Environmental constraints on terrestrial vertebrate behaviour and reproduction in the high Arctic of the Late Cretaceous

Abstract

Reconstructions of temperature and moisture regimes based on fossil leaves, combined with tree ring studies, detail the light regime, length of the growing season, and summer and winter temperatures of the Late Cretaceous Arctic. Such constraints have important implications for dinosaur feeding and reproductive behaviour, and the capacity to reside year-round in near-polar environments.At the highest palaeolatitudes where dinosaurs have been found (82-85 °N) winter darkness lasted for ~120 days and the spring and autumn twilight periods for ~15 days. A * Corresponding author. E-mail address: alexeiherman@yandex.ru (A.B. Herman) Telephone/fax number +7(495) )953-5984/951-0443 ACCEPTED MANUSCRIPT2 mostly cloud and mist-shrouded environment witnessed a mean annual temperature (MAT) of 6-7 °C, a warm month mean temperature (WMMT) of 14.5 ± 3.1 °C and a cold month mean temperature (CMMT) of -2 ± 3.9 °C. Growth rings in wood suggest summer temperatures frequently fell below +10 °C. Winter temperatures as low as -10 °C were likely for short periods. Spring bud break in late February to early March and leaf fall in early October limited the time when fresh food was available in any quantity to not more than 6 months.The diversity of Arctic dinosaur body sizes implies a range of overwintering strategies but year-round residency requires reproduction. Burrowing and enclosed nest building no doubt facilitated overwintering for small animals, but for larger dinosaurs shelter was problematical. No dinosaur egg remains have yet been found as far north as 82° palaeolatitude, but they occur 6° further south in the Early Maastrichtian Kakanaut Formation, Northeastern Russia. Here the winter darkness was shorter (45 days), and the temperature regime warmer (MAT 10 °C, WMMT 19 °C, CMMT +3 °C). The growing season (temperatures > 10 °C) was ~6.3 months and fresh food was available in quantity for slightly longer. These summer temperatures constrain the thermal regime of nest environments and suggest sophisticated nest management and possibly brooding strategies for the necessary rapid incubation and hatching before the onset of winter.

Palaeoclimatic reconstruction for a Cenomanian‐aged angiosperm flora near Schefferville, Labrador

“…The growing season would have been far longer than that of more extreme environments such as Late Cretaceous Alaska's polar deciduous forests (Herman et al . ), which is not surprising considering the Redmond Formation's intermediate palaeolatitude and coincidentally long photoperiod. These quantitative results confer on the Redmond no.1 site a warm temperate and fully humid climate with a hot summer (Cfa) (Kottek et al .…”

“…Comparative CLAMP values were obtained from GRIDMET3BR analyses of three sites: Tuscaloosa, Woodbine (Spicer & Herman ) and Nanushuk (Herman et al . ). Additionally, two floras from the Dakota Formation (age Cenomanian) were scored for CLAMP estimates (see Material and Method, above) to increase the Cenomanian site sample size.…”

“…Raritan (36.4°N) (Wolfe & Upchurch ); Patapsco (36.4°N) (Wolfe & Upchurch ); Tuscaloosa (31.7°N) (Spicer & Herman ); Woodbine (37.4°N) (Wolfe & Upchurch (LMA); Spicer & Herman (CLAMP)); Rose Creek (40.2°N) (this study); Fort Harker (Dakota) (39.0°N) (Wolfe & Upchurch, (LMA); this study (CLAMP)); Redmond (Redmond) (48.8°N) (Hickey & Armstrong (LMA); this study (CLAMP)); Dunvegan (58.4°N) (Wolfe & Upchurch ); Chandler (78.0°N) (Parrish & Spicer ); Nanushuk (79.5°N) (Herman et al . ). Minimum and maximum palaeolatitude estimates for each point projected as error bars.…”

“…These additional variables provide more insight into an extinct ecosystem's seasonal cycle and photoperiod (Herman et al . ). By acknowledging the covariation between many leaf traits and multiple environmental factors (Dolph & Dilcher ), CLAMP assumes that a climate signal can be obtained from more correlations than the single correlation on which LMA is founded (Wolfe ; Spicer ; Yang et al .…”

“…This would also make it one of the earliest known woody dicot floras to flourish far inland, alongside assemblages from central Alaska's Yukon–Koyukuk basin (Herman et al . ), Siberia's Vilui basin (Spicer et al . ) and the Winton Formation of central‐western Queensland (Fletcher et al .…”