Cariamiformes Verheyen, 1957
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publication ID |
https://doi.org/ 10.26879/1340 |
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persistent identifier |
https://treatment.plazi.org/id/03A487DD-4B7A-BA1A-6F21-E0B7FB6AB72B |
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treatment provided by |
Felipe |
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scientific name |
Cariamiformes Verheyen, 1957 |
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Order Cariamiformes Verheyen, 1957 View in CoL View at ENA ? Phorusrhacidae Ameghino, 1889
Figure 4 View FIGURE 4
Material 1. MLP-PV 13-XI-28-546 complete right ungual phalanx ( Figure 4A, C, E, G, I View FIGURE 4 ).
Provenance. Fossil locality IAA 2/13, Seymour Island (Antarctic Peninsula, West Antarctica). Ypresian (early Eocene) Cucullaea I Allomember, La Meseta Formation.
Description. The specimen consists of a robust, laterally compressed, and curved ungual phalanx with a small dorsal fragment of the tip missing ( Figure 4A View FIGURE 4 ). The neurovascular sulcus is present along the entire length of both lateral and medial surfaces, though it is slightly wider and deeper on the medial side ( Figure 4E View FIGURE 4 ). This sulcus is situated closer to the plantar surface than to the dorsal margin and is proximally shallower and wider. On the medial side, the sulcus bifurcates in the proximal region, with the lower branch extending further proximally. As it approaches the tip, the sulcus becomes more dorsally positioned and is partially covered by a thin bony layer in certain areas. The claw becomes increasingly latero-medially compressed toward the tip ( Figure 4C View FIGURE 4 ).
The articular surface exhibits a sub-triangular to ovoidal outline, with a main dorso-ventral axis ( Figure 4G View FIGURE 4 ). The plantar side is rounded and approximately twice as wide as the dorsal margin, making the lateral and medial margins of the articular surface visible in dorsal view. The extensor tubercle is short and rounded, with minimal proximal projection. The articular surface is divided into two cotylae of similar size, slightly asymmetrical and dorsoventrally elongated. The lateral cotyla leans toward the lateral side, while the medial cotyla leans medially. Between them, the articular surface gently rises as a rounded ridge which is more pronounced in the area that contacts the flexor and extensor tubercles. The flexor tubercle is robust, rounded, and extends more toward the plantar and proximal directions than the extensor tubercle.
Material 2. MLP-PV 14-I-10-199 incomplete ungual phalanx ( Figure 4B View FIGURE 4 , DB, D, F, H).
Provenance. GPS S64°14’24.3’’, W56° 40’ 1.9’’, Seymour Island (West Antarctica). Cucullaea I Allomember, La Meseta Formation GoogleMaps .
Description. The overall appearance of this specimen closely resembles MLP-PV 13-XI-28-546, although it is more fragmentary, and some features cannot be observed. The entire proximal face and dorsal surface are lacking, and the entire surface is covered with diagenetic cracks. Only the latero-medial and plantar facies of the phalanx body are preserved ( Figure 4B View FIGURE 4 , DB, D). As a result, it is not possible to obtain linear and angular measurements. The neurovascular sulcus is present on both sides, like in MLP-PV 13-XI-28-546 ( Figure 4B View FIGURE 4 , FB, F).
Anatomical identification. The ungual phalanges display characteristic morphologies for each digit with minor differences between families ( Figure 5 View FIGURE 5 ). The ungual of digit I is the smallest, relatively gracile, and weakly curved, and presents a long flexor tubercle. The ungual of digit II is highly curved, latero-medially compressed, dorsoventrally tall (with a sub-elliptic transverse section) and possesses a well-developed plantarly rounded flexor tubercle. The ungual of digit III is less curved and dorso-ventrally lower than digit II, with a short and plantarly flattened flexor tubercle (although it is caudally expanded in Mesembriornis and Chunga burmeisteri and develops lateral wings in Brontornis burmeisteri ); consequently, it has a sub-triangular section. The ungual of digit IV is less curved and plantarly wider than those of digits II and III.
Given the latero-medial compression, suboval outline of the articular face, and strong curvature, MLP-PV 13-XI-28-546 and MLP-PV 14-I-10- 199 are both assigned to the second digit. Additionally, the outline and asymmetry of the articular facets (medial and lateral cotylae), along with the slight curvature of the central axis of the corpus phalanx, indicate that MLP-PV 13-XI-28-546 belongs to the right foot. The incompleteness of MLP-PV 14-I-10-199 precludes a more precise identification.
ACOSTA HOSPITALECHE & JONES: EOCENE CARIAMIFORMES FROM ANTARCTICA
Principal Component Analysis. In the analysis of absolute values, most of the explained variation is concentrated in the first two components, with the first axis (PC1) explaining 81.73 % of the variation and the second axis (PC2) explaining 14.13%. Together, these two components account for 95.85% of the total variation (Appendix 2). Phorusrhacidae and Cariamidae form distinct groups in the analysis ( Figure 6 View FIGURE 6 ), with Phorusrhacidae mostly located in the upper right quadrant. MLP-PV 13-XI-28-546 is positioned close to Phorusrhacos longissimus presumably within Phorusrhacidae .
The first axis (PC1), which explains most of the variation, is primarily influenced by basal height (BH), followed by maximum width of the articular facet (WAF), total length (TL), and maximum height of the articular facet (HAF). Larger species like Titanis and Devincenzia have higher values in these variables. On the contrary, the flexor tubercle length (LFT), behaves differently. It decreases along the first axis (where it significantly loads) but increases along the second one (in which it has a negligible influence).
The larger Titanis walleri and Devincenzia pozzi occupy the extreme values on the first and second axis, whereas the smaller Psilopterus colzecus and Procariama simplex are at the other end of the Phorusrhacidae polygon.
Living Cariamidae are separated from Phorusrhacidae and other groups of birds and occupy the lower left quadrant. The raptorial Falconiformes ( Caracara plancus ) and Cathartiformes ( Vultur gryphus ) are in the upper left quadrant, whereas the more terrestrial Otidiformes ( Otis tarda , formerly included within Gruiformes ), Anseriformes ( Chauna torquata ), and ratites ( Apteryx australis and Dromaius novahollandiae ), are in the lower left area, distinct from Phorusrhacidae and Cariamidae . The morphology of Dromaius is rescued in this analysis, where it is far from the rest.
In the second analysis, in which the variables were converted into indexes to control the size influence, three components capture 91.95% of the accumulated explained variation (PC1 38.67%, PC2 30.49%, PC3 22.79%). The variables with the greatest weight in each component are total length/ basal height (TL/BH) in PC1, total length/flexor tubercle length (TL/LFT) in PC2, and total length/ outer angle (TL/OCA) in PC3.
When the first two axes are plotted, Phorusrhacidae and Cariamidae are once again distinguished as two separated groups, and MLP-PV 13- XI-28-546 falls in between them, definitively within the Cariamiformes cloud ( Figure 6 View FIGURE 6 ). Interestingly, MLP-PV 13-XI-28-546 is close to Procariama simplex and Phorusrhacos longissimus . Similar graphs are obtained when plotting PC3 against PC1 and PC2. Again, the representatives of other orders remain separated and from Cariamiformes ( Cariamidae and Phorusrhacidae with MLP-PV 13- XI-28-546 included). In both analyses (absolute values and normalized data), Cariamiformes remain distinct from other robust (e.g., Dromaius ), and predatory (e.g., Caracara , Vultur ) forms.
Higher-order taxonomic assignment. MLP-PV 13-XI-28-546 ( Figure 7A View FIGURE 7 ) and MLP-PV 14-I-10-199 are characterized by their large size and robusticity, strong curvature, and moderated projection of the flexor tubercle (only preserved in MLP-PV 13- XI-28-546). These features have not been observed in any previously recorded fossil bird in Antarctica, including Sphenisciformes , Procellariiformes , Anseriformes , Pelagornithidae , Gruiformes , Falconiformes , and flightless “Ratites”). Furthermore, these groups can be easily distinguished based on the following features.
Falconiformes (as well as Accipitriformes and Strigiformes ) exhibit strongly curved and sharp claws, with a pronounced latero-medial compression, a conspicuous flexor tubercle oriented distally with two plantar foramina plantarly, and a large extensor tubercle ( Figure 7D View FIGURE 7 ). Falconiformes are differentiated from Strigiformes ( Figure 7F View FIGURE 7 ) by the presence of well-defined edges that delimit the ventral surface of the talon (as also described in Mosto and Tambussi, 2013).
On the opposite end extreme of spectrum, flightless Ratites ( Figure 7 View FIGURE 7 G-I) and other large, ground-dwelling birds, typically present triangular, short, and flat phalanges. These phalanges are more elongated in Rheiformes ( Figure 7I View FIGURE 7 ) and Struthioniformes ( Figure 7H View FIGURE 7 ) and shorter in Dinornithiformes. However, in all cases, they maintain a large internal angle and are never curved plantarly. Lithonithiformes exhibit phalanges thar are moderately curved and slenderer ( Nesbitt and Clarke, 2016: figs. 4, 10-12, 17, 19, 21). However, none of their phalanges closely resemble the condition observed in MLP-PV 13-XI-28-546 and MLP-PV 14-I-10-199. Other large and flightless birds worth comparing here are Gastornithiformes (Worthy et al. 2017) . In Gastornithidae , the ungual phalanges are only slightly curved, while in Dromornithidae they are essentially flat and rounded.
Teratornithiformes and Cathartiformes also deserve attention due to their large to giant size. A single ungual phalanx (MMP s/n) from the Late Miocene Epecuén Formation (Buenos Aires Province, Argentina), was initially assigned to Argentavis magnificens (Campbell, 1995) , but later reinterpreted as a phorusrhacid (Cenizo et al., 2012). Unfortunately, there are no other known phalanges of Argentavis or any other teratorn for direct comparisons. However, they have traditionally been considered morphologically similar to Cathartiformes in many aspects such as the proportions and anatomy of the limbs (e.g., Miller, 1909; Campbell, 1995). Vultur gryphus ( Figure 7C View FIGURE 7 ) presents a relatively curved and sharp ungual phalanx, with greater latero-medial compression, and a flexor tubercle more ventrally expanded, rather than proximally. Other groups widely recorded in Antarctica, such as Sphenisciformes , Procellariiformes , Anseriformes , and Pelagornithidae , have ungual phalanges that are notably less curved ( Figure 7 View FIGURE 7 O- Q). The ungual phalanges of giant penguins ( Figure 7P View FIGURE 7 ) come closest in robustness and morphology to MLP-PV 13-XI-28-546 and MLP-PV14-I-10- 199. These penguins have unguals that are dorsoventrally lower, less sharply hooked, and with a shorter and less developed flexor tubercle.
In contrast, the unguals of Procellariiformes , Anseriformes ( Figure 7N View FIGURE 7 ), and Pelagornithidae (Howard, 1957: fig. 8) are thinner, more gracile, and notably less curved. Furthermore, with a single record, Gruiformes are also known to have existed in the Antarctic Eocene (Davies et al., 2020). Within Gruiformes , terrestrial psophids exhibit ungual phalanges barely curved, particularly considering the inner curvature. They have a rounded flexor tubercle more distally located than in the fossils studied here, which is completely separated from the articular facets. Other taxa previously considered gruiforms, such as Rhynochetidae , Eurgypygidae, and Aptornithidae , have slightly curved ungual corpus, and exposed neurovascular sulcus, with a very short flexor tubercle that differs from the fossil material studied here ( Parker, 1868; Worthy and Holdaway, 2002).
Finally, Cariamiformes ( Figure 7B View FIGURE 7 ) also possess distinctive phalanges characterized by moderate latero-medial compression, strong internal and external curvature, and a flexor tubercle proximally and plantarly expanded, similar to MLP-PV 13-XI-28-546 and MLP-PV 14-I-10-199. Members of Phorusrhacidae and Cariamidae show even stronger curvatures and sharply hooked ungual phalanges, with these features more pronounced in digit II. In contrast, the phalanges of Idiornithidae (Mayr 2016b, fig. 1) and Bathornthidae (Mayr 2016a, fig. 9) are less curved and have a rounded and shorter flexor tubercle.
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