This fossil specimen is preserved as an impression, the fossil as a whole is relatively well preserved, and the color of the specimen is brown. The pod is oblong, with an aspect ratio of 5:1 (5 cm in length and 1cm in width), the pod is relatively full, the base is incompletely preserved, the tip is rounded with a rostral tip, the suture is straight, the pod has an inconspicuous double wing and dehiscences after maturation; the seeds are spherical, six are preserved, flattened in shape and about 10 mm in diameter.

The fossil is orthogonal and antisymmetric on both sides, this fossil specimen is preserved as an impression, the fossil as a whole is relatively well preserved, and the color of the specimen is brown. The pod is cuneate, broad at the base, flattened, with a length-to-width ratio of 2:1, and single-winged, but the wing pattern is not obvious. The apical part of the pod is short beak-shaped on the side of the ventral suture line and semicircular on the side of the dorsal suture line, the ventral suture line is wider than the dorsal suture line, and both edges are nearly flat; no seed traces are seen, and several grooves can be seen on the side of the ventral suture line, which may be traces of the striae or equivalent to the “seed overflow” structure.

Legumes are capable of adapting to the tropics, and it is widely distributed globally, with its centers of distribution in Africa-Madagascar, tropical America, and southeastern North America, which coincides with the fossil record [14] . Leguminose-related taxa are thought to have originated in the humid tropics during the Late Cretaceous [15] , with the earliest plausible legume fossils found on the African continent (Late Cretaceous or Paleocene) [14] . The paleoclimate of the above-mentioned Late Eocene legume pod fossils from western North America was analyzed using the “extant proximate species method”. A total of five fossil specimens were identified with a total of three genera and four species. Among them, the genus Acacia was numerically dominant, while most of the modern legumes’ modern relatives were distributed in tropical-subtropical regions (Figure 2).

As the Eocene subtropical vegetation in the northern hemisphere moved northward from its modern limits, the distribution of the genus migrated from higher to lower latitudes and the fossil record decreased, and the fossil record of the genus after the Pliocene was mainly found in Oceania [16] . The following figure shows the distribution of Late Eocene legume fossils and extant legumes. It is clear that the Late Eocene legume fossils were widely distributed, and the modern legume distribution area was narrowed and concentrated in tropical-subtropical regions, while the dry climate of western North America today can indicate that the western North America was warm and humid in the Late Eocene at that time.

The modern species of Acacia are basically distributed in tropical and subtropical regions, with latitudes of 0˚N-27˚N, 0˚S-14˚S, and longitudes of 28˚E-122˚E. The main production areas are Oceania, and southwestern to eastern China are the main production areas. The modern species of this genus are mainly distributed in East Africa, and in Asia in India, Myanmar, Sri Lanka and other countries. China’s Guangdong, Guangxi and other places have the genus Acacia in the vine Acacia [17] .

From the following figure (Figure 3 and Figure 4), it can be seen that the distribution of fossils of the genus Acacia in the Late Eocene is wide and the latitude of distribution is higher than that of the extant genus.

The Late Eocene fossils of Acacia spp. were distributed in western North America, but there is no extant distribution of Acacia spp. in western North America today, and the present western North America has a temperate arid climate, so the fossil distribution of Acacia spp. and the distribution of extant species of the genus can indicate a humid climate in western North America in the Late Eocene.

The distribution range of extant Bauhinia and the fossil record of Late Eocene Bauhinia spp. are shown in Figure 5. Late Eocene Bauhinia spp. have fossil records in North America, Colorado, USA, and Oregon, USA, and there are no fossil records elsewhere [13] . The Oligocene genus Bauhinia is distributed in

North America, Europe, and Asia, and there are more fossil localities. The Miocene genus Bauhinia is most widely distributed in the Asian region.

The extant genus Bauhinia is mainly distributed in the mid-latitudes of the Northern Hemisphere, mostly in the northern temperate zone, with a latitude of 15˚N-54˚N, longitude of 14˚E-122˚E, and 65˚W-128˚W. Bauhinia is one of the most widely distributed species in the genus Bauhinia, and is common in provinces and regions from the southwest to Yunnan, as well as in the eastern provinces and regions along the south of the Yangtze River, with a relatively wide range of growth environments [17] .

As can be seen from the figure (Figure 5), the latitude of distribution of fossil Bauhinia spp. in western North America in the Late Eocene is similar to that of the extant species, and the difference is not significant, but the distribution range of the fossil species is smaller than that of the extant species. Therefore, the distribution of fossils of the genus Bauhinia and the distribution of extant species cannot clearly indicate the Late Eocene climate of western North America.

Relatively few fossil records of legumes have been reported from the earliest Eocene strata in Africa, and some fossil pods and pollen of the genera Caesalpinia and Mimosa have been reported mainly from the late Eocene strata, most of which occur in Cameroon and Egypt in Africa [18] , and fossil records of the genus Caesalpinia have also been found in Hainan and other places in China.

The extant genus Caesalpinia is mostly distributed in tropical and subtropical regions, with latitudes of 20˚N-35˚N and longitudes of 98˚E-122˚E. In China, the southern and southwestern parts of the genus have also become the main sources, with Caesalpinia being one of the most widely distributed species in the genu. The latitude of distribution of Late Eocene fossils of the genus Caesalpinia is higher than that of the extant species, and the distribution of Late Eocene fossils of the genus Caesalpinia is extensive (Figure 6). The Late Eocene fossil distribution of the genus Caesalpinia in western North America, however, there is no extant distribution of the genus Caesalpinia in western North America today,

which now belongs to a temperate arid climate, thus can indicate a mild and humid climate in western North America in the Late Eocene.

The results of fossil identification and habitat analysis of the nearest extant relatives can show that the composition and morphological characteristics of legume species from the Late Eocene period in western North America are significantly different from modern vegetation, plant ecological characteristics, and climate. Since the plants maintained close contact with the external environment [19] , the fossils are a good indicator of the climatic environment of the time. Among the extant nearest relatives of the Late Eocene legume family in western North America, the temperate components are mainly Bauhinia spp. and the tropical-subtropical components are Acacia spp. and Caesalpinia spp.

The regional distribution characteristics of fossil legumes and extant legumes from the Late Eocene can be seen: the distribution of Acacia spp. migrated from high latitudes to lower latitudes, the distribution latitude of fossil Bauhinia spp. did not differ much from that of extant species, and the distribution latitude of fossil Caesalpinia spp. was higher than that of extant genera. However, in general, the regional distribution of extant legumes as a whole is in the tropical-subtropical low latitudes, and in comparison with the Late Eocene fossil record, the distribution range of extant legumes is reduced and concentrated in the southeastern part of China. Although the Late Eocene fossil distribution and distribution of extant species of Bauhinia cannot be clearly pointed out from the Late Eocene fossil distribution and distribution of extant species of Bauhinia, it can be basically concluded from the above Late Eocene fossil distribution and distribution of extant species of Acacia and Caesalpinia that there were fossil distributions of Acacia and Caesalpinia in western North America in the Late Eocene, but there are no extant distributions of Acacia and Caesalpinia in western North America nowadays, and The current climate in western North America is temperate and arid, indicating that the present-day climate in western North America is not suitable for the growth of Acacia and Clerodendron, so it can be concluded that the Late Eocene climate in western North America was mild and humid.