological characters with the living humpback whale, Megaptera novaeangliae and, for this reason, its characteristics are investigated here. The comparative anatomical analysis of the new specimen formed the basis of a new phylogenetic analysis of the Mysticeti based on a matrix including 350 morphological character states scored for 82 Operational Taxonomic Units. The stratigraphic age of the specimen was determined based on the analysis of the dinocyst assemblage recovered in the associated sediment. We assessed clade diversity in Balaenopteridae by counting the numbers of clades in given time intervals and then plotted the results. Nehalaennia devossi n. gen. et sp. is described for the first time from the late Tortonian (8.7–8.1 Ma) of the Westerschelde (The Netherlands). This new taxon belongs to Balaenopteridae and shows a surprisingly high number of advanced characters in the skull morphology. Nehalaennia devossi is compared to a large sample of balaenopterid mysticetes and a phylogenetic analysis placed it as the sister group of a clade including the genus Archaebalaenoptera. The inclusion of this fossil allowed to propose a phylogenetic hypothesis for Balaenopteridae in which (1) Eschrichtiidae (gray whales) represents a family of its own, (2) Balaenopteridae + Eschrichtiidae form a monophyletic group (superfamily Balaenopteroidea), (3) Cetotheriidae is the sister group of Balaenopteroidea, (4) living Balaenoptera species form a monophyletic group and (5) living M. novaeangliae is the sister group of Balaenoptera. Our work reveals a complex phylogenetic history of Balaenopteridae and N. devossi informs us about the early morphological transformations in this family. Over time, this family experienced a number of diversity pulses suggesting that true evolutionary radiations had taken place. The paleoecological drivers of these pulses are then investigated.

Comments: An interesting new study reporting the new genus and species Nehaelennia devossi - an Archaebalaenoptera-like early rorqual. When I started working on fossil baleen whales, we were in a state of 'taxonomic paralysis' because of good ole P.J. Van Beneden, who, bless him, named a lot of fossil species of mysticetes from Belgium in the late 19th century - based on chimaeric assemblages of non-associated fossils that he arranged to fit pre-imagined 'archetypes' (e.g. the modern Atlantic fauna has a small minke whale, so all these small bones go to the Pliocene version of the minke whale and surely all go together... right?) and then like, went ahead and fucking renamed a bunch of his own species and genera! Anyway, nobody had the gall to start fixing the problem until 2010 when Bosselaers and Post shit-canned all of his balaenopterids as nomina dubia with the possible exception of "Balaenoptera" borealina. Since then a number of new discoveries of Belgian and Dutch mysticetes have finally been able to be studied without being mired in the taxonomic web of Van Beneden. This new paper says a lot of things, including a very different placement of my own species Balaenoptera bertae which I very much doubt. Regardless, the new specimen is nice.

Boessenecker and Boessenecker. Paleontology of the "Ashley Phosphate Beds" of Charleston: insights from Northbridge Park, Charleston, South Carolina. GSA Field Guidebooks.

Link: https://pubs.geoscienceworld.org/books/book/2152/chapter/120859059/Paleontology-of-the-Ashley-Phosphate-Beds-of

Abstract: A man-made deposit at Northbridge Park near Charleston, South Carolina, consists of phosphatic nodules, fossils, and mud dredged from the bottom of the Ashley River; nodules and fossils lay strewn across the banks of the river. This artificial deposit is likely representative of deposits mined extensively in the late nineteenth century and widely referred to as the “Ashley Phosphate Beds.” Many of the taxa discovered at Northbridge Park were historically reported from the phosphate beds, and include sharks, rays, bony fish, sea turtles, giant birds, whales, dolphins, sea cows, and land mammals. Some of these bear adhering matrix indicating origin from the Oligocene Ashley Formation. Others lack matrix but have short geochronologic ranges and are derived from the Ashley Formation, Lower Miocene Marks Head Formation, Lower Pliocene Goose Creek Limestone, and Pleistocene Wando Formation.

Comments: This paper hilariously started out as a blog post (elsewhere on this very blog) and as the result of many recreational fossil collecting trips to a fossil site near my old apartment. This was the first fossil site I was able to visit now that quarantine closures are easing. GSA publications are notoriously hard to get a hold of, so email me if you want a pdf. This was my only paper in 2019! Coauthored with my lovely wife and coworker.

Bosio. Integrated chronostratigraphy and taphonomic studies in Miocene sedimentary successions of the East Pisco Basin (Peru). Plinius.

Link: http://www.socminpet.it/Plinius2019/bosio.pdf

Abstract: (no abstract, so here's the introduction) Along the western side of the Ica River (Ica Desert, Peru), the Miocene Chilcatay and Pisco formations of the East Pisco Basin crop out. These units are characterized by an extraordinarily preserved marine vertebrate fossil assemblage, especially cetaceans. This work has the purpose of making chronostratigraphic and taphonomic studies on these formations, cropping out in the Ica River valley. The Pisco Basin, in southern Peru, is one of the fault-bounded Cenozoic sedimentary basins along the Peruvian coast, located at 14°30’ S of latitude. Along the coast, the most easterly Outer Shelf High separates the forearc Pisco Basin into an offshore and an onshore portion, referred to as the West Pisco Basin, still submerged, and East Pisco Basin (Fig. 1a). The sedimentary infill of the East Pisco Basin has been described by Dunbar et al. (1990) and DeVries (1998), and consists of five lithostratigraphic units: the Eocene Caballas Formation, the
middle to upper Eocene Paracas Formation (subdivided in Los Choros and Yumaque members), the uppermost Eocene-lower Oligocene Otuma Formation, the uppermost Oligocene to lower Miocene Chilcatay Formation, and the upper Miocene to Pliocene Pisco Formation (Fig. 1b) (e.g., Dunbar et al., 1990; DeVries, 1998; DeVries & Jud, 2018).

Comments: I think there will be a longer followup paper later - I always look forward to taphonomic research!

Buono et al. Eocene Antarctica: a window into the earliest history of modern whales. Advances in Polar Science.

Link: http://www.aps-polar.org/paper/2019/30/03/A190617000001

Abstract: The Eocene–Oligocene Southern Ocean is thought to have played a major role in cetacean evolution. Yet, fossils from its heart—Antarctica—are rare, and come almost exclusively from the Eocene La Meseta and Submeseta formations of Marambio (Seymour) Island. Here, we provide a summary and update of this crucial fossil assemblage, and discuss its relevance in the broader context of cetacean evolution. To date, Eocene specimens from Antarctica include basilosaurids, a group of archaic stem cetaceans that had already fully adapted to life in water; and the archaic toothed mysticete Llanocetus, the second oldest crown cetacean on record (ca. 34 Ma). This Eocene co-occurrence of stem and crown cetaceans is highly unusual, and otherwise only observed in Peru. Though related, at least some of the Antarctic species appear to be different from, and notably larger than their Peruvian counterparts, suggesting an early differentiation of the high latitude cetacean fauna.

Comments: This interesting new paper is a summary of recent papers on basilosaurids and the toothed mysticete Llanocetus from the Priabonian La Meseta Formation of Seymour Island, Antarctica. This unit is an important window into mid-Cenozoic marine vertebrate evolution in the southern ocean. This paper does report some interesting new specimens including a beautifully preserved mysticete pelvis *probably* (but not certainly) belonging to Llanocetus.

Churchill and Uhen. Taxonomic implications of morphometric analysis of earless seal limb bones. Acta Palaeontologica Polonica.

Link: https://www.app.pan.pl/article/item/app006072019.html

Abstract: Fossil Phocidae (earless seals) are mostly known from isolated postcranial material, forcing researchers to rely upon humeri and femora for the diagnosis of taxa and reconstruction of phylogeny. However, the utility of these elements has never been rigorously tested. Here, we provide the first quantitative analysis of morphometric data from the humerus and femur, incorporating measurement data from all extant genera as well as several fossil taxa. Principle components analysis (PCA) found that genera clustered together on PC1 and PC2, although there was poor segregation of taxa and extensive overlap with genera in adjacent regions of the morphospace. Discriminant function analysis (DFA) was able to sort fossil taxa into different subfamilies, but performed poorly at lower taxonomic levels. A preliminary review of phylogenetic characters found that while some characters performed well at distinguishing different subfamilies, many characters were poorly defined and not quantified, possessed greater individual variation than past studies suggested, or were more variable in fossil taxa. Our analyses suggest that the utility of isolated humeri and femora for diagnosis of new taxa has been greatly exaggerated, and that extreme caution should be applied to interpretations of taxonomy of fossil material based on isolated elements. Future research should instead focus on study of associated skeletons and cranial material. A thorough revision of fossil phocid taxonomy is needed, and many described taxa are likely to be nomina dubia and of limited use in phylogenetic analysis.

Comments: This sorely needed paper is a first stab at actually resolving the hopelessly confused study of fossil seal postcranial bones. Lots of noise has been made about limb bones being diagnostic and paleoecologically informative, with non-associated bones being jumbled together into discrete "ecomorphotypes". This paper critically evaluates these claims and finds that there is not much statistical support for the diagnostic value of isolated limb bones.

Collareta et al. A new kogiid sperm whale from northern Italy supports psychrospheric conditions in the early Pliocene Mediterranean Sea. Acta Palaeontologica Polonica.

Link: https://app.pan.pl/article/item/app005782018.html

Abstract: Among living cetaceans, dwarf and pygmy sperm whales (Kogia) are the only members of the family Kogiidae, regarded as diminutive and elusive relatives of the great sperm whale Physeter. Kogiids are known as fossils by several skulls, teeth, and ear bones from Neogene deposits of the Northern Hemisphere and Peru. We report on a fossil kogiid specimen collected at Sant’Andrea Bagni (northern Italy) from Zanclean marine mudstone; these deposits also yielded a rich deep-water elasmobranch assemblage depicting the presence of Atlantic-derived psychrospheric waters. The kogiid specimen, consisting of a partial cranium, one detached tooth, one vertebra, and one fragmentary rib, is here referred to Pliokogia apenninica gen. et sp. nov. Pliokogia is mostly characterised by a long and dorsally flattened rostrum and by the presence of two well-distinct fossae on the right side of the supracranial basin, including an elongated peripheral maxillary fossa on the posterior portion of the right maxilla. Our phylogenetic analysis recovers Pliokogia as a member of the subfamily Kogiinae, which includes Kogia, Koristocetus, Nanokogia, and Praekogia. A low temporal fossa and the absence of dental enamel suggest that, like extant Kogia, Pliokogia was a suction feeder. Since living kogiids do not inhabit the Mediterranean waters, and considering that they feed on deep-water prey in open-sea areas, the association of Pliokogia with a psychrospheric elasmobranch assemblage with Atlantic affinities is noteworthy. Indeed, in early Pliocene times, the Gibraltar connection was controlled by estuarine dynamics, thus allowing the entrance of deep-water organisms (including the putative prey of Pliokogia) in the Mediterranean Basin. The subsequent abandonment of the Mediterranean Sea by kogiids might therefore be related to the definitive establishment of the present-day antiestuarine circulation at Gibraltar, which likely led to a limited deep nutrient supply and resulted in the strong depletion of most Mediterranean deep-water ecosystems.

Cortes et al. Shark‑cetacean trophic interactions during the late Pliocene in the Central Eastern Pacific (Panama). Palaeontologia Electronica.

Link: https://palaeo-electronica.org/content/2019/2652-pliocene-whale-from-panama

Abstract: We provide a description of the remains of a fossil whale from western Panama. The record consists of appendicular remains of a mysticete, which has been assigned to Balaenopteridae. These remains, found in the sediments of the late Pliocene Burica Formation, represent the first record of a marine mammal in the Neogene sedimentary succession of the Burica Peninsula. Two different types of shark bite marks, serrated and deep-unserrated, found on the radius and phalanges suggest scavenging by at least two white shark (Carcharodon) individuals. The deep, unserrated marks were possibly caused by continual biting by sharks. Both the morphology of the shark bite marks and their relative location on the whale limb bones constitute evidence of shark-cetacean trophic interaction. Although the specimen lacks diagnostic features that would allow a species-level identification, it does provide new information on the vertebrate fauna of a very poorly prospected Central Eastern Pacific exposure, thus opening an opportunity for exploring the marine fauna during a critical episode in Earth history, the Plio-Pleistocene transition.

Cuitino et al. Factors affecting the preservation and distribution of cetaceans in the lower Miocene Gaiman Formation of Patagonia, Argentina. Palaeogeography, Palaeoclimatology, Palaeoecology.

Link: https://www.sciencedirect.com/science/article/abs/pii/S0031018218306904

Abstract: Factors affecting cetacean preservation and distribution in ancient sedimentary successions are not well understood. Actualistic studies have focused on coastal and deep marine examples, and little is known about taphonomic processes occurring within shelf environments. In this paper, we integrate sedimentological, taphonomic and palaeontological data for the cetacean-bearing lower Miocene Gaiman Formation from Patagonia, Argentina, to analyse which factors affected the distribution and preservation of cetaceans in several localities of the Southwestern Atlantic. Facies analysis shows that the formation represents a transgressive-regressive stratigraphic cycle, with palaeoenvironments including coastal, storm-dominated shoreface, inner shelf embayment and open inner shelf. Cetacean remains show preservation styles varying from isolated elements to articulated specimens, with nearly all remains restricted to both embayment and open marine inner shelf settings. Two fossil cetacean assemblages are recognized: Assemblage A comprises small-sized odontocetes dominated by Platanistoidea, preserved mostly in inner shelf embayment deposits; and Assemblage B comprises large-sized odontocetes and mysticetes, dominated by Physeteroidea and Balaenopteroidea, preserved mostly in open inner shelf deposits. Cetacean preservation style is controlled by a combination of palaeoenvironmental conditions, such as energy and sedimentation rate, and by biological factors, such as cetacean body plan and its impact on carcass buoyancy. Ecological factors may also explain the stratigraphic distribution of cetaceans between coastal and oceanic assemblages. This novel integrative and multidisciplinary analyses improves our knowledge of cetacean taphonomy in shelf environments.

Comments: This study claims to show evidence of habitat preference in ancient cetacean assemblages - I am skeptical owing to the process of bloat and float, and wonder what a larger sample of additional assemblages would show. Nevertheless, it is an interesting taphonomic study and food for thought.

Davydenko et al. The earliest record of a marine mammal (Cetacea: Basilosauridae) from the Eocene of the Amazonia. Journal of Vertebrate Paleontology.

Link: https://www.tandfonline.com/doi/full/10.1080/02724634.2018.1549060

Abstract: The Amazon region is known by its rich Cenozoic mammalian diversity; however, fully aquatic mammals (cetaceans and sirenians) appear in its fossil record only from the Miocene, and solely as freshwater forms (Antoine et al., 2017). Meanwhile, during the Eocene, there were marine basins deeply intruding into the South American continent and reaching its inner regions (Louterbach et al., 2014); therefore, marine mammals could have inhabited Amazonia during that time. Here, we report the first record of an Eocene marine mammal, namely, a cetacean of the family Basilosauridae, from the northwestern Amazon region and discuss its taxonomic and morphological affinities, as well as its environment in the context of the geographic distribution of basilosaurids during the Eocene.

Diaz-Berenguer et al. The Hind Limbs of Sobrarbesiren cardieli (Eocene, Northeastern Spain) and New Insights into the Locomotion Capabilities of the Quadrupedal Sirenians. Journal of Mammalian Evolution.

Link: https://link.springer.com/article/10.1007%2Fs10914-019-09482-9

Abstract: In the transition from a terrestrial to an aquatic environment, sirenian marine mammals reduced and lost their hind limbs and developed a horizontal caudal fin, the main propulsive organ in extant sirenians. Quadrupedal forms are only known from the Eocene and are represented by three different clades: the amphibious “prorastomids,” the aquatic quadrupedal protosirenids, and Sobrarbesiren cardieli, a four-legged sirenian from the middle Eocene of Spain, considered the sister taxon of the fully aquatic Dugongidae. This ecological shift from terrestrial to an aquatic environment was naturally associated with adaptations, among others, of the skeleton. However, sirenian hind limb bones have been poorly studied because of the scarce material available in the fossil record. Here, we describe in detail the hind limb bones of Sobrarbesiren, analyzing their functional morphology and comparing them with other basal sirenians and cetaceans, and with related terrestrial mammals such as proboscideans and hyracoids. The hind limbs of Sobrarbesiren were capable of a great variety of movements. Based on the presence of a strong sacroiliac articulation, we propose that it swam by dorsoventral pelvic undulation combined with pelvic paddling analogous to extant otters and the “prorastomid” Pezosiren. We also conduct the first microanatomical analysis of hind limb bones of an Eocene sirenian. Data reveal extreme inner compactness in the Sobrarbesiren innominate and femur, with the first description of osteosclerosis in an amniote innominate combined with the highest degree of osteosclerosis observed in amniote femora. The results confirm that the microanatomical changes precede the external morphological changes in such ecological transitions. The process of adaptation of sirenians to an aquatic life was thus a more complex process than previously thought.

Di Celma et al. Allostratigraphy and paleontology of the lower Miocene Chilcatay Formation in
the Zamaca area, East Pisco basin, southern Peru. Journal of Maps.

Link: https://www.tandfonline.com/doi/full/10.1080/17445647.2019.1604439?af=R

Abstract: Based on mapping of laterally traceable stratigraphic discontinuities, we propose a high-resolution allostratigraphic scheme for one of the world’s foremost fossil marine vertebrate Lagerstätten: the lower Miocene strata of the Chilcatay Formation exposed along the Ica River near Zamaca, southern Peru. Measured sections combined with 1:10,000 scale mapping of a 24 km2 area provide an overview of the stratal architecture, as well as a general facies framework and interpretation of the various depositional settings. As a whole, the Chilcatay alloformation is bounded by the CE0.1 unconformity at the base and the PE0.0 unconformity at the top. An internal Chilcatay surface, termed CE0.2, splits the alloformation into two distinct allomembers (Ct1 and Ct2). The Ct1 allomember comprises three facies associations recording deposition in shoreface, offshore, and subaqueous delta settings. The Ct2 allomember comprises two facies associations, recording deposition in shoreface and offshore settings. Using these data, we place the rich marine vertebrate assemblage in a precise spatial and stratigraphic framework. The well-diversified vertebrate assemblage is dominated by cetaceans (mostly odontocetes) and sharks (mostly lamniforms and carcharhiniforms); rays, bony fish, and turtles are also present. Taxonomic novelties include the first records of baleen whales, platanistids, and eurhinodelphinids from the Chilcatay Formation.

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