Megalodon's extinction date by Pimiento

[Grey]

When Did Carcharocles megalodon Become Extinct? A New Analysis of the Fossil Record

Abstract

Carcharocles megalodon (“Megalodon”) is the largest shark that ever lived. Based on its distribution, dental morphology, and associated fauna, it has been suggested that this species was a cosmopolitan apex predator that fed on marine mammals from the middle Miocene to the Pliocene (15.9–2.6 Ma). Prevailing theory suggests that the extinction of apex predators affects ecosystem dynamics. Accordingly, knowing the time of extinction of C. megalodon is a fundamental step towards understanding the effects of such an event in ancient communities. However, the time of extinction of this important species has never been quantitatively assessed. Here, we synthesize the most recent records of C. megalodon from the literature and scientific collections and infer the date of its extinction by making a novel use of the Optimal Linear Estimation (OLE) model. Our results suggest that C. megalodon went extinct around 2.6 Ma. Furthermore, when contrasting our results with known ecological and macroevolutionary trends in marine mammals, it became evident that the modern composition and function of modern gigantic filter-feeding whales was established after the extinction of C. megalodon. Consequently, the study of the time of extinction of C. megalodon provides the basis to improve our understanding of the responses of marine species to the removal of apex predators, presenting a deep-time perspective for the conservation of modern ecosystems.


www.plosone.org/article/info:doi/10.1371/journal.pone.0111086

So, Meg went extinct about 2.6 millions ears ago and it seems like the gigantic mysticetes species only became common after the extinction of the predator. This evaluation will need further investigation though. Mike Siversson similarly suggests that the larger O. orca evolved after Meg's extinction to become the top predators.
Recently found very large cetotheres and balaenopterids from Late Miocene and Early Pliocene might mabe complicate this a bit.

Now remains to wait the paper about the chronoclinal changes in Meg through time.

[creature386]

Doesn't appear far off from the formerly reported 3 million, but the information about the whales is still interesting. I guess we can now conclude that the hypothesis of prey moving into cold waters (that Grey has defended) is the most likely.

[Life]

Evolution of modern Mysteciti whales apparently began during Miocene epoch; the earliest known specimen, identified as Eobalaenoptera harrisoni, is estimated 14 myo (Dooley, Fraser, & Luo, 2004), as far as I am aware. Holistically, this evolutionary process represents development of advanced filter-feeding apparatus, increase in size, and improvement in morphological characteristics associated with swimming and aerobic performance, in Mysteciti whales.

For this topic, Diedrich (2013) provided an excellent snapshot of evolutionary processes of sharks and marine mammals and their linkages throughout history since Paleocene to modern times. More importantly, Diedrich (2013) thoroughly explored the phenomenon of divergence in macropredatory sharks resulting in development of two distinct lineages such as small-toothed Carcharodon lineage and mega-toothed Otodus lineage. The small-toothed Carcharodon lineage continues in modern times with C. carcharias (Great White Shark). The mega-toothed Otodus lineage has ended with extinction of its last known member O. megalodon (Megalodon) during Plio-Pliestocene times. With this information in mind, it is important to pay attention to paleobiographical ground realities of distribution pattern and prey preferences of these lineages throughout ages; Purdy (1996) and Diedrich (2013) have explored these ground realities in great detail addressing lot of misconceptions and confusion along the way.

3.6. Prey Migrations, Water Temperatures, and Shark Paleobiogeography

The new sieving of Middle Eocene material from northwest Germany yielded 2 teeth from the German megatooth shark O. sokolovi [10] (but more then 100 larger teeth are present from another collection of HF), supporting the theory, that megatooth sharks in general were occasionally present in colder oceans/waters and may have migrated through these upwelling and temperate basin areas [1]. The O. sokolovi megatooth sharks were far less abundant (2 teeth recovered) in the Eocene proto North Sea Basin than the C. auriculatus white sharks (455 teeth recovered) [10]. The megatooth sharks may have followed large, migratory mammal prey such as whales and sirenians, which are likely to have made use of the seasonal warm surface-water currents of the Tethys for north- and east-westward migration (Figure 1). Further support for this theory can be found in the same region, but from the Late Oligocene. The northern German Doberg fauna contains remains of the toothed whale Eosqualodon, as well as remains of the siren Anomotherium [31] and the large teeth from its megatooth shark predator O. angustidens [13], but white shark teeth are unknown in the Late Oligocene of northern Germany, yet, also because there are shark-tooth enriched condensation bonebeds absent (teeth are “rare”). Thus the abundant white shark C. auriculatus must have lived in cold-water areas of upwelling, as demonstrated in the Proto North Sea Basin [10]. This temperature control on the distribution of these predatory sharks has also been recorded in more recent periods (extending from the Oligocene to the Pliocene) all around the world [1]. There is a clear correlation in the fossil record between the scarcity of both, megatooth shark ancestors and their prey (whales and sirenians) [1] in areas of cold water upwelling, and the abundance of white sharks, together with seals in some of those areas [1], such as demonstrated herein for the Proto North Sea basin of Europe.

(Diedrich, 2013)

In addition:

Both, megatooth and white shark lineages exhibited convergent serrated saw-blade teeth, but with different (massive or non-massive) roots in the lateral teeth, different dental formulas, and different maximal sizes. The “saw-blade” teeth were the result of adaptation to feeding on various marine mammals, and their development coinciding with the emergence of seals, sirenians, and whales in parallel with the evolution of these large predatory sharks during the Late Paleocene to Early Eocene.

Megatooth sharks specialized in hunting whales and sirenians on the coastal shelves of warm oceans, but also migrated with warm surface currents into northern areas of upwelling in which fishes were abundant, which has been shown from the northernmost records of the Proto North Sea Basin shelf, in northern Europe.

The white sharks, however, were adapted to cold and temperate waters. While the immature white sharks may have hunted in fish-rich areas, the adult sharks must have fed mainly on the early seal populations, along the coastlines of their reproduction beaches which also appear to have been located in cool to temperate waters (southern proto North Sea Basin). This specialization of white sharks in hunting seals, especially in the vicinity of seal colonies, has continued to the present, for example with the great white sharks hunting seals along the Californian and South African coastlines (Figure 6).

With a second marine mammal radiation in the mid- Oligocene and a third radiation during the Middle Miocene, the tooth morphology of megatooth sharks and white sharks developed further, with both lineages again showing similar types of adaptation. The lateral tooth cusplets became smaller, while oppositely the crown base widened and even the overall tooth size enlarged (= “saw blade type”), but this development was much more marked in the megatooth sharks, as they grew in size proportional to their large whale prey during the Neogene, during which time whales became larger, marine mammals radiated once again, and the modern dolphins emerged (in the Serravallian/Tortonian of the Middle/Late Miocene). In parallel with the third marine mammal radiation, a secondary serration evolution again took place again in “short-term” within the Isurus lineage (from I. hastalis to I. escheri), which later became extinct at the beginning of the Pleistocene “Ice Age”, as did the megatooth sharks.

Whereas the warm-water adapted megatooth sharks disappeared globally in the Pleistocene due to climate change and ocean cooling, the cold-water adapted white sharks have survived more than 57 m.y. until the present day as specialized coastal seal hunters. Adult great white sharks today feed on modern seals in temperate to warm seawaters, indicating that they must have modified their habitat during the Ice Age, and even their body temperatures, to take over the niche vacated by the extinction of the megatooth sharks. Mature individuals now also feed on whales and sirenians but still predominantly on seals, as they have started to feed on a new marine mammal prey source for more than 50 million years.

(Diedrich, 2013)

Purdy (1996) have matching observations though he also noted that small-toothed Carcharodon sharks apparently avoided distribution pattern of mega-toothed Otodus sharks throughout history. Probable reasons include differences in habitats of both lineages and predator-avoidance based segregation with small-toothed Carcharodon sharks avoiding interaction with mega-toothed Otodus sharks on purpose (i.e. safety).

Now what exactly went wrong?

We come back to the subject of marine mammals. A careful observation of numerous published literature reveals that marine mammals attained enormous diversity during Miocene epoch but a pattern of decline in diversity and abundance of cetaceans is visible within (Late) Miocene - Pliestocene interval; 20+ genera reduced to 6 (extant) genera. This pattern coincides with geographical changes during this interval including formation of Isthmus of Panama during Pliocene epoch which significantly altered the dynamics of marine ecosystem globally and also accelerated global cooling patterns. In addition, fossil records of modern whales indicate that they adapted to cooling patterns and demonstrated increased activity in polar regions, possibly shifting from tropics to polar regions as a predator-avoidance strategy. These paleoecological developments seem to have challenged the sustenance and survival of mega-toothed Otodus lineage globally. In contrast, small-toothed Carcharodon lineage flourished because it had adapted to cooling patterns and less demanding prey preferences much earlier in history; characteristics such as moderate size and endothermy proved to be beneficial for long-term survival.