Heavy rains in Alaska led to the decline of dry-loving dinosaurs

(ORDO NEWS) — Scientists have found out how the climate in the Late Cretaceous period influenced the distribution of large herbivorous dinosaurs in Alaska – ceratopsids and hadrosaurids.

It turned out that the average annual rainfall was more strongly correlated with the abundance of these dinosaurs than the average annual temperature.

At the same time, hadrosaurids preferred wet conditions, while ceratopsids preferred drier conditions. The study is published in the journal Geosciences.

Alaska at the end of the Late Cretaceous was warmer than today, but still the temperature in winter fell below zero. Despite this, a large number of dinosaur fossils have been found here.

Previously, scientists assumed that with the onset of cold weather, dinosaurs migrated south, but subsequent finds of baby fossils indicated that dinosaurs lived here all year round.

This proves once again that in non-avian dinosaurs, at least in some groups, body temperature did not depend on environmental conditions.

Representatives of two groups prevailed among the large herbivorous dinosaurs of Alaska: ceratopsids (Ceratopsidae) and hadrosaurids (Hadrosauridae).

Today, large herbivorous animals such as elephants are key species in their ecosystems, so paleontologists and geologists from the US and Japan, led by Anthony R. Fiorillo of Southern Methodist University, set out to find out how climate influenced the distribution of ceratopsids and hadrosaurids.

They selected three Alaskan formations for analysis: Prince Creek Formation, lower Cantwell Formation, and Chignik Formation. The age of the formations is dated from Campanian to Maastrichtian (83.6–66 million years ago).

Heavy rains in Alaska led to the decline of dry loving dinosaurs 2
The location of the formations today (A) and in the Late Cretaceous (B). 1 – Prince Creek, 2 – Cantwell, 3 – Chignik
Heavy rains in Alaska led to the decline of dry loving dinosaurs 3
Prince Creek, Cantwell, and Chignik formations on a stratigraphic scale

The mean annual rainfall (AMPR) for Prince Creek and Cantwell and the mean annual temperature (MGT) for all formations were sourced from the literature, while the AGMR for the Chignik Formation was self-calculated using the relationship between the AMMR and the ratio of stable carbon isotopes in plants (in in this case, in fossil wood). Calculations showed that the SGTR for the Chignik formation is 1090 millimeters per year.

Heavy rains in Alaska led to the decline of dry loving dinosaurs 4
Average annual temperature (in degrees Celsius)

The researchers also analyzed the abundance of hadrosaurids and ceratopsids based on bone material for the Prince Creek Formation and based on footprints for two other formations.

It turned out that Prince Creek and Cantwell were dominated by hadrosaurids (83 and 73 percent, respectively), while ceratopsids were absent in the Chignik Formation. The scientists then set out to find out how the abundance of these dinosaurs correlated with climate data.

It turned out that the abundance of hadrosaurids was higher in humid conditions (the Chignik and Prince Creek Formations), and ceratopsids were higher in drier conditions (the Cantwell Formation).

At the same time, hadrosaurids were characterized by a high abundance at low and high values ​​of the mean annual temperature, while ceratopsids were characterized by a high abundance at medium values ​​of this indicator.

Thus, the average annual rainfall is more strongly correlated with the abundance of these dinosaurs than the average annual temperature.

Heavy rains in Alaska led to the decline of dry loving dinosaurs 5
The number of large herbivorous dinosaurs of Alaska depending on: A – average annual rainfall, B – average annual temperature

The scientists note that the results are consistent with previous studies, in particular with work in which, using the analysis of stable isotopes in dinosaur tooth enamel, it was shown that hadrosaurids foraged in coastal areas, and ceratopsids far from them.

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