Odontocetes first appeared in the fossil record by the early Oligocene, and their early evolutionary history can provide clues as to how some of their unique adaptations, such as echolocation, ...evolved. Here, three new specimens from the early to late Oligocene Pysht Formation are described further increasing our understanding of the richness and diversity of early odontocetes, particularly for the North Pacific. Phylogenetic analysis shows that the new specimens are part of a more inclusive, redefined Simocetidae, which now includes
,
sp. 1,
,
sp. nov., and a large unnamed taxon (Simocetidae gen. et sp. A), all part of a North Pacific clade that represents one of the earliest diverging groups of odontocetes. Amongst these,
sp. nov. represents one of the best known simocetids, offering new information on the cranial and dental morphology of early odontocetes. Furthermore, the inclusion of CCNHM 1000, here considered to represent a neonate of
sp., as part of the Simocetidae, suggests that members of this group may not have had the capability of ultrasonic hearing, at least during their early ontogenetic stages. Based on the new specimens, the dentition of simocetids is interpreted as being plesiomorphic, with a tooth count more akin to that of basilosaurids and early toothed mysticetes, while other features of the skull and hyoid suggest various forms of prey acquisition, including raptorial or combined feeding in
spp., and suction feeding in
. Finally, body size estimates show that small to moderately large taxa are present in Simocetidae, with the largest taxon represented by Simocetidae gen. et sp. A with an estimated body length of 3 m, which places it as the largest known simocetid, and amongst the largest Oligocene odontocetes. The new specimens described here add to a growing list of Oligocene marine tetrapods from the North Pacific, further promoting faunistic comparisons across other contemporaneous and younger assemblages, that will allow for an improved understanding of the evolution of marine faunas in the region.
Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this diversity are largely unknown. High primary production of modern oceans is considered a ...prerequisite for the emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We describe the new giant ichthyosaur
sp. nov. with a 2-meter-long skull from the Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.
Biogeographical distributional patterns of cetaceans reflect dispersal events and colonization of the oceans from their ancestral area in the ancient Sea of Tethys ~53 Ma. Likewise, they reveal ...several vicariance events throughout the evolutionary history of this group. However, our understanding of how these processes took place and what biogeographical scenarios occurred among the different groups of cetaceans through time is limited. Consequently, this work focuses on explaining the distributional patterns of the well‐known North Pacific toothed mysticetes, Aetiocetidae, through the power of retrodiction offered by track analysis (panbiogeography) and cladistic biogeography, using the approach of evolutionary biogeography. Our results show that the distributional patterns of Aetiocetidae explain their endemism in the North Pacific, as well as indicating that their hypothetical ancestor probably colonized the Pacific from the Atlantic Ocean by a dispersal event (founder effect) via the Central American Seaway. Furthermore, their biogeographical history shows that the adaptive radiation (cladogenesis) of Aetiocetidae is result of peripatric speciation followed by sympatric speciation within a heterogeneous environment. Finally, the biogeographical framework of Aetiocetidae further supports the relevant role that the Pacific Ocean has played in the evolution of Oligocene cetaceans as a geographical area that promoted endemism, dispersal and colonization. At more local scales, environmental conditions further promoted increased diversity and disparity amongst Mysticeti.
Aim: Given its catastrophic consequences, the extinction of apex predators has long been of interest to modern ecology. Despite major declines, no presentday species of marine apex predator has yet ...become extinct. Because of their vulnerability, understanding the mechanisms leading to their extinction in the past could provide insight into the natural factors that interact with human threats to drive their loss. We studied the geographical distribution patterns of the extinct macro-predatory shark Carcharocles megalodon in order to elucidate its pathway to extinction. Location: World-wide from the Miocene to the Pliocene (c. 23-2.6 Ma). Methods: A meta-analysis of C. megalodon occurrence records was performed using the Paleobiology Database as a platform. The data were binned into geological time slices, and the circular home range around each data point was mapped in reconstructions made in GPlates. We then quantitatively assessed the species' geographical range and global abundance over time, and the relationship between distribution and climate. Results: The pathway to extinction of C. megalodon probably started in the late Miocene with a decrease in its global abundance. This decrease was then followed by a decline in its geographical range during the Pliocene. Although the extinction of C. megalodon has been attributed to climate change, we found no evidence of direct effects of global temperature. Instead, we found that the collapse in geographical distribution coincided mainly with a drop in the diversity of filter-feeding whales and the appearance of new competitors (large predatory whales and the great white shark). Main conclusions: This research represents the first study of the distributional trends of an extinct, cosmopolitan apex predator in deep-time. Our results suggest that biotic factors, and not direct temperature limitations, were probably the primary drivers of the extinction of the largest marine apex predators that ever lived.
A new taxon of stem otariid,
sp. nov., is described from the upper Burdigalian to lower Langhian "Topanga" formation of Orange County, California. The new species is described from mandibular and ...dental remains that show a unique combination of plesiomorphic and derived characters. Specifically, it is characterized by having trenchant and prominent paraconid cusps in p3-m1, lingual cingula of p2-4 with faint crenulations, premolars and molars with vestigial metaconid, bilobed root of m2 and a genial tuberosity located under p3. Furthermore, additional material of the contemporaneous
is described, providing new information on the morphology of this taxon. Both species of
represent the earliest stem otariids, reinforcing the hypothesis that the group originated in the north Eastern Pacific Region. At present, the "Topanga" Fm. pinniped fauna includes
,
, the desmatophocid
sp., the odobenids
sp.,
sp. and includes the oldest records of crown pinnipeds in California. Overall this pinniped fauna is similar to the nearly contemporaneous Sharktooth Hill bonebed. However, unambiguous records of
are still missing from Sharktooth Hill. This absence may be due to taphonomic or paleoenvironmental factors. The new "Topanga" record presented here was integrated into an overview of the late Oligocene through early Pleistocene pinniped faunas of Southern California. The results show an overall increase in body size over time until the Pleistocene. Furthermore, desmatophocids were the largest pinnipeds during the middle Miocene, but were extinct by the beginning of the late Miocene. Odobenids diversified and became the dominant pinnipeds in late Miocene through Pleistocene assemblages, usually approaching or exceeding 3 m in body length, while otariids remained as the smallest taxa. This pattern contrasts with modern assemblages, in which the phocid
is the largest pinniped taxon in the region, odobenids are extinct and medium and small size ranges are occupied by otariids or other phocids.
Seagrasses are a notable component of shallow marine habitats, especially in tropical and subtropical regions. Their fossil record extends back to the Mesozoic, but it is relatively poor and ...fragmentary, with large temporal and geographical gaps. As a result, very little is known about the paleobiogeography of these plants and how physical drivers, such as climatic or oceanic events, have affected their distribution. One approach is to infer the past distribution of seagrasses using fossils of organisms dependent of seagrasses with more complete records as proxies.
Seagrass consumers, such as sirenians (seacows, manatees and dugongs), are much better represented in the fossil record than seagrasses are. The characteristically dense bones of sirenians together with the fact that they are usually found in marginal marine environments increases the potential for preservation and recognition of their fossils. The long evolutionary history of sirenians, extending throughout most of the last 50Ma, together with their diet permits the use of their fossils as a proxy for inferring the paleobiogeography of seagrasses.
Here I looked at the fossil record of sirenians and seagrasses from the Eocene, through the Miocene epochs. This comparison produced several inferences about seagrass paleobiogeography and how physical drivers, such as climate change, ocean currents and tectonic events, have been influential in their distribution: 1) seagrasses were well-established in the Western Atlantic–Caribbean prior to the middle Eocene, making possible at least two instances of trans-Atlantic sirenian dispersal events, either with the aid of Tethyan currents or along the nearly continuous Northern Atlantic coastline that was present in the Eocene; 2) climatic cooling during the early Oligocene seemed to have limited the extent of seagrasses and sirenians, although these groups recovered and further diversified and expanded their distributions by the late Oligocene in tandem with a climatic warming event; 3) by the Miocene, seagrasses and sirenians reached the southern Western Atlantic and the Eastern Pacific aided by the presence of the Central American Seaway, achieving a distribution similar to, and sometimes, surpassing that of today. The fossil record of sirenians can provide a broad overview of seagrass paleobiogeography through time. However, several aspects, such as when sirenians and seagrasses arrived to Australia and the seemingly late arrival of seagrasses to South America and the Eastern Pacific, still need further investigation.
•Seagrasses fossils are scarce; proxies are used to infer their ancient distribution.•Sirenians serve as a good proxy for the presence of seagrasses.•Physical drivers played a prominent role in the paleobiogeography of sirenians.•Early Oligocene climate cooling constricted the range of seagrasses and sirenians.•Seagrasses show near modern day distribution at least since the middle-late Miocene.
Sloths were among the most diverse groups of land vertebrates that inhabited the Greater Antilles until their extinction in the middle-late Holocene following the arrival of humans to the islands. ...Although the fossil record of the group is well known from Quaternary deposits in Cuba, Hispaniola, and Puerto Rico, remains from older units are scarce, limiting our understanding of their evolution and biogeographic history. Here we report the oldest known fossil ground sloth from Hispaniola, represented by an unassociated partial tibia and scapula that are recognized as a single taxon from the late Miocene-early Pliocene of the Dominican Republic. The combination of characters observed on the tibia suggests a close relationship with Megalocnus, otherwise only known from the Pleistocene–Holocene of Cuba. These fossils fill a temporal gap between those previously known from the early Miocene of Cuba and those from Pleistocene–Holocene deposits in the region and provide additional support for a continuous presence of the group in the Greater Antilles since the Oligocene.
Odontocetes first appear in the fossil record during the early Oligocene and soon after show a near-worldwide distribution. However, little is still known of their early diversity, especially in the ...North Pacific Region. A new taxon of stem odontocete with heterodont dentition, Olympicetus avitus, gen. et sp. nov., is described herein from the upper Oligocene Pysht Formation in Washington State, U.S.A. The material consists of two partial skulls belonging to a juvenile and a neonate and includes part of the dentition and a tympanic bulla. Olympicetus shares many similarities with the Oligocene odontocetes Simocetus rayi and Ashleycetus planicapitis but displays a combination of characters that distinguish it from these and other coeval taxa. A phylogenetic analysis shows Olympicetus in a polytomy with Xenorophidae, a clade of early high-frequency-hearing odontocetes mainly known from the western Atlantic. Furthermore, Olympicetus displays characters that can be considered as structural proxies for echolocation, such as having premaxillary sac fossae and the maxilla expanded over the frontal. In addition to Olympicetus, other marine tetrapods from the Pysht Formation include marine birds, desmostylians, pinnipeds, and early mysticetes, giving us a unique insight into late Oligocene marine tetrapod faunas of the North Pacific.
Fossil cetaceans are often found in Miocene marine outcrops across the globe. However, because this record is not homogeneous, the dissimilar increase in occurrences, along with the sampling bias has ...created regions with extensive records and others with great scarcity. Among these, the Caribbean has remained enigmatic due to the lack of well-preserved cetacean fossils. Here, we report new Caribbean fossil cetaceans from the Upper Miocene Chagres Formation exposed along Piña beach, Eastern Panama, including a scaphokogiine kogiid, an
-like physeteroid and the phocoenid
. Along with previous records of the iniid
and the kogiine
, the Chagres cetacean fauna shows some similarities with other Late Miocene cetacean communities such as the Californias in the North Pacific, although their closest affinities lie with the eastern South Pacific Pisco Formation, Peru. Such findings indicate that though deep and intermediate Caribbean-Pacific water interchange was reduced by the Middle Miocene due to the shallowing of the Central American Seaway, shallow waters marine connection that persisted until the Pliocene might have facilitated the dispersal of coastal species across both sides of the Isthmus.
Land-to-sea evolutionary transitions are great transformations where terrestrial amniote clades returned to aquatic environments. These secondarily aquatic amniote clades include charismatic marine ...mammal and marine reptile groups, as well as countless semi-aquatic forms that modified their terrestrial locomotor anatomy to varying degrees to be suited for swimming via axial and/or appendicular propulsion. The terrestrial ancestors of secondarily aquatic groups would have started off swimming strikingly differently from one another given their evolutionary histories, as inferred by the way modern terrestrial amniotes swim. With such stark locomotor functional differences between reptiles and mammals, we ask if this impacted these transitions. Axial propulsion appears favored by aquatic descendants of terrestrially sprawling quadrupedal reptiles, with exceptions. Appendicular propulsion is more prevalent across the aquatic descendants of ancestrally parasagittal-postured mammals, particularly early transitioning forms. Ancestral terrestrial anatomical differences that precede secondarily aquatic invasions between mammals and reptiles, as well as the distribution of axial and appendicular swimming in secondarily aquatic clades, may indicate that ancestral terrestrial locomotor anatomy played a role, potentially in both constraint and facilitation, in certain aquatic locomotion styles. This perspective of the land-to-sea transition can lead to new avenues of functional, biomechanical, and developmental study of secondarily aquatic transitions.
PDF
